title: 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-Al(2)O(3), spinel and tetragonal hausmannite, and explored the relative stability of γ-Al(2)O(3) with respect to α-Al(2)O(3) 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-Al(2)O(3), while Cr stabilizes α-Al(2)O(3). As Si is added, a bond length increase in α-Al(2)O(3) is observed, while strong and short Si-O bonds are formed in γ-Al(2)O(3), consequently stabilizing this phase. On the other hand, Cr additions induce a smaller bond length increase in α-Al(2)O(3) than in γ-Al(2)O(3), therefore stabilizing the α-phase. The bulk moduli of γ-Al(2)O(3) with these additives show no significant changes. The phase stability and elastic property data discussed here underline the application potential of Si alloyed γ-Al(2)O(3) for applications at elevated temperatures. Furthermore it is evident that the tetragonal hausmannite structure is a suitable description for γ-Al(2)O(3).
authors.affiliation: Materials Chemistry, RWTH Aachen University, Aachen, Germany. jiang@mch.rwth-aachen.de
authors.forename: Kaiyun
authors.initials: K
authors.lastname: Jiang
authors.forename: Denis
authors.initials: D
authors.lastname: Music
authors.forename: Kostas
authors.initials: K
authors.lastname: Sarakinos
authors.forename: Jochen M
authors.initials: JM
authors.lastname: Schneider