Synthesis and Characterization of Barium Lanthanum Titanates

Ternary compounds in the system BaO—TiO₂—La₂O₃ were prepared by the solid-state reaction technique at temperatures between 1300° and 1400°C using precursor oxides as the starting materials. In an alternative processing technique, BaTiO₃ was reacted with appropriate proportions of prefabricated lanthanum titanates at 1350°C to obtain the compounds. Two compounds were identified in the TiO₂-rich region of the system. The X-ray powder diffraction pattern of a compound with a chemical composition BaLa₂Ti₃O₁₀ (BaO·La₂O₃·3TiO₂) is indexed on the basis of an orthorhombic unit cell with a = 7.665 × 10⁻¹ nm, b = 28.524 × 10⁻¹ nm, and c = 3.876 × 10⁻¹ nm. The other compound, which has a chemical composition Ba₄La₈Ti₁₇O₅₀ (BaO·La₂O₃·4.25TiO₂) occurs in a narrow homogeneity range within the system. The X-ray powder diffraction pattern of the compound is indexed on the basis of an orthorhombic unit cell with a = 12.317 × 10⁻¹ nm, b = 22.394 × 10⁻¹ nm, and c = 3.881 × 10⁻¹ nm. Both the compounds are compatible with BaTiO₃ and form pseudobinary joins with BaTiO₃ in the system BaO—TiO₂—La₂O₃.     

Semiconducting Bodies in the Family of Barium Titanates

The anomalous resistivity-temperature characteristics found in semiconducting barium titanates were studied in relation to their composition. The resistivity and impedance characteristics and the crystal structures were investigated for different compositions in the systems (Ba, -Sr) (Ti, Sn)O₃, (Ba, Ca, Sr)TiO₃) (Ba, Pb)TiO₃, Ba-(Ti, Zr)O₃, and Ba(Ti, Si)O₃ doped with 0.1 mole % of Ce and also in the system (Ba, Mg, Ce) TiO₃. Bodies whose compositions were quite different from BaTiO₃ could not be semiconducting. The resistivity anomaly in each semiconducting body showed a good correlation with the crystal transition.     

Thermal Analysis of Some Barium and Strontium Titanyl Oxalates

The thermal decompositions of BaTiO(c₂O₄)₂.- 4H₂O, BaTiO(OH)₂C₂O₄.2H₂O, SrTiO(C₂O₄)₂.- 4H₂O, and SrTiO(OH)₂C₂O₄.H₂O were investigated using TGA, DTA, and effluent gas analysis. The stoichiometry of the decompositions is discussed and it is proposed that a reduced state of titanium is formed as an intermediate.     

Structural and Dielectric Properties of Lead-Free Zr-Doped Barium Titanates

Lead-free BaZr _x Ti_1–xO₃ ferroelectrics (x = 0.2, 0.4, 0.6, 0.8) were synthesized by conventional double-sintering technique. The structural, morphological, and dielectric properties of BaZr _x Ti_1–xO₃ were investigated as a function of zirconium content x. A single-phase perovskite structure of tetragonal ceramics was identified by XRD. The SEM images of the ferroelectrics exhibit fine grains of varied porosity. All synthesized samples exhibited dielectric dispersion at low frequencies.     

Barium Titanates With Improved Insulation Resistance and Time Constant

An experimental study was conducted to improve the insulation resistance and time constant of ceramic barium titanates. It was found that the purity of the barium titanate had a notable effect, and several additives were found which improved the time constants by several orders of magnitude. The insulation resistance at elevated temperatures could be improved substantially by additions of high-fluorine compounds of such cations as uranium and chromium.     

Porous Silicon Capacitor Structures with Embedded Barium Strontium Titanates

Theoretical Foundations of Chemical Engineering - The possibility of creating capacitor structures based on porous silicon with oxide ferroelectrics embedded in the pores—barium strontium...     

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.     

Determination of Donor Gradients Within Surface Barriers Formed on Dense Cd-Doped Barium Titanates

Surface barriers were formed on dense Gd-doped barium titanates by a reduction-reoxidation process. The distribution of donors within the partially reoxidized barriers was determined from capacitance measurements using blocking contacts and from resistance measurements using ohmic contacts. The incremental barrier capacitance behaved as a depletion-layer capacitance when measured as a function of bias voltage. A donor gradient α_c was determined from the capacitance-voltage behavior of the depletion layers by using a linear-graded model to describe the donor distribution through the depletion layers. A donor gradient a_r was indirectly determined from resistance profiles of the surface barriers formed on the reduced titanates by a second reoxidation. The donor gradients a_c and a_r were in good agreement, with both gradients decreasing for the higher reoxidation temperatures and/or the longer times used in forming the barriers. This behavior is explained by assuming that the reoxidation process is diffusion-controlled and by qualitatively relating the gradients to assumed oxygen profiles within the barriers.     

水热法合成钛酸盐(MTiO3)超细粉体

本文采用水热法在温和条件下制备出钛酸盐(BaTiO3、PbTiO3、SrTiO3)超细粉体.以Ba(OH)2和钛酸四丁酯为原料,强碱性条件下,水热反应温度150℃、48 h时制备出粒径为20～80 nm的立方相BaTiO3;反应温度为180℃、48 h时制备出粒径为50～80 nm的四方相BaTiO3.以钛酸四丁酯和醋酸铅为原料,在180℃、20h条件下,碱度为c(NaOH)=1.O mol/L时,制备出粒径在100～130 nm之间的四方相PbTiO3粉体.以钛酸四丁酯和硝酸锶为原料,在180℃、2 h条件下,碱度为c(KOH)=0.2 mol/L时,制备的SrTiO3粉体粒径在40～90nm之间.通过控制反应条件制得的钛酸盐粉体分散性好、均匀、纯度高.     

Preparation of White Pigments from Nanosized Alkaline Earth Metal Titanates and Potassium Titanium Oxophosphate

The aim of this work is to produce white pigments having less amount of Ti⁴⁺ than that of pure TiO₂. It develops synthetic methods for the preparation of nanosized white pigments based on alkaline earth metal titanates and potassium titanium oxophosphate with a high surface area (30–80 m²/g) from ilmenite. The preparative methods involve the extraction of titanium as a water-soluble titanium oxychloride from ilmenite and coprecipitation of constituent ions of pigments from their aqueous mixture solutions using a suitable precipitant. All the synthesized pigments have been characterized by X-ray powder diffraction, transmission electron micrscope, and ultraviolet–visible spectroscopy study, energy-dispersive X-ray analysis, and Brunauer–Emmett–Teller surface area measurement.     

Preparation and Thermal Analysis of Mixed Magnesium-Manganese-Iron Oxalates and Hydrated Oxides

A square-loop ferrite composition, Mg_0.675Mn_0.535–Fe_1.8000O₄, having high purity and fine particle size was prepared by pyrolysis of coprecipitated oxalates or hydrated oxides. The control of pH had a marked effect on the stoichiometry of the coprecipitated divalent oxalates, and ap optimum pH of 2.5 to 3.0 was observed. Thermal analysis was performed on the coprecipitated materials and on individual components; it revealed that the coprecipitated oxalates formed a solid solution whereas the hydrated oxides did not.     

钡钛醋酸盐凝胶制备BaTiO3粉体

本文报道了用ｓｏｌ－ｇｅｌ法制备钡醋酸盐凝胶，并分别作高灼烧和水热处理制备ＢａＴｉＯ３粉体。通过对产物的表征，比较了这两种处理过程，进而对水热条件下陶瓷粉体的形成机理作了探讨。由于水热条件，凝胶在反应介质中溶解，进而结晶形成晶粒，因此所形成的ＢａＴｉＯ３晶粒线度小；线度分布范围窄。晶粒形貌完整，明显优于高温灼烧处理后得到的粉体。     

Preparation of BaTi4O9 from Oxalates

A barium titanate precursor with a barium:titanium ratio of 1:4 was prepared by controlled coprecipitation of mixed barium and titanium species with an ammonium oxalate aqueous solution at pH 7. The results of thermal analysis and IR measurement show that the obtained precursor is a mixture of BaC₂O₄·0.5H₂O and TiO(OH)₂·1.5H₂O in a molar ratio of 1:4. Crystallized BaTi₄O₉ was obtained by the thermal decomposition of a precipitate precursor at 1300°C for 2 h in air. The dimensions of the powder calcined at 1000°C are between 100 and 300 nm. The grain dimensions of the sintered sample for 2 h at 1300°C are of the order of 10 to 30 μm. Dielectric properties of disk-shaped sintered specimens in the microwave frequency region were measured using the TE₀₁₁ mode. Excellent microwave characteristics for BaTi₄O₉—ɛ= 38 ± 0.5, Q = 3800–4000 at 6–7 GHz and τ _f = 11 ± 0.7 ppm/°C—were found.     

八水氢氧化钡制取高纯碳酸钡的研究

介绍八水氢氧化钡制取高纯碳酸钡的工艺,产品质量及用户使用结果。     

八水氢氧化钡制取高纯碳酸钡

介绍八水氢氧化钡制取高纯碳酸钡的工艺、产品质量及用户使用结果。     

Thermal Decomposition of Some Substituted Barium Titanyl Oxalates and Its Effect on the Semiconducting Properties of the Doped Materials

Thermal analysis has been performed on BaTiO(C₂O₄)₂.4H₂O, Ba_0.6Sr_0.4TiO(C₂O₄)₂.4H₂O, Sr(TiO(C₂O₄)₂.4H₂O, Ba_0.9Pb_0.1TiO(C₂O₄)₂.4H₂O, and BaTi_0.9Zr_0.1O(C₂O₄)₂.4H₂O. It was observed that the strontium compound decomposes differently than the others. Previous investigators have proposed conflicting mechanisms for the pyrolysis of the barium salt and these results are discussed in comparison with this work. The electrical resistivity and temperature coefficient of fired lanthanum-doped materials were found to vary with the calcination temperature. Maximum conductivity was observed in samples calcined at 900°C whereas maximum positive temperature coefficient was observed for materials calcined at 1050°C. Particle sizes of the calcined material were compared with grain sizes in the fired pieces and correlated with the electrical properties. A cursory examination was made on the effects of fabrication pressure, 1.25 to 15 tsi, on the electrical conductivity. Both the conductivity and positive temperature coefficient were found to increase with decreasing fabrication pressure.     

Preparation of a Barium Titanate-Dispersed-Magnesia Nanocomposite

Ceramic nanocomposites with a perovskite-type ferroelectric dispersoid were studied, to introduce ferroelectricity into structural ceramics. Barium titanate (BaTiO3) was found to be phase compatible with magnesia (MgO) during sintering, and a MgO matrix/BaTiO3 nanocomposite was successfully fabricated by a conventional powder mixing and sintering method. The mechanical strength of the nanocomposite was not degraded, although weak BaTiO3 was incorporated into the composite. The BaTiO3 dispersoid was tetragonal or possibly orthorhombic, although the tetragonality, c/a, was decreased from the starting powder.     

Peroxo-oxalate Preparation of Doped Barium Titanate

The peroxo-oxalate complexation method is a method that can be used for the preparation of doped barium titanate. In this paper we focus on BaTi_0.91Zr_0.09O₃, which can be used for discharge capacitors in lamp starters. The preparation method described here is based on the complexation and subsequent precipitation in basic environment of Ba, Ti, and Zr ions with hydrogen peroxide and oxalate. The influence of several process parameters, like precipitation temperature and pH, on powder properties is described. A single-phase perovskite crystal structure is obtained after calcination starting from a chloride precursor solution using a precipitation temperature of 40°C and a pH of 9. Because the peroxo-oxalate process starts with inexpensive chlorides and is performed in air, the peroxo-oxalate process is suitable for the commercial production of doped barium titanate.