First-principles calculations to investigate electronic structure and magnetic, mechanical and thermodynamic properties of d0 half-Heusler LiXN (X= Na, K, Rb) alloys

Abstract

Density functional theory (DFT) incorporating GGA-PBE approximation has been implemented to study structural, electronic, magnetic, mechanical and thermodynamic properties of the d0 Half-Heusler LiXN (X = Na, K, Rb) alloys. According to the spin-polarized calculations, all the LiXN alloys crystallize in the α-phase ferromagnetic ground state configuration. All three LiXN alloys show a total magnetic moment of 1.00 μB. The integer values of the total magnetic moments, along with the spin-polarized electronic band structures and the density of states plots indicate that the LiXN alloys are true half-metals in nature. The half-metallic nature of the LiXN alloys is further confirmed as the total magnetic moments are in complete agreement with the Slater-Pauling rule of 8. The origin of the half-metallic ferromagnetic behaviour has been investigated and it has been observed that the 2p states of N are the major contributors in case of all the three alloys. The alloys retain the characteristic half-metallicity over a wide range of lattice parameters, thus confirming their robustness and usability in a variety of spintronic applications. The mechanical properties of the LiXN alloys have been investigated and it has been observed that LiKN and LiRbN are found to be mechanically unstable, whereas LiNaN is chemically, energetically and mechanically stable. Various thermodynamic properties have been further computed and analysed using the quasi-harmonic approximation (QHA). Specific heat capacity at room temperature (300K), the Debye temperature, and the zero-point energy for the LiNaN alloy as well as the average velocity of sound inside the LiNaN alloy have been evaluated.