Crystallization and the electrical conductivity of vanadate glass

The 57Fe Mössbauer spectrum of 25K2O·65V2O5· 10Fe2O3 glass showed a doublet due to tetrahedral Fe3+. The linewidth showed a gradual decrease from 0.49 to 0.27 (±0.02) mm s-1 after heat treatment at 340°C for 10--600 min, reflecting an increased uniformity of Fe--O lengths and O--Fe--O angles. The quadrupole splitting showed a gradual decrease from 0.61 to 0.50 (±0.02) mm s-1 after the heat treatment, reflecting a decreased distortion of FeO4. A jump of the electrical conductivity (σ) was observed from the order of 10-8 S cm-1 to 10-4 S cm-1 after treatment at 380°C for 10--30 min because of the structural relaxation which probably caused an increase in the 3d-electron (polaron) hopping from V4+ to V5+. The value of σ decreased gradually after heat treatment of 60--600 min and became comparable to that of original glass when the precipitation of KV3O8 phase became pronounced.