The crystal and melt structure of spinel and alumina at high temperature: An in-situ XANES study at the Al and Mg K-edge

Abstract We present structural information obtained on spinel and alumina at high temperature (298–2400 K) using in-situ XANES at the Mg and Al K-edges. For spinel, [4] (Al x ,Mg 1− x ) [6] (Al 2− x ,Mg x )O 4, with increasing temperature, a substitution of Mg by Al and Al by Mg in their respective sites is observed. This substitution corresponds to an inversion of the Mg and Al sites. There is a significant change in the Al K-edge spectra between crystal and liquid, which can be attributed to a change of the [6] Al normally observed in corundum at room temperature, to a mixture of [6] Al– [4] Al in the liquid state. This conclusion is in good agreement with previous 27 Al NMR experiments. Furthermore, both experiments at the Al and Mg K-edges are in good agreement with XANES calculation made using FDMNES code.