Calorimetric study of the glass transition dynamics in lithium borate glasses over a wide composition range by modulated DSC

Complex specific heat, Cp*=C′p−iC″p, of lithium borate glasses xLi2O·(100 − x)B2O3, where x is molar concentration of Li2O mol%, has been investigated by modulated-temperature DSC (MDSC). In this paper, the wide composition range of Li2O, 0 ≤ x ≤70, has been studied. The Cp* is presented in the form of Cole–Cole plot by the scan of relaxation time. The Havriliak–Negami equation well reproduces the observed Cp* of all of the samples. The nonexponential (non-Debye) behavior of thermal relaxation through a glass transition has been investigated. Composition dependence of nonexponentiality determined by Cole–Cole plot has been discussed in terms of the structural change of borate system, and the origin reflects the coexistence of the different types of the intermediate structural units and the creation of four-coordinated boron atom.