Thermochemical coloration and annealing of spinel and magnesium oxide

Abstract

Heating spinel (MgAl2O4) single crystals in aluminum or magnesium metal vapor at temperatures in excess of 1800 °C results in the introduction of an optical absorption band at 5.3 eV. The same band can be produced by heating in a strongly reducing atmosphere with no metal vapor at 2100 °C. These results strongly support the suggestion of Bunch that the 5.3-eV band, created by atomic displacement collisions resulting from energetic particle bombardment, is associated with an F-type center. Isothermal annealing of the 5.3-eV band in MgAl2O4 and the 5.0-eV band in MgO introduced by thermochemical coloration suggests that the activation energy for oxide-ion vacancy motion is, respectively, 1.8 and 3.4 eV.