Barium Titanate Precursor Research Articles

Synthesis and Functional Characterization of CoxFe3−xO4-BaTiO3 Magnetoelectric Nanocomposites for Biomedical Applications

Nowadays, magnetoelectric nanomaterials are on their way to finding wide applications in biomedicine for various cancer and neurological disease treatment, which is mainly restricted by their relatively high toxicity and complex synthesis. This study for the first time reports novel magnetoelectric nanocomposites of CoxFe3-xO4-BaTiO3 series with tuned magnetic phase structures, which were synthesized via a two-step chemical approach in polyol media. The magnetic CoxFe3-xO4 phases with x = 0.0, 0.5, and 1.0 were obtained by thermal decomposition in triethylene glycol media. The magnetoelectric nanocomposites were synthesized by the decomposition of barium titanate precursors in the presence of a magnetic phase under solvothermal conditions and subsequent annealing at 700 °C. X-ray diffraction revealed the presence of both spinel and perovskite phases after annealing with average crystallite sizes in the range of 9.0-14.5 nm. Transmission electron microscopy data showed two-phase composite nanostructures consisting of ferrites and barium titanate. The presence of interfacial connections between magnetic and ferroelectric phases was confirmed by high-resolution transmission electron microscopy. Magnetization data showed expected ferrimagnetic behavior and σs decrease after the nanocomposite formation. Magnetoelectric coefficient measurements after the annealing showed non-linear change with a maximum of 89 mV/cm*Oe with x = 0.5, 74 mV/cm*Oe with x = 0, and a minimum of 50 mV/cm*Oe with x = 0.0 core composition, that corresponds with the coercive force of the nanocomposites: 240 Oe, 89 Oe and 36 Oe, respectively. The obtained nanocomposites show low toxicity in the whole studied concentration range of 25-400 μg/mL on CT-26 cancer cells. The synthesized nanocomposites show low cytotoxicity and high magnetoelectric effects, therefore they can find wide applications in biomedicine.

Barium titanate coated and thermally reduced graphene oxide towards high dielectric constant and low loss of polymeric composites

Novel barium titanate (BT) layer coated and thermally reduced graphene oxide (TGO) hybrid sheets (BT@TGO) were successfully synthesized by a facile sol-gel method combining with thermal treatment process (600 °C) under nitrogen atmosphere. The BT precursors attached on graphene oxide (GO) sheets were crystallized into perovskite structure with high permittivity and GO sheets were thermally reduced heavily at such high temperature simultaneously. The hybrids were used as filler to fabricate high performance dielectric polyvinylidene fluoride (PVDF) composites by solution blending method and their dielectric performances were studied. It was found that addition of BT@TGO decreases the electrical conductivity when compared with TGO/PVDF composites and pure PVDF, and BT@TGO/PVDF composites exhibit not only high dielectric constant but also low dielectric loss. For instance, at 103 Hz, the dielectric constant of PVDF composites containing 8.0 wt% BT@TGO is up to ∼56.3 at room temperature, which is over 5 times than that of pure PVDF polymer (∼10.3). More importantly, the dielectric loss is suppressed and only 0.058, which should be attributed to the effective encapsulation of insulating BT layer with high permittivity on the TGO surface. In addition, the improved thermal stability and crystallization behavior of BT@TGO/PVDF composites were also investigated.

Synthesis and Characterization of Low Loss Dielectric Ceramics Prepared from Composite of Titanate Nanosheets with Barium Ions

We report a strategy for preparing barium titanate precursor, being the composite of titanate nanosheets (TN) with barium ions (Ba-TN), which subjected to step sintering allows obtaining TiO2 rich barium titanate ceramics of stoichiometry BaTi4O9 or Ba2Ti9O20. These compounds are important in modern electronics due to their required dielectric properties and grains’ size that can be preserved in nanometric range. The morphology studies, structural characterization, and dielectric investigations were performed simultaneously in each step of Ba-TN calcinations in order to properly characterize type of obtained ceramic, its grains’ morphology, and dielectric properties. The Ba-TN precursor can be sintered at given temperatures, so that its dielectric permittivity can be tuned between 25 and 42 with controlled temperature coefficients that change from negative 32 ppm/°C for Ba-TN sintered at 900°C up to positive 37 ppm/°C after calcination at 1300°C. XRD analysis and Raman investigations performed for the Ba-TN in the temperature range of 900÷1250°C showed that below 1100°C we obtained as a main phase BaTi4O9, whereas the higher calcinations temperature transformed Ba-TN into Ba2Ti9O20. Taking into account trend of device miniaturization and nanoscopic size requirements, temperatures of 900°C and 1100°C seem to be an optimal condition for Ba-TN precursor calcinations that guarantee the satisfactory value of dielectric permittivity (ε=26 and 32) and ceramic grains with a mean size of ~180 nm and ~550 nm, respectively.

Hydrothermal synthesis and formation mechanism of tetragonal barium titanate in a highly concentrated alkaline solution

Tetragonal cube-shaped barium titanate (BaTiO3) was produced by the hydrothermal treatment of a peroxo-hydroxide precursor, a single-source amorphous barium titanate precursor, in a highly concentrated sodium hydroxide solution. Phase pure barium titanate with cube-shaped morphology and particle-sizes in the 0.2–0.5µm range were formed at temperatures above 80°C. Also, the cube-shaped morphology of the BaTiO3 product was preceded by spherical- and plate-like morphologies with, respectively, a Ti-excess and Ba-excess. Coinciding with these morphological observations, changes in the reaction product were also observed. The formation of crystalline BaTiO3 proceeded alongside secondary BaTi2O5 and Ba2TiO4 phases. These secondary phases disappeared as the reaction time was increased leaving only BaTiO3 as the sole reaction product. Kinetic analysis of the formation of hydrothermal BaTiO3 crystallization by the Johnson-Mehl-Avrami method showed that BaTiO3 crystallization is a homogeneous dissolution-precipitation reaction. The mechanism is governed by nucleation and growth in the beginning of the reaction and dissolution-precipitation dominating throughout the hydrothermal reaction process.

Hydrothermal Synthesis and Processing of Barium Titanate Nanoparticles Embedded in Polymer Films.

Barium titanate nanoparticles embedded in flexible polymer films were synthesized using hydrothermal processing methods. The resulting films were characterized with respect to material composition, size distribution of nanoparticles, and spatial location of particles within the polymer film. Synthesis conditions were varied based on the mechanical properties of the polymer films, ratio of polymer to barium titanate precursors, and length of aging time between initial formulations of the solution to final processing of nanoparticles. Block copolymers of poly(styrene-co-maleic anhydride) (SMAh) were used to spatially separate titanium precursors based on specific chemical interactions with the maleic anhydride moiety. However, the glassy nature of this copolymer restricted mobility of the titanium precursors during hydrothermal processing. The addition of rubbery butadiene moieties, through mixing of the SMAh with poly(styrene-butadiene-styrene) (SBS) copolymer, increased the nanoparticle dispersion as a result of greater diffusivity of the titanium precursor via higher mobility of the polymer matrix. Additionally, an aminosilane was used as a means to retard cross-linking in polymer-metalorganic solutions, as the titanium precursor molecules were shown to react and form networks prior to hydrothermal processing. By adding small amounts of competing aminosilane, excessive cross-linking was prevented without significantly impacting the quality and composition of the final barium titanate nanoparticles. X-ray diffraction and X-ray photoelectron spectroscopy were used to verify nanoparticle compositions. Particle sizes within the polymer films were measured to be 108 ± 5 nm, 100 ± 6 nm, and 60 ± 5 nm under different synthetic conditions using electron microscopy. Flexibility of the films was assessed through measurement of the glass transition temperature using dynamic mechanical analysis. Dielectric permittivity was measured using an impedance analyzer.

Hydrothermal synthesis of carbonate-free submicron-sized barium titanate from an amorphous precursor: Synthesis and characterization

In this paper, the amorphous barium titanate precursor was prepared by the peroxo-hydroxide method and post-treated by various drying procedures, such as: room temperature drying, room temperature vacuum drying and vacuum drying at 50 °C. The objective in the latter two treatments was to increase the Ti–O–Ba bonds of the precursor. The post-treated precursors were compared with the untreated (i.e., ‘wet’) precursor. Also, a barium titanate precursor was prepared by an alkoxide route. Afterwards, the precursors were hydrothermally treated at 200 °C in a 10 M NaOH solution. Vacuum drying of the precursor seemingly promoted the formation of Ti–O–Ti bonds in the hydrothermal end-product. The low Ba:Ti ratio (0.66) of the alkoxide-route prepared precursor lead to a multi-phase hydrothermal product with BaTiO 3 as the main phase. In contrast, phase pure BaTiO 3, i.e. without BaCO 3 contamination, was obtained for the precursor which was dried at room temperature. Cube-shaped and highly crystalline BaTiO 3 particles were observed by electron microscopy for the hydrothermally treated peroxo-hydroxide-route prepared precursor.

ChemInform Abstract: Sol-Gel Process for the Preparation of Ba2Ti9O20 and BaTi5O11.

Barium titanate precursors with Ba/Ti ratio 2:9 and 1:5 were prepared by first hydrolyzing titanium alkoxide and then mixing the resulting titania sol with a barium alkoxide-methanol solution. After drying, the xerogels of the precursors of barium titanates were sintered at temperatures from 700°C (4 h) to 1200°C (110 h or longer). Characterization of the product was performed using X-ray diffraction and laser Raman spectroscopy. At 700°C, BaTi5O11 was formed from the 1:5 precursor and a two-phase mixture of BaTi2O5 and BaTi5O11 was formed from the 2:9 precursor. After prolonged heating at 1200°C, the latter mixture converted to a single-phase material, Ba2Ti9O20.

Morphology control of anisotropic BaTiO 3 and BaTiOF 4 using organic–inorganic interaction

We proposed a novel concept for morphology control of barium titanate precursor to fabricate platy particles. Organic molecules play an essential role in the crystallization of BaTiOF 4 to synthesize multi-needle particles, polyhedron particles or platy particles in an aqueous solution. Precursors were successfully transformed to barium titanate single phase by annealing. Platy barium titanate precursor particles are expected for future multilayer ceramic capacitors.

Barium titanate sols prepared by a diol-based sol–gel route

A diol-based sol–gel route for preparing barium titanate precursor sols has been developed. The sols were prepared using 1,3 propanediol, barium acetate, and titanium isopropoxide, modified by acetylacetonate. The decomposition behavior of samples of gel, dried at 120°C, was studied by GC–MS, TGA and DSC; phase formation was investigated by XRD and FTIR techniques. From the XRD results for calcined gel powders, crystalline barium titanate began to form at ∼600°C. FTIR spectra showed two absorption bands at 538cm−1 and 400cm−1 in samples calcined at 600°C; these peaks are assigned to barium titanate, in accord with the XRD results. There was also FTIR evidence of a carbonate phase, which persisted until a calcination temperature of ∼1000°C. The sols have been kept in a closed container for ∼6 months without any evidence of precipitation or gel formation.

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 τf= 11 ± 0.7 ppm/°C—were found.

Nanoscale Patterning of BaTiO3 on Block Copolymers

Nanoscale pattering of inorganics can be facilitated by using complex fluids as templates. One such approach is to use block copolymeric nanodomains in solid films (< 50 nm) as the template for patterning ceramic clusters with desired shapes and orientations. For instance, we use a triblock copolymer of polystyrene (PS) -polybutadiene (PB) - polystyrene (PS) - Kraton Dl 102® (MW = 71,000 and PS/PB = 28%/78%) as a template material to pattern barium titanate for energy storage applications. The important features of our approach are that (i) the interdomains of PBs in the preformed solid thin films are chemically OH-functionalized in situ, and (ii) the barium titanate precursors are solely localized within and reacted to the interdomains of PBs in solid thin films by condensation.Thin films were prepared by spin casting a 1% w/w Kraton D1102®/toluene solution on a coverglass. Thin films were transferred to gold TEM specimen grids by the water lift off method.

Nanoscale Patterning of Barium Titanate on Block Copolymers

A triblock copolymer of polystyrene−polybutadiene−polystyrene (Kraton D1102) has been used to pattern barium titanate precursor with nanoscale modulations. The copolymer self-assembles to yield cylindrical polystyrene nanodomains in a polybutadiene matrix. The preorganized thin films of polymer are then selectively OH-functionalized in situ on the unsaturated carbon bonds in the polybutadiene matrix with antistereochemistry. Anchoring the barium titanate precursor onto the hydroxylated polymer thin films is possible only in the trans-1,2 polybutadiol matrix through the condensation between the barium titanium double alkoxides and the hydroxyl groups. The regioselective deposition of the barium titanium double alkoxides on the original polybutadiene matrix of the Kraton thin films was verified by transmission electron microscopy and electron energy loss spectroscopy. The spacing of the coordinated barium titanium double alkoxide pattern was ∼23 nm, equivalent to the interdomain spacing of the original poly...

Thermal decomposition of barium titanate precursor prepared by a wet chemical method

As a part of fundamental study on the kinetics of electroceramics processing by wet chemical methods, barium titanate precursor gel was prepared using barium acetate and titanium tetra-isopropapoxide as starting materials. Experimental results indicated that barium acetate was distributed uniformly in the gel matrix formed by hydrolysis and polymerization of titanium tetra-isopropoxide. In the subsequent calcination of the gel, rapid formation of barium titanate was observed above 823 K, which resulted from the reaction between titania and barium carbonate or barium oxide(s). The dynamics of barium titanate formation under different heat-up programs was successfully simulated based on a proposed reaction model that incorporates a specified reactive portion of barium acetate in the gel matrix.

Preparation of monolithic barium titanate xerogels by sol–gel processing and the dielectric properties of their sintered bodies

Monolithic xerogels of crystalline barium titanate, with dimensions of ∼3 mm thick and ∼6 mm in diameter, have been produced by sol–gel processing using metal alkoxides. An excess amount of water with the H2O/Ba ratio≳100 (for hydrolysis of the barium titanate precursor alkoxides) and aging time≳8 days were necessary to produce the monolithic crystalline xerogels without breaking during drying (at 90 °C). The barium titanate xerogels as-dried, with a porosity of about 70%, have been found to consist of crystalline grains in the range of 10–20 nm. Firing the xerogels at 1000 °C in air yielded porous barium titanate ceramics with an average grain size around 50 nm and a decreased porosity around 60%. The dielectric constant (εr)–temperature (T) characteristics of these ceramics have been found to be rather flat below 120 °C with a broad peak around this temperature, and those above 120 °C showed a specific behavior of ferroelectric materials described by a Curie–Weiss equation, εr=C/(T–T0), with C≊2×104 K and T0≊230 K (−43 °C); although these values are quite different from those of ferroelectric barium titanate.

Effects of metal salts on the thermal decomposition of edta-gel precursors for ferroelectric ceramic powders

Raw chemicals such as metal nitrates and chlorides were found to affect the thermal decomposition behaviour of EDTA-gel precursors used for the production of ceramic powders. Fine, homogeneous ceramic powders were produced from nitrate solutions while chlorides gave segregated phases. In studies on the production of lead zirconate titanate (PZT) using chlorides, the segregation and loss of lead was observed and shown to be caused by the formation and evaporation of PbCl2. Thermal analysis (DTA/TG) quantitatively proved the suggested reaction mechanism for this phase segregation. Crystallization of the desired perovskite phase of lead zirconate titanate (PZT) and barium titanate (BT) initiated at temperatures as low as 250°C in the nitrate-EDTA precursors. Water of crystallization and formation of BaCO3 in the barium titanate precursor were suggested to account for differences in the observed decompositional behaviours of the BT and PZT precursors.

Some Observation on the Aggregate Particles Produced during Pyrolysis of PTC Barium Titanate Precursor Synthesized by the Oxalate Method

In pyrolysis of PTC barium titanate precursor synthesized by the oxalate method, growth and morphological change of the particles formed were studied. Throughout the process, an aggregate particle was observed to be generally composed of a large number of crystallite particles. In the calcination process up to 1000°C, formation of various kinds of phases (dehydrated oxalate, amorphous phase and titanate) and grain growth of the titanate were observed in sequence, but the unique morphology and the size (100-200μm) of the aggregate particles, including the precursor particles, remained unchanged.

チタン酸バリウム前駆体ゲルの熱分解

Barium titanate precursor gel was successfully obtained by a sol-gel process with the use of barium acetate and titanium isopropoxide as starting materials. The calcination process of the barium titanate gel was characterized by FTIRPAS, TG-DTA, XRD and acid extraction method. These analyses indicate that barium acetate was distributed uuiformly in the gel matrix formed by hydrolysis and polymerization of titanium isopropoxide. The barium titanate was formed rapidly at higher temperatures than 823-873K resulted from the reaction between titanium oxide and barium carbonate or barium oxide.

Sol‐Gel Process for the Preparation of Ba2Ti9O20 and BaTi5O11

Barium titanate precursors with Ba/Ti ratio 2:9 and 1:5 were prepared by first hydrolyzing titanium alkoxide and then mixing the resulting titania sol with a barium alkoxide‐methanol solution. After drying, the xerogels of the precursors of barium titanates were sintered at temperatures from 700°C (4 h) to 1200°C (110 h or longer). Characterization of the product was performed using X‐ray diffraction and laser Raman spectroscopy. At 700°C, BaTi5O11 was formed from the 1:5 precursor and a two‐phase mixture of BaTi2O5 and BaTi5O11 was formed from the 2:9 precursor. After prolonged heating at 1200°C, the latter mixture converted to a single‐phase material, Ba2Ti9O20.

Preparation of Barium Titanate Precursor Sol from Metal Alkoxides

A BaTiO3 precursor sol was prepared by controlled hydrolysis of Ba-Ti mixed alkoxide solution in methoxyethanol. SrTiO3, BaZrO3 and SrZrO3 precursor sols were also synthesized by the similar method. The hydrolysis condition of Ba-Ti system was as follows; a water-methoxyethanol mixed solution with less than 50vol% of water was added to 3.6×10-4mol/ml of alkoxide solution at room temperature. On adding over 50vol% of water, partial gelation occurred, and heterogeneous sol or gel was formed. For Sr-Ti system, the hydrolysis condition was the same as that for Ba-Ti system. For Ba-Zr and Sr-Zr system, the concentration of water which produces partial gelation was over 66vol%. The formed precursor sols transformed to one phase BaTiO3, SrTiO3, BaZrO3 or SrZrO3 by calcination. Furthermore, the result of EDX analysis for SrTiO3 showed that the obtained powder had homogeneous composition and its homogeneity was kept up to 1000°C. Similar results may be expected for other systems.

Alkoxide Precursor Synthesis and Characterization of Phases in the Barium‐Titanium Oxide System

Barium titanate precursors with Ba/Ti ratios ranging from 2:1 to 1:9 were prepared by controlled hydrolysis of mixed barium and titanium species in an alcohol medium. Details of the synthesis and characterization of the resultant products are given. Amorphous powders precipitated by hydrolysis from ethanol solutions of barium and titanium alkoxides crystallize to single‐or two‐phase 1:2 and 1:5 compounds at ∼700°C. These compounds transform at higher temperatures to other known crystalline phases, the 1:5 phase being maintained metastably to ∼1100°C.