Analysing the structural, mechanical and thermal stability in lithium-based half-Heusler compounds LiAlSi and LiAlGe: a first-principles study

A first-principles study of half-Heusler (HH) compounds LiAlSi and LiAlGe have been performed using Quantum Espresso code with generalized gradient approximation based on density functional theory. The calculated lattice parameters were found to be in accordance with the available experimental results. The band structure and density of states describe the electronic properties and confirm the semiconducting behaviour of these compounds. Thermoelectric properties like electrical conductivity, electronic thermal conductivity, Seebeck coefficient and power factor are investigated in order to ascertain temperature-dependent response of these materials. The first-time calculated elastic and vibrational properties show the stability of LiAlSi and LiAlGe HH compounds in a cubic MgAgAs-type structure. The thermodynamic behaviour of these compounds is analysed using Quasi Harmonic Approximation in order to determine the thermodynamic properties and their variation with temperature.