ULTRASONIC RELAXATION SPECTRA IN COO-CO2O3-P2O5 GLASSES IN THE TEMPERATURE-RANGE 6 TO 300 K

Formulae attributing acoustic relaxation in glasses to two-well systems with a distribution of barrier heights and asymmetries are related to the phenomenological theory of a standard linear solid. Acoustic wave loss measurements at frequencies ranging from 15 to 135 MHz and temperatures ranging from 6 to 300 K have been used to compute relaxation spectra for the CoO-P//2O//5 glass system. For each glass two alternative sets of spectra have been deduced on the contrary assumptions that the range of asymmetries is very broad, or very narrow. From the quality of the fit of theory with experiment, it is concluded that the former description is more likely to be applicable to the glasses. The spectral analysis also showed that in all the glasses there is evidence of the existence of two-level systems which produce a pronounced upturn in the acoustic relaxation loss at temperatures below 40 K.