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

Amorphous barium germanate of composition BaGe 2.55O 6.10 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 GeO 4 tetrahedra and GeO 6 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.