Low-frequency light scattering and structural defects in samarium phosphate glasses

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Abstract
Low-frequency Raman-scattering measurements have been made on samarium phosphate glasses containing 5 and 25 mol % Sm2O3 from 8 K to room temperature. The scattering due to acoustic modes has been separated quantitatively from the light-scattering excess (LSE). It has been shown that at low frequency the product C(ω)g(ω) of the coupling constant C(ω) and density of states g(ω) has an ω4 behavior, in good agreement with the predictions of the theoretical models for describing Raman scattering in a disordered system. The LSE is Lorentzian in form and its intensity increases with rising temperature in these glasses. Quantitative comparisons have been made between the behavior of the Raman scattering and the ultrasonic behavior determined in the same glass specimens. The magnitude of the LSE decreases with increasing samarium oxide content, while an opposite trend has been observed for the ultrasonic attenuation. This finding indicates that models that presuppose the structural relaxation of intrinsic defects in a glass as a common origin for the LSE and the low-temperature acoustic-loss peaks fail. It is suggested that the LSE and acoustic relaxations may result from different microscopic motions.