Vibrational Spectroscopic Studies of Germanium-High Bismuthate Glasses and Vitroceramics

Bi2O3-rich glasses belonging to the system xGd(2)O(3)(1-x)[0.857Bi(2)O(3)center dot 0.143GeO(2)] with 0.005 <= x <= 0.1, have been obtained by rapid cooling of the melts. Polycrystalline samples have been further obtained by applying a heat treatment at 600 degrees C for 24 h. Both types of samples were structurally characterized by using X-ray diffraction (XRD), and infrared (IR) and Raman spectroscopic techniques. Local structural units for the investigated samples are identified on the basis of vibrational spectroscopic data. The obtained data reveal the presence of GeO4, GeO6, BiO3 and BiO6 groups as basic structural units of the networks. For the vitroceramic samples some changes occur in their network, mainly reflecting the presence of an ordered structure, but much important is that part of the BiO6 structural units from Bi2O3-GeO2 glass network are converting into BiO3 units. The IR and Raman results support the idea that the local structure of the glasses and vitrocerarnics is less affected by the presence of Gd3+ ions but there is strong long range order influence on developed crystalline phases from vitroceramic samples, as proved by XRD. However, the spectral analyses reveal the formation of a structure with a higher disorder degree for x = 0.1 in comparison with the other investigated vitroceramics as a result of the partial replacement of the Bi3+ ions with Gd3+ ions. Starting from the Bi12GeO20 sellenite phase in the samples with low gadolinium content (x <= 0.01), the structure is change to Bi24GeO38 phase, via a BiLa type structure, when the Gd2O3 concentration is increasing up to x = 0.1.