Effect of pressure on dynamical stability, electronic and thermoelectric properties of equiatomic quaternary Heusler alloy LaCoTiGe

Abstract

The equiatomic quaternary Heusler alloys have tremendous applications in many optoelectronic, thermoelectric, and spintronic devices. The proper functioning of these alloys requires the study of lattice dynamics at different values of pressure. Therefore, the lattice dynamical stability of Lanthanum-based LaCoTiGe quaternary Heusler alloy in the face-centered cubic phase has been explored under the effect of pressure by employing density functional perturbation theory followed by density functional theory. The lattice dynamical stability of the face-centered cubic phase of LaCoTiGe is computed with a uniform increase in pressure equal to 2.0 GPa. The pressure-dependent modes are observed in the F-43m phase at the ‘Г’ point. The calculated electronic band structure by implementing density functional theory shows the half-metallic character with a band-gap of the order 0.43 eV for stable LaCoTiGe in the minority spin channel. To evaluate the thermoelectric properties of LaCoTiGe at 2.0 GPa the Boltzmann approximation and constant time relaxation are incorporated as implemented in the BoltzTraP code. The half-metallic behavior of LaCoTiGe results in the high value of the Seebeck coefficient with its maximum value of −50 μV/K at 800K. At relatively higher values of temperature i.e., of the order of 800K, the calculated electronic thermoelectric figure of merit ZT for this material is 0.12, which is much higher than that of other reported similar quaternary Heusler alloys. Based on the results obtained, the Lanthanum-based quaternary Heusler alloy LaCoTiGe could be a suitable candidate for spintronic devices to operate under harsh environmental conditions.