Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Terms modified by BaTiO3

  • batio3 ceramics
  • batio3 grain
  • batio3 particle
  • batio3 suspension
  • batio3 thin film

  • Selected Abstracts

    Low-Temperature Synthesis of Phase-Pure 0D,1D BaTiO3 Nanostructures Using H2Ti3O7 Templates

    Duk Kyu Lee
    Abstract One-dimensional (1D) barium titanate (BaTiO3) nanowires, which were uniformly covered with 0D BaTiO3 nanocrystals, were synthesized by using a simple solvothermal reaction of protonated trititanate (H2Ti3O7) nanowires with barium hydroxide octahydrate [Ba(OH)28H2O] at 80 C in ethanol/water mixed solvent systems. The compositions of the mixed solvents , the volume ratio of ethanol to deionized water , was a key controlling parameter in order to determine the phase formation and primary particle size of the 0D BaTiO3 nanocrystals. Single-phase cubic perovskite BaTiO3 started to form at 80 C in a mixed solvent containing more than approximately 60,% by volume of ethanol. Field-emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) analysis revealed that the as-prepared BaTiO3 retained its wire-shaped morphology with nanocrystals on the surface. Furthermore, the synthetic mechanism of the 0D-1D BaTiO3 nanostructures was demonstrated in view of the dielectric tuning of the mixed solvent and the similarities between the crystal structures of BaTiO3 and H2Ti3O7. [source]

    Dielectric Properties of a Printed Sol,Gel Matrix Composite,

    Tobias Lehnert
    Low temperature processable materials with high dielectric constants are required for application on flexible organic substrates, for example, in printed electronics. To date, mainly organic polymers with embedded functional particles have been investigated for this purpose. For the first time, we present a printable dielectric composite material composed of ferroelectric high permittivity particles (BaTiO3) bonded by a mainly inorganic sol,gel derived network. The exemplary optimization of the properties by varying the sol,gel precursor illustrates the potential of sol,gel chemistry for printable functional materials. An operational gravure printed capacitor including printed silver electrodes is presented. The measured dielectric constants are among the highest reported in literature for low temperature cured films with moderate dissipation factors. Besides these promising dielectric properties, this composite film shows a ferroelectric response. [source]

    High K Capacitors and OFET Gate Dielectrics from Self-Assembled BaTiO3 and (Ba,Sr)TiO3 Nanocrystals in the Superparaelectric Limit

    Limin Huang
    Abstract Nanodielectrics is an emerging field with applications in capacitors, gate dielectrics, energy storage, alternatives to Li-ion batteries, and frequency modulation in communications devices. Self-assembly of high k dielectric nanoparticles is a highly attractive means to produce nanostructured films with improved performance,namely dielectric tunability, low leakage, and low loss,as a function of size, composition, and structure. One of the major challenges is conversion of the nanoparticle building block into a reliable thin film device at conditions consistent with integrated device manufacturing or plastic electronics. Here, the development of BaTiO3 and (Ba,Sr)TiO3 superparaelectric uniform nanocrystal (8,12,nm) films prepared at room temperature by evaporative driven assembly with no annealing step is reported. Thin film inorganic and polymer composite capacitors show dielectric constants in the tunable range of 10,30, dependent on composition, and are confirmed to be superparaelectric. Organic thin film transistor (TFT) devices on flexible substrates demonstrate the readiness of nanoparticle-assembled films as gate dielectrics in device fabrication. [source]

    Chemical Bonding Assembly of Multifunctional Oxide Nanocomposites

    Gary Evans
    Abstract The synthesis, functionalization and assembly of metal oxide nanoparticles BaTiO3 and CoFe2O4 is presented. The ferroelectric (BaTiO3) and ferromagnetic (CoFe2O4) oxide nanoparticle surfaces are directly functionalized via the anchoring of phosphonic acid and aminosilane molecules that engender the nanoparticles with terminal carboxylic acid and amine functional groups, respectively. These promote the electrostatic self-assembly of the particles in non-polar solvents and permit the synthesis of more chemically robust assemblies linked by the covalent amide bond via the addition of the chemical coupling agent N - N, -dicyclohexylcarbodiimide. This functionalization and assembly procedure is applied to two systems: the first comprised of 50,nm BaTiO3 and 10,nm CoFe2O4 particles and the second of 200,nm BaTiO3 and 12.5,nm CoFe2O4 particles. The latter composites possess magnetoelectric properties when processed into dense ceramics and, as a direct result of the assembly performed in solution, have a high degree of homogeneity between the ferroelectric and ferromagnetic phases. The developed functionalization and assembly procedure is considered to be adaptable to the preparation of other hybrid oxide nanomaterials with different property combinations. [source]

    Structural Transformations during Formation of Quasi-Amorphous BaTiO3,

    D. Ehre
    Abstract A model of structural transformations of amorphous into quasi-amorphous BaTiO3 is suggested. The model is based on previously published data and on X-ray photoelectron spectroscopy data presented in the current report. Both amorphous and quasi-amorphous phases of BaTiO3 are made up of a network of slightly distorted TiO6 octahedra connected in three different ways: by apices (akin to perovskite), edges, and faces. Ba ions in these phases are located in the voids between the octahedra, which is a nonperovskite environment. These data also suggest that Ba ions compensate electrical-charge imbalance incurred by randomly connected octahedra and, thereby, stabilize the TiO6 network. Upon heating, the edge-to-edge and face-to-face connections between TiO6 octahedra are severed and then reconnected via apices. Severing the connections between TiO6 octahedra requires a volume increase, suppression of which keeps some of the edge-to-edge and face-to-face connections intact. Transformation of the amorphous thin films into the quasi-amorphous phase occurs during pulling through a steep temperature gradient. During this process, the volume increase is inhomogeneous and causes both highly anisotropic strain and a strain gradient. The strain gradient favors breaking those connections, which aligns the distorted TiO6 octahedra along the direction of the gradient. As a result, the structure becomes not only anisotropic and non-centrosymmetric, but also acquires macroscopic polarization. Other compounds may also form a quasi-amorphous phase, providing that they satisfy the set of conditions derived from the suggested model. [source]

    Ferroelectric Switching in Multiferroic Magnetite (Fe3O4) Thin Films

    ADVANCED MATERIALS, Issue 44 2009
    Marin Alexe
    Real-time ferroelectric polarization switching in magnetite epitaxial thin films is reported, proving that magnetite is not only historically the first material showing magnetism and correlated electron properties, but also that it is ferroelectric with a value of the ferroelectric polarization approaching that of well-known ferroelectric materials such as BaTiO3. [source]

    Self-Assembled Perovskite-Fluorite Oblique Nanostructures for Adaptive (Tunable) Electronics

    ADVANCED MATERIALS, Issue 13 2009
    Tomoaki Yamada
    The relative concentration of BaTiO3 and CeO2 is shown to control the inclination of composite growth. The oblique composite structures consist of tunable BaTiO3 nanofibers embedded in a CeO2 matrix, which lowers considerably the permittivity while significantly enhancing the tunable response to an electric field. This is of interest in reconfigurable microelectronics. [source]

    The Patterning of Sub-500 nm Inorganic Oxide Structures,

    ADVANCED MATERIALS, Issue 14 2008
    Meredith J. Hampton
    Elastomeric perfluoropolyether molds are applied to pattern arrays of sub-500 nm inorganic oxide features. This versatile soft-lithography technique can be used to pattern a wide range of materials; in this work inorganic oxides including TiO2, SnO2, ZnO, ITO, and BaTiO3 are patterned on a variety of substrates with different aspect ratios. An example of TiO2 posts is shown in the figure. [source]

    BaTiO3,Epoxy Composites for Electronic Applications

    Leandro Ramajo
    A brief review related with dielectric properties of BaTiO3/epoxy composites is presented. The composites were obtained using the dipping technique. To facilitate the mixing and modify the filler surface, a solvent and a surface coupling agent were used. Intermediate and low concentrations of solvent and silane improved microstructure and dielectric properties of the composite material, whereas higher concentrations led to composites of poor quality. Finally, a model using finite elements was used, in order to predict the composite permittivity in relation to the percentage of filler. Model results were compared with the effective medium theory and experimental results. [source]

    Synthesis and Dielectric Properties of Niobia Coating on BaTiO3

    Jia-Jia Gan
    Different from conventional powder mixing, this study demonstrates a method of homogeneous coating for niobia (Nb2O5) on ferroelectric barium titanate (BaTiO3) powders. The precipitation of Nb coating with pH has been determined quantitatively by the inductance-coupled plasma method. Crystalline phases were determined by X-ray diffractometry, and the formation of a "core-shell" structure with a Nb concentration gradient was observed by a transmission electron microscope with X-ray energy-dispersive spectroscopy. The dielectric constant (K) of the samples prepared by the nanocoating method showed a more stable temperature coefficient of capacitance and well satisfied the requirements of X7R. [source]

    Multilayer Construction with Various Ceramic Films for Electronic Devices Fabricated by Aerosol Deposition

    Hironori Hatono
    Aerosol deposition (AD) is applicable as a fabrication technology for microstructures comprising different materials. We used this method for electronic devices that consist of ceramic films and metal electrodes. Various ceramic thick films (5,50 ,m thickness), for example, Al2O3, 2MgOSiO2, and BaTiO3, were deposited on substrates using room-temperature aerosol deposition. The dielectric constant of BaTiO3 was 78 at 1 MHz. Multilayer constructions with ceramic films and copper electrodes were obtained using aerosol deposition and sputtering. During deposition, photoresist film masks were applied to produce patterns of ceramic films and connections between upper and lower electrodes through the ceramic films. [source]

    Texture Development in Barium Titanate and PMN,PT Using Hexabarium 17-Titanate Heterotemplates

    Toshio Kimura
    Bulk BaTiO3 ceramics with ,111,-texture have been prepared by the modified templated grain growth method, using platelike Ba6Ti17O40 particles as templates, and the mechanism of texture development is examined. The Ba6Ti17O40 particles induce the abnormal growth of BaTiO3 grains, and a structure similarity between {001} of Ba6Ti17O40 and {111} of BaTiO3 gives ,111,-texture to abnormally grown BaTiO3 grains. Thus, the ,111,-texture develops in the BaTiO3 matrix. The use of platelike Ba6Ti17O40 particles has been extended to a 0.65Pb(Mg1/3Nb2/3)O3,0.35PbTiO3 matrix, but the matrix phase is decomposed by extensive chemical reactions between the matrix and template phases. [source]

    A Novel Percolative Ferromagnetic,Ferroelectric Composite with Significant Dielectric and Magnetic Properties,

    ADVANCED MATERIALS, Issue 3 2007
    Q. Huang
    A series of BaTiO3,Ni0.55Zn0.45Fe2.03O4composites are synthesized. The composites exhibit excellent dielectric and magnetic properties in the neighborhood of the percolation threshold,a high dielectric constant that is nearly temperature and frequency independent (see figure),and considerable initial permeability with excellent frequency stability, and may be useful as a high-performance multifunction ceramic composite. [source]

    Periodic models in quantum chemical simulations of F centers in crystalline metal oxides

    Yuri F. Zhukovskii
    Abstract We present a survey of recent first principles simulations of the neutral oxygen vacancies (F centers) existing as native or radiation-induced point defects in various crystalline metal oxides in different forms (bulk, bare substrate surface, and on the interface with metal adsorbates). We mainly consider periodic models in calculations of point defects using the metal oxide supercell or cyclic clusters. We compare different formalisms of first principles calculations, mostly the Density Functional Theory (DFT) as implemented in the framework of either localized basis set of atomic orbitals or delocalized basis sets of plane waves. We analyze in detail the structural and electronic properties of F centers in binary oxides of light metals (MgO and Al2O3), and ternary metal oxides (SrTiO3, BaTiO3, PbTiO3, KNbO3, and PbZrO3 perovskites). When available, we compare results of ab initio periodic defect calculations with experimental data, results of the first principles cluster calculations (both embedded and molecular) as well as with semi-empirical calculations. 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]

    On the tetragonality of the room-temperature ferroelectric phase of barium titanate, BaTiO3

    Dean S. Keeble
    The room-temperature phase of the important ferroelectric material barium titanate, BaTiO3, was re-investigated by single-crystal X-ray diffraction on a sample grown by the top-seeded solution growth method, with the intention of demonstrating once again that the structure has tetragonal symmetry consistent with the space-group assignment P4mm and thus resolving recent controversy in the scientific community and literature [Yoshimura, Kojima, Tokunaga, Tozaki & Koganezawa (2006). Phys. Lett. A, 353, 250,254; Yoshimura, Morioka, Kojima, Tokunaga, Koganezawa & Tozaki (2007). Phys. Lett. A, 367, 394,401]. To this end, the X-ray diffraction pattern of a small (341,m3) sample of top-seeded solution-grown BaTiO3 was measured using an Oxford Diffraction Gemini CCD diffractometer employing Mo,K, radiation and an extended 120,mm sample-to-detector distance. More than 104 individual diffraction maxima observed out to a maximum resolution of 0.4, were indexed on two tetragonal lattices. These were identical to within the standard deviations on the lattice parameters and were related to each other by a single rotation of 119.7 about the [11] direction of the first tetragonal lattice (the major twin component), although the actual twinning operation that explains the observed diffraction pattern both qualitatively and quantitatively is shown to be conventional 90 twinning by the m[101] operation. Importantly, it is not necessary to invoke either monoclinic symmetry or a coexistence of tetragonal and monoclinic phases to explain the observed diffraction data. [source]

    Polarization switching in BaTiO3 thin films measured by X-ray diffraction exploiting anomalous dispersion

    S. J. Van Reeuwijk
    Films of BaTiO3 ranging from 20,nm to 300,nm in thickness were grown with pulsed laser deposition on Nb:SrTiO3. The quality of the layers was investigated using atomic force microscopy, X-ray reflectivity and X-ray diffraction. Both the micrographs and the X-ray reflectivity spectra indicate a smooth surface of the layers. The X-ray diffraction profiles measured using synchrotron radiation show features characteristic for highly crystalline thin films. The application of an external electric field parallel to the c axis changes an hkl reflection of BaTiO3 to an hk reflection. Due to the anomalous dispersion, the intensities of these two reflections are not equal and the atomic displacements can be determined from the intensity differences. The electric field-induced intensity changes can be as large as a few percent, which makes data collection from a 100,nm film using Cu K, radiation from an X-ray tube feasible. The ,I/I values of a number of reflections from the 20 and 50,nm films were measured using synchrotron radiation. The observed ,I/I values were in good agreement with the intensity changes expected for polarization switching in the bulk. [source]

    Dispersion of nanoscale BaTiO3 suspensions by a combination of chemical and mechanical grinding/mixing processes

    Kuo-Liang Ying
    Abstract The colloidal stability of aqueous nanometer- and micrometer-scale barium titanate (BaTiO3) utilizing poly (methacrylic acid) (PMAA-Na) and polyacrylamide/(,- N,N -dimethyl- N -acryloyloxyethyl)ammonium ethanate (PDAAE) was investigated. In addition to chemical dispersants, the effects of mechanical milling using either conventional ball milling or nanogrinding/-mixing on the dispersion of BaTiO3 suspensions were also studied. Characterization of the particle size distribution (d50), viscosity, and morphology of BaTiO3 particles in the suspensions revealed that a sole chemical dispersant or mechanical milling was insufficient to achieve nanometer-scale dispersion. The best dispersion results were obtained with a combination of PMAA-Na dispersant and nanogrinding/-mixing, which could provide sufficient electronic repulsive force and shear force to disperse the 80-nm BaTiO3 powders uniformly in the aqueous suspension. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source]

    Injectable acrylic bone cements for vertebroplasty with improved properties

    Ral Garca Carrodeguas
    Abstract Currently commercially available acrylic bone cements lack adequate radiopacity and viscosity when they are used in percutaneous vertebroplasty (PVP). In this work improved formulations of radiopaque and injectable poly(methyl methacrylate) bone cements were prepared with different amounts (10,50 wt.%) of BaTiO3 or SrTiO3 particles as the radiopaque agent. Two sets of cements were prepared by using untreated or silanated radiopaque particles, respectively. The influence of the content and nature of the radiopaque agent as well as its silanation with 3-(trimethoxysilyl) propyl methacrylate (,-MPS), on the curing parameters, residual monomer content, radiopacity, mechanical properties, and injectability of the resulting materials, was examined. Doughing and setting times, maximum temperature, and compressive strength of all formulations fulfilled the requirements of standard specifications, with values of peak temperature in the range 57,72 C and those of compressive strength between 114 and 135 MPa. Formulations containing at least 20 wt.% BaTiO3 or SrTiO3 had radiopacities equal to or greater than that corresponding to 2 mm of Al as required for surgical plastics. Injectability of any of the formulations provided 75,80 wt.% of the total mass manually injected through a conventional biopsy needle 4 min after mixing. Silanation of the BaTiO3 or SrTiO3 particles led to formulations with improved mechanical properties and injectability compared to those obtained with the untreated fillers. 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 68B: 94,104, 2004 [source]

    Orientation and Phase Relationships between Titania Films and Polycrystalline BaTiO3 Substrates as Determined by Electron Backscatter Diffraction Mapping

    Nina V. Burbure
    Titania films have been grown on polycrystalline BaTiO3 (BTO) substrates at 700C by pulsed laser deposition. Electron backscatter diffraction (EBSD) was used to determine grain orientations in the substrate before growth, and the phase and orientation of the supported films after growth. All BaTiO3 grains within 26 of (001) were covered by anatase films with an orientation relationship of (001)Anatase||(001)BTO and [100]Anatase||[100]BTO. Rutile with a variety of orientations grew on BaTiO3 grains with orientations closer to (110) and (111). EBSD mapping provides an efficient means for determining phase and orientation relationships of films over all orientation parameters. [source]

    Phase Characteristics and Piezoelectric Properties in the Bi0.5Na0.5TiO3,BaTiO3,K0.5Na0.5NbO3 System

    Shan-Tao Zhang
    Lead-free 0.94Bi0.5Na0.5TiO3,(0.06,x)BaTiO3,xK0.5Na0.5NbO3 (x=0,0.06) ceramics were prepared. All these compositions have a structure close to the rhombohedral,tetragonal morphotropic phase boundary (MPB) and good electric properties at room temperature. No significant composition dependence of ferroelectric property can be established, whereas a dependence of piezoelectric properties can be observed, e.g. the piezoelectric coefficient (d33), planar coupling factor (kp), and field-induced strain (S) increase with increasing x when x,0.01 and then tend to decrease. The highest d33, kp, and bipolar strain are 118 pC/N, 0.29, and 0.32%, respectively, in the composition with x=0.01. The results not only indicate that BNT,BT,KNN lead-free piezoceramics can persist in the structure close to MPB in a wide composition range but that they may also be helpful for further investigation on lead-free piezoceramics. [source]

    The Chemical Interaction of Silver,Palladium Alloy Electrodes with Bismuth-Based Piezomaterials

    Denis Schuetz
    Multilayer technology relies heavily on the chemical compatibility of metal and ceramic. This work focuses on the ceramic,electrode interaction between 92Bi0.5Na0.5TiO3,6 BaTiO3,2K0.5Na0.5NbO3 [(Bi0.46Na0.47Ba0.06K0.01)(Nb0.02Ti0.98)O3], a promising actuator material and forerunner to an emerging class of lead-free actuator materials, and a silver,palladium alloy for inner electrodes, the only currently viable material for the firing temperatures necessary (1100C). Of special concern was the high content of bismuth in the ceramic since prior investigations suggest that Bi2O3 (as well as various bismuth titanates) used as a fluxor in electroceramics are prone to forming the intermediate-phase bismuth palladate (Bi2PdO4), which can lead to poor contacting and delamination of multilayer stacks. Remarkably, no evidence of bismuth palladate formation could be found. However, the phase relations of the bulk ceramic have proven to be quite complex. Potassium was being drained out of the bulk ceramic either constituting the secondary phase K4Na2(TiO3)3 in unmodified experiments or evaporating and being replaced by silver in samples in contact with Ag. Mechanisms for the formation of these phases or the lack thereof are proposed. These findings were obtained by XRD, TG-DSC, and SEM with EDX, and LA-ICPMS. [source]

    Direct Scanning Electron Microscopy Imaging of Ferroelectric Domains After Ion Milling

    Daniel Grner
    A method for directly observing the ferroelectric domain structure by scanning electron microscopy after argon ion milling has been established. Its advantages are exemplified by exposing the domain structure in three widely used ferroelectric ceramics, BaTiO3, (Na,K)NbO3, and Pb(Ti,Zr)O3. Stable high-resolution images revealing domains with widths <30 nm have been obtained. The domain contrast is caused by electron channeling and is strongly dependent on the sample tilt angle. Owing to a strain- and defect-free surface generated by gentle ion milling, pronounced orientation contrast is observed. [source]

    Intragranular Voids and dc Degradation in (CaO+MgO) Codoped BaTiO3 Multilayer Ceramic Capacitors

    Hwan-Wen Lee
    The microstructure of multilayer ceramic capacitors (MLCC) based on BaTiO3 and nickel electrode, have been analyzed using the scanning and the transmission electron microscopy. In order to investigate how MgO improves MLCC against dc degradation, both CaO doped and (CaO+MgO) codoped chips, pristine as well as highly accelerated life-tested, are studied. BaTiO3 grains are characterized by both the types I and II core shell structure, which is typical of MLCC exhibiting the X7R dielectric behavior. Intragranular voids are found in BaTiO3 grains in the vicinity of the electrode,dielectric interface. Void-containing grains are more frequently observed and voids are more abundant in (CaO+MgO) codoped chips than in CaO doped ones. Higher concentration of oxygen vacanciesis induced extrinsically from both MgO codoping and Ni diffusion into BaTiO3 grains along the electrode,dielectric interface during sintering. Such oxygen vacancies have reacted with both cation vacanciesandby an inverse Schottky defect reaction and condensed to form voids. This reaction requiring cation and oxygen vacancies in the stoichiometric BaTiO3 composition of 1:1:3 has significantly decreased the randomly distributed mobile oxygen vacancies, and contributes to improve against dc degradation. [source]

    High-Energy Density Capacitors Utilizing 0.7 BaTiO3,0.3 BiScO3 Ceramics

    Hideki Ogihara
    A high, temperature-stable dielectric constant (,1000 from 0 to 300C) coupled with a high electrical resistivity (,1012,cm at 250C) make 0.7 BaTiO3,0.3 BiScO3 ceramics an attractive candidate for high-energy density capacitors operating at elevated temperatures. Single dielectric layer capacitors were prepared to confirm the feasibility of BaTiO3,BiScO3 for this application. It was found that an energy density of about 6.1 J/cm3 at a field of 73 kV/mm could be achieved at room temperature, which is superior to typical commercial X7R capacitors. Moreover, the high-energy density values were retained to 300C. This suggests that BaTiO3,BiScO3 ceramics have some advantages compared with conventional capacitor materials for high-temperature energy storage, and with further improvements in microstructure and composition, could provide realistic solutions for power electronic capacitors. [source]

    Synthesis of Nano-sized BaTiO3 Powders by the Rotary-Hydrothermal Process

    Takashi Kubo
    Nano-sized BaTiO3 powders with narrow size distribution and high tetragonality were attempted to be synthesized by the rotary-hydrothermal process in a water system as a novel technique, using a mixture of anatase-type TiO2 and Ba(OH)2 as starting material. The rotary-hydrothermal syntheses were performed under conditions with a rotary-speed of 20 revolutions per minute at 423,523 K for 3,96 h. Highly- and mono-dispersed BaTiO3 powders mainly composed of coarse-faceted particles with the tetragonal phase were successfully synthesized by controlling the conditions for rotary-hydrothermal treatments. TEM and TG results revealed that these coarse-faceted BaTiO3 particles contained very few structural defects such as hydroxyl content. Thus, the rotary-hydrothermal process was a useful method to synthesize very high-quality BaTiO3 particles, and the further control of various conditions of the rotary-hydrothermal treatment is expected to control the crystalline phase and microstructures of final BaTiO3 powders. [source]

    Solid-State Synthesis of Nanocrystalline BaTiO3: Reaction Kinetics and Powder Properties

    Maria Teresa Buscaglia
    The formation of BaTiO3 nanoparticles by a solid-state reaction between nanocrystalline raw materials BaCO3 and TiO2 was studied as a function of temperature (400,800C), time (1,24 h), and titania particle size (15 and 30 nm). The reaction starts at 500C and a high reaction rate is already observed at 600C for the finest titania, with up to 90% conversion after 2 h. Two main reaction stages were observed at 600,700C. The first step is dominated by nucleation and growth of BaTiO3 at the TiO2,BaCO3 contact points and at the TiO2 surface. Surface diffusion of BaCO3 is, most likely, the prevailing mass transport mechanism responsible for the rapid formation of BaTiO3, even in the absence of a significant contribution from lattice diffusion. The second stage begins when the residual TiO2 cores are completely covered by the product phase. For longer times, the reaction can only proceed by the slower lattice diffusion, resulting in a strong decrease of the reaction rate. Single-phase BaTiO3 nanopowders with a specific surface area of 12,15 m2/g, an average particle size of 70,85 nm, a relative density of 96.5%,98.3%, and a tetragonality of 1.005 were obtained by calcination at 700,800C. Critical parameters in the preparation of ultrafine powders by solid-state reactions are the particle size of both raw materials, the absence of large hard agglomerates, and the homogeneity of the mixture. The use of fine raw materials and optimization of the reaction conditions make mechanical activation unnecessary. [source]

    Preparation and Electrical Properties of an Anodized Al2O3,BaTiO3 Composite Film

    Xianfeng Du
    A highly stable, water-based barium titanate BaTiO3, BT, sol was synthesized using a sol,gel route through a chelate lactate technique. Dried BT precursor powders were measured by thermal gravimetry,differential thermal analysis and X-ray diffraction. It was found that BT powders first converted into barium carbonate BaCO3, Ti complex, and intermediate phase Ba2Ti2O5CO3, and then transformed into perovskite phase BaTiO3. The crystallization temperature was about 550C. The low-voltage etched aluminum foils were covered with BT sol by dip coating, and then annealed at 600C for 30 min in air. After that, the samples were anodized in a 15 wt% aqueous solution of ammonium adipate. The voltage,time variations during anodizing were monitored, and the electrical properties of the anodic oxide film were examined. It was shown that the specific capacitance, the product of specific capacitance and withstanding voltage, and leakage current of samples with a BT coating were about 48.93%, 38.50%, and 167% larger than that without a BT coating, respectively. [source]

    Comprehensive Linkage of Defect and Phase Equilibria through Ferroelectric Transition Behavior in BaTiO3 -Based Dielectrics: Part 1.

    Defect Energies Under Ambient Air Conditions
    Defect and phase equilibria have been investigated via the ferroelectric phase transition behavior of pure and equilibrated nonstoichiometric BaTiO3 powder samples. Through fabricating the BaTiO3 materials under highly controlled conditions to preserve the equilibrium conditions with respect to Ba/Ti ratio, annealing temperature (T), and oxygen partial pressure (PO2), systematic variations in the phase transition temperature can be noted with respect to Ba/Ti ratio and T. From the data extracted, we can then determine solubility limits. Equilibrating the defect reactions at the solubility limits provides a direct approach to identify and calculate the defect energetics. The phase transition temperature decreased with increasing concentration of the TiO2 partial-Schottky defects (BaTi1,,O3,2,) and the BaO partial-Schottky defects (Ba1,,TiO3,,), and showed discontinuous changes in the two-phase region. The formation enthalpy and entropy for the partial-Schottky defect reactions was evaluated to be 2.320.1 eV and 10.150.7 kB for the BaO partial-Schottky defect, and 2.890.1 eV and 8.01.5 kB for the TiO2 partial-Schottky defects equilibrated under air annealing conditions. [source]

    Physical Modeling and Electrodynamic Characterization of Dielectric Slurries by Impedance Spectroscopy (Part II)

    Vladimir Petrovsky
    Electrical characterization of dielectric slurries, as 0,3 composite systems, can provide valuable information on the dielectric properties of suspended particles. A new approach developed in our laboratory is based on impedance spectroscopy measurements of the slurries containing dispersed dielectric powders. Dielectric constants of the particles are determined through analysis of the low-frequency section of the impedance spectra. It was shown previously that this approach allows accurate and reliable measurement of dielectric constant of particles (,: ,100,2000) using host liquids (,: ,10,65). This study addresses the validation of this new method with physical model experiments using millimeter-sized sintered BaTiO3 model samples suspended in the liquid. Impedance spectra of barium titanate powder slurries were compared with the spectra of the model samples containing macroscopic cubes prepared by sintering of the same starting powder. This comparison shows a good agreement between the impedance spectra of powder and bulk BaTiO3 and validates the reliability of the new method to determine the dielectric constant of particulate materials. [source]

    Raman Spectroscopy of Ferroelectric Thin Films and Superlattices

    Dmitri A. Tenne
    Recent results of Raman spectroscopy studies of lattice dynamics and phase transitions in ferroelectric thin films and superlattices are reviewed. Raman studies of SrTiO3, BaTiO3, and BaxSr1,xTiO3 thin films in comparison with corresponding single crystals are presented; essential differences in the lattice dynamics behavior of thin films and single crystals are discussed. Application of ultraviolet Raman spectroscopy for studies of nanoscale ferroelectric heterostructures, such as BaTiO3/SrTiO3 superlattices, is demonstrated. [source]