Spherical BaTiO3 Research Articles

Effect of nanoparticles on piezoelectric response in polymer composites by quantitative evaluation

The effect of the intrinsic properties of silicone rubber and barium titanate (BaTiO3) nanoparticles on the piezoelectric properties of BaTiO3/silicon rubber composites was studied by the finite element analysis. The data of the simulation show that the stress and voltage of the composite were greatly increased when the concentration of the BaTiO3 nanoparticle increased from 5 to 30 vol. %. As Young’s modulus of silicone rubber increased from 5 to 20 MPa, the compressive stress of the composites raised linearly. With the Poisson’s ratio rising from 0.41 to 0.49, the compressive stress increased by 0.18 MPa in the process. When the dielectric constant of the BaTiO3/silicon rubber composite was less than 30, the potential difference of the piezoelectric film gradually raised with the dielectric constant increasing. When the dielectric constant of the composite was higher than 30, the output voltage of the composite gradually decreased. Therefore, the lower Young’s modulus and Poisson’s ratio of the silicone rubber composite is beneficial to improve the piezoelectric properties of the composite. This article will provide a reference for designing the preparation of spherical BaTiO3 composite materials.

Enhanced energy storage density in poly(vinylidene fluoride-hexafluoropropylene) nanocomposites by filling with core-shell structured BaTiO3@MgO nanoparticals

Filling with high dielectric constant inorganic nanoparticles is an effective approach to enhance the energy storage performance of an organic dielectric. However, the dielectric mismatch between ceramic and polymer causes early breakdown, which limits the storage density of ceramic/polymer nanocomposites in the application of dielectric capacitors. Herein, we employed MgO as a buffer barrier to mitigate the mismatched dielectric characteristics among BaTiO3 (BT) nanoparticles and poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) substrate considering its high insulation and medium dielectric constant. The alien oxide was coated on the spherical BT by a simple chemical precipitation process, forming a BaTiO3@MgO (BT@MgO) core-shell nanostructure, which has been carefully examined by TEM and EDS. The BT-MgO heterogeneous interfacial region provides channels for carriers and promotes charge movement, and therefore the dielectric constant and potential shift have been significantly enhanced. The BT@MgO/P(VDF-HFP) nanocomposite with 1 vol% filling ratio delivered a maximum energy density Ud, and the value reaches up to 5.6 J/cm3 that is 40.0 % and 55.6 % greater than that of the host matrix and BT-filled counterpart with the same filler amount. The BT@MgO core-shell nanostructure demonstrates an alternative way to effectively heighten the energy storage performance of ceramic/polymer composite dielectrics.

High Performance Generation of H2 O2 under Piezophototronic Effect with Multi-Layer In2 S3 Nanosheets Modified by Spherical ZnS and BaTiO3 Nanopiezoelectrics.

Manipulating the separation and transportation of photoexcited charge carriers in photoresponsive semiconductors via the piezoelectric polarization effect is an emerging strategy in the field of artificial photosynthesis. However, existing semiconductor photocatalysts, both with a wide range absorption for visible light and superior piezoelectricity are very scarce, leading to a low reactivity of photocatalysis. Here, a multi-layer In2 S3 nanosheet modified with spherical ZnS and BaTiO3 nanopiezoelectrics (ZnS/In2 S3 /BTO) is reported, generating approximately 378 µm of H2 O2 in 100min (and the concentration is still increasing) under co-irradiation of visible light and ultrasound (piezophotocatalysis) in ethanol-water solution; this concentration is higher compared with two phases piezoelectric heterostructures (i.e., ZnS/BTO, In2 S3 /BTO, and ZnS/In2 S3 ) and pure compounds (i.e., ZnS, In2 S3 , and BTO), and also higher than that of independent piezo- (≈254 µm) and photocatalysis (≈120 µm). Moreover, the concentration of H2 O2 generated on ZnS/In2 S3 /BTO can be as high as approximately 1160 µm in 5 h of piezophotoreaction after experiencing six cycles of visible light concurrent with ultrasound irradiation. The enhancement of H2 O2 yield on ZnS/In2 S3 /BTO in piezophotocatalysis can be attributed to the piezopotential-induced internal electric polarization field promoting the separation of photoexcited charge carriers, thus boosting the rate of surface photoreaction.

Enhanced dielectric properties of polyvinylidene fluoride-based composite films with layered perovskite KCa2Na3Nb6O19-derived fillers

A polyvinylidene fluoride (PVDF)-based composite film embedded with plate-like fillers was investigated as a novel dielectric composite material that can serve as a candidate film capacitor. Plate-like particles of the dielectric Ca2Na3Nb6O19 (CNN6) filler material were prepared through liquid-phase exfoliation of KCa2Na3Nb6O19 synthesized by a conventional solid-state reaction method. CNN6 fillers with an average aspect ratio of 2.0 were successfully dispersed in a PVDF matrix without large aggregation using a solution blending and casting method. The resultant CNN6/PVDF composite film exhibited higher breakdown strength than a dielectric PVDF-based composite embedded with spherical BaTiO3 fillers. The superiority of the plate-like filler particles over spherical filler particles was qualitatively confirmed by finite element simulation using a simplified filler/matrix model. A CNN6/PVDF composite film with a thickness of 3.8 µm exhibited a high capacitance density of 10.1 F m−3, which was three times higher than that of a biaxially oriented polypropylene film currently used for film capacitors in the power control units of hybrid vehicles.

TiO2-Seeded Hydrothermal Growth of Spherical BaTiO3 Nanocrystals for Capacitor Energy-Storage Application

Simple but robust growth of spherical BaTiO3 nanoparticles with uniform nanoscale sizes is of great significance for the miniaturization of BaTiO3-based electron devices. This paper reports a TiO2-seeded hydrothermal process to synthesize spherical BaTiO3 nanoparticles with a size range of 90–100 nm using TiO2 (Degussa) and Ba(NO3)2 as the starting materials under an alkaline (NaOH) condition. Under the optimum conditions ([NaOH] = 2.0 mol L−1, RBa/Ti = 2.0, T = 210 °C and t = 8 h), the spherical BaTiO3 nanoparticles obtained exhibit a narrow size range of 91 ± 14 nm, and the corresponding BaTiO3/polymer/Al film is of a high dielectric constant of 59, a high break strength of 102 kV mm−1, and a low dielectric loss of 0.008. The TiO2-seeded hydrothermal growth has been proved to be an efficient process to synthesize spherical BaTiO3 nanoparticles for potential capacitor energy-storage applications.

Microstructure driven magnetodielectric behavior in ex-situ combustion derived BaTiO3-ferrite multiferroic composites

The present work investigates the magnetodielectric behavior of ex-situ combustion derived 7BaTiO3@3ferrite and 3ferrite@7BaTiO3 multiferroic composites. Three different ferrites, such as CoFe2O4, ZnFe2O4, and Co0.5Zn0.5Fe2O4, have been selected for the preparation of multiferroic composites. Distinct microstructural features were observed in 7BaTiO3@3ferrite and 3ferrite@7BaTiO3 composites. X-ray diffraction study confirmed the presence of hexagonal and tetragonal BaTiO3 in 3ferrite@7BaTiO3 composites. Plate-like and spherical BaTiO3 grains were observed in these composites. However, only spherical or polyhedral BaTiO3 grains were found in 7BaTiO3@3ferrite composites, as confirmed from EDS mapping. Also, plate-like BaFe12O19 and polyhedral ferrite grains were detected in all composites. The presence of BaFe12O19 and its effect on magnetic and dielectric behavior of composites was also analyzed in this work. Maxwell-Wagner polarization phenomenon due to charge depletion at the BaTiO3-ferrite interface was found to be prominent in 7BaTiO3@3ferrite composites because of the maximum connectivity of ferrite phases. The main factors for the magnetocapacitance response in the present systems are due to the combined effects of interface-dominated magnetoresistance, magnetostriction of ferrites and microstructure of composites. The variation in magnetocapacitance response of these multiferroic composites may be suitable for potential applications in the field of sensors and devices.

The Formation and Application of Submicron Spherical BaTiO3 Particles for the Diffusion Layer of Medical Dry Films

Submicron spherical barium titanate (BaTiO3) was prepared by batch precipitation in an alkaline solution of a BaCl2–TiCl4–NaOH reaction system. The influence of various parameters on the morphology of BaTiO3 powders was investigated in this study. Spherical BaTiO3 particles can be obtained by reacting for 20 min, which was used to prepare the dry sheet of a medical dry chemical reagent. The morphology of the particles was affected by the stirring speed and the alkaline concentration; the particle size decreased as the stirring speed increased. The hydroxyl ion in the solution acts as a catalyst that can promote the formation of spherical BaTiO3. The formation mechanism of the BaTiO3 sphere is proposed to have three steps: the formation of a Ba–Ti gel and nucleation, self-combination/growth of the BaTiO3 crystal nucleus, and Ostwald ripening. In addition, it is feasible to apply the prepared BaTiO3 sphere to medical dry chemical detection reagents.

Hydrothermal synthesis of BaTiO3 nanoparticles and role of PVA concentration in preparation

Crystalline BaTiO3 nanoparticles were synthesized by hydrothermal process. The influences of PVA concentration on the phase formation, the size, the shape and dispersibility of BaTiO3 nanoparticles were determined by XRD, FE-SEM, TEM and the thermal analysis. After PVA solution added into the barium precursor, high purity cubic perovskite BaTiO3 nanoparticles were successfully obtained with well dispersion. The size and the shape of BaTiO3 particles were also be controlled by the concentration of PVA with lattice parameters almost unchanged. In addition, spherical BaTiO3 grains with average size of 68.8 nm were obtained when 0.02 g L−1 PVA was added into the barium precursor, which process the best morphology and highest dispersibility.

Comparative study of dielectric properties of the PVDF composites filled with spherical and rod-like BaTiO3 derived by molten salt synthesis method

In the molten salt environment, the BaTiO3 spherical nanoparticles (BTNPs) and BaTiO3 nanorods (BTNRs) have been synthesized, respectively, in which spherical TiO2 and rod-like BaTi2O5 are precursors. The dissolution–precipitation is the main dominated mechanism in the formation of BTNPs, while the dissolution–diffusion is the main mechanism responsible for the formation of BTNRs. The latter is also called as topochemical mechanism, which is associated with the assembly of [TiO6] octahedron units in the transformation from BaTi2O5 to BaTiO3. By using these two kinds of BT as fillers, polyvinylidene fluoride (PVDF)-based composites, BTNPs/PVDF and BTNRs/PVDF, have been constructed and their dielectric properties have been investigated. It was found that there were three main factors related to filler morphology affecting the dielectric properties of the composites, i.e., intrinsic polarization of filler, the interface polarization and electric field distribution between the filler and the matrix. Though the spontaneous polarization of 600-nm-sized BTNPs is larger, the interfacial area of BTNRs/PVDF composite is larger than that of BTNPs (600 nm)/PVDF composite, which is advantageous to enhance the interface polarization. Moreover, the analysis through Potential-Across model revealed that BTNRs/PVDF composite has stronger electric field intensity distribution across BTNRs filler in comparison with BTNPs/PVDF, which plays the key role in improving the dielectric properties of composites. This work not only presents the BTNRs/PVDF composite with good dielectric performance, the related design and the theory analysis also facilitate the development of more new high dielectric composites based on morphology control of ferroelectric filler.

Topological phase transformations and intrinsic size effects in ferroelectric nanoparticles.

Composite materials comprised of ferroelectric nanoparticles in a dielectric matrix are being actively investigated for a variety of functional properties attractive for a wide range of novel electronic and energy harvesting devices. However, the dependence of these functionalities on shapes, sizes, orientation and mutual arrangement of ferroelectric particles is currently not fully understood. In this study, we utilize a time-dependent Ginzburg-Landau approach combined with coupled-physics finite-element-method based simulations to elucidate the behavior of polarization in isolated spherical PbTiO3 or BaTiO3 nanoparticles embedded in a dielectric medium, including air. The equilibrium polarization topology is strongly affected by particle diameter, as well as the choice of inclusion and matrix materials, with monodomain, vortex-like and multidomain patterns emerging for various combinations of size and materials parameters. This leads to radically different polarization vs. electric field responses, resulting in highly tunable size-dependent dielectric properties that should be possible to observe experimentally. Our calculations show that there is a critical particle size below which ferroelectricity vanishes. For the PbTiO3 particle, this size is 2 and 3.4 nm, respectively, for high- and low-permittivity media. For the BaTiO3 particle, it is ∼3.6 nm regardless of the medium dielectric strength.

Numerical simulations of sonochemical production and oriented aggregation of BaTiO3 nanocrystals

Numerical simulations of sonochemical production and oriented attachment of BaTiO3 nanocrystals are performed in aqueous solution with pH 14. It is suggested that most significant effect of ultrasound is the dissolution of Ti-based gel in aqueous solution. It results in the dissolution-precipitation mechanism in the production of BaTiO3 nanoparticles, while with mechanical stirring without ultrasound it is the in situ mechanism that BaTiO3 is gradually formed on Ti-based gel. The oriented attachment of spherical BaTiO3 nanocrystals occurs by van der Waals torque (Casimir torque). Large aggregates of nanocrystals do not attach with each other as the repulsive double layer interaction is stronger for larger aggregates. For smaller spherical nanocrystals, the alignment of the crystal axes is less accurate due to more significant rotational Brownian motion of the nanocrystals.

Improved photon to current conversion in nanostructured TiO2 dye-sensitized solar cells by incorporating cubic BaTiO3 particles deliting incident

Different structures of dye-sensitized solar cells (DSCs) were fabricated with various compositions and arrangement modes of the photoanodes. The solvothermally grown TiO2 nanoparticles and sol–gel derived spherical TiO2 and BaTiO3 particles were employed as the active and scattering layers of DSCs. TiO2 nanoparticles and spherical particles had pure anatase structure with particle size of 15–30nm and 200–400nm, respectively, whereas 300–800nm BaTiO3 particles showed cubic perovskite structure. The efficiency improvement of mono-layer cells made of TiO2 nanoparticles (i.e., 7.22%) was achieved by light harvesting mechanism. Further enhancement of photovoltaic performance was achieved by light scattering mechanism using two different approaches (e.g., in forms of mono- and double-layer structures). For the mono-layer cells, composed of a mixture of TiO2 nanoparticles and BaTiO3, the highest efficiency of 8.63% was achieved for BaTiO3:TiO2=20:80. The double-layer cell containing the active layer composed of nanoparticles and a mixture of spherical TiO2 and BaTiO3 particles as the scattering layer showed the highest efficiency of 8.81%. Such enhancements were attributed to higher incident photon to current conversion yield due to greater fraction of light scattering, high refractive index of BaTiO3 particles, as well as less recombination of photo-generated electrons.

The effect of BaTiO3 particle shape on complex permittivity of 0.98MgTiO3–0.02BaTiO3 composite powders at GHz frequencies

The effect of BaTiO3 particle shape on the properties of 0.98MgTiO3–0.02BaTiO3 composite powders was characterized and analyzed using an indirectly coupled open-ended coaxial cavity resonator at gigahertz frequencies. Elongated micrometre sized BaTiO3 particles were found to have a significantly stronger effect on permittivity when compared to composite powders having micro and nano sized spherical BaTiO3 particles. Inclusion permittivities and dielectric loss tangents of composite powders increased from that of pure MgTiO3 powder, 13.3 and 4.6×10−3, up to 15.7 and 1.7×10−2 with needle shaped BaTiO3 particles, respectively. The presented results give valuable information for tailoring the properties of dielectrics which can be utilized in the vast field of electronic component manufacturing.

Oriented Attachment of Cubic or Spherical BaTiO3Nanocrystals by van der Waals Torque

It has been believed that dipole–dipole interaction is the reason for the oriented attachment (OA) of nanocrystals if they have electric or magnetic dipoles. In this study, the role of van der Waals torque (Casimir torque) originated in dielectric anisotropy of a nanocrystal is numerically studied for the first time on OA of cubic or spherical BaTiO3 nanocrystals. The present numerical simulations of OA have indicated that the alignment of the crystal axes is mainly due to van der Waals torque when the crystal size is smaller than 5 nm both in aqueous and organic solutions with and without electric charge screening by ions, respectively. For larger crystals, the electric dipole–dipole interaction dominates. The mesocrystal formation of 5 nm BaTiO3 nanocrystals in aqueous solution is due to van der Waals torque.

Fabrication and electric-field response of spherical BaTiO3 particles with high tetragonality

Electrorheological elastomer (ERE) is a member of smart material family. Many efforts have been made to develop high-performance EREs for preparing active electrorheological (ER) particles. In this work, an excellent ER particles named spherical tetragonal BaTiO3 were successfully synthesized by hydrothermal method at different conditions using Ba(OH)2·8H2O and amorphous TiO2 as original materials. Analysis of the structure and morphology of the synthesized particles with Raman, XRD, SEM techniques indicates that the additives play a crucial role in determining the surface morphology of the particles. Additionally, we discovered that the spherical tetragonal BaTiO3 particles with different surface morphology possess different tetragonality, surface hydrophilicity and dielectric property, and thus exhibit distinct electric-field response. The response of the BaTiO3 particles to electric-field is in the order of daisy-shaped > walnut-shaped > sphere particles. Further experiments reveal that high tetragonality, fine dielectric performance and super surface hydrophilicity of BaTiO3 particles are the major power in boosting their electric-field response.

Factors influencing formation of highly dispersed BaTiO3 nanospheres with uniform sizes in static hydrothermal synthesis

Highly dispersed BaTiO3 nanospheres with uniform sizes have important applications in micro/nanoscale functional devices. To achieve well-dispersed spherical BaTiO3 nanocrystals, we carried out as reported in this paper the systematic investigation on the factors that influence the formation of BaTiO3 nanospheres by the static hydrothermal process, including the NaOH concentrations [NaOH], molar Ba/Ti ratios (RBa/Ti), hydrothermal temperatures, and durations, with an emphasis on understanding the related mechanisms. Barium nitrate and TiO2 sols derived from tetrabutyl titanate were used as the starting materials. The as-synthesized BaTiO3 samples were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, thermogravimetry, differential thermal analysis, and FT-IR spectra. The highly dispersed BaTiO3 nanospheres (76 ± 13 nm) were achieved under the optimum hydrothermal conditions at 200 °C for 10 h: [NaOH] = 2.0 mol L−1 and RBa/Ti = 1.5. Higher NaOH concentrations, higher Ba/Ti ratios, higher hydrothermal temperatures, and longer hydrothermal durations are favorable in forming BaTiO3 nanospheres with larger fractions of tetragonal phase and higher yields; but too long hydrothermal durations resulted in abnormal growth and reduced the uniformity in particle sizes. The possible formation mechanisms for BaTiO3 nanocrystals under the static hydrothermal conditions were investigated.

BaTiO3 supercages: unusual oriented nanoparticle aggregation and continuous ordering transition in morphology.

Here we report the organic-free mesocrystalline superstructured cages of BaTiO3, i.e., the BaTiO3 supercages, which are synthesized by a one-step templateless and additive-free route using molten hydrated salt as the reaction medium. An unusual three-dimensional oriented aggregation of primary BaTiO3 nanoparticles in the medium of high ionic strength, which normally favors random aggregation, is identified to take place at the early stage of the synthesis. The spherical BaTiO3 aggregates further experience a remarkable continuous ordering transition in morphology, consisting of nanoparticle faceting and nanosheet formation steps. This ordering transition in conjunction with Ostwald ripening-induced solid evacuation leads to the formation of unique supercage structure of BaTiO3. Benefiting from their structure, the BaTiO3 supercages exhibit improved microwave absorption property.

Glass synthesis and particle size control of BaTiO3 by designing different calcinations modes

Different calcinations techniques are adopted to investigate influences of the calcinations modes on the synthesis of BaTiO3 powders. Two step calcinations (TSC), in which the samples are first heated to a higher temperature (T1) and then cooled quickly down to a low temperature (T2) for staying, can retard the grain growth and accelerates the phase transformation effectively. Using BaO, TiO2 and B2O3 oxides as precursors, the spherical BaTiO3 powders with a particle size of 15–20nm can be achieved based on TSC technique. A detailed investigation upon the possible particle growth mechanism of TSC is also carried out in this paper. The optimized T1can accelerate the phase transition rate while the optimized T2 can refrain the particle growth depending upon the transition of the particle growth mechanism.

Fabrication of fibrous BaTiO3-reinforced PVDF composite sheet for transducer application

Fibrous BaTiO3-reinforced polyvinylidene fluoride, BaTiO3/PVDF=30/70 (v/v%), composite sheets were fabricated, and their electric-field-induced strain curves and an energy harvesting output based on longitudinal stretch movement were measured. The mixture solution of BaTiO3 filler and PVDF was drawn on a glass substrate to form composite sheets, then the stacked sheets were thermally pressed and extended toward an uniaxial direction to form a piezoelectric β phase of PVDF by a hot rolling technique. The measured electric-field-induced strain in the 31 direction was enhanced in the sheet having a highly orientation ratio (83%) of fibrous BaTiO3 filler, which was more obvious than the case of the reference specimens using spherical BaTiO3 powders. The electricity energy output from the PVDF sheets increases by increasing the frequency. A highest energy output of 0.63J/m3 per unit cycle, that was 26% higher value than pure PVDF sheet, was achieved at the frequency of 100Hz for the sheet having such highly BaTiO3 orientation ratio.

Sonochemical Synthesis of Spherical BaTiO3 Nanoparticles

Monosized spherical barium titanate (BaTiO3) nanoparticles have been synthesized successfully via sonochemical reaction. The as-synthesized BaTiO3 nanoparticles were characterized using X-ray diffraction of powder, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The XRD pattern of BaTiO3 particles, which were synthesized under irradiation of ultrasonic sound for 0.5 h, showed sharp diffraction peaks that corresponded to the cubic BaTiO3 phase. Only a small amount of BaCO3 contamination was present in the sample. The Raman active modes of the samples in this study were similar to the cubic phase of BaTiO3. The average diameter of sonochemical synthesized particles was ∼99.54 ± 18.25 nm. The synthesized BaTiO3 nanoparticles were almost spherical.