Role of potassium ions in humidity sensitivity of K +-β-ferrite

Abstract

Excess K + ions in K +-β-ferrite (K 1.33Fe 11O 17) have been deintercalated by chemical oxidation using iodine, and humidity-sensitive characteristics have been measured for K +-β-ferrites containing different contents of K + ions. Corresponding to the extent of deintercalation, the impedance change with a change in the relative humidity got smaller. The humidity-sensitive characteristics almost disappeared at the fully deintercalated composition of KFe 11O 17, accompanied by a degradation of the response characteristics. The humidity-sensitive characteristics were independent of the amounts of absorbed water. It was deduced that when water vapour was absorbed on the original K +-β-ferrite, the excess K + ions seeped out from the alkali layer to the adsorbed water to increase the ionic conduction due to K + and OH − ions. This model was discussed on the basis of the effects of co-adsorption of weak acids.