Ab Initio Prediction of the Structural, Elastic and Thermodynamic Properties Under Hydrostatic Pressure of the Ternary Tetragonal Phosphides XRh₂P₂ (X = Ca, Ba) for Superconducting Application

This study uses density functional theory calculations to study the impact of pressure on the structural, elastic, and thermodynamic properties of CaRh₂P₂ and BaRh₂P₂ compounds. The equilibrium structural parameters closely match the experimental values. CaRh₂P₂ shows a greater reduction in lattice parameter “a” under pressure, while BaRh₂P₂ shows the opposite trend. The single-crystal elastic constants calculated for both compounds meet the criteria for mechanical stability under varying pressures up to 18 GPa. The study extends to polycrystalline elastic properties, including bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and related properties, under pressures up to 18 GPa. The Pugh ratio, Cauchy pressure, and Poisson’s ratio indicate the ductile behavior of the title compounds. BaRh₂P₂ exhibits superconducting characteristics, unlike CaRh₂P₂, confirmed by interlayer PP bond length calculations. Debye’s quasi-harmonic model explores the temperature dependencies of various properties, with results that align well with elastic constant data, thus validating the results.