溶胶-凝胶法制备PbTiO3铁电玻璃陶瓷的高频晶粒尺寸效应

首次报道了用溶胶－凝胶法制备的钛酸铅铁电玻璃陶瓷的晶粒尺寸对其高频介电性能的影响。研究表明,铁电玻璃陶瓷的高频介电弛豫主要是由材料内部的畴壁共振引起的。晶粒尺寸增加,畴壁宽度增大,介电弛豫向低频移动;反之,晶粒尺寸减小,畴壁宽度变小,介电弛豫向高频移动,弛豫频率提高,介电损耗变小。     

细晶粒BaTiO3陶瓷介电性能的频谱效应

本文研究了细晶粒纯BaTiO3陶瓷的介电性能与频率的关系,发现陶瓷的介电常数随测量频率有明显变化,细晶粒陶瓷的介电常数随测量频率减小缓慢增加,而常规材料呈明显的上升趋势.细晶粒材料在低频范围的频率稳定性远高于常规材料,并且陶瓷的共振频率随着晶粒尺寸的减小而降低.文章从微观结构与极化机理方面解释了出现这种现象的原因.     

尺寸效应对细晶粒BaTiO3陶瓷电滞现象的影响

考虑到转向极化和反向畴的成核生长过程的综合影响,引入了一个反映两种过程影响程度的比例参数,对细晶粒BaTiO3陶瓷的电滞回线进行了理论分析,其结论与试验结果是极其一致的,这将有助于深入了解晶粒尺寸效应对BaTiO3陶瓷极化影响的机制。     

细晶Ba0.6Sr0.4TiO3(BST)陶瓷材料的制备与介电性能

采用改进的Sol-gel工艺和传统烧结技术制备了晶粒尺寸在0.15～10μm的Ba0.6Sr0.4TiO3(BST)陶瓷,观察了样品的显微结构,并对样品的介电性能进行了测试,分析了晶粒尺寸对材料介电性能的影响.实验结果表明:改进的Sol-gel工艺和两步烧结法可以有效地控制Ba0.6Sr0.4TiO3(BST)陶瓷的晶粒尺寸.晶粒尺寸的降低,材料的介电常数也随之下降,介电峰呈现明显的铁电-顺电弥散相变;但当陶瓷的晶粒尺寸＜1 μm,介电常数出现峰值,铁电相变温区变窄.     

原位XRD测试PLZT铁电陶瓷的电致畴变

通过传统固相法合成了四方相结构、晶粒平均尺寸1~2μm且化学组成约为Pb0.93La0.07(Zr0.52,Ti0.48)O3的铁电陶瓷试样。利用自制的电加载装置与常规XRD测试仪器联用,在不同外加直流电场作用下实现了陶瓷试样的原位XRD测试,通过分析(002)和(200)的相对峰强变化,计算了90°畴转向率,并与非原位XRD测试得到的数据进行比较,初步分析了外加电场卸载前后铁电陶瓷的电致畴变行为。结果表明,高达7%的a畴在电场卸载瞬间会发生回转。     

晶粒可控钛酸钡致密陶瓷的制备及表征

采用超重力反应沉淀法制备的纳米钛酸钡粉体和常规陶瓷工艺,通过控制烧结温度在 1200 ~1300℃,分别制备了晶粒尺寸 0.45~2.2μm的致密陶瓷。实验结果表明超重力反应沉淀法制备的粉体具有良好的烧结和介电性能。烧结温度为 1200℃时,相对密度即可达到95%,晶粒尺寸为 0.45μm,随烧结温度的升高,晶粒逐渐长大,未出现晶粒的异常长大现象,到1300℃相对密度和晶粒尺寸分别达到 97.7%和2.2μm。钛酸钡陶瓷介电性能有明显的粒度效应,晶粒在1.2μm左右时,室温介电常数达到最大(4143)。由于晶粒内部立方相成分的出现,包含更细晶粒的陶瓷(d=0.45μm)呈现低的介电常数。     

纳米钛酸钡陶瓷的特殊烧结方法和新颖特性的研究进展

对近年来有关纳米钛酸钡陶瓷最新的烧结方法、新颖性质进行了综合评述和讨论。当晶粒尺寸减小到纳米尺度时，钛酸钡陶瓷的晶体结构在不同的温度下出现了不同的多相共存。这可以用纳米钛酸钡陶瓷相变产生的应力来解释。纳米钛酸钡陶瓷的铁电性能表现出新颖的特性。它的介电常数先随晶粒尺寸的减小而降低，但当晶粒尺寸降低到小于50nm甚至小于10m时，介电常数表现出反常的增加，同时铁电向顺电的转变峰变为一个很宽的峰，表现出弥散相变的特征。     

晶粒尺寸对细晶钛酸钡陶瓷介电、压电和铁电性能的影响

以采用水热法制备的BaTiO₃粉体作为原料, 利用普通烧结法和两步烧结法制备出晶粒尺寸为0.25~10.15 μm的BaTiO₃陶瓷, 研究了晶粒尺寸效应对BaTiO₃陶瓷的介电、压电以及铁电性能的影响。结果表明: BaTiO₃陶瓷的四方相含量随着陶瓷晶粒尺寸的增大而增加; 当晶粒尺寸在1 μm以上时, 室温相对介电常数(ε° )和压电系数(d₃₃)随着晶粒尺寸的减小而增大, 并在晶粒尺寸为1.12 μm时分别达到最大值5628和279 pC/N, 然后两者随着晶粒尺寸的进一步减小而迅速下降。BaTiO₃陶瓷的剩余极化强度P_r随晶粒尺寸的增大而提高, 而矫顽场E_c却呈现出相反的趋势。晶粒尺寸对介电性能和压电性能的影响是由于90°电畴尺寸和晶界数量的变化。晶粒的晶体场和晶粒表面钉扎作用的变化影响了电畴, 进而改变电滞回线。     

BaTiO3超微粉及其在陶瓷中的晶粒尺寸效应

用Ｓｏｌ－Ｇｅｌ法制备了ＢａＴｉＯ３超微粉并经烧结获得了不同粒径的陶瓷。用Ｘ射线衍射研究了室温晶体结构。在粉末压块和陶瓷上测得了介电常数的温度依赖性。介电常数－温度曲线表明，随着晶粒尺寸减小，居里温度降低，而四方－正交以及正交－三角相变温度升高。在晶粒尺寸减小过程中，三个介电峰逐步降低和宽化并按如下顺序最终消失：三角－正交，正交－四方和四方－立方。用介电测量确定了铁电性消失的临界尺寸，其值与文献中     

粗大晶粒PZT陶瓷中电畴的结构

应用扫描力显微镜(SFM)的压电响应模式观测未经抛光处理的PZT陶瓷片的电畴结构,用纵向压电响应信号和侧向压电响应信号获得PZT陶瓷材料三维电畴结构.结果表明,将样品晶粒的微形貌与SFM的纵向和侧向压电响应信号相结合,能准确表征粗大晶粒样品的三维电畴结构.用SFM可观测表面不经任何处理的陶瓷样品的电畴,不会引入表面应力等影响因素,能得到样品的原生畴结构.对原生畴结构的观察表明,对于受应力较大的晶粒,成畴的主要原因是降低应变能,而受应力较小的晶粒成畴的主要原因是降低退极化能.     

Ba0.65Sr0.35TiO3陶瓷材料的制备及介电特性研究

采用溶胶-凝胶工艺制备了Ba_0.65Sr_0.35TiO₃粉体,并利用微波烧结技术对粉体进行了合成和烧结,研究分析了样品的介电特性,并与传统制备工艺获得的样品进行了性能比较.实验结果表明,获得的Ba_0.65Sr_0.35TiO₃粉体颗粒较细,其合成温度和烧结成瓷温度都较传统工艺有大幅度降低,分别为900和1310℃;可以获得晶粒尺寸在1μm以内的陶瓷;随晶粒的减小,材料的相对介电常数变化不大,而介电损耗大大降低.     

Fabrication and characterization of fine-grained barium strontium titanate ceramics by the heterogeneous precipitation method

The heterogeneous precipitation method has been successfully used to prepare SrCO₃ nanoparticle-coated BTO (BaCO₃ or TiO₂) powders by using PAA (polyacrylic acid) and NH₄HCO₃ as the dispersant and precipitator, respectively. Compared to the mixture obtained by the direct ball milling of the BaCO₃, SrCO₃ and TiO₂ powders during the conventional solid-state process, this coated structure is effective for the low temperature synthesis of barium strontium titanate (BST) powders. Sintering study of the powder synthesized by this method showed the dense and fine-grained BST ceramics could be obtained at a low sintering temperature. The grain size effect on the sensitivity of the dielectric constant vs. frequencies was discussed for the first time. Compared to the coarse-grained material, the fine-grained sample exhibits the better sensitivity of dielectric constant vs. frequency at ferroelectric state. It was shown that as the grain size decreased, the transition became diffuse, transition temperature (T _c) decreased and the dielectric constant increased.     

Abnormal high dielectric constant in SmFeO3 semiconductor ceramics

The dielectric properties and impedance spectroscopy (IS) of perovskite SmFeO₃ ceramics were studied in the frequency range of 100 Hz-1 MHz in the temperature range from 80 K to 300 K. These materials exhibited colossal dielectric constant of ∼10⁴ at room temperature. The response is similar to that observed for relaxor-ferroelectrics. IS data analysis indicates the ceramic to be electrically heterogeneous semiconductor consisting of semiconducting grains with dielectric constant 20 and more resistive grain boundaries. We conclude, therefore that grain boundary effect is the primary source for the high effective dielectric constant in SmFeO₃ ceramics.     

Dielectric Properties of Porous Reaction-boned Si3N4 Ceramics with Controlled Porosity and Pore Size

This paper presents the microwave dielectric properties of reaction bonded porous silicon nitride ceramics with variant porosity and pore size, which were prepared by adding pore-forming agent grains into the silicon powders. The experimental results show that the dielectric constant and the dielectric loss of the samples reduce evidently with increasing porosity in the sample. When the porosity is constant, the dielectric constant and the dielectric loss of the ceramics decrease visibly as the pore size increases. Among all the obtained samples, the minimum dielectric constant is about 2.4.     

粒度对纳米掺杂BaTiO3陶瓷结构和性能的影响

制备了纳米掺杂BaTiO3陶瓷，研究了纳米掺杂剂和BaTiO3的粒度对BaTiO3陶瓷的微观结构和介电性能的影响．结果表明，小粒度、高分散的纳米掺杂剂更易对BaTiO3颗粒实现均匀包裹，有效地抑制晶粒生长并形成更多的壳-芯晶粒，大比表面积使更多高活性的表面原子与BaTiO3发生原子输运形成传质，导致晶粒壳／芯比增大，从而提高其介电性能．纳米掺杂陶瓷的平均晶粒尺寸和四方率与BaTiO3粒度几乎成正比．随着BaTiO3粒度的减小，立方晶粒壳增大而四方晶粒芯减小，陶瓷由四方晶相向赝立方晶相转变，居里峰被显著压制，从而改善介电温度特性．同时，晶粒的壳与芯之间失配产生的内应力随之增加，使居里点向高温方向移动．     

Control of temperature coefficient of resonant frequency in Ba4Sm9.33Ti18O54 ceramics by templated grain growth

A novel tuning method of temperature dependence of dielectric properties in Ba₄Sm_9.33Ti₁₈O₅₄ (BSmT) microwave material was demonstrated by texture engineering. Two kinds of grain-oriented BSmT ceramics were obtained using a templated grain growth technique. Highly fiber-textured ceramics were fabricated by tape casting of slurry with a mixture of 〈001〉-elongated BSmT template particles and fine-grained BSmT powder. On the other hand, partially grain-oriented ceramics were also obtained from the uniaxially pressed mixture of the template particles and the fine-grained powder. Orientation degree of sintered BSmT ceramics increased with a content of template particles. As compared with the specimen prepared by normal sintering technique, the textured ceramics displayed a large anisotropy in the dielectric properties, especially in the temperature coefficient of resonant frequency (τ_f). Consequently, near-zero τ_f was obtained in the textured ceramics with (hk0)-orientation degree of approximately 0.10 in the surface of the disk specimen. In addition, the τ_f could be controlled to a desired value from ranging −90 to +25 ppm/°C by adjusting the grain orientation in the specimen. Measurement of the temperature dependence of dielectric constant, which correlates with τ_f, revealed positive and negative behaviors for (hk0) and (001) textured BSmT ceramics, respectively. The tuning of τ_f was explained as a rule of mixture of dielectric anisotropy in BSmT.     

Effects of grain boundary on dielectric properties in fine-grained BaTiO3 ceramics

BaTiO₃ dielectric ceramics, which have no core–shell structure, were prepared. High-resolution transmission electron microscope (TEM) and the newly developed chemical etching analysis revealed the composition of the grain boundary. The grain boundary has an important role in stabilizing temperature dependence of a dielectric constant. The grain boundary causes a large stress against grains, resulting in a change of the domain structure. So, the stress from the grain boundary is considered to depress the dielectric abnormality at the Curie temperature.     

巨介电常数陶瓷CaCu3Ti4O12的研究进展

CaCu_3Ti_4O_(12)(CCTO)陶瓷具有高介电常数和高热稳定性,这使得CCTO可能在高密度信息储存、高介电电容器、大规模集成电路等领域获得广泛使用。系统地介绍了CCTO高介电常数起源的内禀机制和外禀机制,详细归纳了元素掺杂对CCTO介电特性的影响,阐述了巨介电常数与本征点缺陷的内在关联,肯定了晶粒电导赝极化理论,指出了CCTO巨介电常数陶瓷研究的重点在于:基于外禀机制的IBLC模型,通过晶胞掺杂或晶界掺杂改变晶粒或者晶界的电导,进而调控CCTO的介电损耗,使CCTO保持较高介电常数的前提下,在很宽的频率范围内使介电损耗正切值降低到0.1以下。