A giant electric-field-induced strain of 0.87% is reported for tetragonal (Bi0.5Na0.5)TiO3-(Bi0.5K0.5)TiO3-BaTiO3 single crystals along the [100]cubic direction, which is six times as large as that of Pb(Zr0.52Ti0.48)O3 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.
Single crystals of ferroelectric K0.5Bi4.5Ti4O15 with a Bi-layered structure were grown by the flux method, and the properties of polarization hysteresis, piezoelectric strain, and leakage current were investigated along the polar a axis at 25°C. K0.5Bi4.5Ti4O15 crystals exhibited a large remanent polarization of 31μC∕cm2, which suggests that K0.5Bi4.5Ti4O15 has the largest spontaneous polarization among Bi layer-structured ferroelectrics with four TiO6 layers in the perovskite blocks. Strain measurements showed that the piezoelectric strain constant was 31pm∕V.
Influences of high-oxygen-pressure (350 MPa) annealing on the properties of leakage current, polarization, and strain were investigated for single crystals of (Bi0.5Na0.5)TiO3-(Bi0.5K0.5)TiO3-BaTiO3 with P4mm tetragonal structure The oxygen annealing led to a marked increase in leakage current, showing that the oxidized crystals have a high concentration of electron hole (carrier) and a low concentration of oxygen vacancy compared with the crystals annealed in air. While the air-annealed crystals exhibited a giant strain up to 0.8% at an electric field of 40 kV/cm, the oxidized crystals showed a small strain less than 0.3%. The results can be explained by the interaction between ferroelectric domains and charged defects.
0.999Bi0.5Na0.5TiO3-0.001BaTiO3 (BNT-0.1%BT) single crystals with a maximum size of 1×1×1
mm3 were successfully grown by a flux method using BNT-6%BT powder and Bi2O3 as a flux. The
crystals showed a remanent polarization of 33 μC/cm2 and coercive electric field of 40 kV/cm along
[100]Cubic. Electric-field induced strain measurements along [100]Cubic revealed an effective
piezoelectric strain constant d33
* of 80 pm/V.
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