Stability, thermal and mechanical properties of PtxAly compounds

The stability, thermal and mechanical properties of Pt. _xAl. _y intermetallic compounds are investigated by density functional theory (DFT). The cohesive energy and formation enthalpy of Pt. _xAl. _y phases show that they are thermodynamically stable structures and these are in good agreement with the experiments. The heat capacity of the compounds is calculated by quasi-harmonic approximation (QHA) method. The thermal expansion coefficient as a function of temperature for each compound is also discussed. The elastic properties such as bulk modulus, Young's modulus are evaluated by Viogt-Reuss-Hill approximation. The anisotropic properties of sound velocities for the Pt. _xAl. _y compounds are explored. The calculated Poisson's ratio varies from 0.26 to 0.39 for Pt. _xAl. _y phases and the bonds in the compounds are mainly metallic and covalent types.