Mediated resonance effect of the vanadium 3dstates on phase stability in theAl8V5γ-brass studied by first-principles FLAPW and LMTO-ASA electronic structure calculations

Abstract

The mechanism for the stability of the ${\mathrm{Al}}_{8}{\mathrm{V}}_{5}\phantom{\rule{0.3em}{0ex}}\ensuremath{\gamma}$-brass containing 52 atoms in its cubic unit cell has been investigated by means of first-principles full-potential linearized augmented plane wave (FLAPW) and linearized muffin-tin orbital-atomic sphere approximation (LMTO-ASA) electronic structure calculations. The LMTO-ASA identified a deep valley at $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ above the Fermi level in its density of states (DOS) as arising from orbital hybridizations between V $3d$ and Al $3p$ states. On the other hand, the FLAPW revealed the V $3d$ states mediated resonance of electrons with different sets of lattice planes. The resonance involved is found to be substantial not only at ${\ensuremath{\mid}\mathbf{G}\ensuremath{\mid}}^{2}=18$ or {330} and {411} zones but also at those in the range $14\ensuremath{\leqslant}{\ensuremath{\mid}\mathbf{G}\ensuremath{\mid}}^{2}\ensuremath{\leqslant}30$. A comparison with the electronic structure of the CsCl-type AlV compound proved that the V $3d$ states mediated resonance occurs only in ${\mathrm{Al}}_{8}{\mathrm{V}}_{5}$ but not in AlV compound. The V $3d$ states mediated resonance is proved to result in a significant suppression of the $sp$-partial DOS over the energy range from the Fermi level up to $+2.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. A gain in the electronic energy has been attributed to the formation of highly condensed bonding states below the Fermi level, again caused by the V $3d$ states mediated resonance. It is also proposed that the ${\mathrm{Al}}_{8}{\mathrm{V}}_{5}$ is stabilized at $e∕a=1.94$ rather than $21∕13$ as is expected from the Hume-Rothery electron concentration rule.