Balancing structural stability and thermoelectric performance of GeMnTe2 by manipulating the complexity of cation sublattice

Abstract

GeTe, known for its superior thermoelectric performance, undergoes a structural transition from low temperature rhombohedral to high temperature cubic phase at around 700 K. This phase transition is the primary obstacle to its practical applications. Alloying Mn at the Ge site can inhibit the phase transition and stabilize the cubic structure down to room temperature, while simultaneously degrading thermoelectric properties. In this work, room-temperature cubic GeMnTe₂, is chosen as the matrix, and then the complexity of cation sublattice is manipulated to achieve the best balance between structural stability and thermoelectric performance. Alloying equal amount of Ag and Sb atoms at the Ge site induces lattice softening, local chemical fluctuation, and lattice anharmonicity, leading to a lower sound velocity and significantly reducing the lattice thermal conductivity. Further doping of Sb synergistically modulates the thermoelectric performance by optimizing the electrical properties and reducing the electronic thermal conductivity. Consequently, a dimensionless thermoelectric figure of merit zT of 1.35 at 773 K and an average zT of 0.8 across the temperature range of 300 - 773 K are achieved for the Ge_0.575Ag_0.25Sb_0.375Mn_0.8Te₂, demonstrating its promising potential as a high-performance thermoelectric material.