Ferroelectric behaviours dominated by mobile and randomly quenched impurities in modified lead zirconate titanate ceramics

A comparative study of the influence of both mobile and randomly quenched impurities and their associated defect complexes on ferroelectric phase transformations in lead zirconate titanate ceramics has been performed by dielectric spectroscopy and transmission electron microscopy. These investigations have shown a strong dependence of the structure-property relations on the mobility of impurities and/or defect complexes in the temperature range near and below the phase transformation. Impurities-defects which are mobile until temperatures below the transformation are believed to preferentially locate near domain boundaries, resulting in polarization pinning. For these compositions, no evidence of relaxor ferroelectric behaviour was observed. However, for the compositions whose impurities-defects were essentially immobile from temperatures above the ferroelectric phase transformation, relaxor behaviour and polar nanodomains were found. Studies of the influence of electrical and thermal histories on properties provided additional insights into the influence of impurity-defect mobility. Internal dipolar fields were evidenced by strong asymmetries in the polarization electric field behaviours for materials containing mobile impurities which became quenched on cooling within the ferroelectric phase. A model is proposed to explain domain evolution in systems containing randomly quenched or mobile impurities and defects.