Preparation of Highly Crystallized Strontium Titanate Powders at Room Temperature

Highly crystallized fine powder of strontium titanate (SrTiO₃) was obtained at room temperature simply by leaving a vial containing the powder mixture of Sr(OH)₂·8H₂O and hydrous titania gel (TiO₂·nH₂O) for 10 d. Solvent and additive(s) used in the conventional low‐temperature process were not used. The crystallinity judged from the FWHM of X‐ray diffraction peak was comparable to that obtained by a solid‐state reaction. To cause the reaction at room temperature, the titania gel had to contain a considerable amount of H₂O (n > 0.97). The reaction is considered to be neutralization of titanic acid [H₄TiO₄ or Ti(OH)₄] and strontium hydroxide (base). Using similar process, highly crystallized BaTiO₃ powder was also obtained at 60°C. In comparison with the formation temperature of BaTiO₃, tolerance factor in the perovskite structure was important for the room‐temperature synthesis of SrTiO₃. SrTiO₃ was hardly obtained at room temperature by the addition of saturated strontium hydroxide solution to the hydrous TiO₂ gel (n = 1.29). Therefore, the reaction seems to proceed in the hydrous titania gel. This process is characterized by three important points; “no solvent”, “no additional reagents”, and above all, “no heating”.     

溶剂热技术制备Ni3S2纳米粉体

以硝酸镍和硫脲作镍源及硫源,以乙二醇作溶剂,采用溶剂热技术成功地制备了Ni3S2纳米粉体。用X射线粉末衍射（XRD）和透射电镜（TEM）对Ni3S2粉体的结构及形貌进行表征,结果表明反应温度和物料配比是影响Ni3S2粉体的结构和形貌的重要因素。     

A Novel Method for the Preparation of Retinoic Acid-Loaded Nanoparticles

The goal of present work was to investigate the use of bioerodible polymeric nanoparticles as carriers of retinoic acid (RA), which is known to induce differentiation of several cell lines into neurons. A novel method, named “Colloidal-Coating”, has been developed for the preparation of nanoparticles based on a copolymer of maleic anhydride and butyl vinyl ether (VAM41) loaded with RA. Nanoparticles with an average diameter size of 70 nm and good morphology were prepared. The activity of the encapsulated RA was evaluated on SK-N-SH human neuroblastoma cells, which are known to undergo inhibition of proliferation and neuronal differentiation upon treatment with RA. The activity of RA was not affected by the encapsulation and purification processes.     

Hydroxyl Content of BaTiO3 Nanoparticles with Varied Size

Different types of tetragonal BaTiO₃ particles were synthesized in a wet chemical process including an autoclave treatment. The synthesis and autoclaving medium was varied from isopropyl alcohol to water in different ratios, leading to a size variation of the particles from 38 to 145 nm. By applying combustion analysis of carbon and hydrogen (C/H analysis) released from the samples, it can be demonstrated that the amount of hydroxyl impurities incorporated into the crystal lattices of the particles increases with the water content of the synthesis medium. C/H analysis is a suitable tool for this characterization task as it allows discriminating different sources of these elements, i.e., different impurities. By comparing the self‐synthesized particles with commercial ones, it can be concluded that the particle size has the dominant influence on the tetragonality, if the amount of internal hydroxyl groups is relatively low. In contrast, if the amount of water originating from the internal OH groups is elevated (greater than ~0.4 wt%) an impairment of the tetragonality is caused.     

四方相钛酸钡纳米晶的制备及其表征

以Ti(OC4 H9) 4、H2 O2 和Ba(OH) 2 ·8H2 O为原料 ,在 180℃下溶剂热处理 2 4h ,制备了四方相钛酸钡纳米晶 ,XRD数据计算其格子常数a =3 .9899,c=4.0 3 2 5 ,c/a =1.0 10 7。并对该法四方相钛酸钡的形成机理进行了浅析     

液相还原法制纳米镍粉

用NiSO4.6H2O为原料,N2H4.H2O为还原剂,十二烷基磺酸钠(SDS)为表面活性剂,用NaOH调节反应pH,合成了纳米Ni粉。采用XRD、SEM及FTIR等分析测试方法对所制得的粉体进行了表征。研究结果表明:在反应温度为80℃,反应时间10~25 min,Ni2+浓度为0.75 mol/L,pH=11,n(N2H4)∶n(Ni2+)=(2~3)∶1时,能得到平均粒径75~200 nm的球形纳米Ni粉。     

Synthesis of Highly Dispersed Barium Titanate Nanoparticles by a Novel Solvothermal Method

A novel solvothermal route has been developed to synthesize highly dispersed nanocrystalline barium titanate (BaTiO₃), using a mixture of ethylenediamine and ethanolamine as a solvent. The as-synthesized BaTiO₃ nanoparticles were characterized by X-ray powder diffraction, transmission electron microscopy (TEM), high-resolution TEM, Fourier transform infrared spectroscopy, and thermal analysis. Based on the results of characterizations, the organic solvent was found to influence strongly the crystal growth and dispersibility of BaTiO₃. The BaTiO₃ nanoparticles obtained were highly dispersed and crystalline with a cubic perovskite structure. The particle size derived from the TEM ranged from 5 to 20 nm.     

稳定的BaTiO3陶瓷浆料的制备

本文采用胶体"静电位阻稳定机制",以磷酸酯作为分散剂,以沉降高度作为衡量浆料稳定性的参数,研究了BaTiO3粉末的悬浮流变特性及分散剂磷酸酯加入量对BaTiO3浆料稳定性的影响.在最佳pH值和分散剂加入量条件下,制备了高固相含量(50vol%)、稳定性和分散性好的BaTiO3浆料.     

Preparation of BaTiO3 by homogeneous precipitation

Three different methods are studied for the preparation of fine-grained BaTiO₃ by homogeneous precipitation: (1)Hydrolysis of barium and titanium alkoxide precursors, in which the required water is generated by an esterification reaction; (2)Precipitation of a barium–titanium complex as a result of thermal decomposition of Ba-EDTA; (3)Precipitation of a barium and titanium complex by the increase of pH caused by the hydrolysis of urea. The properties of powders, prepared via these methods, and their sintering behaviour are as follows: (1)The esterification method results in a powder with medium average aggregate size of about 3 μm and a sintered density of 90% which is higher than the value obtained with the other precipitation methods. The considerable differences, in hydrolysis rate between the barium and titanium precursors used, lead to second phase formation; (2)The complexation method gives the most promising results; 1 μm sized spherical aggregates were obtained which consist of smaller particles. Sintered densities obtained were up to 88% and the method can be optimised further to obtain values in excess of 95%; (3)The urea method results in large irregular aggregates and is found to be unsuitable for the preparation of BaTiO₃ ceramics.     

超细钛酸钡粉体的制备方法

本文介绍了国内外钛酸钡（BaTiO3）粉体的丰要制备方法并比较各种制备方法的特点及发展状况,指出了应用前景较好的制备方法。     

Hydrothermal Synthesis of BaTiO3 Nanopowders Using TiO2 Nanoparticles

Anatase TiO₂ nanoparticles, obtained by hydrolyzing titanium isopropoxide in distilled water, were used to synthesize BaTiO₃ (BT) nanopowder by the hydrothermal method. When titanium isopropoxide was used, BT nanopowder with a low tetragonality of 1.0070 was formed because of the presence of OH^? ions in the oxygen sites and Ba vacancies. However, by changing the titanium source from titanium isopropoxide to TiO₂ nanoparticles, a homogeneous BT nanopowder with similar particle size and a high tetragonality of 1.0081 was synthesized. The size of the BT nanopowder particles was decreased by reducing the synthesis time. In particular, the BT nanopowder that was synthesized at 220°C for 16 h with a Ba/Ti molar ratio of 4.0 exhibited a high tetragonality of 1.0083 and a small particle size of 126.0 nm.     

A Novel Approach to Improve Properties of BiFeO3 Nanomultiferroics

In this study we report the synthesis of Bi_1?xIn_xFe_1?yTi_yO₃ (0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.05) nanoparticles by a simple cost effective solution combustion method. Pure BFO samples shows distorted rhombohedral perovskite structure with space group R3c which is also supported by Fourier transform infrared spectra study. The codoping of In and Ti at A–B sites of BFO (BIFTO) partially distorts the crystal structure, increases the lattice strain, reduces the average particle size (14 nm), and increases the Fe³⁺/Fe²⁺ ratio which significantly affect the observed results. The saturation magnetization increases significantly upon codoping (4.60 emu/gm) by about 12 times than that of pure BFO (0.4 emu/gm). The improved ferromagnetic properties upon codoping is further manifestated in large value of linear magnetoelectric coupling coefficient (4.8 mV/cmOe) which further provides an indirect evidence for the collapse of space modulated spin structure. The activation energy increases with codoping (0.68 eV), although less than 1 eV which indicates that the conduction is still dominated by charged defects.     

Preparation of multiferroic composites of BaTiO3–Ni0.5Zn0.5Fe2O4 ceramics

Magneto-electric coupling in ceramic composites formed by ferroelectric and ferromagnetic phases can be obtained via an adequate mechanical coupling between the individual piezoelectric and magnetostrictive phases (product property). In the present work, the possibility of forming diphase ferroelectric–ferromagnetic ceramics has been investigated. Composites of xBaTiO₃–(1 − x)Ni_0.5Zn_0.5Fe₂O₄ with x = 0.5, 0.6 and 0.7 were prepared according two different procedures: (i) by direct mixing powders of perovskite BaTiO₃ and Ni_0.5Zn_0.5Fe₂O₄ spinel prepared by solid state and (ii) by coprecipitating Fe^III–Ni^II–Zn^II nitric salts in a NaOH solution in which the BaTiO₃ powders were previously dispersed. Optimum processing parameters for good homogeneity, densification and for a reduction of the chemical reactions at the interfaces ferroelectric-ferrite were found. A temperature and composition-dependent magnetic order is present in all the composites, with a dilution effect of the magnetisation due to the presence of the non-ferromagnetic phase. A diffuse ferroelectric–paraelectric transition due to the BaTiO₃ phase was identified by the temperature-dependence of the permittivity and losses, showing that at room temperature the material preserves a ferroelectric order. The interfaces play important roles in the dielectric properties, causing space charge effects and Maxwell–Wagner relaxation, particularly at low frequencies and high temperatures. The combined ferroelectric and magnetic ordering will result in magneto-electric coupling in this material; further investigations are necessary.     

超细BaTiO3粉体制备的研究进展

综合评述了超细酸钡BaTiO3粉体制备目前采用的各种方法,包括共沉淀法、微乳液法、柠檬酸法、草酸盐法、水热法、溶液热合成法、Sol-gel法和金属有机物热解法和有机盐-氢氧化物法.评述了目前对先驱体溶液化学对溶胶的形成、溶胶凝胶转变、粉体的形成影响以及晶粒尺寸和粒子尺寸与粉体结构的关系.     

A Novel Approach to the Preparation of Nano-Blends of PPO/PS/PA6

Summary A novel approach of in situ polymerization and in situ compatibilization was adopted to prepare the nano-blend of poly (2,6-dimethyl-1,4-phenylene oxide) (PPO), polystyrene (PS) and polyamide 6 (PA6). Anionic ring-opening polymerization of -caprolactam was carried out in the presence of PPO and PS. And PS, the chain of which bore methylmethacrylate (MMA) groups, acted as macroactivator to initiate PA6 chain growth from the PS chain and formed a graft copolymer of PS and PA6 and pure PA6 simultaneously. Thus the nano-structured PA6 dispersed phase in the PPO matrix could be achieved.     

纳米钛酸钡电子陶瓷粉体的制备技术

本文介绍了功能介电材料BaTiO3粉体主要制备技术及最新进展，讨论了这些技术的优缺点和对介电材料发展的影响，指出液相化学合成法是现阶段制备BaTiO3的主要方法，而作为液相法之一的直接沉淀法由于具有设备简单，操作方便，粉体粒径小，颗粒分布等优点有着诱人的工业应用前景。     

Preparation of BaTiO3 nanopowders by the solution combustion method

Barium titanate was synthesized by the method of exothermal combustion in solutions using barium nitrate, titanium dioxide (TiO₂) and titanyl nitrate (TiO(NO₃)₂) as sources of titanium and barium and reducing agents such as glycine (C₂H₅NO₂), carbamide (СН₄N₂O) and glycerol (C₃H₅(OH)₃). In an effort to form a barium titanate phase, the materials synthesized using titanium dioxide were subjected to additional calcination at 800 °С. With titanyl nitrate the use of glycine and carbamide enabled carrying out a single-step synthesis of barium titanate. The obtained materials have pseudo-cubic lattice and are characterized by high stability of properties in a wide range of temperatures and frequencies of the electromagnetic field.     

Rapid Formation of Nanocrystalline BaTiO3 and Its Highly Stable Sol

Ultrafine BaTiO₃ nanoparticles and their highly stable sols are prepared by a novel and rapid route. In this method, the formation mechanism that lies between the chemical precipitation and the sol–gel process is proposed. The BaTiO₃ nanocrystal sols are synthesized in as fast as 15 min in an air atmosphere. Dynamic light scattering analysis and the observation of the Tyndall effect confirm the existence of crystalline nanoparticles in these sols. After careful separation, nanocrystalline BaTiO₃ powders with an average particle size as small as 2.8 nm are obtained. These particles have perovskite phase structures as determined by X‐ray diffraction and selected‐area electron‐diffraction analysis. Fourier transform infrared spectroscopy (FT‐IR) and thermal analysis are used to detect the characteristic functional groups of the solvents on the particles to reveal the formation mechanism. Uniform BaTiO₃ nanocrystal films with high dielectric constants, low dielectric losses, and paraelectric behavior are prepared through solvent evaporation of the nanocrystal sols, providing a new low‐temperature route for the fabrication of perovskite thin films.     

Ni掺杂对BaTiO3陶瓷物相及介电性能的影响

采用固相反应法制备了BaTi_1-xNi_xO₃（x=0、0.01、0.05、0.08、0.1、0.2）陶瓷,研究了不同Ni掺杂量对BaTi_1-xNi_xO₃陶瓷的相结构和介电性能的影响。采用X射线衍射技术（XRD）分析了BaTi_1-xNi_xO₃陶瓷的相结构;采用阻抗分析仪测试BaTi_1-xNi_xO₃陶瓷介电性能。XRD分析结果表明:随着Ni的掺杂量的增加,BaTi_1-xNi_xO₃陶瓷的晶相由四方相逐渐转变为六方相,当Ni的掺杂量为x=0.1时,BaTi_1-xNi_xO₃完全变为六方相。随着Ni含量的增大,所有六方相的BaTi_1-xNi_xO₃的晶格常数都变大,且相对介电常数ε_r整体降低而介电损耗tanδ呈现先减小后增大的趋势。