IR AND EXAFS ANALYSIS OF XBI(2)O(3).(1-X)GEO2 GLASSES

The glassy system xBi(2)O(3).(1-x)GeO2 with high bismuth content (x=0.9) has been investigated by infrared spectroscopy in the range 200-4000 cm(-1) and by extended X-ray absorption fine structure (EXAFS) spectroscopy at the Ge absorption K-edge. The infrared measurements show that the addition of Bi2O3 to GeO2 causes a shift and splitting into two components of the band associated with the stretching mode occurring in the GeO4 tetrahedra. This result is accounted for by assuming that Bi atoms perturb the environment around GeO4 units rather than change the oxygen coordination around germanium from fourfold to sixfold. A tetrahedral coordination for germanium atoms at all bismuth concentrations is found from the EXAFS analysis. The role of the preparation procedure on the glass infrared transmission is discussed.