Preparation of Stoichiometric Fine Lead Barium Titanate Powder

Lead barium titanate powder with 0.03–0.15 μm particle sizes was prepared from lead barium titanyl oxalate which was previously prepared by reacting high-purity ammonium titanyl oxalate with barium and lead acetate. The critical factor in preparing the barium titanyl oxalate was the reaction time. It was necessary to allow 2–4 h to synthesize the oxalate to get a single-phase barium titanate. The critical factors in preparing the lead titanyl oxalate were pH and the concentration of the solution. It was necessary to adjust the pH to around 0.5 and the concentration to <0.08 M . When lead barium titanyl oxalate is prepared, low pH, low concentration, and a long reaction time are necessary.     

Factors Affecting the Preparation of Barium Titanyl Oxalate Tetrahydrate

Several experiments have been conducted to investigate the preparation of barium titanyl oxalate tetrahydrate (BTO). Differential thermal analysis and thermogravimetric analysis were employed to investigate the thermal decomposition, and an X-ray diffractometer and a transmission electron microscope were used to analyze the phases and crystalline states. It has been found that BTO is a nonstoichiometric compound, in which barium hydrogen oxalate hydrate was inserted by the titanium species. Moreover, it has been shown that a mixture would from rather than BTO, depending on pH, mixing order, and oxalate solution.     

Preparation of Semiconducting Titanates by Chemical Methods

Semiconducting barium titanate has been prepared both by coprecipitating the lanthanum in the preparation of barium titanyl oxalate and by precipitation of lanthanum hydroxide in a slurry of the titanate. Partial substitution of strontium or lead for barium and zirconium for titanium has also been achieved using this oxalate process. The electrical conductivity of these materials was measured and is discussed. The effect of excess titanium on the electrical properties was also determined and an excess of 1 to 2 mole % was found to raise the positive temperature coefficient under the firing conditions employed.     

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.     

Ferroelectrics of Ultrafine Particle Size: I, Synthesis of Titanate Powders of Ultrafine Particle Size

Two methods used to synthesize high-purity ferroelectric titanate powders in controlled, narrow size distributions, with average particle diameters <1000 A, were: (1) isothermal pyrolysis of barium titanyl oxalate or mixed calcium-barium titanyl oxalates as low as 550° and 825°C, respectively, average particle sizes depending strongly on the pyrolysis temperature; and (2) hydrolysis of titanate esters in barium hydroxide. Using solvent media of controlled polarity, high-purity stoichiometric BaTiO₃ was obtained with average sizes as small as 100 A. Factors affecting stoichiometry and particle size are discussed in terms of assumed reaction mechanisms.     

pH dependent coprecipitated oxalate

Effect of pH on the formation of strontium titanyl oxalate starting from strontium nitrate and potassium titanyl oxalate has been investigated. Thermal analysis revealed the formation of stoichiometric strontium titanyl oxalate only at pH 2.5. Progressive increase in pH led to the formation of strontium titanyl hydroxy oxalate at pH 7.0. Further increase in pH up to 9.0 yielded only a physical mixture of strontium oxalate and titanium hydrous oxide.     

Thermal Analysis of Precursors of Barium Titanate Prepared by Coprecipitation

Thermal analysis was performed on coprecipitated materials and on individual components. The detailed decomposition schemes of coprecipitates and individual components are proposed and discussed. According to the proposed decomposition schemes, the values of the observed weight loss are in good agreement with those of the theoretical values of the coprecipitated materials and individual components. The results indicate that barium titanyl oxalate is an inserting compound, i.e., a structure of distorted barium hydrogen oxalate hydrate being inserted by Ti(OH)₃⁺. The results also verify that copreciptation of barium and titanium ions in an oxalate aqueous solution at pH 7 is a mixture of BaC₂O₄· 0.5H₂O and TiO(OH)₂· 1.5H₂O and coprecipitation of barium and titanium ions using the process of Yamamura et al. is a mixture of Ba(NO₃)₂ and Ti(OH)₂C₂O₄.     

Effect of Composition and Size of Crystallite on Crystal Phase in Lead Barium Titanate

Lead titanate, barium titanate, and lead barium titanate powders (>99.9% pure), the particle size of which varied from 0.03 to 0.15 μm depending on the calcination temperature and the composition, was prepared from barium lead titanyl oxalate, which was previously prepared by reacting high-purity ammonium titanyl oxalate with barium and lead acetate. The critical crystallite size of BaTiO₃ powder from the cubic to the tetragonal phase is around 1 μm. Pb_0.3Ba_0.7TiO₃ powder with an average size of 0.057 μm showed the tetragonal phase.     

Properties of BaTiO3 synthesized from barium titanyl oxalate

In order to enhance the tetragonality of BaTiO₃ derived from barium titanyl oxalate (BTO), various treatments were carried out by considering the thermal decomposition mechanism of BTO in air. A multi-step heat treatment process and the addition of carbon black, as a particle growth inhibitor, were effective in increasing the tetragonality, whilst maintaining a particle size smaller than 200 nm. The synthesized BaTiO₃ powder with a mean particle size of 177 nm showed a tetragonality and K-factor of 1.0064 and approximately 3, respectively.     

Alternative Route for Synthesis of Barium Titanyl Oxalate: Molecular Precursor for Macrocrystalline Barium Titanate Powders

An important molecular precursor to barium titanate, namely, barium titanyl oxalate [BaTiO(C₂O₄)₂.4H₂O], has been synthesized by an alternative route. An alcoholic solution containing 1 mol of butyl titanate monomer [(C₄H₉O)₄Ti] is reacted with alcoholic solution containing 2 mol of oxalic acid (H₂C₂O₄:2H₂O) to form an intermediate soluble oxalotitanic acid [H₂TiO(C₂O₄)₂.nH₂O]. The oxalotitanic acid in alcoholic medium is subjected to cation exchange reaction with aqueous solution containing equimolar barium acetate to form an insoluble barium titanyl oxalate (BTO) in yields of 80–85% at room temperature. The pyrolysis of BTO in air at T .750°C/5 h produced barium titanate (BT) powders.     

Preparation of Spherical, Solid Barium Titanate Particles with Uniform Composition at High Precursor Concentration by Spray Pyrolysis

Hydrolysis-assisted spray pyrolysis (HASP) using dimethyl oxalate as hydrolyte was found to be applicable to precipitation of solid, spherical BaTiO₃ powder with uniform composition when the stock solution concentration was high (>1.0 M ). Solid, dense powder with uniform composition was successfully obtained because barium titanium oxalate was prepared from partial hydrolysis of dimethyl oxalate and coprecipitation of oxalate with barium and titanium during the hydrolysis–precipitation process, and then the oxalate particles became seeds in the following process. The sintered sample from the as-prepared BaTiO₃ powder led to a higher dielectric constant and lower loss.     

Synthesis of BaTiO3 by applying the sample controlled reaction temperature (SCRT) method to the thermal decomposition of barium titanyl oxalate

BaTiO₃ samples with a tailored microstructure, specific surface areas ranging from 6.5 to 18.5 m²/g, were obtained from the thermal decomposition of barium titanyl oxalate (BTO) by using a sample controlled reaction temperature (SCRT) method. These samples are constituted by nanosized crystallites with cubic structure. The use of reducing atmosphere promotes the size diminution of the coherently diffraction domains. The crystallite size and the strain of powdered BaTiO₃ samples were measured in several crystallographic directions by using the Warren-Averbach multiple order method. The results have shown that crystallite size is isotropic, whereas the strain has a marked anisotropic character.     

Double Injection Synthesis and Dispersion of Submicrometer Barium Titanyl Oxalate Tetrahydrate

A modified Clabaugh method has been used to produce a well-dispersed barium titanyl oxalate tetrahydrate (BTO) powder with a particle size of less than 0.2 μm. Production of the BTO powder is based on a double injection system, with reactants rapidly mixed using pressurized gas. The mixture resulting from the double injection of the reactants was subsequently quenched into a solution containing polyethyleneimine as a dispersant. The resulting dispersed BTO powder forms a suspension that is stable against coarsening or aggregation for greater than 1400 h. The dispersed BTO powder was also shown to produce BaTiO₃ with a particle size of 0.25 μm or less after calcination.     

Characterization of Barium Titanyl Oxalate Tetrahydrate

The XRD pattern and the thermal behavior of barium titanyl oxalate tetrahydrate (BTOT) were investigated. BTOT crystallizes in the monoclinic system, 2/ m , with unit cell dimensions of a = 14.954 Å, b = 19.332 Å, c = 13.947 Å, and β= 106.43°. Unit cell content ( Z ) is 12 and the Bravais lattice is P. Theoretical density is 2.31 g/cm³. At a relatively low temperature (∼60°C), BTOT starts to dehydrate, resulting in a less-than-calculated weight loss of ignition. Barium titanate powder obtained by calcining the oxalate exists as the cubic perovskite phase, instead of the tetragonal phase at low temperatures. This happens when the particle size of the crystals is smaller than ∼ 30 nm. As the crystal coarsens, barium titanate powder transforms to the tetragonal state.     

Effect of Microstructure on the PTCR Effect in Semiconducting Barium Titanate Ceramics

The microstructural influence on the PTCR effect in semiconducting barium titanate ceramics was studied and a method for preparing the ceramic bodies exhibiting a PTCR effect of more than seven orders of magnitude was established. Commercial barium titanyl oxalate was used as a starting material and Sb₂O₃ was added as a doping substance. The average grain sizes of the ceramic bodies prepared were 2 to 5 μm over a sintering range of 60 to 92%, to examine in detail the microstructural influence on the PTCR effect. No extra element, such as Mn or Cr, was added to develop the PTCR effect in the present PTCR materials.     

钛液水解工艺对金红石二氧化钛消色力的影响

以工业钛液为原料,采用外加晶种常压水解工艺制备了金红石型二氧化钛,研究了水解钛液的组成和操作参数对二氧化钛消色力的影响。实验结果表明：二氧化钛消色力（Tcs）和蓝相光谱值（Scx）随晶种添加量的增加先增大后减小,随判灰延时时间的增加先增大后减小,随钛液F值的增加先稍有增加后明显降低,随钛液二氧化钛质量浓度的增大而增加。在钛液F值（游离硫酸加上与钛结合的硫酸之和与二氧化钛质量浓度的比值）为1.90左右、铁钛比（铁元素与二氧化钛质量浓度的比值）＜0.5、二氧化钛质量浓度为190~200 g/L、晶种添加量（晶种中二氧化钛质量与对应批次水解浓钛液中二氧化钛质量的比值）为2.0%~2.2%、灰点为“基点+20 min”、熟化时间为0~30 min、稀释水在二沸后100 min加入的条件下进行水解,经过一次洗涤—漂白—二次洗涤—盐处理—煅烧,所得金红石型二氧化钛的消色力更好。     

Low-Temperature Synthesis of Fully Crystallized Spherical BaTiO3 Particles by the Gel–Sol Method

The synthesis of spherical BaTiO₃ particles was attempted by a new technique, the "gel–sol method," at 45°C. The (Ba–Ti) gel used as a starting material was prepared by aging mixtures of titanyl acylate with a barium acetate aqueous solution ([glacial acetic acid (AcOH)]/[titanium isopropoxide (TIP)] = 4, [barium acetate]/[TIP] = 1) at 45°C for 48 h. Potassium hydroxide (KOH) was used as a catalyst for the formation of BaTiO₃. Powder X-ray diffractometry (XRD) results and Fourier-transform infrared (FT-IR) measurements for the (Ba–Ti) gel showed that the gel was amorphous, but the spatial arrangement of barium and titanium in the (Ba–Ti) gel is similar to that in crystalline BaTiO₃ particles. Fully crystallized spherical BaTiO₃ powder with a particle size of 40–250 nm formed at the very low reaction temperature of 45°C. Scanning electron microscopy images showed that the final particles formed via aggregation of the fine particles that seem to be the primary particles of bulk (Ba–Ti) gel. From the XRD, FT-IR, and Raman spectroscopy analysis, it was found that the crystal structure of the as-prepared particles continuously transformed from cubic to tetragonal as the calcination temperature increased, and high crystalline tetragonal BaTiO₃ phase was obtained at 1000°C after 1 h of heat treatment.     

Synthesis of nanosized (Pb,Sr)TiO3 perovskite powders by coprecipitation processing

Nanosized perovskite lead strontium titanate (Pb_xSr_1−x)TiO₃ (PST) powders were successfully prepared by a simple coprecipitation method. Lead-strontium titanyl oxalate (PSTO) precursor was first synthesized at room temperature, and the precursor was then calcined at 600 °C for 1 h to produce the single phase perovskite PST powders. Characterization studies were carried out on the as-dried precursor and the calcined PST powders by various techniques. The results showed a strong dependence of the chemical composition of final PST powders on pH value in the coprecipitation reaction. PST powders with desired composition could be synthesized by adding 25 mol% excess Sr. PST particles were found to be spherical in nature with an average size of 10 nm.     

Formation mechanism of barium titanate by thermal decomposition of barium titanyl oxalate

This study examined the formation mechanism of BaTiO₃ from the thermal decomposition of barium titanyl oxalate. A significant amount of O₂ evolution near 357 and 720 °C was observed by gas chromatography/mass spectroscopy, except for the previously known H₂O, CO₂, CO evolution. The metastable Ba₂Ti₂O₅CO₃(CO₂) intermediate phase seemed to be transformed mainly to Ba₂Ti₂O₅CO₃, while a certain amount of crystalline BaCO₃ and amorphous Ti-rich phase were formed simultaneously at 450-600 °C in air. A modification of the decomposition mechanism reported by Gopalakrishnamurthy et al. was proposed based on the experimental findings.     

Thermal Decomposition of Oxalates of Ammonium and Potassium

The thermal decomposition of oxalates of ammonium and potassium was studied by simultaneous TGA, DTA, and EGA (effluent gas analysis). Of the simple oxalates, the potassium compound is more stable than the lithium compound, as has been observed for the corresponding carbonates and sulfates. Ammonium oxalate is much less stable than either of the alkali metal oxalates. Potassium titanyl oxalate is less stable than potassium oxalate, and ammonium titanyl oxalate is more stable than ammonium oxalate.