Low-Energy Modes in Phosphate Glasses: A Comparison with the Soft Potential Model

Low-frequency Raman spectra of samarium phosphate glasses ${\left({\mathrm{Sm}}_2{\mathrm{O}}_3\right)}_x{\left({\mathrm{P}}_2{\mathrm{O}}_5\right)}_{1-x}$ obtained over a wide temperature range 11-973 K, were compared with those of low-temperature specific heat. The temperature and frequency dependencies of the quasielastic scattering and boson peak, as well as the anomalous specific heat, agree qualitatively with predictions of the soft potential (SP) model. The "excess" spectral density may also be consistent with SP predictions, assuming (1) comparatively high phonon spectral density, and (2) approximately linear in frequency light-soft mode coupling. However, these assumptions are in conflict with recent formulations of the theory.