Phase transformation mechanism between γ- and θ-alumina

TL;DRAbstract

\ensuremath{\gamma}-alumina transforms to \ensuremath{\theta}-alumina and finally to \ensuremath{\alpha}-alumina in the sequence of thermal dehydration of boehmite. We report a detailed theoretical investigation of the \ensuremath{\gamma}- to \ensuremath{\theta}-alumina transformation based on first-principles density-functional calculations. Although the unit cells of cubic \ensuremath{\gamma}-alumina and monoclinic \ensuremath{\theta}-alumina look quite different, we have identified cells for both the polytypes (with the composition ${\mathrm{Al}}_{16}{\mathrm{O}}_{24})$ that look very similar and can be continuously transformed one to another. The transformation may be described by a set of aluminum atom migrations between different interstitials while the oxygen atoms remain fixed. Total-energy calculations along the paths of the atomic migrations have been used to map out possible transformation pathways. The calculated conversion rate accurately predicts the experimentally measur

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