Decomposition Of Barium Titanyl Oxalate Research Articles

THE INFLUENCE OF THE PRECURSOR COMPOSITION ON THE PECULIARITIES OF THE BARIUM TITANATE FORMATION

In the process of obtaining barium titanate by the Pechini method, a connection between the conditions of complexes precipitation and the nature of their thermal decomposition was established. X-ray phase analysis of thermally decomposed precursors showed that the formation of a single-phase system based on barium titanate can be achieved in the range of Ba/Ti ratio 0.96-1.01 at high reagent concentration and low solution pH during the precursor deposition process. On the basis of thermogravimetric analysis, a possible mechanism of precursor decomposition and its composition is assumed. It is shown that the number of hydroxide groups in the structure affects the crystallization mechanism, total mass loss, and the amount of water adsorbed on the surface. In particular, samples obtained at low solution pH have a minimal amount of hydroxyl groups and decompose according to a typical four-step mechanism of thermal decomposition of barium titanyl oxalate. Other samples contain hydro and carbo groups, which leads to an increase in the final decomposition temperature above 770 °C and a multistage decomposition process due to the difference in the activation energy of the nucleation of different phases. This, in turn, may determine the dominance of the nucleation process over the growth and nucleation of smaller crystallites, compared to the product of pure oxalate decomposition. On the one hand, the high content of chloride ions at the lowest pH promotes the crystallization of the product and the formation of additional nucleation centers from the phase of amorphous titanium dioxide. On the other hand, the formation of smaller crystallites occurs due to the absence of significant particle collisions in conditions of low concentration of the solution. On the basis of thermogravimetric analysis, it is shown that at high concentration, barium titanyl oxalate decomposes mainly by the mechanism of formation of intermediate oxycarbonates, and not barium carbonate and titanium dioxide. Thus, the optimization of the precursor precipitation parameters and the study of the barium titanate formation mechanism allow for better regulation of the composition and crystallite size of the final product.

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

This study examined the formation mechanism of BaTiO 3 from the thermal decomposition of barium titanyl oxalate. A significant amount of O 2 evolution near 357 and 720 °C was observed by gas chromatography/mass spectroscopy, except for the previously known H 2O, CO 2, CO evolution. The metastable Ba 2Ti 2O 5CO 3(CO 2) intermediate phase seemed to be transformed mainly to Ba 2Ti 2O 5CO 3, while a certain amount of crystalline BaCO 3 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.

Microwave synthesis of nano-sized barium titanate

Nano-sized barium titanate powders have been synthesized by microwave processing at 2.45 GHz. Using barium titanyl oxalate (BTO) as a precursor, microwave processing was carried out by heating the precursor to a temperature between 600 °C and 750 °C with different heating rates from 10 °C/min to 20 °C/min without isothermal holding. X-ray diffraction analysis indicates that the decomposed product at 680 °C was pure cubic BaTiO 3. The BET specific surface area of barium titanate powder, after microwave heating to 680 °C, was 14.2 ± 0.5 m 2/g, corresponding to an average particle size of 70 nm. This particle size was confirmed by the scanning electron microscopy (SEM). Parallel study shows that the conventional heating in a regular resistance furnace using a similar heating schedule did not result in complete conversion of BTO. This study shows that the microwave processing significantly accelerated the decomposition of barium titanyl oxalate and reduced the temperature of barium titanate nano-powder formation, resulting in nano-sized pure cubic barium titanate powder.

Size and temperature induced phase transition behaviors of barium titanate nanoparticles

High density, almost impurity-free and defect-free barium titanate (BaTiO3) fine particles with various sizes from 20to1000nm were prepared by the two-step thermal decomposition of barium titanyl oxalate and postheating treatment. The crystal structures of these particles were investigated as a function of the size and the temperature using synchrotron radiation x-ray diffraction (XRD) measurement. As a result, the size-induced ferroelectric (tetragonal-cubic) phase transition observed at around 30nm. Moreover, the temperature dependence of the crystal structures revealed that one phase transition at 135°C separated into two kinds of phase transition behaviors with decreased particle sizes, i.e., the tetragonal-cubic phase transition temperature was constant at 135°C despite particle sizes while the cell volume expansion temperature shifted to low temperature with decreasing particle sizes. Moreover, the temperature dependence of Raman scattering spectra clarified that the temperature at a discontinuous change of damping factor was almost consisted with the cell volume expansion temperature from the XRD measurement. These results suggested that the phase transition behavior of the BaTiO3 nanoparticles was quite different from that of the BaTiO3 single crystals.

Barium titanate characterization by differential scanning calorimetry

Differential scanning calorimetry (DSC) was used to characterize barium titanate formed after decomposition of barium titanyl oxalate. Three different methods of the oxalate precipitation reaction were used to prepare barium titanyl oxalate which after calcinations result in barium titanates with different barium to titanium ratio ( A/ B). It appears that two factors have effect on Curie temperature: barium to titanium ratio and mechanical stress introduced by milling.

Preparation of nm-Sized BaTiO<sub>3</sub> Crystallites by The 2-Step Thermal Decomposition of Barium Titanyl Oxalate and their Dielectric Properties

Preparation of nm-Sized BaTiO<sub>3</sub> Crystallites by The 2-Step Thermal Decomposition of Barium Titanyl Oxalate and their Dielectric Properties

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

BaTiO 3 samples with a tailored microstructure, specific surface areas ranging from 6.5 to 18.5 m 2 /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 BaTiO 3 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.

Thermal Decomposition Process of Barium Titanyl Oxalate Tetrahydrate.

Thermal decomposition of barium titanyl oxalate tetrahydrate was investigated in air and nitrogen atmospheres, respectively. Decomposition process is divided into four steps; dehydration, decomposion, crystallization and the production of BaTiO3. In air atmosphere, after dehydration and the decomposition of barium titanyl oxalate, a small amount of BaCO3 and TiO2 is formed through the reaction between the decomposition product and the generated CO2 gas in air atmosphere, while the other large part of the decomposition product crystallizes out as intermediate phase (Ba2Ti2O5CO3) in intermediate process of decomposition. In nitrogen atmosphere, however, BaTiO3 is only formed through decomposition of intermediate phase.

Constant Rate Thermal Analysis (CRTA) as a Tool for the Synthesis of Materials with Controlled Texture and Structure

Some examples of the use of the CRTA method for the synthesis of materials with controlled texture and structure are given. BaTiO 3 has been obtained from the thermal decomposition of Barium Titanyl Oxalate (BTO) and Barium Titanyl Citrate (BTC) by controlling the reaction temperature in such a way that the partial pressure of the gases generated in the reaction was maintained constant at a value close to 10 -2 mbar. It has been shown that this method allows getting BaTiO 3 with crystal sizes considerably lower than those obtained by decomposing the same precursors by conventional methods. This small crystal sizes lead to the stabilisation of the metastable cubic phase with regards to the tetragonal phase. It has been also shown that the control of the CO generated in the carbothermal reduction of silica allows tailoring the phase composition of the silicon nitride obtained as final product.

Synthesis and sintering of nanocrystalline barium titanate powder under nonisothermal conditions. IV. Electron microscope study of the evolution of barium titanate powder morphology

The dependence of BaTiO3 powder morphology evolution during decomposition of barium titanyl-oxalate and subsequent barium titanate synthesis on heating rate is studied. It is established that the mechanisms of morphology development depend upon the heating mode and the necessity of a nonlinear heating schedule is proven. This schedule makes it possible to avoid some limitations of linear heating schedule and to use their advantages.

Synthesis and sintering of nanocrystalline barium titanate powder under nonisothermal conditions. III. Chromatographic analysis of barium titanyl-oxalate gaseous decomposition products

Gas chromatography is performed during the decomposition of barium titanyl-oxalate and the subsequent synthesis of barium titanate under nonisothermal conditions. It is shown that the path of the decomposition process is different under different heating conditions. A new mechanism of barium titanyl-oxalate decomposition and subsequent barium titanate synthesis under high heating rates is suggested. The change in mechanism is caused by barium titanyl-oxalate oxidation by free oxygen.

Kinetics and mechanism of the thermal decomposition of barium titanyl oxalate

Thermal analysis of barium titanyl oxalate reveals that the decomposition proceeds through four distinct rate processes. Among them, the decomposition of oxalate occurs in the temperature range 230–350°C, and has been studied by TG and gas pressure measurements, supplemented by IR spectroscopy, electron microscopy and chemical analysis. Oxalate decomposition proceeds differently in vacuum and in flowing gas atmospheres. Analytical results indicate the formation of a complex carbonate together with CO, CO2 and water vapour below 400°C. Schemes for each type of decomposition are proposed and discussed. For decomposition in vacuum, kinetic observations fitted the three-dimensional, diffusion controlled, rate equation for almost the entire α-range (0.028≤α≤0.92). The activation energy is calculated to be3 189±6 kJ mol−1.

Thermal decomposition of titanyl oxalates—II: Kinetics of decomposition of barium titanyl oxalate

Kinetics of the thermal decomposition of barium titanyl oxalate have been studied. Decomposition of the anhydrous oxalate is complex and deceleratory throughout. Kinetics of decomposition of the intermediate carbonate Ba 2Ti 2O 5CO 3 is greatly influenced by the thermal effects during its formation. The sigmoidal (α, t) curves obey a power law equation followed by first order decay. Presence of carbon in the vacuum prepared carbonate has a strong deactivating effect. Decomposition of the carbonate is accompanied by growth in particle size of the product, barium titanate.