Electrical conductivity and epr investigations in iron doped polycrystalline K 2Ti 4O 9

Abstract

D.C. electrical conductivity studies are reported in K 2Ti 4O 9 and its iron doped derivatives in the temperature range from 370 to 750 K. Three distinct regions were identified in the log (σ T) vs 1000 T plots. The lowest temperature region I is attributed to free vacancy conduction or electronic hopping conduction through Ti-Ti chains, when the interlayers are blocked. The intermediate region II is assigned to associated ionic conduction through contracted interlayer space and the next region III to unassociated ionic conduction. Furthermore, anomalous peaks in the conductivity plot exist due to hydroxylated cations, the trapping of water groups being activated by iron substitution and hydroxylation stabilized through hydrogen bonding. For the sample with maximum doping, three anomalous peaks were identified in the conductivity plot and explained to be due to water molecules sitting at three different sites in the lattice. The EPR investigations indicate that the iron ions occupy Ti 4+ sites for lower percentages of doping and attain the 3 d 4 configuration (Fe 4+) with an FeO 4 tetrahedral arrangement. For increased doping, the substitution of iron ions occurs as Fe 3+ for interlayer K + ions. The EPR results correlate well with the conductivity data.