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Local order in silicate glasses has been observed by many experimental techniques to be similar to that in crystalline materials. Details of the intermediate-range order are more elusive, but essential for understanding the lack of long-range symmetry in glasses and the effect of composition on glass structure. Two-dimensional 17O dynamic-angle-spinning nuclear magnetic resonance experiments reveal intermediate-range order in the distribution of inter-tetrahedral (Si-O-Si) bond angles and a high degree of order in the disposition of oxygen atoms around the network-modifying cations.

Using 207Pb magic angle spinning and static NMR, we have resolved and assigned different lead sites in crystalline lead oxides and lead silicates to their isotropic chemical shifts. Chemical shift anisotropies were also obtained for lead sites from the intensities of spinning sidebands. Empirical correlations between 207Pb isotropic chemical shifts and structural parameters are proposed. For ionic compounds, we show good correlations between chemical shift and coordination number or mean bond length. For more covalent compounds, the best empirical correlation has been obtained by using the degree of oxygen s−p hybridization and second neighbor electronegativity similar to that previously used to characterize 29Si shifts in aluminosilicates. The Pb2+ chemical shift anisotropies increase with more positive chemical shifts. These correlations, established for simple crystalline compounds, should allow better characterization of lead environments in disordered materials of complex composition.

Raman spectroscopy of radiation-damaged natural zircon samples shows increased line broadening and shifts of phonon frequencies with increasing radiation dose. Stretching and bending frequencies of SiO 4 tetrahedra soften dramatically with increasing radiation damage. The frequency shifts can be used to determine the degree of radiation damage. Broad spectral bands related to Si-O stretching vibrations between 900 and 1000 cm −1 were observed in metamict/amorphous zircon. The radiation-dose-independent spectral profiles and the coexistence of this broad background and relative sharp Raman modes in partially damaged samples indicate that these bands are correlated with amorphous domains in zircon. The spectral profiles of metamict zircon suggest that in comparison with silica, the SiO 4 tetrahedra are less polymerized in metamict zircon. This study also shows that ZrO 2 and SiO 2 are not the principal products of metamictization in zircon. No indication of bulk chemical unmixing of zircon into ZrO 2 and SiO 2 was found in 26 samples with a large variation of radiation damage (maximum dose: 23.5 × 10 18 α-events g −1). Only one sample showed clearly, in all measured sample areas, extra sharp lines at 146, 260, 312, 460 and 642 cm −1 characteristic of tetragonal ZrO 2. The geological (and possibly artificial heating) history of this sample is not known. It is concluded that radiation damage without subsequent high temperature annealing does not cause unmixing of zircon into constituent oxides.

Five distinctly resolved I7O solid-state NMR resonances in room temperature coesite, an Si02 polymorph, have been observed and assigned using dynamic-angle spinning (DAS) at 11.7 T along with magic-angle spinning (MAS) spectra at 9.4 and 11.7 T. The I7O quadrupolar parameters for each of the five oxygen environments in coesite are correlated with the Si-0-Si bridging bond angles determined by diffraction experiments. The sign of e2qQ/h along with the orientation of the electric field gradient for oxygen in the Si-0-Si linkage were determined from a Townes-Dailey analysis of the data.

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The atomic-scale dynamics of the glass-to-liquid transition are, in general, poorly understood in inorganic materials. Here, two-dimensional magic angle spinning nuclear magnetic resonance spectra collected just above the glass transition of K(2)Si(4)O(9) at temperatures as high as 583 degrees C are presented. Rates of exchange for silicon among silicate species, which involves Si-O bond breaking, have been measured and are shown to be closely related in time scale to those defined by viscosity. Thus, even at viscosities as high as 10(10) pascal seconds, local bond breaking (in contrast to the cooperative motion of large clusters) is of major importance in the control of macroscopic flow and diffusion.