PSEUDO-LATTICE VIBRATIONS AND GLASS TRANSITIONS IN METAL OXIDE CLASSES

Author Institution: Department of Chemistry, Brown UniversityThe far IR spectra of metal metaphosphate and tetraborate glasses yield broad absorption bands whose resonant frequencies $(\omega_{Res})$ and half-band-widths $(\Delta_{\omega 1/2})$ are strongly dependent on the mass and charge of the glass-modifying cation. Metal cations in the glass undergo localized vibrations on near-octahedral oxygen sites; however, in the crystalline form of these materials, the broad cation motion band splits into the crystal lattice spectrum. That these low frequency cation modes in glass arise from translational pseudo-lattice vibrations is shown by the linear dependences of relative integrated intensities with $\omega^{2}_{Res}$, and $\omega_{Res}$ with $\Delta_{\omega 1/2}$. A classical underdamped $(\omega_{Res}>\Delta_{\omega 1/2})$ forced harmonic oscillator model is suggested to explain the large half-bandwidths of the cation motion bands. At their respective glass transition temperatures, mean square amplitudes of vibration $$ for metal metaphosphate glasses vary linearly with the square of the equilibrium cation-oxygen separations $$, which implies that at some critical ratio, $/$ , the glass transition phenomenon ensues