CRYSTAL CHEMICAL STUDY ON 90°DOMAIN SWITCHING PEROVSKITE TYPE FERROELECTRICS

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There are two domain structures, 180 degree domains and 90 degree domains, in tetragonal perovskite type ferroelectrics. The 90 degree domains can be reorientated by an external electric field. The 90 degree domain reorientation induces the changes in strain and polarization, therefore, it is very important to understand the behavior of the reorientation for practical application of ferroelectric materials. This study was carried out for the purpose of understanding crystal chemical characters dominating the 90 degree domain- reorientation behaviors in lead titanate (PT)-based materials and lead titanate-lead zirconate solid solutions (PZT).The relationship between the crystal structures and properties was investigated for (Pb, R)TiOィイD23ィエD2(R=Ca, Sr, Ba) ceramics with different tetragonarity (c/a ratio). It was found that the coercive field which determines the easiness of the domain-reorientation depended on the c/a ratio, while the spontaneous polarization was depended on the alkali earth elements incorporated into PT. The (Pb,Sr)TiOィイD23ィエD2 showed the largest spontaneous polarization in the three specimens with c/a ratio = 1.03. In order to understand the origin of the difference in the spontaneous polarization, the crystal structure analysis was carried out using the Rietveld method. The result of analysis indicated that the displacement of Ti ion from the ideal position of cubic perovskite structure was largest in (Pb, Sr)TiOィイD23ィエD2, which explained the large spontaneous polarization.The dynamic behavior of the 90 degree domain-reorientation in PZT ceramics was investigated from the measurement of the frequency dependence of electric field induced strains using a Mach-Zehnder type laser interferometer. It was found that the reorientation had a velocity limit and a piezoelectric relaxation was observed at ca. 10kHz. This method gave the information of the contribution of 90 degree domain reorientation to the piezoelectric strains.