稀土复合掺杂钛酸钡基纳米介电陶瓷的研制及其性能、结构的研究

【作者】 杨晓兵；

【导师】 陈慧英；

【作者基本信息】 中央民族大学 ， 生态学， 2007， 硕士

【摘要】 电介质陶瓷作为功能陶瓷在传感、电声和电光等技术领域具有广泛的应用价值。剑桥大学的H．A．Pohl教授于1978年提出介电力学体系这一理论体系，根据这一理论，电介质陶瓷还可以应用在介电力学分离工艺中。目前该工艺已经被应用于环境中污染物的去除和燃料油中颗粒杂质的去除，并取得了良好的效果，并且介电性能优异的电介质可以降低能耗、节约能源，起到保护环境的作用。钙钛矿介电材料由于其特有的铁电、热点、压电等性质受到人们的广泛关注。钛酸钡作为最代表性的介电材料具有较高的介电常数，被广泛应用于多层陶瓷电容器的制备。结构分析表明：在温度高于120℃时，钛酸钡晶体为立方相空间群O_h^I-Pm3m。在温度高于120℃时，钛酸钡的介电常数最高，约为室温介电常数的6倍。然而，制备条件以及掺杂组分（如稀土的掺杂）对钛酸钡介电性质具有较大的影响，因此在电子陶瓷领域中，钛酸钡的制备和掺杂是人们普遍关注的一个焦点。溶胶—凝胶法可以合成多组分钛酸钡基粉体，这种方法被认为是一种接近绿色的“软化学”合成方法。只要将用这种方法制备的干凝胶在一定温度下（通常低于1000℃）煅烧去除有机组分就可获得陶瓷粉体。本文首先综述了钛酸钡粉体制备的各种方法，认为液相法制备的粉体因具有纯度高、成分均匀、粒径小等特点而成为制备粉体主要方法，其中溶胶-凝胶法因其可制得多组分均匀掺杂的钛酸钡粉体，是极具发展前景的制粉方法；此外，总结了掺杂改性钛酸钡系陶瓷研究进展。本论文采用溶胶-凝胶法制备了钛酸钡陶瓷、BCST(Ba_0.62Ca_0.08Sr_0.3TiO₃)陶瓷，制备了用固相、液相两种方式掺杂稀土Pr₆O₁₁的BT：xPr₆O₁₁陶瓷，以及用溶胶-凝胶法合成BCST(Ba_0.62Ca_0.08Sr_0.3TiO₃)基质粉体，二次固相同时掺杂两种稀土Pr₆O₁₁和Nd₂O₃的BCST：0.001Pr₆O₁₁·xNd₂O₃系列陶瓷。采用XRD和SEM，等对粉体和陶瓷的相组成、微观形貌进行了表征，并测试了陶瓷的介电性能。得出如下结论：1．采用溶胶-凝胶法合成制备了钛酸钡纳米晶粉体及陶瓷。经XRD粉体衍射测试，所得钛酸钡粉体主要为四方相纳米粉体；经过SEM扫描电镜观察到陶瓷陶瓷平均晶粒大小约为5μm；通过介温测试，所得陶瓷的居里温度Tc为134℃。2．采用溶胶-凝胶法合成制备了BCST纳米晶粉体及陶瓷。经XRD粉体衍射测试，所得BCST粉体主要为四方相纳米粉体；经过SEM扫描电镜观察到陶瓷平均晶粒大小约为8μm；通过介温测试，与纯BT陶瓷相比，陶瓷的居里峰向低温方向移动并展宽压低，而介电损失比较低，所得陶瓷的居里温度Tc为12℃。3．制备了用固相、液相两种方式掺杂稀土Pr₆O₁₁的BT：xPr₆O₁₁纳米粉体及陶瓷，并进行了对比。发现：对于液相掺杂稀土Pr₆O₁₁稀土Pr₆O₁₁的BT：xPr₆O₁₁纳米粉体及陶瓷，x=0.005为最佳掺杂量，经XRD粉体衍射测试，所得BT：0.005Pr₆O₁₁粉体主要为四方相纳米粉体，经过SEM扫描电镜观察到陶瓷陶瓷平均晶粒大小约为300nm，通过介温测试，与纯BT陶瓷相比，BT：0.005Pr₆O₁₁陶瓷的居里峰向低温方向移动，介损也明显降低，陶瓷的居里温度Tc为68℃；对于固相掺杂稀土Pr₆O₁₁的BT：xPr₆O₁₁纳米粉体及陶瓷，x=0.001为最佳掺杂量，经XRD粉体衍射测试，所得BT：0.001Pr₆O₁₁粉体主要为四方相纳米粉体，经过SEM扫描电镜观察到陶瓷陶瓷平均晶粒大小约为500nm，通过介温测试，与纯BT陶瓷相比，BT：0.001Pr₆O₁₁陶瓷的居里峰向低温方向移动并展宽，介损也明显降低，所得陶瓷的居里温度Tc为118℃，此外，在大约34℃曲线有另一较低介电峰值，呈现双峰效应。经过对比发现：与液相掺杂所获得的BT：0.005Pr₆O₁₁陶瓷相比，固相掺杂所获得的BT：0.001Pr₆O₁₁陶瓷晶粒发育较好，气孔较少，晶粒间结合更加紧密；固相掺杂所获得的陶瓷居里点虽没有液相掺杂所获得的陶瓷的居里点低，但是，固相掺杂的居里峰明显展宽压低，比液相掺杂所获得的陶瓷在室温时具有较高的介电常数和较低的介电损失。4．采用溶胶-凝胶法合成了BCST纳米晶粉体，制备了用二次固相掺杂法掺杂稀土Pr₆O₁₁和Nd₂O₃的BCST：0.001Pr₆O₁₁·xNd₂O₃粉体及陶瓷。发现x=0.002为最佳掺杂量，经XRD测试，所得BCST：0.001Pr₆O₁₁·0.002Nd₂O₃粉体主要为四方相纳米粉体；经过SEM扫描电镜观察到陶瓷陶瓷平均晶粒大小约为6μm；通过介温测试，与纯BT陶瓷相比，陶瓷的居里峰向低温方向移动，而介电损失比较低；与BCST陶瓷（Tc=12℃）相比，BCST：0.001Pr₆O₁₁·0.002Nd₂O₃陶瓷的居里峰（Tc=10℃）并无显著变化，但居里点的介电常数却显著提高。更多还原

【Abstract】 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.更多还原