Preparation of Barium Titanate Nanopowder through Thermal Decomposition of Peroxide Precursor and Its Formation Mechanism

H₂TiO₃ was dissolved in the mixture of hydrogen formed peroxide and ammonia under the pH range of 8–10 with a transparent yellow solution formed. When an equivalent mole of Ba²⁺ solution was added into the yellow solution, the precipitate produced was the peroxide precursor of barium titanate. The cubic nanopowder of barium titanate was obtained when the precipitate was washed, stoved, and then calcined at 600°C for 1 h. The peroxide precursor of barium titanate and barium titanate nanopowder prepared were characterized to be BaTi(H₂O₂)₂O₃ by TGA‐DTA, XRD, TEM, SEM, and XREDS. The peroxide precursor of barium titanate was determined to be BaTi(H₂O₂)₂O₃. The particle size of the barium titanate nanopowder, the calcined product of BaTi(H₂O₂)₂O₃, was in the range of 20–40 nm. A formation mechanism of the barium titanate nanopowder through thermal decomposition of its peroxide precursor was proposed and then validated.     

高分子分散剂在陶瓷浓悬浮体制备中的应用

良好分散的陶瓷浓悬浮体是胶态成型实现的前提和关键。本文阐述了高分子分散剂的分散稳定作用及其在多种单相复相陶瓷浓悬浮体制备中的研究和应用,进而从高分子分散剂自身特性,陶瓷分散相和分散介质的物理化学性质以及陶瓷胶态成型工艺操作等方面,分析了各因素对高分子分散剂分散效果的影响,最后指出了能够优化陶瓷浓悬浮体性能的高分子分散剂的研究趋势。     

Negative Electrorheological Effect of Silicone Gels Containing Barium Titanate

Summary: We observed the negative electrorheological phenomenon on swollen silicone gels containing barium titanate. Contrary, no negative electrorheological effect was observed in unswollen silicone gels containing barium titanate and silicon gels without barium titanate. The change in storage modulus increased with increasing DC electric field strength. The effects of frequency, degree of swelling, and the field strength have been investigated.

Electric‐field dependence of the change in storage modulus at f = 0.1 Hz for swollen silicone/BaTiO₃ gels with varying CAT content; (○): CAT 0.1, (□): CAT 0.2, (⋄): CAT 0.3, (×): SG.     

The electrical properties of chemically obtained barium titanate improved by attrition milling

Barium titanate ceramics were prepared using the nanopowder resulting from a polymeric precursor method, a type of modified Pechini process. The obtained nanopowder was observed to agglomerate and in order to de-agglomerate the powder and enhance the properties of the barium titanate the material was attrition milled. The impact of this attrition milling on the electrical properties of the barium titanate was analysed. The temperature dependence of the relative dielectric permittivity showed three structural phase transitions that are characteristic for ferroelectric barium titanate ceramics. The relative dielectric permittivity at the Curie temperature was higher for the attrition-treated sample than for the non-treated barium titanate. The dielectric losses were below 0.04 in both barium titanate ceramics. The grain and grain-boundary contributions to the total resistivity were observed using impedance analyses for both ceramics. A well-defined ferroelectric hysteresis loop and piezoelectric coefficient d₃₃ = 150 pC/N were obtained for the ceramics prepared from the de-agglomerated powder. In this way we were able to demonstrate that by attrition milling of chemically obtained powders the ferroelectric and piezoelectric properties of the ceramics could be enhanced.     

Dielectric and optical properties of BaTiO<Subscript>3</Subscript> thin films prepared by low-temperature process

Barium titanate (BaTiO₃) thin films have been prepared by low temperature processing on Pt/Ti/SiO₂/Si substrates using sol-gel-hydrothermal (SGHT) technique, which combined the conventional sol-gel process and hydrothermal method. X-ray diffraction analysis showed that the barium titanate thin films are polycrystalline. As-reacted barium titanate films grown on Pt(111)/Ti/SiO₂/Si(100) substrates had a dielectric constant (ε) and loss tangent (tanδ) of 80 and 0.05 at 1 MHz, respectively. The optical constants including refractive index n, extinction coefficient k, and absorption coefficient α of the barium titanate thin films in the wavelength range of 2.5–12.6 μm were obtained by infrared spectroscopic ellipsometry.     

Chemical Preparation of Ferroelectric Mesoporous Barium Titanate Thin Films: Drastic Enhancement of Curie Temperature Induced by Mesopore‐Derived Strain

Mesoporous barium titanate (BT) thin films are synthesized by a surfactant‐assisted sol–gel method. The obtained mesoporous BT thin films show enhanced ferroelectricity due to the effective strains induced by mesopores. The Curie temperature (T_c) of the mesoporous BT reaches approximately 470 °C.     

Pyroelectricity and dielectric anisotropy in polarized and niobium modified barium titanate ceramics

The effect of time of soaking on bulk density and dielectric constant has been measured on pure and niobium-doped barium titanate pyroelectric specimens. The temperature dependence of the dielectric constant for both pure and niobium-doped barium titanate samples has been investigated before and after poling. The percentage dielectric anisotropy and ferroelectricity was also calculated for various pure and modified barium titanate pyroelectric materials. Our results can be explained in terms of the redistribution of the barium titanate lattice in a different crystallographic orientation, polarization, as well as the existence of lattice imperfection accompanying temperature, poling and niobium doping. The obtained results were in good conformity, and correlated with the increased proportion of the remnant 90° domains (induced electrically charged vacancies as a result of Nb³⁺ substitution of Ti⁴⁺ in octahedral lattice sites). It was concluded that poling of Nb-doped barium titanate samples produces the best quality ceramic pyroelectrics.     

Formation and some properties of barium titanate embedded into porous matrices

Embedding of barium titanate into porous oxide matrices via sol–gel synthesis and introduction in structured slurry based on fumed oxides has been carried out. Prepared compositions have been studied using XRD, DTA-TG, FTIR, TEM, and adsorption of nitrogen. It has been established that simultaneous formation both barium titanate crystal structure and porous structure of matrices occurs. Crystallites of barium titanate, which arise in pores, possess lesser size in comparison with that for bulk BaTiO₃.     

Enhanced electro-optical properties of a nematic liquid crystals in presence of BaTiO3 nanoparticles

Composites of nematic liquid crystals (NLCs) and ferroelectric barium titanate (BaTiO₃) nanoparticles (NPs) have been prepared. The alignments of NPs in the host medium have been demonstrated. Effect of NPs doping on various display parameters of NLCs, namely, threshold voltage, dielectric anisotropy and splay elastic constant has been studied using electro-optical and dielectric studies. The nematic ordering of host supports alignment of NPs parallel to the director which consequently improves electro-optical parameters in the composite system. The dielectric and electro-optic properties of LC–NPs composites have been discussed in frame of conventional theories of NLCs.     

Extended Hückel Molecular Orbital Calculations II. The Sigma and Pi Overlap Populations in Titanium Oxides

A method for analysis of separate sigma and pi overlap populations in a system of very low symmetry has been proposed. The calculations are performed in Ti₃O₃, rutile, anatase, brookite and tetragonal barium titanate. The examination of the various bond overlap populations has led to reasonable explanation on the infrared absorption spectra of CO and CO₃ chemisorption on rutile and anatase and the relative heats of formation of anatase, rutile and brookite.     

Fabrication and characterization of cerium doped barium titanate/PMMA nanocomposites

The cerium doped barium titanate (BaTiO₃:Ce)/poly methyl methacrylate(PMMA) polymer nano-composites (PNC) were successfully fabricated via solvent evaporation method with microwaves (2.4 GHz) heating. The X-ray diffraction measurements confirm the formation of barium titanate (BT) with crystallite size ranges from 55 to 62 nm. Differential scanning calorimetry study shows that the glass transition temperature (T_g) directly affected by microwaves heat treatment and particle size of filler. The broadband dielectric spectroscopy was employed to investigate the frequency and temperature dependence of the dielectric properties of the nanocomposites in a frequency range from 75 kHz to 5 MHz and temperature range 80–400 K. The introduction of different BT fillers in PMMA enhance the dielectric constant of PNCs drastically and give a smooth response in frequency range mentioned above. The loss factor of the composite can be suppressed by using cerium doped barium titanate filler rather than pure barium titanate filler.     

Hydrothermally assisted complex polymerization method for barium strontium titanate powder synthesis

Barium strontium titanate was obtained by hydrothermal treatment of barium strontium titanate citric precursor solution, previously prepared by complex polymerization method. The thermally induced phase evolution was followed at various temperatures up to 800 °C using thermogravimetric and differential thermal analysis, X-ray diffraction analysis, and Raman spectroscopy. Microstructural characterization of barium strontium titanate powders was performed by scanning and transmission electron microscopy. The proposed synthesis route has been proven as a better and faster method for barium strontium titanate powder preparation as compared to the conventional complex polymerization route. The method was found efficient for production of low agglomerated, fine, nanosized barium strontium titanate powder with well defined stoichiometry, and sub-micron particle size. The results of structural and microstructural characterization showed the complete crystallization of carbonate-free barium strontium titanate powder at 700 °C with an average size of crystallites below 50 nm.     

Etude theorique de la dynamique du réseau de batio3 en phase quadratique

The lattice dynamics of barium titanate BaTiO₃ is discussed quantitatively in the framework of a shell model taking into account the electronic polarizabilities of the constituent ions and including Coulomb and short-range interactions. The results of calculations point out the important role of the anisotropic oxygen polarizability. There is a good agreement between calculated and experimental dispersion curves.     

Effects of metal salts on the thermal decomposition of edta-gel precursors for ferroelectric ceramic powders

Raw chemicals such as metal nitrates and chlorides were found to affect the thermal decomposition behaviour of EDTA-gel precursors used for the production of ceramic powders. Fine, homogeneous ceramic powders were produced from nitrate solutions while chlorides gave segregated phases. In studies on the production of lead zirconate titanate (PZT) using chlorides, the segregation and loss of lead was observed and shown to be caused by the formation and evaporation of PbCl₂. Thermal analysis (DTA/TG) quantitatively proved the suggested reaction mechanism for this phase segregation. Crystallization of the desired perovskite phase of lead zirconate titanate (PZT) and barium titanate (BT) initiated at temperatures as low as 250°C in the nitrate-EDTA precursors. Water of crystallization and formation of BaCO₃ in the barium titanate precursor were suggested to account for differences in the observed decompositional behaviours of the BT and PZT precursors.     

Effect of donor-acceptor sites at a barium titanate surface on the properties of composites based on cyanoethyl polyvinyl alcohol

The changes in the specific surface area and composition of donor-acceptor sites caused by hydration and thermal treatment of dispersed BaTiO₃ were determined. Modified barium titanate was mixed with cyanoethyl polyvinyl alcohol to form composite films with a relative permittivity of up to 180. The relationship between the functional composition of the surface and the particle size of modified barium titanate, on the one hand, and the relative permittivity of the composite film, on the other, was derived within the framework of the thermodynamic model. This relationship makes it possible to predict the effect of modification on the electrophysical properties of polymer composites.     

Toward a more environmentally benign synthesis of doped barium titanate

Abstract

Barium titanate is one of the most thoroughly studied members of the perovskite family due to its prominent place in the electroceramic industry. To be used as a capacitor at room temperature, a high-dielectric constant is needed which is achieved through doping. The focus of this research was to develop a more environmentally benign alternative to the doping of barium titanate. The barium source was barium titanyl catecholate, Ba[Ti(cat)₃] (aq) and the doping sources were strontium oxalate (SrC₂O₄) and strontium carbonate (SrCO₃). The doping strategies included a solid-state synthetic pathway as well as microwave- and centrifuge-assisted methods which both employed water as the only solvent. The last two benign by design methods were tested with respect to their thermodynamic control over barium-to-strontium stoichiometric ratios. These methods of doping proved to be more environmentally friendly and economical while combining green chemistry and materials science.     

Cation-induced collapse of low-molecular-weight polyacrylic acid in the dispersion of barium titanate

Observations on the steric layers formed by the adsorption of low-molecular-weight polyacrylic acid (PAA) were taken using the colloidal probe method in an atomic force microscope. The effects of divalent barium ions and of monovalent potassium ions at varying concentrations were observed on the repulsive interaction profiles. High ionic concentrations screened double-layer forces to small distances, whereby the acting forces were reduced to steric interactions. De Gennes scaling theory was used to model the effect of electrolyte on an aqueous barium titanate system, which was stabilized with PAA. The brush model was found to represent the force curves better than the mushroom model. The collapse of PAA layers with increasing salt approximated a grafted polymer brush in monovalent electrolyte, but the addition of barium ions caused markedly less steric collapse. It is suggested that the formation of a Ba(2+)-PAA complex in the adsorbed layer increases its compressibility parameter.     

The disproportionation of Cu(I)X mediated by ligand and solvent into Cu(0) and Cu(II)X2 and its implications for SET‐LRP

Disproportionation of Cu(I)X is the major step in Single‐Electron Transfer Living Radical Polymerization (SET‐LRP). The disproportionation of Cu(I)X mediated by Me₆‐TREN in various solvents was studied through UV–vis spectroscopy and Dynamic Light Scattering (DLS). UV–vis experiments reveal that disproportionation is dependent on both solvent composition and concentration of Me₆‐TREN, consistent with a revised equilibrium expression and corroborated by mathematical models. Electrochemistry data do not accurately predict the extent of disproportionation in the presence of Me₆‐TREN. Exemplified by DMSO, a favored solvent for SET‐LRP, UV–vis spectroscopy shows that under certain conditions disproportionation is four‐orders of magnitude greater than the value reported from electrochemistry experiments. Through UV–vis and DLS analysis, it was demonstrated that DMSO, DMF, DMAC, and NMP, stabilize colloidal Cu(0), while acetone, EtOH, EC, MeOH, PC, and H₂O facilitate agglomeration of Cu(0) particles. Additionally, for colloidal Cu(0) stabilizing solvents, the amount of ligand and solvent composition decide the particle size distribution. Therefore, the kinetics of SET‐LRP are cooperatively and synergistically determined by the complex interplay of solvent polarity, the extent of disproportionation in the solvent/ligand mixture, and the ability of that mixture to stabilize colloidal Cu(0) or control particle size distribution. The implications of these results for SET‐LRP are discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5606–5628, 2009     

纳米钛酸钡的水热合成进展

综述了水热合成纳米钛酸钡的影响因素、发展现状及存在的问题，并指出其发展趋势。参考文献57篇。     

The calculation of the optimum pH range for synthesizing BST nanopowders by sol–gel auto-combustion process

The optimum pH range for synthesizing barium strontium titanate (Ba_0.5Sr_0.5TiO₃, BST) nanopowders by sol–gel auto-combustion method was calculated based on the principles of matter balance and charge balance. The effectiveness of the calculation was proved by the successful synthesis of highly dispersive, spherically shaped and pure BST nanoparticles with setting the pH in the range pre-decided by theoretical evaluation. Ours might have provided an effective path for pre-deciding the solution pH in synthesizing various oxide nanopowders by sol–gel auto-combustion method.