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ABSTRACT: Barium titanate (BaTiO3) crystallites with various particle sizes from 22 to 500nm were prepared by the two-step thermal decomposition method of
barium titanyl oxalate. Various characterizations revealed that these particles were impurity-free, defect-free, dense BaTiO3 particles. The powder dielectric measurement clarified that the dielectric constant of BaTiO3 particles with a size of around 58nm exhibited a maximum of over 15,000. To explain this size dependence, the THz region
dielectric properties of BaTiO3 fine particles, especially Slater mode frequency, were measured using the far infrared (FIR) reflection method. As the result,
the lowest Slater mode frequency was obtained at 58nm. This tendency was completely consistent with particle size dependence
of the dielectric constant.
Journal of Electroceramics 05/2012; 21(1):198-201. · 1.19 Impact Factor
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ABSTRACT: A new measuring method and analyzing procedure were proposed to determine the complex dielectric constant of materials with
relatively high dielectric constant by a lumped impedance measurement using impedance analyzer. Samples used for the measurement
were (Ba0.6Sr0.4)TiO3 (BST) and Ba(Zr0.25Ti0.75)O3 (BZT) ceramics. Micro planar electrodes were formed on the surface of samples by electron beam lithography followed by lift-off
method. Complex admittances of these samples were measured up to 3GHz at different temperatures. Electromagnetic simulations
were performed for determining the relative dielectric constant and dielectric loss. The complex dielectric constant vs frequency
curves of Ba(Zr0.25Ti0.75)O3 showed a broad dielectric relaxation, while that of (Ba0.6Sr0.4)TiO3 was almost flat up to 3GHz on high-temperature side of T
m at which dielectric constant shows maximum value. Dielectric dispersion properties were discussed from the viewpoint of diffuse
phase transition in ferroelectrics.
Journal of Electroceramics 04/2012; 21(1):427-430. · 1.19 Impact Factor
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ABSTRACT: Capacitance aging under DC electric fields has been studied on multilayer ceramic capacitors (MLCCs) with the X7R characteristics.
The capacitance change with time was divided into two stages, the first- and the second-stage. The first-stage was due to
the nonlinear permittivity of dielectrics and it should not be involved in the aging phenomenon. The second-stage depended
on the MnO content, grain size and firing condition of dielectrics. From the behavior of the second-stage, it was concluded
that the capacitance aging was caused by the 90-degree domain switching in BaTiO3 in the core. The first-stage was due to the nonlinear permittivity but the domain switching was also included in the first-stage
if the domain walls moved by the first application of DC field. The change in the aging behavior with the intensity of DC
field could be explained by separating capacitance change into the nonlinear permittivity and the domain switching according
to the mechanism proposed in this study.
Journal of Electroceramics 04/2012; 21(1):17-21. · 1.19 Impact Factor
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ABSTRACT: A new measurement technique using micro planar electrode and electromagnetic field analysis was developed to measure the microwave dielectric properties of materials with high dielectric constant and high loss factor. Dielectric dispersions of (Ba0.6Sr0.4)TiO3 and Ba(Zr0.25Ti0.75)O3 were measured up to 3 GHz as a function of temperature, and were well explained by the stretched exponential model of the decay function in dielectric relaxation. The phase transition in these ceramics was investigated by dielectric relaxation analysis, X-ray diffraction analysis and specific heat measurement. (Ba0.6Sr0.4)TiO3 showed a diffused phase transition and its relaxation frequency was much high than Ba(Zr0.25Ti0.75)O3, while Ba(Zr0.25Ti0.75)O3 showed typical relaxors behavior.
Ferroelectrics. 10/2011; 356(October 2007):134-139.
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ABSTRACT: Due to an environmental concern, a lead-free ferroelectric with properties comparable to those of lead zirconate titanate is required. Based on the tolerance factor, the single perovskite phase of Bi1/2K1/2(X1/3Nb2/3)O3 (X = Cu BKCuN, X = Mg BKMgN or X = Zn BKZnN). The X-ray diffraction (XRD) patterns showed that all the samples sintered largely consisted of the perovskite phase, with small amounts of second phases. By adding BaTiO3, these ceramics were observed perovskite single phase. Those electric properties were investigated.
IOP Conference Series Materials Science and Engineering 09/2011; 18(9):092057.
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06/2011: pages 185 - 191; , ISBN: 9781118144121
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06/2011: pages 105 - 113; , ISBN: 9781118144077
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ABSTRACT: Barium titanate (BaTiO3) nanoparticles were prepared by a two-step thermal decomposition method using barium titanyl oxalate nanoparticles of 30 nm with and without dry-jet milling. Dry-jet milled barium titanyl oxalate nanoparticles (BTO-B) were well-dispersed whereas those without the dry-jet milling procedure (BTO-A) were partially aggregated. A heat annealing of obtained BaTiO3 nanoparticles at the same temperature resulted in crystallite sizes of the BTO-A derived BaTiO3 nanoparticles much smaller than those of the BTO-B derived. A mesoscopic particle structure analysis revealed much thinner surface cubic layer thickness of the BTO-B derived BaTiO3 nanoparticles, as compared with the BTO-A derived BaTiO3 nanoparticles. This indicated that the particle growth rate is the most important parameter for the surface cubic layer thickness determination.
Integrated Ferroelectrics 01/2010; 114(1):35-41. · 0.30 Impact Factor
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ABSTRACT: Barium titanate (BaTiO3, BT)—potassium niobate (KNbO3, KN) solid solution system (0.5BT-0.5KN) ceramics with various microstructures were prepared by two-step sintering method, and their piezoelectric properties were investigated. For 0.5BT-0.5KN ceramics, two phases, ferroelectric tetragonal and ferroelectric orthorhombic, coexisted in different grains at room temperature, owing to the limited solid solution system. The volume fraction of interface region between BT-rich tetragonal and KN-rich orthorhombic grains was controlled by sintering temperatures, and increased with decreasing sintering temperatures. Apparent piezoelectric constant d 33* was measured using slope of strain vs. electric field curves. As the results, the d 33* increased with decreasing sintering temperatures, which revealed that interface region between tetragonal and orthorhombic grains could contribute to enhancement of piezoelectric properties.
Ferroelectrics 01/2010; 402(1):121-129. · 0.39 Impact Factor
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ABSTRACT: Nanostructures of barium titanate (BaTiO3) nanoparticles were analyzed using a composite structure model. It was found that BaTiO3 nanoparticles had a composite structure consisting of (i) inner tetragonal core, (ii) gradient lattice strain layer (GLSL), and (iii) surface cubic layer. The crystal structure of each region did not depend on particle size while the volume fraction of the GLSL and the surface cubic layer increased with decreasing the particle size. These results suggested that the size effect of BaTiO3 nanoparticles originated from the composite structure.
Applied Physics Letters 11/2008; 93(19):192914-192914-3. · 3.84 Impact Factor
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ABSTRACT: Barium titanate (BaTiO(3)) nanoparticles from 27 to 192 nm were prepared by the 2-step thermal decomposition method from barium titanyl oxalate nanoparticles. These particles were dispersed well into 1-propanol, and dense BaTiO(3); nanoparticle sphere arrays without stress-field were prepared by the meniscus method. Temperature dependence of dielectric properties was successfully measured using these dense nanoparticle sphere arrays, and size effect on dielectric properties was discussed.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 10/2008; 55(9):1895-9. · 1.80 Impact Factor
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ABSTRACT: The modification of thermoelectric figure of merit was estimated from enhanced mobility of [100] oriented beta-FeSi2 film. beta-FeSi2 on Si(001) substrate was prepared by molecular beam epitaxy method using an Fe source. The crystallographic orientation of
beta-FeSi2 film on Si(001) substrate was characterized by using X-ray diffraction. Using scanning electron microscopy, surface morphology
and film thickness of samples were observed and estimated, respectively. The mobility of beta-FeS2 film on Si(001) substrate were also characterized by Hall measurement at room temperature. A part of the enhancement of figure
of merit was evaluated as the functions of mobility and crystallographic orientation of samples.
Journal of Materials Science Materials in Electronics 03/2008; 19(4):311-314. · 1.08 Impact Factor
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ABSTRACT: The powder dielectric measurement of barium titanate (BaTiO3) fine particles with sizes from 17 to 1,000 nm revealed the maximum dielectric constant at a certain particle size. Moreover, the sizes with maximum dielectric constants were strongly dependent on the preparation methods. When the BaTiO3 fine particles were prepared using the original 2-step thermal decomposition method, a dielectric constant maximum of 15,000 was observed at 70 nm particle size. On the other hand, when the BaTiO3 fine particles were prepared using the modified 3-step thermal decomposition method, a dielectric constant maximum of 5,000 was observed at 140 nm. The former BaTiO3 was prepared in vacuum of 10−2 torr while the latter BaTiO3 was prepared in air. Structure refinement of BaTiO3 particles using a Rietveld method revealed that all of BaTiO3 particles were always composed of two parts; (a) surface cubic layer and (b) bulk tetragonal layer. Moreover, a thickness of surface cubic layer for BaTiO3 nanoparticles prepared in vacuum of 10−2 torr was much thinner than that for BaTiO3 nanoparticles prepared in air. Thus, to explain these differences, a new model on the basis of “surface relaxation” was proposed.
03/2008: pages 89 - 100; , ISBN: 9780470291252
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ABSTRACT: Perovskite-type BaTiO(3)/SrTiO(3) (BTO/STO) artificial superlattices were fabricated by the molecular beam epitaxy method. The X-Ray diffraction (XRD) profiles and reflection, high-energy, electron diffraction (RHEED) oscillations during the growth of superlattices indicated that crystalline orientation toward [001] direction and two-dimensional layer-by-layer growth were achieved. The capacitance, dielectric loss tangent, and complex admittance were measured up to 145 degrees C and up to the frequency of 100 MHz with the microplaner interdigital electrodes. Dielectric permittivity of superlattices was evaluated from the complex admittance with an electromagnetic field analysis as a function of temperature. The [BTO(10)/STO(10)](4) superlattice showed the enormous relative permittivity of 19,000 at room temperature and the dielectric relaxation was observed. The linear relations in the charge versus voltage curves were observed in these superlattices, and the shape of Q-V curves were not changed as a function of temperature. Temperature dependence of dielectric properties of the BTO/STO superlattices was evaluated. It was found that the BTO/STO superlattices did not show a peak in the dielectric permittivity versus temperature curve, which was different from the behavior of BTO-STO bulk ceramics and normal thin films. These results strongly supported that the high permittivity of the superlattices was caused by temperature-stable anisotropic strains induced in the superlattices.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 01/2008; 54(12):2541-7. · 1.69 Impact Factor
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ABSTRACT: Recently, it was reported that the alkaline niobate-based (K,Na,Li)(Nb,Ta,Sb)O3 (LF4) perovskite ceramics showed excellent piezoelectric properties and has been regarded as a new candidate of lead-free piezoelectric materials. However, the effects of additives on the piezoelectric property of LF4 have not been studied intensively so far. In this study, the effect of CuO addition to the LF4 was investigated. The sample showed a tetragonal phase at room temperature and also a second phase with low melt point. The Cu2 + can replace both A-site and B-site because of its radii. The mechanical quality factor (Qm) increased from 26 to 137 as the CuO increased.
Ferroelectrics 10/2007; 358(1):153-160. · 0.39 Impact Factor
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ABSTRACT: Recently, it was reported that the alkaline niobate-based (K,Na,Li)(Nb,Ta,Sb)O3 (LF4) perovskite ceramics showed excellent piezoelectric properties and have been regarded as a new candidate of lead-free piezoelectric materials. However, the effects of additives on the piezoelectric property of LF4 have not been studied intensively so far. In this study, the effect of CuO addition to the LF4 was investigated. The sample showed a tetragonal phase at room temperature and also a second phase with low melt point. With 0.05 wt% CuO added, the Cu2+ firstly incorporated into the A site, while higher amounts of Cu2+ substituted B-site ions. The CuO-doping changed the LF4 to “hard” piezoelectric ceramics with improvement of mechanical quality factor from 26 to 137 but the piezoelectric d31 constant and the electromechanical coupling constant reduced drastically at the same time.
Journal of the American Ceramic Society 06/2007; 90(6):1787 - 1791. · 2.27 Impact Factor
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ABSTRACT: Antiangiogenic therapy is now considered to be one of promising approaches to treat various types of cancer. In this study, we examined the possibility of developing antiangiogenic cancer vaccine targeting vascular endothelial growth factor receptor 1 (VEGFR1) overexpressed on endothelial cells of newly formed vessels in the tumor.
Epitope-candidate peptides were predicted from the amino acid sequence of VEGFR1 based on their theoretical binding affinities to the corresponding HLAs. The A2/Kb transgenic mice, which express the alpha1 and alpha2 domains of human HLA-A*0201, were immunized with the epitope candidates to examine their effects. We also examined whether these peptides could induce human CTLs specific to the target cells in vitro.
The CTL responses in A2/Kb transgenic mice were induced with vaccination using identified epitope peptides restricted to HLA-A*0201. Peptide-specific CTL clones were also induced in vitro with these identified epitope peptides from peripheral blood mononuclear cells donated by healthy volunteers with HLA-A*0201. We established CTL clones in vitro from human peripheral blood mononuclear cells with HLA-A*2402 as well. These CTL clones were shown to have potent cytotoxicities in a HLA class I-restricted manner not only against peptide-pulsed target cells but also against target cells endogenously expressing VEGFR1. Furthermore, immunization of A2/Kb transgenic mice with identified epitope peptides restricted to HLA-A*0201 was associated with significant suppression of tumor-induced angiogenesis and tumor growth without showing apparent adverse effects.
These results strongly suggest that VEGFR1 is a promising target for antiangiogenic cancer vaccine and warrants further clinical development of this strategy.
Clinical Cancer Research 11/2006; 12(19):5841-9. · 7.74 Impact Factor
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ABSTRACT: Silver lithium niobate (Ag1-xLixNbO3,
0<x<0.1, ALN) single crystals were grown by a slow cooling method
without flux under oxygen flow. By optimizing growth conditions,
Ag0.9Li0.1NbO3 (ALN10) crystals with
sizes of ca. 30 mm cube were successfully grown in this study. The
crystal symmetries in the ALN system were investigated by high energy
X-ray diffraction (XRD) measurement, and finally, the space group of the
ALN10 crystals at 24 °C was assigned to a ferroelectric
Pc21b orthorhombic symmetry. The ALN10 crystals were oriented
using the back reflection Laue method along the [010]o and
[110]o directions, and the polarization-electric field (P-E)
hysteresis loop was measured along these two directions. The
Pr of [010]o oriented ALN10 crystals was 21
μC/cm2, while that of [110]o oriented ALN10
crystals was 15 μC/cm2. The Pr along the
[010]o direction was \sqrt{2} times larger than that along
the [110]o direction, confirming that the [010]o
direction is the polar direction. Moreover, these piezoelectric
properties were measured using the 31 resonators of the ALN10 crystals
as a function of crystallographic orientation, i.e., [010]o
or [110]o.
Japanese Journal of Applied Physics 08/2006; 45:7389. · 1.06 Impact Factor
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ABSTRACT: Ba(Zr0.25Ti0.75)O3 (BZT) and (Ba0.6Sr0.4)TiO3 (BST) ceramics were prepared as typical samples of lead-free relaxors and ferroelectrics with the diffuse phase transition, respectively. A suitable measurement technique using microplanar electrode and electromagnetic field analysis was developed to measure the microwave dielectric properties for materials with high permittivity and high dielectric loss. Frequency dependence of complex permittivity of the two ceramics was measured up to 3 GHz as a function of temperature. The dielectric dispersion of both ceramics was well explained by the stretched exponential model of the decay function in dielectric relaxation. In BST, a phase transition was observed at the permittivity peak temperature in the results of x-ray diffraction analysis, specific heat measurement, and the analysis of dielectric relaxation. The relaxation frequency of dipole fluctuation in BST was much higher than that of BZT. This high relaxation frequency enables us to use BST for dielectrics with high permittivity and low loss factors in microwave region. The continuous change from normal ferroelectrics to relaxors in BaTiO3-based ceramics was discussed.
Journal of Applied Physics 07/2006; 100(2):024106-024106-6. · 2.17 Impact Factor
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ABSTRACT: A slurry method was used to determine the dielectric permittivity (ɛr) of BaTiO3 powders with different characteristics, such as tetragonality (c/a ratio), density, particle size, and specific surface area. The ɛr of powders highly depended on their characteristics. In order to extract the effect of each characteristic, a statistical analysis was carried out to represent the ɛr of powders with an empirical formula. A fairly good agreement was obtained between observed data and those estimated from the formula. The ɛr decreased with particle size because of the size effect of BaTiO3 and high tetragonality and density was essential to obtain high ɛr of powders.
Journal of the American Ceramic Society 03/2006; 89(4):1337 - 1341. · 2.27 Impact Factor
