Homogenizing Liquid-like Cu Sublattice for High-performance Cu2Te0.5Se0.5 Thermoelectric Materials

Abstract

Liquid-like thermoelectric materials continuously draw significant attention because of their extraordinary performance. However, liquid-like Cu atoms usually aggregate into clusters, resulting in charge carrier concentration far above the optimized value. Herein, we demonstrate that the dynamic Cu atoms can be homogenized throughout the matrix by a phase-dependent diffusion process. We directly visulized that the typical equilibrium process periodically aggregates Cu atoms into clusters along the grain boundaries, leaving abundant vacancies within the dynamic cation sublattice and thereby causing carrier concentrations that are much higher than the optimal value. We developed a solid-state non-equilibrium quenching process to freeze the homogeneous Cu sublattice in the symmetry cubic phase to ambient environment and removed the unfavorable Cu segregation. This substantially decreases the hole concentration from 1.2 × 1022 cm−3 for the equilibrium sample to 0.8 × 1022 cm-3 for the quenched sample, approaching the calculated optimal value. Notably, the highly uniform Cu sublattice reduces the lattice thermal conductivity to predicted minima of 0.3 W·m−1·K−1 from 300 to 1000 K. The reduced hole concentration and lattice thermal conductivity collectively give rise to a high ZT value of 1.5 at 1000 K, lying in the ballpark of all previously reported stoichiometric copper chalcogenides.