Papers by Author: Xiao Hui Wang

Abstract: Nanocrystalline lead zirconate titanate (PZT) powders with composition at the morphotropic phase boundary (MPB) were synthesized by a simple aqueous based sol-gel method, using lead nitrate, zirconium nitrate and tetrabutyl titanate as the starting materials. The sol could be easily transformed into gel, firstly heated at 120°C for 10h, then at 180°C for 24h. The thermal decomposition process of the gel was investigated by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. The effect of citrate addition amount on the calcining temperature was discussed. The results reveal that pure perovskite phase PZT powders can be obtained at a calcining temperature as low as 600°C. The average grain size of the powders was determined by transmission electron microscope and X-ray diffraction. The influences of calcining temperature and the pH value of the solution on the grain size were investigated. The sintering temperature and electrical properties of the ceramics derived by nano-powders were compared with those prepared by the conventional ceramic processing. The result shows that using the nanopowder, the sintering temperature could be reduced by about 100°C and the ferroelectric properties were enhanced.

Abstract: In this paper, a typical Li- and Ta/Sb- modified alkaline niobate-based ceramics are prepared by conventional sintering and two-step sintering respectively. The ceramics sintered by two-step sintering exhibit better electrical properties than the samples prepared by conventional sintering. The related mechanisms are also discussed in terms of phase-structures and microstructures. Results show that two-step sintering can restrain the volatilization of alkali elements and compositional segregation during the process of sintering dense alkaline niobate-based ceramics, and enhance the electrical properties accordingly. Therefore, two-step sintering is a promising approach to achieve high performance alkaline niobate-based ceramics.

Abstract: Dispersion plays an important role in aqueous chemical coating process for the preparation of BaTiO3 based next generation BME MLCC powder, since it affects coating coverage and layer morphology of the BaTiO3 particles as well as the microstructure and dielectric properties of the ceramics. In this paper, Poly (acrylic acid-co-maleic acid) (PAM) is used as dispersant, its content influences are carefully investigated. It is known that low content of dispersant leads to not only poor dispersion, low coverage and irregular coating layer of BaTiO3 particles, but also bad temperature coefficient of capacitances and inhomogeneous microstructure of the resultant BaTiO3 ceramics, while excessive dispersant deteriorates the microstructure and performance by reducing the density of ceramic. With proper dispersant content, the particles are dispersed and coated perfectly, finally the dense X7R-satisfied ceramic are obtained with average grain size 103nm and fine microstructure, meeting the requirement of next generation MLCCs.

Abstract: Highly ordered ZrO2 nanotube (NT) arrays were fabricated by anodization in organic electrolyte containing NH4F. The NTs have an opened porous structure at the top end. A facile electro-deposition technique was used to prepare ZnO quantum dots (QDs) in the pores of the ZrO2 NTs. Characterizations of SEM, XRD, HR-TEM were performed on the NTs. The results confirmed the formation of single-phase wurtzite ZnO nanoparticles in the ZrO2 NTs with a size around 20 nm. Photoluminescence (PL) spectra proved that the ZnO QDs coating had strongly enhanced the PL signal for blue (366nm) and green (503nm) light emissions of the hybrid NT arrays. That maybe arose from structure-dependent defects and oxygen vacancy in the hybrid layers.

Abstract: A convenient one-step solvothermal method has been developed to synthesize monodispersed barium titanate nanocrystals with an average size of 5 nm. The key point of this method is the controlling of hydrolysis of Ti (OC₄H₉)₄ with Diethylene glycol (DEG). The as-prepared BaTiO₃ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), FT-IR and TG/DTA analysis. The monodispersed BaTiO₃ nanoparticles obtained by this method have an average size of 5 nm with a narrow size distribution and a lattice tetragonality of 1.0069, which is promising for the ferroelectric science and its industry application.

Abstract: A solvothermal method to synthesize barium titanate nanoparticles is employed. In this method many raw materials such as oleic acid, surfactant, sodium hydroxide, alkali barium acetate, alcohol, tetrabutyl titanate are used. When the samples are collected, oleic acid which has mush an account will cover the whole particles. To make the samples cleaner, nitric acid is used to transition oleic acid to elaidic acid which is lighter than water then it will float up to be removed. In the progress to wash off the oleic acid the particles were found to reunite unusually: bigger and cubic particles are formed and the shape seems like single crystal but they are reunitions indeed, we used HTEM to prove this. It means self–assembling might happen through the progress, the spontaneous polarization orient, polarity of molecules will affect this progess.

Abstract: Zinc-doped TiO2 nanotube arrays were fabricated by immersing TiO2 nanotube arrays in zinc-containing solution for hours. And subsequent heat-treatment was crucial for Zn2+ coming into the crystal lattice of TiO2 nanotubes. TEM analysis was used as main technique to investigate the structure of zinc-doped TiO2 nanotubes, and found that the Zn2+ ions only combine into the lattice of TiO2 nanotubes. This kind of doping can change the valence structure in the surface of TiO2 nanotube array. The obtained zinc-doped TiO2 nanotube arrays have potential application in photocatalysis.

Abstract: In this paper, the effect of gel-calcination on piezoelectric property in (1-x) BiScO3-xPbTiO3 with the composition of x=0.635 is investigated. According to previous work, the heating rate of 200°C/h and holding for 210min having been taken as the basic processing condition. The BSPT powders were obtained from the same sol solution but calcined at different temperatures, and then the powders were used to prepare BSPT ceramics. The result shows that for the bulk ceramics with higher relative density ( higher than 95%), with the increasing calcining temperature of the gel (from 420°C to 500°C), the piezoelectric coefficient d33 of ceramic specimens first increases to maximum of 636pC/N at 450°C, then shows a fluctuation. In this work how the powder activity and the grain size affect (which was leaded by powder particle size) piezoelectric properties of BSPT ceramics are discussed.

Abstract: In this paper, a method to synthesis barium titanate nanorods at room temperature and normal pressure by soft chemical is devoloped. Oleic acid is one important raw material in this method which will help to form reaction containers. The nanorods crystallized in the process. Samples were investigate by XRD, TEM and SAD and so on.

Abstract: The optimized composition and sintering process of the low sintering X7R-type temperature-stable dielectric ceramics based on Barium Titanate in reducing atmosphere have been investigated. Flux aids SiO2-B2O3-Li2O were used in the experiments. The influence of composition and the content of flux agent on the microstructures and properties of ceramics materials were systemically studied. The X7R-type dielectric ceramics materials could be sintered at low temperature of 950oC in H2/N2 atmosphere, by optimizing flux content and adjusting process parameters. The dielectric constant of ceramics was effectively improved using two-step sintering process.