Concentration of Cr4+ impurity ions and color centers as an indicator of saturation of forsterite crystals Mg2SiO4 with oxygen

Abstract

The influence of the oxygen partial pressure P O 2 in the growth atmosphere on the coefficient of chromium distribution between the crystal and the melt of forsterite, the Cr3+ and Cr4+ ion contents in crystals, and the concentration of color centers induced by irradiation has been investigated. It has been established that the crystals grown at low oxygen partial pressures P O 2 (0.01–0.05 kPa) are characterized by low concentrations of Cr4+ ions and color centers. A change in the oxygen partial pressure to P O 2 ∼ 0.85 kPa leads to an increase in the Cr4+ center concentration by a factor of ∼10 and in the color center concentration by a factor of ∼5. A further increase in the oxygen partial pressure to P O 2 to 12 kPa remains the concentration of these centers almost unchanged. A model has been proposed according to which the intrinsic defects formed under conditions of a relative excess of oxygen leads to both the self-oxidation of chromium and the formation of color centers in the forsterite crystals under irradiation.