Pressure-induced Structural Phase Transition and Thermoelectric Properties of Bulk Mg₃Bi₂

Abstract

The thermoelectric materials Mg₃Bi₂ and related compounds exhibit a high figure of merit (zT) combined with attractive properties for commercialization, such as low cost, elemental abundance, non-toxicity, and good processability. These advantages make them highly promising candidates for developing high-performance flexible thermoelectric devices. While previous research has primarily focused on improving thermoelectric properties through chemical doping, the effects of pressure on the crystal structure and corresponding thermoelectric properties have not been fully investigated. In this study, we combined first-principles calculations, crystal structure prediction, and X-ray Absorption Near-Edge Structure (XANES) measurements to probe the behaviour of this material under extreme conditions. Our investigation revealed a low-lying P2₁/m structure at 5 GPa, competitive in energy with the known C2/m phase, and two novel high-pressure phases: a Pnnm structure at 30 GPa and a P2₁/c structure above 80 GPa. To understand the pressure-induced structural evolution, we systematically evaluated the energy stability, dynamical stability, and thermoelectric properties of each phase.