【作者】 单丹；

【导师】 曲远方；

【作者基本信息】 天津大学 ， 材料学， 2007， 博士

【摘要】 本文以具有钙钛矿结构的无铅电容器陶瓷材料[BaTiO₃、Bax(Bi_0.5Na_0.5)_1-xTiO₃和Ba(Zr_xTi_1-x)O₃]为研究对象,分析了其组成和晶体结构对材料微观形貌和介电性能等方面的影响,并以探索高介电性能、良好弛豫特性的无铅电容器介质材料为目标,提出微区居里温度随机分布的数学模型,分析了材料居里温度的分布与微区成分、结构差异的关系。主要内容包括:讨论了Ce和Cu掺杂对BaTiO₃陶瓷材料介电性能、晶体结构和微观形貌的影响。Ce的掺杂使BaTiO₃陶瓷的介电性能有了一定的提高。Ce⁴⁺离子进入钙钛矿结构中取代部分Ti⁴⁺离子,使BaTiO₃的自发极化降低强度,BaTiO₃陶瓷材料的居里温度向低温方向移动,并使陶瓷材料显示出高介电常数;而CuO的加入降低了试样的烧结温度,由于液相传质作用,试样的微观形貌有了较大的改变。研究了(Bi_0.5Na_0.5)TiO₃-BaTiO₃二元陶瓷晶体结构、微观形貌和介电性能方面的变化规律。由于Ba²⁺离子对Na⁺离子进行取代时产生了离子空位,介电常数在各个温度区间有明显的上升; Ba²⁺的加入还会以BaO的形式填充部分Bi³⁺和O₂^-离子空位,从而降低材料的介质损耗。同时,准同相界的高晶格活性及四方相的出现也是陶瓷材料介电性能提升的原因之一。Y₂O₃的掺杂则对材料的介电峰产生了压低展宽的作用;而在BNBT₆试样基础上掺杂CeO₂使试样的介电损耗大幅下降,其影响机理与在BaTiO₃陶瓷中相同。之后,通过研究BNT基陶瓷的介电温谱,分析了BNT基材料的高温相变过程。而后,受Pb（ZrTi）O₃基陶瓷启发,尝试合成了Ba（ZrTi）O₃二元陶瓷,在Zr含量在20-30at%之间这一组成附近存在着立方、四方共存的准同相界,由于准同相界的高晶格活性,材料在介电常数和弛豫特性上有了较大的提高。以Ba(Zr_0.25Ti_0.75)O₃为基础,研究了Y₂O₃掺杂对陶瓷材料的影响。结合X衍射结果和试样的介电常数-温度关系曲线,我们推断在Y₂O₃掺杂过程中,Y³⁺对钙钛矿结构中原始离子的取代分为两个步骤,不同的步骤中Y³⁺的掺杂对晶格参数和居里温度产生了截然不同的影响。CeO₂的掺杂虽然未使陶瓷材料在介电性能上有所提高,但是掺杂量为0.4、0.6at%时试样出现半导化现象,我们对此进行了分析,并总结其规律,相信会对锆钛酸钡基陶瓷在半导体材料方面的研究提供参考。最后,结合锆钛酸钡基陶瓷的实验结果,在成分起伏理论的基础上,利用随机过程理论,进一步提出了微区居里温度正态分布的数学模型。并结合具体实验结果,对数学模型进行了验证。该结果为提高陶瓷材料弛豫特性、开发低温度变化率的电容器介质材料提供了新的思路和可靠依据。更多还原

【Abstract】 The effects of composition and crystal lattice of lead-free ceramics with perovskite type structure, which is employed in dielectric capacitor applications, have been widely investigated. And then, aiming at exploring materials with high dielectric performance and relaxer character, a theoretical model of normal random distribution of Curie point has been put forward, which can tell the influence of the fluctuation in content and structure of micro-domains on the Curie point of the ceramics.Firstly, we study the Ce and Cu doping effects on dielectric properties, crystal lattice and the microstructure of BaTiO3 ceramics. Ce4+ replace Ti4+ ions in B-site of perovskite type structure, which restrain the spontaneous polarization. Owning to the shifting of Curie point towards low temperature, the permittivity becomes higher at room temperature; Cu doping can enhance the mass transfer in liquid phase during the sintering process, as a result, the microstructure is changed and the sintering temperature is lowered.And then, the crystal lattice and dielectric performance of (Bi0.5Na0.5)TiO3- BaTiO3 have been analyzed. The permittivity is lifted in whole temperature range, because of the ion vacancy generating during the substitution of Ba2+ on Na+. Due to the stuffing of BaO in Bi3+ and O2- vacancies, the dielectric loss is depressed. Meanwhile, the high lattice energy of morphotropic phase boundary (MPB) and the appearance of tetragonal contribute a lot in the enhancement of dielectric property. Y3+ doping presses the dielectric peak of ceramics; Ce doping restrains the loss tangent of BNBT6 samples, which shows similar function in BaTiO3 ceramics. Then, we analyze the phase transition process of BNT-based ceramic by studying the thermogram of permittivity.Further, we synthesize Ba(ZrTi)O3 ceramics and find MPB in 20-30at% of Zr content, in which trigonal and tetragonal coexist. Owning to the high lattice energy, the permittivity and relaxation property are improved notably. Then, we investigate the Y3+ doping in Ba(Zr0.25Ti0.75)O3 sample and conclude that there are two step in the substitution of Y3+ on original ions, combining the X ray diffraction analysis and thermogram of permittivity; Ce doping doesn’t enhance the dielectric properties much, but we detect a phenomenon of semi-conduction in the sample with 0.4 and 0.6at% Ce4+ content.Finally, combining the theory of random process and experimental results of Ba(ZrTi)O3-based ceramics, we put forward the theoretical model of normal random distribution of Curie point, basing on the theory of composition fluctuation. Then we verify the model with the experiment data, and the results match up well. The model offers a guide for exploring new lead-free ceramics with high relaxation and dielectric property for capacitor applications.更多还原