RECENT ATTEMPTS TO DETECT MAGNESIUM IN A HEAVILY-DOPED SAPPHIRE BICRYSTAL BY SPATIALLY-RESOLVED ELECTRON-ENERGY-LOSS SPECTROSCOPY

Needle-shaped spinel precipitates in a matrix of heavily MgO-doped alpha-Al2O3 bicrystal containing a near Sigma = 11 tilt boundary were examined by spatially resolved electron energy-loss spectroscopy. The Mg content was consistent with the precipitate being an alumina-rich spinel of composition MgO.(Al2O3)(2). The Al and Mg K and L(2,3) absorption edge structures were recorded. No evidence could be found for preferential Mg segregation to the tilt boundary. Using the precipitates as a calibration standard, a limit of detection equivalent to about 0.01 monolayer is deduced. Comparison of the Al-L(2,3) edge recorded at the Sigma = 11 boundary to that of the same boundary in undoped material suggests that the local structure is independent of Mg doping. The lack of Mg segregation to the Sigma = 11 boundary is perhaps attributable to the low energy and close packing of this interface.