Pressure-induced enhancement of thermoelectric performance of CoP3 by the structural phase transition

Abstract

Using particle swarm optimization and first-principles calculations, we discovered a novel high-pressure orthorhombic structure of CoP3 with the space group of Pnma, which is stable above 24.6 GPa. According to our calculations based on Boltzmann transport theory, the Seebeck coefficient of the Pnma phase is 6.5 times as great as that of the ambient Im-3 phase at a hole concentration of 1 × 1020 cm−3. The calculation further indicates the Pnma-CoP3 exhibits a maximal figure of merit ZT of 0.56 and 0.74 for p- and n-type at 800 K, respectively. Especially for p-type, the Pnma-CoP3 is quintuple better than the ambient phase which has a ZT of 0.1. The higher ZT value can be attributed to the deeper projected density of states generated by hybridization between P p states and Co d states near the Fermi level. Therefore, the high pressure mainly improves the ZT value by modulating electron properties. Current results demonstrate that the Pnma-CoP3 material is a competitive candidate for thermoelectric applications, especially under high temperature condition (800 K). This work provides a convenient alternative route to increase the thermoelectric performance of skutterudites.