Effect of Li2O on the structure, electrical and dielectric properties of xLi2O·(20−x)CaO·30P2O5·30V2O5·20Fe2O3 glasses

Glasses of the general formula xLi2O·(20−x)CaO·30P2O5·30V2O5·20Fe2O3 with x=0, 5, 10, 15 and 20 mol% were prepared; IR, density, electrical and dielectric properties have been investigated. Lithia-containing glasses revealed more (P2O7)4−, FeO6, V–O− and PO− groups and mostly have lower densities than those of lithia-free ones. The electrical properties showed random behavior by replacing Li2O for CaO, which has been assigned to the change of the glass structure. The results of activation energy and frequency-dependent conductivity indicate that the conduction proceeds via electronic and ionic mechanisms, the former being dominant. The mechanism responsible for the electronic conduction is mostly thermally activated hopping of electrons from Fe(II) ions to neighboring Fe(III) sites and/or from V4+ to V5+. The dielectric constant (ε′) showed values that depend on the structure of glass according to its content of Li2O. The (ε′) values are ranging between 3 and 41 at room temperature for 1 kHz, yet at high temperatures, glass with 20 mol Li2O exhibits values of 110 and 3600 when measurement was carried out in the range 0.1–1 kHz, and at 5 MHz, respectively.