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.     

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.     

Influence of core-shell structured grain on dielectric properties of cerium-modified barium titanate

The dielectric properties and chemical inhomogenity of BaTiO₃ ceramics sintered with additions of CeO₂:1.5TiO₂ were investigated using TEM XRD and EDS. Grains had three regions: grain shell severely doped with cerium, grain core BaTiO₃ of greater purity, and a concentration gradient region where Curie temperatures were distributed. With decreasing temperatures, the volume fraction of ferroelectric domains in the concentration gradient region increased. Addition of CeO₂:1.5TiO₂ to BaTiO₃ decreased the tetragonality (c/a ratio) and the grain size, and lowered the Curie temperature by approximately 30 C per mol%. Even a small addition of 0.005 mol CeO₂:1.5TiO₂ to BaTiO₃ reduced the average grain size from 25 m to less than 1.25 m and grains of an average grain size were completely doped with cerium, which explained why the 130 C ferroelectric transition peak did not exist. The inhomogenity of the cerium concentration had a large influence on the dielectric temperature characteristic.     

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.     

钛酸锶钡(BST)薄膜的介电性能研究

采用射频磁控溅射法制备了BaxSr1-xTiO2（简称BST）薄膜材料,研究了不同膜厚,晶粒尺寸的BST薄膜的介电系数温度特性（ε1-T),频率特性（ε-r-f),电压特性（εr-U)及损耗的温度特性（tgδ-T),频率特性（tgδ-f),找出了BST薄膜的非线性,损耗随尺度变化的规律。     

The hydroxyl concentration and the dielectric properties of barium titanate nano-powder synthesized by water-based ambient condition sol process

Nanocrystalline barium titanate, BaTiO₃, powders have been successfully synthesized via water-based ambient condition sol (WACS) process, using barium hydroxide and titanium isopropoxide. The properties of the powder were investigated as a function of various processing parameters such as the concentration of Ba²⁺ ions ([Ba²⁺]), the concentration of base, and reaction time. The concentration of hydroxyl (OH⁻) groups in the BaTiO₃ powder was greatly affected by changing the values of each processing parameter. The dielectric constant and tetragonality of the powders which contain lattice OH⁻ more than 0.35 wt% were little affected with further increase in the lattice OH⁻ concentration. The dielectric loss was highly varied with the concentration of the OH⁻ groups, and it was increased with increasing OH⁻ concentration. Calcination treatment significantly improved the dielectric properties of the powder. With higher calcination temperature, the dielectric constant increased and the dielectric loss decreased.     

Characterization,sintering and dielectric properties of nanocrystalline barium titanate synthesized through a modified combustion process

Nanocrystalline barium titanate has been synthesized through a modified combustion process in a single step for the first time. The as-prepared barium titanate powder is cubic perovskite with lattice constant a = 4.018 Å. The phase purity of the nanopowder was examined using thermo gravimetric analysis, differential thermal analysis and Fourier transform infrared spectroscopy. Transmission electron microscopic investigations have shown that the particle size of the as-prepared powder is in the range 20–40 nm. The agglomerate size distribution of the as-prepared powder was studied using atomic force microscopy. The nanoparticles of barium titanate were sintered to 97% of the theoretical density at a temperature of 1350 °C for 3 h. The microstructure of the sintered surface was examined using scanning electron microscopy. The dielectric constant and loss factor of the sintered pellets at 1 MHz measured at room temperature were 1223 and 3.5 × 10^? 3 respectively.     

Structural characteristics and dielectric properties of neodymium doped barium titanate

Neodymium (Nd) doped barium titanate powder (Ba_(1−x)Nd _x TiO₃) with x value varying from 0, 0.01, 0.03, 0.05, 0.07, 0.10 and 0.13 was prepared using the sol gel method. The powder samples were calcined at 700 °C and tetragonal phase appeared in the powders before they were sintered at 1250 °C for 3 h. The undoped samples have a polycrystalline tetragonal structure, but Nd doping into the BaTiO₃ caused phase transformation from tetragonal to cubic. The smaller grains (0.35 μm) produced with the addition of Nd is associated to the inhibition of grain growth of samples. The powders for each composition were pressed into pellets and tested as dielectric resonator antenna (DRA). It was found that on the actual antenna circuit, each sample showed a resonance frequency at X-band application and a dielectric constant value in the range of 51.25–56.89 and tangent loss was 0.039–0.045, depending on the concentration of the Nd at room temperature.     

改进的sol-gel工艺制备细晶Ba0.6Sr0.4TiO3陶瓷及其介电性能的研究

用改进的sol-gel工艺制备了细晶钛酸锶钡(Ba0.6Sr0.4TiO3,BST)陶瓷块体,研究了BST陶瓷的结晶与介电性能.在这种改进sol-gel的工艺中,用传统的固相反应煅烧形成BST粉体,经高能球磨制备BST纳米陶瓷粉体,再将一定质量的纳米粉体加入到相同化学组成的BST的溶胶液中,经普球球磨12h后,制备成悬浮性好,分散均匀的浆料.浆料可用来制备BST陶瓷,并在1200℃保温2h烧结成瓷,结果显示,BST陶瓷块体结构致密,晶粒尺寸在0.15～2μm之间.分析了样品的介电性能和晶粒尺寸对材料介电性能的影响.介电温谱显示,在0℃,100kHz时,相对介电常数为2500,介电损耗为0.02;并且存在明显的弥散相变.     

Synthesis, characterization and dielectric properties of europium-doped barium titanate nanopowders

Europium-doped cubic barium titanate (BT) nanocrystals with % [Eu/Ti] mol ratio varying from 0.05 to 0.25 were prepared through hydrothermal route. The nano nature of these powders was confirmed by XRD and TEM studies. Pellets were prepared after calcining the powders at 1000 °C for 2 h. These pellets were annealed at 200, 500, 700 and 1000 °C for 2 h at each temperature and used for dielectric measurements. Raman spectra of two typical pellets with %[Eu/Ti] Eu/Ti mol ratios of 0.15 and 0.25 showed all the peaks characteristic of tetragonal BaTiO₃. Pure BT showed a low dielectric constant (DC) with a value of 398. Doping with small amounts of Eu resulted in many fold increase of DC values. A maximum value of 10576 at 1 KHz frequency was observed for the sample with % [Eu/Ti] mol ratio of 0.15. Lowering of Curie temperature T_c (95 to 110 °C) was observed for pure as well as Eu-doped barium titanate.     

Preparation of barium titanate nanoparticle sphere arrays and their dielectric properties

Barium titanate (BaTiO3) nanoparticles from 27 to 192 nm were prepared by the 2-step thermal decomposition method from barium titanyl oxalate nanoparticles. These particles were dispersed well into 1-propanol, and dense BaTiO3 nanoparticle sphere arrays without stress-field were prepared by the meniscus method. Temperature dependence of dielectric properties was successfully measured using these dense nanoparticle sphere arrays, and size effect on dielectric properties was discussed.     

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.     

The effect of glass addition on the dielectric properties of barium strontium titanate

Ba_0.7Sr_0.3TiO₃ (BST) ceramics were prepared by the conventional solid state ceramic route. Different weight percentages of twelve different glasses were added to the calcined BST ceramics and sintered. The structure and microstructure of the sintered materials were investigated by X-ray diffraction and Scanning Electron Microscopic techniques. The low frequency dielectric properties of the glass-ceramic composites were measured using LCR meter. Some of the glasses improved the dielectric properties and considerably lowered the sintering temperature. The glasses were prepared and characterized under identical conditions. Among the different glasses, 1.5 wt% addition of 71ZnO–29B₂O₃ lowered the sintering temperature of BST to 975 °C with a dielectric loss of 9 × 10⁻³ and dielectric constant of 875 at 1 MHz. The curie temperature of BST ceramics was found to shift towards lower temperature with glass addition.     

掺杂Y2O3对钛酸锶钡铁电陶瓷材料显微结构和介电性能的影响

钛酸锶钡(BSTO)铁电陶瓷材料的介电常数随外加直流电场的变化呈现非线性特性.纯BSTO材料由于较高的介电常数和较大的介电损耗不能满足移相器介质材料的要求.通过在BSTO中添加Y2O3来改善BSTO铁电陶瓷材料的介电性能.研究结果是:(1)在BSTO体系中微量掺杂Y2O3,Y3 以取代Ba2 的方式存在于钙钛矿的晶格中,形成均匀的固溶体Ba0.5-xYxSr0.5TiO3;(2)随Y3 添加量的增加,居里峰逐渐变宽,峰高逐渐降低,相变弥散效应增强;(3)Y3 的掺杂能促进BSTO陶瓷的致密化烧结,并显著降低BSTO陶瓷的介电常数.     

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.     

Physical and electromechanical properties of barium zirconium titanate synthesized at low-sintering temperature

Barium zirconium titanate or (Ba(Zr_xTi_1 − x)O₃, BZT) was prepared using homogeneous BZT powders derived from a sol-gel process. With a sintering aid, the firing temperature for the BZT ceramics was lower by about 30%, meanwhile, the electromechanical properties of the material were not degraded. Crystallographic phases of the BZT system were identified by the XRD data and Raman spectra and we found that the orthorhombic-perovskite BZT ceramic with x = 0.05 has the best dielectric and piezoelectric properties.     

Dielectric properties of vanadium doped barium titanate synthesized via high-energy ball milling

The study shows the advisability of using a mechanochemical synthesis method, based on a high-energy planetary ball milling, to a modification of barium titanate by a vanadium doping. This method improves useful properties of BaTi_0:95V_0:05O₃ as a capacitor material. It has a high value of electric permittivity ?′ in the wide range of temperature and low dielectric losses ?″ as well as a low electrical conductivity.     

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.