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134 results on '"Takesada, M."'

1. Calorimetric study of multiaxial fluctuations in ferroelectric BaTiO3 in nonpolar cubic phase

Author

Grabovsky, S. V., Shnaidshtein, I. V., Takesada, M., Onodera, A., and Strukov, B. A.

Subjects
Condensed Matter - Materials Science
Abstract

Precise specific heat of barium titanate single crystals of different quality has been measured with special attention to the temperature region above the ferroelectric phase transition. It is shown that excess specific heat of the multiaxial barium titanate in the paraelectric phase has a fluctuation nature and its temperature dependence is in accordance with the theoretical predictions of Levanyuk theory for multiaxial ferroelectrics. In this study the first observation of fluctuation contribution to the specific heat is presented.

Published
2013

3. Brillouin scattering study of ZnO.

Author

Azuhata, T., Takesada, M., Yagi, T., Shikanai, A., Chichibu, SF., Torii, K., Nakamura, A., Sota, T., Cantwell, G., Eason, D. B., and Litton, C. W.

Subjects
*SCATTERING (Physics), *ZINC oxide, *CRYSTALS, *ELASTICITY, *PHOTOELASTICITY
Abstract

Polarized Brillouin scattering measurements were carried out for a bulk ZnO single crystal. The whole set of elastic stiffness constants was determined to be c[SUB11]=19.0, c[SUB12]=11.0, c[SUB13]=9.0, c[SUB33]=19.6, c[SUB44]=3.9, and c[SUB66]=4.0 in units of 10[SUP11]dyn/cm[SUP2]. The relationships between photoelastic constants at wavelength of 514.5 nm were also obtained: p[SUB11], p[SUB13], p[SUB44], and p[SUB66]=1.8, 2.3, 0.50, and 0.38, respectively, relative to p[SUB12]. [ABSTRACT FROM AUTHOR]

Published
2003
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7. Monoclinic-orthorhombic transition in K_2ZnBr_4 and Rb_2ZnI_4

Author

Takesada, M. and Kojima, M.

Abstract

The first-order transition from the monoclinic α-phase to the orthorhombic β-phase in K_2ZnBr_4 and Rb_2ZnI_4 is investigated by X-ray diffraction. The structure of β-phase is confirmed to be isostructural with disordered β-K_2SO_4. Although structures of α and β-phases are different so much with each other, the transformation proceeds without cracking or deforming the crystal.

Published
1994

8. Structural aspects in A -site ordered perovskite CaCu 3 Ti 4 O 12 : Colossal dielectric behavior and Ca/Cu disordering.

Author

Hori, T., Takesada, M., and Onodera, A.

Subjects
*CRYSTAL structure, *PEROVSKITE, *CALCIUM compounds, *DIELECTRICS, *COPPER
Abstract

Precise analysis of crystal structure ofA-site ordered perovskite CaCu3Ti4O12was studied at 298, 517 and 785 K, where Ca/Cu disordering is taken into account. The ratio of Ca/Cu disordering is 11% at 785 K, which decreases to 1.7 % at 298 K with decreasing temperature. This Ca/Cu dynamical disordering produces meta-stable intermediate atomic configurations which force to have a polar structure for TiO6octahedra. This structural heterogeneity may induce an instantaneous dipolar fluctuations and results in a colossal dielectric response, while the average stable state is non-polar. [ABSTRACT FROM PUBLISHER]

Published
2017
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11. Perfect Softening of the Ferroelectric Mode in the Isotope-Exchanged Strontium Titanate of SrTi^18O3 Studied by Light Scattering

Author

Takesada, M., Itoh, M., Yagi, T., Takesada, M., Itoh, M., and Yagi, T.

Abstract

The Eu mode of the isotope-induced ferroelectric strontium titanate SrTi^18O3 shows a perfect softening at the ferroelectric phase transition temperature Tc, where the frequency of the underdamped mode approaches completely to zero within the instrumental resolution. The spectra of the Raman inactive soft Eu mode have been successfully observed owing to local symmetry breaking and by long-term accumulation of the spectral intensity with a high resolution technique. The mechanism of the phase transition is concluded to be an ideal displacive-type accompanied with perfect softening of the Slater-type polar Eu mode. The difference between the soft mode behavior of SrTi^16O3 and SrTi^18O3 indicates that the origin of the quantum paraelectric state of SrTi^16O3 lies in the quantum fluctuation of the oxide octahedron in the perovskite structure.

Published
2006

12. Isotope effect on the soft-mode dynamics of SrTiO3 studied by Raman scattering

Author

Taniguchi, H., Yagi, T., Takesada, M., Itoh, M., Taniguchi, H., Yagi, T., Takesada, M., and Itoh, M.

Abstract

he oxygen isotope effect on the soft-mode dynamics in quantum paraelectric SrTi(18Ox16O1-x)3 [STO18-x] is investigated by Raman scattering in terms of local symmetry breaking in the paraelectric phase. The exchange rates x of the 18O atoms are 0.23 [STO18-23] and 0.32 [STO18-32], which are less than the critical value xc(=0.33). In STO18-32, whose exchange rate is just below xc, the soft Eu mode shows hardening behavior in a low-temperature region indicating the onset of local ferroelectric order. On the other hand, the soft Eu mode in STO18-23 does not show any hardening behavior until 0 K. The enhancement of the inhomogeneity in the crystal by the exchange of 18O is concluded to play an essential role in the soft-mode dynamics of the quantum paraelectric and ferroelectric STO18-x. The relation between the soft-mode dynamics and quantum fluctuation is discussed.

Published
2005

33. Static and dynamic order of cooperative multi-electron transfer

Author

Luty, T, primary, Cailleau, H, additional, Koshihara, S, additional, Collet, E, additional, Takesada, M, additional, Lemée-Cailleau, M. H, additional, Cointe, M. Buron-Le, additional, Nagaosa, N, additional, Tokura, Y, additional, Zienkiewicz, E, additional, and Ouladdiaf, B, additional

Published
2002
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35. Specific Heat Study of Multiferroic LuFe 2 O 4 Single Crystal.

Author

Hasegawa, N., Mitsumura, T., Takesada, M., Onodera, A., Kano, J., and Ikeda, N.

Subjects
LUTETIUM compounds, SPECIFIC heat, MULTIFERROIC materials, SINGLE crystals, CALORIMETERS, PHASE transitions
Abstract

Precise measurements of specific heat were performed on high quality single crystals of multiferroic LuFe2O4by using anaccalorimeter. The thermal anomalies corresponding to four known phase transitions were observed at 220 K(Tg), 260 K (TN), 380 K (T3CO) and 590 K (T2CO). In addition to them, a new clear anomaly was detected at 305 K. No other distinct anomaly could be observed below 220 K down to 100 K. It is clarified that the temperature dependence of the order parameter associated with this new phase transition at 305 K is quite similar to those of spontaneous polarization reported previously by Ikedaet al. [ABSTRACT FROM PUBLISHER]

Published
2014
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40. Huge Dielectric Properties of CdCu3Ti4O12 with CCTO Structure.

Author

Sasaki, M., Tashiro, T., Abiko, K., Kamimura, Y., Takesada, M., and Onodera, A.

Subjects
CERAMICS, PEROVSKITE, DIELECTRIC measurements, DIELECTRICS, PHASE transitions, PHASE equilibrium, DISPERSION (Chemistry)
Abstract

The giant dielectric response in Cd-doped CaCu3Ti4O12 ceramics was studied over the temperature range from 40 K to 850 K. In all CaxCd1-xCu3Ti4O12 system, two broad dielectric dispersions around 150 K and 650 K and a dielectric anomaly at T1 were observed. The T1 decreases linearly with increasing Cd-molar ratio (x) from 733 K for CaCu3Ti4O12 to 632 K for CdCu3Ti4O12. CdCu3Ti4O12 exhibits ε ∼ 0.6 × 104 at room temperature and 1.4 × 104 at T1 (1 MHz). This evidence shows CdCu3Ti4O12 is still a member of high-dielectric materials in contrast to a previous work (ε ∼ 409 at 100 kHz). [ABSTRACT FROM AUTHOR]

Published
2011
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41. Dielectric Properties in CaCu3Ti4O12 Single Crystal at High Temperatures.

Author

Kawatani, K., Takesada, M., Fukunaga, M., Oda, M., Ido, M., and Onodera, A.

Subjects
*DIELECTRICS, *CRYSTAL growth, *HIGH temperatures, *PEROVSKITE, *POLYCRYSTALS, *PHASE transitions, *CRYSTAL grain boundaries, *TEMPERATURE effect
Abstract

High-temperature dielectric properties of perovskite-related CaCu3Ti4O12 single and polycrystalline samples were studied. Both samples show a very similar high dielectric response, while the value of single crystal is about two times as large as those of polycrystalline ceramic samples. The dielectric constant shows a shoulder-like round anomaly around 600 K with increasing temperature, and a dielectric anomaly at 726 K for the present single crystal (732 K for ceramic samples). The present evidence means that a structural phase transition occurs in CaCu3Ti4O12 at 726 K. The origin of high dielectric response is not related to an extrinsic one due to grains and grain boundary layers. [ABSTRACT FROM AUTHOR]

Published
2010
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42. Central Peak of Bismuth Layered Ferroelectrics Pb2Bi4Ti5O18 Studied by Brillouin Scattering.

Author

Takesada, M., Ueki, A., Hiramatsu, S., Kawatani, K., and Onodera, A.

Subjects
*BRILLOUIN scattering, *SPECTRUM analysis, *FABRY-Perot interferometers, *FERROELECTRIC crystals, *PHASE transitions
Abstract

Brillouin scattering spectra have been observed in ceramic sample of Bi-Layered Perovskites Pb2Bi4Ti5O18 using a Sandercock type tandem Fabry-Perot interferometer. A central peak was observed in the spectrum, which shows the anomalous increase of relaxation time with approaching to T1 = 450 K. The temperature dependences of intensity and width in the central peak spectrum show anomaly at T2 = 740 K in addition to T1. However, no anomalous behavior has been obtained at Tc = 583 K reported as a ferroelectric phase transition point with a dielectric measurement by E. C. Subbarao. [ABSTRACT FROM AUTHOR]

Published
2009
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44. Monoclinic-orthorhombic transition in K2ZnBr4 and Rb2ZnI4

Author

Mashiyama, H., Takesada, M., Kojima, M., and Kasano, H.

Abstract

The first-order transition from the monoclinic α-phase to the orthorhombic β-phase in K2ZnBr4 and Rb2ZnI4 is investigated by X-ray diffraction. The structure of β-phase is confirmed to be isostructural with disordered β-K2SO4. Although structures of α-and β-phases are different so much with each other, the transformation proceeds without cracking or deforming the crystal.

Published
1994
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