Papers by Author: Hui Zhang

Abstract: Sand-milling machine was firstly utilized to crush and disperse the raw materials. A homogenous and well-dispersed mixture of TiO₂ and BaCO₃ (<30nm) was obtained. The solid state reaction temperature can be reduced by 200°C for nanosized reactants compared with coarse ones. In order to increase tetragonality of nanosized BaTiO₃, an innovative two-step calcination method, which includes solid state reaction process between reactants at a low temperature T₁ and phase transition process at a high temperature T₂, was subsequently adopted. The microstructure evolution of BaTiO₃ by two-step calcination was investigated as a function of T₂ and corresponding dwelling time t₂. Pure-perovskite BaTiO₃ nanopowders with the mean particle size as small as 75nm and tetragonality (c/a ratio) higher than 1.0096 could be fabricated by two-step calcination through altering T₂ and/or its dwelling time t₂.

Abstract: Nanocrystalline BaTiO₃ powder was directly synthesized by a convenient one-step solvothermal route. 8~10 nm BaTiO₃ with different Ba/Ti ratios are obtained by adjusting the raw material ratios. The optimum raw material ratio of Ba/Ti is obtained. And the as-prepared BaTiO₃ nanoparticles are all small and uniform. Influence of the nominal Ba/Ti ratios on diameter of nanocrystalline BaTiO₃ powder was investigated by XRD, TEM and XRF analyses. It was found that the Ba/Ti ratios of the raw materials have a great influence on the process of powder fabrication. When the raw material Ba/Ti ratio is low (<0.9), the reaction cannot be finished and strong BaCO₃ peaks were founded as the alkalinity of the system at the later reaction stage is too low. Besides, the Ba/Ti ratio of the product rises as the raw material Ba/Ti ratio increases.

Abstract: In this paper, (Na_0.52K_0.44Li_0.04)(Nb_0.86Ta_0.06Sb_0.08)O₃ (LTS-KNN) ultrafine-grained ceramic were fabricated over a low and wide temperature range, by using the nanopowder prepared from a water-based sol-gel method. nanopowders are demonstrated to be suitable for preparing fine-grained potassium-sodium niobate ceramics with desirable properties.

Abstract: 5 nm BaTiO₃ powder has been successfully prepared by the one-step solvothermal method. The different grain size BaTiO₃ powders have been achieved after calcining the 5 nm Nanocrystalline BaTiO₃ powders at 700°C, 850°C and 950°C for 3 h. In-situ heating Raman spectroscopy revealed the dispersive phase transition character in the nanocrystalline BaTiO₃ powders. As the BaTiO₃ grain size decreases, wider phase transition temperature and the Raman intensity becomes weak. The BaTiO₃ powders of the 5 nm nanocrystalline exhibited the similar phase transformations from rhombohedral to orthorhombic to tetragonal to cubic transitions as those in the coarse BaTiO₃ 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.