Influence of ceria addition on thermal properties and local structure of bismuth germanate glasses

Bismuth germanate glasses are interesting materials due to their physical properties and their unique structural characteristics caused by the coordination changes of bismuth and germanium atoms. Glasses of the bismuth germanate system were prepared by melting/molding method and were investigated concerning their thermal and structural properties. The structural analysis of the samples was carried out by micro-Raman and Fourier transform infrared spectroscopes. It was observed that the glass structure is formed basically by GeO4 tetrahedral units also having the formation of the GeO6 octahedral units. BiO2 was considered a network former by observing the presence of octahedral BiO6 and pyramidal BiO3 groups in the local structure of the samples. An absorption band observed at 1103 cm−1 in the IR spectrum of the undoped glass was attributed to the Bi–O–Ge and/or Bi–O–Bi linkage vibration. The said band shifted to lower wavenumbers after the CeO2 addition thus reflecting changes in the glass network. Cerium oxide was an efficient oxidant agent to prevent the darkening of the glasses which was probably associated to the reduction of Bi ions. However, CeO2 was incorporated as a local network modifier in the glass structure even at concentrations of 0.2 mol%.