Aili Ding

Ferroelectric and piezoelectric properties of (Na, K)0.5Bi0.5TiO3 lead free ceramics

(1 − x)Na0.5Bi0.5TiO3 − xK0.5Bi0.5TiO3 (NKBT100x; x being the mole ratio) piezoelectric ceramics were prepared by a conventional solid reaction method. The microstructure and ferroelectric properties of NKBT100x solid solution ceramics with compositions of Na0.5Bi0.5TiO3 (NBT)-rich and K0.5Bi0.5TiO3 (KBT)-rich were investigated by SEM, XRD, temperature dependence of dielectric constant, and hysteresis loop, respectively. XRD studies showed that the pure perovskite structure existed in NKBT100x ceramics with x ≤ 0.50, while a small amount of a second phase, K4Ti3O8, appeared in the ceramics with x ≥ 0.70 due to the structural instability of KBT-rich ceramics. The grain size decreased with increasing KBT content, showing that the KBT-rich solid solutions were very difficult to densify fully. The temperature dependence of the dielectric constant of NKBT100x ceramics showed that the depolarization temperature (Td) reached a minimum value at the composition of x = 0.16 (NKBT16) near the morphotropic phase boundary, which suggested that the ferroelectric state of co-existence between the rhombohedral phase of NBT and tetragonal phase of KBT were not as stable as the single phase of NBT and KBT, respectively. The poled density NKBT50 (x = 0.50) showed high piezoelectric properties, high Td and low dielectric loss, which was a good candidate for lead free piezoelectric ceramics working at relatively high temperatures.

Evidence for oxygen vacancy inducing spontaneous normal-relaxor transition in complex perovskite ferroelectrics

The relaxor ferroelectrics—0.3Pb(Zn1∕3Nb2∕3)O3–0.7(Pb,La)(Zr,Ti)O3—have been produced by sintering in reductive nitrogen ambient and postannealing in oxygen ambient. The two kinds of specimens exhibited great differences in the conductivity as a function of temperature, which indicated a high concentration of oxygen vacancies in the as-sintered specimen. On the other hand, this specimen underwent an evident spontaneous normal-relaxation transition, whereas the as-annealed one did not. The corresponding reason has been analyzed on the basis of the facts, which provide some evidence that the interior stresses due to oxygen deficiency induce the spontaneous normal-relaxor transition in the specimen sintered in reductive ambient.

Pinning and depinning mechanism of defect dipoles in PMnN–PZT ceramics

The frequency and temperature dependences of the hysteresis loops in Pb[(Zr0.52Ti0.48)0.95(Mn1/3Nb2/3)0.05]O3 ceramics have been investigated. The polarization-field hysteresis curves show ‘pinched’ shapes at room temperature and higher frequencies, whereas they display normal square-like loops at 200uC and frequencies lower than 10 mHz. Critical ferroelectric features such as the coercive field, polarization and internal bias field show a strong frequency or temperature dependence. The close relations between the P –E loops and the applied frequency and temperature indicate that the defect dipolar moment may change its magnitude with variation of the frequency or temperature. Comparing with the intrinsic depinning procedure induced by the changes in the distribution of defect dipoles, we provide new evidence for an extrinsic depinning mechanism of the defect dipoles in the bulk ceramics.

Origin of the giant electro-optic Kerr effect in La-doped 75PMN-25PT transparent ceramics

Transparent ceramics of La-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) x/75/25 are prepared, and the ferroelectric domains, dielectric, and ferroelectric properties of x/75/25 are investigated. A double hysteresis loop and small fingerprint domains with uniform distribution observed for 3/75/25 indicate an intermediate ferroelectric state. The dielectric behavior under dc bias and the evolution of the hysteresis loop with increasing electric field for 3/75/25 indicate an electric field-induced phase transition, and it is proposed that the unstable intermediate ferroelectric state which would experience obvious field-induced phase transition is the origin of the giant electro-optic Kerr effect observed in La-doped PMN-PT 3/75/25.

Characterization of the high-power piezoelectric properties of PMnN-PZT ceramics using constant voltage and pulse drive methods

In this paper we investigate the powder size dependences of the high-power piezoelectric properties in Pb[(Zr0.52Ti0.48)0.95(Mn1/3Nb2/3)0.05]O3 (PMnN–PZT) ceramics using the constant voltage method and the pulse drive technique. It has been demonstrated that coarse powders enlarge the grain sizes of the sintered ceramics and tend to deteriorate the high-power piezoelectric properties. The vibration velocity and temperature rise during vibration are measured with the constant voltage method. Both exhibit good characteristics upon reduction in powder size. For the same sintered ceramics, the mechanical quality factors are estimated at high-power level using the pulse drive method, which can depress the temperature rise during vibration. It is found that the larger vibration velocity originates from the stability of the mechanical quality factor at high-power level. These phenomena may be explained by consideration of both combination of grain boundaries and effect of grain size.

Peculiar Hysteresis Loop of Pb(Mn1/3Nb2/3)O3–Pb(Ti, Zr)O3 Ceramics

The P–E curves of Pb[Zr0.52Ti0.48(Mn1/3Nb2/3)]O3 ceramic with different sintering temperatures and variations of strontium (Sr) compositions have been investigated. It has been demonstrated that the polarization–field hysteresis curves show pinched shapes instead of the normal square-like P–E loops. In this paper we present the temperature dependence of the P–E curves for the ceramic with different firing temperatures and Sr dopants and show that the critical transitional temperature at which disappearance of the pinched shape occurs is highly dependent on the tetragonality (c/a ratio). In the meantime, the peculiar hysteresis loops are assumed to be the result of the pinning effect of the defect dipoles, which are slowly oriented antiparallel to the poling direction, and are finally broken down by the thermal activation.

Ferroelectricity of a hemicyanine dye in ultrathin organized molecular films: hysteresis and pyroelectric effects

Pyroelectricity of the optical nonlinear hemicyanine dye in organized molecular films has been demonstrated by using the electric polarization and second harmonic generation measurements. The typical hysteresis loop of the samples confirmed existence of the remnant polarization of hemicyanine molecules which is 600 μCu200am−2. The pyroelectric coefficient of hemicyanine was found to be 12 μCu200am−2u200aK−1 at room temperature and enhanced with increasing temperature monotonically which was well explained by using a molecular dipole reorientation model.

Martensitelike spontaneous relaxor-normal ferroelectric transformation in Pb(Zn1∕3Nb2∕3)O3–PbLa(ZrTi)O3 system

The spontaneous relaxor-normal ferroelectric transformation was found in the tetragonal composition of Pb(Zn1∕3Nb2∕3)O3–PbLa(ZrTi)O3 (0.3PZN–0.7PLZT) complex ABO3 system. The corresponding dielectric permittivities and losses of different compositions located near the morphotrophic phase boundary were analyzed. By reviewing all of the results about this type of transformation in previous references, the electric, compositional, structural, and thermodynamic characteristics of the spontaneous relaxor-normal transformation were proposed. Additionally, the adaptive phase model for martensite transformation proposed by Khachaturyan et al. [Phys. Rev. B 43, 10832 (1991)] was introduced into this ferroelectric transformation to explain the unique transformation pathway and associated features such as the tweedlike domain patterns and the dielectric dispersion under the critical transition temperature. Due to the critical compositions near the MPB, the ferroelectric materials just fulfill the condition, in which...

LOCAL ELASTICITY RESPONSE IN FERROELECTRIC CRYSTALS STUDIED BY AFM-BASED NOVEL PROBE TECHNIQUES

ABSTRACT A novel probe technique, low frequency scanning probe acoustic microscope, was firstly developed based on the commercial atomic force microscope. The excitation frequency is in the range of several kHz up to teen-kHz, which is much lower than that in the conventional acoustic microscopes. The acoustic images of nanoscale domain structures in Pb(Mg1/3Nb2/3)O3-33%PbTiO3 single crystals were successfully visualized. Different electric polarizations show the variation of the elasticity in ferroelectrics, so the contrast of the acoustic images reflects the domain structure or the subsurface elasticity. In addition, the elasticity of the sample in response to the modulation of the excitation source is also discussed.

DIELECTRIC AND PIEZOELECTRIC PROPERTIES OF PZN-PZT CERAMICS WITH NEODYMIUM DOPING

ABSTRACT The structure and electrical properties of Pb(Zn1/3Nb2/3)0.3(Zr0.55Ti0.45)0.7O3-xNd ceramics system with the composition near to the morphotropic phase boundary (MPB) were investigated as a function of Nd doping content. PZN-PZT specimens shifted from rhombohedral phase towards tetragonal phase with increasing Nd doping. Dielectric spectroscopy exhibited that Nd doping increased dielectric permittivity and the degree of diffuse phase transition (DPT) with lower ferroelectric phase transition temperature. The P-E curves showed that Nd doping decreased coercive field (Ec) and the remnant polarization (Pr).