Effect of solvents on the morphology and structure of barium titanate synthesized by a one-step hydrothermal method

Tetragonal barium titanate was synthesized from barium hydroxide octahydrate and titanium tetrachloride through a simple one-step hydrothermal method.The effect of different solvents on the crystal structure and morphology of barium titanate nanoparticles during the hy-drothermal process was investigated.Except for ethylene glycol/water solvent,impurity-free barium titanate was synthesized in pure water,methanol/water,ethanol/water,and isopropyl alcohol/water mixed solvents.Compared with other alcohols,ethanol promotes the formation of a tetragonal structure.In addition,characterization studies confirm that particles synthesized in methanol/water,ethanol/water,and isopropyl al-cohol/water mixed solvents are smaller in size than those synthesized in pure water.In the case of alcohol-containing solvents,the particle size decreases in the order of isopropanol,ethanol,and methanol.Among all the media used in this study,ethanol/water is considered the optimum reaction media for barium titanate with high tetragonality(defined as the ratio of two lattice parameters c and a,c/a=1.0088)and small aver-age particle size(82 nm),which indicates its great application potential in multilayer ceramic capacitors.

New method for measuring high field electrostrictive response of barium titanate/polyurethane elastomer

A new method for measuring the characteristic of electrostriction by a digital speckle correlation method （DSCM） is presented. The in-plane displacement is obtained by using the DSCM, and the out-plane displacement is obtained by the geometrical relation of the triangle theory. In this application, high field electrostrictive strains of barium titanate/polyurethane elastomer composite materials are measured. The electrostrictive strain is evaluated when the application of an electric field is repeated, and then the electrostrictive coefficient of the sample is obtained. To improve the measuring accuracy, the bilinear interpolation of gray value is used to obtain the sub-pixel gray value. The results are compared with those obtained from the surface fitting algorithm. The experimental results demonstrate that the electrostrictive response of polyurethane increases with the introduction of barium titanate into polyurethane. And by using the DSCM, the measurement of the characteristic of electrostriction can be done quickly and accurately. The DSCM provides an effective tool for the evaluation of electrostrictive response.

Optimized growth and dielectric properties of barium titanate thin films on polycrystalline Ni foils

Barium titanate（BTO） thin films were deposited on polycrystalline Ni foils by using the polymer assisted deposition（PAD） technique.The growth conditions including ambient and annealing temperatures were carefully optimized based on thermal dynamic analysis to control the oxidation processing and interdiffusion.Crystal structures,surface morphologies,and dielectric performance were examined and compared for BTO thin films annealed under different temperatures.Correlations between the fabrication conditions,microstructures,and dielectric properties were discussed.BTO thin films fabricated under the optimized conditions show good crystalline structure and promising dielectric properties with εr～ 400 and tan δ 〈 0.025 at 100 kHz.The data demonstrate that BTO films grown on polycrystalline Ni substrates by PAD are promising in device applications.

Low Temperature One Step Synthesis of Barium Titanate: Particle Formation Mechanism and Large-scale Synthesis

The formation of BaTiO3 nanoparticles via the reaction of BaCl2, TiCl4 and NaOH in aqueous solution has been systematically studied. The formation of BaTiO3 from the ionic precursors has been elucidated to be a very rapid process, occurring at temperature higher than 60℃. Furthermore, the particle size could be controlled by the proper selection of the synthesis conditions (e.g. reactant concentration of 0.5—1.0mol·L-1, temperature of 80— 95℃ and pH≥13). A two-step precipitation mechanism was proposed. The first stage of the synthesis involved the formation of amorphous Ti-rich gel phase. The second stage of the synthesis was the reaction between the amor-phous phase and the solution-based Ba2+ ions, which led to the crystallization of BaTiO3. Based on the particle for-mation mechanism, a novel method, high gravity reactive precipitation, was proposed and used to mass production of BaTiO3 of average particle size of about 60 nm and with narrow particle size distribution. Because it could break up the amorphous Ti-rich gel into small pieces, intensify mass transfer, promote the reaction rate of amorphous Ti-rich gel with Ba2+ ions.

Effects of Dysprosium Oxide Doping on Microstructure and Properties of Barium Titanate Ceramic

Different amounts of dysprosium oxide were incorporated into barium titanate powders synthesized by hydrothermal method. Relations of substitution behaviors and lattice parameters with solid-solubility were studied. Furthermore, the influences of dysprosium oxide doping fraction on grain size and dielectric properties of barium titanate ceramic, including dielectric constant and breakdown electric field strength , were investigated via scanning electron microscope, X-ray diffraction and electric property tester. The results show that dysprosium oxide can restrain abnormal grain growth during sintering and that fine-grained and high density of barium titanate ceramic can result in excellent dielectric properties. As mass fraction of dysprosium oxide is 0.6%, the lattice parameters of grain increase to the maximum because of the lowest vacancy concentration. The electric property parameters are cited as following： dielectric constant （25 ℃ ） reaches 4100, the change in relative dielectric constant with temperature is - 10% to 10% within the range of - 15 - 100 ℃, breakdown electric field strength （alternating current） achieves 3.2 kV·mm^-1, which can be used in manufacturing high voltage ceramic capacitors

Low Temperature One-Step Synthesis of Barium Titanate:Thermodynamic Modeling and Experimental Synthesis

A thermodynamic model has been developed to determine the reaction conditions favoring low temperature direct synthesis of barium titanate (BaTiO3). The method utilizes standard-state thermodynamic data for solid and aqueous species and a 0ebye-Huckel coefficients model to represent solution nonideality. The method has been used to generate phase stability diagrams that indicate the ranges of pH and reagent concentrations, for which various species predominate in the system at a given temperature. Also, yield diagrams have been constructed that indicate the concentration, pH and temperature conditions for which different yields of crystalline BaTiO3 can be obtained. The stability and yield diagrams have been used to predict the optimum synthesis conditions (e.g., reagent concentrations, pH and temperature). Subsequently, these predictions have been experimentally verified. As a result, phase-pure perovskite BaTiO3 has been obtained at temperature ranging from 55 to 85℃ using BaCl2, TiCl4 as a source for Ba and Ti, and NaOH as a precipitator.

Modulating the Selectivity of Photocatalytic CO_(2)Reduction in Barium Titanate by Introducing Oxygen Vacancies

Artifi cial photosynthetic reduction of CO_(2) into valuable chemicals is one of the most promising approaches to solve the energy crisis and decreasing atmospheric CO_(2) emissions.However,the poor selectivity accompanied by the low activity of photocatalysts limits the development of photocatalytic CO_(2) reduction.Herein,inspired by the use of oxygen vacancy engi-neering to promote the adsorption and activation of CO_(2) molecules,we introduced oxygen vacancies in the representative barium titanate(BaTiO 3)photocatalyst for photocatalytic CO_(2) reduction.We found that oxygen vacancies brought signifi cant diff erences in the CO_(2) photoreduction activity and selectivity of BaTiO 3.The intrinsic BaTiO 3 showed a low photocatalytic activity with the dominant product of CO,whereas BaTiO 3 with oxygen vacancies exhibited a tenfold improvement in photocatalytic activity,with a high selectivity of~90%to CH 4.We propose that the presence of oxygen vacancies promotes CO_(2) and H 2 O adsorption onto the BaTiO 3 surface and also improves the separation and transfer of photogenerated carriers,thereby boosting the photocatalytic CO_(2) reduction to CH 4.This work highlights the essential role of oxygen vacancies in tuning the selectivity of photocatalytic reduction of CO_(2) into valuable chemicals.

Electro-rheological Effect of Barium Titanate Particles Coated with Urea and Suspended in Methyl Silicone Oil

Barium titanate nano-powders were synthesized under defined conditions. The surface of these particles was successfully modified by coating with urea. The characteristics of these composite particles were studied by X-ray diffraction,transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy. The electro-rheological (ER) effects of these particles suspended in methyl-silicone oil were measured. The particle,methyl-silicon oil ratio was 30%-35% weight percent. The experimental results indicate that these ER particles exhibit a remarkable ER effect. The ER fluid shows Bingham characteristics and the static shearing stress increases with an increase of the electric field strength. The highest static shearing stress under a 4 MV/m electric field is 13.2 kPa at room temperature,an increase of about 8.7 kPa compared to untreated BaTiO(C2O4)2 powders.

HYBRID AND CHARACTERISTIC OF POLYANILINEBARIUM TITANATE NANOCOMPOSITE PARTICLES

Polyaniline-barium titanate (PAn-Ba-TiO3) ultrafine composite particles were prepared by the oxidative polymerization of aniline with H2O2 while barium titanate nanoparticles were synthesized with a sol-gel method. The infrared spectrogram shows that the polymerization of PAn in the hybrid process of PAn-BaTiO3 is similar with the polymeric process of pure aniline, and there is interaction of PAn and BaTiO3 in the PAn-Ba-TiO3. SEM and TEM results show that the average diameter of the composite particles is 1.50μm and the diameters of BaTiO3 nanoparticles are 5 - 15 nm in the composite particle. The electrical conductivity of the ultrafine com-posite particles is transformable from 10°to 10-11S/cm by equilibrium doping or dedoping method using various concentration of HCl or NaOH solutions.

Preparation and characterization of nanometer-sized barium titanate powder by complex-precursor method

A new complex-precursor method was proposed to prepare nanometer-sized BaTiO3 powder. Firstly,Ti2O(O2)2(ta)24-complex ions were prepared by the reaction of H2O2,Ti4+ and ta3-(ta=C6H6O6N3-) with a desirable amount of surface active agent,and then the Ba2Ti2O(O2)2(ta)2·2H2O precursor was obtained by reaction between Ti2O(O2)2(ta)24-and Ba2+. Finally,the precursor was annealed at 800 ℃ for 2 h to obtain BaTiO3 powder. The morphology,the particle size distribution,the purity and the molar ratio of Ba to Ti of BaTiO3 powder were investigated systematically by TEM,XRD,IR,Raman and chemical analysis,respectively. The results show that the BaTiO3 powders with the grain size of about 40 nm have a tetragonal crystalline structure at room temperature and a spherical morphology.

Characterization and growth dynamics of barium titanate crystallite on nanometer scale

Barium titanate powder on nanometer scale was synthesized by means of co-precipitation. The thermal mass loss, crystal grain growth and phase transition of the barium titanate nanometer powder were investigated by TG (Thermogravimetric)-DTA (Differential scanning calorimetric) and XRD (X-ray powder diffractometer) at different heat treatment temperatures. The results show that amorphous barium titanate powder can transfer into tetragonal symmetry structure after heat treatment. When the heat treatment temperature is below 900℃, the grains grow rapidly because the activation energy at low temperature is greatly less than that at high temperature. By controlling the heat treatment temperature, the optimization of the barium titanate crystallite size and formation of tetragonal phase can be realized.

Enhancing energy storage density of poly(arylene ether nitrile)via incorporating modified barium titanate nanorods and hotstretching

Dielectric energy storage materials that are extensively employed in capacitors and other electronic devices have attracted increasing attentions amid the rapid progress of electronic technology.However,the commercialized polymeric and ceramic dielectric materials characterized by low energy storage density face numerous limitations in practical applications.In this study,we report the simultaneous enhancement of dielectric properties of poly(arylene ether nitrile)(PEN)through the incorporating of sulfonated PEN(SPEN)modified barium titanate nanorods(BTNR)(SPEN@BTNR)and hot-stretching.BTNR is synthesized using a two-step hydrothermal method,aminated with KH550,and then reacted with SPEN to form the cladding-modified SPEN@BTNR.Due to the intrinsic high permittivity of barium titanate(BT)and enhanced compatibility between SPEN@BTNR and PEN stemming from the cladding of SPEN,the dielectric constant and breakdown strength of SPEN@BTNR/PEN composite are as high as 14.0 at 103 Hz and 198.1 kV/mm at the doping amount of 15 wt.%,respectively.As a result,the energy storage density of SPEN@BTNR/PEN is increased to 2.43 J/cm^(3),compared with that of 0.82 J/cm^(3)for PEN.In addition,derived from the rearrangement of SPEN@BTNR and orientation of PEN after hot-stretching,the dielectric constant and breakdown strength of SPEN@BTNR/PEN with 15 wt.%fillers are further enhanced to 17.1 and 204.8 kV/mm,respectively,resulting in an energy storage density of 3.36 J/cm^(3).The boosting of energy storage density up to 310%provides a new idea for improving the performances of dielectric energy storage materials.

Temperature/electric field induced photoluminescence-modulation effect in dysprosium-doped barium titanate ferroelectric ceramics

Lanthanide(Ln^(3+))based ferroelectric phosphors,with an integration of PL emission and ferroelectric effect,are unveiling an exciting realm of possibilities for multifunctional ferroelectric-optic materials.However,how the ferroelectric host enables the tuning on the PL emissions through modulating the local structure(e.g.,lattice site,symmetry,strains etc.)of the Ln^(3+)activator is not established yet.In this work,a luminescent-ferroelectric material,i.e.Dy^(3+)doped BaTiO_(3) ceramic(Ba_(1–x)Dy_(x)TiO_(3)(x=0–0.07),abbr:BTO:Dy^(3+)),was explored to address the aforementioned issues.The BTO:Dy^(3+)ceramics were synthesized by a solid-state reaction method.The crystal structure,photoluminescence(PL)and electric properties(dielectric constant,ferroelectric hysteresis and piezoelectric hysteresis loop)were systematically investigated.The BTO:Dy^(3+)ceramics show two predominant emission peaks,corresponding to the blue magnetic dipole transition(477 nm,4F_(7/2)→6H_(15/2))and yellow electric dipole transition(573 nm,4F_(7/2)→6H_(13/2)),the intensity ration of which can be modulated by the ferroelectric polarization that causes the slight lattice deformation.Such a polarization-emission modulation combining with the Dy3+doping could accelerate the color change,from yellow to blue,which is characterized to detect the phase transition,with a method and mechanism were proposed,that is,the phase change is reflected by the PL characteristic peak intensity ratio.Therefore,the current results offer a convenient photoluminescence method for detecting the ferroelectric phase transition and a feasible approach to study the interaction between the photoluminescence and polarization in ferroelectric materials,for providing new insights for the development of multifunctional materials.

Frequency-dependent ferroelectric and electrocaloric properties in barium titanate-based ceramics based on Maxwell relations

In this work,the frequency dependence of ferroelectric and electrocaloric properties in barium titanate-based ceramics was studied based on Maxwell relations.It is found that the maximum and remnant polarization will decrease while the coercive field increases a lot with rising frequency from 0.1 to 10 Hz,indicating that polarization rotation and domain switching become difficult at high frequencies.The electrocaloric properties show the different frequency dependence at different phase structures.Isothermal entropy change(ΔS)and adiabatic temperature change(ΔT)are similar around/above Curie temperature(TCT,showing tiny frequency dependence.However,ΔS andΔT display the obvious frequency dependence below T_(C),especially in the orthorhombic–tetragonal phase-transition region with a stable ferroelectric phase,and this frequency dependence becomes more obvious under a low-electric field.It is also found that increasing the frequency can weaken the electric field dependence of electrocaloric strength.This work gives a general profile of frequency dependence for electrocaloric properties in ferroelectric ceramics.

Ultrasmall barium titanate nanoparticles modulated stretchable dielectric elastomer sensors with large deformability and high sensitivity

Large deformability and high sensitivity is difficult to be realized simultaneously in flexible sensors.Herein,taking advantage of the high permittivity and highly active surfaces of the ultrasmall barium titanate nanoparticles(BT NPs)and the high stretchability of the p(BA-GMA)elastomer matrix,we propose a high-performance soft stretchable sensor.The addition of the ultrasmall BT NPs can not only increase the permittivity and capacitance of polyacrylate-matrix composite dielectric material to obtain a high sensitivity,but also basically maintains the excellent mechanical properties of the polymer matrix.The dielectric constants of the composite films increase from 5.68 to 13.13 at 10 kHz with the increase of BT NPs content from 0 to 15 vol.%,which results in a high capacitance of 236.16 pF for 15 vol.%BT/p(BA-GMA)sensor.Combining the high permittivity and the large deformability(a maximal deformation of 87.2%),the 15 vol.%BT/p(BA-GMA)sensor has high sensitivity and shows high linearity and stable output even if under dynamic measurement.The dual-mode sensor that utilizes the orthogonality of capacitance-resistance is designed,which shows excellent performance in monitoring human body movements and noncontact measurement.The results present that the BT/p(BA-GMA)-based sensor has high stability and reliability not exceed 65C,which can meet the application requirements in dynamic monitoring.

Dielectric properties and phase transitions of La_2O_3- and Sb_2O_3-doped barium strontium titanate ceramics

The dielectric properties and phase transition characteristics of La2O3- and Sb2O3-doped barium strontium titanate ceramics prepared by solid state route were investigated. The microstructure was identified by X-ray diffraction method and scanning electron microscope was also employed to observe the surface morphologies. It is found that （La,Sb）-codoped barium strontium titanate ceramics exhibit typical perovskite structure and the average grain size decreases dramatically with increasing the content of Sb2O3. Both La3＋ ions and Sb3＋ ions occupy the A-sites in perovskite lattice. The dielectric constant and dielectric loss of barium strontium titanate based ceramics are obviously influenced by La2O3 as well as Sb2O3 addition content. The tetragonal-cubic phase transition of La2O3 modified barium strontium titanate ceramics is of second order and the Curie temperature shifts to lower value with increasing the La2O3 doping content. The phase transition of （La,Sb）-codoped barium strontium titanate ceramics diffuses and the deviation from Curie-Weiss law becomes more obvious with the increase in Sb2O3 concentration. The temperature corresponding to the dielectric constant maximum of （La,Sb）-codoped barium strontium titanate ceramics decreases with increasing the Sb2O3 content, which is attributed to the replacement of host ions by the Sb3＋ ions.

Electroactive barium titanate coated titanium scaffold improves osteogenesis and osseointegration with low-intensity pulsed ultrasound for large segmental bone defects

For large segmental bone defects,porous titanium scaffolds have some advantages,however,they lack electrical activity which hinders their further use.In this study,a barium titanate(BaTiO3)piezoelectric ceramic was used to modify the surface of a porous Ti6Al4V scaffold(pTi),which was characterized by scanning electron microscopy,energy dispersive spectroscopy,X-ray photoelectron spectroscopy,and roughness and water contact angle analyses.Low intensity pulsed ultrasound(LIPUS)was applied in vitro and in vivo study.The activity of bone marrow mesenchymal stem cells,including adhesion,proliferation,and gene expression,was significantly superior in the BaTiO3/pTi,pTi+LIPUS,and BaTiO3/pTi+LIPUS groups than in the pTi group.The activity was also higher in the BaTiO3/pTi+LIPUS group than in the BaTiO3/pTi and pTi+LIPUS groups.Additionally,micro-computed tomography,the mineral apposition rate,histomorphology,and the peak pull-out load showed that these scaffold conditions significantly enhanced osteogenesis and osseointegration 6 and 12 weeks after implantation in large segmental bone defects in the radius of rabbits compared with those resulting from the pTi condition.Consequently,the improved osteogenesis and osseointegration make the BaTiO3/pTi+LIPUS a promising method to promote bone regeneration in large segmental bone defects for clinical application.

Preparation of Oriented Barium Titanate Thin Films by Combination of Electrophoretic Deposition with Hydrothermal Treatment

Highly oriented barium titanate （BaTiO 3） thin films on Pt substrate were fabricated by combination of electrophoretic deposition with hydrothermal treatment.The structure and morphology of thin films were characterized by X-ray diffraction and field-emission scanning electron microscopy.It is found that the titania precursor film,Ba（OH）2 concentration and hydrothermal temperature play crucial roles in the film morphology and orientation.The BaTiO3 thin films with highly （110） preferred orientation can be formed on polycrystalline Pt substrate by appropriate adjustment of the reaction conditions.The orientation parameter f of highly oriented BaTiO3 films was up to 1.00.The films exhibited a smooth and crack-free surface and remained in the layered structure.In situ topotactic transformation and dissolution-crystallization mechanisms were proposed to explain the morphology and orientation of BaTiO3 films during hydrothermal treatment.

Enhanced energy storage properties of barium titanate ceramics made from surface modified particles

Surface modification of barium titanate particles has been carried out using a wet chemical method.The microstructural and dielectric properties of the ceramics made from surface modified particles were extensively investigated by X-ray diffraction,scanning electron microscopy,transmission electron microscopy,and dielectric properties measurements.The breakdown strength increased by 69%and 117%for the Al_(2)O_(3) and B_(2)O_(3)–SiO_(2) modified ceramics,respectively.An energy storage density of up to 3.2 J/cm^(3) has been obtained.The suppression of grain boundary electron transport and reduction in pore defects lead to the energy storage properties enhancement of the modified ceramics.These results indicated that surface modification of ceramic particles is a promising approach to obtain dielectric ceramics with high energy storage density.

Preparation of optical active single-handed helical barium titanate nanotubes and characterization of dielectric properties

Left and right-handed helical barium titanate nanotubes are prepared with the impregnation of Ba（OH）2 into single-handed helical titania nanotubes.Wide angle X-ray diffraction pattern and transmission electron microscopy image indicate that they are constructed by nanoparticles with a partially crystalline structure.The diffuse reflertance circular dichroism spectra indicate that they exhibit optical activity which was proposed to originate from chiral defects on the inner surfaces of the nanotubes.Both the dielectric constant and tanδ decrease with increasing the frequency.At 10 and 100 Hz,one dielectric constant peak at 9.6℃ and one tanδ peak at 5.0℃ are observed at -120℃ to 180℃.