The preparatory optimal conditions of barium titanate thin film from a hydrothermal method at low temperature

The preparation of barium titanate thin films on Ti substrates at low temperature using the hydrothermal process was studied. In addition, the interface relationship between film and substrate was investigated, revealing that the Ba²⁺ ion diffused into the Ti(OH)₄ gel formed by Ti in a strong alkaline solution, resulting in a homogeneous film. A 3-level orthogonal array design was utilized to optimize the experimental conditions. The effects of preparatory conditions such as the barium-concentration, NaOH concentration, reaction time and substrate surface treatment were systematically studied. Results indicate that the effects of the NaOH concentration and substrate surface treatment are the significant variables influencing the relative crystal intensity (intensity of (110) BaTiO₃ peaks in XRD spectrum/intensity of (001) Ti peak in XRD spectrum) of the films obtained. Polycrystalline, BaTiO₃-films were obtained, with improved crystallinity and a dielectric constant of about 915 at 1 MHz.     

国内外水热法钛酸钡性能的对比研究

对国产的两种水热法钛酸钡和日本生产的两种水热法钛酸钡进行了对比研究.结果表明国产的两种水热法钛酸钡的介电性能比日本生产的两种水热法钛酸钡的介电性能要差,其原因主要是原始钛酸钡粉体的颗粒形貌不同日本生产的两种水热法钛酸钡颗粒棱角分明,而国产的两种水热法钛酸钡颗粒圆化非常严重,这直接导致了其烧结性能的不同.颗粒园化的原因可能是水热反应的温度过高,保温时间过长,或者碱性过强.     

钛酸锶钡纳米粒子的低温煅烧法制备与表征

以氢氧化钡、氢氧化锶和钛酸丁酯为原料,采用低温煅烧(300～500℃)法合成了钛酸锶钡(BST)纳米粒子.用XRD、SEM、TEM和IR对产品进行了表征;用TG-DTA对前驱物的热演化过程进行了分析.结果表明,所得钛酸锶钡纳米粒子大小分布均匀,粒径约为13～20nm,粒子形状近似为球形,晶相结构为立方相.该粉体为完全互溶体的固溶体,随Sr含量的增加,晶胞参数a和晶胞体积V减小,a随组成呈线性关系,符合Vegard定律.     

Frequency and temperature dependence dielectric behavior of barium zirconate titanate nanocrystalline powder obtained by mechanochemical synthesis

Nanocrystalline barium zirconium titanate ceramic has been synthesized by high-energy ball milling. This nano-ceramic is characterized by X-ray diffraction, scanning electron microscopy, dielectric study and impedance spectroscopy. The X-ray diffraction pattern shows single phase ceramic of tertragonal symmetry with space group P4 mm. Temperature and frequency dependent dielectric study of the sample shows a normal ferroelectric phase transition behavior. Impedance spectroscopy analyses reveal a non-Debye type relaxation phenomenon. A significant shift in impedance loss peaks toward higher frequency side indicates conduction in material and favoring the long range motion of mobile charge carriers. Grain and grain boundary conduction is observed from complex impedance spectrum by the appearance of two semicircular arcs in the Nyquist plot. The frequency dependent ac conductivity at different temperatures indicates that the conduction process is thermally activated. The variation of dc conductivity exhibited a negative temperature coefficient of resistance behavior.     

以偏钛酸为原料常压水热法合成纳米钛酸钡的研究

系统地研究了以廉价的偏钛酸为原料,经常压水热法一步合成钛酸钡.通过考察不同的钡钛比,反应温度,反应时间,溶液pH等条件下反应产物在浓盐酸溶液中的透射比的变化,得出了最佳的制备条件.当反应原料的钡钛比为1.4,反应温度是100℃,反应时间为6 h,溶液pH为12,所制备出的钛酸钡粉体为立方相,a值约为4.030,粉体一次平均粒径为40.9 nm.     

水热合成高纯四方相钛酸钡纳米粉末研究

以廉价易得氯化钡,四氯化钛为原料,在240℃下仅用12h水热合成得到四方相钛酸钡纳米粉末,从而为纳米粉末的产生化提供了简便条件。水热产物经XRD,SEM,XRF等手段特征,发现提高氢氧化钠过量的浓度,降低反应物四氯化钛浓度有利于四方相钛酸钡纳米粉末的生成,同时在水热产物中没有发现碳酸根和氯离子等残余的杂质表明产物具有较高的纯度。产物粒度小于100nm,比表面积为12m^2/g.     

Rate-controlled synthesis and sintering of nanocrystalline barium titanate powder

The densification and grain size during sintering as well as particle size, of the barium titanate powder during Pechini decomposition-synthesis depends on the heating rate and this dependence originates from the kinetic competition between elementary transformation mechanisms, inherent in the two processes. The given competition is the main reason for development of the optimum mode of the mentioned thermal activated processes. As developed at the NCSU (USA) the Rate-Controlled Sintering (RCS) is known to allow the obtaining of dense and finegrained ceramics with improved properties. As developed at the IPMS (Ukraine) the Rate-Controlled Synthesis is directed to prepare nanocrystalline unagglomerated ceramic powders suitable for RCS. The extreme behavior of the BaTiO₃ particle size as a function of heating rate is established and the optimal temperature-time path is calculated and verified to obtain the best powder of 20–25 nm particles. The change in microstructure and phase composition with heating rate is considered in details. The advantages of the RCS to achieve density of 99.9% and grain size around 100–150 nm are presented in comparison with the linear heating rate regime.     

微乳液-共沸蒸馏法制备钛酸钡纳米粉体

以水/正辛烷/正己醇/司班80油包水体系中的微乳液滴为纳米反应器,通过微乳液滴中增溶的醋酸钡和油相中草酸酰化的钛酸四丁脂反应生成钛酸钡前驱体,并通过共沸蒸馏去除前驱体中的水分,以减小煅烧过程纳米钛酸钡粉体的团聚.实验结果表明,此方法制备的前驱体只需在550℃煅烧就可以生成钛酸钡晶粒,只需在600℃煅烧10min就可以得到粒径只有40nm左右的高纯立方钛酸钡纳米粉体,而且粉体具有粒度分布窄、形貌规则、优越的钛钡摩尔比、低团聚等优点.     

Coating of CaTiO3 on titanium substrates by hydrothermal reactions using calcium-ethylene diamine tetra acetic acid chelate

Titanium plates were treated in [Ti(O₂)EDTA]^2-– -Ca(EDTA)^2- mixed solutions and/or Ca(EDTA)^2- solutions (where EDTA is ethylene diamine tetra acetic acid) at pH 9–13 and 150–250 °C for 0.5–12 h. The film, about 50 m thick, and consisting of mixtures of CaTiO₃ and TiO₂ was formed in 0.01 M [Ti(O₂)EDTA]^2- – 0.01 M Ca(EDTA)^2- mixed solution at pH 13 and 250 °C for 6 h. The film consisted of large icosahedral and hexagonal particles, of about 10 m diameter, and small aggregated particles, of about 1 m diameter. On the other hand, the film, about 20 m thick, consisted of hexagonal plate-like CaTiO₃ particles, of about 1 m diameter, was formed in 0.01 M Ca(EDTA)^2- solution at pH 13 and 250 °C for 6 h. The thickness of both films increased with time, where the film formation rate in 0.01 M [Ti(O₂)EDTA]^2- – 0.01 M Ca(EDTA)^2- mixed solution was much faster. The CaTiO₃ film formed on the surface of titanium promoted the precipitation of hydroxyapatite on the substrate by the hydrothermal reactions in Ca(EDTA)^2-–PO ₄ ^3- mixed solutions.     

Synthesis and properties of manganese-doped barium titanate

An oxalate route for the production of BaTiO₃ has been modified to incorporate Mn (upto 2%) as a dopant and the reaction sequence has been studied. The resulting Mn-doped BaTiO₃ exhibits a dielectric constant with an increasing insensitivity to temperature and applied a.c. field as the Mn content is increased. These samples possess a high electrical resistivity even after treatment in hydrogen at 1100°C and are therefore suitable as dielectric for multilayer capacitors with base metal electrodes.     

Effect of temperature schedule on the particle size of barium titanate during solid-state reaction

Nano-sized BaTiO₃ particles were synthesized by a solid-state reaction in air using a 2-step heat treatment process. The dependence of the particle size and tetragonality (=c/a) on the temperature schedule was investigated. The temperature was held for 10 h at an intermediate temperature before heating to the target temperature of 1000°C for 1 h. Although more heat was consumed, the powders synthesized by the 2-step heat treatment method showed a much smaller particle size with higher tetragonality than those produced by direct heating. For example, the mean particle size was <100 nm at a holding temperature ranging from 500-700 °C, while it was 246 nm for direct heating to the same target temperature of 1000 °C. This was explained by the enhanced nucleation rate during temperature holding stage based on the TG/DTA and high temperature XRD results.     

Immobilization of nanoparticle titanium dioxide membrane on polyamide fabric by low temperature hydrothermal method

A thin layer of nanoparticle titanium dioxide was immobilized on polyamide 6 (PA6) fiber using titanium sulfate and urea at low temperature hydrothermal condition. The titanium dioxide loaded fabric was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry and thermal gravimetry techniques. The optical and mechanical properties, water absorption and degradation of methylene blue dye under ultraviolet (UV) irradiation of the PA6 fabric before and after treatments were also examined. It was found that when PA6 fabric was treated in titanium sulfate and urea aqueous solution, anatase nanocrystalline titanium dioxide was synthesized and simultaneously adhered onto the fiber surface. The average crystal size of titanium dioxide nanoparticles was about 13.2 nm. The thermal behavior of PA6 fiber distinctly changed and the onset decomposition temperature decreased. As compared with the untreated fabric, the protection against UV radiation was improved. The water absorbency increased slightly. As the fabric dimensions were reduced in warp and weft directions, the breaking load and tensile strain increased to some extent. The titanium dioxide coated fabric could degradate methylene blue dye under UV irradiation.     

Influence of microstructure on dielectric properties of Nd-doped barium titanate synthesized by hydrothermal method

Nd-doped barium titanates were successfully synthesized via a hydrothermal route. The as-prepared barium titanate was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transformation infrared spectroscopy (FTIR), and Vis–NIR spectroscopy respectively. The results show that pure and Nd-doped barium titanate powders have cubic perovskite structure. After sintering at a temperature of 1,250 °C for 2 h, the phase compositions of all barium titanate are tetragonal phase structure. Vis–NIR spectra well confirmed that Nd³⁺ have been doped into barium titanate. The particle diameters of Nd-doped barium titanate powders and ceramics become samller with the increase of Nd³⁺ content. When Nd/Ba molar ratio is 0.02, the dielectric loss (0.0008) of the powder measured at 1 MHz and room temperature dramatically decreases by 99 % comparing with pure barium titanate (0.083) and shows frequency independence with the frequency increasing from 40 Hz to 1 MHz. The dielectric constant and dielectric loss are 436 and 0.09 after sintering. The Nd-doped BaTiO₃ show an improvement in the dielectric quality which possess a decreased sensitivity to frequency for both the dielectric constant and dielectric loss. Such improvements are of potential importance for high energy density and low loss.     

Synthesis of barium titanate nanopowder by a soft chemical process

A simple soft chemical method of synthesizing barium titanate nanopowders and nanorods is described here, where titanium dioxide/titanium isopropoxide was taken as a source of titanium, tartaric acid was taken as a template material, nitric acid as an oxidizing agent. The synthesized powders and rods were characterized by XRD, TG and DTA, SEM and IR spectroscopy. In this process phase pure barium titanate nanopowders and nanorods can be prepared at a temperature of 900 °C and the process is simple and cost-effective.