TY - JOUR

T1 - Endotaxial Intergrowth of Copper Telluride in GeTe-Rich Germanium Antimony Tellurides Leads to High Thermoelectric Performance

AU - Schwarzmüller, Stefan

AU - Souchay, Daniel

AU - Wagner, Gerald

AU - Kemmesies, Paul

AU - Günther, Daniel

AU - Bittner, Michael

AU - Zhang, Guanhua

AU - Ren, Zefeng

AU - Feldhoff, Armin

AU - Snyder, G. Jeffrey

AU - Oeckler, Oliver

N1 - Funding Information: Beam time at the European Synchrotron Radiation Facility (ESRF, proposals CH-4020, CH-4988, and CH-5142) and a PhD scholarship for S.S. from the Studienstiftung des deutschen Volkes. Z.R. gratefully acknowledges funding from the Ministry of Science and Technology of China (2018YFA0208700) and the National Natural Science Foundation of China (22073097). Ackowledgments: We thank the ESRF for granting beamtime (proposals CH- 4020, CH-4988, and CH-5142) and Dr. Christopher Benndorf, Lucien Eisenburger, Dr. Nicholas Harker, Markus Nentwig, Dr. Pavel Sedmak, Tobias Stollenwerk, and Dr. Jonathan Wright for help during synchrotron measurements. A PhD scholarship for S.S. from the Studienstiftung des deutschen Volkes is gratefully acknowledged. Z.R. gratefully acknowl- edges funding from the Ministry of Science and Technology of China (2018YFA0208700) and the National Natural Science Foundation of China (22073097). We further thank Alex Gocke for help with some preliminary investigations as well as Dr. Katrin Siefermann, Andreas Neff, and Falk Niefind for test measurements on a laboratory PEEM instrument. Samuel A. Miller is acknowledged for help with Hall measurements and Matthias T. Agne for inspiring discussions.

PY - 2022/11/22

Y1 - 2022/11/22

N2 - In composite materials with nominal compositions Cu2GexSb2Tex+4 (11 ≤ x ≤ 18, i.e., between Cu6.7Ge36.7Sb6.7Te50 and Cu4.5Ge40.9Sb4.5Te50), precipitates consisting of copper tellurides are endotaxially intergrown in a matrix of Cu-doped germanium antimony tellurides. The precipitates as well as the matrix material undergo various phase transitions as shown by temperature-dependent X-ray diffraction and X-ray absorption contrast imaging. Eventually, the precipitates dissolve in the matrix at temperatures exceeding 580 °C. The temperature-dependent behavior was also traced by photoemission electron microscopy up to 460 °C. At high temperatures, the thermoelectric properties are superior to those of pure germanium antimony tellurides obtained by comparable syntheses; a maximal zT value of 1.83 for Cu2Ge16Sb2Te20 is reached at 500 °C. The application of an effective mass model reveals optimal charge carrier concentrations for all three compositions investigated. The p-type Cu2Ge16Sb2Te20 material was used in combination with PbTe:In (n-type) to construct a thermoelectric module. Concludingly, the measurement of the Hall effect that suggests no significant changes in Cu-doping levels of the matrix with temperature application of grain boundary optimization and a temperature-induced reset of the microstructure are proposed as strategies for overcoming material degradation upon applying electrical currents.

AB - In composite materials with nominal compositions Cu2GexSb2Tex+4 (11 ≤ x ≤ 18, i.e., between Cu6.7Ge36.7Sb6.7Te50 and Cu4.5Ge40.9Sb4.5Te50), precipitates consisting of copper tellurides are endotaxially intergrown in a matrix of Cu-doped germanium antimony tellurides. The precipitates as well as the matrix material undergo various phase transitions as shown by temperature-dependent X-ray diffraction and X-ray absorption contrast imaging. Eventually, the precipitates dissolve in the matrix at temperatures exceeding 580 °C. The temperature-dependent behavior was also traced by photoemission electron microscopy up to 460 °C. At high temperatures, the thermoelectric properties are superior to those of pure germanium antimony tellurides obtained by comparable syntheses; a maximal zT value of 1.83 for Cu2Ge16Sb2Te20 is reached at 500 °C. The application of an effective mass model reveals optimal charge carrier concentrations for all three compositions investigated. The p-type Cu2Ge16Sb2Te20 material was used in combination with PbTe:In (n-type) to construct a thermoelectric module. Concludingly, the measurement of the Hall effect that suggests no significant changes in Cu-doping levels of the matrix with temperature application of grain boundary optimization and a temperature-induced reset of the microstructure are proposed as strategies for overcoming material degradation upon applying electrical currents.

UR - http://www.scopus.com/inward/record.url?scp=85141629809&partnerID=8YFLogxK

U2 - 10.1021/acs.chemmater.2c02477

DO - 10.1021/acs.chemmater.2c02477

M3 - Article

VL - 34

SP - 10025

EP - 10039

JO - Chemistry of materials

JF - Chemistry of materials

SN - 0897-4756

IS - 22

ER -