The structures of (Na_0.5Ca_0.5)Ga_1.5Ge_2.5O₈ and CaGa₂Ge₂O₈ glasses

Abstract

The short-range structures of (Na_0.5Ca_0.5)Ga_1.5Ge_2.5O₈ and CaGa₂Ge₂O₈ glasses have been analysed by X-ray diffraction and EXAFS spectroscopy techniques. Structural differences have been found between these two glasses. The structure of (Na_0.5Ca_0.5)Ga_1.5Ge_2.5O₈ glass is similar to that of NaGaGe₃O₈ glass, and seems to be made of GaO₄ and GeO₄ tetrahedra. On the other hand, the coordination number of T (Ga and Ge atoms) atoms of CaGa₂Ge₂O₈ glass is larger than 4 (and about 5) and the T–O distance (=1.83 Å) is longer than that of NaGaGe₃O₈ glass.
Therefore, on CaGa₂Ge₂O₈ glass, it is supposed that the coordination number of Ga atom is larger than 4 because of its larger Ga–O distance obtained by EXAFS analysis.