Lattice Distortions and Multiple Valence Band Convergence Contributing to High Thermoelectric Performance in MnTe

Abstract

Here, a new route is proposed for the minimization of lattice thermal conductivity in MnTe through considerable increasing phonon scattering by introducing dense lattice distortions. Dense lattice distortions can be induced by Cu and Ag dopants possessing large differences in atom radius with host elements, which causes strong phonon scattering and results in extremely low lattice thermal conductivity. Density functional theory (DFT) calculations reveal that Cu and Ag codoping enables multiple valence band convergence and produces a high density of state values in the electronic structure of MnTe, contributing to the large Seebeck coefficient. Cu and Ag codoping not only optimizes the Seebeck coefficient but also substantially increases the carrier concentration and electrical conductivity, resulting in the significant enhancement of power factor. The maximum power factor reaches 11.36 µW cm^-1 K^-2 in Mn_0.98 Cu_0.04 Ag_0.04 Te. Consequently, an outstanding ZT of 1.3 is achieved for Mn_0.98 Cu_0.04 Ag_0.04 Te by these synergistic effects. This study provides guidelines for developing high-performance thermoelectric materials through the rational design of effective dopants.

Keywords: Chalcogenide; Lattice Distortions; Thermoelectric materials; band convergence.