Role of ZnO in Dc Electrical Conductivity of Lithium Bismuthate Glasses

Glasses of various compositions belonging to the Bi2O3-B2O3-ZnO-Li2O quaternary system were prepared using melt quench technique. Dc electric measurements were done on the samples, and activation energies are determined. Arrhenius plots showed straight line behaviour. It is observed that the conductivity of the samples increased with temperature and also with Li2O content, whereas the activation energy decreased with Li2O content. The isothermal plots for constant ZnO and constant Bi2O3 glasses revealed that the conduction in these glasses is due to lithium ions only. The isothermal plots for constant lithium containing glasses varied nonlinearly with two maxima, which is attributed to mixed former effect. The variation is explained based on Anderson-Stuart model. 1. Introduction Glasses and glass-ceramics are technologically important materials when compared with their crystalline counterparts. These materials show superior thermomechanical, electrical and other physicochemical properties, which make them suitable for use in vacuum, high-voltage, and biomedical applications [1]. Conventional glass formers such as P2O5 and TeO2 containing transitional metal ions have been studied earlier [2–5]. In recent years, bismuth-based glasses have attracted the attention of researchers due to technological applications, useful physical properties and among them bismuth borates are of interest [6–9]. The introduction of alkali ions into these glasses exhibits high electrical conductivity and can be used as solid electrolytes in high energy density batteries, sensors, and so forth [10]. Further, transition metal ion glasses based on unconventional glass network formers such as Bi2O3 and PbO have been reported [11–14]. Especially, zinc-oxide based glasses/ceramics have special applications in the area of varistor designing, dielectric layers, barrier ribs in plasma display panels, and so forth [15, 16]. In the literature, it is reported that Bi2O3 occupies both network forming and network modifying positions. Therefore, the physical properties of such glasses exhibit discontinuous changes when the structural role of the cation changes [17, 18]. Especially, efforts are made to enhance the conductivity in lithium ion conducting glasses in this way [19, 20]. There have been two main approaches to improve the conductivity of the glass. The first approach is to dissolve alkali compounds such as Li2O, LiCl, and Na2O into an oxide glass. The second strategy is to combine the network forming oxides, which is known as mixed former effect, although the reason for this is not