Ab initio study of effects of substitutional additives on the phase stability of γ -alumina

Abstract

Using ab initio calculations, we have evaluated two structural descriptions of γ -Al2O3, spinel and tetragonal hausmannite, and explored the relative stability of γ -Al2O3 with respect to α-Al2O3 with 2.5 at.% of Si, Cr, Ti, Sc, and Y additives to identify alloying element induced electronic structure changes that impede the γ to α transition. The total energy calculations indicate that Si stabilizes γ -Al2O3, while Cr stabilizes α-Al2O3. As Si is added, a bond length increase in α-Al2O3 is observed, while strong and short Si-O bonds are formed in γ -Al2O3, consequently stabilizing this phase. On the other hand, Cr additions induce a smaller bond length increase in α-Al2O3 than in γ -Al2O3, therefore stabilizing the α-phase. The bulk moduli of γ -Al2O3 with these additives show no significant changes. The phase stability and elastic property data discussed here underline the application potential of Si alloyed γ -Al2O3 for applications at elevated temperatures. Furthermore it is evident that the tetragonal hausmannite structure is a suitable description for γ -Al2O3. © 2010 IOP Publishing Ltd.