Computational investigation of X3BiN (X = Mg, Ca, Sr) anti-perovskites: Highly efficient thermo-electric materials in focus

Abstract

We present physical properties of X₃BiN (X = Mg, Ca, Sr) anti-perovskites by using the full-potential augmented plane wave (FP-APW) approach within density functional theory (DFT), which is implemented in Wien2k simulation code. As per band structure studies have been found that these materials shows direct band gap at the Γ point with the values of 1.670 eV for Mg₃BiN, 1.331 eV for Ca₃BiN and 0.971 eV for Sr₃BiN. From the optical properties calculations, the refractive index values for Mg₃BiN, Ca₃BiN, and Sr₃BiN are 3.26, 2.68, and 2.64 at zero photon energy and the dielectric constant real part, ε₁(0) values are 10.64 for Mg₃BiN, 7.21 for Ca₃BiN, and 7.01 for Sr₃BiN at zero frequency. To ensure the structural stability of these materials, Pugh's ratio is calculated and observed that Mg₃BiN and Ca₃BiN show the brittleness and Sr₃BiN shows the ductile nature. For the application point of view, we have analysed thermoelectric properties by using the BoltzTrap simulation code. The results show that p-type conduction is dominant and figure of merit (ZT) values are 0.98, 0.93, and 0.91 for Mg₃BiN, Ca₃BiN, and Sr₃BiN, respectively, at 600 K. These high ZT values suggest they are promising candidates for efficient next-generation thermoelectric devices.