Dynamic Specific Heat, Glass Transition, and Non-Debye Nature of Thermal Relaxation in Lithium Borate Glasses

Abstract

The physical properties of lithium borate glasses, x Li 2 O·(100- x )B 2 O 3 , 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 ω and the non-Debye nature (or stretched exponentiality β KWW ) in the vicinity of T g have been investigated over a wide composition range. Since T g ω depends on the frequency of the temperature modulation, a more precise composition dependence can be discussed. The trend of T g ω shows a single 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 β 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 ω and β KWW can be explained using the structure-superposition model.