Structural, electronic and vibrational properties of ordered intermetallic alloys CoZ (Z = Al, Be, Sc and Zr) from first-principles total-energy calculations

Abstract

Self-consistent band calculations on four intermetallic compounds of the CsCl structure are presented. The calculations were performed employing the self-consistent ultrasoft pseudopotential method based on the density functional theory, within the local density approximation and the generalized gradient approximation. The calculations predicted that the equilibrium lattice constants are in excellent agreement with the experiment for CoAl and are 1% smaller than experimental values for CoBe, CoSc and CoZr, respectively. In the present study, ordered CoAl do not show any magnetic moment, whereas the other three compounds have moderate magnetic moments of about 0.2 and 0.7 Bohr magnetons (μ_B ) per atom. The elastic constants are calculated using two approaches, the energy-strain method and the use of phonon dispersion curves. The values obtained from the two methods are in reasonable agreement for the studied intermetallic compounds CoZ (Z = Al, Be, Sc and Zr). The brittleness and ductility properties of CoZ (Z = Al, Be, Sc and Zr) are determined by Poisson’s ratio σ criterion and Pugh’s criterion. The calculated elastic constants satisfy the mechanical stability criterion and the ductility of CoZr and CoSc is predicted by Pugh’s criterion. The band structure and density of states, and phonon dispersion curves have been obtained and compared with the available experimental results as well as with existing theoretical calculations. We studied and discussed the position of Fermi level for the selected four intermetallic compounds.

Keywords:

• density-functional theory
• elastic constants
• ductility
• intermetallic alloys
• vibrational properties

Acknowledgement

This work was supported by the Gazi University Research Project Unit under Project No 05/2012-07, 05/2012-08, 05/2012-62, 05/2012-63 and Hacettepe University Research Project Unit under Project No 0701602005.