FERROELECTRIC BEHAVIORS DOMINATED BY MOBILE AND RANDOMLY QUENCHED IMPURITIES IN MODIFIED LEAD-ZIRCONATE-TITANATE CERAMICS

A comparative study of the influence of both mobile and randomly quenc hed impurities and their associated defect complexes on ferroelectric phase transformations in lead zirconate titanate ceramics has been per formed 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 comple xes in the temperature range near and below the phase transformation. Impurities-defects which are mobile until temperatures below the trans formation are believed to preferentially locate near domain boundaries , resulting in polarization pinning. For these compositions, no eviden ce of relaxor ferroelectric behaviour was observed. However, for the c ompositions whose impurities-defects were essentially immobile from te mperatures above the ferroelectric phase transformation, relaxor behav iour and polar nanodomains were found. Studies of the influence of ele ctrical and thermal histories on properties provided additional insigh ts into the influence of impurity-defect mobility. Internal dipolar fi elds were evidenced by strong asymmetries in the polarization electric field behaviours for materials containing mobile impurities which bec ame quenched on cooling within the ferroelectric phase. A model is pro posed to explain domain evolution in systems containing randomly quenc hed or mobile impurities and defects.