Elastic and anelastic properties of rare earth phosphate glasses

The behaviour of the ultrasonic attenuation between 10 K and 400 K in Sm2O3-P2O5 glasses is characterized by the presence of very broad peaks, due to thermally activated relaxations of structural defects, typical of amorphous materials. A study of these anomalies reveals that the addition of Sm2O3 to P2O5 has little influence on the mean activation energy of the relaxation process, but does cause a decrease in the number of relaxing particles. The effect of temperature on the anomalous negative hydrostatic pressure derivatives of the elastic moduli of samarium phosphate glass is also examined experimentally. Reduction of the temperature below 300 K causes dC11/dP and dB/dP to increase steeply to more negative values: both longitudinal and shear Gruneisen parameters, which are negative, become much larger. It is suggested that application of pressure drives the samarium ion f → d transition and that the ion size collapse couples to the acoustic modes, strongly enhancing acoustic mode softening.