A giant electric-field-induced strain of 0.87% is reported for tetragonal $\left({\mathrm{Bi}}_{0.5}{\mathrm{Na}}_{0.5}\right)\mathrm{Ti}{\mathrm{O}}_3\text{-}\left({\mathrm{Bi}}_{0.5}{\mathrm{K}}_{0.5}\right)\mathrm{Ti}{\mathrm{O}}_3\text{-}\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3$ single crystals along the ${\left[100\right]}_{\text{cubic}}$ direction, which is six times as large as that of $\mathrm{Pb}\left({\mathrm{Zr}}_{0.52}{\mathrm{Ti}}_{0.48}\right){\mathrm{O}}_3$ ceramics. In situ x-ray diffraction measurements and transmission electron microscope observations show that the giant strain mainly originates from switching of nanosized 90° domains. Strain measurements indicate that the strain caused by the 90° domain switching is reversible for both unipolar and bipolar electric-field applications. The reversibility of the 90° domain switching can be explained by the interaction between the spontaneous polarization and the defect dipole composed of $A$ -site vacancy and oxygen vacancy.

The piezoelectric, ferroelectric and dielectric properties of Nd-modified Bi₃TiTaO₉ (Bi_3-xNd_xTiTaO₉, BNTT-x) (0 ≤x ≤0.75) and La-modified Bi₃TiTaO₉ (Bi_3-xLa_xTiTaO₉, BLTT-x) (0 ≤x ≤1.00) ceramics were investigated and compared. The specimens were fabricated by a conventional ceramic fabrication technique. BNTT-0.50 and BLTT-0.25 ceramics showed the highest coercive field, E_c, of approximately 150 kV/cm in the BNTT and BLTT systems, respectively. Furthermore, BNTT-0.50 and BLTT-0.25 ceramics also showed the highest mechanical quality factor, Q_m, of approximately 11000 in the BNTT and BLTT systems at the (33)-mode, respectively. On the basis of result of this study, it was found that both BNTT-0.50 and BLTT-0.25 are high-Q_m material.

We have investigated ferroelectric domain structures in the pseudo-cubic structure of (1-x)BiFeO₃-xBaTiO₃ with 0.33 < x < 0.50 by the transmission electron microscopy (TEM). High-resolution lattice image reveals that the psudo-cubic structures in the x = 0.33, 0.40 and 0.50 compounds are characterized as nano-scaled coexisting state of the polar rhombohedral structure and the non-polar cubic one. Furthermore, P-E hysteresis curve measurements showed that the x = 0.33, 0.40 and 0.50 compounds are regarded as ferroelectric materials with the spontaneous polarizations of 41 μC/cm², 21 μC/cm², and 5 μC/cm², respectively.

The crystal structures and dielectric, polarization, and piezoelectric properties of high-density $x\left({\text{Bi}}_{0.5}{\text{K}}_{0.5}\right){\text{TiO}}_3–\left(1-x\right){\text{BiFeO}}_3$ ceramics were investigated. The results obtained using x-ray and neutron powder diffractions and transmission electron microscopy showed that a morphotropic phase boundary between the rhombohedral (ferroelectric) and pseudocubic (ferroelectric) phases is present in $0.4<x<0.43$ . Ceramics with $x=0.4$ exhibited a large remanent polarization of $52\mu \text{C}/{\text{cm}}^2$ at $25°\text{C}$ and their piezoelectric properties were maintained up to $300°\text{C}$ . It is suggested that the presence of nanosized domains with a polar rhombohedral structure observed for $x=0.4$ is the origin of relaxor-like dielectric properties.

We have investigated the effects of high-oxygen-pressure crystal growth of ferroelectric ${\mathrm{Bi}}_4{\mathrm{Ti}}_3{\mathrm{O}}_{12}$ on the polarization properties along the $\mathit{a}\left(\mathit{b}\right)$ axis. Domain observations by piezoresponse force microscope demonstrate that a small remanent polarization $\left(P_r\right)$ for the crystals grown at $0.02\mathrm{MPa}$ is attributed to the clamping of 90° domain walls by oxygen vacancies. The vacancy formation of Bi and O during crystal growth at high temperatures is suppressed at a higher oxygen pressure, leading to a larger $P_r$ of $47\mu \mathrm{C}∕{\mathrm{cm}}^2$ for the crystals grown at $1\mathrm{MPa}$ oxygen. High-oxygen-pressure sintering is proposed to be effective for obtaining ${\mathrm{Bi}}_4{\mathrm{Ti}}_3{\mathrm{O}}_{12}$ -based devices with enhanced polarization properties.