Vibrational excitations ofAs2O3. I. Disordered phases

Raman, depolarization, and infrared spectra of the glass, liquid, and gaseous disordered phases of ${\mathrm{As}}_2$ ${\mathrm{O}}_3$ have been studied at temperatures between 4.5 and 1200 K. Spectra recorded at temperatures in the range of the glass-liquid transition indicate that the microstructures of the glass and liquid are quite similar near $T_g$ and can best be characterized as distorted layerlike remnants of the monoclinic crystalline phase, claudetite. Our results have been contrasted to corresponding results for ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ and ${\mathrm{As}}_2$ ${\mathrm{Se}}_3$ and have been compared with the predictions of current models of the structure of ${\mathrm{As}}_2{X}_3$-type glasses. The observed spectra are most compatible with the composite model which combines aspects of the layer and molecular models. No evidence is found to support the conjecture of Taylor, Bishop, and Mitchell that for layer-type ${\mathrm{As}}_2{X}_3$ glasses a characteristic temperature $T_s$ exists such that $T_s>T_g$ and the layers catastrophically disintegrate at temperatures $T>\mathrm{}{T}_s$. The temperature dependence of the Raman shift, full width at half-maximum (${\Gamma }_{\frac{1}{2}}$), and integrated intensity of the 376-${\mathrm{cm}}^{-1\mathrm{}}$ band associated with the symmetric stretching mode of the As-O-As linkage have been studied as have the shifts with temperature of other prominent spectral features. We find that the glass transition temperature can be accurately determined from a plot of $\ln {\Gamma }_{\frac{1}{2}}$ vs $\ln \left(\frac{1000}{T}\right)$ and that above $T_g$ ${\Gamma }_{\frac{1}{2}}\left(376\mathrm{} {\mathrm{cm}}^{-1\mathrm{}}\right)\propto T^{\frac{1}{2}}$. The temperature dependence of the ${\nu }_1$ and ${\nu }_3$ modes of the As${\mathrm{O}}_3$ pyramidal unit indicates that the apex angle decreases with increasing temperature. The low-frequency (8-30 ${\mathrm{cm}}^{-1\mathrm{}}$) region of the Raman spectrum of vitreous ${\mathrm{As}}_2$