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

Abstract

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 (${a}_{0}$=3.61 A\r{}) or the bcc (${a}_{0}$=2.89 A\r{}) crystal structure. The fcc precipitates were found to have a matrix relationship of 〈001${〉}_{p}$\ensuremath{\parallel}〈001${〉}_{m}$ and 〈010${〉}_{p}$\ensuremath{\parallel}〈010${〉}_{m}$. The bcc precipitates were found to have a relationship of 〈001${〉}_{p}$\ensuremath{\parallel}〈001${〉}_{m}$ and 〈110${〉}_{p}$\ensuremath{\parallel}〈010${〉}_{m}$.