High Temperature Brillouin Scattering of Potassium Borate Glasses

概要

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High temperature elastic properties of potassium borate glasses, $x$K2O$\cdot$($100-x$)B2O3 ($x=4$, 10, 14, 20, 28, and 34 mol %), have been investigated between 20 and 1100 °C by Brillouin scattering. Longitudinal sound velocity of the glasses changes only slightly up to the glass transition temperature ($T_{\text{g}}$), and, with further heating above $T_{\text{g}}$, it decreases markedly. This sudden decrease in sound velocity is caused by structural rearrangements that make glass networks soft above $T_{\text{g}}$. With an increase in K2O composition, the slope of sound velocity just above $T_{\text{g}}$ 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 28K2O$\cdot$72B2O3 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.
2010-07-25