Structural, elastic and thermodynamic characteristics of trigonal-type Zintl phases CaZn2X2 (X = P or As) under hydrostatic pressure: prospects for advanced materials in high pressure and thermoelectric devices

Abstract

We used density functional theory calculations to explore the structural, elastic, and thermodynamic properties of the Zintl phases CaZn₂P₂ and CaZn₂As₂ under hydrostatic pressure. The excellent agreement between predicted structural features and experimental data validates our method. The [001] crystal orientation demonstrates greater compressibility in both compounds compared to the [100] direction. The anticipated monocrystalline elastic constants for both compounds meet mechanical stability criteria up to 18 GPa. We also examined the polycrystalline mechanical properties. Pugh's ratio, Poisson's ratio, and Cauchy pressure suggest the materials are brittle. The quasiharmonic Debye approximation was utilized to assess the dependence of key macroscopic physical parameters, including lattice constants, bulk modulus, volumetric thermal expansion coefficient, Debye temperature, and both isobaric and isochoric heat capacities, on temperature at constant pressures of 0, 4, 8, 12, and 16 GPa. The agreement between elastic constant data and the Debye quasiharmonic results confirms the reliability of our findings.