Reflectivity Study of Sillenite Compounds Bi12M020 (M= Si, Ge, Ti)

Three sillenite compounds Bi12MO20 (M=Si, Ge, Ti) were synthesized, and the resulting single-phase crystals were then investigated in the energy range from 1.5 to 6eV at room temperature by reflectance method. A rich structure corresponding to the optical interband transitions were observed in the reflectivity spectra. The electronic band structure of modification of sillenite compounds resulting from the above data is analyzed and discussed. An analysis of the optical properties of the Bi12MO20 (M=Si, Ge, Ti) single crystals has been correlated with the structure of the bismuth-oxygen network of the sillenite crystals. The optical transitions occur at the saddle points on the -P() line. The probability of transitions at the P and H points is low, because of the density of states is expected to be low there. The results contribute to the model of the electronic structure of these materials