First-principles investigation of structural stability, mechanical and thermal properties of TiRM3 (RM = Cr, Mo, and W) compounds

This work presents first-principles calculations of the physical properties of cubic (Fm $\bar{3}$ m) and orthorhombic (Immm) TiRM₃ (RM = Cr, Mo and W) compounds, with a particular focus on their mechanical and thermal properties. The structural stability is assessed by the enthalpy of formation ΔH, elastic constants, and phonon spectrum. The TiCr₃, with positive ΔH greater than 0.01 eV/atom, may be metastable, while the TiMo₃ and TiW₃ compounds, with negative ΔH less than −0.05 eV/atom, are ground-state stable. From TiCr₃, TiMo₃ to TiW₃, the elastic modulus as well as the isothermal bulk modulus at finite temperature is enhanced, while the volumetric thermal expansion coefficient, elastic/thermal-expansion anisotropy are weakened. Furthermore, a comparative analysis with pure bcc-RM is conducted. All TiRM₃ compounds exhibit excellent ductility, which is superior to that of their bcc-RM counterparts, however, the elastic modulus is inferior. The volumetric thermal expansion coefficients of the TiRM₃ compounds are higher than that of the pure bcc-RM metal. The selection and evaluation of materials for use in nuclear fusion should benefit from these theoretical insights.