Electronic structure and phase stability of disordered hexagonal close-packed alloys

Abstract

We report a systematic study of the electronic structure and phase stability of some of the hexagonal close-packed random binary alloys such as ${\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Re}}_{x}$, ${\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{Zr}}_{x}$, ${\mathrm{Rh}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}$, and ${\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}$. First-principles calculations have been carried out using the augmented space recursion based on the tight-binding linear muffin-tin orbital basis. In particular, we have generalized our earlier applied augmented space recursive technique [T. Saha et al., J. Phys.: Condens. Matter 6, L245 (1995)] to the case of systems with more than one atom per unit cell, as is needed for hexagonal close-packed alloys. This involved development of a code that can handle any crystal structure with multiple sublattices. Ordering tendencies and phase stability are examined via effective pair interactions and their lattice Fourier transforms for TiAl alloy system, the low-temperature phase of which exhibits both face-centered cubic and hexagonal symmetry upon varying concentration. For each of the considered concentrations, the correct ordering tendency is obtained.