Density of Color Centers in Barium Oxide as a Function of the Vapor Pressure of Barium

Single crystals of barium oxide were exposed at a temperature of 1423°K or 1473°K to barium vapor of different pressures ranging from 3.4×10⁻⁵ mm Hg to 7.6×10⁻² mm Hg. The resulting blue coloration was measured in an absorption spectrometer, which provided estimates of the number of color centers per cm³, N_F. The relation between N_F and the number of barium atoms per cm³ in the vapor, N_v, was $N_F{\text{=1.5×10}}^{13}{N}_v^{\frac{1}{3}}$ . This relation can be tentatively explained by assuming total dissociation of the color centers into oxygen vacancies and free electrons at the temperature of formation.