Electrical Conductivity of Crystallized Glasses of the System Na<sub>2</sub>O-V<sub>2</sub>O<sub>5</sub>-P<sub>2</sub>O<sub>5</sub> Containing Vanadium Bronze Crystals

Abstract

In order to obtain highly conductive glass-ceramics containing vanadium bronze, MxV2O5 (M=alkali metal, etc), which is known to have high electronic conductivity, Na2O-V2O5-P2O5 glasses were heat treated to perform crystallization. The dc conductivities of the glasses containing 60 to 77mol% V2O5, in which [Na2O]/[V2O5] molar ratio was 1/6 to 1/3, were about 10-4 to 10-2ohm-1cm-1 at 150°C, and the activation energies were about 0.4eV. Exothermal peaks accompanied by weight losses were observed by TG-DTA in the temperature range from 250° to 300°C. Broad peaks of β-NaxV2O5 were observed by X-ray diffraction after 2 to 5 h-heat treatment at 260° to 300°C. Glass blocks and disks of glass powders were heat-treated in two steps, at 300°C for 2h and at 500°C for 1 to 4h in air. After the heat treatment at 500°C, sharp diffraction peaks of β-NaxV2O5 developed. The dc conductivity of the crystallized glasses was more than 3 orders of magnitude higher than that of as-cast glasses. The activation energy decreased to less than 0.1eV, similar to that of vanadium bronze. The microstructure of the crystallized glasses was observed by SEM and optical microscopy.