Optical and transmission-electron-microscopy characterization of metal precipitates in doped thermochemically reduced magnesium oxide

MgO crystals doped with Co, Cu, and V were thermochemically reduced at high temperatures. Changes in coloration were observed in all these crystals due to broad optical extinction bands in the visible region. These bands are impurity related. Analytical transmission-electron-microscopy techniques indicated the presence of metallic precipitates consisting of Co in the Co-doped sample, Cu with some precipitates of Fe in the Cu-doped sample, and a V-Fe-Cr alloy in the V-doped sample. Microdiffraction patterns indicated that the Co precipitates possessed the fcc (a₀=3.54 A{}) crystal structure and V-Fe-Cr alloy precipitates showed a bcc (a₀=2.89 A{}) crystal structure.