The 57Fe Mossbauer spectrum of semiconducting xK,O (90-x)V205 * 10Fe203 glasses (20 < x d 30) consists of a quadrupole doublet peak. The linewidth and the quadrupole splitting decreased gradually after heat treatment at the crystallization temperature, reflecting an increased uniformity of Fe-0 bonds and a decreased distortion of FeO, tetrahedra, respectively. FTIR spectra of heat-treated vanadate glasses revealed an evident peak separation between VO, and FeO, tetrahedra. The FeO, units were not observed in non-treated glass because they occupy substitutional sites of VO,. An X-ray diffraction study of heat-treated glasses established the formation of a KV308 phase composed of VO, pyramids. Additional diffraction peaks due to a K3V5014 phase, composed of VO, tetrahedra and VO, pyramids, were observed in 30K20*60V205 lOFe,O, and 35K2O*65V2O5 glasses after the heat treatment. Weak peaks due to K4V10027 phase were also observed in 20K20.70V20, 10Fe,03 glass. A Kissinger plot of the differential thermal analysis (DTA) data yielded activation energies of 2.0-2.9 (d0.3) eV, indicating that cleavage of Fe-0 bonds with bond energies of ca. 2.6 eV triggers the crystallization. Magnetic susceptibility measurements of 25K20 * 65V,05 * 10Fe203 glass revealed an antiferromagnetic behaviour with Curie-Weiss constants of -13, -93 and -108 K after the heat treatment at 340 "C for 0,2100 and 5000 min, respectively. A jump of the electrical conductivity from 6.3 x lo-' S cm-' to 4.3 x lo-, S cm-' was observed when 25K20*65V20, 10Fe203 glass was heat treated at 380 "C for 10 min, and this can be ascribed to an increased probability of electron hopping from V4+ to V5+ which was brought about as a result of a decreased distortion of VO,, FeO, and V 0 5 units.Electrical conducting glasses have attracted much interest in the field of solid-state chemistry and materials science because they can be used as an electrode, solid-state electrolyte, sensor, etc. Several vanadate (V,O,-based) glasses show a semiconductivity with the electrical conductivity ( B ) of the order of about lo-' to Scrn-',' which is known to be due to the electron hopping from V4+ to V5+ in the 'skeleton' structure. The mechanism of semiconductivity was explained by Mott2 and by Austin and Mott3 with a small polaron hopping theory, in which the activation energy, W, was estimated to be equal to the summation of the electron-hopping energy, W', and half of the lattice disorder energy, W,. In the case of Sb2O3-Sr0-V2O5 glasses,' W was reported to be 0.41-0.61 eV and W, <0.1 eV.The electrical conductivity of insulating oxide glasses is generally less than lo-'' S cm-l and the alkali-metal ions are known to be representative 'carriers'. Crystallization of oxide glass generally results in a decrease in the electrical conductivity. By contrast, if a conducting crystalline phase like 'vanadium bronze', R,V205, precipitates in the matrix glass, the electrical conductivities of glass ceramics will become higher than those of non-treated glass. In the case of potassium vanada...