ABNORMAL BEHAVIOR IN HIGH DENSIFICATION OF GLASS UNDER HIGH PRESSURE TREATMENT AND ITS CORRELATION TO FRAGILITY CONCEPT

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The local structures around glass-constituent cations in the undensified and densifid fluorozirconate glasses are examined by means of Raman scattering spectroscopy, Eu^<3+> fluorescence spectroscopy, and EXAFS spectroscopy. The mechanism of peculiar ligh-pressure behavior is clarified based on the results of the structural analyses. The permanent densification experiment in SiO_2-K_2O-CaO-SrO silicate glasses is conducted. The structures of invert-composition glasses, whose structure has not been cleared yet, are clarified by ^<29>Si MAS NMR spectroscopy. Ionic ZrF_4-based fluoride glasses, mixed ionic and covalent SiO_2-based oxide glasses, and a covalent GeS_2 sulfide glass are employed as densification experiments. The densification behavior of glasses having different chemical-bond properties and structures is discussed. The structure of densified GeS_2 glasses is examined by means of Raman scattering spectroscopy, XAFS spectroscopy, and X-ray radial distribution analysis. The local structural-change around Ge in GeS_2 glass through compression and decompression processes, i.e., densification process, is examined by an in-situ KXAFS method. The thermal relaxation behavior of densified GeS_2 glass is examined. In the analyses of thermal relaxation the presence of two types of relaxation processes, that is, the fast and slow processes, is found in the thermal relaxation in densified GeS_2 glass. Then, the activation energies of each relaxation process is estimated. The structural relaxation during both processes is examined by the measurements of Raman scattering spectra and EXAFS spectra. The relationship between the red shift of visible absorption edge and the structural change through thermal relaxation is discussed.