Structural stability of intermetallic phases in the Ga-Ti system

The total energies of intermetallic compounds in the Ga-Ti system are calculated employing electronic density functional theory (DFT) using pseudopotentials constructed by the projector augmented waves (PAW) method in the generalized gradient (GGA) approximation for the exchange and correlation energy. The calculations are performed for the experimentally observed compounds at their ideal stoichiometry as well as for structures which are stable in systems of early transition metals or rare earth elements with p elements of columns IIIB, IVB, and VB. The calculated formation enthalpy of the hexagonal B8₂-GaTi₂ compound is in excellent agreement with the value obtained by direct reaction calorimetry. The composition dependence of the enthalpies of formation is slightly asymmetric, the values of the enthalpies of formation being slightly more negative in the Ga-rich side. For the stable intermetallic compounds, the calculated zero-temperature lattice parameters agree well with those obtained experimentally at ambient temperature. Furthermore, for stable phases with unit-cell-internal degree(s) of freedom, the results of ab initio calculations show good agreement when compared with data obtained by structural analysis of X-ray diffraction.