Iberian Thermoelectric Workshop - ITW '23 Lisbon: Book of Abstracts

3rd Iberian Thermoeletric Workshop ITW-2023 Campus Tecnológico e Nuclear of IST-UL Lisboa, Portugal, 30-31 March 2023 Book of Abstracts Editors: Francisco P. Brito António Pereira Gonçalves Elsa Branco Lopes 2 Foreword We are excited to make available the Book of Abstracts of the oral and poster presentations made at the third edition of the Iberian Thermoeletric Workshop (ITW-2023). The conference was hosted at Campus Tecnológico e Nuclear of IST-UL, Lisbon, Portugal, between March 30th and the 31st, 2023 and chaired by António P. Gonçalves (IST, C2TN). The ITW meeting occurs every two years, alternating between Portugal and Spain. It aims to provide opportunities to improve the collaboration between researchers and specialists in the thermoelectricity field and also allow an open discussion about the most recent advances on materials, properties measurement, module fabrication, and device applications, with exchange of ideas, experiences, opinions and discussion about the most recent trends and priorities in this exciting topic. This Book of Abstracts is published exclusively as a digital document containing a DOI (Digital Object Indentifier see below) for persistent online availability and referencing. The Editors of this Book of Abstracts were Francisco P. Brito (University of Minho,MEtRICs / Mechanical Eng. Department), António P. Gonçalves (IST, C2TN) and Elsa Branco Lopes (IST, C2TN), who also formed the local organizing committee of the conference. All submissions were approved after a peer review process. The Official Workshop site can be found here. This Book of Abstracts has the following DOI: https://doi.org/10.21814/1822.83648 Lisbon, March 30th, 2023 The Editors, Francisco P. Brito ([email protected]) António Pereira Gonçalves ([email protected]boa.pt), ITW Chair Elsa Branco Lopes ([email protected]lisboa.pt) 3 ITW 2023 Program March 30 March 31 9:15 Materials & Processing Theory and Modelling (MT) I.02 - Maria Ibañez 9:45 MT.01 - Viviana Sousa 10:00 MT.02 - Pablo Cerviño Solana 10:15 MT.03 - Norbert Marcel Nemes 10:30 MT.04 - José Javier Plata Ramos 10:45 Coffee Break 11:05 Materials & Processing (MP) I.03 - Sergi Riera Galindo 11:35 MP.01 - Clara Gomez 11:50 MP.02 - Mario Culebras Rubio 12:05 MP.03 - Javier Gainza Martín 12:20 MP.04 - Federico Miguel Serrano Sanchez 12:35 Lunch+Posters 14:15 Registration Materials & Processing Theory and Modelling (MT) I.04 - Jose Antonio Alonso 14:45 MT.05 - Marta Maria González Barrios 15:00 Welcome MT.06 - Duarte Moço 15:15 Other Topics (OT) I.01 - Jorge Garcia Cañadas MT.07 - Antonio M. Márquez 15:30 MT.08 - Diogo Lopes 15:45 OT.01 - Óscar Juan Dura Coffee Break 16:00 OT.02 - Sergio Castro Ruiz Devices & I.05 - Nuno Ferreira 16:15 OT.03 - Rodrigo Coelho 16:30 Coffee Break DA.06 - Ana Pires 16:50 Devices & Applications (DA) DA.01 - Olga Caballero DA.07 - André Pereira 17:05 DA.02 - Catarina Bianchi DA.08 - Patricia Alegría 17:20 DA.03 - Marc Salleras DA.09 - Lorenzo Pimpolari 17:35 DA.04 - Álvaro Casí DA.10 - Leyre Catalán Ros 17:50 DA.05 - Irantzu Erro Iturralde Closing Session 20:00 Workshop Dinner 4 Thursday, March 30, 2023 15:00 – 15:15 Welcome Address 15:15 – 16:30 Other Topics Session Chair: António Pereira Gonçalves 15:15 – 15:45 I.01 Influencing the thermoelectric properties of materials using redox electrolytes, Jorge Garcia Cañadas 15:45 – 16:00 OT.01 Soft thermoelectricity based on hybrid gels, Óscar Juan Dura 16:00 – 16:15 OT.02 A Cr complex solution able to produce a 2.5 times power factor improvement in a nanostructured and porous Sb:SnO2 film, Sergio Castro Ruiz 16:15 – 16:30 OT.03 Protective coatings for Cu10.5Ni1.5Sb4S13 tetrahedrites, Rodrigo Coelho 16:30 – 16:50 Coffee Break 16:50 – 18:05 Devices & Applications Session Chair: Francisco Brito 16:50 – 17:05 DA.01 Flexible nanostructured thermoelectric devices grown inside polyester templates, Olga Caballero 17:05 – 17:20 DA.02 Transparent photothermoelectric thin film devices, Catarina Bianchi 17:20 – 17:35 DA.03 Power enhanced all-Si based micro-thermoelectric generators with integrated heat sink, Marc Salleras 17:35 – 17:50 DA.04 Thermoelectric subcooling system to improve the performance of vapour compression refrigeration systems, Álvaro Casí 17:50 – 18:05 DA.05 Optimization of a thermoelectric heat pump system for heating, Irantzu Erro Iturralde 20:00 Workshop Dinner 5 Friday, March 31, 2023 9:15 – 10:45 Materials & Processing / Theory and Modelling Session Chair: Óscar Juan Dura 9:15 – 9:45 I.02 Sintering solution processed nanoparticles: a way to tune microstructure through surface chemistry, Maria Ibáñez 9:45 – 10:00 MT.01 Screen-printing of thin film TEGs from PbSe quantum dots, Viviana Sousa 10:00 – 10:15 MT.02 Nanostructured bismuth telluride thin films grown by electrochemical deposition, Pablo Cerviño Solana 10:15 – 10:30 MT.03 Structural evolution and nanostructure of thermoelectric materials, Norbert Marcel Nemes 10:30 – 10:45 MT.04 High-throughput optimization of the thermoelectric efficiency of chalcogenides through nanostructuring: ab-initio calculations, machine learning and more, José Javier Plata Ramos 10:45 – 11:05 Coffee Break 11:05 – 12:35 Materials & Processing Session Chair: Elsa Branco Lopes 11:05 – 11:35 I.03 Doping strategies to improve organic thermoelectric performance, Sergi Riera-Galindo 11:35 – 11:50 MP.01 Textile-based wearable TEG by electrochemical coating of felt fibers with conductive polymers, Clara Gomez 11:50 – 12:05 MP.02 Thermoelectric properties of layered nanocomposites based on conducting polymers, Mario Culebras Rubio 12:05 – 12:20 MP.03 Unexpected abrupt bond lengthening in GeTe as the origin of the anomaly in the experimental Seebeck coefficient, Javier Gainza Martín 12:20 – 12:35 MP.04 Investigation of the low-temperature thermoelectric transport and intrinsic electronic structure of half-Heusler TiCoSb, Federico Miguel Serrano Sanchez 12:35 – 14:15 Lunch+Posters 6 Friday, March 31, 2023 14:15 – 15:45 Materials & Processing / Theory and Modelling Session Chair: André Pereira 14:15 – 14:45 I.04 High-pressure synthesis of thermoelectric materials, Jose Antonio Alonso 14:45 – 15:00 MT.05 Microwave-assisted synthesis of thermoelectric chalcogenides, Marta María González Barrios 15:00 – 15:15 MT.06 Co-doping tetrahedrite: impact of Nickel and Selenium in thermoelectric properties, Duarte Moço 15:15 – 15:30 MT.07 Physical insights on the chemical factors that influence the thermoelectric properties in Cuand Agbased sulvanite, Antonio M. Márquez 15:30 – 15:45 MT.08 SrTiO3 – based thermoelectrics prepared by Laser Floating Zone technique, Diogo Lopes 15:45 – 16:00 Coffee Break 16:00 – 17:50 Devices & Applications Session Chair: Olga Caballero 16:00 – 16:30 I.05 Advancements in Laser Floating Zone processing for optimizing the thermoelectric properties of oxide materials, Nuno Ferreira 16:30 – 16:45 DA.06 The impact of collectors/absorbers on the efficiency of photo-thermoelectric devices, Ana Pires 16:45 – 17:00 DA.07 Wireless energy transfer using printable devices based on thermoelectricity: from concept to application, André Pereira 17:00 – 17:15 DA.08 Field operation and modelling of thermoelectric generators for high enthalpy geothermal anomalies, Patricia Alegría 17:15 – 17:30 DA.09 Flexible carbon-based thermoelectric generator with a phase change material for cold-chain monitoring, Lorenzo Pimpolari 17:30 – 17:45 DA.10 Prospects of volcano surveillance powered by thermoelectric generators: the Antarctica challenge, Leyre Catalán Ros 17:45 – 18:00 Closing Session 7 Posters Friday, March 31, 2023, 12:35 – 14:15 P.01 Implementation of arrays of thermoelectric generators for nanosatellites: evaluation under atmospheric and space conditions, Rui Costa P.02 On the thermal conductivity of thermoelectric polymers upon doping, Jiali Guo P.03 Impedance spectroscopy: an excellent tool to fully characterize a thermoelectric device, Jorge García Cañadas P.04 PDADMA-based solid electrolytes to significantly enhance the power factor of a thermoelectric oxide film, Mauricio Solís de la Fuente P.05 Characterization of a possible thermoelectric material prepared from natural pyrite, Vanina Gisela Franco P.06 Synthesis, optical band gap and thermoelectric properties of Sr1+xTiS3-y chalcogenide perovskites, Jinan Hussein Awadh Alshuhaib P.07 Maximizing exhaust heat utilization in lightand heavy-duty driving cycles through phase-change: Simulations and Experimental validation, Rui Carvalho P.08 Soft Thermoelectric Materials: Design of 3D Printed Hydrogels, Carlos Martin Topic: Other Topics on Thermoelectricity (OT) Invited Oral Presentation I.01 8 Influencing the thermoelectric properties of materials using redox electrolytes Jorge García-Cañadas1, Mauricio Solis-De La Fuente1, Lourdes Márquez-García1, Sergio Castro-Ruiz1, Estelle Liautaud2, Lucie Fournier2, Camille Chatard2, Pankaj Priyadarshi3, Neophytous Neophytou3 1 Universitat Jaume I, Department of Industrial Systems Engineering and Design, Av. Vicent Sos Baynat s/n, 12006 Castelló de la Plana, Spain, e-mail: [email protected] 2 Specific Polymers, 150 Avenue des Cocardières, 34160 Castries, France. 3 School of Engineering, University of Warwick, CV4 7AL Coventry, United Kingdom. Low-grade heat (<200 ºC) is an abundant and ubiquitous source of energy widely available in our surroundings (e.g. body heat, heat from the sun, hot exhausts, industrial processes, etc.). The temperature dependency of the redox potential of electrolytes containing redox couples is employed in thermo-electrochemical cells to convert heat into electricity [1]. These devices are formed by two electrically conducting electrodes (usually Pt) separated by a redox electrolyte (e.g. 0.4 M aqueous ferro/ferricyanide). When the electrodes are under a temperature difference, an electrical voltage of a few mV/K can be achieved, and electrical current can be generated. Here, we propose a new device for the conversion of heat into electricity. It consists of a film of an electrically conducting material (Pt, PEDOT:PSS, porous C or fluorine-doped SnO2), contacted by metallic contacts at its ends, which is combined in parallel with a redox electrolyte (0.4 M aqueous ferro/ferricyanide). Under this configuration, an open-circuit voltage can be generated when a temperature gradient is established due to the temperature dependency of the redox electrolyte, and the electrical current can flow through both the electrolyte and the conducting materials. It was observed that the highest open-circuit voltages (Seebeck coefficients) were achieved when most of the current flows through the electrolyte. This new device can offer other benefits that will be discussed. References [1] Y. Liu et al., Energy & Environmental Science 15, 3670 (2022). Topic: Other Topics on Thermoelectricity (OT) Oral Presentation OT.01 9 Soft Thermoelectricity based on hybrid gels Oscar J. Dura,1, 2 Carlos Martín2, Ana López-Hazas2, Sonia Merino2, 3, Ester Vázquez2, 3 1Dpto. Física Aplicada, Universidad de Castilla-La Mancha, Ciudad Real 13071, Spain 2 Instituto Regional de Investigación Científica Aplicada (IRICA), Ciudad Real 13071, Spain 3Facultad de Ciencias y Tec. Químicas, Universidad de Castilla-La Mancha, Ciudad Real 13071, Spain e-mail: oscar.ju[email protected] Organic compounds are interesting for the thermoelectric conversion due to their abundance and sustainability, resulting in a cheap and versatile approach towards energy harvesting. In addition, they offer the possibility to design soft and flexible devices and also the ability to profit from non-conventional thermoelectrical effects such as the thermogalvanic effect [1], which we develop in this work. Through this effect, a temperature difference in an electrolyte produces the gradient of a redox couple which reacts at electrodes producing a charge difference and current. Here focus is on electrolytes based on gels which offer advantages over conventional liquids related to their better stability and safety [2]. We employ a Digital Light Processing printer, settled to print hydrogels, which allows designing specific shapes and sizes offering a large versatility. We have prepared hydrogels with different functional groups to explore the ability to anchor different redox couples: Fe3+/2+ and Fe(CN)64-/3-. The influence of the couple concentration and swelling (water content) over the thermogalvanic behavior and the output power is systematically analyzed. Fig. 1. (left) Schema of thermogalvanic effect [3] and blanc and doped Fe3+/2+ complex hydrogels analyzed here. (center) Thermovoltage and temperature difference evolution through time. (right) current and voltage relation due to the temperature gradient. References [2] C-G. Han et al., Science 368, 1091 (2020). [3] Y. Zhang et al., Nature Communiations 12, 5269 (2021). [4] M. Massetti et al., Chemical Reviews 121, 12465 (2021). Topic: Devices & Applications (DA) Oral presentation DA.03 16 introducing it into an oven preheated to 65 ºC under three different conditions: on the bare sample (gold curve), on the sample with a block of poly(methyl methacrylate) (PMMA3, mm thick) placed on one side (orange curve), and on the sample with a block of PMMA filled with the PCM placed on one side (black curve). While in the first case the voltage is negligible, in the other two cases there is a voltage peak due to the PMMA acting as a thermal insulator, unbalancing the thermal transient between the two sides of the thermoelement. However, the response in the presence of the PCM is different, showing a second peak attributed to the melting of the PCM material. The presence of the PCM generates a larger thermal transient that can be correlated to a sample exposure to an undesired temperature for a certain time. This represents an interesting proof of concept, although a detailed analysis becomes necessary to evaluate the dependence between amount of energy exchanged with the environment and the volume of the PCM, before extending this approach to an entire TEG for the application of interest. Fig. 1. Schematic representation of the device (a) and detail representing the structure of the TEG (b). Square resistance (c) and Seebeck coefficient (d) of 5 different thermocouples over more than 100 days. The insets show the respective mean values over time (the error bars are the standard deviation). Fig. 2. (a) open circuit voltage of a TEG on paper as a function of the temperature difference. In the inset, a photograph of the TEG. (b) Evolution of the open circuit voltage of a single thermoelement initially measured at room temperature and then placed at 65 ºC under different measurement conditions: exposed (gold curve), covered with a dummy PMMA square (orange curve), and covered with a PMMA block filled with the PCM (black curve). In the inset, a schematic cross section of the device under measurement. References [4] D. MacKay, Sustainable Energy-without the Hot Air, UIT, Cambridge (2008). [5] M. Burton, G. Howells, J. Atoyo, and M. Carnie, Adv. Mat., 34(18), 2108183 (2022). [6] D. Tobjörk, and R.Österbacka, Adv. Mater., 23(17), 1935-1961 (2011). H. R. Lee et al., Appl. Phys. Lett., 118, 173901 (2021). Topic: Devices & Applications (DA) Oral presentation DA.04 17 Thermoelectric subcooling system to improve the performance of vapour compression refrigeration systems Á. Casi1, P. Aranguren1, M. Araiz1, L. Catalan1, P. Alegría1, I. Erro1, N.Pascual1, D. Chavarren1, I. Alzuguren1, D. Sanchez2, R. Cabello2, A. Rodriguez1, D. Astrain1 1 Thermal and Fluids Engineering Research Group, Public University of Navarra, Campus Arrosadia, 31016 Pamplona, Spain e-mail: [email protected] 2 Thermal Engineering Research Group, Jaume I University of Castellon, Campus Riu Sec 12071 Castellon, Spain The refrigeration sector plays an important role in confronting climate change, being responsible for 7.8 % of the global emissions and consuming 20 % of the electricity worldwide [1-2]. In addition, energy consumption of the sector is expected to double or triple by 2050 [3], which remarks the paramount importance of developing efficient and environmentally friendly refrigeration systems. This work focuses on reducing the environmental impact of the refrigeration sector by the development of a Thermoelectric Subcooling System (TESC) that is able to boost the performance of environmentally friendly vapour compression cycles that use natural refrigerants such as CO2 or NH3. The main objective of the thermoelectric system is to efficiently subcool the refrigerant at the outlet of the gas-cooler/condenser in order to increase the cooling capacity of the refrigeration system and compensate the extra consumption of the system, so that the performance of the refrigeration system is enhanced. Through the development of an experimental test bench the thermoelectric subcooler in combination with an internal heat exchanger is able to boost the performance of the vapour compression refrigeration system by 22.5 % [4]. References [7] International Institute of Refrigeration. 35th informatory note on refrigeration technologies (2019). [8] International Institute of Refrigeration. 38th informatory note on refrigeration technologies (2017). [9] International Energy Agency. The future of cooling opportunities for energy efcient air conditioning (2018). [10] A.Casi et al., Energy conversion and Management Vol. 268, 115963 (2022). Topic: Devices & Applications (DA) Oral presentation DA.05 18 Optimization of a Thermoelectric Heat Pump System for Heating Irantzu Erro1, Patricia Aranguren1, Patricia Alegría1, Álvaro Casi1, Leyre Catalán1, David Astrain1 1 Institute of Smart Cities, Public University of Navarre, Campus Arrosadia 31006 Pamplona (Spain) e-mail: irantz[email protected] The current need to carry out an energy transition towards a 100 % renewable energy horizon places the energy storage as the key. Numerous researchers are studying an optimum method to enhance a reliable energy storage, where thermal energy storage presents a great potential [1]. In 2019, the first delocalized thermal energy storage (TES) installation based on electrical resistances was placed in Hamburg. In this case, electrical resistances were used to heat an airflow, which stored thermal energy together with crushed volcanic rocks in a deposit [2]. Electrical resistances used for energy conversion from electricity to heat stands out for its simplicity. However, the use of electrical resistances presents a limited energy conversion efficiency of one. The Coefficient of Operation (COP) is the value that relates the heat dissipated (Q 󰇗h) to the hot reservoir to the consumed electric power (W 󰇗e). This work proposes the use of thermoelectric technology working as a heat pump to improve the load process of TES systems based on solid materials heated up by a hot airflow. This technology not only is able to achieve COP values greater than one, but also it is very easy to control, a scalable technology, with no moving parts and it does not need refrigerants. Therefore, three different thermoelectric heat pumps (TEHP) have been developed, built and experimentally tested to obtain an optimized thermoelectric system. The first configuration is the simple one, which is composed with a unique module. The second configuration is the direct multistage one, where two TEMs are located are thermally connected to each other. Finally, the third configuration is a two-stage TEHP configuration with a phase change intermediate heat exchanger (pc-intHX) with a relation of thermocouples between stages of two [3]. Experimental tests were carried out in a climate chamber at 25 °C to study the COP of the different configurations when heating an airflow of 15 m³/h. The obtained experimental results were analysed and used to computationally optimize a final configuration of TEHP system. The performance study showed that for low temperature differences between heat sinks, the simple TEHP presents a better performance than the multistage ones. However, when the temperature difference increases, the use of a multistage configuration is needed, where the multistage TEHP with pc-intHX obtains a better performance Thanks to the experimental results, a configuration that combines the different TEHP configurations for a real application has been developed. The system presents three simple TEHP followed by three multistage TEHP with pc-intHX. An improvement of the COP between 18 - 44 % could be reached in the TES load procedure when the optimized TEHP system is included and to heat the airflow from 90 to 200 °C. In conclusion, this work an optimal TEHP system to heat up an airflow used to thermally store energy and based on experimental results has been designed. This system is able to drastically improve the load process of a TES, reaching COP increments bigger than the 22 % in all the studied cases. Therefore, the great potential of thermoelectric technology in this kind of applications has been demonstrated. Acknowledgement We would like to acknowledge the support of the Government of Navarre funds under the grants PC066-067-068 FlexORCstorage Topic: Devices & Applications (DA) Oral presentation DA.05 19 References [1] IRENA, Electricity storage and renewables: Costs and markets to 2030, no. October. 2017. [2] Energética, “La primera instalación de almacenamiento térmico de energía eléctrica con piedras volcánicas entra en funcionamiento - Almacenamiento,” 2019. [3] X. D. Wang, Q. H. Wang, and J. L. Xu, “Performance analysis of two-stage TECs (thermoelectric coolers) using a three-dimensional heat-electricity coupled model,” Energy, vol. 65, pp. 419–429, 2014, doi: 10.1016/j.energy.2013.10.047. Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Invited Oral Presentation I.02 20 Sintering solution processed nanoparticles: a way to tune microstructure through surface chemistry Maria Ibáñez,1 1 Institute of Science and Technology (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria, e-mail: [email protected] Nanoparticles can be used as tunable precursors to produce macroscopic solids with specific structural features by controlling the density and microstructure of the solids through the consolidation process. The consolidation process, such as hot pressing or spark plasma sintering, is preferred in order to provide the material with densities as close as possible to the respective theoretical density. The characteristics of the particles, such as size, shape, composition, and surface chemistry, determine the sintering process and therefore dictate densification, grain growth, and the final microstructure of the material. A nanoparticle can be considered as a multi-structured system consisting of an inorganic nanocrystalline domain, named the inorganic core, surrounded by surface species. Both the inorganic and surface species are tunable parameters in the design of nanoparticle-based precursors. The surface chemistry of the nanoparticles can be adjusted during sintering to achieve a solid with specific targeted features. Two approaches to controlling the surface chemistry of the particles need to be separated. One refers to the particle termination atoms, the other to the connected adsorbates that can be covalently bonded molecules or electrostatically adsorbed ionic groups. The surface adsorbates, intentionally or unintentionally introduced, are critical to controlling densification, grain growth, and the final microstructure of the material. Herein, we will discuss the structural properties controlled through different surface species and discuss their effect on the electrical and thermal transport to evaluate their potential as thermoelectric materials. Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Oral Presentation MT.01 21 Screen-printing of thin film TEGs from PbSe quantum dots Viviana Sousa1,2, Eliana M. F.Vieira3,4, Pedro Alpuim1,2, and Yury V. Kolen’ko2 1 Center of Physics of the Universities of Minho and Porto, University of Minho, Braga 4710-057, Portugal, e-mail: [email protected] 2 International Iberian Nanotechnology Laboratory, Braga 4715-330, Portugal 3 CMEMS – UMinho, University of Minho, Guimarães 4800-058, Portugal 4 LABBELS –Associate Laboratory, Braga/Guimarães, Portugal Thin film thermoelectric generators (TEGs) afford an interesting opportunity for powering wearable electronics and internet-of-things. As the range of such applications continuously broadens, it is becoming important to develop less energy-demanding fabrication routes towards thin film TEGs [1]. Here, we propose screen-printing approach as an easy to scale-up and industry-relevant technology to fabricate thin film TEGs from PbSe quantum dots (QDs). The PbSe QDs with spherical morphology and monodisperse size of 11 nm were successfully synthesized through colloidal heating-up method. Next, PbSe QD ink was formulated, and used for the fabrication of the thermoelectric (TE) thin films by means of screen-printing followed by annealing. Notably, the phase composition, size, and morphology of the PbSe QDs were maintained after annealing at 600 ºC. The annealing treatment is essential to remove organic matter from the screen-printed TE thin films, since carbon residues from QDs’ capping ligand and ink binders can reduce charge carrier mobility within the resultant film [2]. Electrical properties, measured at room temperature by Hall effect, reveal that the as-fabricated PbSe QD thin films have a bulk carrier concentration of 3.8  1018 cm–3, electron mobility of 7.9  10–1 cm2 V–1 s–1 and electrical conductivity of 50 S m–1. A maximum Seebeck coefficient of 561 μV K–1 was obtained at 143 ºC and a highest electrical conductivity of 123 S m–1 was reached at 197 C. Positive Seebeck coefficient indicates p-type nature of the thin films [3]. Further, several TEG geometries were explored with screen-printed p-type PbSe QDs and ntype Ag commercial paste. TEGs performance with 6 pairs of PbSe/Ag legs was characterized using a custom-built setup which can accurately control the temperature gradients by 4 commercial TE modules. An Optris PI 450 infrared (IR) camera placed over the setup was used to acquire thermal images of the TEGs (Figure 1), and the obtained results will be presented and discussed. Fig. 1. Thermogram of 20 C gradient within the screen-printed TEG with p-type PbSe and n-type Ag legs. References [11] M. Z. et al., Chem. Soc. Rev. 51, 485 (2022) [12] D.C. et al, ACS Appl. Energy Mater. 3, 2120–2129 (2020) V. S. et al., Materials 15, 8805 (2022) Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Oral Presentation MT.02 22 Nanostructured bismuth telluride thin films grown by electrochemical deposition Pablo Cerviño-Solana,1 Marisol Martín-González1, Olga Caballero-Calero1 1 1 Instituto de Micro y Nanotecnología, IMN-CNM, CSIC (CEI UAM+CSIC) Isaac Newton, 8, E28760, Tres Cantos, Madrid, Spain e-mail: olga.caba[email protected] Electrochemical deposition is a scalable and widely used technique in the fabrication of nanostructured materials and is optimal for the fabrication of thermoelectric generators. In this work, bismuth telluride thin films have been grown using a three-electrode electrochemical cell, obtaining a nanometric structure without using any template, thus simplifying the fabrication process and reducing its cost. This upgrade is achieved by adding sodium lignosulfonate [1, 2] into the electrochemical bath, and, as a result, we obtain stoichiometric thin films preferably oriented along the [110] direction and nanostructured in 12 nm thick nano-platelets. This kind of nanostructuration is expected to reduce the thermal conductivity, as it is the case in bismuth telluride electrodeposited nanowires [3] and 3D-nanowire networks [4]. Because the nano-platelets are interconnected, the thermoelectric effect is produced in two directions: in plane and out of plane, resulting in highly anisotropic films. Our objective is to optimize the thermoelectric properties of these films, enhancing their figure of merit, zT. To do so, we studied the influence of the different fabrication parameters, such as the composition of the bath, the voltage applied, and the deposition time, on the final properties of the films. The films have been characterized obtaining promising zT values. References [13] M. Martin Gonzalez et al., Journal of the Electrochemical Society 149., 546-554 (2002). [14] O. Caballero-Calero et al., Electrochemical Acta 123, 117-126 (2014). [15] M. M. Rojo et al. Nanoscale 9 6741 (2017). [16] A. Ruiz-Clavijo, et al. ACS Appl. Energy Mater. 4 13556 (2021) Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Oral Presentation MT.03 23 Structural Evolution and Nanostructure of Thermoelectric Materials Norbert M. Nemes1, Javier Gainza2, Federico Serrano-Sánchez2, Oscar J. Dura3, Neven Biskup1, José-Luis Martínez2, Juan J. Meléndez4, Michael M. Koza5, María-Teresa Fernández-Díaz5, José-Antonio Alonso2 1Departamento de Física de Materiales, Universidad Complutense de Madrid, E-28040 Madrid, (Spain) [email protected] 2Instituto de Ciencia de Materiales de Madrid, C.S.I.C., Cantoblanco, E-28049 Madrid (Spain) 3Departamento Física Aplicada and INEI, Universidad de Castilla La Mancha, Ciudad Real E-13071 (Spain) 4Departamento de Física, Universidad de Extremadura, Badajoz 06006, Spain 5Institut Laue–Langevin, BP 156, Grenoble Cedex 9, F-38042 (France) A good thermoelectric material must have a high Seebeck coefficient (S), be a good electrical conductor and a good thermal insulator. The efficiency of a thermoelectric is commonly characterized with its thermoelectric figure of merit, zT=σS2T/κ. Thermoelectrics could play an important role in saving energy in a future, sustainable, economy, if only they had a zT>4. Today, the best materials, commercial highly doped semiconductors, do not exceed by much zT ~ 1, while state-of-the-art zT reported very recently in materials such as SnSe or GeTe do not exceed zT ~ 2.5. The electrical (σ) and thermal (κ) conductivity in metals is tied by the Wiedemann-Franz law. However, κ also has an important contribution in semiconductors due to the vibrations of the crystal lattice (κlatt). There are several strategies pursued to improve thermoelectric properties, including nanostructuring or the so-called "phonon glass, electric crystal" (PGEC) approach, aiming to decrease κlatt in different ways, while preserving the good electronic properties (S and σ). We use straight-forward arc-melting synthesis to obtain thermoelectric materials with promising properties. We characterize the static and dynamic structure with neutron scattering, with Rietveld refinement analysis to obtain both the crystalline structure and the dynamics of the constituent atoms through thermal factors (atomic displacement parameters). We correlate this structure with the thermoelectric properties, in particular with the contribution of the crystalline network to the thermal conductivity in families of intermetallics: alloys of Bi2Te3 with Sb and Se, GeTe and its alloys, and PbTe and its alloys, and finally SnSe and its alloys, where we obtained the highest figure of merit (zT~1.8) to date in any n-type polycrystalline sample. We also show how a simple analysis of the atomic displacement factors in terms of independent Einstein oscillators sometimes can yield surprisingly good approximations of the relevant phonon energies, when compared to inelastic neutron spectra and ab-initio calculations [1]. In this talk several examples of these material families will be described, always aiming to establish correlations between the structural peculiarities with the observed properties. Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Oral Presentation MT.03 24 Figure 1. SnSe: Structure as a function of temperature (top) from NDP, Einstein-oscillator analysis of the ADPs (bottom left), and inelastic neutron spectra (bottom right) References [1] J. Gainza et al Cell Reports Physical Sciences, 2020, 1, 100263. https://doi.org/10.1016/j.xcrp.2020.100263 298 K 573 K 773 K 773 K 873 K Pnma Cmcm Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Oral Presentation MT.04 25 High-throughput optimization of the thermoelectric efficiency of chalcogenides through nano-structuring: ab-initio calculations, machine learning and more. José J. Plata,1 Ernesto J. Blancas1, Antonio M. Márquez1, Victor Posligua,2 Javier Fdez. Sanz,1 and Ricardo Grau-Crespo3 1Departamento de Qumica Fsica, Universidad de Sevilla, Seville, Spain, e-mail: [email protected] 2 Department of Chemistry, Imperial College London, Molecular Science Research Hub, 82 Wood Lane, London W12 0BZ, UK 3Deparment of Chemistry, University of Reading, Reading RG6 6DX, UK The optimization of new and more efficient thermoelectric, TE, materials has been hindered by the interdependence of electronic and phonon transport properties and the multitude of variables that affect the thermoelectric figure of merit, ZT. Traditional approaches involving timeconsuming and expensive synthesis and characterization processes are not practical for exploring large chemical spaces and optimizing properties that depend on numerous variables. This work employs a high-throughput framework that combines ab-initio calculations and machine learning to chart systematically and accurately the thermoelectric properties of chalcogenides [1,2]. In addition to examining the already well-established temperature dependence of ZT, the study investigates the effect of carrier concentration and polycrystalline average grain size on ZT (Fig. 1). By calculating the mean free paths of electrons and phonons, the study demonstrates the potential for automating and rationalizing the optimization of TE materials through nano-structuring [3]. The study finds that the difference in the mean free paths of electrons and phonons for different chalcogenides disentangles the connection between the power factor and lattice thermal conductivity when reducing the crystal size. The study predicts ZT values up to 2 for some p-type chalcogenides at 700 K when the average grain size is in the 10-100nm range. Furthermore, the ZT of some of the nanocrystalline samples are almost three times larger than that of single-crystal or micro-metric polycrystalline materials. The results demonstrate the potential of computational approaches in accelerating the discovery of thermoelectric materials. Fig. 1. Thermoelectric figure of merit, ZT, dependence on average grain size, L, and carrier concentration, n, at 700 K for a p-type chalcopyrite. Acknowledgements. This work was funded by Spanish MICIN/AEI/10.13039/501100011033 and by “European Union Next Generation EU/PRTR” (grants PID2019-106871GB-I00 and TED2021-130874B-I00). Topic: Thermoelectric Materials & Processing (MP) Oral Presentation MP.04 32 Investigation of the low-temperature thermoelectric transport and intrinsic electronic structure of half-Heusler TiCoSb Federico Serrano-Sanchez1,2, Mengyu Yao2, Bin He2, Dong Chen2, Andrei Gloskovskii3, Alexander Fedorov4,5, Gudrun Auffermann2, Enke Liu6, Ulrich Burkhardt2, Gerhard H. Fechera, Chenguang Fu2,7, Claudia Felser2, Yu Pan2 1Instituto de Ciencia de Materiales de Madrid (ICMM), Campus de Cantoblanco, C. Sor Juana Inés de la Cruz, 3, 28049 Madrid, Spain e-mail: [email protected] 2Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany 3Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany 4Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany 5Institute for Solid State Research, Leibniz IFW Dresden, 01069 Dresden, Germany 6Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences Beijing, 100190 (P. R. China) 7State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, 310027 Hangzhou, China In an energy-sustainable context, thermoelectric materials offer the remarkable capability to convert heat gradients into electrical energy and viceversa. In the last decade, the investigations on the intrinsic electronic structure of thermoelectric materials1 have brought forward encouraging enhancements of the energy conversion performance. More precisely, band structure engineering has a strong beneficial impact on thermopower and conductivity optimization, and to implement it, the electronic structures are theoretically determined and analysed. Among promising thermoelectric materials, half-Heusler alloys exhibit a high performance at high temperatures and a variety of compositions with complex band structures2. Several reports reveal that disorder and defects in the TiCoSb C1b type structure are still under discussion3–5. Those are recognized as the main factors determining the electrical transport in this material, altering the band structure as forming in-gap states, modifying the Fermi level (EF), and acting as scattering centers. Thus, TiCoSb properties has shown significant deviations depending on its preparation conditions3–5. Here, we have grown TiCoSb half-Heusler single crystals to allow the experimental angleresolved photoemission spectroscopy (ARPES) analysis of the electronic structure. The thermoelectric transport properties have been measured as well, showing a stark sensitivity to crystallographic defects within samples, while hard X-Ray spectroscopy (HAXPES) allows us to discard interstitial defects which could induce in-gap states. Single crystals of TiCoSb show p-type transport, in contrast to the n-type behaviour found in polycrystalline studies. Still, slight differences in the defect concentration of two different crystal batches, which were prepared by an identical method, display distinct metallic and semiconductive behaviours, even though the elemental analysis could not find any compositional difference. Thus, each of the crystal batches present a different effective mass, which is in agreement with the electronic structure and band convergence picture found by ARPES. This investigation provides new insights on the strong impact of point defects on the optimization of thermoelectric properties. References 1 J. P. Heremans, B. Wiendlocha and A. M. Chamoire, Energy Environ. Sci., 2012, 5, 5510–5530. 2 T. Graf, C. Felser and S. S. P. Parkin, Prog. Solid State Chem., 2011, 39, 1–50. 3 J. Tobola, L. Jodin, P. Pecheur and G. Venturini, J. Alloys Compd., 2004, 383, 328–333. 4 T. Sekimoto, K. Kurosaki, H. Muta and S. Yamanaka, J. Alloys Compd., 2005, 394, 122–125. 5 E. Rausch, M. V. Castegnaro, F. Bernardi, M. C. Martins Alves, J. Morais and B. Balke, Acta Mater., 2016, 115, 308–313. Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Invited Oral Presentation I.04 33 High-pressure synthesis of thermoelectric materials José Antonio Alonso,1 Javier Gainza1, Federico Serrano,1 Norbert Nemes2, João Elias F. S. Rodrigues,3,4 Jose Luis Martínez1 1 Instituto de Ciencia de Materiales de Madrid (ICMM), CSIC, Sor Juana Inés de la Cruz 3, E-28049 Madrid, Spain, e-mail: [email protected] 2 Departamento de Física de Materiales, Universidad Complutense de Madrid, E-28040 Madrid, Spain 3 European Synchrotron Radiation Facility (ESRF), 71 Avenue des Martyrs, 38000 Grenoble, France. 4 CELLS-ALBA Synchrotron, E-08290 Barcelona, Spain. In this talk, I will describe different families of thermoelectric materials that can be stabilized at moderate pressures 2–3.5 GPa in a piston-cylinder press. The synthesis of some of these systems had been previously reported under higher hydrostatic pressures (6–10 GPa), but can be accessed under milder conditions in combination with reactive precursors prepared by softchemistry techniques. These systems include perovskite oxides with transition metals in unusual oxidation states, such as RNiO3 with Ni3+ (R = rare earths); pnictide skutterudites MxCo4Sb12 (M = La, Yb, Ce, Sr, K) with inhomogeneous filling factor at the structural voids (2a sites); oxychalcogenides with chalcopyrite structure (e.g. BiCuOSe) or black phosphorous, to quote some. The availability of substantial amounts of sample (0.5–1.5 g), already sintered in pellets, allows a complete characterization of the thermoelectric properties (viz., Seebeck coefficient, thermal and electrical conductivity), as well as the structural analysis by neutron, synchrotron X-ray diffraction, and X-ray absorption spectroscopy techniques. As a brief overview, the high hydrostatic pressure favors the formation of the short and strongly covalent chemical bonds characterizing the high oxidation states; on the other hand, the pressure prevents the decomposition of unstable reactants at the synthesis temperature and the oxidation or volatilization of certain reactants (typically P, As, Sb, S, Se, Te…). Those factors act to increase the coordination numbers and to enable the achievement of denser phases in perovskite-like materials, skutterudites, etc. Finally, the high pressure enhances the reaction kinetics substantially. All those features make the high-pressure synthesis methods a good and promising choice to prepare novel compounds with a low stability or a metastable character. Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Oral Presentation MT.05 34 Microwave-assisted synthesis of thermoelectric chalcogenides Marta María González-Barrios1, Óscar Juan Durá2, David Ávila-Brande1, Jesús PradoGonjal1 1 Departamento de Química Inorgánica, Universidad Complutense de Madrid, E-28040 Madrid, España, e-mail: martam5[email protected] 2 Departamento de Física Aplicada, Universidad de Castilla-La Mancha, E-13071 Ciudad Real, España. The remarkable increase in global energy consumption and the current climate crisis has promoted research into new and efficient approaches for energy generation. In this context, thermoelectric technology has an important role because of their ability to convert waste heat into electrical energy. Nevertheless, the low conversion efficiency of commercial thermoelectric devices, as well as the high toxicity and scarcity of the constituent materials (Bi2Te3, Sb2Te3, PbTe…) hinder their large-scale implementation [1]. This motivates research into materials that are more environmentally friendly, abundant and highly efficient. On the other hand, sustainable synthetic routes based on "soft chemistry" or "fast chemistry", which follow the principles of "green chemistry", are currently strongly appealing for the preparation of thermoelectric materials rather than the traditional ceramic method. Among the alternative synthesis methods, microwave-assisted hydrothermal synthesis has emerged as a powerful route to prepare thermoelectric chalcogenides. The use of microwaves makes possible an efficient, uniform and direct heat transference owing to remarkable coupling of the microwave to the polar molecules in the solution (e.g., water), and therefore allows the increase of the crystallization kinetic [2]. Furthermore, processing time by this route (minutes) is noticeably shorter than the ceramic technique (days), which results in energy savings. Fig. 1. a) X-ray diffraction patterns of CuFeS2 (blue) and Sn0.84S (red) prepared by microwave-hydrothermal synthesis; b) HRTEM image of SnS0.8Se0.2 crystal along the [100] zone axis. The FFT in the inset shows extra spots observed along 0–11 confirming the modulation of the structure. Herein, an ultra-fast microwave-hydrothermal synthesis of pure polycrystalline phases of SnS1xSex (x=0, 0.1, 0.2, 1) and CuFeS2 is shown. In the case of SnQ (Q = S, Se) samples, one minute of microwave irradiation is enough to synthesize the compounds. This allowed the generation of randomly distributed tin vacancies in the crystal structure (Sn:Q ≈ 0.84:1), as demonstrated by synchrotron X-ray diffraction. This phenomenon influences the physical properties of the Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Oral Presentation MT.05 35 synthesized compounds by modifying the concentration and mobility of the charge carriers [34]. Furthermore, chalcopyrite CuFeS2 sample, which is considered a promising thermoelectric material when its lattice thermal conductivity κlat is successfully reduced, can also be efficiently produced in minutes. In this communication, synthetic aspects, structural and microstructural characterization as well as the thermoelectric properties of the aforementioned phases will be presented. Funding: MCIN/AEI/10.13039/501100011033 (TED2021-129569A-I00; PID2020112848RB-C21), Community of Madrid - UCM (PR65/19-22459; PEJ-2020-AI/IND-17706). References [27] Z. Ma et al., Mater.Sci. Semicond. Process. 121., 105303 (2021). [28] R. Schmidt et al., Concise Encyclopedia of Nanotechnology, Eds. CRC Press Taylor & Francis Group, pp. 561-572 (2018). [29] M.M. González-Barrios et al., Ceramics International 48 (9), 12331-12341 (2022). [30] J. Prado-Gonjal et al., Materials Advances, 1(4), 845-853 (2020). Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Oral Presentation MT.06 36 Co-doping tetrahedrite: impact of Nickel and Selenium in thermoelectric properties Duarte Moço,1 José F. Malta1,2, Elsa B. Lopes1, Luís F. Santos3, António P. Gonçalves 1, 1 C2TN, DECN, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066, Bobadela, Portugal; duarte[email protected]o.ulisboa.pt 2Centre for Physics of the University of Coimbra, Department of Physics, University of Coimbra, R. Larga,3004-516 Coimbra, Portugal, 3Centro de Química Estrutural, Institute of Molecular Sciences and Departamento de Engenharia Química, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001, Lisboa, Portugal For several decades, despite extensive research, the wide application of thermoelectric generators had seemingly been a piped dream, as other heat conversion technologies were more efficient and cheaper, with the added benefit of not relying in highly toxic and increasingly rarer thermoelectric materials, like those based in Bi, Pb and Te. Thus, the application of thermoelectric devices was reduced to very specific niche fields, where durability, reliability or compactability were prioritized. Recent advancements in material sciences and computational models capable of better simulating transport properties in solids, changed this perspective. Thermoelectric materials are now being more intensively researched, as new materials are being discovered with each passing year. For the most part, these materials cannot yet replace conventional materials, as their thermoelectric performance is still lower. However, most of the new materials are far more cheap and less toxic than the classic (Bi, Pb and Te-based) ones.[1] Tetrahedrite (Cu12Sb4S13), an earth-abundant mineral, is one of these novel, cheaper and more sustainable thermoelectric materials, which has been growing in popularity. An ample research has been carried out to improve the already naturally good pristine properties, because of its abnormally low thermal conductivity, by fine tuning the composition by introducing dopants or adjusting the content of each element. [2] Generally, the studies conducted on tetrahedrite focused on a single dopant or varying a single element, while those conducted by simultaneously doping with two different elements are sparse. Thus, in the present study, the impact of Ni and Se in both the thermoelectric properties and in phase composition will be presented, both experimentally and simulated with Wien2K and BoltzTrap softwares. [3,4] The characterization of the samples with various contents of Ni and Se, following the formula Cu12-xNixSb4S13-ySey, revealed samples after casting and after annealing to be mainly composed of tetrahedrite phase with some occasional secondary phases of copper/nickel sulphides and chalcostibite (CuSbS2). SEM-EDS, powder X-ray and Raman spectroscopy revealed that both Ni and Se were integrating the tetrahedrite matrix, with the semi-quantitative EDS analyses placing the actual composition of these samples to values very similar to what was expected. Both simulations and experimental measurements pointed to an optimum composition around Cu11.5Ni0.5Sb4S12.5Se0.5. According to the simulations, it would have a figure of merit around 0.30 at 300K, and an experimental power factor of 1280 µW/m.K2 was obtained, which, after estimating thermal conductivity with the Wiedemann-Franz law, resulted in a figure of merit of ~0.32 at 300K. Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Oral Presentation MT.06 37 Fig. 1. BoltzTrap simulations of the figure of merit for various tetrahedrites with different Ni and Se content, based on the chemical formula Cu12-xNixSb4S13-ySey. Fig. 1. Calcuted Power factor (A) and figure of merit (B) with the experimental measurements of the Seebeck coefficient and electrical resistivity of the annealed samples with the formula Cu12-xNixSb4S13-ySey. References [1] D.M. Rowe. Thermolectrics Handbook-Macro to Nano. CRC Press; 2006 [2] R. Chetty et al., J Mater Chem, 48 (2015) [3] Blaha, P. "WIEN2K, an Augmented Plane Wave Local Orbitals Program for Calculating Crystal Properties Karlheinz Schwarz." Techn. Universität Wien, Austria (2001). [4] K.H. Georg, et al., Comput. Phys. Commun., 175, issue 1 (2006), 67-71 Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Oral Presentation MT.07 38 Physical Insights on the Chemical Factors that Influence the Thermoelectric Properties in Cuand Agbased Sulvanites Antonio M. Márquez,1 Irene Caro1, Jose J. Plata1, and Javier Fdez. Sanz,1 1Departamento de Qumica Fsica, Universidad de Sevilla, Seville, Spain, e-mail: [email protected] Traditionally, the search for more efficient and affordable thermoelectric (TE) materials relied on discoveries through repetitive experiments involving synthesis, characterization, and property measurement. Computational methods were only used retrospectively to gain insight. However, recent developments in computational techniques, such as high-throughput frameworks and machine learning algorithms combined with density functional theory (DFT) methods, have allowed for the optimization of TE efficiency and a better understanding of the physicochemical factors governing thermoelectricity. In this study, we apply a rational design approach to sulvanites, which are a group of ternary copper chalcogenides Cu3MX4 (M = V, Nb, Ta; X = S, Se, Te) consisting of Earth-abundant, non-toxic, and sustainable elements. Sulvanites have shown promise for use in thin film photovoltaics [1] and TE technologies [2], and their facile synthesis via standard solid-state [3] methods make them even more desirable. However, despite their potential, experimental data on the TE properties of Cu-based sulvanites are scarce and, as well as the few theoretical studies available, limited to a few members of the family in most studies and, in no case, there is a rationalization of the trends found in 𝜅𝑙 (se Fig. 1) in terms of the chemical composition of these materials. Our focus here is on understanding the factors affecting phonon thermal transport, which is crucial for the rational design of new materials with excellent TE properties. Fig. 1. Calculated lattice thermal conductivities of copper-based sulvanites. Acknowledgements. This work was funded by Spanish MICIN/AEI/10.13039/501100011033 and by “European Union Next Generation EU/PRTR” (grants PID2019-106871GB-I00 and TED2021-130874B-I00). [1] C. Chen et al., Mater. Lett. 211, 179 (2018) [2] X. Liu et al., Int. J. Mod. Phys. C 30, 1950045 (2019) [3] R. Nitsche and P. Wild, J. Appl. Phys. 38, 5413 (1967) Topic: Thermoelectric Materials & Processing / Theory and Modelling (MT) Oral Presentation MT.08 39 SrTiO3 – based thermoelectrics prepared by Laser Floating Zone technique Diogo Lopes,1,2 Nuno Ferreira2, Andrei Kovalevsky1 1 CICECO – Aveiro Institute of Materials, Department of Materials and Ceramic Engineering, University of Aveiro, 3810-193 Aveiro, Portugal, e-mail: djlope[email protected] 2 i3N, Physics Department, University of Aveiro, 3810-193 Aveiro, Portugal Global energy consumption is expected to continue increasing, and the need for more efficient and renewable sources for energy production is essencial to assure energy demands are achieved without environment degradation and/ or over relying on finite resources [1]. Thus, green energy production and energy-efficient technologies are necessary. Thermoelectric (TE) energy harvesting can become one of the viable solutions to increase the efficiencies of various high-temperature industries [2]. For this, highly-performing TE materials are fundamental. Traditional and commercialized TE mostly are not stable at higher temperatures and harsh environments. Consequently, TE oxides are expected to be a prime candidate for these applications due to their high chemical and thermal stability [3]. Despite these advantages, most oxides usually show lower ZT values when compared with “traditional” thermoelectrics. Still, it can be overcome by designing new compositions and micro-/nanostructures, and involving new processing techniques leading to increases in TE oxide performance [4]. Amongst the studied families of oxides for TE applications, SrTiO3 -based TE are among the most promising, with a composite composition, STN + 0.5% reduced graphene, achieving a ZT value of 1.42 [5]. In this work, we demonstrate a new approach to prepare SrTiO3-based TE materials using the Laser Floating Zone (LFZ) technique. LFZ processing offers a number of advantages for TE materials like high density, uniform distribution of the cations composition in the melt, tunable phase formation and cation distribution controlled by the cooling rate, as well as LFZ processing could be an attractive technique for high-volume production [6]. This study analyzes and characterizes the effects of growth rate and thermal post-treatment on relevant structural and thermoelectric properties of donor substituted SrTi1-xNbxO3. The results indicate the ability to prepare these materials by LFZ, resulting in mechanically strong fibres with adequate electrical and TE properties. The post-annealing resulted in a considerable increase in electrical conductivity and relatively high power factor values of the samples, derived from the further reduction and consequent charge carrier generation. References [1] T. Ahmad and D. Zhang, “A critical review of comparative global historical energy consumption and future demand: The story told so far,” Energy Reports, vol. 6, pp. 1973–1991, Nov. 2020, doi: 10.1016/j.egyr.2020.07.020. [2] J. He, Y. Liu, and R. Funahashi, “Oxide thermoelectrics: The challenges, progress, and outlook,” J. Mater. Res., vol. 26, no. 15, pp. 1762–1772, 2011, doi: 10.1557/jmr.2011.108. [3] G. Ren et al., “High Performance Oxides-Based Thermoelectric Materials,” Jom, vol. 67, no. 1, pp. 211– 221, 2015, doi: 10.1007/s11837-014-1218-2. [4] X. L. Shi et al., “SrTiO3-based thermoelectrics: Progress and challenges,” Nano Energy, vol. 78, no. August, 2020, doi: 10.1016/j.nanoen.2020.105195. [5] M. Acharya, S. S. Jana, M. Ranjan, and T. Maiti, “High performance (ZT>1) n-type oxide thermoelectric composites from earth abundant materials,” Nano Energy, vol. 84. 2021, doi: 10.1016/j.nanoen.2021.105905. [6] F. Rey-García, R. Ibáñez, L. A. Angurel, F. M. Costa, and G. F. d. la Fuente, “Laser floating zone growth: Overview, singular materials, broad applications, and future perspectives,” Crystals, vol. 11, no. 1, pp. 1–29, 2021, doi: 10.3390/cryst11010038. Topic: Devices & Applications (DA) Invited Oral Presentation I.05 40 Advancements in Laser Floating Zone processing for optimizing the thermoelectric properties of oxide materials. Properties N.M. Ferreira1,*, G. Marques1, D.J. Lopes1,2, M.A. Madre3, A. Sotelo3, O.J. Dura4, A.V Kovalevsky2, F.M. Costa1 Presenting author: [email protected] 1 i3N & Physics Department, Universidade de Aveiro, Portugal; 2 CICECO - Aveiro Institute of Materials, Department of Materials and Ceramic Engineering, University of Aveiro, Portugal; 3 ICMA (CSIC-Universidad de Zaragoza), C/Maria de Luna 3, 50018 Zaragoza, Spain; 4 Applied Physics Department, University of Castilla-La Mancha, Ciudad Real, Spain Abstract. Transition oxides-based ceramics are known as potential alternative thermoelectric materials in scenarios where high thermal and chemical stability are required. Many oxides also allow flexible tuning of the relevant electrical and thermal transport properties through doping/substitution and by using specific processing approaches. This work discusses the prospects for growing oxide-based thermoeelctrics by the laser floating zone (LFZ) technique assisted by an external magnetic field. Various opportunities for tuning the structural, microstructural and thermoelectric properties are explored. This technique allows the growth of fully dense fibres, as well as the formation of metastable phases and/or promoting different oxidation states by adjusting the growth conditions under various pulling rates and using different growth atmospheres. The external magnetic field was found to promote notable variations of the microstructure and phase composition of the LFZ-grown fibers. The obtained guidelines suggest that LFZ is a suitable technique for processing thermoelectric oxides, if optimized control over growth parameters and re-equilibration conditions is imposed. Fig. 1. Magnetically Assisted Laser Floating Zone setup and microstructural effect on field direction. References [31] G. Marques et al., Materials Letters 329 (2022), 133174, DOI: 10.1016/j.matlet.2022.133174 [32] N.M. Ferreira et al., J. Alloys & Compounds 918 (2022) 165678, DOI: 10.1016/j.jallcom.2022.165678 Topic: Devices & Applications (DA) Oral Presentation DA.06 41 The Impact of Collectors/Absorbers on the Efficiency of PhotoThermoelectric Devices A. L. Pires1, M. A. S. Almeida1, M. M. Maia1, M. Rocha1, P. Robalinho2, C. Fortado3, O. Frazão2, A. M. Pereira1 1IFIMUP - Institute of Physics for Advanced Materials, Nanotechnology and Photonics, Faculdade de Ciências da Universidade do Porto, 4169-007 Porto, Portugal. email: [email protected] 2INESC - Institute for Systems and Computer Engineering, Technology and Science, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal. 3CeNTI - Centre for Nanotechnology and Smart Materials, Famalicão, Portugal Collectors and/or plasmonic systems can be used when combined with electromagnetic waves to increase the temperature promoting temperature gradients to be used in thermoelectric generators (TEGs) [1]. The influence of different screen-printed collectors will be investigated in this work to understand how they affect the ultimate performance of the TEGs. Several radial printed TEGs were created for this purpose, employing 8 thermoelectric stripes manufactured using commercial p-type chalcogenide Sb2Te3-based inks [2]. The radial arrangements allow us to integrate the different absorbers/collectors in the device's core. As a result, with this thermoelectric design, a long-distance near-infrared fiber laser with a wavelength of 1450 nm hits its center, causing heat to flow straight along the thermoelectric printed stripes from the inside to the outside of the TEG. Different laser powers were used to generate temperature gradients in the photo-TEG (Plaser from 0.15 W to 1 W). Herein, commercial carbon black, titanium nitrate, zinc oxide, and bismuth oxide (Bi2O3)-based inks were employed for the absorbers or collectors-based systems. To better understand the impact of the produce absorbers or collectors on the efficiency of the TEGs, a comprehensive characterization of the production devices was conducted before and after the deployment of each collector. Bering in mind the implementation of this systems in the CubeSat technology, all the TEGs are characterized under extreme conditions namely in vacuum (~10-6 Torr). Additionally, all the printed collectors were analyzed by UV-Vis-NIR spectrophotometer reaching an absorbance higher than 60%. We will demonstrate that implementing a collector can boosted the produced temperature gradient by 50%, resulting in a 47% boost in total performance. Ultimately, the technological viability of such hybrid systems, such as high-resolution sensors in high-wavelength lasers (Near-infrared Region), will be discussed. Acknowledgements: Financial support from UIDB/04968/2020, and NORTE-01-0145FEDER-022096 from NECL is gratefully acknowledged. ALP, MMM, MR and AMP thank the funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 863307 (Ref. H2020FETOPEN-2018-2019-2020-01). MMM thanks FCT for grant SFRH/BD/144229/2019. References: [1] C. Xin et al., Materials Today Energy, 22, 100859 (2021). [2] A.L. Pires et al., ACS Applied Materials & Interface 11, 8969–8981 (2019). Topic: Devices & Applications (DA) Oral Presentation DA.10 48 Prospects of volcano surveillance powered by thermoelectric generators: the Antarctica challenge Leyre Catalán1, Nerea Pascual1, Miguel Araiz1, Patricia Alegría1, Irantzu Erro, Álvaro Martínez1, David Astrain1 1 Institute of Smart Cities, Public University of Navarre, Campus Arrosadia 31006 Pamplona (Spain) e-mail: leyre.cata[email protected] Thermoelectric generators have recently arisen as a solution to guarantee a robust, compact and reliable power supply for volcanic vigilance stations, which are indispensable to predict eruptions. These stations are normally located in areas with access difficulties, lack of power grid, and adverse meteorological conditions. Nonetheless, in those areas it is always possible to find fumaroles, hot gases that emerge from the ground, since it is one of the characteristics of active volcanoes. Transforming this heat into electricity by means of thermoelectric generators suppose a continuous, robust, compact, scalable, and reliable autonomous power supply. These advantages have been demonstrated with the prototype depicted in Figure 1 that has been in operation since December 2019 in an 83.5°C fumarole at Teide volcano (Canary Islands, Spain) [1]. The prototype is made of high-efficiency heat exchangers based on phase change that maximize power generation with no moving parts. With only two Bi-Te thermoelectric modules, the prototype generates enough energy to measure different variables and emit them to a center located 14 km away, leading to a completely autonomous monitoring station. Fig. 1. Thermoelectric generator installed at Teide volcano in December 2019. Although the viability of the proposed solution has been demonstrated for more than three years without maintenance, the present work goes a step further, designing a thermoelectric generator for Deception Island (Antarctica). The conditions in this island are extremely harsh, and yet to date none of the solutions tested have lasted a complete austral winter. Thus, if the proposed solution overcomes the challenge, new possibilities for thermoelectric generators will arise, becoming a great solution in order to obtain an autonomous power supply in any volcano in the world. Topic: Devices & Applications (DA) Oral Presentation DA.10 49 Acknowledgements We would like to acknowledge the support of the Spanish State Research Agency and FEDERUE funds under the grants TED2021-129359B-I00 and PID2021-124014OB-I00, as well as the Public University of Navarre under the grant PJUPNA14-2022. References [38] Leyre Catalan, Amaia Garacochea, Alvaro Casi, Miguel Araiz, Patricia Aranguren, David Astrain, “Experimental Evidence of the Viability of Thermoelectric Generators to Power Volcanic Monitoring Stations”, Sensors 20 (2020). DOI: 10.3390/s20174839 Topic: Thermoelectric Devices & Applications (DA) Poster Presentation P.01 50 Implementation of Arrays of Thermoelectric Generators for Nanosatellites: Evaluation under Atmospheric and Space Conditions R. S. Costa,1 F. Carpinteiro,1 M.M. Maia,1 M. Rocha,1 A. L. Pires,1 A. M. Pereira1 1 IFIMUP, Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Porto, Portugal, email: r[email protected] The CubeSats Era is revolutionizing space exploration field in the last years. Several areas, such as weather information, space weather, transportation, navigation and security, are evaluating to resort to this technology. The CubeSat market generated $143.7 million in 2017 and is estimated to grow at a CAGR of 13.43% during 2018-2023 [1]. The powering of the CubeSat systems relies on larger solar arrays that still present some limitations such as low efficiency on non-illuminated areas as well as weight problems. Thus, our team purposed an innovative wireless power device using Thermoelectric (TE) Generators arrays combined with a laser and a specific absorber allowing a Wireless Energy Transfer (WET) [2]. Since CubeSats are exposed to continuous temperature changes, e.g., due to changing sun irradiation during orbits, and for materials to be suitable for space applications, their performance under thermal cycling in vacuum must be validated. Herein, the fabrication of photo-thermoelectric plasmonic (HPTP) system composed of an array of 9 radial thermoelectric generators connected in series was performed by a simple screenprinting process. The TE strips were fabricated using an optimized Bi2Te3/polyvinyl alcohol (PVA) ink, while the electrical contacts between them were made using a commercial silver ink. In parallel, the design and implementation of a vacuum cryogenic chamber for performance evaluation of the HPTP as well as validation of the robustness of all components under space conditions is also presented. The cryogenic chamber presents a rectangular-shape being its walls made of an aluminum alloy. This chamber will allow to evaluate the performance of the HPTP measuring the generated voltage over the time while the inside temperature is increase/decrease from 100 to 400 K (vice-versa) under ultra-high vacuum conditions. At room temperature and atmospheric pressure conditions, the HPTP showed a generated voltage output of 40 mV power laser of 4.5 W. Acknowledgements This work was funded by H2020-EU.1.2.1. - FET Open Project (WiPTherm, grant agreement ID: 863307). R.S.C., M.R. and A.L.P thank the junior researcher contract funded by European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 863307 (H2020-FETOPEN-2018-2019-2020-01). References [1] Global Nano Satellite Market - Analysis and Forecast (2018-2023), available online at https://bisresearch.com/industry-report/nano-satellite-market.html. [2] Mauser, K., et al., Nature Nanotechnology 12, 770–775 (2017). Topic: Thermoelectric Materials & Processing (MP) Poster Presentation P.02 51 On the Thermal Conductivity of Thermoelectric Polymers Upon Doping Jiali Guo1, Kai Xu1, Jesika Asatryan2, Matías Jesús Alonso Navarro3,4, Osnat ZapataArteaga1, Mariavittoria Craighero5, M. Mar Ramos4, José L. Segura3, Jaime Martín2,6, Christian Müller5, Juan Sebastian Reparaz1, and Mariano Campoy-Quiles1* 1 Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus UAB, Bellaterra 08193, Spain, Presenting author e-mail: [email protected] 2 Centro de Investigación en Tecnologías Navales e Industriales, CITENI, University of A Coruña, 15403, Spain. 3 Department of Organic Chemistry, Faculty of Chemistry, UCM, 28040, Madrid, Spain. 4 Chemical and Environmental Technology Department. Univ. Rey Juan Carlos, Móstoles, 28933, Spain. 5 Department of Chemistry and Chemical Engineering Chalmers University of Technology Göteborg 41296, Sweden. 6 POLYMAT and Polymer Science and Technology Department, Faculty of Chemistry, University of the Basque Country UPV/EHU, Paseo Manuel de Lardizabal 3, 20018 Donostia-San Sebastián, Spain Understanding the general correlation between electrical and thermal transport in organics is a key element to fabricating high-performance thermoelectric generators.[1] In order to investigate this issue in a systematic fashion, we have looked at eight conjugated polymer materials (PBTTT, DPP-DTT, PDPP4T, NIP3H, NIP3H-BDT, Regio Random P3HT, Regio Regular P3HT, p(g4 2T-T)) and four doping systems, namely, F4TCNQ, FeCl3, FeCl3-Li-TFSI, FeCl3BMP-TFSI. The thermal conductivity of selected samples was analysed by Frequency-domain thermoreflectance (FDTR)[2]. Upon doping, the out-of-plane thermal conductivity of all five semicrystalline polymers reduces with respect to the neat polymers, while that of the amorphous material increases. As the electronic contribution to the thermal conductivity increases with doping following Wiedemann Franz law[3], the observed reduction in the overall thermal conductivity is intriguing and could be a very interesting feature for thermoelectrics. Several hypotheses are being investigated, namely an alloying effect of the dopant, a reduction in crystallinity, and an increase in anisotropy (orientation induced by doping). GIWAXS data suggest that the degree of order is not reduced. We managed to produce free standing films of the two DPP-based polymers in order to measure their in-plane thermal conductivity. We found that in both cases, the in-plane thermal conductivity increases upon doping. Our current understanding is that doping induces an increase in orientation within the plane of the film, thus thermal transport within the polymer chain is favoured in the plane, while the two directions of low thermal conductivity, i.e. pi-pi stacking and sidechains, are preferentially distributed perpendicular to the plane of the film, thus reducing the thermal conductivity out-of-plane. References [39] Zapata-Arteaga, O. et al., ACS Energy Letters, 2020, 5, 9, 2972. [40] Schmidt A J. et al., Review of scientific instruments, 2009, 80(9): 094901. [41] Scheunemann, D. et al., Phys. Rev. B: Condens. Matter Mater. Phys. 2020, 101 (7), 075206. Topic: Measurement and Characterization Poster Presentation P.03 52 Impedance spectroscopy: a suitable tool to fully characterize a thermoelectric device Jorge García-Cañadas1, Braulio Beltrán-Pitarch1 1 Universitat Jaume I, Department of Industrial Systems Engineering and Design, Av. Vicent Sos Baynat s/n, 12006 Castelló de la Plana, Spain, e-mail: [email protected] The fabrication of thermoelectric devices is not a simple task, since it involves the optimisation of many parameters, such as the thermoelectric materials themselves, their connection with the metallic strips, the thermal influence of the electrically insulating layers, etc. Impedance spectroscopy offers many advantages to characterize thermoelectric devices, since from simple measurements that just require the connection of the device to the impedance equipment and vacuum, it is able to quantify many of the key properties of the device, such as the materials properties and the thermal contact resistances at the thermoelectric material/metallic strip junctions [1]. In addition, when integrating the devices into generators the efficiency of conversion of heat into electricity is not only influenced by the material properties, but it also depends on the temperature of operation, which is governed by the thermal resistances from the thermoelectric legs up to the heat source/sink [2]. The thermal contact resistances between the outer ceramics of the thermoelectric devices and the heat exchangers is especially essential. We recently proved that these thermal contacts can be determined by performing an impedance measurement in suspended conditions and a measurement with the device assembled [3]. In this work, we show all the advantages and benefits of the impedance method, and its enormous potential to fully provide all the key properties of a thermoelectric device. References [42] B. Beltrán-Pitarch et al., Applied Energy 299, 117287 (2021). [43] S. Wang et al., Applied Thermal Engineering 130, 847 (2018). [44] B. Beltrán-Pitarch et al., Applied Thermal Engineering 165, 114361 (2020). Topic: Other Topics on Thermoelectricity Poster Presentation P.04 53 PDADMA-based solid electrolytes to significantly enhance the power factor of a thermoelectric oxide film Mauricio Solis-de la Fuente1, Sergio Castro-Ruiz1, Lourdes Márquez-García1, Pauline Rullière2, Sébastien Fantini2, Jorge García-Cañadas1 1 Universitat Jaume I, Department of Industrial Systems Engineering and Design, Av. Vicent Sos Baynat s/n, 12006 Castelló de la Plana, Spain, e-mail: [email protected] 2 Solvionic SA, 11 Chemin des Silos, 31100 Toulouse, Francia The performance of thermoelectric materials is estimated by the device figure of merit (ZT=S2σT/λ, being S the Seebeck coefficient, σ the electrical conductivity, λ the thermal conductivity, and T the absolute temperature). Recently, large power factor (PF=S2σ) enhancements have been shown in a novel hybrid solid-liquid thermoelectric system, consisting of a porous nanostructured solid material (Sb-doped SnO2) in contact with diverse liquid electrolytes [1]. In this contribution, we have investigated the nanostructured Sb-SnO2 film in contact with different solid electrolytes based on the poly-diallyl dimethylammonium cation (PDADMA). From all the electrolytes tested, the poly-diallyl dimethylammonium chloride (PDADMAC) was found to provide more than 2 times improvement in the power factor. This large improvement was due to a ≈60% decrease in the electrical resistance of the device accompanied by a slight reduction of less than 10% in the absolute value of the Seebeck coefficient. Impedance spectroscopy analysis was carried out to understand the role of the solid electrolyte in the device performance. This notable power factor improvement paves the way to use polyelectrolytes to fabricate all-solid-state hybrid solid-electrolyte devices with enhanced power factors. References [45] L. Márquez-García et al., ACS Applied Energy Materials 1, 254 (2018). Topic: Thermoelectric Materials & Processing (MP) Poster Presentation P.05 54 Characterization of a Possible Thermoelectric Material prepared from Natural Pyrite Vanina G. Franco,1,2 Adriana E. Candia,1,3 Jorge M. Nuñez1,4, Miguel Rengifo1, Jorge Lobo-Checa,1 Myriam H. Aguirre1,5 1 Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia y Materiales de Aragón-INMACSICUniversidad de Zaragoza, Campus Río Ebro, Edificio I+D+i, C/ Mariano Esquillor, s/n, 50018, Zaragoza, España 2 Departamento de Física, Facultad de Ingeniería Química, Universidad Nacional del Litoral, Santiago del Estero 2829, 3000, Santa Fe, Argentina, e-mail: [email protected] 3 Instituto de Física del Litoral, CONICET-UNL, Güemes 3450, 3000, Santa Fe, Argentina 4 Instituto de Nanociencia y Nanotecnología, CNEA, CONICET, S. C. Bariloche 8400, Río Negro, Argentina 5 Departamento de Física de la Materia Condensada, Universidad de Zaragoza, C/ Pedro Cerbuna 12, 50009, Zaragoza, España Thermoelectric (TE) materials have been the subject of numerous studies for some decades as they can effectively contribute to reducing greenhouse gas emissions, which lowers the environmental impact due to the use of green technologies. Another important aspect is the raw material used in the generation of these materials, and its abundance and availability is crucial [1]. Pyrite (FeS2) is one of the most abundant minerals in the earth's crust, as well as being easy to extract and inexpensive, which makes it a material of choice for technological developments. By heat treatment of the mineral, it is possible to generate a thin film of magnetite (Fe3O4) that confers magnetic properties of the pyrite. Starting from magnetic materials, and using the properties associated with the presence of spins, materials with TE characteristics can be designed [2]. However, for these materials to be efficient, it is necessary to clearly understand the interrelationships between their structure, magnetic behaviour and Seebeck effect. In this work, we prepare and characterise a material with TE properties from a natural mineral. Pyrite single-crystals were sectioned and chemically treated for cleaning. These films were placed at different temperatures and exposure times, under normal conditions of pressure and aerobic atmosphere. The chemical species of each surface film were determined by XPS; the structure and composition of the different materials generated using TEM, STEM, EELS; the magnetic properties by MFM and magnetometry measures and the charge carriers through Seebeck effect. For the 3 exposure temperatures, films with different characteristics were obtained, as well as for the different exposure times. XPS and EELS spectra, revealed the presence of oxidised Fe and Oxygen species. TEM and STEM images revealed different structural arrangements for the magnetite: amorphous thin film, epitaxial formation and nanoparticle clusters which correlates with the magnetisation measurements that evidenced characteristic behaviour of magnetite. The topography and phase MFM images showed significant differences in the configuration of the magnetic domains of each material. The behaviour in relation to the Seebeck effect correlates with the structural data. From the above, we can infer that the use of pyrite as a raw material for the development of thermoelectric materials is possible given the advantages and results obtained in the present study. References [46] M. Culebras et al., Applied Surface Science Vol 615, 156432 (2023) [47] A. Portavoce et al., Scientific Reports Open Access Vol 13, 172 (2023) Topic: Thermoelectric Materials & Processing (MP) Poster Presentation P.06 55 Synthesis, optical band gap and thermoelectric properties of Sr1+xTiS3-y chalcogenide perovskites Jinan H. Al Shuhaib 1, Jose F. Fernández1,2, Julio Bodega1, Fco. Javier García-García3 José R. Ares 1, Isabel J. Ferrer 1,2, Fabrice Leardini 1,2 1 Departamento de Física de Materiales, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid, Spain. 2 Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid, Spain 3 ICTS-Centro Nacional de Microscopía Electrónica, Universidad Complutense de Madrid, E-28040, Madrid, Spain [email protected] Inorganic chalcogenide perovskites are semiconductors with the general formula ABX3, with A being a group II cation (i.e., Ca2+, Sr2+, or Ba2+), B a group IV transition metal (i.e., Ti4+, Zr4+, or Hf4+), and X a chalcogen anion (S2− or Se2−) [1]. Recent theoretical studies have shown that these materials may exhibit a high Seebeck coefficient and low thermal conductivity, suggesting that the chalcogenide perovskite compounds are good candidates for thermoelectric applications [2,3,4]. Some of these compounds have been poorly investigated to date. For instance, the thermoelectric data of SrTiS3 have been scarcely reported, both experimental and theoretical. Herein, we present a novel synthesis procedure to obtain Sr1+xTiS3-y powders from the sulphuration of SrTiO3 ones at different temperatures. Moreover, we show an experimental characterization of some fundamental properties of this compound that may be relevant for potential thermoelectric applications. First, we determine the crystalline structure by x-ray powder diffraction (Figure 1 a) and electron diffraction. Tilting experiments of several crystals in the electron microscope tackled the reconstruction of the whole associated reciprocal lattice. In addition, high-resolution electron microscopy images of this compound have been acquired for the first time. Chemical composition was characterized by Energy Dispersive x-ray Analysis in a Scanning Electron Microscope. We experimentally determined the optical band gap (of about 0.96 eV) corresponding to a direct allowed transition, in agreement with previous predictions [5]. In addition, thermogravimetric analysis and differential scanning calorimetry measurements demonstrate the very high thermal stability of this perovskite (up to 700 °C in air and up to 1200°C in Argon atmosphere). Finally, we investigated the thermoelectric properties by measuring the Seebeck coefficient for samples obtained at different sulfurization temperatures (Figure 1b). There is a strong dependence of the Seebeck coefficient on the amount of sulfur vacancies, including a change from n-type to p-type behavior, as it can be seen in Figure 1c. The characteristics of the obtained chalcogenide perovskite SrTiS3 may open new opportunities for the design of novel devices for high temperature thermoelectric applications. Topic: Thermoelectric Materials & Processing (MP) Poster Presentation P.06 56 References [1] Y. Sun et.al., Nano Letters, 15, 581−585 (2015) [2] H. Shahmohamadi and S. Naghavi, ACS Appl. Mater. Interfaces, 13, 14189−14197 (2021) [3] X. Song et al., J. Phys. Chem. C, 126, 11751−11760 (2022) [4] E. Agyemang. et al , J. Mater. Chem. C, 9, 3892–3900 (2021) [5] Y. Sun et.al., Nano Lett.,15 ,581−585, (2015) Figure 1. (a) x ray diffraction patterns of the starting SrTiO3 oxide (upper panel) and SrTiS3 chalcogenide (bottom panel). Miller indexes of the main diffraction peaks are indicated. (b) Thermoelectric voltage (ΔV) as a function of the temperature difference (ΔT) along the Srx+1TiS3-y pellets recorded during a warming up and cooling down cycle. (c) Seebeck coefficient as a function of the S/(Sr+Ti) ratio in the samples. Topic: Thermoelectric Devices & Applications (DA) Poster Presentation P.07 57 Maximizing exhaust heat utilization in lightand heavy-duty driving cycles through phase-change: Simulations and Experimental validation Rui Carvalho1, Carolina Sousa1, Óscar Carvalho2, J. Martins1, Ana Moita3, F.P. Brito1 1 Dept. Mech. Eng., MEtRICs, Univ. of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal, email: francis[email protected] 2 Dept. Mech. Eng., CMEMS, Univ. of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal 3 Dept. Mech. Eng, IN+, IST-Univ. of Lisbon, Av Rovisco Pais 1049-001 Lisbon, Portugal The increasing electrification degree in urban mobility seems now an irreversible trend. However, the internal combustion engine seems to be far from dead, even considering the longterm goal of going towards the decarbonization of the economy. The use of sustainable fuels is an effective way of minimizing global life-cycle impact even below current battery electric vehicles (BEVs) [1]. Full vehicle electrification is still not viable for heavy duty vehicles (HDVs). Finally, current vehicles must comply with emissions standards that are impossible to attain without some degree of hybridization and efficiency-oriented strategies [1]. For these reasons, on-board electricity generation from exhaust heat seems especially attractive for the next few decades. In fact, growing vehicle electrification levels favours this approach, especially when long, high load driving cycles are frequent. This is the case of HDVs and hybrid (HEV) or plug-in hybrid vehicles used for frequent long distances, as is the case of a lot of corporate fleets. Thermoelectric generators (TEGs) would seem to be especially suited for this task given their simplicity and low maintenance needs when properly designed. However, most systems developed so far have failed to be viable, namely for cost and performance reasons. Recent advances in affordable TE materials such as the tetrahedrite-silicide TEGs explored by the authors [2] may address the cost issue. Additionally, the authors have been exploring ways of thermally optimizing the TEG for maximum use of the available, highly variable exhaust heat of real-world driving. This included optimizing heat absorption at the exhaust, its delivery to the hot side of the TEG at an optimized level irrespective of engine regime, and its efficient removal at the cold side of the TEG [3]. An ongoing project (COOLSPOT) is dedicated to the latter part through the use of microchannels and surface modification with laser ablation. The authors have been researching temperature controlled thermoelectric generators (TCTGs). One of the concepts is illustrated in Fig 1. It consists of using chambers located along the heat path, between the exhaust heat absorption surface and the TE modules. These chambers contain a non-condensable gas (NCG) and a working fluid that vaporizes only when close to the optimal TEG hot side temperature. This way, whenever a region of the TEG reaches this temperature, the working fluid starts absorbing heat by boiling preventing further temperature rise. Subsequently, this heat is released to under-heated regions of the system by condensation. This way, not only overheating is avoided, but also the available exhaust heat is optimally distributed along the various TE modules. This allows designing low thermal resistance heat exchangers to maximize exhaust heat absorption, without overheating risk under high engine loads, or thermal dilution under low engine loads. The potential of the TCTG concept was illustrated in previous publications, with peak/average outputs exceeding 1.5/0.25 kW in a light duty vehicle under the WLTC driving cycle [3] and 5/2.4 kW in a HDV vehicle under a Long Haul cycle [4]. However, experimental evidence of the effectiveness of the TCTG concept had not been presented until recently. The present study illustrates both theoretically, as well as experimentally, that the proposed concept works similar to expected. Fig 1b shows two of the downsized proof-of-concept prototypes tested, which incorporate stainless steel corrugated pipes for the exhaust heat absorption and copper (MK1)