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

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](Alx,Mg1−x)[6](Al2−x,Mgx)O4, 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 27Al NMR experiments. Furthermore, both experiments at the Al and Mg K-edges are in good agreement with XANES calculation made using FDMNES code.