Investigation of the physical properties of Li2XAl (X = Be, Mg and Ca) Heusler alloys by ab-initio method

In this thesis, the structural, electronic, elastic, thermodynamic, and vibrational properties of Li₂XAl (X = Be, Mg, Ca) full-Heusler alloys have been investigated in detail using first-principles calculations based on density functional theory (DFT). The computations were performed using the Quantum ESPRESSO software package. The structural properties were initially evaluated by calculating the equilibrium lattice parameters and analyzing the energy–volume relationship. Electronic band structures and density of states (DOS) analyses revealed that all alloys exhibit metallic behavior. The elastic constants were computed to assess the mechanical stability and to determine the ductility, stiffness, and mechanical robustness of the alloys. Thermodynamic properties, including Debye temperature, specific heat, and entropy, were calculated as functions of temperature using the quasi-harmonic approximation. Phonon dispersion curves demonstrated that while Li₂MgAl and Li₂CaAl are dynamically stable, Li₂BeAl exhibits imaginary frequencies, indicating dynamic instability in its lattice structure. These findings collectively suggest that Li₂XAl alloys possess favorable electronic and mechanical properties for potential use in applications such as energy storage systems, electrical conductivity components, and spintronic devices. In particular, Li₂MgAl and Li₂CaAl stand out as promising candidates for advanced material technologies. This study aims to enhance the understanding of Li-based Heusler alloys, offering valuable insights and theoretical benchmarks for future experimental and computational research in the field.