Guochu Deng

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.

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...

Normal-to-relaxor ferroelectric transformations in lanthanum-modified lead zinc niobate–lead zirconate titanate (PZN–PZT) ceramics

Dielectric permittivities of unpoled and poled lanthanum-modified lead zinc niobate–lead zirconate titanate (PZN–PZT) ceramics were investigated. Results showed that the relaxor characteristics were enhanced with an increase in La doping. Two characteristic temperatures Tnr (normal-to-relaxor transformation) and Trt (rhombohedral-to-tetragonal phase transition) were spontaneously observed in the poled specimens. Tnr and Trt both decreased with increasing La doping content. Temperature-dependent Sawyer–Tower polarization studies revealed a double hysteresis loop near Trt. The presence of the double hysteresis loop and the step in permittivity–temperature curves at Trt might imply a rhombohedral-to-tetragonal phase transition.

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).

Phase diagram for the 0.3Pb(Zn1/3Nb2/3)O3–0.7Pb0.96La0.04 (ZrTi)0.99O3 solid solution in the vicinity of morphotropic phase boundary

The dielectric behaviours of numerous specimens near the morphotropic phase boundary (MPB) of the 0.3Pb(Zn1/3Nb2/3)O3–0.7Pb0.96La0.04 (ZrxTi1 − x)0.99O3 (x = 0.50–0.53) relaxor ferroelectric system were measured. The results revealed that the poled specimens on the rhombohedral side underwent a rhombohedral–tetragonal transition on heating, and the depoled specimens on the tetragonal side experienced a spontaneous relaxor–normal transition on cooling. A phase diagram based on the dielectric permittivity measurements was proposed for this solid solution. The diagram showed that the polarization made the MPB bend sharply towards the rhombohedral-rich region. On the basis of these results in this and previous similar investigations, some common characteristics of complex relaxor ABO3 perovskite systems near the MPB were proposed.

OPTICAL AND PIEZOELECTRIC PROPERTIES OF TRANSPARENT PZN-PLZT CERAMICS

ABSTRACT 0.3Pb(Zn1/3Nb2/3)O3-0.7Pb0.96La0.4(ZrxTi1−x)O3(PZN-PLZT, x = 0.5∼0.53) transparent piezoelectric ceramics with high density and pure perovskite have been synthesized by a two-stage hot-pressing procedure. The bulk densities of the specimens were measured by Archimedes method, and they are very close (> 99%) to the theoretical density. With the Zr/Ti ratios varying from 50/50 to 53/47, the d33 and kp show an ascending and descending trend, namely a peak of piezoelectric properties. The maximum of d33 and kp are 845pC/N and 0.70, respectively. The transmittances of the specimens were tested at the wavelength ranging from 300 nm to 800 nm. The transmittance of the specimens was enhanced with the increase of the wavelength. And the specimens with Zr/Ti = 52.5/47.5 have maximum transmittance. Transparence and high piezoelectric properties of PZN-PLZT brighten its application in optical and electrical devices.

STUDY ON DIELECTRIC AND FERROELECTRIC ANISOTROPY FOR HOT-FORGED PZN-PLZT CERAMICS

ABSTRACT Dielectric and ferroelectric properties of Pb0.88La0.12(Zn1/3Nb2/3)0.3(Zr0.4Ti0.6)0.67O3 ceramics prepared by hot forging method and conventional sintering have been studied. For temperature dependence, the maximum value of dielectric loss measured in the direction perpendicular to the pressing axis was 7 times higher than that measured in the parellel direction and a more broadened dielectric permittivity peak was also observed in the perpendicular direction. Taking into account the fact that no obvious grain orientation was evidenced from the XRD patterns of the compared samples, this anisotropy in dielectric property was attributed to difference in the distribution of stresses and defects in the parallel and perpendicular direction.