Synthesis of barium titanate nanopowder by a soft chemical process

A simple soft chemical method of synthesizing barium titanate nanopowders and nanorods is described here, where titanium dioxide/titanium isopropoxide was taken as a source of titanium, tartaric acid was taken as a template material, nitric acid as an oxidizing agent. The synthesized powders and rods were characterized by XRD, TG and DTA, SEM and IR spectroscopy. In this process phase pure barium titanate nanopowders and nanorods can be prepared at a temperature of 900 °C and the process is simple and cost-effective.     

Semiconducting properties of barium titanate and iron substituted barium titanate

Single crystals of barium titanate and members of the series BaTi_1?xFe_xO_3?xF_x have been grown from a potassium fluoride flux. These crystals were made conductive by heating in a sealed evacuated silica tube in the presence of freshly ground titanium. Electrical, optical and magnetic measurements were performed in order to characterize these crystals. Optical measurements indicated a decrease in the band edge from 3.2(1) eV for barium titanate to 2.8(1) eV for Bati_1?xFe_xO_3?xF_x(x = 0.02, 0.05, 0.07, 0.10). The photoelectrolytic behavior of reduced barium titanate was strongly quenched upon the substitution of iron and fluorine.     

Semiconducting barium titanate

Barium titanate, which is well known as a basic ferroelectric material, is also of interest when doped because of the interaction between semiconductivity and ferroelectricity. The resistance of blocking layers at surfaces and grain-boundaries is governed mainly by the ferroelectric properties, so that a resistance jump of four decades is observed on heating above the Curie temperature. A survey of the chemical and physical properties of such blocking layers both at surfaces and interfaces is presented. Doped titanates have been used as the basis of two new types of material:

1. Semiconductors with high positive temperature-coefficient of resistivity in special temperature ranges suitable for temperature-sensors and stabilisers.
2. Dielectrics with extremely high dielectric constant, used in so-called barrier-layer condensers.

     

Doped barium titanate nanoparticles

We have synthesized nickel (Ni) and iron (Fe) ion doped BaTiO₃ nanoparticles through a chemical route using polyvinyl alcohol (PVA). The concentration of dopant varies from 0 to 2 mole% in the specimens. The results from X-ray diffractograms and transmission electron micrographs show that the particle diameters in the specimen lie in the range 24–40 nm. It is seen that the dielectric permittivity in doped specimens is enhanced by an order of magnitude compared to undoped barium titanate ceramics. The dielectric permittivity shows maxima at 0.3 mole% doping of Fe ion and 0.6 mole% of Ni ion. The unusual dielectric behaviour of the specimens is explained in terms of the change in crystalline structure of the specimens.     

Preparation of powder barium titanate

Phase-pure BaTiO₃ powder (free of Ba₂TiO₄, BaCO₃, Ba(NO₃)₂, and OH impurities) with an average particle size of about 100 nm is prepared by solid-state reaction between titanium oxyhydroxide and barium hydroxide ground and mixed by sonication in an inert organic liquid.     

Optimization of non-aqueous nickel slips for manufacture of MCFC electrodes by tape casting method

Tape casting is a powerful method for the manufacture of carbonyl nickel green tape, which is sintered at a given condition and then used as the electrode for molten carbonate fuel cells. In this work, the rheological behaviors of non-aqueous carbonyl nickel slips for tape casting was investigated considering different solvent and binder systems, by controlling the total binder and plasticizer content and the binder to plasticizer ratio. Glycerol trioleate was used as the dispersant and its content in the slip was also optimized. The characteristics of the green tapes obtained in different conditions were studied in terms of densities, tensile strength and microstructure, and related with the rheological properties of the slips.     

Some barium titanate based dielectrics

Some new potential dielectric materials have been made through the cross-substitution of Ba²⁺ by a 1:1 molar combinations of tri-(La³⁺) and mono-valent (Li⁺, Na⁺, K⁺) ions at the Ba²⁺ site in BaTiO₃. Chemical analysis shows that compositions in the potassium series are about 6·1% deficient in their K₂O content and exhibit interesting dielectric relaxations. The cross-substitution has lowered theT _c down to room temperature. The disorder in the larger ‘A’ cation sublattice of the three systems has been established by infra-red and x-ray data. This leads to microscopic compositional variations, which in turn can account for the diffuseness of the dielectric anomalies observed in the barium titanate-rich compositions (0⩽x⩽0·3). since deceased.     

Characteristics of barium ferrite tape for magnetic contactduplication

The magnetic properties and electromagnetic characteristics of Ba-ferrite tape for R-DAT magnetic contact duplication (MCD) were investigated. The tapes employed Ba-ferrite particles averaging 0.06 μm in diameter with an aspect ratio between 4 and 5. Ba-ferrite tapes were prepared with perpendicular, longitudinal, and no orientation, and their MCD and ring-head recording (RHR) characteristics were compared. Several distinctive characteristics were observed in MCD, and the desirability of perpendicular orientation at short wavelengths in MCD applications is clear. Tilted orientation was also investigated, and its output level was similar to that of perpendicular orientation in MCD, while in RHR it proved superior to perpendicular orientation in the short wavelength region. The magnetization mode of the slave tape was studied by waveform analysis using the FFT method and in conjunction with the tapes' magnetic properties, such as uniaxial anisotropy energy, remanence coercivity, and squareness ratio     

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 BaTiO₃. The BET specific surface area of barium titanate powder, after microwave heating to 680 °C, was 14.2 ± 0.5 m²/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.     

A modified method for barium titanate nanoparticles synthesis

In this research, a modified, cost effective sol-gel procedure applied to synthesize BaTiO₃ nanoparticles. XRD and electron microscopy (SEM and TEM) applied for microstructural characterization of powders. The obtained results showed that the type of precursors, their ratio and the hydrolysis conditions had a great effect on time, temperature and therefore the costs of the synthesis process. By selection, utilization of optimized precursor's type, hydrolysis conditions, fine cubic BaTiO₃ nanoparticles were synthesized at low temperature and in short time span (1 h calcination at 800 °C). The proposed procedure seems to be more preferable for mass production.The result indicated that the polymorphic transformation to tetragonal (ferroelectric characteristic) occurred at 900 °C, which might be an indication of being nanosized.     

Effects of barium dissolution on dispersing aqueous barium titanate suspensions

Dissolution of barium ion and its effect on dispersion behavior of aqueous barium titanate suspensions at various pH values have been investigated. The amount of leached barium ion decreases with increasing pH value. The dissolution of barium ion also causes an increase in pH value of suspension, but the change decreases with increasing initial pH value. The iso-electric point (IEP) of leached barium titanate powder increases with increasing leaching pH value and solid loading as well. The dissolution of barium ion enhances the colloidal stability of aqueous barium titanate suspension, in agreement with zeta potential measurement.     

Synthesis of single-crystal barium titanate nanorods transformed from potassium titanate nanostructures

Single-crystal barium titanate (BaTiO₃) nanorods were synthesized by a hydrothermal reaction using precursors of potassium titanate (K₂O·nTiO₂, n = 4 or 6) nanostructures. The precursors of potassium tetratitanate (K₂Ti₄O₉) and potassium hexatitanate (K₂Ti₆O₁₃) nanostructures were prepared by a sol-gel method in which a growth of K₂O·nTiO₂ (n = 4 or 6) nanorods was induced by a role of pre-crystallized K₂O phase at defined heating temperatures. The specific morphologies of BaTiO₃ nanorods featured with flat or stepped surfaces and rectangular or polygonal cross-section, were obtainable by selecting the structure of precursors.     

Non-Newtonian fluid flow model for ceramic tape casting

The current device of miniaturisation and higher device counts in integrated circuit (IC) packages has significantly increased the use of both multilayer ceramic packages (MLCP) and multilayer capacitors (MLC). Currently, one of the main methods used for the manufacture of flat ceramic packages with precise thickness control and consistency is the tape casting technique. Since these tapes can be cast with thickness of about 100 μm, it is crucial that the control of green tape thickness is precise, and that these thickness values are reproducible consistently. The flow of the slurry onto the casting surface can be modelled as a two dimensional fluid flow through a parallel channel. By choosing a suitable constitutive model, the predictions of the proposed model and existing models were compared with experimental results. The proposed model accurately described the fluid flow characteristics of the process, and had good agreement with experimental results.     

A modification of tape casting for aligning the whiskers

Tape casting was modified in order to align the silicon nitride whiskers in the silicon nitride slurry. Based on a simplified fluid dynamics model, it was understood that torque for aligning the whisker was increased by n² times by dividing the flow into n narrow ones. Samples with 3 wt % silicon nitride whiskers of a hexagonal crystal structure were prepared by using three different tape casting methods; conventional tape casting, tape casting modified by using an array of razor blades, and tape casting modified by using an array of sharpened pins. The razor blades of 13 mm in length were 5 mm apart from each other in the array, and the sharpened pins of 0.08 mm in diameter 0.7 mm apart from each other in the array. Samples were fully densified by gas pressure sintering. Both the sintering shrinkage anisotropy and X-ray diffraction analysis showed that the sample prepared by employing the pins had the best whisker alignment among the three samples.     

Europium incorporated barium titanate thin films for optical applications

BaTiO₃:Eu (BT:Eu) thin films were deposited onto quartz substrates by RF magnetron sputtering. The effect on structural, morphological, optical and photoluminescence (PL) properties in the films with different Eu concentrations (0–5 wt%) were investigated. The X-ray diffraction (XRD) pattern of the undoped BT thin film revealed a tetragonal (T) phase with orientations along (101) plane. From XRD pattern, the crystallinity of the films increased with increase in Eu concentration. The SEM images revealed that the films exhibited tetragonal shape, crack free and good adherence to the substrate. Atomic force microscopy studies showed an increase of grain growth with doping concentration. The rms roughness value increased with increase in Eu concentration and the film surface revealed positive skewness and high value of kurtosis which make them suitable for tribological applications. X-ray photoelectron spectroscopy revealed the presence of barium, titanium, europium and oxygen in BT:Eu film. An average transmittance of >80 % (in visible region) was observed for all the films. Optical band gap of Eu doped BT films decreased from 3.86 to 3.53 eV. Such films with optical properties such as high transparency, decrease in band gap and high refractive index are suitable for optoelectronic applications. PL properties showed a sharp line at 625 nm and a broad line at 552 nm due to europium (Eu³⁺) transitions. PL phenomena were observed, owing to the electronic structure of Eu³⁺ ions as well as BT nanocrystallites in the films. The sharp and intense red luminescence is useful for photoelectric devices and optical communications.     

Low-temperature synthesis and analysis of barium titanate nanoparticles with excess barium

BaTiO₃ nanoparticles with excess barium are directly synthesized from solution at 65 °C. It is noted that a small amount of BaCO₃ exists in the as-prepared samples. A series of standard mixtures with different proportion of BaTiO₃ and BaCO₃ are measured by XRD analysis to quantify the amount of BaCO₃ in our synthesized samples. After a deduction of the amount of BaCO₃, the concentration of excess barium in the lattice of BaTiO₃ nanoparticles can be determined and the results show that the excess barium can reach a considerable concentration. The influences of defects and surfaces on BaTiO₃ nanoparticles with excess barium are analyzed and two important reasons for the high concentration are also given.     

Defect chemistry of nano-grained barium titanate films

Polycrystalline barium titanate thin films have been prepared with 100 ppm of B-site acceptor dopants Ca, Mg, and Mn via chemical solution deposition on base metal substrates. The films are fired in low pO₂ atmospheres at 900 °C to prevent substrate oxidation. All dopant species produce low loss, space-charge free material without secondary reoxidation anneals. We note that the dopant concentrations required to compensate for oxygen non-stoichiometry are substantially greater than expected by equilibrium thermodynamic calculations. This observation is rationalized in the context of a composite oxygen defect model with differing reduction enthalpies for grain interiors and surfaces.     

Sn掺杂BZT薄膜性能研究

采用sol-gel法在Pt/Ti/SiO2/Si衬底上制备了Sn掺杂Ba(Zr0.2 Ti0.8)O3 (BZT)薄膜.结果表明,掺锡的BZT薄膜为钙钛矿结构,当Sn掺量超过4％时,出现了第二相BaO;SEM观察发现掺锡BZT薄膜表面光滑平整,孔洞和裂纹较少;当Sn掺量达到8％时,BZT薄膜的介电常数达到最大值,而介电损耗最小;BZT薄膜的剩余极化强度为2.29μC/cm2,矫顽场强为10.36kV/cm.