超快速高温烧结钛酸钡压电陶瓷的制备及性能

烧结工艺直接影响陶瓷的显微结构及性能。利用超快速高温工艺制备钛酸钡压电陶瓷,并与常规烧结工艺制备的钛酸钡陶瓷进行对比。研究了超快速高温烧结电流对钛酸钡陶瓷组成、结构以及性能的影响。结果表明：超快速高温烧结可以抑制晶粒的生长,采用超快速高温烧结工艺在电流为180 A保温5 min后,钛酸钡陶瓷的室温相对介电常数为3 450、介电损耗为1.89%、压电常数为283 p C·N^–1,这些性能均与常规烧结钛酸钡性能相当,超快速高温整个烧结时间较常规工艺缩短了196倍,是一种新型高效功能陶瓷烧结方法。     

钛酸钡超细粉末的制备

德国莱比锡表面改善研究所莱比锡大学和波恩大学的科研人员使用钡钛丙烯酸酯作单体金属—有机前体 ,先将钡钛丙烯酸酯聚合 ,然后进行高温分解。制备出钛酸钡超细粉末 ,粒度范围在 1 0nm～1 5mm之间。钙钛矿型的BaTiO3是最重要的铁电材料之一 ,柔软的铁电陶瓷与聚合物的复合材料箔 ,用来作工业技术上有前途的集成电容器薄膜材料 ,以提供高介电常数和低的损耗钛酸钡超细粉末的制备     

溶胶-凝胶法制备钛掺杂BaFe_(12)O_(19)陶瓷

通过溶胶-凝胶法制备了钛掺杂的M型钡铁氧体BaFe12-x Tix O19(BFTO)粉末以及陶瓷材料。利用X射线衍射谱对掺杂体系的物相形成进行了研究,利用扫描电子显微镜对掺杂体系的结晶形貌进行了观察,采用磁学测试系统和阻抗分析仪测试了掺杂体系的磁学性能。结果表明:800℃可以得到结晶性较好的BFTO原料粉末,并在1 200℃可烧结得到晶型完整的钡铁氧体相陶瓷,其烧结温度比未掺钛钡铁氧体相陶瓷低约100℃。这种陶瓷的磁导率≥5,比未掺钛陶瓷的提高了3~4倍,且频率稳定性好(≤70MHz时基本保持不变)。陶瓷相应的矫顽力下降≥65%,饱和磁化强度和剩余磁化强度仅降低10%~15%。在相关器件中使用时,有望在保持高剩余磁化强度的同时有效地降低能耗,显著改善器件的性能,推动相关领域向小型化和微型化发展。     

固相法烧结温度对钛酸钡陶瓷介电性能的影响

研究了固相法烧结温度对钛酸钡陶瓷介电性能的影响.采用固相法在不同温度下烧结钛酸钡陶瓷.结果表明,不同烧结温度对钛酸钡陶瓷晶体结构、微观形貌、介电常数、介电损耗、居里温度等都会产生不同的作用效果.钛酸钡陶瓷只有在最佳烧结温度附近才具有最好的结构和性能,烧结温度过低会使烧结过程不充分,引起过多的点缺陷;而过高的烧结温度也会由于过烧现象的存在而使晶粒与晶界间相互作用出现异常,两种情况都会导致钛酸钡陶瓷介电性能的劣化.     

撞击流反应器制取纳米钛酸钡

在浸没循环撞击流反应器中，以四氯化钛、氯化钡和草酸为原料，采用沉淀法制取纳米钛酸钡，并对产品进行了透射电子显微镜（TEM）表征。通过均匀实验设计，研究了反应温度、加料时间、反应后陈化时间及钡钛物质的量比等因素对产品粒径的影响；初步确定了制备纳米钛酸钡适宜的工艺条件为：反应温度75℃，陈化时间200min，加料时间20min，反应物中钡与钛的物质的量比1．01。制取的钛酸钡产品经TEM表征，其形状皆为球状，具有沉淀法制取的钛酸钡的典型粉体特征，在适宜工艺条件下制取的产品平均粒径为60nm。     

水热反应条件对合成BaTiO3纳米粉体影响的研究

通过正交实验法,对不同钡钛比、反应温度、保温时间进行了水热合成钛酸钡纳米粉体的实验研究,对所得粉体进行了DTA,XRD,TEM等分析表征,分析研究了不同水热反应条件对合成钛酸钡纳米粉体的影响。     

钛酸钡基厚薄膜PTCR的研究

介绍了钛酸钡基厚、薄膜PTCR的制备方法与研究进展。射频磁控溅射和溶胶-凝胶成膜技术是制备陶瓷PTCR薄膜的较理想的方法。陶瓷PTCR厚膜技术由于具有成本低和较好的市场前景受到人们的高度重视。目前钛酸钡基PTCR厚、薄膜技术的研究已经取得了较大的进步和发展。PTCR膜材正向着低室温电阻、高升阻比和集成化的方向发展。     

钛酸钡的制造方法

本发明是关于粒径为0.07～0.5μm微细的、比表面积小的、粒度分布窄的、球状新型钛酸钡的制造方法。特别是可以低温烧结的新型钛酸钡粉末的制造方法。 该方法是含水氧化钛和钡的氯化物和/或硝酸盐,以碱金属氢氧化物对钡的氯化物和/或硝酸盐摩尔比为2.1～5∶1,在以钛计120～10000倍摩尔水的存在下,于60～110℃下反应,得到钛酸钡;钡的氯化物和/或硝酸盐对含水氧化钛的摩尔比为1～3;碱金     

水热法制备钕掺杂BaTiO3粉体及其介电性能研究

以BaCl2·2H2O、TiCl4和NdCl3为原料,采用水热法制备了掺钕的BaTiO3纳米粉体,并经高温烧结后得到瓷体。利用DTA、XRD、SEM等测试手段,分析了钕掺杂对钛酸钡粉体及其陶瓷电性能的影响。研究表明,掺杂后,钕固溶到了钛酸钡的晶格中并取代钡位或钛位。钕的掺杂有助于获得细晶高致密的陶瓷,当W(NdCl3)%为0.6时,致密度最高,常温下相对介电常数高达5650,击穿场强达到3.5kV/mm。     

TiSi_2改善TiB_2陶瓷烧结性能的研究进展

本文介绍了硼化钛陶瓷的性能与应用,重点介绍了不同的烧结方法、不同的烧结助剂对硼化钛陶瓷烧结性能的影响,在对TiSi2材料性能特点分析的同时,阐述了TiSi2作为烧结助剂改善硼化钛陶瓷烧结性能与抗氧化性能的依据,指出了开展TiSi2改善TiB2陶瓷的烧结性能与抗氧化性能的研究亟待解决的问题,提供了一条改善TiB2陶瓷烧结性能的新途径,具有理论意义与应用价值。     

掺镁钛酸钡的抗还原研究

对掺镁钛酸钡进行了．抗还原研究。研究了Ba／Ti摩尔比、镁掺杂摩尔分数和烧结气氛对陶瓷的致密化、电阻率以及介电性能的影响。结果表明：在氮气气氛中烧结的样品比在空气中烧结的样品具有更大的介电常数、较小的介电损耗。当烧结温度和保温时间都相同时,与在空气中烧结的样品相比,在氮气气氛条件下烧结的样品具有较大的密度,较大的电阻率．较大的介电常数和较小的介电损耗。当镁掺杂摩尔分数为1％时、随着Ba／Ti摩尔比的增加,介电损耗的变化不大;而当镁掺杂摩尔分数为2％时,随着Ba／Ti摩尔比的增加,介电损耗增加。     

Influence of Ba/Ti Ratio on the Positive Temperature Coefficient of Resistivity Characteristics of Ca-Doped Semiconducting BaTiO3 Fired in Reducing Atmosphere and Reoxidized in Air

The positive temperature coefficient of resistivity (PTCR) characteristics of donor-doped BaTiO₃ fired in a reducing atmosphere and reoxidized in air are investigated. The result reveals that conventional semiconducting BaTiO₃ ceramics fired in a reducing atmosphere and reoxidized at a low temperature of 800°C in air show minimal PTCR characteristics, as reported earlier; however, Ca-doped BaTiO₃ with compositions in the range of 1.005≤(Ba+Ca+La)/Ti≤1.010 exhibit pronounced PTCR characteristics, even when reoxidized at such a low temperature. The semiconducting BaTiO₃ ceramics with {(Ba+Ca+La)/Ti}=1.005 and Ca-doped to 20 mol% exhibit remarkable PTCR characteristics with a resistivity jump of two orders of magnitude when they have been reoxidized at 800°C after firing in a reducing atmosphere.     

Influence of Stoichiometry on the Microstructure and Positive Temperature Coefficient of Resistivity of Semiconducting Barium Titanate Ceramics

The influence of stoichiometry, i.e., Ba/Ti ratio, on the microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of BaTiO₃ was investigated. Fine-grain microstructures are obtained for Ba-rich, stoichiometric, low-temperature-sintered, Ti-rich materials. The room-temperature resistivities ( ρRT ) of the fine-grain Ti-rich samples are large (>10⁸Ω·cm). Excess Ba²⁺ ions can decrease the ρRT , by more than 2 orders of magnitude, because of the compensation of barium vacancies near the grain-boundary regions. Rapid cooling after sintering can also decrease ρRT (⋍100×) and is ascribed to the suppression of reoxidation. Large-grain microstructures and low ρRT , on the other hand, are generally observed for Ti-rich and Al₂O₃-SiO₂-TiO₂-added samples after sintering at a temperature higher than the corresponding eutectic point.     

Effect of Ba: Ti Ratio on Densification of LiF-Fluxed BaTiO3

The literature on LiF-fluxed BaTiO₃ has shown substantially lower sintering temperatures compared to that of unfluxed BaTiO₃. In an effort to understand densification behavior in this system, shrinkage was studied for various Ba: Ti ratios and 2 wt% LiF additions. Sintering of BaTiO₃ with LiF is sensitive to the Ba:Ti ratio. Excess Ba reduced the sintering temperature and increased the fired bulk density. The starting powder stoichiometry, net Ba:Ti ratio, and addition of LiF appear to be independently important.     

Hydrothermal Synthesis of Nanometer-Sized Barium Titanate Powders: Control of Barium/Titanium Ratio, Sintering, and Dielectric Properties

Nanometer-sized BaTiO₃ powders have been synthesized hydrothermally from Ba(OH)₂ and titanium alkoxide at 150°C for 2 h, and the Ba/Ti ratio has been measured with an accuracy of ±0.003. Stoichiometric powders can be obtained by adjusting the Ba/Ti ratio of the reactants to a value of 1.018. At a lower Ba/Ti ratio, the solubility of Ba(OH)₂ prevents full incorporation of barium, and barium-deficient powders result. A higher Ba/Ti ratio leads to the incorporation of excess barium in the powder. K _s(BaTiO₃,-25°C) = 7 × 10^-8 has been calculated for the equilibrium reaction. From this result, two reproducible processes for the synthesis of stoichiometric BaTiO₃ are proposed. The processes rely only on very accurate control of the chemical composition (Ba/Ti ratio) of the precursor suspension. The sintering behavior of powders having Ba/Ti ratio values between 0.965 and 1.011 is described from results of dilatometric measurements and isothermal sintering. Room-temperature dielectric constants as high as 5600 and losses as low as 0.009 have been obtained for a stoichiometry slightly less than 1.000. It is expected that optimum sintering behavior and electrical properties are obtained in the stoichiometry range 0.995-1.000.     

Proposed Phenomenological PTCR Model and Accompanying Phenomenological PTCR Chart

The positive temperature coefficient of resistivity (PTCR) behavior of semiconductive BaTiO₃ is well explained by the Heywang model, which predicts the resistivity behavior above the Curie point based on the acceptor state density at the grain boundaries, the charge carrier density, and the energy gap, E _s, between the conduction band and the acceptor levels. However, the relationship between these parameters and the production parameters (sintering time, composition, and cooling rate) is not well understood. Recently, the present authors have found that E _s can be increased by thorough oxidation. This increase is attributed to a change in the oxidation state of the acceptor. Based on this finding and results from the literature, a phenomenological PTCR model and an accompanying PTCR chart for acceptor–donor-codoped BaTiO₃ are proposed to clarify this relationship. The PTCR chart clarifies that acceptor dopant concentrations, oxidation time, and oxygen partial pressure during oxidation or cooling can be optimized simultaneously to obtain optical PTCR properties.     

Ti3AlC2陶瓷的制备及其摩擦磨损性能

以钛、铝、碳粉为反应物原料,采用反应烧结技术制备了Ti3AlC2陶瓷,研究了各工艺参数对制备试样物理性能的影响,同时也对其摩擦磨损性能进行了分析。实验结果表明：按照摩尔比x（Ti）：y（Al）：z（C）=3.0：1.2：2.0的配比进行反应烧结,在1 300℃烧结0.5 h,能够制备出高纯致密的Ti3AlC2陶瓷,其质量含量高达94.6%,孔隙率为9.4%。当烧结温度过低时,得到的Ti3AlC2陶瓷含量较低,且杂质较多;当烧结温度过高时,会导致Ti3AlC2陶瓷发生分解反应。当载荷较小时,Ti3AlC2陶瓷磨损以磨损面的解理流变和粒子脱落造成的磨粒磨损为主;而载荷较大时,其磨损机理以轻微划痕和轻微黏着磨损为主。     

Exceptional reliability of MLCCs enabled by defect-engineered BaTiO3

It has generally been believed that the reliability of BaTiO₃-based multilayered ceramic capacitors (MLCCs) is mainly contributed by hydroxyl (OH⁻), and the contribution of CO₃²⁻ can be neglected. However, in this work, we demonstrated that the contributions of Ba/Ti ratio and CO₃²⁻ play important roles in the delivering high reliability for BaTiO₃-based MLCCs. The structure and performance of MLCC devices and ceramic chips based on BaTiO₃ powders prepared by different approaches were studied. It is found that the intracrystalline pores in ceramics or MLCCs are mainly derived from the decomposition of BaCO₃ during sintering, which has been demonstrated by ceramic derived from hydrothermal method powder and its modified powders. The point defects of Ba and Ti vacancies mainly originating from nonstoichiometric Ba/Ti rather than thermally stimulated have substantial influence on the migration of grain boundary that determines the grain size and whether the pores can be annihilated from the bulk material. Particularly, the Ti vacancies have a strong pinning effect and inhibit the migration of grain boundary effectively, due to their shorter migration distance comparing to Ba vacancies. Therefore, the synergetic effect of the second phase BaCO₃ and point defects leads to the differences in the structure and performance.     

多施主掺杂PTC陶瓷材料的研究

本文在双施主掺杂高ＴｃＢａＴｉＯ_３基ＰＴＣ陶瓷材料的基础上,对ＢａＴｉＯ_３的Ａ、Ｂ、Ｏ位同时进行离子置换以实现多施主掺杂,同时还研究了烧结温度对阻温特性的影响。研究结果表明,多施主掺杂试样的烧成温度对ｐ－Ｔ性能影响很大,在一定配方及工艺条件下,获得的ＰＴＣ陶瓷材料的室温电阻率变化不大,升阻比明显提高。     

Positive Temperature Coefficient of Electrical Resistivity below 150 K in Barium Strontium Titanate

The resistivity of Ba_{(1– y )(1– x )}Sr _y (1– x )La _x TiO₃ceramics with x = 0.0025 and y = 0.25, 0.5, 0.75, and 0.9 was measured between 50 and 400 K. A resistivity anomaly corresponding to the positive temperature coefficient of electrical resistivity (PTCR) effect was observed for all compositions. The onset temperature decreased from 320 K ( y = 0.25) to 70 K ( y = 0.9). The extent of the PTCR effect was significantly enhanced for the strontium-rich composition and reached ∼8 orders of magnitude for y = 0.9. These results strongly suggested the possibility to fabricate PTCR devices based on (Sr,Ba)TiO₃ ceramics for application at cryogenic temperatures.