High Temperature Brillouin Scattering of Potassium Borate Glasses

High temperature elastic properties of potassium borate glasses, xK(2)O center dot(100 - x)B2O3 (x = 4, 10, 14, 20, 28, and 34 mol %), have been investigated between 20 and 1100 degrees C by Brillouin scattering. Longitudinal sound velocity of the glasses changes only slightly up to the glass transition temperature (T-g), and, with further heating above T-g, it decreases markedly. This sudden decrease in sound velocity is caused by structural rearrangements that make glass networks soft above T-g. With an increase in K2O composition, the slope of sound velocity just above T-g increases. The composition dependence of the fragility of potassium borate glass is suggested on the basis of the slope. The activation energy of the relaxation process of 28K(2)O center dot 72B(2)O(3) measured by Brillouin scattering is estimated to be 6.84 kcal/mol, which is comparable to the energy of formation of a boroxol ring structure in a liquid phase. (c) 2010 The Japan Society of Applied Physics