The structure analyses of NaGaSi₃O₈, NaAlGe₃O₈ and NaGaGe₃O₈ glasses by X-ray diffraction and EXAFS measurements.

The short-range structures of NaGaSi₃O₈ and NaGaGe₃O₈ glasses, which have feldspar structures in crystalline phases, have been determined by XRD and EXAFS spectroscopy techniques. The X-ray radial distribution functions showed coordination numbers of T atoms (T=Si,Al,Ge,Ga) of = or >4 in the glasses. Correspondingly, the T-O distances in NaAlGe₃O₈ and NaGaGe₃O₈ glasses obtained by X-ray radial distribution analyses are a little larger than those of NaAlGe₃O₈ and NaGaGe₃O₈ feldspars. The Ge-O and Ga-O distances of NaGaSi₃O₈, NaAlGe₃O₈ and NaGaGe₃O₈ glasses obtained by EXAFS spectroscopy are also a little longer than those in low-quartz type GeO₂ and in GaO₄ tetrahedra of beta -Ga₂O₃, respectively. If the Si-O and Al-O distances are 1.61 and 1.75 A respectively, the T-O distances obtained from EXAFS analyses are considered to agree with the values determined by X-ray radial distribution analyses. These results suggest that the structures of the glasses are essentially based on GeO₄ and GaO₄ tetrahedra and contain a small amount of GeO₆ and GaO₆ octahedra. The radial distribution functions of these glasses are well interpreted by model structures with cristobalite type linkages of GeO₄ and GaO₄ tetrahedra. The long-range order diminishes from NaGaSi₃O₈, NaAlGe₃O₈ to NaGaGe₃O₈ glasses in this order; the densities approach those of the corresponding feldspar crystals in the same order.-T.Y.