Detail investigation of thermoelectric performance and magnetic properties of Cs-doped Bi2Sr2Co2Oy ceramic materials

Vol.:(0123456789) SN Applied Sciences (2021) 3:114 | h ps://doi.o g/10.1007/s42452-020-04066-2 Resea ch A icle De ail in es iga ion o  he moelec ic pe o mance andmagne ic p ope ies o Cs-doped Bi2S 2Co2Oy ce amic ma e ials B.Özçelik1 · M.Gü sul1· G.Çe in1· C.Özçelik2· M.A.To es3· M.A.Mad e3· A.So elo3 Recei ed: 8 Sep embe 2020 / Accep ed: 22 Decembe 2020 © The Au ho (s) 2021 OPEN Abs ac Bi2S 2−xCsxCo2Oy ma e ials wi h 0 ≤ x ≤ 0.15, ha e been ab ica ed ia he classical ce amic echnique. XRD esul s ha e indica ed ha undoped and Cs-subs i u ed samples a e composed o Bi2S 2Co2Oy phase as he majo one. Mic os uc u al s udies ha e demons a ed he o ma ion o a liquid phase, which allows a d as ic g ain g ow h. This ac o is esponsible o a d as ic imp o emen o ela i e densi y, eaching abou 95% o he heo e ical one o 0.125 Cs con en . On he o he hand, elec ical esis i i y has been educed up o 14 mΩ cm a 650°C o 0.125 Cs con en , a ound 40% lowe han he ob ained in undoped samples. As a consequence, Seebeck coe icien has been dec eased due o he aise in cha ge ca ie concen a ion. The highes powe ac o a 650°C (0.21 mW/K2 m) has been ound o 0.125 Cs subs i u ed sample, abou 40% la ge han he ob ained in undoped samples, and e y simila o he no i ied in single c ys als (0.26 mW/K2 m). Magne isa ion wi h espec o empe a u e esul s ha e demons a ed ha measu ed samples ha e a pa amagne ic p ope y abo e 50K, excep 0.10 Cs. Magne ic hys e esis cu es ha e shown ha he slopes and he magni udes ha e inc eased wi h dec easing empe a u e. Keywo ds Bi2S 2Co2Oy· Elec ical p ope ies· Seebeck coe icien · Powe ac o · Laye ed cobal i es 1 In oduc ion Since he es ablishmen o undamen al equa ions o explain he moelec ic (TE) phenomena [1, 2], many di - e en amilies o TE ma e ials ha e been disco e ed [3–5]. Nowadays, he mos a ac ing cha ac e is ic o hese ma e ials is hei abili y o di ec ly ans o m, wi hou he need o mo ing pa s, hea in o elec ic powe [6]. The ma e ial e iciency o pe o m his p ocess can be e alua ed h ough he dimensionless ZT (Figu e o Me i ) ob ained om [7]: (ZT = S2σT/κ), whe e S, σ, T, and κ, a e Seebeck coe icien , elec ical conduc i i y, absolu e em- pe a u e, and he mal conduc i i y, espec i ely. Mo eo- e , he S2σ ac o , ep esen ing he elec ical pa in his exp ession is known as he TE Powe Fac o , PF. Usually, i is conside ed ha TE ma e ials o p ac ical applica ions should p esen ZT ≥ 1. Recen ly, he la ges ZT alues ha e been ob ained in in e me allic ma e ials, as PbTeSe [3]. On he o he hand, hese ma e ials show limi ed wo king empe a u es due o oxida ion a high empe a u e unde ai , e y expensi e cos s [6], and less plen y in he ea h c us [8]. Howe e , in spi e o he majo abundance o silicon in he ea h c us [8], he bes pe o - mances a e ob ained in high cos s ma e ials [6]. The dis- co e y o high TE p ope ies in oxide ma e ials [5], which combine high wo king empe a u es, low cos s and ela- i ely high abundance in he ea h c us [6, 8], opened a b oad esea ch ield. Following his disco e y, and p o- ided by he impo an ad an ages o oxides, new ma e- ials wi h a ac i e TE p ope ies, such as Bi2S 2Co1.8Ox [9], * B. Özçelik, oz[email p o ec ed] | 1Depa men o Physics, Facul y o Sciences andLe e s, Çuku o a Uni e si y, 01330Adana, Tu key. 2Ins i u e o Enginee ing andSciences, Iskende un Technical Uni e si y, Ha ay, Tu key. 3Dp o. de Ciencia de Ma e iales, ICMA (CSIC-Uni e sidad de Za agoza), C/Ma ía de Luna 3, 50018Sa agossa, Spain. Vol:.(1234567890) Resea ch A icle SN Applied Sciences (2021) 3:114 | h ps://doi.o g/10.1007/s42452-020-04066-2 we e also ound. Mo eo e , he in e es in hese ma e i- als g ew when ZT o 1.2 in Bi2S 2Co1.8Ox whiske s was achie ed [10]. Howe e , in spi e o he many wo ks pub- lished on TE oxides, bulk polyc ys alline ma e ials canno each hese ZT alues, being usually much lowe han 1. As a consequence, one o he main objec i es o esea che s is enhancing hei TE pe o mances o be used in p ac i- cal applica ions. Among he la ge numbe o app oaches pe o med o enhance he TE p ope ies o hese oxides, i can be highligh ed he use o we -syn hesis me hods [11, 12], ex u ing [13, 14], and doping [15, 16]. The s udies pe o med on TE oxides o he CoO amily ha e allowed o de e mine ha he subs i u ion o any ca - ion o he Rock Sal laye by a lowe oxida ion one, leads o an inc ease o cha ge ca ie concen a ion due o he pa - ial p omo ion o Co3+ ca ions o Co4+ in he conduc ing laye [17], which induces a dec ease o Seebeck coe icien [18]. This e ec can be p oduced by alkaline ea h sub- s i u ion in he s uc u e by an alkaline elemen , leading o impo an mic os uc u al and elec ical modi ica ions, as demons a ed in p e ious wo ks [19, 20]. The e o e, we aim o de e mine he e ec o a la ge alkaline ca ion (Cs) pa ial subs i u ion in he alkaline ea h posi ion o Bi2S 2Co2Oy he moelec ic compound. The s uc u al and mic os uc u al changes induced by his subs i u ion will be de e mined and linked o he modi ica ions o elec ical p ope ies in classically sin e ed ma e ials. 2 Expe imen al Cs-doped Bi2S 2−xCsxCo2Oy p ecu so s, wi h 0 ≤ x ≤ 0.15, ha e been p epa ed, h ough he classical ce amic me hod, using comme cial Bi2O3 (98+ %, Pan eac), S CO3 (98.5%, Pan eac), CoO (99.99%, Sigma-Ald ich), and Cs2CO3 (99.8%, Pan eac) powde s as s a ing ma e ials. A e weighing hem in he app op ia e p opo ions, hey we e well mixed and subjec ed o ball milling, using wa e media, a 300 pm o 30min. The p oduced slip was sub- sequen ly d ied and hea ed o decompose he ca bon- a es using a wo-s ep p ocess: 750°C o 12h, and 800°C o 12h, wi h an in e media e manual milling. Finally, he powde s we e uniaxially p essed in o pelle s (2 × 2 × 14 mm3) unde 400MPa applied p essu e, and sin e ed a 810°C o 24h and u nace cooled. Powde X- ay di ac ion (XRD) pa e ns we e ob ained in a Rigaku D/max-B X- ay powde di ac ome e wo k- ing wi h Cu Kα adia ion, and ixing 2θ be ween 10 and 40 deg ees, in o de o iden i y he phases in he ex u ed ma e ials. Mic os uc u al cha ac e iza ion has been made in a Zeiss–Me lin ield emission scanning elec on mic oscope (FESEM) associa ed o an ene gy-dispe si e spec oscopy (EDS) sys em used o quali a i e elemen al analysis. Samples we e analysed h ough su ace mic o- g aphs o de e mine mic os uc u al modi ica ions induced by Cs doping. Mo eo e , densi y o ma e ials has been ob ained by A chimedes’ me hod in se e al speci- mens o each composi ion o minimize e o s. Elec ical p ope ies o he di e en samples we e de e mined h ough simul aneous measu emen o Seebeck coe icien and elec ical esis i i y using he well-known di ec cu en ou -p obe con igu a ion in a LSR-3 sys em (Linseis GmbH). These p ope ies ha e been ob ained unde s eady-s a e condi ions be ween 50 and 650°C using He a mosphe e. Elec ical pe o mance o samples, PF, was calcula ed using hese da a. Finally, he magne ic p ope ies we e measu ed by using a PPMS sys- em (Dynecool PPMS, Quan um Design). The magne ic hys e esis da a we e aken in be ween—5 o 5T, and he magne iza ion measu emen s we e ob ained in ZFC mode unde a DC- ield o 20 Oe, om 300K down o 5K. 3 Resul s anddiscussion Rep esen a i e XRD pa e ns ob ained on g inded Bi2S 2−xCsxCo2Oy ma e ials a e p esen ed in Fig.1. In his g aph, i may be easily deduced ha mos o he peaks (indica ed by hei di ac ion planes) can be associa ed o he Bi2S 2Co2Oy phase, being he majo one, which is Fig. 1 Rep esen a i e powde X- ay di ac ion pa e ns o Bi2S 2−xCsxCo2Oy samples; o x = (a) 0; (b) 0.025; (c) 0.075; and (d) 0.125. Di ac ion planes show he peaks associa ed o he TE phase, while * iden i ies he co esponding o he Bi–S –O phase Vol.:(0123456789) SN Applied Sciences (2021) 3:114 | h ps://doi.o g/10.1007/s42452-020-04066-2 Resea ch A icle consis en wi h li e a u e [21]. Mo eo e , he * shows he Co- ee seconda y phase [22], which is p esen in e y small p opo ions. Consequen ly, i can be easily deduced ha all samples a e o med by nea ly single Bi2S 2Co2Oy phase. On he o he hand, in compa ison o undoped sam- ples, e y small shi in he di ac ion peaks o Cs-doped samples has been ound, esul ing om highe ionic adius o Cs. In addi ion, no Cs-based seconda y phases ha e been obse ed. Figu e2 displays ep esen a i e SEM mic og aphs pe - o med on he su ace o Bi2S 2−xCsxCo2Oy samples. F om hese mic og aphs, i is easy o obse e a d as ic g ain g ow h and dec ease o po osi y when he amoun o Cs is inc eased. This e olu ion can be associa ed o he o ma- ion o a liquid phase induced by he alkaline ca ion, which can be due o he low mel ing poin o Cs2CO3 (793°C [23]), in ag eemen wi h p e ious s udies on simila com- pounds [24]. Up o 0.05 Cs subs i u ion (Fig.2b), he g ain sizes a e only sligh ly la ge han in pu e samples (Fig.2a). On he o he hand, highe Cs addi ions lead o much la ge g ains, indica ing he p esence o a la ge amoun o liq- uid phase along he g ain bounda ies, which enhances ca ions mobili y. This e ec , and he sys em endency o dec ease su ace ene gy, a e he esponsible pa ame e s o inc easing g ain sizes. On he o he hand, ano he impo an mic os uc u al modi ica ion is he appea - ance, besides he g ey con as (#1, associa ed h ough EDS o he he moelec ic Bi2S 2Co2Oy phase), o a ligh g ey one (#2, co esponding o he Bi–S –O phase) when Cs is added o he samples. Finally, o he highes Cs con- aining samples, a black con as can be ound (#3), wi h Co-oxide composi ion. On he o he hand, Cs doping leads o a sligh Ca2+ by Cs+ subs i u ion, ound by EDS analysis o he he moelec ic phase in se e al samples o each Cs subs i u ion. The EDS esul s ha e shown ha he subs i- u ing Cs amoun co esponds o, app oxima ely, one hal o he nominal one in he inne pa o he samples, while i is ha dly de ec ed in he su ace o samples. Mo eo e , no Cs has been iden i ied in any o he seconda y phases. These da a clea ly ag ee wi h p e ious obse a ions in simila compounds [24]. In o de o de e mine he e ec o his liquid phase in he sin e ing p ocess, densi y measu emen s ha e been pe o med using A chimedes’ me hod and he esul s a e p esen ed, as a unc ion o nominal Cs con en , in Fig.3. As i can be obse ed in he g aph, undoped samples display he lowes densi ies, 5.45g/cm3, which a e abou 80% o he heo e ical one ( aking heo e ical densi y as 6.8g/cm3 [25]). When Cs is added, ela i e densi y mono onically inc eases wi h Cs con en up o a ound 95% o 0.125 Cs Fig. 2 Rep esen a i e SEM mic og aphs pe o med on su aces o Bi2S 2−xCsxCo2Oy samples, wi h x = a 0; b 0.05; c 0.1; and d 0.15. G ey con- as (#1) co esponds o he he moelec ic phase, ligh g ey (#2) o he Co- ee one (Bi–S –O), and black one (#3) o Co-oxide Vol:.(1234567890) Resea ch A icle SN Applied Sciences (2021) 3:114 | h ps://doi.o g/10.1007/s42452-020-04066-2 samples, sligh ly dec easing o highe Cs amoun s. These da a clea ly con i m he d as ic dec ease o po osi y when Cs is added, eaching alues compa able o he epo ed o ho -p essed o mel -g own ma e ials (96, and 97%, espec i ely) [25, 26], and only lowe han he epo ed in pa ially mel ed ma e ials wi h subsequen ho -p ess- ing p ocess (a ound 99%) [25]. Fu he mo e, i should be highligh ed ha hese e y high densi y alues ha e been ob ained h ough a e y simple and sho p ocess, when compa ed o hose p e iously men ioned in li e a u e. Elec ical esis i i y a ia ions o all samples wi h em- pe a u e, as a unc ion o Cs con en , a e shown in Fig.4. As can be seen in he plo , he gene al sample’s beha - iou is signi ican ly changed by Cs subs i u ion; i is semi- conduc ing (dρ/dT < 0) o he pu e and 0.025 Cs samples (much less e iden o hese las samples), while highe Cs subs i u ion leads o me allic (dρ/dT > 0) one. Mo eo- e , he inc ease o Cs subs i u ion leads o lowe elec i- cal esis i i y alues han he measu ed in undoped ones. This e olu ion is in ag eemen wi h he S 2+ subs i u ion by Cs+, which dec eases he oxida ion s a e o he ock sal s uc u e, p omo ing he Co3+ in he conduc ing laye o Co4+. Consequen ly, he cha ge ca ie concen a ion (holes), a e inc eased, dec easing elec ical esis i i y. On he o he hand, he inc ease de e mined in he 0.15 Cs subs i u ed samples can be associa ed o he aise in he numbe o de ec s, which is esponsible o hei highe elec ical esis i i y alues. O he a ou able e ec s o his dec ease in elec ical esis i i y a e he aise in den- si y, and he impo an g ain g ow h, which dec eases he numbe o g ain bounda ies in he bulk ma e ial. The lowes esis i i y alues a 650°C (14 mΩ cm) ha e been de e mined in 0.125 Cs subs i u ed samples, abou 40% lowe han hose ob ained in undoped samples in his wo k. Mo eo e , hey a e much lowe han he epo ed in ex u ed ma e ials ia ho p essing (40 mΩ cm [27]), o lase p ocessing (20 mΩ cm [13]), while hey a e close o hose ob ained in sin e ed ma e ials unde oxygen (15 mΩ cm [28]), o in single c ys als (18 mΩ cm a oom em- pe a u e [29], and 10 mΩ cm a 600°C [16]). These esul s clea ly ag ee wi h he d as ic enhancemen o g ain sizes, dec ease o po osi y and, p obably, he imp o emen o g ains elec ical connec i i y, p oduced by Cs subs i u ion. The endency obse ed in elec ical esis i i y wi h Cs subs i u ion may be due o he modi ica ion o mic o- s uc u e and elec onic pa ame e s. Howe e , mo e in o - ma ion and expe imen al wo k is necessa y o p ecisely de e mine and explain his e olu ion. The e o e, in o de o be e unde s and he mechanism o esis i i y, he small pola on hopping model [30] has been used hough he ollowing ela ion: whe e A, n, e, x, Ea, kB, and T a e he p e-exponen ial e m ela ed o he sca e ing mechanism, ca ie concen- a ion, elemen a y cha ge, in e si e hopping dis ance, (2) 𝜌(T)=(T Anex2)exp (Ea kBT) Fig. 3 E olu ion o Bi2S 2−xCsxCo2Oy samples densi y, oge he wi h i s s anda d e o , as a unc ion o nominal Cs con en Fig. 4 Elec ical esis i i y e olu ion wi h empe a u e o Bi2S 2−xCsxCo2Oy samples. The inse shows he linea i s o ln(ρ/T) e sus 1000/T o all samples Vol.:(0123456789) SN Applied Sciences (2021) 3:114 | h ps://doi.o g/10.1007/s42452-020-04066-2 Resea ch A icle pola on ac i a ion ene gy, Bol zmann cons an and abso- lu e empe a u e, espec i ely. As i is shown in he inse o Fig.4, he linea ela ionship o ln(ρ/T) wi h espec o 1/T abo e 500K i s well wi h he pola on hopping model o elec ical esis i i ies o all samples. In o de o calcula e he ac i a ion ene gies o samples, he slopes o s aigh lines ha e been used, and he calcula ed alues o he pu e, 0.025, 0.050, 0.075, 0.10, 0.125, and 0.15 samples a e 165.62, 59.21, 33.20, 25.80, 27.21, 26.60, and 25.72meV, espec i ely. Acco ding o hese alues, he Ea alues o undoped samples a e much highe han he de e mined in Cs doped ones. Ini ially, he alues d as ically dec ease up o 0.05 Cs, emaining p ac ically cons an o highe dop- ing. The hopping o cha ge ca ie s akes place be ween Co3+ and Co4+ in he CoO2 laye o BiS CoO sys em. The e- o e, he a io be ween Co3+ and Co4+ di ec ly in luences he hopping dis ance, x. The dec ease o his a io sugges s an inc emen o Co4+ concen a ion due o Cs subs i u- ion, educing he hopping dis ance. This ac also leads o he dec ease o hopping ac i a ion ene gy. This esul suppo s he a gumen ha he Co3+ is p omo ed o Co4+ in he conduc ing laye , as discussed abo e. Figu e5 illus a es Seebeck coe icien a ia ion wi h empe a u e, and Cs subs i u ion. In he g aph, i can be obse ed ha all alues a e posi i e in he whole meas- u ed empe a u e ange, which is cha ac e is ic o hole- domina ing anspo mechanism. A oom empe a u e, he Seebeck coe icien is dec eased in Cs subs i u ed samples, when compa ed o he undoped ones. This is in ag eemen wi h Koshibae’s exp ession [18], which indica es ha he inc ease o Co4+ p opo ion in he conduc ion band leads o a educ ion o Seebeck coe - icien . Howe e , oom empe a u e Seebeck coe icien alues a e only sligh ly modi ied in he Cs doped samples, which could be in e p e ed as a close Cs con en in all doped samples, when compa ed o he nominal compo- si ion. This ac could also explain he ac ha lowe Cs con en han he nominal one has been ound by EDS in he samples, as obse ed in p e ious wo ks [24]. The high- es S alues a 650°C (195μV/K) ha e been measu ed in undoped samples, a ound 10% highe han hose meas- u ed in Cs subs i u ed samples in his s udy. These alues a e la ge han hose in o med in ho -p essed samples (~150μV/K) [27], o single c ys als (160μV/K) [16], and close o hose de e mined in sin e ed samples ob ained by so chemis y ou es (205μV/K) [31]. Using elec ical esis i i y and Seebeck coe icien al- ues p e iously p esen ed, PF e olu ion wi h empe a u e, and Cs subs i u ion, has been calcula ed and p esen ed in Fig.6. As i can be seen in he plo , in spi e o hei lowe Seebeck coe icien alues, Cs subs i u ed samples display highe PF alues han he undoped ones. Mo eo e , PF is inc eased wi h empe a u e in he whole measu ed em- pe a u e ange, and wi h Cs con en up o 0.125, sligh ly dec easing o highe con en . The highes PF alues a 650°C (~0.20 mW/K2 m) ha e been ob ained in 0.125 Cs subs i u ed samples, which a e a ound 40% highe han hose de e mined in undoped samples in his wo k. Mo eo e , hey a e much la ge han he p esen ed in ho -p essed samples (0.06 mW/K2 m) [27], and simila o he ob ained in ce amics p epa ed h ough so chemis- y ou es (0.20 mW/K2 m) [31], a he same empe a u e. Fig. 5 Seebeck coe icien e olu ion wi h empe a u e o Bi2S 2−xCsxCo2Oy samples Fig. 6 Powe ac o e olu ion wi h empe a u e o Bi2S 2−xCsxCo2Oy samples Vol:.(1234567890) Resea ch A icle SN Applied Sciences (2021) 3:114 | h ps://doi.o g/10.1007/s42452-020-04066-2 Howe e , hey a e s ill sligh ly lowe han he bes epo ed esul s in single c ys als (0.26 mW/K2 m) [16], due o he absence o g ain bounda ies. The moelec ic appa a us di ec ly con e s a empe a- u e g adien in o elec ici y called as he Seebeck e ec , while he e e se coun e pa is he he moelec ic cooling phenomenon named as Pel ie e ec . As i is known, he magne ic cooling is based on he Magne o Calo ic E ec (MCE) and i is p omisingly applicable on e ige a ion sys- ems. Hence, o he po en ial payo , i is necessa y o p o- duce and op imize new he moelec ic ma e ials, which can be sui able o ope a ion o e wide low empe a u e anges. Since he he moelec ic pa ame e s like Seebeck coe icien , powe ac o and o he s a e e y sensi i e o he small a ia ion o he ex e nal applied magne ic ield, he magne ic cha ac e iza ion can be e y impo an issue o p esen new candida e samples o he moelec ic- cooling applica ions. The e o e, he samples we e in es- iga ed om he magne ic poin o iew. Fo his pu pose, he empe a u e and ield dependen magne iza ion, and hys e esis cu es o all samples ha e been de e mined. In Fig.7 he magne iza ion o all samples wi h espec o empe a u e down o 10K, measu ed in ze o- ield cooled mode, unde 20 Oe ex e nal applied magne ic ield, a e p esen ed. As i can be seen in his igu e, e y simila magne ic p ope ies ha e been de e mined in all samples, i.e. magne iza ion o samples sha ply dec eases om 5K up o 25K, and hen slowly dec eases, excep o 0.1 Cs ones. Acco ding o he Cu ie–Weiss law, in he high empe a u e egion, he da a o each sample should be i - ed o a s aigh line by plo ing in e se suscep ibili y (1/χ) wi h espec o empe a u e, T, as gi en in inse o Fig.7, o he 0.05 Cs samples. By ex apola ing he high-T pa o he cu es (1/χ ĺ 0), nega i e pa amagne ic empe a u es, θ, we e ob ained o he pu e (≈−60K), 0.05 (≈−50K), and 0.075 (≈−15K), samples. Consequen ly, an i e omagne ic luc ua ions a e p e ailing in hese samples. Howe e , o Cs subs i u ion ≥ 0.10, he ͹(T) cu es exhibi a shallow maximum a a ound 150 K. This e ec may be a ibu ed o an an i e omagne ic s a e p omo ed by his highe Cs-con en . The Cu ie cons an s o all samples ha e been calcula ed om he slope o he 1/͹ e sus T cu es, being a ound ≈3 × 10–3 emu K/g. The e ec i e magne ic momen s, μe , o undoped, 0.05 Cs, 0.075 Cs and 0.1 Cs samples ha e been calcula ed by using he equa ion gi en in [32], as 2.40μB, 2.35μB, 1.25μB, and 3.83μB, espec i ely. The M–H cu es, measu ed a 15K o he undoped and Cs-doped samples ha e been plo ed in Fig.8. No hys e - esis beha io can be obse ed in hese cu es, demon- s a ing ha he pa amagne ic phase is s ill dominan a empe a u es ≥15K. In addi ion, he slopes a e inc eased when he Cs-con en is highe . I is necessa y o highligh ha he linea ield dependence o magne iza ion poin s o a no mal canonical pa amagne ic o de in connec ion wi h he applied magne ic ield. The empe a u e dependence o magne ic hys e esis has been also in es iga ed, and he esul s a e p esen ed in Fig.9. Since he gene al beha io o undoped and Cs- doped samples is he same o Cs con en up o 0.10, o he sake o cla i y, only he esul s ob ained in 0.05 Cs and 0.10 Cs samples a e shown. In he igu e, i can be seen ha he slopes and he magni ude o magne iza ion is dec eased when he empe a u e is inc eased o samples wi h Cs con en ≤ 0.10. I can be a gued ha when empe - a u e dec eases, he magne ic momen s in andom di ec- ions a e a ec ed by inc easing ex e nal applied magne ic Fig. 7 DC-magne iza ion o pu e and 0.05 Cs, 0.075 Cs, and 0.10 Cs. The inse shows he in e se DC-magne ic suscep ibili y cu es o he 0.05 Cs doped samples measu ed a 20 Oe Fig. 8 Hys e esis cu es o he pu e and 0.05 Cs, 0.075 Cs, and 0.10 Cs samples a measu ed 15K Vol.:(0123456789) SN Applied Sciences (2021) 3:114 | h ps://doi.o g/10.1007/s42452-020-04066-2 Resea ch A icle ield. Then, all he spins in andom di ec ions a e o ien ed he di ec ion o ex e nal applied magne ic ield. Hence, he magne iza ion alues s a o inc ease wi h dec easing empe a u e alues. As a esul , when conside ing all hese esul s, i may be concluded ha Cs-doping is e y use ul o imp o ing he he moelec ic p ope ies o Bi2S 2Co2Oy ma e ials. An impo an inc ease in powe ac o , PF, ob ained in his wo k using a simple p epa a ion p ocess, leads o conside hese ce amic ma e ials as e y p omising candida es o hei in eg a ion in p ac ical he moelec ic de ices. 4 Conclusions Bulk sin e ed Bi2S 2−xCsxCo2Oy (0 ≤ x ≤ 0.15) he moelec ic ce amics ha e been success ully ab ica ed ia he clas- sical ce amic p epa a ion echnique. I has been ound ha Cs subs i u ion has led o he o ma ion o a liquid phase du ing sin e ing p ocedu e, d as ically enhancing g ain g ow h and dec easing po osi y. On he o he hand, his g ain g ow h is accompanied by he o ma ion o a Co poo egion close o he g ain bounda ies. These mic o- s uc u al modi ica ions ha e been e lec ed in a d as ic inc ease o ela i e densi y, eaching alues o abou 95% o he heo e ical one. Mo eo e , elec ical esis i i y is dec eased wi h Cs doping, due o he inc ease in cha ge ca ie concen a ion, which has been con i med by he dec ease o Seebeck coe icien when compa ed o he undoped samples. Fu he mo e, he inc ease o elec ical esis i i y in 0.125 Cs samples is associa ed o he aise o de ec s which ac as elec onic sca e ing cen e s. All hese cha ac e is ics led o high powe ac o alues in Cs sub- s i u ed samples, which makes hem p omising ce amic ma e ials o p ac ical applica ions. On he o he hand, magne ic p ope ies do no e lec hese imp o emen s since Cs-addi ion is andomly in lu- encing hem. Acknowledgemen s This s udy was ca ied ou wi hin he scope o Cuku o a Uni e si y Scien i ic Resea ch P ojec s Uni FBA-2020- 13007 and FBA-2020-12784. The au ho s wish o hank he Spanish MINECO-FEDER (MAT2017-82183-C3-1-R), and Gobie no de A agón (Resea ch G oup T 54-17 R) o unding. 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To iew a copy o his licence, isi h p://c ea i eco mmons .o g/licen ses/by/4.0/. Re e ences 1. Al enki ch E (1909) Ube den Nu ze eck de The mosaule. Phys Z 10(16):560–568 2. Al enki ch E (1911) Elec o he mische Kal ee zeugung und e e sible elec ische Heizung. Phys Z 12:920–924 3. Fu T, Yue X, Wu H, Fu C, Zhu T, Liu X, Hu L, Ying P, He J, Zhao X (2016) Enhanced he moelec ic pe o mance o PbTe bulk ma e ials wi h igu e o me i zT > 2 by mul i- unc ional alloying. J Ma e iomics 2:141–149 Fig. 9 Hys e esis cu es o he a 0.05 Cs, b 0.10 Cs doped samples measu ed a 15, 30, and 45K Vol:.(1234567890) Resea ch A icle SN Applied Sciences (2021) 3:114 | h ps://doi.o g/10.1007/s42452-020-04066-2 4. Niki in E (1958) In es iga ion on empe a u e dependencies o elec ical conduc i i y and he mopowe o silicides. Zhu nal Tekhnicheskoj Fiziki 28:23–25 5. Te asaki I, Sasago Y, Uchinoku a K (1997) La ge he moelec ic powe in NaCo2O4 single c ys als. Phys Re B 56:12685–12687 6. LeBlanc S (2014) The moelec ic gene a o s: linking ma e ial p ope ies and sys ems enginee ing o was e hea eco e y applica ions. Sus Ma e Technol 1–2:26–35 7. Rowe DM (eds) (2006) The moelec ics handbook: mac o o nano, 1s edn. CRC P ess, Boca Ra on 8. He J, Liu Y, Funahashi R (2011) Oxide he moelec ics: he chal- lenges, p og ess, and ou look. J Ma e Res 26:1762–1772 9. Funahashi R, Ma suba a I, Sodeoka S (2000) The moelec ic p ope ies o Bi2S 2Co2Ox polyc ys alline ma e ials. Appl Phys Le 76:2385–2387 10. Funahashi R, Shikano M (2002) Bi2S 2Co2Oy whiske s wi h high he moelec ic igu e o me i . Appl Phys Le 81:1459 11. So elo A, Rasekh Sh, To es MA, Bosque P, Mad e MA, Diez JC (2015) E ec o syn hesis me hods on he Ca3Co4O9 he mo- elec ic ce amic pe o mances. J Solid S a e Chem 221:247–254 12. Wu NY, Holga e TC, Nong NV, P yds N, Linde o h S (2014) High empe a u e he moelec ic p ope ies o Ca3Co4O9+δ by au o- combus ion syn hesis and spa k plasma sin e ing. J Eu Ce am Soc 34:925–931 13. Rasekh Sh, Cos a FM, Fe ei a NM, To es MA, Mad e MA, Diez JC, So elo A (2015) Use o lase echnology o p oduce high he - moelec ic pe o mances in Bi2S 2Co1.8Ox. Ma e Des 75:143–148 14. Wang H, Sun X, Yan X, Huo D, Li X, Li J-G, Ding X (2014) Fab- ica ion and he moelec ic p ope ies o highly ex u ed Ca9Co12O28 ce amic. J Alloy Compd 582:294–298 15. Xu GJ, Funahashi R, Shikano M, Ma suba a I, Zhou YQ (2002) The moelec ic p ope ies o Bi2.2−xPbxS 2Co2Oy sys em. J Appl Phys 91:4344–4347 16. Sun N, Dong ST, Zhang BB, Chen YB, Zhou J, Zhang ST, Gu ZB, Yao SH, Chen YF (2013) In insically modi ied he moelec ic pe - o mance o alkaline-ea h iso alen ly subs i u ed [Bi2AE2O4] [CoO2]y single c ys als. J Appl Phys 114:043705 17. Maignan A, Pelloquin D, Hebe S, Klein Y, He ieu M (2006) The - moelec ic powe in mis i cobal i es ce amics: op imiza ion by chemical subs i u ions. Bol Soc Esp Ce am 45:122–125 18. Koshibae W, Tsu sui K, Maekawa S (2000) The mopowe in cobal oxides. Phys Re B 62:6869–6872 19. Çe in Ka akaya G, Ozcelik B, Nane O, So elo A, Rasekh Sh, To es MA, Mad e MA (2018) Imp o emen o Bi2S 2Co2Oy he moelec- ic pe o mances by Na doping. J Elec oce am 40:11–15 20. Li Y-N, Wu P, Zhang S-P, Chen S, Yan D, Yang J-G, Wang L, Huai X-L (2018) The moelec ic p ope ies o lowe concen a ion K-doped Ca3Co4O9 ce amics. Chin Phys B 27:057201 21. So elo A, Rasekh Sh, Cons an inescu G, To es MA, Mad e MA, Diez JC (2013) Imp o emen o ex u ed Bi1.6Pb0.4S 2Co1.8Ox he moelec ic pe o mances by me allic Ag addi ions. Ce am In 39:1597–1602 22. Me cu io D, Champa naud-Mesja d JC, F i B, Con lan P, Boi in JC, Vog T (1994) The mal e olu ion o he c ys al-s uc u e o he hombohed al Bi0.75S 0.25O1.375 phase—a single-c ys al neu on-di ac ion s udy. J Solid S a e Chem 112:1–8 23. Hammond CR (2009) Handbook o physics and chemis y, 90 h edn. CRC P ess, Boca Ra on, FL 24. So elo A, Cos a FM, Fe ei a NM, Ko ale sky A, Fe o MC, Ama al VS, Ama al JS, Rasekh Sh, To es MA, Mad e MA, Diez JC (2016) Tailo ing Ca3Co4O9 mic os uc u e and pe o mances using a ansien liquid phase sin e ing addi i e. J Eu Ce am Soc 36:1025–1032 25. Combe E, Funahashi R, Ba bie T, Azough F, F ee R (2016) Dec eased he mal conduc i i y in Bi2S 2Co2Ox bulk ma e ials p epa ed by pa ial mel ing. J Ma e Res 31:1296–1305 26. Çe in G, Özçelik B, Gu sul M, To es MA, Mad e MA, So elo A (2020) E ec o annealing and po assium subs i u ion on he he moelec ic and magne ic p ope ies o di ec ionally g own Bi2S 2Co2Oy ce amics. Bol Soc Esp Ce am Vid 59:121–128 27. Shin W, Mu ayama N (2000) The moelec ic p ope ies o (Bi, Pb)–S –Co–O oxide. J Ma e Res 15:382–386 28. I aha a H, Xia C, Sugiyama J, Tani T (2004) Fab ica ion o ex u ed he moelec ic laye ed cobal i es wi h a ious ock sal - ype lay- e s by using β-Co(OH)2 pla ele s as eac i e empla es. J Ma e Chem 14:61–66 29. I oh T, Te asaki I (2000) The moelec ic p ope ies o Bi2.3−xPbxS 2.6Co2Oy single c ys als. Jpn J Appl Phys 39:6658–6660 30. Bosman AJ, Daal HJV (1970) Small-pola on e sus band conduc- ion in some ansi ion-me al oxides. Ad Phys 19:1 31. Mad e MA, Rasekh Sh, Diez JC, So elo A (2010) New solu ion me hod o p oduce high pe o mance he moelec ic ce amics: a case s udy o Bi–S –Co–O. Ma e Le 64:2566–2568 32. Çe in Ka akaya G, Özçelik B, To es MA, Mad e MA, So elo A (2018) E ec o Na-doping on he moelec ic and magne ic pe o mances o ex u ed Bi2S 2Co2Oy ce amics. J Eu Ce am Soc 38:515–520 Publishe ’s No e Sp inge Na u e emains neu al wi h ega d o ju isdic ional claims in published maps and ins i u ional a ilia ions.