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

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2023-04, Vol.11 (15), p.8119-8130
• Main Authors: Kim, Hyunji, Samuel Kimani Kihoi, Shenoy, U Sandhya, Joseph Ngugi Kahiu, Shin, Dong Hyun, Bhat, D Krishna, Ho Seong Lee
• Format: Article
• Language: English
• Subjects: Alloying; Banded structure; Carrier density; Electronic structure; Figure of merit; Heat conductivity; Heat transfer; Majority carriers; Mechanical properties; Point defects; Power factor; Room temperature; Thermal conductivity; Thermoelectric materials
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d2ta09280h

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 (Ge0.93Bi0.05Te0.98)(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 (Ge0.93Bi0.05Te0.98)(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.