Title: Thermoelectric Transport Studies on GeTe alloys and single crystals: from Defects to Band Engineering

Speaker: Prof. Vinayak Kamble, IISER, Thiruvananthapuram

Abstract: Germanium Telluride is a narrow bandgap semiconductor and a potential candidate for high thermoelectric efficiency (ZT > 2) due to its high power-factors and low lattice thermal conductivity [1]. This member of the chalcogenide family shows a phase transition at high temperatures where one phase shows high ZT and the other does not. GeTe has a high figure of merit at temperatures 400-650K, however at temperatures greater than 670 K, the power factor is observed to decrease due to bipolar onset post phase-transition [2]. Besides, Ge vacancies are the equilibrium defects in GeTe that impart degenerate nature as well as contribute to lattice anharmonicity along with metavalent bonding. In this talk I shall discuss some of our results [3], on polycrystalline GeTe alloys with doping to band engineering to mitigate the bipolar onset to achieve an overall increase in power factor at temperatures 700-800 K. Furthermore, we have investigated the thermal transport in GeTe single crystals that offers insights into the role of Ge defects in lattice anharmonicity as well power factor optimization.

References: 1. Yang, Lei, et al. - High performance thermoelectric materials: progress and their applications, Advanced Energy Materials 8.6 (2018): 1701797. 2. Zhang, Xinyue, et al. - GeTe thermoelectrics. - Joule 4.5 (2020): 986-1003. 3. Saptak Majumder, Vinayak Kamble and coworkers, unpublished. 4. Jiang, et al. Nature Communications vol13, 6087 (2022)