Properties and structure of glasses in the system BaO-B2O3-ZnO

BaO-B2O3-ZnO glasses have been studied in order to prepare lead-free glasses with a low-melting point. A glassforming region in the system was determined and thermal expansion coefficients, glass transition temperatures, dilatometric softening temperatures, and densities of the glasses were measured. A glass with a low thermal expansion coefficient comparable to that of PYRES glass was obtained. The behavior of ZnO, an amphoteric oxide, in the glasses was discussed on the basis of viscosities of the melts and chemical shifts of ZnKbeta 1 in the glasses. In the glass system, the behavior of ZnO depending on the basicity of the glass such as ZnO in silicate glasses was not observed. It was revealed that ZnO in the glass system tended to become the four-fold coordination and contributed as network former (NWF) to maintain the stability of the network structure in the glasses. The change in the properties of the glasses in the system BaO-B2O3-ZnO was termed "the zinc oxide anomaly": since it was caused by the coordination number change of ZnO as NWF.