Short-range and medium-range order in amorphous barium germanate

Amorphous barium germanate of composition BaGe2.55O6.10 was prepared by ultra-rapid quenching using a double-roller melt-spinning device. The short-range and medium-range order was investigated by high-energy synchrotron X-ray diffraction. resonant scattering at the Ba K-absorption edge and by electron diffraction. There are indications that 6-fold coordinated germanium exists in the structure of the present amorphous alkaline earth germanate, i.e. both GeO4 tetrahedra and GeO6 octahedra are supposed to be basic building units. The ratio of 6-fold coordinated Ge to 4-fold coordinated Ge is approximately 1:3. A structure model is proposed which favours the existence of barium chains and/or barium layers, similar to the structure of barium silicate glasses. (C) 2002 Elsevier Science B.V. All rights reserved.