A new plastic crystal composition with thermal energy storage potential

FACULTAD DE CIENCIAS TRABAJO FIN DE GRADO Grado en Química A new plastic crystal composition with thermal energy storage potential Autora: María Paz Cosgaya Tutores: Julian Walker, José Miguel Martín Álvarez Año 2023 ii Preface I want to thank my supervisor in NTNU, Julian Walker, for letting me work with him during my stay in Norway and teaching me new ways of working in the lab. I want to also thank my supervisor in Valladolid, José Miguel Martín Álvarez, for assisting me during this year and agreeing on helping me with my thesis. It has been a pleasure to write my thesis with you both. I also want to thank my family and friends, who supported me a lot, and the new friends that I made during my Erasmus. I really loved this year with you guys, and I hope we see each other soon. Thank you all! iii Abstract Plastic crystals are supramolecular materials with a long-range crystallographic order that go through a phase transition to a phase where the crystal structure is maintained but a local structural disorder is introduced. This phase transition is a mesophase transition, and it is a solid-solid transition where the molecules gain enough free energy so they can rotate freely but there are still weak interactions that maintain the crystal structure. Due to this higher entropy change, these types of compounds can store more energy than other solid-solid state materials. Bis-[(3,4-dimethylphenyl)oxonium](dibromo dichloro zincate) ((DMP)2 [ZnBr2Cl2]) is a new composition with thermal energy storage potential that has been synthetized by in this project, with the aim of identifying new plastic crystal compositions. As the structure of the material was unknown, it was determined with X-ray diffraction, and the thermal properties of the material were studied using differential scanning calorimetry, so the different phase transitions of the material and its properties could be determined and decide whether or not the material is a plastic crystal. The results showed that small modifications of the synthesis change the crystal habit and properties of the final crystals. The DSC analyses showed that the material has a phase transition in a temperature range below 100 ºC that might be applicable to domestic (personal housing) applications, rather than industrial applications. iv Resumen Los cristales plásticos son unos materiales supramoleculares con un gran orden cristalográfico que tienen transiciones de fase a fases donde la estructura cristalina se mantiene, pero aparece un desorden estructural local. Esta transición de fase es conocida como la transición de mesofase, y es una transición sólido-sólido donde las moléculas ganan suficiente energía libre, por lo que pueden rotar libremente, pero aún mantienen interacciones débiles que mantienen la estructura cristalina. Estos compuestos tienen un mayor cambio de entropía en la transición a la mesofase que otros materiales con transiciones de fase sólido-sólido, con lo que pueden almacenar más energía. Bis-[(3,4-dimetilfenil)oxonio](dibromo dicloro zincato) ((DMP)2 [ZnBr2Cl2]) es un nuevo material con potencial de almacenamiento de energía térmica. Este compuesto ha sido sintetizado en este proyecto con el objetivo de identificar nuevas composiciones de cristales plásticos. La estructura de este material era desconocida, así que ha sido determinada por difracción de rayos X, y las propiedades térmicas del material han sido estudiadas utilizando calorimetría diferencial de barrido (DSC), para poder determinar las diferentes transiciones de fase del material y sus propiedades para poder determinar si es un cristal plástico o no. Los resultados del proyecto demostraron que pequeñas modificaciones del método de síntesis pueden cambiar el hábito cristalino y las propiedades de los cristales obtenidos. Los análisis de DSC mostraron que el material tiene una transición de fase en un rango de temperaturas menor de 100 ºC que puede ser usado para aplicaciones domésticas (vivienda personal), en lugar de aplicaciones industriales. v Contents Abstract ........................................................................................................................... ii Resumen ......................................................................................................................... iv List of abbreviations ..................................................................................................... vii 1 Background .......................................................................................................... 1 1.1 Motivation .......................................................................................................... 1 1.2 Aim of work ....................................................................................................... 2 2 Introduction ......................................................................................................... 3 2.1 Latent heat and solid-state phase change materials for thermal energy storage 3 2.2 Plastic crystals .................................................................................................... 6 2.3 Crystallization .................................................................................................... 8 2.3.1 Nucleation ................................................................................................... 8 2.3.2 Growth ...................................................................................................... 11 2.3.3 Crystal habit .............................................................................................. 12 2.4 Thermodynamics of phase transitions ............................................................. 13 2.5 Quenching ........................................................................................................ 14 3 Experimental ...................................................................................................... 15 3.1 Synthesis of (DMP)2 [ZnBr2Cl2] ...................................................................... 15 3.2 Structural determination .................................................................................. 16 3.2.1 XRD .......................................................................................................... 16 3.2.2 Raman spectroscopy ................................................................................. 17 3.3 Thermodynamic characterization..................................................................... 17 3.3.1 DSC .......................................................................................................... 17 4 Results ................................................................................................................. 20 4.1 Sample clarification ......................................................................................... 20 4.2 Synthesis observations ..................................................................................... 21 4.2.1 June 2022 crystals ..................................................................................... 21 4.2.2 Crystallization attempt 1 ........................................................................... 22 4.2.3 Crystallization attempt 2 ........................................................................... 23 4.2.4 Crystallization attempt 3 ........................................................................... 24 4.2.5 Crystallization attempt 4 ........................................................................... 24 4.3 Crystal structure ............................................................................................... 25 4.3.1 June 2022 crystals ..................................................................................... 26 4.3.2 Determination of the crystal structure ...................................................... 26 vi 4.3.3 Crystallization attempt 1 ........................................................................... 29 4.3.4 Crystallization attempt 2 ........................................................................... 29 4.3.5 Crystallization attempt 3 ........................................................................... 31 4.3.6 Crystallization attempt 4 ........................................................................... 32 4.3.8 Structural stability as a function of thermal treatment ............................. 32 Air-cooled sample ................................................................................................... 33 Quenched sample .................................................................................................... 35 4.4 Phase transitions .............................................................................................. 36 5 Discussion ........................................................................................................... 42 5.1 Synthesis observations ..................................................................................... 42 5.1.1 Crystallization attempt 1 ........................................................................... 42 5.1.2 Crystallization attempt 2 ........................................................................... 42 5.1.3 Crystallization attempt 3 ........................................................................... 43 5.1.4 Crystallization attempt 4 ........................................................................... 43 5.2 Crystal structure ............................................................................................... 43 5.2.1 Crystallization attempt 2 ........................................................................... 43 5.2.2 Crystallization attempt 3 ........................................................................... 44 5.3 Determination of the crystal structure ............................................................. 44 5.3.1 Structural stability as a function of thermal treatment ............................. 45 Air-cooled sample ................................................................................................... 45 Quenched sample .................................................................................................... 46 5.3.2 Raman spectroscopy ................................................................................. 49 5.4 Phase transitions .............................................................................................. 49 6 Conclusion .......................................................................................................... 52 Bibliography .................................................................................................................. 53 Appendix ....................................................................................................................... 56 Indexing results ......................................................................................................... 56 Pawley fitting ............................................................................................................. 58 vii List of abbreviations Phase Change Materials (PCMs) Thermal Energy Storage (TES) Plastic Crystals (PCs) X-ray diffraction (XRD) Organic PCMs (OPCMs) Inorganic PCMs (IOPCMs) Room temperature (RT) Goodness of fit (Gof) Bis-[(3,4-dimethylphenyl)oxonium](dibromo dichloro zincate) ((DMP)2 [ZnBr2Cl2]) 1 1 Background 1.1 Motivation In order to maximize the use of renewable energy sources that provide electricity intermittently rather than on demand, thermal energy storage (TES) is a crucial component of Europe's energy future. Additionally, it enables us to recover extra heat that would otherwise be lost through industrial processes or from the sun (solar thermal). The integration of renewable energy into our energy systems may thus be boosted, and CO2 emissions can be decreased, with the help of TES. 1 Based on how they store thermal energy, thermal energy storage materials can be classified into three groups, which are chemical heat, sensible heat, and latent heat storage. Comparing these mentioned types of thermal energy storage systems, a promising technology for future development is latent heat storage, because of its potential for space optimization and efficiency. Furthermore, many thermal storage systems use toxic materials, but latent heat TES systems can be based on solid-state PCMs which are safer and could replace dangerous compounds for less toxic and environmentally friendly ones. 2 According to their composition, PCMs can be classified into three groups: organic (for example paraffins, fatty acids and alcohols), inorganic (salt hydrates and metallic compounds), and eutectic (combination of organic-organic, inorganic-inorganic, and organic-inorganic PCMs). There is not much information about the last type, and organic PCMs are preferred over the inorganic ones because they have more advantages and less disadvantages, for instance, low volume changes, compatible with conventional construction materials, large working temperature range, recyclable and low cost. Some disadvantages are that they are flammable and have low thermal conductivity. Due to their chemical composition and crystal structure, the properties of PCMs can change, rendering different materials more suitable to different temperature ranges and others altogether unsuitable for energy storage purposes. Some of the desired properties are: 3 a) Phase transition temperatures that fit in the desired temperature range. There are three distinct low temperature range categories: up to 15 ºC for cooling application, 15-90 ºC for thermal comfort and above 90 ºC for hot water applications. b) High density to occupy less volume and increase thermal energy stored. 2 c) High thermal conductivity, so that only minor temperature differences are required for charge and discharge the energy storage. d) Non-toxicity. e) Small volume change during in phase transitions. f) Chemical stability. g) Low cost. A subclass of PCMs are plastic crystals (PCs), which were first categorized by Timmermans in 1935. These are supramolecular materials that possess a solid-mesophase transition before melting. The mesophase is a crystalline phase with long range structural order and a local molecular orientational disorder that is associated with a large entropy change; hence they are good phase change materials and interesting for TES and other applications. 4,5 The search for new PC materials is ongoing and of interest for thermal energy technologies, for finding more accessible compounds with better thermophysical properties, i.e., enthalpy of transition, temperature of transition, thermal conductivity, thermal stability, and basic mechanical properties. Also, for substituting toxic and polluting compounds employed in energy storage applications. 1.2 Aim of work The project’s aim is to evaluate a potentially new phase change material, (DMP)2 [ZnBr2Cl2], and its potential use for TES. It is composed by an organic cation, [(3,4dimethylphenyl)oxonium]+ which has been protonated with H+ from a HCl solution, and an inorganic anion ZnBr2Cl22that is produced from the dissolution of ZnBr2∙2H2O and combination with dissolved Cl-. As the organic components have similar characteristics as other plastic crystal materials, that is, they are small and globular in shape, which was identified by Timmermans et al. as a prerequisite for plastic crystals, it is expected that it may behave similarly. However, the different combination of fragments and specific structural symmetry may provide additional influences on the thermal properties. Since there is no known literature report of this material, the present work will develop a synthesis pathway and characterize the basic crystal structure and thermodynamic properties of the material. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were employed to determine the lattice parameters of the compound and calculate the total entropy and enthalpy change of the compound’s transitions. 9 Figure 2.3: The different phases are stable depending on the temperature. If it is below the solidification temperature, the solid state will be more stable than the liquid one because the energy required in the solid phase will be less. On the contrary, if the temperature is higher, the stable phase will be the liquid one, because in this case its energy is the lowest and is more spontaneous. When there are two phases coexisting, a solid-liquid interface is formed and there is an associated free surface energy, σ, a positive energy unfavorable to the solid formation. Considering this factor, the total ΔG would be: Δ𝐺 = ΔG𝑣+ Δ𝐺𝑠 (2.1) Δ𝐺 = 4 3𝜋𝑟3Δ𝐺 + 4𝜋𝑟2𝜎 (2.2) where ΔG𝑣 is the volume of the spheric particle per Δ𝐺 and has a negative value, and Δ𝐺𝑠 is the spheric surface per surface energy (σ). An embryo is a small solid particle that is formed from the liquid solution when the atoms agglomerate and is unstable and it may grow or not depending on the conditions. 22 10 Figure 2.4: The dependence of the two energy contributions, ΔG𝑣 and Δ𝐺𝑠 on r, the crystal size, shows the critical change in free energy, which, as a sort of activation energy, is the energy that must be overcome for the nucleus to be able to expand. 23 At first, Δ𝐺𝑠 contributes more to free energy than ΔG𝑣, and if the particle has a higher radius than the critical radius, r*, this will continue growing while the energy decreases and a nucleus is formed and will keep growing. If the size of the radius is lower than critical one, the embryo will redissolve and disappear because that is the most stable option. The formation of the embryos is a statistic process because lots of them are formed and redissolved. A posterior growth makes the total free energy to decrease only if by any chance an embryo with a higher radius than the critical one is formed. The number of stable nuclei is temperature-dependent, therefore rising temperatures will result in higher activation free energies and fewer stable nuclei. Since the system has a lower temperature than the melting one, it is considered subcooled. Subcooling is the difference between the solidification temperature and the real system’s temperature. Sometimes, when the material is too pure, a bigger subcooling is necessary for forming stable nuclei. Heterogenous nucleation occurs when there are impurities in the system, and the critical radius is achieved when a spheric portion with the exact curvature of r* is added. This type of nucleation is easier, because for achieving the critical radius, less subcooling is required and nucleation will occur faster. 22 11 2.3.2 Growth Growth is the incorporation of new molecules to the formed and stable nuclei to increase their size. There are two types of growth: Planar growth occurs when there is a heterogeneous nucleation. At the solidification temperature, some liquid particles are incorporated into the solid surfaces and inside this solid phase, the temperature decreases when the distance to the melting temperature is greater, because it is more stable at lower temperatures. Inside the liquid phase, the temperature increases when the distance to the solidification temperature is greater because it is more stable at higher temperatures. As the temperature increases, latent heat of fusion is released to the solid state, where the temperature is lower, for continuing growth. In the solid-liquid interface there is a protuberance and a flat surface. If the particle incorporates to the protuberance, the heat will be expanded to the interior in an angle lower than 180 º. If the particle joins to the flat surface, the heat spreads in a 180 º angle to the interior. This last situation is preferable because the heat can travel faster, and the protuberance will disappear. 22 Figure 2.5: If the temperature is above the melting temperature, there will not be any protuberance and the flat surface will persist. 22 Dendritic growth takes place in a homogeneous nucleation. At the melting temperature, liquid particles are incorporated into the solid’s surface. Inside the solid state the temperature decreases when the difference between the temperature and the melting one is greater because it is stable at a less temperature. In the liquid state there will be a decrease in the temperature below the solidification point because there is subcooling, and then it increases as usual. 12 If the nucleus grows, latent heat of fusion is released and will be directed to the coldest regions, but preferable the liquid one because absorbs heat better. There is also a protuberance and a flat surface. If a particle incorporates into the flat surface, the heat will be spread in a 180 º angle into the interior. However, if the particle joins the protuberance, the angle will be higher than 180 º and growth will be faster than in the other surface, and another protuberance will be formed and when it grows another will be created. The result of this process is a dendrite. 22 Figure 2.6: If the liquid is subcooled, a protuberance can grow into a dendrite faster. Latent heat of fusion will be released, and the liquid’s temperature will increase to the solidification temperature. 22 2.3.3 Crystal habit The faces of a crystal are the crystal habit, and its development depends on several factors, such as environmental conditions and defects. There can be different variations in their growth, such as in one direction in a needle-shape, which is an acicular habit, or a slow-growing that produces a flat plate-like crystal, which is a tabular habit. Saturated solutions or supercooling can affect considerably the crystal habit and its growth control. 13 Figure 2.7: Different crystal habits of a hexagonal crystal.24 The most influential crystal faces are those with the lowest Miller indices and highest reticular densities. In order words, the faces with the greatest interplanar faces, dhkl . In addition, due to the surface energy theories of crystal growth, the equilibrium form should be such that the crystal has the least amount of total surface free energy per unit volume. 24 2.4 Thermodynamics of phase transitions When a substance gains enough energy or pressure, a phase transition takes place and the material changes from one state to another, e. g. solid to liquid. However, materials can also undergo structural transitions while remaining in the solid state, this is known as a polymorphic phase transition. In these transitions, materials can lose or gain different properties such as superconductivity, ferromagnetism, or ferroelectricity. These transitions also have different thermodynamic characteristics depending on what type of structural changes are taking place. As a result, polymorphic phase transitions can be associated with a change in the materials latent heat, or not. By the Ehrenfest classification, first order transitions are the ones where the first derivative of a magnitude is discontinuous, and the second order transitions are the one that have a discontinuity in the second derivative. Heat capacity is a product of the second derivative of the Gibbs free energy. It is discontinuous for a second order transition and infinite at a first order transition. 25 The search of new hybrid plastic crystal compositions involves finding combinations of organic and inorganic molecules. The inorganic molecules are mainly metal halide tetrahedra, including transition metals like Fe, Zn, Mn, and halides such as Cl, Br, I. In this project, it was interesting 14 to look at higher charged systems beyond the +1 and -1 charge ions. This was due to the fact that there had been less investigations on these systems, so the Zn-Halide4 tetrahedra with a -2 charge was investigated. In combination with this, a polar globular cation was also investigated. The cyclic amine species fit this description. 3,4-dimethylphenol was chosen because it was commercially available and fit the description above. For studying and determine the entropy and enthalpy of the transitions of the material, the equation (2.3) was used: Δ𝐺 = Δ𝐻 − 𝑇Δ𝑆 (2.3) With DSC, the enthalpy is calculated, and it can be related thanks to the equation with the entropy and free energy. It is important to know the value of the entropy because it is what measures the storage capacity of the material. 2.5 Quenching Rapidly cooling a substance to modify its mechanical properties is a process known as quenching. Quenching is typically done to give materials the desired mechanical qualities, such as improved strength and hardness. It is usually used among metallurgists, glass scientists and ceramicists, for developing microstructures and crystal structures and hence the desired properties in difference metals. For a quenching process, the material is heated to a temperature above its recrystallization temperature but below the melting point. Then, after keeping the material in this temperature for some time, it is quenched to room temperature or below. This practice has recently started to be used for retaining phase structures at high temperatures. 26 It has also been used in molecular crystals in their plastic phase for obtaining glasses of a new kind. These crystals are rapidly cooled for preventing the transition towards the low temperature ordered phase, and the disordered system goes into a glassy state. On gradual reheating, a “glass transition” takes place in which the glassy form, in which the orientational disorder is frozen, and is irreversibly transformed into the low temperature metastable form of the plastic phase. 27 15 3 Experimental 3.1 Synthesis of (DMP)2 [ZnBr2Cl2] The synthesis of (DMP)2 [ZnBr2Cl2] was carried out in two ways in which the ratio of the reactants was varied. It was first done three times with some small changes to the synthesis, however here the main method is presented and later on the differences will be explained. Synthesis (illustrated in Figure 3.1) of the plastic crystal material was carried out using 3,4dimetylphenol and ZnBr2∙H2O as precursors, and they were weighed out to achieve a 1:1 stoichiometric ratio. First, 1,757 g of the 3,4-dimethylphenol was weighed and then dissolved in 4 mL of ethanol. For protonation of the organic molecule to [3,4-dimethylphenol]H+, 0.874 mL of HCl was added to the dissolved organic precursor and mixed for 12 hours with a magnetic stirrer at room temperature. During this process the liquid was allowed to evaporate as a means of dehydrating the material from any residual moisture in the starting precursor, and the product crystallized. Once the protonation was completed the product was redissolved with EtOH. Afterwards, 3,759 g of ZnBr2∙H2O were weighed and dissolved in 4 mL of ethanol. Then, the organic cation was mixed with the dissolved inorganic anion in the organic solvent for forty minutes and subsequently allowed to naturally cool to room temperature, crystallizing by evaporation of the solvent, without covering the beaker at any time. The same synthetic route was performed two additional times with a different reactants ratio (Figure 3.1), but the amount of 3,4-dimethylphenol used was 2,3 g. 0,3 mL of HCl were used for the protonation of the organic compound, and the quantity of the inorganic compound, ZnBr2∙H2O, was 2,1 g. Materials Chemical formula Manufacturer Purity (%) 3,4-dimethylphenol C8H10O Sigma-Aldrich 98 Zinc bromide dihydrate ZnBr2∙H2O Sigma-Aldrich 99 Table 3.1: List of chemicals used in the synthesis. 16 Figure 3.1: Synthesis route for the plastic crystal. 3.2 Structural determination 3.2.1 XRD XRD analyses were performed to determine the crystal structure of the plastic crystal. The crystals were crushed in a mortar and then placed into a kapton holder. With a sliding glass, the surface of the sample was made smooth and flat. Once the sample holder was prepared, it was placed into the D8-Focus X-ray diffractometer with CuKα radiation (ℎ𝜔 = 8.04 keV, 𝜆 = 1.5406 Å). All samples were characterized from 5-55 degrees 2θ, for 30 minutes with 0.6º slitopening. The XRD data was then studied using DIFFRAC.SUITE TOPAS® software. First, a peak indexing of the analysis was done, and different crystal structures were studied. In each structure, several space groups were chosen according to their goodness of fit (Gof). The space groups with higher values of Gof fitted better with the material’s structure. These space groups, their respective Gof and lattice parameters were noted. Next, a Pawley fit was done with each of those space groups, and the better fits were the ones with the lowest Gof. (The change in the Gof from the highest to lowest being the better fit is an anomaly of the DIFFRAC.SUITE TOPAS® software). A new hkl phase was created every time 17 a new space group was studied. The lattice parameters that were determined during the initial peak indexing were introduced in the hkl phase structure as the starting parameters and were refined one by one. Each fit was performed independently in order to always start with the same background parameters. This was important to ensure the same starting point for each refinement and reproducibility of the fitting. 3.2.2 Raman spectroscopy Raman spectroscopy is a non-destructive method of evaluation that gives details on the chemical structure, phase, and molecular interactions of a sample. It is based on how light interacts with molecular vibrations, phonons or other excitations in the system. 28 This analysis was performed for studying the material’s structure and checking if the samples suppressed under a thermal cycle changed, so the instability in their crystal system could be explained. 3.3 Thermodynamic characterization 3.3.1 DSC DSC was used to observe the phase transitions as a function of temperature. In these analyses, an empty aluminum crucible and a closed lid were weighed, and then approximately 10 mg of (DMP)2 [ZnBr2Cl2] was added into the crucible. The crucible was closed with the lid using a pressing tool. After weighing the mass of the reference crucible with lid and the sample mass was added to the software and the sample was placed in the Netzsch Polyma DSC 214. Different thermal programs were used to observe different phenomena. In the first program two consecutive thermal cycles were run with a maximum temperature of 80 ºC and a minimum temperature of -20 ºC (Figure 3.2). The heating and cooling rate was 10 K/min and the holding time at the maximum temperature was 5 minutes. This was the standard program intended to examine the reversibility of the transitions occurring within this temperature range and calculate the enthalpy of the transition. In addition, another run of two thermal cycles was done but with a minimum temperature of 20 ºC (Figure 3.3). This measurement was first conducted due to a malfunction in the cooling program but was actually used to reveal the sensitivity of the transition on set temperature on cooling. There were further temperature cycles conducted as well, with minimum temperatures 18 of -20°C and maximum temperatures of 80°C, which was executed five times, and another one with the same minimum temperature but with a maximum temperature that first was 75 ºC and it was increased every cycle 5 ºC until 100 ºC (Figure 3.4). Both these measurements were designed to study the degradation of the material by looking at the transition enthalpy reduction with each consecutive thermal cycle and with increasing maximum temperature respectively. In all the analyses the flow gases were synthetic air gas mixture (20 mL/min), nitrogen (40 mL/min), nitrogen as safety gas (60 mL/min) and liquid nitrogen for controlled cooling. Figure 3.2: Thermal profile of the DSC analysis from -20 to 80 ºC. Figure 3.3: Thermal profile of the DSC analysis from 20 to 80 ºC. 25 Figure 4.6: (a) White crystals at the bottom of the beaker. (b) Crystals placed in a crystallizer for drying. (c) Pinkish crystals, still wet. 4.2.6 Crystallization attempt 5 In the fifth crystallization the crystals crystallized at the bottom of the beaker and were also white, like in Crystallization attempt 4. They were still wet, so they were dried with a Kitasato flask, and the color did not change the color during the drying process. Figure 4.7: (a) White crystals at the bottom of the beaker. (b) Drying with Kitasato flask. (c) Dried crystals in a vial. 4.3 Crystal structure The crystal structure of the plastic crystal was determined by XRD. The determination of its structure was done using the X-ray powder diffractogram from the June 2022 crystals and then compared with more XRD analyses from the samples synthetized this semester. 26 4.3.1 June 2022 crystals Figure 4.8: Diffractogram of the June 2022 crystals done in this semester. Note: The Miller indices of the Bragg diffraction peaks are not labelled in this thesis until after the crystal structure identification process has been discussed, in order to highlight that the crystal structure was initially unknown. 4.3.2 Determination of the crystal structure The crystal structure of the material is unknown, and no references were found about it, so in this specialization project the determination of the crystal system, the space group symmetry and the lattice parameters were attempted. For the characterization of the structure, the data from the diffractogram showed in the Figure 4.8 was used, which was obtained from the June 2022 crystals. The data was loaded into the DIFFRAC.SUITE TOPAS® software and the peaks were identified and then indexed. In the indexing range, each of the crystal structures were systematically checked and in each one the space groups with a higher goodness of fit (Gof) were selected and their lattice parameters were noted. This process was repeated three times in 27 order to ensure reproducibility of the results. The best fitted space groups with their lattice parameters are shown in the Table 4.2. These are the results from the last repetition of the indexing process. The other two tables are in the Appendix, and there was not significant variation between each subsequent attempt. Crystal structure Space group Gof a (Å) b (Å) c (Å) Cubic Pa-3 3.67 24.495 24.495 24.495 Trigonal P31 3.35 14.944 14.944 15.955 Tetragonal P4bm 4.37 14.958 14.958 6.529 I41/a 4.14 14.953 14.953 13.038 P41212 4.14 14.958 14.958 6.529 P42212 4.10 14.958 14.958 6.529 I41 4.10 14.953 14.953 13.066 I41/a 3.90 14.953 14.953 13.066 Orthorhombic P222 4.21 18.424 12.642 5.092 P2221 3.62 10.546 10.574 6.532 P222 3.46 6.502 10.539 10.572 P2221 3.45 10.521 6.537 10.610 Monoclinic P2 4.67 10.280 10.589 5.628 P2 4.72 12.475 10.635 5.597 P2 4.37 11.023 10.613 5.589 Triclinic P-1 4.20 4.994 7.558 13.386 P-1 4.86 6.697 8.055 12.735 Table 4.2: The best space groups fits found during the peak indexing process. Once the peak indexing was done, these best fitting space groups were fitted to the powder XRD pattern using a Pawley fit. In order to do this, a separate hkl phase was added in TOPAS for each space group, and each space group and its lattice parameters were introduced and refined one by one. In this Pawley fit the better fits were the ones with the lowest Gof. The fitting process was repeated three times for all the space groups in order to provide some idea of reproducibility of the fitting results. The results obtained the first two times are in the Appendix. The results from the last round of fitting are represented in the Table 4.3. 28 Crystal structure Space group Gof a(Å) b(Å) c(Å) Cubic Pa-3 14.12 24.541 24.541 24.541 Trigonal P31 13.63 14.762 14.762 15.822 Tetragonal P4bm 9.67 15.097 15.097 6.579 I41/a 16.26 15.098 15.098 13.130 P41212 9.75 15.098 15.098 6.580 P42212 9.70 15.097 15.097 6.579 I41 9.89 15.093 15.093 13.148 I41/a 16.26 15.097 15.097 13.129 Orthorhombic P222 10.14 18.519 12.663 5.103 P2221 7.35 10.636 10.739 6.566 P222 7.34 6.567 10.637 10.739 P2221 7.34 10.637 6.567 10.739 Monoclinic P2 8.46 10.770 10.658 5.608 P2 20.25 12.439 10.657 5.598 P2 8.51 10.738 10.635 5.589 Triclinic P-1 12.51 5.0915 7.553 13.489 P-1 13.36 6.856 8.235 12.941 Table 4.3: Results obtained after the Pawley fit of each space group in different crystal structures. The value of the lattice parameters changed from the initial indexing process in order to allow a better fit to the powder diffractogram. Figure 4.9: Comparison between the Pawley fit refinement and the powder diffractogram data. 29 Figure 4.10: Raman analysis of June 2022 crystals. In Figure 4.10, several peaks are shown which represent the structure of the material. According to the literature, the bands located at lower frequencies correspond to the inorganic compound and the ones located at higher frequencies are from the organic compound. 29,30 4.3.3 Crystallization attempt 1 Since the obtained material was more of a gel than crystals, no XRD measurement was performed. 4.3.4 Crystallization attempt 2 Then, more analyses were done with the new synthetized materials. From Crystallization attempt 2, the white long-needle crystals were separated from the brownish ones, and both were analyzed. The brownish ones were still a bit wet even though they were left in the fume hood several days for letting them dry and its diffractogram did not have intense peaks. However, the white crystals were analyzed and showed similar data as in Figure 4.11. These results have the same peak position as the other sample, but there is a lot of difference in the relative intensities compared with the crystals made in June. 30 Figure 4.11: X-ray diffractogram of the white long-needle crystals made in the second synthesis attempt (Crystallization attempt 2). For assuring that this new synthetized material was the same as the one made in June, a Pawley fit of the diffractogram was carried out. The structure and the lattice parameters used were the ones obtained after the structure determination of June 2022 crystals in the section 4.3.2. Figure 4.12: Comparison between the Pawley fit refinement and the powder diffractogram data. 31 After the Pawley fit with the orthorhombic system and the P2221 space group, the lattice parameters were a=10.637 Å, b=10.711 Å, c=6.553 Å with a Gof of 16.01. 4.3.5 Crystallization attempt 3 The last diffractogram made was from the latest sample synthetized this semester. This time, the peaks were less intense with respect to the background. There was also a hump in the background observed between 2θ 15º and 35º. Figure 4.13: X-ray diffractogram of the Crystallization attempt 3 crystals. As in Crystallization attempt 2, the data of the diffractogram of this material was Pawley fitted so it can be assured that the new synthetized material has the same structure as the crystals synthetized in June 2022. 32 Figure 4.14: Comparison between the Pawley fit refinement and the powder diffractogram data. The lattice parameters after the Pawley fit were a=10.675 Å, b=10.721 Å and c=6.566 Å, with a Gof of 4.21. 4.3.6 Crystallization attempt 4 This sample was not analyzed with X-ray diffraction. 4.3.7 Crystallization attempt 5 This sample was not analyzed with X-ray diffraction. 4.3.8 Structural stability as a function of thermal treatment The structure of the (DMP)2 [ZnBr2Cl2] was observed to be stable at room temperature, with stability observed for periods of over 12 months. However, the fact that the transition temperature on cooling was just below room temperature (21°C) created an opportunity to study the transition ex situ (i.e. after thermal cycling). A study of the cooling rate was thus conducted to observe the effect this had on the crystal structure. Two samples of (DMP)2 [ZnBr2Cl2] were melted by heating to 80 ºC and holding for 30 minutes in an oven at ambient pressure. Each sample was then cooled down under different conditions. One of the samples was removed from the oven to ambient conditions and allowed to cool naturally in a desiccator. The second sample was removed from the oven and placed immediately in a freezer at -18 ºC so that the sample was quenched. After 30 minutes it was then placed in a desiccator at room temperature (RT). 33 X-Ray analyses were carried out on both samples as a function of time after their return to room temperature. For scheduling reasons, the exact same intervals were not used for both samples. The diffractograms showing the results from the study are shown below. Air-cooled sample Figure 4.15: Diffractograms of the air-cooled sample. XRD powder diffractograms of intensity vs 2θ for (DMP)2 [ZnBr2Cl2] heated and cooled in ambient conditions. Each panel shows the (DMP)2 [ZnBr2Cl2] at a different time with respect to the heating cycle. (a) Before heating. (b) Immediately after cooling to room temperature. (c) 14 days after cooling. (d) 60 days after cooling. (e) 90 days after cooling. 34 Figure 4.16: Raman analysis of the air-cooled sample. The bands present in Figure 4.16 are the same for the June 2022 crystals. 41 Cycle Tmelt (ºC) ΔH (J/g) First 54.9 126.7 Second 54.1 122.6 Third 54.6 115.1 Fourth 53.4 116.1 Fifth 53.5 113.5 Sixth 53.9 116.1 Table 4.5: Melting temperatures and enthalpies of the endothermic transitions of each cycle in the thermal analysis with a minimum temperature of -20 ºC and a maximum temperature of 75 ºC which increases 5 ºC with each cycle until it reaches 100 ºC. 42 5 Discussion 5.1 Synthesis observations 5.1.1 Crystallization attempt 1 There was some crystallization that looks to be metastable, and when dried out, it redissolved, leaving the gel form, it could also be that the material is hygroscopic. So, because there was no crystal growth, the nucleation must have been suppressed, and because crystallization and nucleation are associated with the interaction of charge molecules, and the crystals are ionic, maybe there was no proper charge and the embryos could not properly, leading to no nucleation and subsequently to no growth, resulting in the amorphous material. The protonation process is problematic and maybe it went old because the cation precursor was a bit old and may have absorbed some moisture from the air, which may impact how the protonation happens. The origin of the reddish crystals was unknown but could have been related to contamination with the Al or dissolved Brions. 5.1.2 Crystallization attempt 2 The crystals were growing out of the walls and the temperature of evaporation was higher in the other attempts. The reason of that type of growth is that in the vicinity of the walls, the dissolution forms a meniscus, which is a curve in the surface of a molecular substance when it touches another material. When the solvent in the surface of the dissolution is evaporated, the concentration of the sample is locally higher than in the rest of the dissolution, but as the solvent molecules are in continuous movement, new solvent molecules quickly arrive from within the solution and the concentrations are homogenized. Since the solvent molecules' access to the meniscus portion is more restricted this procedure is more challenging there. As a result, there is a larger local concentration of solute there than in the rest of the solution, which causes that region to be where the solid crystallizes first. At the bottom of the beaker, brownish crystals precipitated, and this is a cause of an error in the crystallization procedure. The solutions were totally evaporated instead of being purified first, so both the sample (with a white color) and impurities precipitated, and that is why the discoloration of the sample is present. 43 On the walls, there was a planar growth, because the shape of the crystals was in a needle shape, which is like an elongated prism, and can only be obtained with planar growth. This needle shape can be associated with an acicular crystal habit. 5.1.3 Crystallization attempt 3 These crystals are related more to a homogenous crystallization (although it is still heterogeneous since nothing is perfectly homogeneous), and the solution was growing from the bottom because the beaker was evaporating at room temperature, which is lower than the temperature used in the previous attempts, so the molecules in the solution were not evaporated as much this time. A small modification of the synthesis approach changed the result of the synthesis, that is how it crystallized at the bottom and the growth was more stable this time, since it was more isotropic. These crystals are more like a tabular crystal habit, and the discoloration is still present because of the mistake in the evaporation process, as explained before in section 5.1.2. 5.1.4 Crystallization attempt 4 These crystals were white at the beginning of the crystallization, but once they were left longer in the fume hood for drying completely, they turned brown. This is because the sample was not correctly purified before letting it dry and the impurities precipitate with the material. 5.1.5 Crystallization attempt 5 These crystals did not turn into a brownish color, because before letting the solution dry, it was purified by filtration with a Kitasato flask by separating the mother liquors with the impurities from the sample. For this reason, this is the correct crystallization method and the obtained compound is the desired one. 5.2 Crystal structure 5.2.1 Crystallization attempt 2 The results of Figure 4.11 compared to the ones from Figure 4.8 show that the peaks have the same position in both, but their relative intensities change. This difference is likely related to the highly orientated crystal growth and the crystal habits because the needle-like growth occurs in one direction and it was expected to have different ratios of crystallographic direction, which 44 changes the intensity. After the Pawley fit, the Gof was 16.01, not really low, which indicates that the structures are similar but not completely the same. It could probably be because only the long white crystals which were attached to the walls of the beaker were analyzed, and the brownish crystals at the bottom of the beaker were set aside. 5.2.2 Crystallization attempt 3 In this last diffractogram (Figure 4.13), there are not additional peaks so there is not a crystalline secondary phase that is seen, but there is a lower peak intensity and a higher background. Since the intensity of the peaks from the diffractograms of June 2022 crystals and Crystallization attempt 2 is higher, it can be said that there is a less crystalline phase and the hump of the background shows that there is more amorphous material. The brownish color can be related to an amorphous phase or uncrystallized material remaining. The reason of the color can probably be related with the age of the precursors and the fact that they may have hydrated by bonding with OHcoming from moisture. Before the protonation, the precursors were not properly dehydrated, so maybe the same degree of protonation in the June 2022 crystals is not achieved in the Crystallization attempts 1, 2 and 3. Even though there was discoloration in this sample, the structure is almost the same as the one determined from June 2022 crystals, since after the Pawley fit the Gof obtained was 4.21, which is low and indicates that it was a good fit. 5.3 Determination of the crystal structure Looking at the Gof of each crystal structure, the better fits (shown in Table 4.3) are found in the orthorhombic system, and the chosen space groups for the structure of the material was P2221 with a=10.636 Å, b=10.739 Å, c=6.566 Å as lattice parameters. However, two of the three lattice parameters of these systems have always a similar value, so the structure is quite close to a tetragonal structure if it were to be approximated or simplified. Even so, the orthorhombic systems had the lowest Gof, and it makes sense because in the orthorhombic systems one more degree of freedom is added, and it allows the system to fit better to the diffractogram. 45 5.3.1 Structural stability as a function of thermal treatment Air-cooled sample Figure 4.15a shows the structure of the material before it was heated. The powder diffraction pattern shows major peaks at 9, 12, 16, 19, 24 and 25 º 2θ with other minor reflections and is indicative of a single-phase material with the orthorhombic P2221 crystal structure. This structure fitting is described previously in the thesis. Figure 4.15b shows the structure at room temperature, after heating and cooling to room temperature. Only one major peak is visible at 18º 2θ with a few additional minor peaks present. While not directly comparable, it is noted that the intensity of the peaks was significantly higher than those found in other structural phases of this material. This type of diffractogram with only a few high intensity peaks is characteristic of the mesophase structures observed in plastic crystals. 5 These phases are related to the high degrees of molecular orientational disorder, which is explained in the introduction section of the thesis. This structure was determined as previously stated in the thesis, and it mostly belongs to a tetragonal system with a P42/n space group with a= 13.799 Å, b = 13.799 Å and c = 17.641 Å as lattice parameters (Figure A.5). The structural pattern observed in Figure 4.15b raises some interesting questions about the material when combined with other experimental observations. Firstly, we note that the material has only one first order phase transition visible between 25 and 80 ºC. Secondly, the material was observed to melt at this transition. The combination of these two facts suggests that the material does not form a mesophase on heating, but instead it has a solid to liquid transition consistent with standard crystalline materials. 31 The XRD data immediately after cooling however, indicates the presence of a mesophase. When we again consider the DSC data (figure), which shows that the large hysteresis of the transition causes the transition temperature on cooling to be 21 ºC, i.e., right at room temperature, this indicates that the diffractogram after heating may in fact capture the material during the solidification transition, before the transition is complete. If this is true, it would mean that the mesophase is accessible as a metastable phase of the solidification process. This phase was probably obtained because the phase transition temperature is right at room temperature, around 22 ºC, and an intermediate stage of the phase transition process was captured. There is not enough kinetic energy to continue quickly so it is progressing slowly. The diffractogram in Figure 4.15c was obtained 2 weeks after the sample was heated. It is most notable that the diffraction pattern resembles neither the original room temperature pattern nor 46 the mesophase pattern captured immediately after cooling. Firstly, this indicates that the mesophase must be metastable, as the structure changes from the mesophase structure with time. However, as the structure does not return to the original room temperature structure there must be some additional influential factors. After trying to determine the structure of this sample, the most possible one resulted to be orthorhombic F222, with a=20.576 Å, b=27.518 Å, c=18.974 Å as lattice parameters (Figure A.6). One hypothesis is that the organic molecules changes during heating. This may be likely as the 3,4-dimethylphenol has an oxygen atom which likes to bond with H forming a hydrate. It is thus likely that the molecule has a high affinity to moisture which may change the charge of the molecule and stability of the structure. Another one could be that the inorganic anion is the one that changes when the samples are heated. It can condense with others and begin to form different structures. 32 Figures 4.15d and 4.15e represent the structures after 2 and 3 months respectively. Both are similar, which indicates that the materials structure eventually stabilizes with time, however, there is a significant difference between diffractograms at 2 weeks (Figure 4.15c) and 2 months (Figure 4.15d). While the underlying cause for this change is unknown the behavior generally fits with a kind of structural relaxation taking place slowly over time but with a more rapid changes happening in the period immediately following cooling. This could fit approximately with the kinetics of structural relaxation in system with constrained dynamics. 33 The structure for the sample after 2 months belongs to a monoclinic system with P21 as space group and a=14.452 Å, b= 20.440 Å and c=6.518 Å as lattice parameters (Figure A.7). The structure for the sample after 3 months belongs to a monoclinic system, with P2 as space group and a=23.113 Å b=12.907 Å and c=13.708 Å as lattice parameters (Figure A.8). Quenched sample Figure 4.17 represents a plot of the different diffractograms obtained from this sample. The Figure 4.17a represents the structure of the material before it was heated. This was the same material as used for the ambient cooling experiment and thus the structures of Figure 4.15a and Figure 4.17a are the same. Figure 4.17b shows the powder diffraction pattern of the material at room temperature, immediately after being quenched to -18 ºC and then being allowed to return to room temperature. The XRD powder pattern of the quenched structure is distinctly different from the mesophase structure in Figure 4.15b, this is seen by the multiple peaks present and the lack of 47 the major high intensity mesophase peak at 18º 2θ. The structure that was determined for this material is from a hexagonal structure and P61 as space group, with a= 20.453 Å, b= 20.453 Å, and c=48.0522 Å as lattice parameters (Figure A.9). However, there is a lower intensity peak in this vicinity, thus we are currently unable to rule out phase coexistence between the mesophase and another structure. The material was driven quickly through the one known phase transition observed with DSC by quenching, which further suggests that the mesophase structure is an intermediate phase state thermally stabilized by slow kinetics during a slow cooling process. The room temperature structure after quenching however has lower peak intensities and fewer peaks, compared to the structure before heating, indicating that the structure may have less crystalline order. If this is the case, it may be explained by a freezing of the molecule orientational disorder due to the quenching process. Such behavior is seen in the literature in similar materials and is often referred to as reordering frustration or orientational glass phases. However, this is just a plausible hypothesis to explain the XRD observations, but further work is required to confirm. Figure 4.17c shows the diffraction pattern of the structure after two days in the desiccator. The pattern shows a general increase in the peak intensities, with the peaks appearing sharper and more well defined and with the appearance of some new peaks, compared to that from the structure immediately after quenching (Figure 4.17b). While the intensities are not directly comparable between measurements, their increase relative to the background suggests that the degree of crystallinity of the material may have continued to increase with time at room temperature, indicating that if there was orientational disorder frozen into the structure due to quenching, then it is also metastable and relaxes as a function of time. This indicates relaxation of the quenched disorder at room temperature. One of the most probable structures of this sample was determined to belong a orthorhombic crystal structure with C2221 as space group and a=18.409 Å, b=21.175 Å and c=32.643 Å as lattice parameters (Figure A.10). Figure 4.17d shows the structure of the material after five days. The diffraction pattern is similar to the pattern after 2 days (Figure 4.17c) but many of the peaks again have higher intensities with respect to the background, which indicates that the relaxation process is continuing. Even though the intensity of the peaks is changing, the positions are the same, so the structure does not change. The hypothesis is that the structure is not fully crystalline after quenching, and it is slowly relaxing to a fully ordered structure. The structure that is more likely 48 to belong to this sample, is from an orthorhombic system, with Pmc21 as the space group, and a=17.606 Å, b=27.588 Å and c=13.968 Å as lattice parameters (Figure A.11). Figure 4.17e represents the structure after two weeks. The pattern is similar to the one after 2 days with some further intensity change and a notable peak splitting present at approximately 18º 2θ. This indicates that the structure is still changing, although it appears that the crystal system and symmetry remains constant. The slight changes however indicate that there is still relaxation and perhaps some structural instability. The structure determined for this sample is monoclinic P2, with a=17.695 Å, b=10.278 Å and c=14.831 Å as lattice parameters (Figure A.12). Figure 4.17f shows the structure 1 month after quenching. There is significant difference between this powder diffraction pattern and the one taken after two weeks (Figure 4.17e). the main peak appearing at 18º 2θ has a much high intensity than the other peaks. The other less intense peaks appear to match up with positions of peaks seen in Figure 4.17e. This change is unexpected as it does not indicate an increased structural stability and slowed relaxation with time, as was seen with the structure after ambient cooling. At this point in time, we have no explanation for this behavior, although it may be possible that the structural stability is affected by the humidity of the laboratory, which is not controlled. From both data sets the main conclusion is that the crystal structure after the material has been melted is less stable than the structure after crystallization. This indicates that the thermal cycling is less stable than the structure after crystallization and that the structure obtained from the melt is not as stable as the structure grown during crystallization from solution precipitation. The changes of the structure in each study might be caused by the by organic cation, which possesses an oxonium group, coming from the protonation of an alcohol by an acid. Because they have a positive charge, protonated alcohols are significantly more reactive toward nucleophiles than neutral alcohols. 34 Figure 5.1: Protonation of an alcohol by an acid which produces an oxonium ion. 49 The relaxed structure of the quenched material is possibly from a monoclinic or triclinic system. However, the monoclinic with C2 as space group and a=19.5655611 Å, b=13.048461 Å, c=18.5732793 Å and β=115.3134 º as lattice parameters was chosen because it has a low Gof and the range of the lattice parameters is similar to the ones from the original structure, whereas the triclinic system and P-1 space group has higher lattice parameters and since does not impose any symmetry conditions on the structure (Figure A.13). A Pawley fit of this C2 monoclinic structure was done to the relaxed air-cooled sample, and the Gof after doing it was 11.07, which is quite high. This means that there is a poor correlation between the structures because they relax differently. It cannot be known if this difference comes from the heat treatment conditions or if it just not reproducible and the structures change over time because the material is being degraded. A repetition of the same experiment but with different conditions would be needed for proving this. It can also be seen from this study that there is a mesophase on cooling but not on quenching. The mesophase state is not thermodynamically stable in this material, but it is kinetically stabilized on air cooling as the transition is not allowed to complete due to the temperature stopping at the transition temperature (22 ºC). 5.3.2 Raman spectroscopy This analysis was performed in order to check if there was something affecting the structure and its stability. Water was thought to be the cause of the instability but since the characteristic water bands did not appear, which are located at 3355 and 3583 cm-1, for two OH bands, 35 the compounds seem to not have absorbed any moisture during the thermal cycle that they were suppressed under. In the region of 200 and 300 cm-1 the bands from Zn-Cl and Zn-Br appear. A band at 200 cm-1 is visible and due to its high intensity, it could come from a combination of both Zn-Cl and Zn-Br, indicating that the condensation process could take place. 32 5.4 Phase transitions In DSC analyses, there are different phase transitions where the material can absorb or release energy. In the transitions that absorbs energy, occurs an endothermic process, and when it is released, there is an exothermic process. As seen as in the Figure 4.19, the material has a phase transition when the energy is absorbed at 56 ºC and this energy is later released at 22 ºC. These transitions are reversible, so the material 50 can store and release energy in more than one cycle, and there is a hysteresis of 34 ºC, which is important because depending on this hysteresis the material can be used for different applications, and because of its temperature range, it can be used for domestic applications in homes. It could not be applied for industry applications since it would need to have the transitions at higher temperatures. In Figure 4.20 and Figure 4.21, other DSC analyses are represented, which go from -20 to 80 ºC and -20 to 100 ºC respectively. Even though the exothermic transition that takes place while cooling was not represented, since the data was not accurate due to cooling malfunctioning of the instrument, it is proven that both phase transitions are reversible and stable, because the energy absorbed with each cycle is constant after several cycles. Another analysis of June 2022 crystals was performed, but with a thermal profile that goes from 25 to 80 ºC. Figure 5.2: DSC analysis carried out of June 2022 crystals. The analysis has a thermal profile with a minimum temperature of 25 ºC and a maximum temperature of 80 ºC. Only one phase transition can be seen, it occurs at 56 ºC, as in the previous made by the previous students. The cooling phase transition is not seen because the material was not cooled enough, so it stayed all the time in the same phase even in the second cycle of the analysis. The enthalpy of the phase transition in the Figure 5.2 is 126.1 J/g, which is higher than the enthalpy of a commercial plastic crystal, which is around 100 J/g. 1 57 Crystal structure Space group Gof a (Å) b (Å) c (Å) Cubic P213 2.08 16.720 16.720 16.720 Pa-3 2.08 16.779 16.779 16.779 P23 2.00 16.779 16.779 16.779 P4332 2.96 28.268 28.268 28.268 Trigonal-Hexagonal P3c1 2.33 21.226 21.226 5.389 P3 2.81 21.206 21.206 5.359 Tetragonal P4 2.57 10.456 10.456 6.618 P4 2.7 9.978 9.978 13.251 P42 2.64 10.456 10.456 6.618 P4cc 2.59 14.464 14.464 11.680 P41 2.51 10.248 10.248 13.052 P42cm 2.44 14.423 14.423 11.697 Orthorhombic P222 3.67 16.458 10.043 10.509 P222 3.07 10.535 12.966 9.9484 P21212 3.56 16.504 10.515 10.065 P2221 3.44 16.458 10.043 10.509 Pmc21 3.33 9.958 10.503 12.956 Pmc21 3.21 10.631 9.669 7.473 Pmn21 3.28 10.631 9.669 7.473 Pmn21 3.05 12.947 9.951 10.561 Pca21 2.85 10.631 9.669 7.473 Monoclinic P21 5.83 8.806 10.579 10.679 P21 4.56 9.956 12.895 7.261 P2 4.68 5.522 10.569 10.603 Triclinic P-1 7.76 6.905 7.397 12.112 Table A.2: Second results from the peak indexing. 58 Pawley fitting Crystal structure Space group Gof a (Å) b (Å) c (Å) Tetragonal P4/nbm 12.69 14.993 14.993 10.401 P41 8.74 10.651 10.651 13.121 P42cm 8.67 10.652 10.652 13.119 P4 9.66 10.675 10.675 6.578 P42 8.75 10.651 10.651 13.121 Orthorhombic Cmc21 8.33 15.065 14.979 6.541 C222 8.42 15.056 14.966 6.537 Pbcn 8.75 15.047 14.956 6.532 C2221 8.35 14.971 15.059 6.538 Monoclinic Cc 20.70 15.441 5.968 10.639 C2 20.37 15.490 5.996 10.649 P21 15.62 12.473 7.534 10.264 P21 15.22 12.686 7.557 10.285 Triclinic P-1 18.38 3.883 5.748 8.702 Table A.3: First results from the Pawley fitting. 59 Crystal structure Space group Gof a (Å) b (Å) c (Å) Cubic P213 18.66 16.902 16.902 16.902 Pa-3 18.42 16.905 16.905 16.905 P23 18.69 16.880 16.880 16.880 P4332 15.64 28.314 28.314 28.314 Trigonal-Hexagonal P3c1 16.35 21.578 21.578 5.348 P3 17.07 21.551 21.551 5.345 Tetragonal P4 9.66 10.675 10.675 6.579 P4 15.22 10.091 10.091 13.209 P42 9.66 10.675 10.675 6.578 P4cc 13.52 14.628 14.628 12.053 P41 15.22 10.105 10.105 13.224 P42cm 11.18 14.673 14.673 12.078 Orthorhombic P222 8.57 16.437 10.082 10.498 P222 9.66 10.524 12.929 9.929 P21212 8.61 16.427 10.485 10.069 P2221 8.57 16.435 10.080 10.496 Pmc21 10.43 9.922 10.471 12.916 Pmc21 16.19 10.610 9.667 7.472 Pmn21 16.18 10.611 9.668 7.473 Pmn21 9.33 12.921 9.920 10.565 Pca21 16.42 10.622 9.681 7.474 Monoclinic P21 13.92 8.741 10.634 10.684 P21 11.13 9.892 12.883 7.180 P2 8.46 5.590 10.636 10.737 Triclinic P-1 17.01 6.905 7.259 12.165 Table A.4: Second results from the Pawley fitting. 60 Crystal structure Space group Gof a (Å) b (Å) c (Å) Cubic Ia-3 10.03 39.517 39.517 39.517 Ia-3 9.90 39.533 39.533 39.533 Ia-3 9.91 39.554 39.554 39.554 P4332 7.59 26.959 26.959 26.959 P4332 7.30 27.031 27.031 27.031 Trigonal-Hexagonal R3c 6.19 14.569 14.569 60.006 R3c 6.27 14.589 14.589 60.172 R3c 6.20 14.568 14.568 60.007 R3 7.05 10.346 10.346 87.972 R3 6.99 10.233 10.233 88.791 Tetragonal P42/n 5.82 13.799 13.799 17.641 I4 8.10 9.797 9.797 70.892 I4 7.21 13.906 13.906 28.843 I41/a 9.12 18.548 18.548 24.652 P41 7.48 13.163 13.163 17.897 Orthorhombic C222 7.26 8.512 6.074 65.265 P212121 6.33 11.696 17.232 14.653 C222 7.48 8.472 6.228 70.202 P2221 6.97 10.550 17.188 13.679 Pca21 6.33 17.140 18.798 5.351 Monoclinic P2 6.03 18.867 6.100 11.986 P2 7.18 19.959 13.368 5.429 P2 7.72 17.300 4.916 10.367 P2 6.66 21.863 4.935 10.114 P21 6.03 18.869 6.101 11.987 Triclinic P-1 6.25 6.789 5.518 37.871 P-1 8.46 7.219 8.373 18.085 P-1 6.04 6.144 7.322 24.111 P-1 6.13 7.240 16.139 26.480 P-1 6.15 7.369 10.752 18.506 Table A.5: Results of air-cooled sample immediately after cooling at room temperature. 61 Crystal structure Space group Gof a (Å) b (Å) c(Å) Cubic Pa-3 11.64 30.608 30.608 30.608 Pa-3 11.61 30.616 30.616 30.616 Pa-3 11.64 30.614 30.614 30.614 Pa-3 11.82 33.696 33.696 33.696 I-43d 9.55 41.944 41.944 41.944 Trigonal-Hexagonal R3 41.53 64.600 64.600 11.929 R3 9.52 44.850 44.850 12.448 R3 10.70 55.398 55.398 10.286 R3c 9.21 64.632 64.632 11.944 R3 9.69 16.342 16.342 128.266 P31 10.45 20.855 20.855 23.229 Tetragonal P4/n 8.35 10.355 10.355 68.817 P4/n 10.52 7.697 7.697 74.090 P4/n 9.40 10.452 10.452 57.536 I41 9.79 14.255 14.255 111.868 I41/a 10.09 16.219 16.219 96.440 P4212 10.18 7.701 7.701 74.120 Orthorhombic F222 6.66 20.582 27.532 18.992 F222 6.66 18.984 20.579 27.527 F222 6.63 20.576 27.518 18.974 Ccc2 6.85 16.466 18.946 19.348 Pba2 7.62 19.439 18.733 16.535 Monoclinic P21 7.08 10.178 16.290 10.978 P21 7.08 10.178 16.294 10.980 P2 6.87 10.179 16.304 10.986 P2 6.81 10.173 16.293 10.984 Pc 8.18 10.382 13.259 13.656 Triclinic P-1 6.67 8.565 11.023 19.751 P-1 6.61 10.978 12.343 15.968 P-1 6.44 10.907 12.035 17.388 P-1 6.60 10.110 16.428 12.035 P-1 6.81 7.531 13.049 20.555 Table A.6: Results of air-cooled sample 14 days after cooling at room temperature. 62 Crystal structure Space group Gof a (Å) b (Å) c(Å) Cubic I23 25.67 39.017 39.017 39.017 I23 24.70 39.159 39.159 39.159 I23 24.70 39.159 39.159 39.159 I4132 20.23 39.012 39.012 39.012 I4132 20.24 39.012 39.012 39.012 Trigonal-Hexagonal P3 21.62 13.503 13.503 21.431 P3 21.64 13.508 13.508 21.444 P3 21.81 13.467 13.467 21.359 P61 20.84 31.679 31.679 7.000 P3 21.75 13.485 13.485 21.456 Tetragonal P42212 10.91 18.584 18.584 24.389 P42212 10.91 18.584 18.584 24.389 P4212 10.49 18.582 18.582 24.388 I41 12.51 11.897 11.897 91.509 I41 19.60 12.665 12.665 92.926 Orthorhombic C2221 10.00 38.483 8.944 20.425 P21212 11.09 14.656 13.883 12.805 C222 10.02 38.483 8.944 20.425 Pba2 9.84 20.420 13.537 10.887 Monoclinic P21 8.80 14.452 20.440 6.518 P2 8.81 14.450 20.438 6.516 C2 10.86 67.118 4.290 6.473 C2 11.01 63.689 4.289 6.472 C2 11.01 63.689 4.289 6.472 Triclinic P-1 9.20 10.624 13.323 9.000 P-1 9.86 10.681 12.878 8.996 P-1 8.73 10.650 11.286 11.416 P-1 14.72 7.439 12.055 16.343 P-1 8.53 6.815 16.281 21.381 Table A.7: Results of air-cooled sample 60 days after cooling at room temperature. 63 Crystal structure Space group Gof a (Å) b (Å) c(Å) Cubic Fd-3 22.18 55.523 55.523 55.523 F4132 14.60 55.536 55.536 55.536 Fd-3 22.11 55.542 55.542 55.542 F23 25.06 55.539 55.539 55.539 F4132 14.66 55.543 55.543 55.543 Trigonal-Hexagonal P3 15.76 11.657 11.657 76.070 P61 11.25 11.657 11.657 76.063 P31 15.60 11.658 11.658 76.069 P63 11.28 11.657 11.657 76.060 P3 (tri) 15.83 11.888 11.888 50.936 Tetragonal P4 13.19 14.561 14.561 50.934 P4/n 13.60 13.096 13.096 82.082 I41/amd 11.35 13.041 13.041 82.340 I4 16.26 13.074 13.074 81.561 P42212 10.77 14.565 14.565 50.946 Orthorhombic C222 13.49 25.306 6.072 51.721 C222 10.53 27.738 5.689 71.242 C222 11.34 8.970 9.197 90.154 C222 11.79 20.451 4.254 50.636 C222 11.86 9.147 9.423 63.979 Monoclinic Cc 11.36 91.691 12.877 6.492 P2 14.77 11.854 10.405 27.169 P2 12.47 23.154 12.907 13.708 P21 12.84 23.113 12.889 13.686 C2 9.56 155.981 14.359 12.518 Triclinic P-1 10.31 11.402 15.448 26.306 P-1 13.46 10.885 25.974 26.904 P-1 8.68 9.531 17.449 13.127 P-1 12.67 14.469 31.624 26.878 P-1 11.42 9.454 15.512 26.744 Table A.8: Results of air-cooled sample 90 days after cooling at room temperature. 64 Crystal structure Space group Gof a (Å) b (Å) c (Å) Cubic Pa-3 13.29 36.909 36.909 36.909 I4132 8.78 52.133 52.133 52.133 I23 7.82 52.064 52.064 52.064 I4132 8.73 52.144 52.144 52.144 Pn-3n 8.76 40.411 40.411 40.411 P213 10.66 32.849 32.849 32.849 Trigonal-Hexagonal P61 6.16 11.940 11.940 97.432 P61 6.16 20.453 20.453 48.052 P61 6.98 20.387 20.387 47.799 P64 6.83 20.397 20.397 47.820 R3 6.74 13.127 13.127 95.437 P63 7.52 26.019 26.019 23.668 Tetragonal P41 6.10 10.180 10.180 131.189 P4 5.93 10.173 10.173 131.238 P42/n 7.43 10.224 10.224 131.980 P41212 5.36 10.225 10.225 132.001 P42 5.61 10.156 10.156 131.251 P41 5.56 10.160 10.160 131.309 Orthorhombic C2221 6.60 57.313 35.814 5.304 C222 6.61 57.365 35.845 5.311 F222 6.99 25.790 32.975 18.287 I222 5.42 62.942 10.776 17.259 F222 6.96 25.754 18.275 32.957 P222 5.96 49.737 10.256 8.645 Monoclinic Pc 5.63 12.622 50.813 9.289 C2 6.93 54.645 11.034 16.810 Cc 25.65 21.806 28.310 29.234 P21 9.12 17.572 6.354 16.803 P2 9.16 17.567 6.351 16.799 P21 9.25 17.560 6.328 16.782 Triclinic P-1 5.09 6.640 15.662 16.961 P-1 4.31 6.534 15.729 20.911 P-1 11.70 6.638 17.827 25.133 Table A.9: Results of quenched sample immediately after quenching. 65 Crystal structure Space group Gof a (Å) b (Å) c (Å) Cubic Ia-3 6.07 55.586 55.586 55.586 Ia-3d 9.25 55.587 55.587 55.587 Ia-3 6.10 55.572 55.572 55.572 Fd-3 10.94 66.592 66.592 66.592 Pa-3 10.50 30.749 30.749 30.749 Trigonal-Hexagonal R3c 10.63 41.471 41.471 34.148 R3 10.04 26.139 26.139 48.223 R3 10.36 24.391 24.391 32.592 P3 9.79 10.618 10.618 90.492 R3 10.68 24.394 24.394 32.596 Tetragonal P4/n 7.57 10.100 10.100 87.843 P4bm 7.94 21.127 21.127 23.799 P4/n 7.64 10.112 10.112 87.997 P4 7.70 10.109 10.109 87.952 P4 8.01 12.791 12.791 41.096 Orthorhombic Cmc21 6.35 18.383 21.147 32.614 C2221 5.85 18.409 21.175 32.643 I222 9.26 40.980 25.606 10.479 F222 8.35 25.255 15.025 48.656 Ccca 6.88 17.753 12.220 128.303 F222 8.37 25.290 48.658 15.002 Monoclinic Pc 10.63 10.004 37.370 10.296 P21/c 9.39 14.554 24.953 12.099 P21 11.53 9.656 32.820 13.612 P21 9.63 18.034 9.645 14.642 P2 12.11 12.258 12.826 20.090 C2 6.39 13.848 34.861 16.775 Triclinic P-1 6.50 10.676 13.728 13.860 P-1 6.73 16.410 10.859 21.768 P-1 6.11 10.678 13.426 13.879 P-1 6.19 13.918 9.630 13.660 Table A.10: Results of quenched sample 2 days after quenching. 66 Crystal structure Space group Gof a (Å) b (Å) c (Å) Cubic I-43d 11.60 50.078 50.078 50.078 P4332 9.46 38.702 38.702 38.702 P23 17.46 38.698 38.698 38.698 P213 17.73 38.697 38.697 38.697 P23 17.36 38.697 38.697 38.697 P213 17.77 38.700 38.700 38.700 Trigonal-Hexagonal P3 14.53 11.212 11.212 71.701 P63 14.20 10.382 10.382 104.134 P63 9.27 13.137 13.137 70.935 P3 15.27 10.237 10.237 104.107 P6cc 9.14 19.994 19.994 31.799 P3 14.53 11.212 11.212 71.701 R3 9.74 21.147 21.147 62.366 Tetragonal I4 18.95 17.493 17.493 106.437 P4 10.18 10.190 10.190 88.614 P4 10.05 10.124 10.124 88.228 P4/n 9.96 10.139 10.139 88.310 I4 9.03 18.436 18.436 62.244 Orthorhombic I222 7.03 18.518 61.569 9.356 Ima2 7.60 18.453 61.453 9.324 I222 7.51 18.368 61.981 9.424 Abm2 6.74 19.415 9.289 83.663 C2221 8.32 25.780 9.497 66.778 P222 10.35 16.131 17.629 13.356 Pmc21 8.94 17.606 27.588 13.968 Monoclinic C2 8.02 69.393 13.514 11.090 P2 10.81 10.142 17.621 16.015 C2 8.89 20.684 9.461 17.813 C2 8.91 20.682 9.462 17.815 Triclinic P-1 6.89 8.059 12.462 33.305 P-1 10.57 9.696 16.767 32.352 P-1 8.33 8.648 20.574 26.957 P-1 7.76 9.481 11.459 43.896 Table A.11: Results of quenched sample 5 days after quenching.