Dynamic specific heat, glass transition, and non-Debye nature of thermal relaxation in lithium borate glasses

The physical properties of lithium borate glasses, xLi(2)O center dot(100 - x)B2O3, vary anomalously with the lithium oxide content. known as "borate anomaly". In this study, the compositional variations of the dynamic glass transition temperature T-g(omega) and the non-Debye nature (or stretched exponentiality beta(KWW)) in the vicinity of T-g have been investigated over I wide composition range. Since T-g(omega) depends on the frequency of the temperature modulation, a more precise composition dependence can be discussed. The trend of T-g(omega) shows a sin-le broad maximum at about x = 26-28. Moreover, the composition dependence of the non-Debye behavior has been presented. It shows a broad maximum at about x = 40 mol %. It is found that beta(KWW) is systematically controlled using the fraction of each intermediate structural unit, particularly the tetrahedron composed of the 4-coordinated boron atom. Both the composition dependences of T-g(omega) and beta(KWW) can be explained using the structure-superposition model.