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Domain Wall Engineering in Lead-free Piezoelectric Materials
S. Wada 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
Grain-oriented barium titanate (BaTiO3) ceramics were prepared by using a templated grain growth (TGG) method with [110]-oriented BaTiO3 platelike particles as a template and hydrothermal BaTiO3 spherical particles with different particle sizes as a matrix. The degree of orientation along the [110] direction, F110 was measured from the X-ray diffraction (XRD) pattern by using the Lotgering method. To obtain both a high density and a high F110, we optimized the preparation conditions as functions of the matrix particle size, the volume fraction of the template to the matrix, and the sintering temperature. BaTiO3 grain-oriented ceramics with a high density of more than 96% were successfully prepared, despite various F110 values from 0 to 98%. Scanning electron microscopy (SEM) revealed that the average grain sizes were always approximately 75 μm, despite various F110 values, and that there were no anisotropic microstructures. These grainoriented BaTiO3 ceramics were poled at 100℃ and their piezoelectric properties (d31 and d33) were measured. The d31 values were almost constant at −50 pC/N, despite various F110 values, while the d331 values increased with increasing F110 values, and at around an F110 of 85%, d33 reached a maximum of 788 pC/N. Grain-oriented barium titanate (BaTiO3) ceramics were prepared by using a templated grain growth (TGG) method with [110]-oriented BaTiO3 platelike particles as a template and hydrothermal BaTiO3 spherical particles with different particle sizes as a matrix. The degree of orientation along the [110] direction, F110 was measured from the X-ray diffraction (XRD) pattern by using the Lotgering method. To obtain both a high density and a high F110, we optimized the preparation conditions as functions of the matrix particle size, the volume fraction of the template to the matrix, and the sintering temperature. BaTiO3 grain-oriented ceramics with a high density of more than 96% were successfully prepared, despite various F110 values from 0 to 98%. Scanning electron microscopy (SEM) revealed that the average grain sizes were always approximately 75 μm, despite various F110 values, and that there were no anisotropic microstructures. These grainoriented BaTiO3 ceramics were poled at 100℃ and their piezoelectric properties (d31 and d33) were measured. The d31 values were almost constant at −50 pC/N, despite various F110 values, while the d331 values increased with increasing F110 values, and at around an F110 of 85%, d33 reached a maximum of 788 pC/N.
Piezoelectric Properties of Potassium Niobate Single Crystals by Domain Engineering
S. Wada,H. Kumagai,H. Kakemoto,K. Muraoka,T. Tsurumi 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
Potassium niobate (KNbO3) single crystals were grown by a TSSG method. At rst, the electric eld was applied along the [001]c (cubic notation system) direction of KNbO3 crystals to induce the engineered domain congurations into KNbO3 crystals. Prior to domain engineering, the piezoelectric properties of [001]c-oriented KNbO3 single-domain crystals were measured. These measurement values were completely consistent with the calculated apparent d31 and d32. Finally, the engineered domain congurations were induced into KNbO3 crystals. As a result, piezoelectric properties increased with decreasing domain sizes of the engineered domain conguration. However, the symmetry of the KNbO3 crystals was mm2, and there were four kinds of domain structures such as 90,180, 60 and 120 domains. Thus, the engineered domain structure induced in this study was very complicated, and the piezoelectric properties were also ependent on domain pattern and kinds of domain walls.
Size Dependence of Dielectric Properties for nm-sized Barium Titanate Crystallites and Its Origin
S. Wada,H. Yasuno,H. Kakemoto,M. Yashima,S.-M. Nam,T. Tsurumi,T. Hoshina 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
Barium titanate (BaTiO3) crystallites with various particle sizes from 17 to 1,000 nm were prepared by the modiffed 2-step thermal decomposition method. Investigation of impurities in these particles by using both TG-DTA and FT-IR measurements revealed that no impurity was detected in the BaTiO3 lattice, while hydroxyl and carbonate groups were detected only on the surface. Moreover, their relative densities were always above 99 %.The dielectric constants of these powders were measured by using slurries by a modied powder dielectric-measurement method. As a result, the dielectric constant of BaTiO3 particles with a size of around 140 nm exhibited a maximum of around 5,000. By using a synchrotron-radiation X-ray powder experiment, the crystal structure of the BaTiO3 particles with sizes below 100 nm was investigated. As a result, in the BaTiO3 particles with sizes over 40 nm, it was conrmed that their crystal structure was assigned to 4 mm. In the particle size with a maximum dielectric constant of 5,000, its c=a ratio was smaller than 1.011. Finally, to explain the origin of the high dielectric constant, a model related to \superparaelectric behavior" was proposed.
Terahertz Time-Domain Spectroscopic Study of Ferroelectrics
M. Wada Takeda,S. Kojima,S. Nihizawa 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
A new compact instrument of terahertz time-domain spectrometry (THz-TDS) has been developed to expand the THz-TDS adaptation for far-infrared quantitative measurements on functional materials. THz-TDS enables us to measure simultaneously the spectral amplitude and phase shift in the far-infrared region between 1 and 100 cm..1 so that the real and imaginary parts of complex dielectric function can be estimated independently without the Kramers-Kronig analysis. The details of the new compact instrument of THz-TDS are introduced, and the complex dielectric function and the phonon-polariton dispersion relation of ferroelectric Li2Ge7O15 at 295 K are estimated and they are elucidated in terms of the Kurosawa formula.E?
The North Ecliptic Pole Wide survey of AKARI: a near- and mid-infrared source catalog
Kim, S. J.,Lee, H. M.,Matsuhara, H.,Wada, T.,Oyabu, S.,Im, M.,Jeon, Y.,Kang, E.,Ko, J.,Lee, M. G.,Takagi, T.,Pearson, C.,White, G. J.,Jeong, W.-S.,Serjeant, S.,Nakagawa, T.,Ohyama, Y.,Goto, T.,Takeuch EDP Sciences 2012 Astronomy and astrophysics Vol.548 No.-
OVERVIEW OF THE NORTH ECLIPTIC POLE DEEP MULTI-WAVELENGTH SURVEY (NEP-DEEP)
Matsuhara, H.,Wada, T.,Takagi, T.,Nakagawa, T.,Murata, K.,Churei, S.,Goto, T.,Oyabu, S.,Takeuchi, T.T.,Ohyama, Y.,Miyaji, T.,Krumpe, M.,Lee, H.M.,Im, M.,Serjeant, S.,Peason, C.P.,White, G.,Malkan, M.A The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
An overview of the North Ecliptic Pole (NEP) deep multi-wavelength survey covering from X-ray to radio wavelengths is presented. The main science objective of this multi-wavelength project is to unveil the star-formation and AGN activities obscured by dust in the violent epoch of the Universe (z=0.5-2), when the star formation and black-hole evolution activities were much stronger than the present. The NEP deep survey with AKARI/IRC consists of two survey projects: shallow wide (8.2 sq. deg, NEP-Wide) and the deep one (0.6 sq. deg, NEP-Deep). The NEP-Deep provides us with a $15{\mu}m$ or $18{\mu}m$ selected sample of several thousands of galaxies, the largest sample ever made at these wavelengths. A continuous filter coverage at mid-IR wavelengths (7, 9, 11, 15, 18, and $24{\mu}m$) is unique and vital to diagnose the contribution from starbursts and AGNs in the galaxies at the violent epoch. The recent updates of the ancillary data are also provided: optical/near-IR magnitudes (Subaru, CFHT), X-ray (Chandra), FUV/NUV (GALEX), radio (WSRT, GMRT), optical spectra (Keck/DEIMOS etc.), Subaru/FMOS, Herschel/SPIRE, and JCMT/SCUBA-2.
NUCLEAR STAR-FORMING RING OF THE MILKY WAY: SIMULATIONS
Kim, Sungsoo S.,Saitoh, Takayuki R.,Jeon, Myoungwon,Figer, Donald F.,Merritt, David,Wada, Keiichi IOP Publishing 2011 ASTROPHYSICAL JOURNAL LETTERS - Vol.735 No.1
<P>We present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that is modeled with a three-dimensional bar potential. Our simulations consider realistic gas cooling and heating, star formation, and supernova feedback. A ring of dense gas clouds forms as a result of X-1-X-2 orbit transfer, and our potential model results in a ring radius of similar to 200 pc, which coincides with the extraordinary reservoir of dense molecular clouds in the inner bulge, the Central Molecular Zone (CMZ). The gas clouds accumulated in the CMZ can reach high enough densities to form stars, and with an appropriate choice of simulation parameters, we successfully reproduce the observed gas mass and the star formation rate (SFR) in the CMZ, similar to 2 x 10(7) M-circle dot and similar to 0.1 M-circle dot yr(-1). Star formation in our simulations takes place mostly in the outermost X-2 orbits, and the SFR per unit surface area outside the CMZ is much lower. These facts suggest that the inner Galactic bulge may harbor a mild version of the nuclear star-forming rings seen in some external disk galaxies. Furthermore, from the relatively small size of the Milky Way's nuclear bulge, which is thought to be a result of sustained star formation in the CMZ, we infer that the Galactic inner bulge probably had a shallower density profile or stronger bar elongation in the past.</P>