Enhanced Thermoelectric Performance and Low Thermal Conductivity in Cu₂GeTe₃ with Identified Localized Symmetry Breakdown

Abstract

Highly efficient and eco-friendly thermoelectric generators rely on low-cost and nontoxic semiconductors with high symmetry and ultralow lattice thermal conductivity κL. We report the rational synthesis of the novel cubic (Ag, Se)-doped Cu2GeTe3 semiconductors. A localized symmetry breakdown (LSB) was found in the composition of Cu1.9Ag0.1GeTe1.5Se1.5 (i.e., CAGTS15) with an ultralow κL of 0.37 W/mK at 723 K, the lowest value outperforming all Cu2GeCh3 (Ch = S, Se, and Te). A joint investigation of synchrotron X-ray techniques identifies the LSB embedded into the cubic CAGTS15 host matrix. This LSB is an Ångström-scale orthorhombic symmetry unit, characteristic of multiple bond lengths, large anisotropic atomic displacements, and distinct local chemical coordination of anions. Computational results highlight that such an unusual orthorhombic symmetry demonstrates low-frequency phonon modes, which become softer and more predominant with increasing temperatures. This unconventional LSB promotes bond complexity and phonon scattering, highly beneficial for extraordinarily low lattice thermal conductivity.

Phase-Controlled Synthesis and Phase-Change Properties of Colloidal Cu–Ge–Te Nanoparticles

“…Finally, our work offers a broader perspective, since ternary telluride colloids are of growing interest, e.g., for thermoelectric applications − as well as for optoelectronic devices, including photodetectors and transistors. , Due to the simplicity in depositing the colloids through spin coating or printing, ternary telluride nanoparticles may become a cost-effective alternative for those technologies. The surface of nanoparticles, although offering an additional design toolkit, needs to be better controlled in order to achieve a high packing density of thin films as well as to eliminate detrimental surface defects and to suppress oxidation processes …”

“…Finally, our work offers a broader perspective, since ternary telluride colloids are of growing interest, e.g., for thermoelectric applications 59 − 62 as well as for optoelectronic devices, including photodetectors and transistors. 63 , 64 Due to the simplicity in depositing the colloids through spin coating or printing, ternary telluride nanoparticles may become a cost-effective alternative for those technologies.…”