SURFACE-LAYER ON KNBO3 AND THE HYSTERESIS LOOP ANOMALY

An anomaly in the hysteresis loop of the polarisation of KNbO3 is obse rved at low frequencies. This gives a value for the remanent polarisat ion which is an order of magnitude larger than that in the frequency r egime of traditional measurements. We correlate this observation with the specific properties of the surfaces of ABO(3)-type perovskites. Su rface analytical methods are used to characterise the structure of ele ctrochemically induced surface layers of KNbO3. We find that the chemi cal composition, together with the crystallographic structure of the s urface, differs drastically from the crystal bulk. In particular we ob serve a network of extended defects which serves as a fast diffusion p ath for oxygen and potassium and allows special segregation and redox processes.