Ab-Initio study of substitution at alkaline earth site on quaternary Heusler alloys LiXNiSb

In this study, we have studied the quaternary Heusler alloys with the formula LiXNiSb (X = Be, Mg, Ca, Sr, Ba) to investigate the effect of alkaline earth elements at the X site. We explored the structural, lattice dynamics, electronic, and magnetic properties by employing the density functional theory framework in FPLAPW formalism. All the studied alloys are nonmagnetic with no magnetic moment on the Ni atom. LiBeNiSb and LiBaNiSb are dynamically unstable and exhibit imaginary phonon frequencies. The lattice constant of the studied alloys systematically increases with the size of the alkaline earth element, whereas the bulk modulus decreases. Among the stable alloys, LiMgNiSb is metallic, whereas LiCaNiSb and LiSrNiSb are semiconducting with band gap values of 0.43 and 0.34 eV, respectively. The lattice specific heat and optical properties of the semiconducting alloys have also been computed. Our results demonstrate that the studied LiXNiSb alloys can be good candidates for photovoltaic applications.