Potassium Ion Conduction in Potassium Beta Ferrites

Abstract

Potassium Ion Conduction in Potassium Beta Ferrites Takehiko TAKAHASHI, Katsumi KUWABARA and Yuji KASE Department of Applied Chemistry, Faculty of Engineering, Nagoya University; Nagoya-shi 464 Japan Potassium ion conduction in beta-alumina type potassium beta-ferrites was investigated. Dense products were obtained by prefiring K2CO^3-Fe2O^2- mixtures at 950°C for 10 hr and sintering them at 1350-1450°C for 1-3 hr. Cylindrical specimens of about 7 mm in diameter and 5-15 mm long were cut from the sintered bodies. Using A. C. impedance bridge at 10 kHz, the conductivities were measured in the range from room temperature to 500°C. Electronic and ionic conductions were examined by the use of D. C. polarization method and electrolysis, respectively. The sintered polycrystal having the composition of Fe2O^2-/K20 =6.0 was revealed to be a mixed conductor responsible for ca.1-2% ionic conduction and predominantly electronic one due to hopping of electrons between iron (II) and iron (ll) ions. Total conductivity of the specimen was 1 X 10° mho m^-1 at 300°C and the potassium ion conductivity was 1.5x 10-2 mho cm^-1 at the same temperature. In order to keep ionic conduction and to reduce electronic conduction, three oxides, such as ZnO, MgO or NiO, were doped in terms of the formula K20. (6x) Fe2O^2- MO (x = 0-1.0). Both total conductivity and rate of electronic conduction decreased with increasing x, and the potassium ion conductivities of the samples doped with ZnO (x =O.8), MgO (x = O.8) and NiO (x=1.0) were 1.8x 10-2, 5. Ox 10-3 and 3.5x 10-3 mho cm-' at 300°C, respectively, and electronic conduction became negligibly small. MO doping in terms of the above formula would be supposed to have the lowering effects on the concentra- tion of total iron and that of iron (II) ion in potassium beta-ferrites.