【作者】 李统业；

【导师】 王豫；

【作者基本信息】 西南交通大学 ， 材料学， 2009， 博士

【摘要】 稀土元素广泛地应用于发光材料、激光材料、永磁材料、磁致冷材料、磁致伸缩材料、储氢材料、高温超导材料等高技术领域,已经引起了广泛的重视。这些功能材料都是基于稀土作为掺杂元素或者其中的复合元素,对稀土基功能材料的研究,特别是稀土基电性功能材料的研究基本上还是一个空白。本文对稀土基陶瓷的电学性能展开了系统地研究,发现Pr6O11和Tb4O7陶瓷具有非线性电学行为,可以作为电子和电力系统的保护装置。第1章介绍了稀土元素的种类、基本性质和主要应用,强调了对稀土基电性功能材料研究的必要性,然后对压敏电阻的研究现状进行了综述,最后提出了本文的研究内容。第2章对本论文涉及的实验方法和表征手段进行了阐述。实验方法方面,详细描述了本论文所采用的传统陶瓷制备工艺技术。表征手段方面,对微结构、缺陷能级和晶界势垒参数的分析过程进行了介绍。第3章对纯氧化镨陶瓷的微结构和电学性能进行了系统地研究。当烧结温度为600℃时开始出现非线性电学特性,烧结温度超过1000℃时氧化镨陶瓷的相对密度才有明显的提高。交流阻抗分析表明在陶瓷晶界处存在晶界高阻层。鉴于在晶界处没有偏析相,提出晶界高阻层起源于晶界势垒。通过不同温度下测量的伏安特性曲线,证明了双肖特基势垒的存在,并计算了晶界势垒参数。氧化镨具有OSC(氧存储)特性,在升温过程中释放氧,在降温过程中吸收氧。我们认为晶界势垒起源于降温过程中的氧吸附,并且此观点得到了AES深度分析的支持。根据Gupta和Carlson提出的ZnO压敏电阻的缺陷势垒模型,提出了修正的缺陷势垒模型用来解释氧化镨晶界势垒的形成,在耗尽层内存在VO*和VO**。两种类型的施主缺陷。与ZnO具有过量的填隙锌离子不同的是氧化镨是氧空位型的n型半导体,因此氧化镨压敏电阻具有优良的电学稳定性和抗老化能力。第4章利用液相烧结和替代反应的方法对氧化镨陶瓷进行了致密化研究。Bi203在烧结过程中能够形成液相偏析于晶界区域促进了陶瓷的烧结性,CuO和ZnO能够替代氧化镨晶格中的镨离子,产生的缺陷促进了烧结过程中的体扩散和晶界扩散,从而提高了氧化镨陶瓷的致密度。提出除了离子半径,化学键类型也是影响替代反应的重要因素。第5章对氧化铽陶瓷的非线性电学行为和导电机理进行了研究。氧化铽压敏电阻具有较低的压敏电压,同时表现出优良的介电性能和能量吸收能力,可以应用于微电子电路的过压保护。结合不同气氛处理的氧化铽陶瓷的晶界势垒参数,我们认为氧化铽压敏电阻和氧化镨压敏电阻一样,其非线性也是起源于晶界氧吸附。第6章制备了Tb系ZnO压敏电阻和ZnO-Pr6O11复合压敏电阻。与Pr6O11一样,Tb4O7对ZnO压敏电阻非线性的产生有关键的作用。根据氧化镨和氧化铽的共性,我们认为Tb系ZnO压敏电阻的非线性应该与Tb4O7的氧存储特性有关,有必要作进一步的研究。制备的ZnO-Pr6O11复合压敏电阻具有在1.5～26.9范围内的非线性系数和在26～829V／mm范围内的压敏电压,因此可以通过改变复合陶瓷的成分获得满足不同实际需要的压敏电阻。此外,还给出了稀土氧化物线性电阻的实验数据。更多还原

【Abstract】 Rare-earth elements have received a great deal attention due to wide application in luminescent materials, laser materials, permanent-magnet materials, magnetic refrigeration materials, magnetostrictive materials, hydrogen storage materials, high temperature superconductor and other high technology fields. Rare earth elements as doping or composition exist in these functional materials, rare earth-based functional ceramics, especially for rare earth-based electrical functional ceramics, have received comparatively little attention. In this work, the electrical properties of rare earth-based ceramics have been systematically studied, it was found that Pr6O11 and Tb4O7 ceramics have nonlinear electrical properties, which can be used in protection devices for electronic and electrical power systems.In Chapter 1, the category, basic properties and main application of rare earth elements were introduced, the necessary to study rare earth-based electrical functional ceramics was emphasized, the current status of varistors was then described, and finally the research contents of this paper were provided.In Chapter 2, the experimental process and characterization methods used in this paper were introduced. As for experimental process, the conventional ceramic processing techniques were particularly described. As for characterization methods, the analysis process of microstructure, defect energy level and grain boundary barrier parameters were provided.In Chapter 3, the microstructure and electrical properties of pure Pr6O11 ceramics were systematically studied. The ceramic samples began to present nonlinear electrical properties when sintered at 600℃, the density has a significant increase when sintering temperature exceeds 1000℃. Ac impedance analysis indicated that grain boundary high resistance layer present at the grain boundary region. Since there are no segregation phase located at the grain boundary, it was proposed that the grain boundary high resistance layer originates from the grain boundary barriers. The existence of double Schottky-type barriers was affirmed by analyzing the I-V curves measured at different temperature and the corresponding parameters were calculated. Pr6O11 can release oxygen with the increase of ambient temperature and then incorporate oxygen in the process of cooling due to the OSC (oxygen storage capacity) characteristics. It was proposed that the formation of grain boundary barriers can be attributed to the oxygen absorption during the cooling process, which was supported by AES profile analysis. Based on the defect barrier model for ZnO based varistors proposed by Gupta and Carlson, a modified defect barrier model was introduced to explain the formation of the grain boundary barriers, (?) and (?) as the donor defect exist in the depletion layer. Pr6O11 is an n-type semiconductor with oxygen vacancies, which is different from n-type ZnO semiconductor with excess interstitial zinc ions, so Pr6O11 varistors present excellent electrical stability and anti-ageing capacity.In Chapter 4, the densification of Pr6O11 ceramics was studied by liquid phase sintering and substitution reaction. Bi2O3 can improve the sintering process by forming liquid phase segregated to the grain boundary regions, CuO and ZnO can substitute the Pr ions in the lattice, the produced defects can facilitate the densification process by improving the bulk diffusion and grain boundary diffusion. Besides the ionic radius factor, the chemical bonding type should be considered during the substitution reaction.In Chapter 5, the nonlinear electrical properties and conduction mechanism of Tb4O7 varistors were studied. Tb4O7 varistors have low breakdown voltage, and present excellent dielectric properties and energy absorption capability, which is suitable for application in overvoltage protection for microelectronic circuit. According to grain boundary barrier parameters of the samples treated in different atmospheres, it was proposed that the nonlinear electrical properties of Tb4O7 varistors can be attributed to the adsorbed oxygen on the grain surfaces, which is similar to Pr6O11 varistors.In Chapter 6, Tb-based ZnO varistors and ZnO-Pr6O11 mixed oxide varistors were prepared. Similar to Pr6O11, Tb4O7 also play a key role in the formation of nonlinear electrical properties of ZnO varistors. According to the similarity between Tb4O7 and Pr6O11, it was proposed that the nonlinear behavior of Tb-based ZnO varistors should be concerned with the oxygen storage characteristic of Tb4O7, further study is necessary. The prepared ZnO-Pr6O11 mixed oxide varistors have the nonlinear coefficient range from 1.5 to 26.9 and breakdown voltage range from 26 to 829V/mm, so the varistors can satisfy different application by changing the composition of the mixed oxide varistors. In addition, the experimental data of rare earth oxide ceramics with linear electrical properties was also provided.更多还原