Exploring the Thermodynamic, Elastic, and Optical properties of LaRh2X2 (X = Al, Ga, In) low Tc Superconductors through First-Principles Calculations

Abstract

LaRh2X2 (X = Al, Ga, In) compounds crystallize in a tetragonal layered ThCr2Si2-type structure and belong to a family of low critical temperature superconductors. Using first-principles density functional theory calculations implemented in the CASTEP code, we systematically investigated their structural, mechanical, elastic, electronic, vibrational, thermophysical, and optical properties for the first time. The optimized structural parameters show good agreement with available experimental data. The Born stability criteria and negative formation energies confirm the mechanical and thermodynamic stability of these materials. Poisson and Pugh ratios indicate a ductile nature, while low Debye and melting temperatures together with low Vickers hardness suggest that the compounds are relatively soft. The electronic band structures and density of states reveal metallic behavior. Charge density distribution and Mulliken population analysis indicate mixed covalent, ionic, and metallic bonding. The calculated Fermi surfaces contain both hole-like and electron-like sheets, suggesting possible multiband characteristics. Phonon dispersion analysis confirms the dynamical stability of LaRh2Al2 and LaRh2Ga2, while LaRh2In2 shows dynamical instability associated with a possible structural phase transition. Optical property analysis indicates that these superconductors may be promising candidates for high-density optical data storage applications. The estimated electron-phonon coupling constant of about 0.56 indicates that LaRh2X2 compounds are weakly coupled low critical temperature superconductors.