Strain-Induced Medium-Temperature Thermoelectric Performance of Cu4TiSe4: The Role of Four-Phonon Scattering

Motivated by the synthesized Cu4TiSe4 with ultralow room-temperature thermal conductivity [Angew. bining Boltzmann transport equations and first-principles calculations. The results show that the thermal conductivity of Cu4TiSe4 determined considering only three-phonon scattering is reduced by about 40% after including four-phonon scattering at room temperature, indicating the importance of four-phonon scattering in phonon transport. On the other hand, the coexistence of high dispersion and valley degeneracy at the top valence band in the electronic structure causes a high power factor. Consequently, the isotropic figure of merit (ZT) value of 1.5 at 500 K is captured in the p-type doped Cu4TiSe4. In addition, the value of ZT can be further enhanced to 2.2 by applying 2.25% triaxial tensile strain, which is ascribed to the remarkably enhanced four-phonon scattering processes induced by the tensile strain. Meanwhile, the significant suppression of thermal conductivity allows the optimal carrier concentration for the ZT peak to be reduced, which is of important practical significance for the experimental preparation of Cu4TiSe4-based TE devices. Our results pave a way for the design of adjustable medium-temperature TE devices.

Automated summary

The study reveals the importance of four-phonon scattering in phonon transport, as the thermal conductivity of Cu4TiSe4 is reduced by about 40% after considering four-phonon scattering at room temperature. Additionally, the high dispersion and valley degeneracy in the electronic structure result in a high power factor. By applying triaxial tensile strain, the ZT value of Cu4TiSe4 can be further enhanced to 2.2 through remarkably enhanced four-phonon scattering processes. The suppression of thermal conductivity allows for the reduction of the optimal carrier concentration for the ZT peak, which is significant for practical preparation of Cu4TiSe4-based TE devices.