Elastic Properties of Potassium Borate Glass in a Wide Composition Range Studied by Brillouin Scattering

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The elastic properties of potassium borate glass, $x$K2O$\cdot$($100 - x$)B2O3, where $x$ is the molar composition of K2O in mol %, have been investigated by Brillouin scattering spectroscopy over a wide composition range of $2 \leq x \leq 42$ mol %. From the observed values of longitudinal sound velocity, the elastic constant has been determined and compared with that of lithium borate glass. The sound velocity increases with increasing $x$ below $x = 30$; however, for a further increase in $x$, it decreases owing to the softening caused by the formation and increase in the number of nonbridging oxygen atoms. The absorption coefficient also increases markedly above $x = 30$ owing to the scattering of acoustic waves by nonbridging oxygen atoms. The temperature dependences of both sound velocity and absorption coefficient of 14K2O$\cdot$86B2O3 show a markedly change at approximately the glass transition temperature $T_{\text{g}}$ of 395 °C.
2009-07-25