RAMAN-STUDY OF POTASSIUM SILICATE-GLASSES CONTAINING RB- IMPLICATIONSFOR CATION SOLUTION MECHANISMS IN MULTICOMPONENT LIQUIDS(, SR2+, Y3+,AND ZR4+ )

The parallel- and perpendicular-polarized Raman spectra of (1 - x)K2O. xM(z+)2/zO.4SiO23 glasses are presented, where M is one of the Period V cations Rb+, Sr2+, Y3+ or Zr4+. These compositions represent the equ al-oxygen substitution of a Period V cation for K+, which preserves th e ratio of non-bridging oxygen (NBO) to Si atoms but not, in general, the ratio of all oxygen to all cations. Rb+ and K+ occupy very similar sites and appear to share the same NBO with virtually no energetic pe nalty. As the valence of the Period V cation increases, so does the te ndency of the cation to form silicate species that am depolymerized re lative to the species dominating the structure of the bulk glass. The tendency to form regions comparatively rich in Si-O-Si bonds increases in the same sense. The dominant silicate species are those with 0 or 1 NBO in all glasses. The spectra indicate that K+ shares NBO with Rb or Sr2+, that there is relatively little sharing of NBO by K+ and Y3, and that K+ and Zr4+ share the same NBO in what appears to be a near ly fixed bulk stoichiometric K:Zr ratio of 2:1. The latter provides a mechanism for the substantial increase in ZrO2 solubility seen in pera lkaline liquids. A novel means of expressing homogeneous equilibria in silicate liquids is presented, whereby it is possible to make concret e predictions about the coordination numbers of cations in silicate li quids and to predict how they might be affected by the presence of oth er cations.