Optical and analytical transmission-electron-microscopy studies of thermochemically reduced MgO crystals

MgO crystals from five sources were thermochemically reduced at high temperatures. Optical-absorption measurements indicated that anion vacancies were present in all of the crystals. In addition, crystal darkening was observed and was due to a broad absorption in the visible region. The dark coloration was impurity related. Analytical transmission-electron-microscopy techniques indicated the presence of metallic precipitates that were primarily Fe in content. Microdiffraction patterns indicated that the precipitates possessed the fcc (a₀=3.61 A{}) or the bcc (a₀=2.89 A{}) crystal structure. The fcc precipitates were found to have a matrix relationship of 〈001〉ₚ{∥}〈001〉ₘ and 〈010〉ₚ{∥}〈010〉ₘ. The bcc precipitates were found to have a relationship of 〈001〉ₚ{∥}〈001〉ₘ and 〈110〉ₚ{∥}〈010〉ₘ.