Spectrum-Line Profile Analysis of a Magnesium Aluminate Spinel Sapphire Interface

Spatially resolved chemical composition and spectroscopic line profiles have been gath- ered from the space charge region across a spinel/sapphire interface using a dedicated scanning trans- mission electron microscope. The electron energy-loss spectra reveal an excess of Mg (relative to stoichiometric spinel) along with Cr segregated to the interfacial zone. A quantitative least squares decomposition of a spectrum-line profile of the Al L2, 3 absorption edge fine structures into two stan- dard components clearly highlights the transition from sapphire into spinel; further analysis indicates that the degree of site inversion, which is the fractional occupancy of tetrahedral sites by trivalent Al, increases within 5 nm of the boundary. The overall charge neutrality at the interface is maintained by the increased concentration of negative charge, probably interstitial O anions which are also present in excess quantity relative to stoichiometric spinel and sapphire.