Ab-initio investigation of structural, mechanical, thermodynamic, electronic, magnetic and thermoelectric properties of half-metallic d0 half-Heusler alloys LiXSi (X=Ca, Sr)

Structural, mechanical, thermodynamic, electronic, and magnetic properties of LiXSi (X = Ca, Sr)d(0) half-Heusler alloys have been evaluated by implementing the GGA-PBE approximation in the Density Functional Theory calculations. The Boltzmann transport theory has been implemented for examining the thermoelectric properties of the alloys. The spin-polarized calculations show that LiCaSi and LiSrSi crystallize in the ferromagnetic alpha-phase equilibrium states. Spin-resolved band structures depict complete spin polarization obtained at the Fermi level and confirm the true half-metallic nature of the alloys. The calculated total magnetic moment is 0.99 mu B for LiCaSi and 1.00 mu B for LiSrSi, which very closely follow the Slater-Pauling rule. The observed ferromagnetic characteristics arise mostly from the spin-polarization of the 2p states in Si for both alloys. The LiXSi (X = Ca, Sr) alloys are found to be mechanically stable according to the Born stability criteria for cubic structured systems. Both the alloys are predicted to be ductile in nature. Important thermodynamic properties such as Debye temperature and C-v have been calculated by implementing the quasi-harmonic approximation. The calculations for the transport properties show that the alloys are p-type materials with high Seebeck coefficients and electrical conductivities. The dimensionless thermoelectric figure of merit obtained for both the alloys at 300K is close to unity, which confirms the high thermoelectric efficiency of the alloys.