Thermoelectric transport properties of metal phosphide XLiP (X = Sr,Ba)

Metal phosphides are stable and have excellent electrical characteristics, their high thermal conductivity has prevented them from being used as thermoelectric materials. In this paper, the thermoelectric transport properties of XLiP (X = Sr Ba) are investigated on the basis of first-principles calculations, Boltzmann transport equation and self-consistent phonon theory. In addition, we also consider the effect of quartic anharmonicity on the thermal transport properties and lattice dynamics of SrLiP and BaLiP. The strong anharmonicity of the two compounds make the lattice thermal conductivity decrease rapidly with the increase of temperature. At 300 K, the lattice thermal conductivity of SrLiP and BaLiP on thea(b)-axis is only 2.98 and 2.93 Wm^-1K^-1, respectively. Due to its excellent electron transport properties, it has greater conductivity in thea(b) axis. Finally, due to the energy pocket and anisotropy at the bottom of the conduction band, the n-type maximum ZT values of trapped SrLiP and BaLiP on thea(b) axis are 0.87 and 0.94 at 900 K, respectively. The high thermoelectric performance of both compounds encourages further studies on the thermoelectric properties of metal phosphides.