Polarization behavior of ferroelectric Bi/sub 4/Ti/sub 3/O/sub 12/ ceramics

The effect of oxidation and reduction atmospheres on the ferroelectric behavior of bismuth titanate was investigated. The effective surface density /spl sigma//sub eff/ of free charges in samples polarized by applying an electric field E/sub p/=1 MV m/sup -1/ at a temperature of 100/spl deg/C for 90 min was determined by compensation voltage measurements. The thermally treated samples in oxidation atmospheres exhibit a significant decrease of /spl sigma//sub eff/ while those treated in a reducing atmosphere exhibit an increase accompanied by an improvement in the stability of the electret charge. Such observations indicate that the formation as well as the transformation of the electret state of Bi/sub 4/Ti/sub 3/O/sub 12/ ceramics may be related to the enhancement and diminishing of oxygen vacancies. In all cases homocharge with a time independent sign was obtained.