Y. N. Wang

Doping effect on the dielectric property in bismuth titanate

The dielectric property complemented by the mechanical measurement (internal friction) in the doped Bi4Ti3O12 [Bi4−xLaxTi3O12 (x=0.5,0.75,1) and Bi4−y/3Ti3−yNbyO12 (y=0.015,0.03,0.06)] was systematically investigated from room temperature to 350 °C. In the plot of dielectric loss versus temperature for Bi4Ti3O12 (BiT), a relaxation peak was confirmed to be associated with the motion of the oxygen vacancy. It is found that the La doping at site A is in favor of improvement of the fatigue property, in contrast, the Nb doping at site B can mainly enhance the remanent polarization. Appropriate La doping at site A of perovskite-type unit in BiT enhances the chemical stability of oxygen vacancy by improving the height of the potential barrier for hopping and enhances the mobility of domain by the changing of domain structures. While the Nb doping at site B could induce the distortion of oxygen octahedral and reduce the oxygen vacancy concentration by a compensating effect so that it results in an enhancement of...

Why lanthanum-substituted bismuth titanate becomes fatigue free in a ferroelectric capacitor with platinum electrodes

Bi4Ti3O12, (BTO) a Bi-layered perovskite oxide, shows fatigue after repeated ferroelectric polarization reversals. On the other hand, Bi3.25La0.75Ti3O12 (BLT) is fatigue free. From an extensive transmission electron microscopy study, it was found that there is a high density of antiphase boundaries (APBs) in BLT like in the fatigue-free SrBi2Ta2O9 but not in BTO. It is proposed that the existence of APBs possibly plays a key role in the fatigue-free behavior of Bi-layered perovskite oxides.

Resonance magnetoelectric effect in bulk composites of lead zirconate titanate and nickel ferrite

Magnetoelectric (ME) Pb(Zr0.52Ti0.48)O3 (PZT)–NiFe2O4 bulk composites with various PZT volume fractions were prepared. The ME coupling coefficient, impedance, and flux density versus the frequency were measured. The magnetic bias and PZT volume fraction in the composites are investigated to optimize the ME output. It is revealed that ME resonances are caused by electromechanical resonance in the piezoelectric phase and magnetomechanical resonance in the magnetostrictive phase. Maximum magnetoelectric voltage coefficient resonance values of 6.7 V/cm Oe at 132.6 kHz and 6.12 V/cm Oe at 427.2 kHz for the composite with optimized PZT volume fraction of 0.55 were obtained at optimized magnetic bias of 0.6 kOe.

PREPARATION OF LA-DOPED BIFEO3 THIN FILMS WITH FE2+ IONS ON SI SUBSTRATES

La-doped BiFeO3 thin films with Fe2+ ions have been prepared on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition in order to enhance the ferroelectric and magnetic properties. The targets for the film deposition were synthesized using a rapid liquid phase sintering technique to ensure the low leakage. The dielectric properties at room temperature and above were investigated. It was observed that the La doping greatly enhances the ferroelectric polarization at room temperature by modifying the film structure from rhombohedral to monoclinic. The saturation magnetization was enhanced about two times due to the Fe2+ ions in the thin films

Trapping light by mimicking gravitational lensing

We propose a distorted optical waveguide around a microsphere to mimic curved spacetimes caused by the “gravitational fields”. Gravitational lensing effects analogues are experimentally demonstrated and this can be used to prospective light harvesting.

Fatigue characteristics of SrBi2Ta2O9 thin films prepared by metalorganic decomposition

Polycrystalline SrBi2Ta2O9 (SBT) ferroelectric thin films were synthesized on Pt/Ti/SiO2/Si substrates by metalorganic decomposition. Electric measurements demonstrate that fatigue increases with decreasing switching voltage and frequency, and the suppressed polarization caused at a lower switching voltage can be recovered by switching at a higher voltage. This suggests that the domain walls of SBT thin films are weakly pinned and easily depinned by a higher external field. The polarization of SBT thin films annealed in air shows more degradation than that annealed in oxygen, which indicates that the oxygen vacancy also plays an important role in fatigue behavior of SBT thin films.

Optical study on the size effects in BaTiO3 thin films

To study the size effects in ferroelectric thin film, we measured the optical transmittance and Raman spectra in BaTiO3 thin films deposited by the rf-magnetron sputtering technique on fused quartz and (111) Si substrates. A variation in the energy gap and Raman peaks with film thickness and grain size was observed and the possible origin was analyzed.

Enhanced chilling tolerance in Zoysia matrella by pre-treatment with salicylic acid, calcium chloride, hydrogen peroxide or 6-benzylaminopurine

Following leaf application of salicylic acid (SA), calcium chloride, hydrogen peroxide and 6-benzylaminopurine (BA), Manila grass (Zoysia matrella) plants were exposed to day/night temperature of 7/2 °C for 120 h in a growth chamber. The lower content of malondialdehyde (MDA) and H2O2 and higher activities of ascorbate peroxidase (APX), guaiacol peroxidase (POD) and catalase (CAT) during exposure to low temperature in pre-treated plants in comparison with control plants demonstrated that these compounds improved the chilling tolerance of Manila grass.

Enhanced fatigue-endurance of ferroelectric Pb1−xSrx(Zr0.52Ti0.48)O3 thin films prepared by sol-gel method

The polarization fatigue behaviors of ferroelectric Pb1-xSrx(Zr0.52Ti0.48)O-3 (PSZT) thin films deposited on Pt-coated silicon wafers are investigated. Significantly enhanced fatigue endurance with increasing Sr doping and decreasing temperature is observed, and the almost fatigue-free performance up to 10(10) switching cycles for PSZT (x=0.2) thin films at room temperature is identified. The dc-conductivity measurements suggest almost 20 times decreasing of the oxygen vacancy density as the Sr doping increases from x=0 to x=0.2. It is believed that the Sr-doping enhances the stability of oxygen ions and suppresses oxygen vacancies, consequently resulting in the improved fatigue endurance. (c) 2006 American Institute of Physics.

Magnetoelectric resonance-bandwidth broadening of Terfenol-D/epoxy-Pb(Zr,Ti)O3 bilayers in parallel and series connections

The bandwidth of magnetoelectric (ME) resonance for a combined structure where several Terfenol-D/epoxy-Pb(Zr,Ti)O3 bilayers are connected in parallel and series was measured. A relationship between the bilayer length and resonance frequency was used to design the combined structure, in which the bilayered components of different lengths were connected in the parallel and series forms, respectively. The measured giant ME effect of the combined structure showed a much wider frequency response to external field than a single bilayered structure, and the ME effect far from the resonance ranges was enhanced significantly too. A qualitative analysis based on the equivalent circuit concept was presented to explain these effects.