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

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 CuInTe₂ 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 m₀ to 1.95 m₀. 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_0.93Bi_0.05Te_0.98)(CuInTe₂)_0.01 sample is reported. Moreover, the introduced point defects and nano-deposits reduce the lattice thermal conductivity to amorphous levels. As a result, the (Ge_0.93Bi_0.05Te_0.98)(CuInTe₂)_0.01 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 CuInTe₂ alloying appear to be an effective strategy for increasing the ZT values of GeTe-based compounds.