Electrical Conductivity of Potassium Ferrite with the Beta-Alumina Structure

Abstract

The d-c conductivity of the beta-alumina form of potassium ferrite has been measured in crystals grown from KF flux and in crystals and polycrystalline specimens grown using solid state reactions. Both electronic and ionic conduction was observed. The former depends on the ferrous ion concentration, which can be varied by equilibration with varying partial pressures of oxygen at temperatures above 300°C. Typical conductivities ranging from σ = 1.4 exp(—3570/RT) to 12.3 exp(—2420/RT) ohm−1 cm−1 were observed in specimens containing 0.22 and 1.6% Fe+2, respectively. The electronic and ionic conductivities are comparable at 300°C and Fe2+ ~0.2%; the former becomes dominant at higher ferrous ion concentration and/or low temperature. Transient polarization-type phenomena were observed and tentatively explained by a model based on the coexistence of ionic conduction and electronic conduction due to the presence of Fe2+ and Fe3+ ions. Some observations are reported on the crystallography, existence range, and chemical composition of hexagonal potassium ferrite. © 1969, The Electrochemical Society, Inc. All rights reserved.