POLARIZATION BEHAVIOR OF FERROELECTRIC BI4TI3O12 CERAMICS

The effect of oxidation and reduction atmospheres on the ferroelectric behavior of bismuth titanate was investigated. The effective surface density sigma(eff) of free charges in samples polarized by applying th e electric field E(p) = 1 MVm(-1) at the temperature of 100 degrees C during 90 min was determined by compensation voltage measurements. The thermally treated samples in oxidation atmospheres exhibit a signific ant decrease of sigma(eff) while those treated in a reducing atmospher e exhibit an increase accompanied by the improvement in stability of t he electret charge. Such observations indicate that the formation as w ell as transformation of electret state of Bi4Ti3O12 ceramics may be r elated to the enhancement and diminishing of oxygen vacancies. In all cases homocharge with a time independent sign was obtained.