First-Principles Calculations of the Thermal Expansion Path of the Co7Mo6 μ-Phase

The thermal expansion path is calculated for the Co7Mo6 compound, with the structure of mu-phase, from T= 0 to 1500 K which is below its decomposition temperature. The method allowing to reduce the problem to a 1D case and considering the energy as depending on only one variable, the volume, is used. The thermodynamic properties of Co7Mo6 are studied using first-principles-based quasiharmonic Debye-Gruneisen approximation and by comparing the free energies calculated along different paths of thermal expansion. The electronic, vibrational, and magnetic energy contributions to the free energy are accounted. The thermal expansion of Co7Mo6 is not isotropic. The influence of electronic, magnetic, and vibrational entropy on the stability of Co7Mo6 is analyzed. The isobaric heat capacity, thermal expansion, elastic constants, bulk modulus, sound wave velocities, and Debye and Curie temperatures are reported. The calculated results are analyzed and are in agreement with the available experimental and theoretical data.