Rare Earth Compound Doped Barium Titanate Based Nano-dielectric Ceramics Developed And Its Performance, The Structure Of The Study

As functional ceramics, dielectric ceramics has extensive application value in such as sensor, electro-optical and electro-acoustic technology. Professor H.A.Pohl of the University of Cambridge put forward the theory of dielectrophoresis in 1978. According to this theory, dielectric ceramics can be used in dielectrophoresic mechanical separation process. This separation process has now been used to treat the pollutants in environment and remove micro-particles in petroleum, and some achievements have been achieved. Dielectric materials with excellent dielectric properties can reduce energy consumption and protect the environment.Perovskite dielectric materials have been receiving much attention due to their excellent functional properties, such as pyroelectricity, piezoelectricity, electrooptic effect, and so on. Barium titanate which has high dielectric constant and is used widely in multilayer ceramics capacitors is one of the most common dielectric materials. Structural analysis shows that barium titanate crystallizes in the cubic system space group O_h¹-Pm3m assuming at temperatures above 120℃. And the dielectric constant of barium titanate at about 120℃ reaches a maximum which is about 6 times of that at room temperature. However, the preparation and doping components, for example the doping of lanthanon,influence the dielectric properties of barium titanate strongly. Therefore the research of preparation and dielectric properties of doped barium titanate ceramics has been a focal point in electronic ceramics field. Sol-gel method which can prepare multicomposition barium titanate powders is considered as a "chimie douce" or soft chemical approach to the synthesis of metastable oxide material. Ceramic powders can be obtained after heat treatment of xerogel to a temperature high enough to remove the organic components.Methods of the synthesis of BaTiO₃, technical characteristics, research situation and recent progress had been presented in this paper firstly. Low temperature wet chemical routes offer an exciting possibility for the synthesis of high purity, homogeneous, ultrafine powders which meet the need of electric components in factual application. Sol-gel method, which can prepare multicomposition barium-titanate powders, was the one of the prospective routes for manufacturing barium-titanate powders. Besides, we summarized recent progress of the doping of microelement in BaTiO₃ based ceramics.Therefore, in this paper, first of all, barium-titanate powder and ceramics were prepared by sol-gel method. Second, different kinds of doping methods were used to synthesize BT:xPr₆O₁₁ series ceramics. Third, BCST (Ba_0.62Ca_0.08Sr_0.3TiO₃) powder was prepared by sol-gel method, Pr₆O₁₁ and Nd₂O₃ were mixed into the BCST powder by solidstate method to synthesize BCST:0.001Pr₆O₁₁·xNd₂O₃ series ceramics. The main phases of predecessor powders were characterized by X-ray Diffraction. The patterns of the BT-based ceramics were observed by SEM. The dielectric properties of the ceramics were determined. In general, the main work is as follows:1. Nanometer-sized barium-titanate powder and ceramics were prepared by sol-gel method. Tetragonal phase nanometer-sized barium-titanate powder had been synthesized by sol-gel process and was characterized by X-ray Diffraction. The pattern of the BT ceramics was observed by SEM and the average grain size of the ceramics was about 5μm. The Curie temperature Tc is 134℃ measured by Dielectric Frequency and Temperature Spectrum Analyzer.2. Nanometer-sized BCST powder and ceramics was prepared by sol-gel method. Tetragonal phase nanometer-sized BCST power was characterized by X-ray Diffraction. The pattern of the BCST ceramics was observed by SEM and the average grain size of the ceramics was about 8μm. Compared with the Curie point of pure BT ceramics, the Curie point of BCST ceramics shifted to lower temperature and the Curie peak was broadened and depressed distinctly, and the Curie temperature is 12℃ measured by Dielectric Frequency and Temperature Spectrum Analyzer. Besides, the dielectric loss of BCST ceramics was lower than that of BT ceramics.3. Nanometer-sized BT:xPr₆O₁₁ series powders and ceramics were prepared and different kinds of doping methods , solid state and liquid state doping methods, were used to synthesize BT:xPr₆O₁₁ series ceramics. The properties of BT:xPr₆O₁₁ series ceramics synthesized by those two methods were compared. The optimal sample of BT:xPr₆O₁₁ powders and ceramics synthesized by liquid state doping method was BT:0.005Pr₆O₁₁; BT:0.005Pr₆O₁₁ powder was found to be tetragonal phase and nanometer-sized tested by X-ray Diffraction; the pattern of the BT:0.005Pr₆O₁₁ ceramics was observed by SEM and the average grain size of the ceramics was about 300nm; compared with the Curie point of pure BT ceramics, the Curie point of BT:0.005Pr₆O₁₁ ceramics, which is 68℃ shifted to lower temperature, and the dielectric loss of BT:0.005Pr₆O₁₁ ceramics was lower than that of BT ceramics. For the BT:xPr₆O₁₁ powders and ceramics synthesized by solid state doping method, the optimal sample was BT:0.001Pr₆O₁₁; the BT:0.001Pr₆O₁₁ powder was found to be tetragonal phase and nanometer-sized tested by X-ray Diffraction; the pattern of the BT:0.001Pr₆O₁₁ ceramics was observed by SEM and the average grain size of the ceramics was about 500nm; compared with the Curie point of pure BT ceramics, the Curie point of BT:0.005Pr₆O₁₁ ceramics, which is 118℃ shifted to lower temperature, and the Curie peak was broadened; besides, the dielectric loss of BT:0.001Pr₆O₁₁ ceramics was lower than that of BT ceramics; arelative lower dielectric peak which lead the temperature dependence of the dielectric curve double-peak like was found at 34℃. The BT:0.001Pr₆O₁₁ ceramics prepared by solid state doping method was better matured in crystalline grain, and had less pores than those of the BT:0.005Pr₆O₁₁ ceramics synthesized by liquid state doping method. Also the Curie temperature of BT:0.001Pr₆O₁₁ ceramics was higher than that of BT:0.005Pr₆O₁₁ ceramics, the Curie peak was wider than that of BT:0.005Pr₆O₁₁ ceramics. Thus, the BT:0.001Pr₆O₁₁ ceramics prepared by solid state doping method had higher dielectric constant and lower dielectric loss at room temperature.4. Nanometer-sized BCST powder was prepared by sol-gel method, then Pr₆O₁₁ and Nd₂O₃ were doped through solid state doping method, and BCST:0.001Pr₆O₁₁·xNd₂O₃ powders and ceramics were prepared. The optimal sample of BCST:0.001Pr₆O₁₁·xNd₂O₃ ceramics was BCST: 0.001Pr₆O₁₁·0.002Nd₂O₃ ceramics. The BCST:0.001Pr₆O₁₁·0.002Nd₂O₃ powder was found to be tetragonal phase and nanometer-sized tested by X-ray Diffraction. The pattern of the BCST:0.001Pr₆O₁₁·0.002Nd₂O₃ ceramics was observed by SEM and the average grain size of the ceramics was about 6μm. Compared with the Curie point of pure BT ceramics, the Curie point of BCST:0.001Pr₆O₁₁·0.002Nd₂O₃ ceramics, which is 10℃ shifted to lower temperature. Besides, the dielectric loss of BCST:0.001Pr₆O₁₁·0.002Nd₂O₃ ceramics was lower than that of BTceramics. Compared with the Curie point of BCST ceramics, which is12℃ , the Curie point of BCST:0.001Pr₆O₁₁·0.002Nd₂O₃ ceramics didn'tshift to lower temperature apparently, but the dielectric constant ofBCST:0.001Pr₆O₁₁·0.002Nd₂O₃ ceramics at Curie temperature increasedobviously.