STRUCTURAL STUDY OF RB AND (RB, AG) GERMANATE GLASSES BY EXAFS AND XPS

The interatomic distance, R, coordination number, CN, and degree of disorder, DELTAsigma2, around the mobile (Rb,Ag) as well as the network-forming (Ge) cations are obtained using EXAFS (extended X-ray absorption fine structure) of xRb2O. (1 - x)GeO2 and mixed rubidium-silver germanate 0.2[yAg. (1 - y)Rb]2O.0.8GeO2 glasses with x = 0.01, 0.02, 0.05, 0.10, 0.15, 0.20, 0.30, 0.40 and y = 0, 0.25, 0.50, 0.75, 1.00. The non-bridging oxygen (NBO) and bridging oxygen (BO) concentrations are determined by X-ray photoelectron spectroscopy. With the addition of Rb2O, both GeO6 and NBOs are produced for all x less-than-or-equal-to 0.2. For x > 0.2, NBOs continue to increase at the expense of GeO6 units. A comparison of molar volume with various bond lengths indicates the presence of an 'unoccupied volume' which may vary with composition without affecting various interatomic distances. Replacement of Rb by Ag in mixed germanate glasses has the same effect on R(Rb-O) and DELTAsigma(Rb-O)2 as the reduction of Rb content in single Rb germanate glasses. The R(Ag-O) and DELTAsigma(Ag-O)2 show a trend opposite to that of the bond around Rb when Ag and Rb replace each other.