Anomalous strain-dependent thermoelectric properties of cubic stuffed-diamond LiCu3TiQ4 ( Q = S,Se )

• DOI: 10.1103/physrevapplied.23.034085
• Publication Date: 2025-03-31T14:27:31Z
• Authors: Xue-Kun Chen; Jian Zhu; Meng Qi; Pin-Zhen Jia; Zhong-Xiang Xie

Developing high-performance thermoelectric (TE) materials composed of low-toxic elements alternative to $\mathrm{Pb}$-based compounds is essential for the widespread application TE technology. Recently, a new stuffed-diamond structure ${\mathrm{Li}\mathrm{Cu}}_{3}{\mathrm{Ti}\mathrm{Q}}_{4}$ ($\mathrm{Q}$ = $\mathrm{S},\phantom{\rule{0.2em}{0ex}}\mathrm{Se}$) with moderate band gap and low hole carrier effective masses has been synthesized [J. Am. Chem. Soc. 144, 12789 (2022)], which could be promising candidate applications. Here, based on first-principle calculations combined Boltzmann transport theory, we systematically study electronic thermal properties elucidate performance. The results show that lattice conductivities ${\mathrm{Li}\mathrm{Cu}}_{3}{\mathrm{Ti}\mathrm{S}}_{4}$ ${\mathrm{Li}\mathrm{Cu}}_{3}{\mathrm{Ti}\mathrm{Se}}_{4}$ are 2.4 2.1 W/mK at 300 K within framework four-phonon scattering, respectively, comparable various typical such as $\mathrm{Pb}\mathrm{Te}$ ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$. In addition, behaves degenerate semiconductor possesses large power factor [0.6--1.5 mW/(cm ${\mathrm{K}}^{2}$)] in temperature range 300--700 K. Consequently, calculated figure merit (ZT) value p-type can reach 0.8 700 K, ZT further improved \ensuremath{\sim}1.6 under small strain 3%, mostly owing strain-induced conductivity reduction. It also found abnormally lower than conditions, contradiction conventional Keyes theory heavier tend have conductivity. A comparative analysis phonon anharmonicity reveals weakening bond stiffness, high charge transfer between $\mathrm{Cu}$ $\mathrm{Q}$ atoms, narrowing lead strong acoustic scattering rates, arises from unique metavalent bonding ${\mathrm{Li}\mathrm{Cu}}_{3}{\mathrm{Ti}\mathrm{S}}_{4}$. Our findings provide valuable insights into strain-modulated anharmonic dynamics suggest promise an intermediate-temperature thermoelectricity.