Formation Of BaTiO3 Research Articles

BaTiO3 formation by thermal decomposition of a (BaTi)-citrate polyester resin in air

Barium titanate nanosized powders were prepared by a slightly modified Pechini method. The obtained polymerized resin was used as the precursor for BaTiO3 powder production. DTA TG thermal analysis indicated that thermal decomposition of the precursors proceeds through four major step processes: (i) dehydration reaction; (ii) combustion reactions; (iii) intermediate phases formation; (iv) decarbonation of the intermediate to give BaTiO3. X-ray diffractometry (XRD) and Raman spectroscopy results indicated that, depending on the heating rate, the BaTiO3 formation took place via a predominant solid-state reaction between nanosized BaCO3 and amorphous TiO2 (TiO2−x) when crystallized by a low-heating rate (1.5 °C/min), although a small amount of a quasi-amorphous intermediate phase was also present. BaTiO3 crystallization by rapid heating rate (5 °C/min) took place through a quasi-amorphous intermediate phase formation as the main rate-controlling factor for the crystallization process. The fact that the low heating rate minimizes the intermediate phase content indicates the strong influence of the thermal heating on the kinetics of the involved transformation or in the mechanism. Although XRD results seem to indicate the formation of pseudocubic BaTiO3 as the final reaction product, the Raman spectra indicated as more probable the formation of a mixture of an oxygen-deficient hexagonal and tetragonal BaTiO3 phases below 700 °C. Above that temperature the tetragonal BaTiO3 was the only phase present. As-prepared BaTiO3 strongly agglomerated powders were relatively sinter active, leading to dense ceramic bodies (≥95% of the theoretical value). Microstructural (grain size approximately 1 mm) and room-temperature dielectric properties (ετ ≈ 2000 and tan δ ≤ 2%) at 10 kHz indicated that the obtained powders have to be optimized.

Nucleation and Inhibition Control during the Hydrothermal–Electrochemical Growth of Barium Titanate Films

The control of the microstructure of BaTiO3 films grown on titanium by the hydrothermal–electrochemical method was investigated. Experiments were conducted in a three‐electrode high‐pressure electrochemical cell in a 0.1M Ba(OH)2 electrolyte at 150°C. Results showed that the spontaneous initial nucleation linked to pure hydrothermal BaTiO3 formation can be inhibited by cathodically protecting the titanium electrode from the moment it is immersed in the electrolyte. The application of initial nucleation pulses of varying cathodic potentials affected the grain size of the deposit. It is suggested that the formation of a titanium oxide layer is a necessary step previous to the nucleation of BaTiO3.

Interpretation of hydrothermal crystallization of fine BaTiO3 powders

In the preparation of fine BaTiO3 powders under hydrothermal conditions, the reaction mechanism was interpreted through solid-state kinetic analysis of the Johnson-Mehl-Avrami plot. In this experiment reactants were dissolved and consumed to spherical particles of 50 nms from aggregation of several nanometer-sized particles. The particulate formation of BaTiO3 underwent a 1st-order hydrolysis-condensation reaction with phase-boundary transition in the early stage of the reaction regardless of the initial concentration of the feedstock. However, as the concentration of nutrients was reduced, dissolution followed by precipitation became dominant, and a diffusioncontrolled reaction proceeded. When the concentration of nutrients was reduced to an extent that was not high enough to sustain supersaturation, the reaction was controlled by solidification for encapsulation of aggregated particles, inside of which the diffusion-controlled reaction slowly proceeded.

BaTiO3 Particle Formation Mechanism under Hydrothermal Conditions.

Solid-state kinetic analysis by the Johnson-Mehl-Avrami plot was introduced to understand the reaction mechanism of fine BaTiO3 powders prepared under hydrothermal conditions. In the experiment reactants were dissolved and consumed to spherical particles of 50nm from aggregation of several nanometer-sized particles. The particulate formation of BaTiO3 underwent 1st-order hydrolysis-condensation reaction with phase-boundary transition in the early stage of the reaction regardless of the initial concentration of the feedstock. However, as the concentration of nutrients reduced, dissolution followed by precipitation became dominant, and a diffusion-controlled reaction proceeded. When the concentration of nutrients reduced to an extent that was not high enough to sustain supersaturation, the reaction was controlled by solidification for encapsulation of aggregated particles, inside of which the diffusion-controlled reaction slowly proceeded.

ＢａＴｉＯ３微粒子の固相合成と特性に対する原料混合物の湿式摩砕の効果

Effects of agitation milling of either TiO2 or a mixture of TiO2 and BaCO3 on the solide-state synthesis and properties of BaTiO3 are studied. Milling TiO2 produces the surface defects. For a mixture of TiO2 and BaCO3, milling brings not only high compositional homogeneity but also forms BaTiO3 precursor. The rate of formation of BaTiO3 is examined by high temperature X-ray diffraction analysis. Synthesis of BaTiO3 is accelerated by compositional homogeneity and BaTiO3 precursor formation from the stating mixture by agitation milling. BaTiO3 powders that have been mechanically treated starting mixture, and calcined at 1100°C comprise homogeneous spherical particles with narrow particle size distribution.

Thermal Properties of Mechanochemically Pretreated Precursors of BaTiO3 Synthesis

The changes of physico-chemical properties of mechanochemically pretreated (BaCO3 +TiO2 +PbO) powders were investigated. The values of apparent activation energy of BaTiO3 formation calculated by the Freeman and Carroll method decrease with milling time. The changes of precursors density may be interpreted as a consequence of mechanochemical reactions during milling.

Hydrothermal Synthesis of Tetragonal Barium Titanate from Barium Hydroxide and Titanium Dioxide under Moderate Conditions

Tetragonal BaTiO3 powders were prepared hydrothermally, using Ba(OH)2·8H2O and TiO2 (anatase), in the absence of anions such as chloride ions, at a temperature of 220°C for several days. Characterization via X‐ray diffractometry, scanning electron microscopy, and differential scanning calorimetry confirmed that increasing the Ba:Ti molar ratios (from 1:1 to 4:1) and alkaline concentrations (from 1.0M to 3.0M) promotes the formation of tetragonal BaTiO3.

The combustion synthesis of the ferroelectric material, BaTiO3, studied by time-resolved X-ray diffraction

The combustion synthesis of the common ferroelectric material, BaTiO3, was developed using the stoichiometry: BaO2+0.2 Ti+0.8 TiO2→BaTiO3+0.3 O2. An adiabatic temperature, Tad, of the reaction was calculated from known thermodynamic data to be 1917 °C. Real time chemical changes in the formation of BaTiO3 during the reaction have been monitored using time-resolved X-ray diffraction with synchrotron radiation as the X-ray source. A time resolution of 250 ms was achieved. The combustion synthesis of BaTiO3 was followed by observing the intensities of reactant and product Bragg diffraction peaks in order to qualitatively identify the phases present. Because BaTiO3 forms initially as a cubic phase, X-ray diffraction of the product was monitored for a period of 20 min after the reaction to observe the phase transformation to the tetragonal form. This transformation is evident in these post-reaction scans as the cubic 110 and 220 peaks are split to the tetragonal 101/110 and 202/220 ones, respectively.

Low temperature evolution of crystalline BaTiO3 from alkali-metal free precursor using sol-gel process

Bulk structure and surface texture of BaTiO3 materials synthesized at low temperature using sol-gel technique have been investigated. The materials were produced by the pyrolysis of an xerogel precursor of the tentative formula BaTiO3-x(CH3COO)2x, which was prepared using 1: 1 molar ratio of barium acetate and titanium oxyacetate solution. The present method avoids using alkali-metal hydroxides (as a hydrolyzing agent), and thus produces an alkali-metal free precursor. The decomposition course of the xerogel at the onset of formation of crystalline BaTiO3 was probed applying thermogravimetry (TG), differential scanning calorimetery (DSC), Fourier-transform infrared spectroscopy (FTIR), and Xray diffraction (XRD) techniques. Results indicated that most of the precursor weight loss occurs below 400°C, with the formation of titania rich intermediates. However, it was not until the temperature reached ≥600°C that well crystallized BaTiO3 was produced. The specific surface area and porosity were assessed for BaTiO3 produced at 600–1000°C using N2 adsorption at liquid N2 temperature.

Evolution of the formation of barium titanate in the citrate process: the effect of the pH and the molar ratio of barium ion and citric acid

In this investigation, several experiments were conducted to study the effects of the molar ratio of barium ion and citric acid and the pH value on the formation of BaTiO3 by the citrate process. It was found that the molar ratio of barium ion and citric acid and the pH value could affect the chelation of carboxylate groups and Ba/Ti ions at temperatures below 450 °C but they seemed not to influence the formation of BaTiO3. The development of an oxycarbonate intermediate during the thermal decomposition of (Ba,Ti) gel was confirmed, which was suggested to possess a structure of BaTiO3, whereby CO−23 was located inside the layer structure.

積層コンデンサの電気的特性に与える添加物の影響

The effect of the some additions on the electrical properties of the BaTiO3-based dielectrics have been investigated. The addition of every additives decreased the dielectric constant. Cr2O3 and MgO improved the temperature dependence of dielectric constant. But, the addition of NiO, Co3O4 and MnO didn't improved the temperature depen-dence.Dielectric constant of MgO added sample is 2600, but that of Cr2O3 added sample is 2400. We thought this difference is caused the formation of hexagonal BaTiO3. The Cr2O3 added sample contained hexagonal BaTiO3, though MgO added sample contained only tetragonal BaTiO3.

Formation of BaTiO3 from a Barium Titanium Isopropoxide Complex

The mechanism for the formation of BaTiO3 from a single-crystal barium titanium isopropoxide complex with the presumed composition BaTi[OCH(CH3)2]6·C6H6 was investigated in this study. When the alkoxide complex was treated in Ar at 29° C for 2.5 h, 80 wt% of the organic constituents in the crystal were eliminated as isopropanol, propene and benzene, thus forming BaTiO3; 95 wt% of the organic constituents were eliminated in the same manner at a temperature below 100° C. The remaining organic constituents were eliminated as alkyl benzene at around 460° C in Ar. Crystalline BaTiO3 with ultrafine particles, ranging in size from 5 to 7.5 nm, formed even at room temperature under these experimental conditions.

The influence of anions on the products of BaTiO3 under hydrothermal conditions

Tetragonal BaTiO3 has been prepared from a reactive titanium source, tetrabutyl titanate, with barium acetate in alkaline aqueous solution at temperatures as low as 200–240 °C. Various methods, such as X-ray diffraction, differential scanning calorimetry and scanning electron microscopy have been used to investigate the effects of alkalinity, anions, reactivity of the titanium source and degrees of fill, on the particle sizes and morphologies of BaTiO3 generated hydrothermally. The most appropriate KOH concentration is about 1.0 mol l−1 in which BaTiO3 is the stablest phase in the BaO-TiO2 system. Compared with chloride and nitrate ions, the acetate ion accelerates the formation of large-grained particles of BaTiO3 more prominently. A more reactive titanium source and a higher fill can promote the formation of tetragonal BaTiO3.

Polymerized Complex Route to Barium Titanate Powders Using Barium‐Titanium Mixed‐Metal Citric Acid Complex

Barium titanate (BaTiO3) powders were prepared by a polymerized complex method based on the Pechini‐type reaction route, wherein a mixed solution of citric acid (CA), ethylene glycol (EG), and barium and titanium ions, with a molar ratio of CA:EG:Ba:Ti = 10:40:1:1, was polymerized to form a transparent resin, which was used as a precursor for BaTiO3. Characterization of the initial precursor solution of EG, CA, and barium and titanium ions by Raman scattering and 13C‐NMR spectroscopy indicated that barium and titanium ions were simultaneously stabilized with CA to form a barium‐titanium mixed‐metal CA complex with a stoichiometry similar to Ba:Ti:CA = 1:1:3. Raman and 13C‐NMR spectra of the liquid mixture at various reaction stages indicated that the fundamental coordination structure of the mixed‐metal complex remained almost unchanged throughout the polymerization process. X‐ray diffractometry (XRD) measurements indicated formation of pseudo‐cubic BaTiO3 free from BaCO3 and TiO2 when the barium‐titanium polymeric precursor was heat‐treated in air at 500°C for 8 h or at 600°C for 2 h. However, the Raman spectra of the same powders indicated the formation of tetragonal (rather than cubic) BaTiO3, with traces of high‐temperature hexagonal BaTiO3 stabilized at room temperature. XRD of a pyrolyzed product at 500°C for 2 h revealed a simple mixture of BaTiO3 and an intermediate phase, Ba2Ti2O5.CO3. A solid‐state reaction between BaCO3 and TiO2 was concluded as not being responsible for the BaTiO3 formation; rather, BaTiO3 formed directly by thermal decomposition of the intermediate Ba2Ti2O5.CO3 phase at temperatures >500°C. In addition, by Raman scattering measurements, the intermediate Ba2Ti2O5.CO3 phase was found to be unstable in ambient air, yielding BaCO3 as one of the decomposed products.

Grain growth during sintering of BaTiO3 with LiF

Abstract The sintering behavior of BaTiO3 with LiF showed that it was possible to sinter barium titanate at temperatures below 1000°C. Different combinations of the sintering powders were prepared by adding 1 to 5 w% LiF and sintering at the temperature of 950°C for 20 hours. The grain growth of LiF fluxed BaTiO3 was studied, and electron microscopy was used to investigate and characterize the microstructure of the samples. The dielectric constant and dielectric losses were determined. It was shown that the composition of the liquid phase formed during this process had a prominent influence on the grain growth and on the formation of BaTiO3 with better dielectric properties.

Effects of Temperature and Atmosphere on the Formation Mechanism of Barium Titanate Using the Citrate Process

In this investigation, several experiments have been conducted to study the effects of temperature and atmosphere on the formation of BaTiO3 using the citrate process. It was found that BaTiO3 could be completely formed when the precursor powder was heated at 300°C in O2 for 24 h and then heated in situ at 475°C for 1 h, during which no intermediate phase was observed throughout the process. Moreover, BaTiO3 could be formed at 400°C in O2 via the combustion of organic materials, in which the amount of the residual BaCO3 depended on the partial pressure of O2. The development of BaCO3 and oxycarbonate intermediate was found to be dependent on the temperature, the atmosphere, and the organic materials, and their formation mechanisms are discussed.

Characteristics and Formation Mechanism of BaTiO3 Powders Prepared by Twin‐Fluid and Ultrasonic Spray‐Pyrolysis Methods

Spherical fine (micrometer and submicrometer in size) homogeneous BaTiO3 powders were synthesized from ethanol: water solutions of BaCl2 and TiCl4 using the spray‐pyrolysis technique. Two different atomizers—twin‐fluid and ultrasonic, with a resonant frequency of 2.5 × 106 Hz—were used for mist generation. Hollow spherical particles containing a certain amount of unreacted BaCl2 phase and having a mean particle diameter of 2.5 μm were obtained at 1173 K using a twin‐fluid atomizing system. Decomposition of precursors and their transition to the cubic BaTiO3 phase occurred, even at 973 K in the case of the ultrasonic atomizing system. For the initial droplet size of 2.2 μm and residence time of ∼60 s, spherical BaTiO3 particles with the mean particle diameter of 0.53 μm were obtained. A BaTiO3 formation mechanism has been proposed as a reaction between TiO2 and BaCl2 rather than a reaction of oxides.

Formation of BaTiO3 and PbTiO3 thin films under mild hydrothermal conditions

Well-crystallized polycrystalline thin films of cubic barium titanate (BaTiO3) have been synthesized on Ti-covered Si substrates by exposing the substrates to a Ba(OH)2 aqueous solution at 160 °C and a low pressure less than 1 MPa. It was presumed that the film formation of BaTiO3 involved a dissolution-crystallization mechanism, which provides an attractive approach to produce other titanate films and powders. Also, we have used for the first time this hydrothermal technique to deposit epitaxial (001)-textured PbTiO3 thin films on SrTiO3(100) substrates.

Structure Evolution in Hydrothermally Processed (<100°C) BaTiO3 Films

Thin films of cubic BaTiO3 were processed hydrothermally at 40°–80°C by reacting thin layers of titanium organo metallic liquid precursors in aqueous solutions of either Ba(OH)2 or a mixture of NaOH and BaCl2. All films (thickness ∼1 μm) were polycrystalline with grain sizes ranging from nano‐ to micrometer dimensions. BaTiO3 formation was facilitated by increasing [OH‐], [Ba2+], and the temperature. The film structure was related to the nucleation and growth behavior of the BaTiO3 particles. Films processed at relatively low [OH‐], [Ba2+], and temperatures were coarse grain and opaque, but increasing [OH‐], [Ba2+], and temperature caused the grain size to decrease, resulting in transparent films.

Barium and titanium aryl oxides as precursors for the preparation of thin-film oxides. The effect of bombardment by O2+

A set of barium aryl oxides of composition [Ba(OC6H2But2-2,6-X-4)2(thf)n](X = H 1, Me 2, OMe 3 or But4; thf = tetrahydrofuran) has been prepared together with the related adducts [Ba(OC6H2But2-2,6-X-4)2{P(NMe2)3O}2](X = H 5 or Me 6), which can be obtained by treating compounds 1 and 2 with neat P(NMe2)3O respectively. X-Ray studies showed that 6 has a distorted-tetrahedral structure, with the two Ba–O bonds to the aryl oxide ligands somewhat shorter than those to the P(NMe2)3O groups [2.414(8)vs. 2.579(8)A]. Samples of complex 4 and [Ti(OC6H3Pri2-2,6)4], respectively, and a third homogeneous sample obtained by mixing equimolar amounts of these have been subjected to bombardment by Ar+ and O2+ ions of relatively low energy (3.5 keV) and the ensuing transformation investigated by X-ray photoelectron spectroscopy. No significant variation of the C/M ratio was observed when employing Ar+ ions, but O2+ produced a remarkable decrease in the carbon content which leads eventually to the formation of inorganic compounds, BaCO3, TiO2 and BaTiO3, respectively, for the three samples. Action of oxygen plasma on the titanium aryl oxide did not result in a marked decrease in the C/M ratio, but it produced instead high concentrations of carbon- and oxygen-containing species.