中文论文文摘

钛酸盐包括钛酸钡，钛酸铋等以及其各自掺杂系列是目前颇为流行的电子陶瓷材料。钛酸钡（BaTiO3）是性能优异的强介电和铁电材料，被广泛应用于制造热敏电阻器、多层陶瓷电容器、电光器件和DRAM器件。钛酸铋（Bi4Ti3O12）具有优良的铁电、电光特性，自发极化强度大，居里温度高，矫顽电场小，抗疲劳性能好，在现代微电子、微电机系统、存储器等方面有着广泛的应用前景。通过掺杂特定元素对钛酸盐材料进行改性可满足不同用途所需的温度特性、介电常数和频率特性等。总之，随着电子元件的飞速发展，钛酸盐粉体在航天、火箭、电力、视频设备等方面的应用越来越普遍。

目前，钛酸盐粉体的制备方法有：固相法、熔融法、高能球磨法、共沉淀法、溶胶凝胶法和水热法。其中水热法制成的纳米粉体纯度高，粒度分布窄，团聚程度轻，晶粒组分和形态可控，反应活性好，有利于掺杂，是陶瓷粉体理想的合成方法。

本课题采用水热法以BaCl2·2H2O、Bi(NO3)3·5H2O、TiCl4为前驱物源，MgCl2·6H2O、Dy2O3、La(NO3)3·6H2O为添加剂，NaOH、KOH为矿化剂，分别制备了掺Mg、Dy的BaTiO3和掺La的Bi4Ti3O12粉体，利用XRD、AES、TEM和SEM等手段对所得粉体的晶相组成、晶粒度、晶粒形貌等进行了分析，并且测试了相应瓷体的介电常数和击穿场强等电性能。讨论了水热反应温度、反应时间、矿化剂浓度、掺杂量对晶相组成、微观结构、晶粒度和电性能的影响。结果表明：①Mg固溶到BaTiO3晶体中取代钛位，起受主掺杂，其对BaTiO3的居里峰有移峰作用，r（Mg/Ti）= 0.06是Mg的最佳掺入量，此时瓷体致密度最高，常温下表现出较高的介电常数4100。②微量Dy掺杂时，发生Ba位取代，掺杂量较高时，Dy3+占据Ti4+的位置。Dy2O3掺杂量为0.6wt%时，能有效控制晶粒的生长，瓷体晶粒尺寸约为480 nm。Dy对于BaTiO3没有明显的移峰和压峰作用，室温下介电常数达到4250且随温度变化率在–10%～10%内，稳定性良好。交流击穿场强高达3.2 kV/mm。③[Ti]＝0.1M，矿化剂[KOH]＝1.0 M，在220～260℃条件下，保温2～6 h，得到纳米级La掺杂Bi4Ti3O12粉体。La掺杂抑制了Bi4Ti3O12的晶粒生长，尤其是在b轴方向，抑制了晶核的生长速度，所得晶粒呈方形片状结构。

此外，本课题还借鉴温度调制式示差扫描量热法的技术原理，设计了一套水热反应－在线热分析一体化系统，将两个不同的升温速率同时作用于试样，一是平均的慢速升温，另一是叠加了一个正弦调制(振荡)温度波形以产生一个随时间连续增加但不是线性的升温模式。结果便在同一实验中实现了水热保温过程，同时以基础升温的慢速率来改善分辨率，并以瞬时快速升温速率提高灵敏度。此系统能够对密闭的水热反应实现在线监控，获得一系列实时的热数据，能够分离水热反应中相重叠的热力学和动力学变化，探测一些微小甚至被覆盖隐藏的热变化等传统DSC，TDA不能获取的大量信息。

外文论文文摘

Titanate including barium titanate, bismuth titanate and their doped series are the best-known electronic ceramic materials at present. Barium titanate (BaTiO3) has been broadly used as the raw material for heat variable resistor, multi-layer ceramic capacitors, electro-optic device and dynamic random access memories. Owing to excellent ferroelectric, electro-optic trait, large spontaneity polarization intensity, low coercive field and better fatigue endurance, bismuth titanate (Bi4Ti3O12) has been receiving extensive investigations for its potential applications in microelectronics, micromachine and memories. Through introducing a certain elements into titanate, materials’ properties can be modified to meet temperature, dielectric and frequency demands. In all, with fast development of electronic components, titanate will has universal applications in aerospace, rocket, electrical power and video devices.

So far, several methods, including solid-state reaction, fused state synthesis, high-energy ball milling, co-precipitation, sol-gel and hydrothermal synthesis, have been developed for the synthesis of titanate powders. Among them, hydrothermal synthesis is considered as a promising way to prepare nanometer powders, which presents the following major advantages: high purity, narrow particle size distribution, low coacervation, high crystallinity, controllability of composition and morphology, high activity and workability to dope.

In the hydrothermal experiment, BaCl2·2H2O, Bi(NO3)3·5H2O and TiCl4 were used as precursors for barium, bismuth and titanium respectively. MgCl2·6H2O, Dy2O3, La(NO3)3·6H2O were used as additives and NaOH or KOH was used as mineralizer. Nanosized Mg or Dy doped barium titanate and La doped bismuth titanate powders were prepared by the method respectively. The effects of doping on composition, morphology, microstructure and electrical properties of BaTiO3 and Bi4Ti3O12 were investigated by X-ray diffractometer (XRD), atomic emission spectrum (AES), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) characterizations. As is indicated by results: ①Mg, as a kind of acceptor, entered into the BaTiO3 lattice and existed substitutionally in Ti site, which made the ceramics exhibit a microstructure with small grains and high density. Mg had evident function on shifting Curie peak. The optimized atomic ratio of Mg/Ti was 0.06, and the MgO-BaTiO3 ceramics showed high dielectric constant up to 4100. ②Ba site was replaced if a little Dy2O3 was doped but some more Dy would take up the positions of Ti. Dy had no influence on shifting and depressing Curie peak. When Dy2O3 content was 0.6 wt%, grains growth was effectively restrained and ceramic grain size was 480 nm. The dielectric constant rose up to 4250 at room temperature and varied from –10% to 10% at –15～100℃. Breakdown electric field rose up to 3.2 kV/mm without any sintering aids. ③ La-doped Bi4Ti3O12 powders were prepared at 220～260℃ for 2～6 h under the conditions of [Ti]＝0.1M, [KOH]＝1.0M. La doping restrained grains growth of Bi4Ti3O12, especially along b axis, which leaded to square slide-shape structure of grains.

Further more, a set of system integrating hydrothermal synthesis and online thermal analysis was designed according to the technical principle of temperature modulated differential scanning calorimetry. It applies two different heating velocities to the sample. One is basic slow heating, and the other is sine function of modulated temperature. In this way, keeping hydrothermal temperature could be guaranteed. Besides this, distinguishability and sensitivity are both enhanced. The system enables to monitor and control airtight hydrothermal reaction online, obtain a series of thermal data, separate thermodynamics changes from dynamics ones and probe some slight even hided thermal changes, which can not be collected by traditional DSC and TDA.