Crystallization and the electrical conductivity of vanadate glass

The Fe-57 Mossbauer spectrum of 25K(2)O . 65V(2)O5 . 10Fe(2)O(3) 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 degrees 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 (sigma) was observed from the order of 10(-8) S cm(-1) to 10(-4) S cm(-1) after treatment at 380 degrees 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 sigma 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.