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.     

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.     

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.     

Dependence of magnetoelectric properties on the magnetostrictive content in 0–3 composites

The magnetoelectric response in composites of barium titanate (BTO) and cobalt ferrite (CFO) has been determined by measuring the magnetoelectric susceptibility coefficient. This was done by two different methods: magnetocapacitance measurements and magnetoelectric voltage measurement using a lock-in technique. These composites were prepared by the sol–gel method. Four different compositions with different molar ratios of the magnetostrictive phase (CFO) embedded in a piezoelectric matrix of BTO were studied to investigate the effect of the magnetostrictive content and the number density of interfaces on the magnetoelectric response. It was found from both techniques that the magnetoelectric coupling effect increases with the increase of applied field and it had a non-linear dependence on the percentage of magnetostrictive content in the composites.     

Chemical Vapor Synthesis of FeOx–BaTiO3 Nanocomposites

Nanocomposite powders of FeO_x–BaTiO₃ (FO‐BTO) have been prepared by chemical vapor synthesis (CVS) in a single‐step process. The optimal parameters (reactor temperature, reactor length, precursor ratio) for the synthesis were investigated in an initial step for the individual systems, iron oxide (FO), and barium titanate (BTO); and in a second step optimized for the synthesis of the nanocomposites. The solid iron precursor was thermally evaporated, whereas the solid Ba‐ and Ti precursors were vaporized using laser flash evaporation to obtain ultrafine crystalline FO, BTO, and FO‐BTO nanoparticles. The possibility to influence the mass ratios of the two phases in FO‐BTO mixture by adjusting the ratio of the precursor in the two precursor delivery units has been investigated. The potential of CVS for the synthesis of nanocomposites containing iron oxide and barium titanate ultrafine crystalline nanopowders with particle size bellow 10 nm is demonstrated.     

Water-Induced Degradation of Barium Titanate Ceramics Studied by Electrochemical Hydrogen Charging

Water-induced degradation of barium titanate (BTO) ceramics has been investigated using electrochemical hydrogen charging, in which the silver electrodes of BTO ceramic specimens are made cathodes in a 0.01 M NaOH solution to evolve hydrogen by electrolysis of water. After 80 h of treatment, the resistance of BTO decreases by ∼3 orders of magnitude, and the dielectric loss obviously increases. The degradation can be explained by the reduction reaction of atomic hydrogen with BTO. Hydrogen acts as a donor in BTO, and electrons are formed by the reduction. It is proposed that the reduction reaction of atomic hydrogen at ambient temperature by electrolysis of water is an important origin for degradation of BTO-based ceramic devices.     

Fabrication of barium titanate ceramics via digital light processing 3D printing by using high refractive index monomer

A digital light processing (DLP) technology has been developed for 3D printing lead-free barium titanate (BTO) piezoelectric ceramics. By comparing the curing and rheological properties of slurries with different photosensitive monomer, a high refractive index monomer acryloyl morpholine (ACMO) was chosen, and a design and preparation method of BTO slurry with high solid content, low viscosity and high curing ability was proposed. By further selecting the printing parameters, the single-layer exposure time was reduced and the forming efficiency has been greatly improved. Sintered specimens were obtained after a nitrogen-air double-step debinding and furnace sintering process, and the BTO ceramics fabricated with 80 wt% slurry shows the highest relative density (95.32 %) and piezoelectric constant (168.1 pC/N). Furthermore, complex-structured BTO ceramics were prepared, impregnated by epoxy resin and finally assembly made into hydrophones, which has significance for the future design and manufacture of piezoelectric ceramic-based composites that used in functional devices.     

Electrophoretic deposition of BaTiO3 thin films from stable colloidal aqueous solutions

Polycrystalline BaTiO₃ (BTO) thin films were electrodeposited on titanium foils from colloidal aqueous solutions of BTO nanoparticles which were synthesized by a hydrothermal process, under autogenous conditions. Two kinds of reactants have been studied: one involves an aqueous solution of titanium tetrachloride and barium hydroxide octahydrate without any added solvent, whereas the second was obtained by dispersing amorphous titanium oxide in different volumes of barium hydroxide aqueous solutions. The nanoparticles were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The particle size distribution (PSD) and the zeta potential measurements indicate that the colloids in the solution are polydisperse when using the first synthesis method, and they tend to be quasi monodisperse in the case of the second synthesis route. A porous microstructure of the electrodeposited films was detected by SEM. Finally, the dielectric properties of the BTO thin films were investigated.     

Synthesis and Characterization of Bismuth Titanate by an Aqueous Sol–Gel Method

A highly stable, reproducible and water-based bismuth titanate (BTO) sol system has been synthesized by an aqueous sol–gel method. First bismuth nitrate was dissolved in acetic acid, and then it was mixed with a solution of lactic acid dissolved tetra- n -butyl titanate, subsequently, water was added to adjust sol concentration. As-obtained sols or gels were characterized by Ultraviolet–Visible Spectrophotometer, derivative differential thermal analysis-differential thermal analysis–thermal gravimetry, in situ Raman, and high-temperature X-ray diffraction. Results show that the BTO sol can remain stable for more than 1 year and BTO can start to crystallize at about 450°C.     

Control of tetragonality via dehydroxylation of BaTiO3 ultrafine powders

Nanosized barium titanate (BaTiO₃ (BTO)) powders with a pure perovskite phase and high c/a ratio were prepared using a two-step hydrothermal approach followed by removal of hydroxyl groups using organic solvents. No trace of carbonate was observed during the preparation process. The tetragonality of the BTO powder increased with an increase in the hydrothermal process duration on treating the powder at 240 °C with the two-step and one-step processes. The tetragonality increased with a decrease in the hydroxyl group content. The advantages of the two-step process can be ascribed to the two-step nucleation and growth process, and in the second step, BTO particles nucleate directly on the BTO crystallites, resulting in a higher crystallinity and tetragonality (c/a ratio). The new method has the potential to be scaled up for mass production of high-quality BTO nanopowder samples suitable for capacitor and sensor applications.     

Vanadium doping effects on microstructure and dielectric properties of barium titanate ceramics

V-doped barium titante ceramics were prepared by conventional solid state reaction method. XRD patterns show that V⁵⁺ ions have entered into the tetragonal perovskite structure of solid solution to substitute for Ti⁴⁺ ions on the B sites. Addition of vanadium accelerates grain growth of BTO ceramics and there is abnormal grain growth of barium titanate ceramics with higher vanadium concentration. Vanadium doping can increase the Curie temperature and decrease the dielectric loss of barium titanate ceramics. As vanadium concentration increases, the remnant polarization of V-doped BTO ceramics begins to increase and reaches the maximum and then decreases. The coercive electric field for V-doped barium titanate ceramics decreases with the increasing of vanadium concentration. As temperature rises, the remnant polarization and the coercive electric field of V-doped barium titanate ceramics decrease simultaneously.     

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 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.     

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.     

(BaTiO3)1-x + (Co0.5Ni0.5Nb0.06Fe1.94O4)x nanocomposites: Structure,morphology, magnetic and dielectric properties

Two phase-based nanocomposites consisting of dielectric barium titanate (BaTiO₃ or BTO) and magnetic spinel ferrite Co_0.5Ni_0.5Nb_0.06Fe_1.94O₄ (CNNFO) have been synthesized through solid state route. Series of (BaTiO₃)_1-x + (Co_0.5Ni_0.5Nb_0.06Fe_1.94O₄)_x nanocomposites with x content of 0.00, 0.25, 0.50, 0.75, and 1.00 were considered. The structure has been examined via X-rays diffraction (XRD) and indicated the occurrence of both perovskite BTO and spinel CNNFO phases in various nanocomposites. A phase transition from tetragonal BTO structure to cubic structure occurs with inclusion of CNNFO phase. The average crystallites size of BTO phase decreases, whereas that for the CNNFO phase increases with increasing x in various nanocomposites. The morphological observations revealed that the porosity is highly reduced, and the connectivity between grains is enhanced with increasing x content. The optical properties have been investigated by UV−vis diffuse reflectance spectroscopy. The deduced band gap energy (E_g) value is found to reduce with increasing the content of spinel ferrite phase. The magnetic as well as the dielectric properties were also investigated. The analysis showed that CNNFO ferrite phase greatly affects the magnetic properties and dielectric response of BTO material. The obtained findings can be useful to enhance the performances of magneto-dielectric composite-based systems.     

The effect of pH control on synthesis of Sr doped barium titanate nanopowder by oxalate precipitation method

Sr substituted BaTiO₃ (BST) nanopowders were prepared using oxalate co-precipitation methods. During synthesis, oxygen was applied to the oxalate solution in order to control the oxidation states of Ti. Control of pH in the solution results in different crystalline phases of the powders after calcination; pure perovskite BST was obtained in the powder prepared at pH 3 solution, while perovskite BaTiO₃ (BTO) and impurities were observed in powders prepared at pH 1 solution. Phase transformation from amorphous to crystalline BST during heat treatment was discussed by different analysis technique. Also, morphology and elemental distribution of the pure BST was investigated.     

The effect of barium titanate ceramic loading on the stress relaxation behavior of barium titanate-silicone elastomer composites

The stress relaxation behavior of barium titanate (BTO)-elastomer (Ecoflex) composites, as used in large strain sensors, is studied using the generalized Maxwell-Wiechert model. In this article, we examine the stress relaxation behavior of ceramic polymer composites by conducting stress relaxation tests on samples prepared with varying the particle loading by 0, 10, 20, 30, and 40 wt% of 100 and 200 nm BTO ceramic particles embedded in a Ecoflex silicone-based hyperelastic elastomer. The influence of BTO on the Maxwell-Wiechert model parameters was studied through the stress relaxation results. While a pristine Ecoflex silicone elastomer is predominantly a hyperelastic material, the addition of BTO made the composite behave as a visco-hyperelastic material. However, this behavior was shown to have a negligible effect on the electrical sensing performance of the large strain sensor.     

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.     

Synthesis of flexible BaTiO3 nanofibers for efficient vibration-driven piezocatalysis

The development of high-performance catalysts for applications in advanced oxidation processes to degrade organic pollutants can contribute significantly to environmental protection. However, current nanoparticle-based catalysts are energy consuming, hazardous, and unrecyclable, therefore the development of clean energy-driven and reusable catalysts with high performance remains challenging. Herein, flexible barium titanate (BTO) nanofibers were fabricated via a combination of electrospinning and sol-gel methods. The large surface area, interconnected porous structure, good piezoresponse, and relatively high piezoelectric coefficient endow the resultant BTO nanofibers membranes with good piezocatalytic degradation performance toward organic contaminants. With the assistance of ultrasonic waves, the membranes could degrade 96% of organic dyes within 60 min, with a reaction rate of 0.0537 min⁻¹. The radical detection and trapping experiments proved that superoxide radicals and holes played vital roles in piezocatalytic reaction process. Furthermore, the flexible BTO nanofibrous membranes with a tensile strength of 2.2 MPa exhibited good reusability over five cycles, without the tedious recycling operations needed for micro/nanoparticle-based catalysts. The successful fabrication of BTO nanofibrous membranes would provide a route for the fabrication of clean energy-driven and high-performance catalysts for wastewater treatment.