Liaoying Zheng

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.

Microstructure and Electrical Properties of Tungsten-Doped Bismuth Titanate Ceramics

Bismuth-layer-structured Bi4Ti3-xWxO12+x (BiTW) ceramics, where x=0, 0.02, 0.04, 0.08, 0.10 and 0.20, have been prepared by a conventional sintering technique. The conducting, dielectric and ferroelectric properties of BiTW were investigated. The microstructure results revealed randomly oriented grains with a needle structure, and the grain size decreased gradually with increasing W6+ doping content. The conducting properties were studied in a direct-current circuit at various temperatures. W6+ donor doping enhanced the electrical resistivity markedly above 108 Ωcm at 400°C on the whole. BiTW with suitable W6+ replacement showed good temperature stability from the temperature dependence of dielectric constant. Tc decreased gradually with W doping. Ferroelectric hysteresis loops were also determined for various x values. Excellent properties could be found at x=0.04, i.e., the composition Bi4Ti2.96W0.04O12.04, which possessed a high electrical resistivity and a good temperature stability of dielectric properties than other composition materials.

Synthesis of novel core-shell nanocomposites for fabricating high breakdown voltage ZnO varistors

A novel varistor-composite synthesis for the fabrication of high breakdown voltage ZnO varistors has been successfully developed. It involves coating ZnO nanoparticles with SiO2 through the hydrolysis of tetraethyl orthosilicate (TEOS) and the subsequent coating of additives on the core of the SiO2-coated ZnO particles, producing a double core-shell structure. The effect of the amount of TEOS used on the morphology of the synthesized composites and the microstructure, as well as the electrical property of the sintered samples from the double core-shell composites are fully studied. Such materials, with the appropriate amount of TEOS added (Si4+/Zn2+ = 0.15 moles) enables the superior electrical performance of ZnO varistors: high breakdown voltage (VB = 1123 V mm−1), excellent nonlinear coefficient (α = 42.5) and low leakage current (IL = 8.5 μA), compared with current commercial varistors and the sample from single core-shell composites. The high performance is attributed to the smaller ZnO grain size and perfect additive homogeneity. The SiO2-coating provides a better way to control the varistor microstructure through the formation of a nearly circular distribution of blocky Zn2SiO4 around the ZnO grains.

Manufacture of epoxy-silica nanoparticle composites and characterisation of their dielectric behaviour

Nanoparticles as fillers for epoxy composites sometimes result in unexpected dielectric properties. This paper presents a study on the dielectric properties of E-51 epoxy resin incorporated with surface modified 20 and 100 nm silica particles, respectively. The nanoparticles and composites were examined under infrared spectroscopy and it was found that the surface modification of the nanoparticles lead to a good hydrophobic property and made particles easier to form bonds with the resin. Extensive experiments were performed on the dielectric properties of the composites and the results and analysed. It was found that by adding low dielectric constant nanosilica particles, the dielectric constants of the composite were notably increased as opposed to a drop as one might expect, while the dielectric losses were lowered. The increase in dielectric constant phenomenon is explained in terms of long chemical chains created in forming the composites. It was also found that the high dielectric constant phenomenon is relevant to higher surface area of the nanofillers.

Observation of an unusual optical switching effect in relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3-Pb(Zr0.53,Ti0.47)O3 transparent ceramics

We present an unusual optical switching effect in relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3-Pb(Zr0.53,Ti0.47)O3 transparent ceramics under strong AC electric fields, which is accompanied by a peculiar dielectric response rarely reported previously and attributed to the disruption of the ferroelectric domain structure by the strong AC field. The results provide further understanding on the domain behaviors under electric fields of the relaxor ferroelectrics and the potential for advancing electro-optic applications.

Phase transition behaviour and enhanced electromechanical properties in Sr modified 0.65PbMg1/3Nb2/3O3–0.35PbTiO3 ceramics

The phase transition behaviour and its effect on the electromechanical properties of 0.65Pb1−xSrx(Mg1/3Nb2/3)O3–0.35PbTiO3 ceramics with 0 ≤ x ≤ 0.08 were investigated. A morphotropic phase boundary between tetragonal and rhombohedral phases was revealed by XRD results in compositions with 0.02 ≤ x ≤ 0.06. An electric field induced monoclinic–tetragonal phase transition was determined by dielectric constant and elastic constant measurements. Enhanced electromechanical properties were obtained by shifting the electrical field induced phase transition to room temperature. An optimal performance corresponding to d33 = 706 pC N−1 and kp = 0.587 was obtained for the composition with x = 0.02.

The unique dielectric behaviour of nanosilica epoxy composites

Nanofillers in epoxy composites sometimes results in unexpected properties. Presented in this paper are some findings on the dielectric properties of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin incorporated with surface modified nanosilica particles. 20 nm particles were used in the investigation and the results were compared with those of 100 nm silica composite. The composites were examined under infrared spectroscopy and XRD and it was found that the surface modification of the nanoparticles lead to a good hydrophobic property and made particles easier to form bonds with the resin. The measurements of the dielectric properties of the composites showed that by adding low dielectric constant nanosilica particles, the dielectric constants of the composite were notably increased as opposed to a drop as one might expect, while the dielectric losses were lowered. The increase phenomenon in dielectric constant is explained in terms of water molecules existence in the composites produced during the process.

Abnormal electric-field-induced light scattering in Pb(Mg1/3Nb2/3)O3-PbTiO3 transparent ceramics

We present a strong electric-field-induced light scattering phenomenon in relaxor ferroelectrics 75Pb(Mg1/3Nb2/3)-25PbTiO3 transparent ceramics under a weak threshold electric field, which is attributed to the abrupt growth of polar nanoregions above the threshold field with a significant change of local crystal symmetry, dielectric, and Raman response. These results provide further understanding on the electric field-induced domain behaviors and peculiar properties in relaxor ferroelectrics.

Large and temperature-independent piezoelectric response in Pb(Mg1/3Nb2/3)O3-BaTiO3-PbTiO3

The temperature dependence of elastic, dielectric, and piezoelectric properties of (65-x)[Pb(Mg1/3Nb2/3)O3]–xBaTiO3-35PbTiO3 ceramics with x=0, 1, 2, 3, and 4 was investigated. Compound with x=2 was found to exhibit a large piezoelectric response (d31=170 pC/N, d33=530 pC/N at 300 K). Particularly, its d31 value was nearly a constant over a temperature range from 185 to 360 K. A broad ferroelectric phase transition tuned by BaTiO3 doping was deduced from the dielectric constant, elastic compliance constant, and Raman spectra. The temperature-stable piezoelectric response was attributed to the counter-balance of contributions from the dielectric and elastic responses.

Contribution to the large and stable electric field induced strain for textured Pb(Mg1/3Nb2/3)0.675Ti0.325O3 ceramics

Textured Pb(Mg1/3Nb2/3)0.675Ti0.325O3 (PMN-PT) ceramics were prepared by the templated grain growth method with 3% plate-like BaTiO3 as templates. The degree of grain orientation was about 81% by calculating from the XRD pattern. Temperature dependence of electric field induced strain was measured for both untextured and textured PMN-PT ceramics. The results show that the electric field induced strain for textured PMN-PT ceramics is much larger and more stable than that for untextured PMN-PT ceramics in a wide temperature range. The contribution from the piezoelectric effect and electrostrictive effect to the strain was analyzed, and it was found that textured PMN-PT ceramics exhibited electrostrictive coefficient Q33 as high as 5.19 × 10−2 m4 C−2 and it was comparable to that of PMN-PT single crystals. The electrostrictive effect contributed the main part of the enhancement of electric field induced strain for textured PMN-PT ceramics.