Correlation Between Domain Structures and Dielectric Properties in Single Crystals of Ferroelectric Solid Solutions

Abstract

In the present chapter, the growth of single crystals in relaxor–PbTiO₃ (PT) solid solution system by the flux method and the solution Bridgman method, the observation of domain wall structures under an electric field, optical birefringence, and the correlation between the domain structure and the permittivity are described. By the flux method and the solution Bridgman method, high-quality PIN–PT single crystals with a composition near the morphotropic phase boundary (MPB) with a high Curie temperature have been grown. In a (100) plate of a 0.72PIN–0.28PT single crystal with a composition near the MPB, complex domain structures were observed under no bias field, where coexistence of the rhombohedral and tetragonal phases was found. It was found from observations of the domain structure under a dc electric field that a field-induced R-to-T phase transition starts to take place abruptly in the (110) planes at about 6 kV/cm. The phase boundary between the R and T phases along a (110) plane moves in such a way that the T region expands at the expense of the R region, and the R and T phases coexist in a dc field range from 6 kV/cm to 12 kV/cm. The temperature dependence of the birefringence of 0.72PIN–0.28PT is also presented. It was found in the crystal system (1–x)PMN–xPT that the field dependence of the dielectric constant (E < 25 kV/cm) in crystals with x=0.06 and 0.1 is reversible, while in a crystal x=0.15 it is not reversible. Observation of domain structures and simultaneous permittivity measurement was performed on a (001) plate of a 0.85PMN–0.15PT crystal under various dc electric fields E. It was found that the dielectric constant decreases abruptly as the ferroelectric domain wall structure grows under a biasing field of about 1.6 kV/cm.