MgCu2-type laves phases CaPt2, SrPd2 and SrPt2: A DFT based ab-initio investigation

Abstract

First principle calculations have been performed to study the structural, elastic, electronic, Vickers hardness, optical and thermodynamic properties of Laves phase compounds CaPt2, SrPd2 and SrPt2for the first time. The optimized structural parameters such as lattice constants, unit cell volume and bulk modulus are well agreed with experimental values. The calculated elastic constants of all phases obey the well-known Born stability criteria and indicate the mechanical stability of CaPt2, SrPd2 and SrPt2. The calculated values of Cauchy pressure, Pugh's ratio and Poisson's ratio indicate the ductile nature of all three studied phases. The positive values of Cauchy pressure reveal the metallic nature of CaPt2, SrPd2 and SrPt2. The band structures show no band gap at the Fermi level which indicates the metallic nature of all these phases. The calculated total density of states (TDOS) of CaPt2, SrPd2 and SrPt2 are 3.90, 2.81 and 4.06 states per unit cell per eV respectively. These non-zero values of density of states at the Fermi level further indicate the metallic nature and the sequence of increasing metallic behavior is SrPd2< CaPt2< SrPt2. The detailed investigation of Mulliken atomic population indicates the covalent nature of PtPt and PdPd bonds because of the positive bond populations. The calculated values of Vickers hardness reveal that these phases are relatively soft materials. The various optical functions such as dielectric function, refractive index, conductivity, refractivity, absorption coefficient and loss function have also been investigated for the first time. The reflectivity spectra indicate that all studied phases are suitable to use as a good coating material in UV energy range. The calculated values of Debye temperatures are 271 K, 123 K and 230 K for CaPt2, SrPd2 and SrPt2 respectively. The melting temperature, Dulong-petit limit and thermal conductivity have also been calculated.