【作者】 黄静；

【导师】 周东祥；

【作者基本信息】 华中科技大学 ， 微电子学与固体电子学， 2004， 博士

【摘要】 随着微波技术不断发展及其应用领域的不断扩大,对微波器件的要求向高性能、高品质和小型化的方向展开,微波陶瓷介质以其优异的微波介电性质作为微波器件的重要组成,正在发挥越来越重要的作用,并被国际和国内的研究领域视为研究的热点和重点。钙钛矿结构微波介质陶瓷在微波频段下仍具有高相对介电常数、低介电损耗和接近零的介电温度系数,采用经典电介质物理理论很难解释其优异性能的由来,有必要从理论上研究钙钛矿结构微波陶瓷的介电机理和结构之间的相互关系,从而为材料的研究提供改性基础和设计指导。本论文以国家863高科技重大研究项目:高介电常数微波介质陶瓷及其器件的研制(2001AA-ZB3201-02)为依托,主要从以下四个方面进行了研究,取得初步成果,为进一步的研究奠定了基础。利用量子力学的微扰理论研究钙钛矿结构微波介质陶瓷的极化机理,进而解释高介电常数的由来;利用缺陷化学理论,研究钙钛矿结构微波介质陶瓷的损耗机理;通过分解钙钛矿结构微波介质陶瓷的缺陷来源和作用机理,探索降低非本征损耗的有效途径;探讨了在钙钛矿结构中掺入稀土元素显著提高微波介电性能的原因是由于稀土元素的活性对微波介质陶瓷进行了结构梳理。论文围绕钙钛矿结构微波介质陶瓷的结构和性能的关系,对介质极化和损耗机理展开了研究,主要内容包括:在总结实验事实的基础上,提出类钙钛矿钨青铜结构系列,复合钙钛矿系列以及铅基钙钛矿等系列材料的微波特性是由结构中都存在基于顶角相连的氧八面体所决定的。利用内电场理论,参考洛仑兹模型得到钙钛矿结构微波陶瓷的极化方程,通过有效化简得到可以说明极化能力的近似方程,该方程可以在一定程度上解释本征钙钛矿结构微波介质的极化能力,但由于微波介质陶瓷的离子组成很复杂,通常在晶格点上存在的离子不止一个,而且晶体结构也不是单纯的立方体等复杂因素将导致内电场理论具有局限性,另外内电场考察的是离子在静电场下的平均极化效果,当外界电场为高频的微波电场时,以上简单的计算得出的结论尚待进一步实验证实。利用量子力学的微扰理论研究电子和离子极化过程。在微波电场作用下,把钙钛矿结构氧八面体内B-O离子链中的B离子的振动与O离子的振动之间相互作用看成<WP=4>是一种微扰量,分别计算微扰对两个离子系统能量简并造成的影响,根据Jahn-Teller效应,氧八面体的B-O链将产生畸变,首先是O离子的电子云畸变,可使氧八面体极化率增高,如果消除简并的能量降低超过O离子格点位置的改变造成的晶格能量增加,将会使得O离子格点位置畸变导致氧八面体极化率进一步增高。利用缺陷化学的方法研究了电导损耗。通过分析钙钛矿结构微波陶瓷在本征状态、施主掺杂和受主掺杂状态下的缺陷模型,研究陶瓷的电导率与结构成分的关系,从而揭示在不同成分的结构中电导损耗的产生规律。从晶粒缺陷、粒界缺陷和杂相缺陷三个角度研究缺陷的产生来源、相关规律及与损耗的关系等。还进行了点缺陷控制、晶体生长模型控制和工艺控制等与降低缺陷损耗密切相关的实验研究工作。从微波介质陶瓷的制作过程中加入镧()系稀土元素微波介电性能显著提高这一现象出发,结合目前高微波介质陶瓷研究中三个主要体系的改性实验结果,初步探讨了稀土元素对微波介质陶瓷结构的“催化”活性作用,结果表明结构梳理是提高微波性能的主要原因,稀土元素的引入是提高微波介质陶瓷介电性能的有效途径。黄昆方程是研究晶格振动比较有效的方法,它将离子自身的振动与外电场作用下的激发振动合起来考虑,符合晶体中离子的实际振动形态。本论文对比黄昆方程对晶格振动的研究,采用量子力学方法对钙钛矿结构陶瓷的晶格振动进行分析,得到描述晶格系统的哈密顿方程,通过分析能量状态的改变,获得晶格振动引起本征损耗的状况。更多还原

【Abstract】 With the development of microwave technology, its application has been found in every relative part of science and technology. The development of microwave devices trends to high quality, high performance and miniaturization, and the microwave dielectric ceramics are playing more and more important role in microwave technology. The microwave dielectric ceramics with perovskite structure have the characteristics of high dielectric constant, low dielectric loss as well as temperature coefficient in high frequency, however the coexistence of the above parameters was difficult to explain when by the classic dielectric physics theory. So it was necessary to investigate the relationship between dielectric principles and the microstructure of ceramics in order to provide the basic theory of improving performance and the principle of design.In the present dissertation, we have conducted the investigation from the following four respects :Firstly the dielectric polarization theory in perovskite ceramics based on the perturbation theory of quantum was researched in order to explain the source of high dielectric constant; secondly the dielectric loss theory was investigated using the defect chemistry; thirdly the effective ways to reduce the non-intrinsic loss was investigated by resolving the source of defects in microwave dielectric ceramics and its affecting principles; lastly the reason of the significant improvement of microwave dielectric performance in perovskite ceramics doped by rare-earth elements was primarily investigated.The relationship between properties and structures in microware dielectric ceramics with perovskite structure was discussed in the total dissertation, as well as the principle of dielectric polarization and loss mechanism.On the base of summarizing the experiment data, it was proposed that the microware characters in perovskite-like tungsten bronze type structure BaO-Ln2O3-TiO2 series, complex perovskite CaO-Li2O-Ln2O3-TiO3 series and Pb-based perovskite Pb-Ca-Fe-Nb series were decided by the structure of BO6 octahedron connected each other through the point angle. By use of the in-electric field theory and Lorentz Model, the polarization equation of perovskite structure microware ceramics was obtained, and the approximate equation to explain polarization can be got by proper simplifying, with which the polarization of intrinsic perovskite structure microware ceramics can be explained at a certain degree. <WP=6>However, the ion structure of microware dielectric ceramics was so complicated that the result of the simplified calculation would be confirmed further by experiment.The electronic and ionic polarizing process were researched by the perturbation theory of quantum mechanics. In microwave field, when B-O ion polarized in BO6 octahedral, the field can be taken as the electron movement of B ion acting with O ion, if the interaction between B ion and O ion vibration was treated as a perturbation quantity and the impact of this perturbation quantity on the degenerate energy was evaluated. According to Jahn-Teller effect, the B-O chain in octahedral would be changed: the electron cloud of O ion would firstly be distorted and the polarization of octahedral increased, if the amount of the decreasing energy was greater than the amount of degenerate energy increase caused by the replacement of O ion, and the O ion replacement distortion would result in higher polarization of Octahedral.The dielectric loss in ceramics was investigated by defect chemistry. Through analyzing the defect model of microwave ceramics in intrinsic, donor and acceptor doping situation, the relationship between conductivity and structure in ceramics was investigated in order to study the regularity of conductive loss. The relationship of the source of defect、regularity and the loss was investigated from the grain defect, crystal edge and miscellaneous aspects. The research of point defect controlling, grain growth model controlling and process controlling were initially studied in this work.Base on the micr更多还原