Preparation and properties of barium titanate glass-ceramics sintered from sol–gel-derived powders

Homogeneous Ba–Ti–B–Si, Ba–Ti–Al–Si and Ba–Ti–B gels have been successfully prepared by the sol–gel process. A novel method is presented for fabricating barium titanate glass-ceramics by sintering the gel powders with small barium titanate crystallites. The structural development, grain size, crystallization process and dielectric properties were systematically studied by differential thermal analysis, thermogravimetric analysis, X-ray diffraction techniques, scanning electron microscopy and dielectric measurements. The glass-ceramic samples were sintered at lower temperatures compared to the barium titanate ceramic sintering, and showed improved dielectric properties. It was found that the small size effect of the barium titanate grains on the dielectric constant in the glass-ceramics was quite evident. Ferroelectric hysteresis loop analyses were also performed to manifest the ferroelectric nature of the barium titanate grains in situ grown from the gels. This revised version was published online in November 2006 with corrections to the Cover Date.     

The microstructure developments and electrical properties of calcium-modified barium titanate ceramics

The microstructure and electrical behaviour of calcium-modified BaTiO₃ ceramics of compositions (a) (Ba_1-x Ca _x )TiO₃, (b) Ba(Ti_1-x Ca _x )O_3-x and (c) (Ba_1-x/2Ca _x/2) (Ti_1-x/2Ca _x/2) O3_3-x/2 have been investigated. These characteristics are observed to vary systematically with the cationic ratio, = (Ba + Ca)/Ti, rather than the amount (x-value) and sites that Ca²⁺ ions are supposed to occupy. A large uniform grain microstructure and normal dielectric behaviour are obtained for 1.01 samples (groups I and II), whereas an ultra-fine grain microstructure and diffuse phase transformation (DPT) characteristics are observed for 1.08 samples (groups III). The latter is proposed to be the suppression of tetragonal to cubic transformation due to the formation of second phase. When the sintering atmosphere is changed from air to H₂/N₂ mixture, the electrical resistivity decreases and dielectric loss increases tremendously for = 0.99 samples (groups I), whereas the high electrical resistivity and low dielectric loss characteristics are preserved for 1.01 samples (groups II and III). The mechanism by which the cationic ratio improves the resistance of the materials to a reducing atmosphere is proposed to be the formation of hexagonal BaTiO_3- phase which consumes the oxygen vacancies generated.     

Effect of copper substitution on the microstructure and ferroelectric properties of barium titanate

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Semiconducting properties of barium titanate and iron substituted barium titanate

Single crystals of barium titanate and members of the series BaTi_1?xFe_xO_3?xF_x have been grown from a potassium fluoride flux. These crystals were made conductive by heating in a sealed evacuated silica tube in the presence of freshly ground titanium. Electrical, optical and magnetic measurements were performed in order to characterize these crystals. Optical measurements indicated a decrease in the band edge from 3.2(1) eV for barium titanate to 2.8(1) eV for Bati_1?xFe_xO_3?xF_x(x = 0.02, 0.05, 0.07, 0.10). The photoelectrolytic behavior of reduced barium titanate was strongly quenched upon the substitution of iron and fluorine.     

Effect of phosphor doping on the microstructure and dielectric properties of barium titanate ceramics

The effect of phosphor doping on the sintering behaviour, microstructure and dielectric properties of BaTiO₃ has been investigated. Diisopropyl phosphinate is added to high-purity BaTiO₃ powder prepared by the wet chemical method with a final amount of 0.14 wt.% P₂O₅ with respect to the BaTiO₃. Phosphor-doped BaTiO₃ ceramics with a high density and uniform grain size have been produced by using wet processing and pressureless sintering without any binder. A scanning electron microscope, thermometric analysis, X-ray diffraction and an impedance analyser have been used to determine the microstructure as well as the dielectric properties. The phosphor cations can form a liquid phase belonging to the ternary system BaO-TiO₂-P₂O₅, leading to the formation of BaTiO₃ ceramics with high density at low temperature. Phosphor-doped BaTiO₃ ceramics with a high density of 96% D_th are obtained by sintering at 1200°C with a soaking time of 2 h. The dielectric constants of samples sintered at 1150 and 1200°C are as high as 6100 and 5500, respectively; the Curie temperature of samples decreases with decreasing sintering temperature. Doping with a small amount of phosphor can improve the sintering and dielectric properties of BaTiO₃ ceramics.     

Pure and doped barium titanate. Crystal growth and chemical composition

Barium titanate single crystals are grwon in two ways, i.e. by the Remeika and the Czochralski method. Doping ions (FeCoCu) are introduced into Remeika crystals and determined by a spectro photometric method. Impurity ions (FKPtSb) are determined in both kinds of crystals; pulled crystals are purer than Remeika crystals. The stoichiometry Ti/Ba + Sr is excellent in pulled crystals but the Ti, Ba, Sr, K concentrations in Cu-doped crystals show ion size effects in the compensation mechanism.     

Effect of sintered temperature on structural and piezoelectric properties of barium titanate ceramic prepared by nano-scale precursors

Lead-free piezoelectric ceramics barium titanate has been successfully fabricated by a facile modified (nano-scale precursors) solid phase method. The sintered temperature was employed as the main regulatory factor to control the growth of the grain size and crystallinity of the sample. When the sintered temperature was set as 1350?°C, the pure phase barium titanate ceramics could be prepared with the grain size of about 1 μm. In addition, piezoelectric tests showed that, the samples sintered at this temperature possessed the maximum ?_r, P_r and d₃₃ values, 3533, 16.24 μC/cm² and 420 pC/N, respectively. These characteristics make them promising candidates as lead-free piezoelectric ceramic materials.     

Si-B-O系BST玻璃陶瓷制备及介电弥散研究

采用硝酸钡、硝酸锶、钛酸丁酯、正硅酸乙脂和硼酸三正丁脂为原料的溶胶凝胶方法制备了Si-B-O系BaxSr1-xTiO3玻璃陶瓷。通过差热分析(DTA)、热失重(TG)、X射线衍射(XRD)分析Si-B-O系BST玻璃陶瓷超细粉体合成过程及其相结构变化。采用X射线衍射(XRD)、扫描电子显微镜(SEM)描述Si-B-O系BST玻璃陶瓷烧结体的相结构和显微组织结构变化。阻抗分析仪测量Si-B-O系BST玻璃陶瓷的-50～100℃介电温谱。实验结果表明：Si-B-O系BST玻璃陶瓷粉体的相结构为立方钙钛矿相结构,其合成温度为700℃．不存在第二相。Si-B-O系BST玻璃陶瓷的烧结温度低于传统工艺。Si-B-O系BST玻璃陶瓷的显微结构呈细晶结构。Si-B-O系BST玻璃陶瓷的介电常数ε随着烧结温度升高而增大．介电损耗tgδ随测试温度的增加而降低。随着晶粒平均尺寸的减小．Si-B-O系BST玻璃陶瓷样品的介电峰变低．平坦．宽化．存在介电峰弥散化的现象。     

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.     

退火工艺对钛酸锶钡铁电多层膜结构与物性的影响

立足于无铅型钛酸锶钡(BST)铁电多层膜的制备及物性研究.采用溶胶-凝胶方法制备了Ba0.9Sr0.1TiO3铁电多层膜,并利用快速退火炉对多层膜进行热处理.重点分析两种不同热处理工艺对钛酸锶钡多层膜微观结构及相关物理性能的影响.通过X射线衍射(XRD),扫描隧道显微镜(SEM)及可见光范围反射谱测量等的表征方法,研究钛酸锶钡铁电多层膜微观结构的演化和形成机理,为制备性能优良的钛酸锶钡铁电多层膜提供基础数据.     

Effect of sintering temperature on the microstructure and electrical properties of zirconium doped barium titanate ceramics

Lead-free Ba(Zr_0.15Ti_0.85)O₃ (BZT15) ceramics were synthesized by adopting the solid-state synthesis method. The effect of increasing sintering temperature (T_s) in the range of 1,350–1,450 °C on the microstructure, dielectric, polarization, and electric field induced strain of the ceramics was studied. Fine grained (~260 nm) BZT15 ceramics displayed single phase perovskite structure with relative densities >94 % of the theoretical density. Both grain size and shape were influenced by the sintering parameters. With increase in T_s, not only the maximum dielectric constant decreased from 11,412 to 8,734 along with an increase in the degree of diffuseness, but also interestingly the Curie temperatures were found to vary within an interval of 61–73 °C. Optimum sintering temperature has been found resulting in high remnant polarisation and strain in these ceramics. The properties observed are attributed to a contribution from all polar vectors present in coexistent phases.     

Effects of barium dissolution on dispersing aqueous barium titanate suspensions

Dissolution of barium ion and its effect on dispersion behavior of aqueous barium titanate suspensions at various pH values have been investigated. The amount of leached barium ion decreases with increasing pH value. The dissolution of barium ion also causes an increase in pH value of suspension, but the change decreases with increasing initial pH value. The iso-electric point (IEP) of leached barium titanate powder increases with increasing leaching pH value and solid loading as well. The dissolution of barium ion enhances the colloidal stability of aqueous barium titanate suspension, in agreement with zeta potential measurement.     

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.     

Preparation of powder barium titanate

Phase-pure BaTiO₃ powder (free of Ba₂TiO₄, BaCO₃, Ba(NO₃)₂, and OH impurities) with an average particle size of about 100 nm is prepared by solid-state reaction between titanium oxyhydroxide and barium hydroxide ground and mixed by sonication in an inert organic liquid.     

Effect of calcination on characteristics,surface texture and sinterability of chemically prepared barium titanate

Highly pure and finely divided barium titanate powders have been obtained by the pyrolysis of barium titanyl oxalate. The effect of time and temperature of calcination on the degree of crystallinity, fineness, and surface texture of the powders obtained have been demonstrated. The densification properties of the sintered bodies are discussed in relation to the characteristics of the calcined materials.     

Synthesis, microstructure and dielectric properties of zirconium doped barium strontium titanate obtained by solvothermal method

(Ba_0.8Sr_0.2Zr_yTi_1?yO₃) (y = 0.05, 0.1, 0.15 and 0.2) nanosized powders is synthesized by solvothermal method. The formation of (Ba_0.8Sr_0.2Zr_yTi_1?yO₃) was confirmed by XRD, FT-IR and XPS analysis. The purity of the (Ba_0.8Sr_0.2Zr_yTi_1?yO₃) was examined using FT-IR spectroscopy. The X-ray analysis proves that all as-synthesized Ba_0.8Sr_0.2Zr_yTi_1?yO₃ powders have a cubic perovskite structure. The surface characterization indicates the powder contains Zr and Sr elements. SEM investigation shows that the average particle size is reduced with increasing the Zr content and the average particle size is in the range 37–50 nm, the well dispersed nano powders have narrow particle size distribution. The study of dielectric properties shows that the Curie peaks of dielectric constant become broader and shift towards lower temperature on the basis of Ba_0.8Sr_0.2TiO₃ and the dielectric loss decreases with increasing Zr content.     

钛酸锶光催化材料研究进展

近年来,钙钛矿型化合物以其特有的结构在光催化领域成为国内外研究的热点。钛酸锶(SrTiO3)是一种典型的钙钛矿型复合氧化物,具有稳定性高、无毒性,载流子迁移率高,光催化活性高等特点,作为半导体有低阻的电子运输结构和对小分子高效的氧化还原能力,是一种极具开发潜力和应用前景的光催化材料。主要介绍了SrTiO3材料的结构、制备方法与光催化机理,并对近年来SrTiO3在光催化领域的改性研究进行综述。最后在现有研究成果的基础上,对SrTiO3光催化材料的未来发展动向进行简要分析,有助于研究者取得进一步突破。