Electrical characterization of borate glasses containing metallic granules

Abstract

Borate glasses in the systems Na₂O---B₂O₃ and PbO---B₂O₃ respectively have been prepared with a dispersion of metallic bismuth in them by melting a suitable mixture of oxides. Electron microscopic investigation shows that the microstructures of these materials consist of bismuth granules of dimensions varying between 100Å and 700Å dispersed in glass matrices. d.c. and a.c. resistivities of these composites have been measured in the temperature range 30°C to 200°C. The d.c. resistivity at temperatures below 120°C arises due to electron tunnelling between the metallic particles whereas the high temperature conduction is controlled by an ionic transport. The low temperature resistivity obeys a relation of the type (f) f^-n with n having a value around 1.0.