ChemInform Abstract: DEFECT STRUCTURE OF α‐ALUMINA DOPED WITH MAGNESIUM

Abstract

Die elektrische Leitfähigkeit sowie die Ionen‐ und Elektronenüberführungszahlen (EMK‐Messungen) fürAl2O3: Mg‐Einkristalle werden bei hohen Temperaturen als Funktion der Orientierung , des Og‐Partialdruckes (l‐ 1 04 atm) und der Temperatur (T 1600°C) gemessen.

Beryllium Diffusion of Ruby and Sapphire

“…In April 2002, we initiated a set of experiments to determine the origin of the color induced by Be diffusion. We believed that we were observing trapped-hole-center absorption, similar to that observed much earlier in both natural and synthetic corundum (Mohapatra and Kröger, 1977;Wang et al, 1983;Emmett and Douthit, 1993;Häger, 1993). Because holes only form in corundum under highly oxidizing conditions, the concentrations of Mg-or Be-hole pairs are very sensitive to the oxygen partial pressure at which they are equilibrated in the furnace.…”

“…Fe 2+ also can be charge compensated by tetravalent donor ions (e.g., Si 4+ or Ti 4+ ) forming donor-acceptor pairs; by hydrogen, which is also a donor; or, in the absence of either of these options, by an oxygen vacancy or an aluminum interstitial ion. Mg 2+ in corundum is also an acceptor (Mohapatra and Kröger, 1977;Wang et al, 1983). It can be charge compensated by tetravalent donor impurities (e.g., Si 4+ or Ti 4+ ) or, in their absence, by an oxygen vacancy or a hole.…”

“…One of the unusual properties of the Mg 2+ -trapped-hole coloration in corundum is its sensitivity to oxygen partial pressure (oxygen concentration in the furnace atmosphere; Mohapatra and Kröger, 1977;Wang et al, 1983;Emmett and Douthit, 1993). If corundum containing Mg 2+ is heat treated in pure oxygen, the color saturation is maximized.…”