The first-principles examination of the structural, electronic, elastic, phonon, and thermoelectric properties of Cubic LiXN (X = Be, Mg, Zn)

In this study, the structural, electronic, lattice dynamics, mechanical and thermoelectric properties of LiXN (X = Be, Mg, and Zn) were investigated using first principle calculations as implemented in the quantum espresso (QE) code within the framework of density function theory (DFT). The band calculations show an indirect band gap for LiBeN, and direct band gap nature for LiMgN and LiZnN respectively. The band gaps obtained for LiXN (X = Be, Mg and Zn) are 2.81 eV, 2.32 eV and 0.54 eV in excellent agreement with previous works. The lattice dynamics stability for the compounds were investigated using DFPT (Density Perturbation Theory) method and found to be stable with non-existence of negative frequency in their phonon dispersion spectrum. Elastic and mechanical stability of the compounds were examined as the elastic constants calculated satisfied the Born-Huang stability criteria. All the investigated compounds are confirmed to be brittle in nature as justified by Poisson ratio, Pugh ratio and Cauchy pressure reported. The inter-atomic strength, sound velocity and Debye temperature of the compounds increase with decrease in X atomic mass of the compounds LiXN (X = Be, Mg, Zn). The lattice thermal conductivity (kp) of LiXN at room temperature were deduced and found to be 11.148 W/mK(LiBeN), 19.470(LiMgN) and 16.713(LiZnN). At 1200 K, significant figure of merit were obtained as 0.86(LiBeN), 0.85(LiZnN) and 0.83(LiZnN) for the p-type region. This investigation demonstrates that LiXN (X = Be, Mg, Zn) compounds are potentially favourable for high temperature power generation.