Ab initiocalculations on the effects of additives on alumina phase stability

The effects of substitutional additives on the properties and phase stability of θ- and α-alumina (Al₂O₃), are investigated by density functional theory total energy calculations. The dopants explored are 5 at. % of Cr, Mo, Co, and As substituting for Al, respectively, N and S substituting for O, in the θ and α lattices. Overall, the results show that it is possible to shift, and even reverse, the relative stability between α- and θ-alumina by substitutional additives. The alumina bulk moduli are, in general, only slightly affected by the dopants but density of states profiles reveal additional peaks in the alumina band gaps. We also show that phase separations into pure oxides are energetically favored over doped alumina formation, and we present results on a number of previously unstudied binary oxides.