Spectrum of Volume Relaxation Times in B2O3

Abstract

Time-index of refraction isotherms were measured for B2O3 glass starting from both a high and a low temperature in the transformation region. The equilibrium index values at each temperature, obtained from both types of approach curve, were identical. As in the case of the density values, the equilibrium refractive index curve as a function of temperature for this glass is not a straight line. The two-relaxation-times (crossover) model was applied to B2O3 glass and fitted the data as well as it did in previous experiments with borosilicate crown and GeO2 glasses. The reverse crossover which was predicted by the model was experimentally confirmed with the B2O3 glass. The spectrum of relaxation times narrowed with decreasing temperature, indicating approach to another region of single relaxation associated with the low-temperature Arrhenius region. The relaxation times for the low-temperature crossover agreed well with those from the high-temperature curves, indicating complete linearity in the experiments. The spectrum of relaxation times was slightly asymmetrical at constant pressure and very asymmetrical at constant volume.