Promising thermoelectric transport properties of new <i>γ</i> -SnSe single crystals with full <i>ab initio</i> calculations

Abstract

α- and β-SnSe have emerged as promising thermoelectric materials owing to their excellent performance. Recently, a new phase, γ-SnSe, has been identified, offering new opportunities for thermoelectric research. Using first-principles molecular dynamics simulations combined with the Wigner thermal transport model, we demonstrate that γ-SnSe is structurally similar to α-SnSe with the Pnma space group, while exhibiting thermoelectric characteristics reminiscent of β-SnSe. These include strong lattice anharmonicity, particle-like-dominated thermal transport, and remarkably low and weakly anisotropic lattice thermal conductivity. The lattice thermal conductivity (κL) shows a nonlinear temperature dependence, κL ∝ T−0.72, with optical phonons playing a dominant role in heat transport. Electronic structure analysis reveals distinct thermoelectric behaviors depending on the doping type. As a p-type material, γ-SnSe exhibits strong carrier scattering and a large Seebeck coefficient, which are beneficial for thermoelectric performance. In contrast, n-type γ-SnSe shows weak carrier scattering, high carrier mobility, and superior electrical conductivity, making it particularly suitable for high-performance thermoelectric devices. The thermoelectric figure of merit ZT reaches 0.5 for n-type γ-SnSe at 700 K with a carrier concentration of ∼1019 cm−3, while p-type γ-SnSe achieves a maximum ZT exceeding 0.3 at room temperature at a carrier concentration of ∼1020 cm−3. This work not only underscores the potential of γ-SnSe but also paves the way for further exploration of its properties and applications, driving innovations in thermoelectric materials and energy conversion technologies.