First-Principles Study of Mechanical and Thermodynamic Properties of Binary and Ternary CoX (X = W and Mo) Intermetallic Compounds

In this study, the structural, elastic, and thermodynamic properties of DO19 and L1(2) structured Co3X (X = W, Mo or both W and Mo) and mu structured Co7X6 were investigated using the density functional theory implemented in the pseudo-potential plane wave. The obtained lattice constants were observed to be in good agreement with the available experimental data. With respect to the calculated mechanical properties and Poisson's ratio, the DO19-Co3X, L1(2)-Co3X, and mu-Co7X6 compounds were noted to be mechanically stable and possessed an optimal ductile behavior; however, L1(2)-Co3X exhibited higher strength and brittleness than DO19-Co3X. Moreover, the quasi-harmonic Debye-Gruneisen approach was confirmed to be valid in describing the temperature-dependent thermodynamic properties of the Co3X and Co7X6 compounds, including heat capacity, vibrational entropy, and Gibbs free energy. Based on the calculated Gibbs free energy of DO19-Co3X and L1(2)-Co7X6, the phase transformation temperatures for DO19-Co3X to L1(2)-Co7X6 were determined and obtained values were noted to match well with the experiment results.

Automated summary

This study investigated the structural, elastic, and thermodynamic properties of Co3X and Co7X6 compounds using density functional theory, revealing different mechanical stability and ductile behavior among compounds with different structures. The quasi-harmonic Debye-Gruneisen approach was found to accurately describe the temperature-dependent thermodynamic properties of the compounds.