Barium Titanate Particles Research Articles

Preparation of nm-sized BaO3 particles using a new 2-step thermal decomposition of barium titanyl oxalate

To obtain inpurity-free and nm-sized barium titanate (BaTiO3) particles, a new 2-step thermal decomposition method from barium titanyl oxalates (BaTiO(C2O4)2 · 4H2O) was proposed. At the 1st step, BaTiO(C2O4)2 · 4H2O was annealed at 400°C for 1 h in the O2 flow. The annealing temperature of 400°C was chosen for the following reasons; (1) no formation of BaCO3 and TiO2 and (2) the complete removal of H2O and other carbon species. This compound obtained at 400°C was amorphous phase, and its chemical composition was BaCO3-TiO2. When this compound was annealed in air at higher temperatures, the large BaTiO3 particles were prepared with by-products such as BaCO3. Thus, at the 2nd step, to prevent the crystal growth and the formation of BaCO3, this compound was annealed above 600°C in vacuum. Finally, the BaTiO3 single crystals with a size with 16.5 nm were prepared around 620°C. These BaTiO3 fine particles were characterized using various methods to investigate defects and impurities in the particles. As a result, it was confirmed that there was no impurity in the BaTiO3 lattices.

Mechanism of nanocrystalline BaTiO 3 particle formation by hydrothermal refluxing synthesis

The nanocrystal-formation mechanisms of barium titanate (BaTiO3) particles in a hydrothermal refluxing process have been studied. The refluxing method allows in situ sampling and requires ambient conditions (i.e., temperature below the boiling point of solvent and atmospheric pressure). It was found that the formation of BaTiO3 from the amorphous precursor was a very rapid process. BaTiO3 nuclei were formed at around 75 °C, 15 min after the beginning of the hydrothermal reaction. Individual BaTiO3 particles with dimensions in the range of 70–130 nm were formed 5 min after the nucleation of nanocrystals. Further reaction for crystal growth proceeded by consumption of the remaining precursors and possible aggregation of BaTiO3 particles via Ostwald ripening. It is proposed on the basis of the microscopic observations that the in situ transformation mechanism, rather than dissolution–precipitation mechanism, is dominant in the early stage of BaTiO3 formation.

Sintering behaviour and microstructural evolution of agglomerated spherical particles of high-purity barium titanate

Abstract Densification and grain growth of high-purity BaTiO 3 spherical particle compacts have been studied in the temperature range of 25–1300 °C by the CRH method. A rapid densification of the samples between 1000 and about 1230 °C with the formation of a continuous interconnected porosity, and a negligible grain growth took place. Above 1230 °C grains grew rapidly and the interconnected porosity progressively collapsed into isolated pores. Measurements of grain size as a function of density showed that the grain-growth behaviour change took place at about 92% of theoretical density, which coincides with the end of the intermediate-stage sintering. From the present experimental results it can be tentatively stated, for the first time in barium titanate, that a linear correlation between density and grain size in the intermediate-stage of sintering exists. In the final-stage of sintering a bloating or desintering feature was present as consequence of the loss of carbon dioxide from the barium carbonate in the barium titanate environment.

Barium titanate particle model inquiry through effective permittivity measurements and boundary integral equation method based simulations of the BaTiO3–epoxy resin composite material

The heterogeneous mixture properties depend on its constituents' characteristics. We examine the effective permittivity of a two-phase composite material made of epoxy resin host matrix and barium titanate (BaTiO3) filler for different volume fractions in the matrix. The task we undertake consists in finding a model of BaTiO3 particles through the computer simulations executed in PHI3D-electric field calculating package, based on the resolution of the Laplace equation using boundary integral equation method. With this aim in view we compare the measured results of the effective permittivity of the BaTiO3–epoxy resin composite samples with the simulation results for different BaTiO3 particle geometric models and for the same experimental conditions, with regard to the given volume fraction of the powder in the matrix. The experimental results are obtained through the measurements with an impedance meter in the range of frequencies from 50 Hz to 1 MHz.

Additive controlled crystallization of barium titanate powders and their application for thin-film ceramic production: Part II. From nano-sized powders to ceramic thin films

Nano-sized barium titanate (BaTiO3) particles prepared by the sol-to-precipitate method in aqueous/organic medium served to obtain thin-layer ceramic films of the tetragonal electroactive phase. Poly(methacrylic acid) works efficiently to process the suspensions and to obtain green films. Sintering the green films under O2–Ar atmosphere gave thin-layered ceramics of a thickness of 0.5–1.0 mm with a dielectric constant of 3750 at 20 °C (1 kHz).

Structural Characterizations of Organo-Capped Barium Titanate Nanoparticles Prepared by the Wet Chemical Route

In the present study, nanoscale barium titanate particles were chemically prepared with organic shells on their surfaces. Their chemical and physical structures were characterized by FT-IR, FT-Raman, XRD, and XPS. Based on the results of characterizations, it can be concluded that the presence of organic ligands greatly influences the nucleation and surface chemistry of BaTiO3 nanoparticles. Surface Ti4+ tends to bond to stearate ions instead of the previous Ba2+ in the starting materials. The usual preferable orientation growths of lattice, i.e., (101), (111), and (200), were significantly restrained due to surface coordination. Although poor crystallinity was observed, a tetragonal phase of BaTiO3 nuclei could be inferred from both XRD and Raman patterns. Finally, the formation mechanism and structural model of organo-capped nanoparticles are discussed.

Critical size and anomalous lattice expansion in nanocrystallineBaTiO3particles

Nanocrystalline barium titanate particles are prepared by the alkoxide method. The lattice constants are obtained from the electron diffraction patterns for various orientations of single particles in the size range of 15--250 nm in diameter. The present result indicates that the structural change from a tetragonal (ferroelectric) phase to a cubic (paraelectric) one occurs around 80 nm in diameter, which is in good agreement with a critical diameter recently reported. Large lattice expansions of more than 2.5% are detected in the particles down to 15 nm in diameter. The origin of the expansion is discussed on the basis of x-ray photoelectron spectroscopic analyses and a computer simulation.

A TEM and HREM study of particle formation during barium titanate synthesis in aqueous solution

The formation mechanisms of barium titanate particles from an amorphous TiO 2 gel during synthesis in aqueous solution at temperatures between 20 and 80°C have been investigated. It was found that barium ions diffuse into the gel almost immediately, with nanocrystalline BaTiO 3 particles being formed after heating to just 40°C. These particles grew to dimensions of about 100 nm as the temperature was increased to 80°C, consuming the remaining TiO 2 gel. Some remnants of gel were found on particle surfaces in a sample taken at this temperature but after holding the sol at 80°C for 2 or 4 h, the particle surfaces became “cleaner” and more rounded. It is proposed on the basis of these observations that the BaTiO 3 particles were formed by an in-situ transformation of the amorphous TiO 2 gel. The mechanism by which (i) the particles were then rounded off and (ii) the final gel fragments were incorporated into the main BaTiO 3 particles was, however, less clear.

Defect structure and physical properties of barium titanate ultra-fine particles

Barium titanate ultra-fine particles prepared by sol–gel (SG) and stearic acid-gel (SAG) methods are studied by high-resolution transmission electron microscopy (HRTEM). Physical property measurements showed that the barium titanate particles made by the SAG method are quite different from those particles prepared from sol–gels and from normal barium titanate ceramics and crystals (Ren et al., Chin. Phys. Lett. 11(5) (1994) 310). SAG barium titanate fine particles contain a high density of defect structures such as multiple-twins and intergrowth structures containing hexagonal BaTiO 3. Image processing of the HRTEM images also showed a high density of small defects for the SAG barium titanate fine particles and ceramics. The defect density was much lower and no such defects were observed for SG barium titanate. The unusual ferroelectric properties of SAG barium titanate particles and ceramics are discussed in terms of the observed defect structures.

Rheological and dielectric studies of aggregation of barium titanate particles suspended in polydimethylsiloxane

Viscoelastic and rheo–dielectric properties were investigated for suspensions composed of barium titanate (BaTiO3) particles having an average size of 0.3μm and polydimethylsiloxane (PDMS). Steady shear viscosity decreased with increasing shear rate. Stepwise increase of shear rate resulted in a thixotropic decrease of the viscosity due to reorganization of aggregates of the BaTiO3 particles in the shear field. The transient change occurred through the fast and slow processes with the time constants of 5–30 and ca 100s, respectively. Yield stress and plasticity were also observed for suspensions of high BaTiO3 content. Since BaTiO3 particles possess a strong dipole moment due to spontaneous polarization, the suspensions exhibited dielectric dispersion due to reorientation of the particles. The dielectric constant decreased with increasing viscosity of PDMS due to the increase of the dielectric relaxation time in the viscous medium. In order to investigate the aggregation of the particles in a shear field, we also carried out rheo–dielectric measurements in shear fields. The dielectric constant in a shear field decreased with increasing shear rate. After sudden stop of shear flow, a recovery of the dielectric constant was observed and was resolved into the fast and slow processes. The characteristic time for the fast process was close to the relaxation time for the thixotropy. Those results were explained by assuming chain-like aggregates of BaTiO3 particles formed by the dipole–dipole interactions.

Wet-chemical synthesis of monodispersed barium titanate particles — hydrothermal conversion of TiO 2 microspheres to nanocrystalline BaTiO 3

A low-temperature hydrothermal reaction scheme has been developed to produce pure, ultrafine, uniform-sized, nanocrystalline barium titanate (BaTiO 3) microspheres from two inorganic precursors: synthesized titania microspheres and barium hydroxide solutions. The size and morphology of titania (TiO 2) microspheres were controlled using isopropanol to fine-tune the dielectric constant of the isopropanol–water mixed solvent system. Monodispersed titania microspheres approximately 0.1–1 μm in diameter were successfully synthesized for the further conversion to barium titanate. Barium titanate and titania microspheres were characterized by scanning electron microscopy (SEM) and room-temperature X-ray diffraction (RTXRD). High-temperature XRD (HTXRD) was also utilized for in situ study of the phase transformations and changes of crystallite size with calcination temperatures. The titania microspheres were predominant in the anatase (plus some brookite) phase at room temperature and were converted to the rutile phase when the calcination temperature was increased from 650°C to 900°C. Monodispersed barium titanate microspheres were successfully synthesized from optimized titania via a hydrothermal reaction (≤100°C) in barium hydroxide solutions. The size and morphology of the barium titanate particles remained the same as the precursor titania particles, indicating a “shrinking-core” diffusion–reaction mechanism. Barium carbonate in the form of witherite was also found along with the formation of barium titanate, especially under conditions with higher Ba/Ti ratios, but a formic acid washing procedure effectively removed this impurity phase from the barium titanate samples. The as-prepared barium titanate was in the cubic nanocrystalline form and did not change when the temperature was increased from room temperature to as high as 750°C. The cubic phase was also stable at high temperatures for over 5 h.

Crystal structure of barium titanate fine particles including Mg and analysis of their lattice vibration

Fine barium titanate crystallites with various Mg contents were prepared by a hydrothermal method. These particles were spherical single crystallites with an average size of about 63 nm, regardless of Mg contents from 0 to about 0.15 wt%. It was confirmed that Mg replaced substitutionally on Ti site. On the refinement of the crystal structure with a Rietveld method, the crystal structure of the particles without Mg was tetragonal with a tetragonality of 1.0015 while those including Mg approached from tetragonal to cubic gradually with increasing Mg content. On the other hand, a Raman measurement indicated that the local structure remained tetragonal regardless of Mg contents. Moreover, the resonance frequency for each phonon mode was independent of Mg contents while their damping factor increased with increasing Mg content, which suggested that state of the phonon became more unstable with increasing Mg content. Therefore, the lattice defects induced by Mg into the barium titanate particles can give the phonon a similar effect to that of temperature in barium titanate single crystal.

Homogeneous (co)precipitation of inorganic salts for synthesis of monodispersed barium titanate particles

Various processes of coprecipitation or crystallization of inorganicsalts of barium and titanium from homogeneous solutions were studiedin this work. In particular, barium hydroxide and barium chloridesalt as well as titanium tetrachloride were used as the startingmaterials for dielectric-tuning homogeneous precipitation in mixedsolvents of isopropanol and water. Hydroxypropylcellulose was used asa steric dispersant. Evaluations of size, shape, and composition ofsynthesized particles were made using scanning electron microscopy,high-temperature X-ray diffractometry, and differential thermalanalysis. Results show that salt concentration, pH, and reaction timeare important in determining the morphology and composition of thefinal powder. The titania particles from dielectric-tuningprecipitation are perfect microspheres with narrow size distribution(near monodispersed), while the particles from barium salts areflake-like, irregular in shape and size. Instead of particlescontaining uniform compositions of barium and titanium compounds,dielectric-tuning coprecipitation yielded powders of two separatedphases, i.e., monodispersed titania microspheres (∼1 μm) coated onbarium chloride salt flakes. Titanium-rich barium titanate wasobtained after calcination of coprecipitated powders. However,preliminary results show that the titania particles obtained bydielectric-tuning precipitation can be hydrothermally converted toBaTiO3 particles that are fully crystallized after calcination above950°C.

BaTiO 3 particles prepared by microwave-assisted hydrothermal reaction using titanium acylate precursors

Microwave-assisted hydrothermal reaction to prepare barium titanate (BaTiO 3) particles using titanium acylate precursors was investigated. Experimental variables taken into account in this study were the reaction type (reflux and autoclave), the reaction time and the Ba to Ti ratio in sol solutions. Autoclave reactions were more effective than reflux reactions in terms of time and barium utilization efficiency. In both type reactions, the variation in Ba to Ti ratio in sol solutions led to substantial changes in particle morphology as well as Ba:Ti stoichiometry in resulting particles. Mechanisms for those changes were proposed. Characterization of synthesized particles were performed via SEM, XRD, Raman, XPS and elemental analysis based on ICP.

Piezoelectric and dielectric properties of siloxane elastomers filled with bariumtitanate

Piezoelectric elastomers were prepared from suspensions of bariumtitanate (BaTiO3) particles in a telechelic polydimethylsiloxane (t-PDMS) by crosslinking the t-PDMS under an electric field. Crosslinking reaction was monitored by measurement of complex dielectric constant ε′ − iε″. Dielectric constant ε′ increased with increasing BaTiO3 content, and agreed approximately with the theoretical ε′ calculated with the Maxwell–Wagner theory. Piezoelectric constant d33 of the poled elastomers was measured by application of compressions in the direction of the poling field. It was found that d33 was of the order of 10−11 C/N and increased steeply with increasing content of BaTiO3 but became almost independent of composition in the range of BaTiO3 content from 3 to 14 vol %. To examine the effect of electric field on the aggregation structure of the particles, we observed light scattering of the suspension under an electric field, and found that the scattering pattern became anisotropic. This indicated that the particles are connected like a pearl necklace and are stretched in the direction of the poling field. The dependence of d33 on the volume fraction of BaTiO3 was explained by a model proposed by Banno. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3065–3070, 1999

Characterization of Barium Titanate Powders: Barium Carbonate Identification

A range of methods for the detection of barium carbonate contaminant in barium titanate powder has been assessed, namely: X‐ray diffraction (XRD), scanning electron microscopy (SEM), with EDS‐X‐ray microanalysis, Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), gas chromatography (GC) for analysis of carbon, and X‐ray photoelectron spectroscopy (XPS). The most satisfactory procedure for the detection of the small amounts of BaCO3 commonly present is FT‐IR. Surface analyses by XPS show that the carbonate is present as a discrete phase and is not a surface film on barium titanate particles.

Near-Stoichiometric Barium Titanate Synthesis by Low Temperature Hydrothermal Reaction

AbstractBarium-deficiency of barium titanate particles prepared by low temperature hydrothermal reaction has been notorious. It has been believed that barium-deficiency is caused by the high solubility of barium source compared with titanium. Here is reported the synthesis of nearstoichiometric barium titanate powders with ultrafine particle size and high crystallinity by low temperature hydrothermal reaction from barium acetate and titanium tetra(methoxyethoxide). Barium titanate particles were synthesized in the spherical, metastable cubic crystalline grains with size distribution between 60 ∼ 90 nm in diameter. Ultrafine particle size was resulted from the control of the hydration rate and the decrease of Ti-O-Ti cross-linking extent of titanium precursor. Increasing barium to titanium molar ratio in reactant could not overcome the notorious barium-deficiency but, improved stoichiometry and produced finer and less agglomerated particles. Interestingly, adding a slight pressure to autogeneous one to make total 4 ∼ 10 atm has yielded near-stoichiometric, highly crystalline, and less agglomerated barium titanate particles. It seems like that the total pressure around 4 ∼ 10 atm provides strong force enough to push barium ions into the interstitial points of perovskite structure and stabilize it. These particles, which were in metastable cubic form as synthesized, initiated phasetransition to tetragonal form by calcination at 400 °C.

Preparation and Properties of Nb-Coated Barium Titanate Composite Particles by Surface Modification with Nb Alkoxide in Hydrophobic Solvent

Chemical processing for the preparation of Nb-coated barium titanate composite particles was investigated using surface modification technology, hydrolyzing Nb ethoxide on the surface of barium titanate particles dispersed in hydrophobic solvent. It was confirmed from the measurements of specific surface area and zeta potential as well as SEM, TEM and EDX observations of the resulting composite particles that the original barium titanate particles were coated uniformly with hydrolysis product of Nb ethoxide. Barium titanates coated with 1 wt% of Nb as oxide were well sintered at 1200–1300°C. The dielectric constants of the sintered barium titanates showed flattened temperature dependence, but it depended upon the average particle size of original barium titanate. The sintered bodies of Nb-coated barium titanate powders with average particle size of ∼0.2 μm gave dielectric constants of 2000–3000 and those of barium titanate with average particle size of ∼0.5 μm showed dielectric constants of 3000–4000 at room temperature. The microstructure of the sintered barium titanate coated with Nb oxide consisted of grains of about 1 μm, smaller than those of sintered original barium titanate.

Sol-Emulsion-Gel Synthesis of Shaped Powders in the System BaO-TiO2

Shaped tetragonal barium titanate (BaTiO3) particles were prepared by the sol-emulsion-gel method with systematic variation of the concentration of a non-ionic surfactant in the organic phase (“oil phase”) of water-in-oil (w/o) emulsions above or below the critical micelle concentration (CMC). An acetate-based sol with equivalent oxide ratio BaO : TiO2 = 1 : 1 was selected for the study. Micelle formation of the surfactant and their self-aggregation apparently played an important role in controlling the shape and size of the droplets and accordingly shape and size of the final barium titanate particles resulting therefrom. Transmission electron microscopy (TEM) revealed that with low concentration of the surfactant (2–5 vol%) ill-formed spheres were obtained. Spherical particles were formed with increasing the surfactant concentration to 7 vol%. At 12 vol% of the surfactant, rod-like particles were first found to form, which with further increase in surfactant concentration to 15–20 vol%, gradually transformed to cube-like/lamellar type particles. Attempts have been made to explain the various particle shapes in terms of surfactant aggregation.

Preparation of barium titanate ultrafine powders from a monomeric metallo-organic precursor by combined solid-state polymerisation and pyrolysis

A recipe has been elaborated for preparing barium titanate (BaTiO3) particles in a nucleation route which is mediated by thermal decomposition of polymeric barium titanium methacrylate. Adjustment of particle size d in the range from 10 nm to 1.5 μm is easily done by choosing appropriate reaction temperatures and tempering atmospheres. In particular, doping with paramagnetic probe ions such as Mn2+, Gd3+ or Cr3+ can be readily accomplished by just adding the corresponding metal acetates to the monomeric precursor. In addition to well approved standard techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC), the complementary spectroscopic methods electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), X-ray absorption near edge structure (XANES) and FT-Raman are applied to characterise the micro- and nanocrystalline BaTiO3 powders prepared and to study the phase transition behaviour in dependence on the mean particle size. In contrast to expectation from literature, the dimensionality effect does not manifest itself in a temperature shift of the ferroelectric phase transition but, instead, the tetragonal-to-cubic phase transition is smeared out at reduced particle size and an increasing tetragonal-to-cubic phase admixture is detected.