Crystallization and the electrical conductivity of vanadate glass

Abstract

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.