First-principles study on the structural, electronic, elastic, optical and thermodynamic properties of double antiperovskites X6BiSbN2 (X = Mg, Ca, Sr)

Abstract

The perovskite materials have been widely used because of their excellent properties. Based on density functional theory, the structural, electronic, elastic, optical and thermodynamic properties of double antiperovskites X6BiSbN2 (X = Mg, Ca, Sr) are calculated. The results show that X6BiSbN2 (X = Mg, Ca, Sr) have stable crystal structures, and their band gaps are 1.172eV, 1.303eV and 0.965eV, respectively. Mg6BiSbN2 is an indirect bandgap semiconductor, which may be more suitable for use as a photocatalyst. Ca6BiSbN2 and Sr6BiSbN2 are direct bandgap semiconductors with high polarization and absorption coefficients, low reflectivity in the visible light region and good mechanical durability, which may be suitable candidates for the absorption layer of perovskite solar cells. In addition, X6BiSbN2 (X = Mg, Ca, Sr) have broad absorption range and high absorption coefficient in the ultraviolet region, which indicates that they may be potential photodetector materials. Sr6BiSbN2 has no entanglement between acoustic and optical branches in the phonon spectrum and a low Debye temperature, which helps to improve the thermoelectric coefficient, so it may be suitable for thermoelectric devices. The calculation results in this paper show that X6BiSbN2 (X = Mg, Ca, Sr) are expected to be used in the absorption layer of solar cells and photodetector field, and Sr6BiSbN2 may also be suitable for thermoelectric devices.