Papers by Author: Long Tu Li

Abstract: Al₂O₃-doped Ba_0.9Ca_0.1Ti_0.8Zr_0.2O₃ (short for BCTZ) based dielectric ceramics were fabricated by sintering samples at 1300°C for 2h with conventional ceramic processing method. The microstructure and electrical properties of the as-prepared samples were investigated. X-ray diffraction analysis showed that after the addition of Al₂O₃ with the amount designed in this study, no new phase was examined in the detection limit. Through scanning electron microscopy it was found that the doping of Al₂O₃ can help the growth of BCTZ grains, and the relative permittivities of the samples. The result of electrical properties indicated that the resistance and the break voltage of the samples could be improved to some extent with appropriate doping amount of Al₂O₃ resulting in the highest dielectric constant ~17000, low dielectric loss <10%, and highest break voltage 8.4 kV/mm, respectively.

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: Microstructure control in thin-layer multilayer ceramic capacitors (MLCCs) is one of the nowaday challenges for increasing capacitive volumetric efficiency and high voltage dielectric properties. In this paper, the ultrafine-grained BaTiO3 dielectric ceramics with uniform grain size distribution were prepared by chemical coating approach. The doping effects of rare-earth element (Ho) on the microstructures and dielectric properties of the ceramics were investigated. The addition of Ho in nano BaTiO3-based ceramics was found to improve the temperature coefficient of capacitance (TCC) performance, which could be attributed to a significant reduction in the grain size. Moreover, the effects of two-step sintering (TSS) method on the microstructures and dielectric properties, compared with conventional sintering (CS) method, were also discussed. The dielectric constant of ceramics sintered by the TSS method was higher than that of ceramics prepared by CS method. The results reveal that the adoption of TSS method could control the grain size and suppress the abnormal grain growth more effectively, which improves the TCC characteristics.

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: 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: In this paper, a kind of Mg, Nb co-doped multilayer piezoelectric ceramic is prepared and a non-contact accurate testing method is introduced. Using Pb(Mg1/3Nb2/3)O3- Pb(Ni1/3Nb2/3)O3- Pb(ZrTi)O3 low temperature co-fired ceramics powder and 90/10 Ag-Pb internal electrodes, the sample is prepared with tape casting processing method and low temperature co-fired technique at 960°C. Based on non-contact method, the piezoelectric constant, butterfly curve, and temperature characters are tested. Experiments show that non-contact method is more accurate for d33 testing. The effect of mechanical load on piezoelectric performance is also investigated. Under external mechanical load, switching polarization (Ps) and remnant polarization (Pr) increase respectively. Mechanical load press is also favorable to dominate the temperature rise of the piezoelectric device.

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.