| Titanate including barium titanate, bismuth titanate and their doped seriesare 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 accessmemories. Owing to excellent ferroelectric, electro-optic trait, large spontaneitypolarization intensity, low coercive field and better fatigue endurance, bismuthtitanate (Bi4Ti3O12) has been receiving extensive investigations for its potentialapplications in microelectronics, micromachine and memories. Throughintroducing a certain elements into titanate, materials' properties can be modifiedto meet temperature, dielectric and frequency demands. In all, with fastdevelopment of electronic components, titanate will has universal applications inaerospace, 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 nanometerpowders, which presents the following major advantages: high purity, narrowparticle size distribution, low coacervation, high crystallinity, controllability ofcomposition and morphology, high activity and workability to dope.In the hydrothermal experiment, BaCl2·2H2O, Bi(NO3)3·5H2O and TiCl4were used as precursors for barium, bismuth and titanium respectively.MgCl2·6H2O, Dy2O3, La(NO3)3·6H2O were used as additives and NaOH or KOHwas used as mineralizer. Nanosized Mg or Dy doped barium titanate and Ladoped bismuth titanate powders were prepared by the method respectively. Theeffects of doping on composition, morphology, microstructure and electricalproperties 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 isindicated by results: ①Mg, as a kind of acceptor, entered into the BaTiO3 latticeand existed substitutionally in Ti site, which made the ceramics exhibit amicrostructure with small grains and high density. Mg had evident function onshifting Curie peak. The optimized atomic ratio of Mg/Ti was 0.06, and theMgO-BaTiO3 ceramics showed high dielectric constant up to 4100. ②Ba sitewas replaced if a little Dy2O3 was doped but some more Dy would take up thepositions of Ti. Dy had no influence on shifting and depressing Curie peak.When Dy2O3 content was 0.6 wt%, grains growth was effectively restrained andceramic grain size was 480 nm. The dielectric constant rose up to 4250 at roomtemperature and varied from –10% to 10% at –15～100℃. Breakdown electricfield rose up to 3.2 kV/mm without any sintering aids. ③ La-doped Bi4Ti3O12powders 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 onlinethermal analysis was designed according to the technical principle oftemperature modulated differential scanning calorimetry. It applies two differentheating velocities to the sample. One is basic slow heating, and the other is sinefunction of modulated temperature. In this way, keeping hydrothermaltemperature could be guaranteed. Besides this, distinguishability and sensitivityare both enhanced. The system enables to monitor and control airtighthydrothermal reaction online, obtain a series of thermal data, separatethermodynamics changes from dynamics ones and probe some slight even hidedthermal changes, which can not be collected by traditional DSC and TDA.
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