Strontium Titanate Powders Research Articles

Hydrothermal synthesis of strontium titanate powders with nanometer size derived from different precursors

Nanocrystalline SrTiO 3 powders have been successfully synthesized under a moderate condition derived from different precursors by the hydrothermal method. Reaction conditions such as temperature, time and alkali concentration have been investigated and the product is characterized in detail by XRD, TEM and other techniques. Comparing with those from the conventional method, the hydrothermal SrTiO 3 powders with a simple mode of size distribution appear to have smaller particle size and a lower agglomeration, and can give the dense sintering bodies at lower temperature.

Fractional factorial design applied to optimize experimental conditions for preparation of ultrafine lanthanum-doped strontium titanate powders

A fractional factorial design was implemented to optimize the experimental conditions for the preparation of ultrafine lanthanum-doped strontium titanate from titanyl acylate precursors. The effects of preparation conditions such as the molar ratio of acetic acid to titanium alkoxide, the water to titanium alkoxide ratio, pH value, the reaction temperature, and stirring speed were systematically studied by using Taguchi orthogonal array design. Results indicated that the effects of the reaction temperature and stirring speed on the reaction were the key variables influencing the average particle size of powders obtained. By combining the optimal settings of the two influential processing variables, it was possible to obtain an ultrafine powder with a particle size of about 340 Å. This was put to a test in the laboratory, and a polycrystalline, narrow size distribution ultrafine SrTiO3 powder that had a particle size of about 380 Å and readily sintered at 1150–1250 °C was obtained.

Preparation of barium strontium titanate powder from citrate precursor

TiCl 4 or titanium isopropoxide reacted with citric acid to form a titanyl citrate precipitate. Barium strontium citrate solutions were then added to the titanyl citrate reaction to form gels. These gels were dried and calcined to (Ba,Sr)-TiO 3 powders. The gels and powders were characterized by DSC/TGA, IR, SEM and XRD analyses. These results showed that, at 500 °C, the gels decomposed to Ba,Sr carbonate and TiO 2 , followed by the formation of (Ba,Sr)-TiO 3 . The onset of perovskite formation occurred at 600 °C, and was nearly complete at 1000 °C. Traces of SrCO 3 were still present. The cation ratios of the titanate powder prepared in the pH range 5-6 were closest to the original stoichiometry. Only 0.1 mol% of the free cations remained in solution. The titanyl citrates were precipitated in either ethanol or acetone. The acetone-derived precipitates were always viscous, but those with a sufficient quantity of alcohol were powdery. The specific surface areas of the ceramic powders obtained by air-, vacuum- and freeze-drying methods were 8.3 × 10 3 , 10.2 × 10 3 and 12.5 × 10 3 m 2 kg -1 , respectively. The powder obtained by freeze-drying had the lowest degree of agglomeration. The precipitated powders of titanyl citrate which were freeze-dried and calcined at 1100°C were compacted and sintered at 1300 °C to obtain dense ceramic bodies with 95% of the theoretical density.

Preparation and electrical properties of fine strontium titanate powder from titanium alkoxide in a strong alkaline solution

The particle size of the forming ceramic powder is related to the morphology of forming precipitated precursor. The rates of hydrolysis and condensation of titanyl acylate gel were slow because of the chelating action of acetic acid. Therefore, the particle size of the precursor gel was uniform and finer, and the formation rate of the powder was quicker. The powder obtained contained fine particles of size ∼ 0.04–0.05 μm and was readily sintered at 1423–1523 K. The dielectric constant and dissipation factor of strontium titanate were determined.

Preparation and electrical characterisation of strontium titanate ceramic from titanyl acylate precursor in strong alkaline solution

Strontium titanate powder can be obtained from titanyl acylate precursor by using acetic acid chelating with titanium isopropoxide in a strong alkaline solution (pH > 13) at room temperature. Infrared spectroscopy, differential scanning calorimetry/thermogravimetric analysis and X-ray diffraction were used to investigate the effects of the size and properties of the precipitated precursor on the properties of the powder and the sinterability for ceramics. It was found that the strontium ion diffused into the gel made by the hydrolysis of the titanyl acylate precursor to form strontium titanate powder. The reaction rate of forming powder at higher temperature such as 100 °C and higher water content (the ratio of water to titanium alkoxide is 20) or higher acetic acid (the ratio of acetic acid to titanium alkoxide is 10), is rapid and the particle size is less than 0.1 μm. Without adding any reagent the density of the sintered strontium titanate at 1300 °C from powder after freeze drying was over 95% of its theoretical density. The dielectric constant and dissipation factor of the strontium titanate body sintered at 1250, 1300, 1400 and 1450 °C, were also determined at a frequency of 1 kHz to 10 MHz at constant temperature.

Sol–gel synthesis of strontium titanate powders of various compositions

The strontium titanates SrTiO3, Sr2TiO4, Sr3Ti2O7 and Sr4Ti3O10 can be synthesized by a sol–gel method at low temperatures. The reaction between strontium acetate solution and titanium(IV) isopropoxide leads to the formation of strontium titanate gels. The gels can be converted to the strontium titanates by drying and calcination. The resulting ultrafine, phase-pure strontium titanate powders have a low impurity content. They are very sinter active above 1000 °C. The rate of densification (which considers the green densities at a given time and the theoretical densities of the titanates for the calculations) during the sintering of compacts increases as Sr2TiO4 < Sr3Ti2O7 < Sr4Ti3O10 < SrTiO3. The strontium titanate gels and the titanate powders were characterized by differential thermal analysis (DTA), thermal gravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM) and chemical analysis.

Low temperature synthesis of ultrafine strontium titanate (SrTiO3) powders

Ultrafine (≍0.4 μm) strontium titanate powder was synthesized using strontium nitrate and potassium titanyl oxalate as precursors. An aqueous (0.1 M) potassium titanyl oxalate solution was added dropwise to a (0.1 M) strontium nitrate solution with continuous stirring at room temperature to precipitate strontium titanyl oxalate (STO). The precipitate, after careful washing with distilled water several times, was air-dried and calcined at 550 °C/6 h to obtain homogeneous, spherical, stoichiometric powder of SrTiO3 ≍0.4 μm in size. The calcined powder was characterized using different techniques such as XRD, DTA/TG/DTG, SEM, and IR.

Preparation of Strontium Titanate Powders by Decomposition of Polymeric Precursors

ABSTRACTThe effects of substituting poly(acrylic acid), PAA, and mucic acid for citric acid in the standard Pechini powder synthesis process was studied. Strontium titanate was chosen as the model system for this study. Powders were prepared from precursor solutions in which PAA (average molecular weight = 2,000 and 5000) was substituted for citric acid (up to 70% by weight), and with reduced weight of total organic reagents (50% reduction). The powders prepared with a 30% substitution of PAA for citric acid produced weakly agglomerated submicron particles after calcining. These powders contained a larger fraction of weak agglomerates than the powders prepared by the original Pechini process. As such, the PAA derived powder could be easily fractionated and dispersed with greater than 70% of the calcined powder having particle sizes less than 0.5 μm

Peroxide route to synthesize strontium titanate powders of different composition

Abstract The calcium titanates CaTiO 3 , Ca 3 Ti 2 O 7 and Ca 4 Ti 3 O 10 can be synthesized by the wet chemical peroxide route. The first step of the preparation is the precipitation of peroxo-precursors of definite stoichiometry which are transformable into the corresponding titanates by thermal decomposition. The resulting ultra-fine, phase-pure calcium titanate powders have only a small impurity content. They are very sinter active above 1200°C. The rate of densification during sintering of compacts is improved in the sequence Ca 3 Ti 2 O 7 4 Ti 3 O 10 3 , considering the green densities, the densities at a given time and the theoretical densities of the titanates for the calculations. The phase CaTi 4 O 9 can be obtained after thermal degradation of a corresponding peroxo-precursor at temperatures below 700°C. There are also indications of the formation of the phase CaTi 2 O 5 below 700°C. A phase Ca 2 TiO 4 can not be synthesized using the peroxide route.

The Molten Salt Synthesis of Large Crystal‐Sized SrTiO3

A process was developed for the preparation of strontium titanate powder with a relatively narrow crystal size distribution and an average crystal size ranging from 0.3 to 13.0 μm, as determined from the powder specific surface area.

Effect of Particle Size and Shape on the Infrared Absorption Spectra of Barium Titanate and Strontium Titanate Powders

Effects of particle size and particle shape have been studied in the infrared absorption spectra of BaTiO3 and SrTiO3 powders to determine whether previously developed methods to treat such effects are applicable to crystals having high dielectric constant and ``soft'' lattice modes. The spectrum of both materials exhibits three absorption bands (BaTiO3: 545, 400, and 180 cm−1; SrTiO3: 605, 400, and 175 cm−1) that are considerably removed from the TO-mode frequencies computed from bulk single-crystal reflection data (BaTiO3: 510, 183, and 33.8 cm−1; SrTiO3: 546, 178, and 87.5 cm−1). These frequencies were successfully correlated with the bulk-crystal frequencies by use of classical electromagnetic scattering theory and an extension of Fröhlich's method. The low-frequency ``soft'' modes of both crystals were found to have an unusually large dependence on particle shape with the consequence that the powders absorb radiation at the corresponding LO-mode frequency.

Solid State Reaction between Barium Titanate and Strontium Titanate

The first stage of the sintering process between barium titanate and strontium titanate powders, which are responsible for the formation of solid solution, was investigated. We measured the variation of permittivity vs . temperature characteristics and crystal structure of the mixtures, with sintering conditions. The shift of the effective Curie temperature and the broadening of diffracted lines were observed in the transient states of the reaction. A diffusion mechanism was introduced in order to interpret these phenomena qualitatively.