High thermoelectric and mechanical performance achieved by a hyperconverged electronic structure and low lattice thermal conductivity in GeTe through CuInTe2 alloying

Abstract

GeTe-based thermoelectric materials have a very high hole carrier concentration (∼1021 cm−3), and thus, improving the figure of merit, ZT, is substantially challenging. In this work, we foremost dope Bi to lower the majority carrier concentration, followed by alloying CuInTe<inf>2</inf> to further adjust the hole concentration to an optimal level (0.5-2.0 × 1020 cm−3). This strategy also improves the structural symmetry and leads to hyperconverged valence sub-bands and resonance levels, increasing the effective mass from 1.42 m<inf>0</inf> to 1.95 m<inf>0</inf>. Consequently, a high power factor of ∼23 μW cm−1 K−2 at room temperature and ∼41 μW cm−1 K−2 at 623 K in the (Ge<inf>0.93</inf>Bi<inf>0.05</inf>Te<inf>0.98</inf>)(CuInTe<inf>2</inf>)<inf>0.01</inf> sample is reported. Moreover, the introduced point defects and nano-deposits reduce the lattice thermal conductivity to amorphous levels. As a result, the (Ge<inf>0.93</inf>Bi<inf>0.05</inf>Te<inf>0.98</inf>)(CuInTe<inf>2</inf>)<inf>0.01</inf> sample has a peak ZT value of ∼2.16 at 623 K and an average ZT value of ∼1.42 at 300-773 K. A record high hardness value (∼277 Hv) is achieved. Simultaneous Bi doping and CuInTe<inf>2</inf> alloying appear to be an effective strategy for increasing the ZT values of GeTe-based compounds. © 2023 The Royal Society of Chemistry.