Ab initio prediction of the structural, electronic, elastic and thermodynamic properties of the tetragonal ternary intermetallics XCu 2 Si 2 (X=Ca, Sr)

Structural parameters, electronic structure, elastic constants and thermodynamic properties of the tetragonal ternary intermetallics CaCu 2 Si 2 and SrCu 2 Si 2 are investigated theoretically for the first time using the plane-wave ultra-soft pseudopotential method based on the density functional theory. The calculated equilibrium structural parameters agree well with the existing experimental data. Pressure dependence of the structural parameters is also explored. Analysis of the band structure, total and site-projected l-decomposed densities of states and valence charge distributions reveals the conducting character of both considered materials with a mixture of ionic-covalent chemical bonding character. Pressure dependences of the single-crystal elastic constants C ij for CaCu 2 Si 2 and SrCu 2 Si 2 are explored. The elastic wave velocities propagating along the principal crystallographic directions are numerically estimated. The elastic anisotropy is estimated and further illustrated by 3D-direction-dependent of the Young’s modulus. A set of some macroscopic elastic moduli, including the bulk, Young’s and shear moduli, Poisson’s coefficient, average elastic wave velocities and Debye temperature, were calculated for polycrystalline CaCu 2 Si 2 and SrCu 2 Si 2 from the C ij via the Voigt-Reuss-Hill approximations. Through the quasiharmonic Debye model, which takes into account the phonon effects, the temperature and pressure dependencies of the bulk modulus, unit cell volume, volume thermal expansion coefficient, Debye temperature and volume constant and pressure constant heat capacities of CaCu 2 Si 2 and SrCu 2 Si 2 are explored systematically in the ranges of 0–40 GPa and 0–1400 K. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2014