The metastable system Ga–Al and the atomic volume of twelvefold coordinated Ga

Abstract

While Ga and Al do not form extended solid solutions in equilibrium, metastable single phase Ga–Al alloys were prepared by rapid quenching from the melt to −1190°C (splat cooling), yielding a wide extension of the Al-rich solid solution α; at higher Ga contents, this phase is followed by a tetragonal phase α′. Another metastable phase rich in Ga was also observed. The mean atomic volumes of α and α′ permit a quadratic extrapolation to pure Ga, for which V(Ga) = 18.27 Å3 at −190°C. The solid solution formation and the structural instability of the cubic and tetragonal phases α and α′ are discussed in terms of pseudopotential theory; the analogy of α′ to a high-pressure phase of Ga has been noted.