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296 results on '"Higuchi, Mikio"'

26. Ferroelectric BaTaO2N Crystals Grown in a BaCN2 Flux

Author

Hosono, Akira, Masubuchi, Yuji, Yasui, Shintaro, Takesada, Masaki, Endo, Takashi, Higuchi, Mikio, Itoh, Mitsuru, and Kikkawa, Shinichi

Subjects
Oxynitride, Ferroelectricity, Crystal growth, Metal carbodiimide, Perovskite
Abstract

Perovskite-type oxynitride BaTaO2N has been attracting attention for its large dielectric constant, which is almost independent of the temperature by measurements on its ceramics. Its dielectric characteristics are attributed to polar nanoregions (PNRs) in the average cubic crystal structure. Polarization saturation to produce a butterfly-like piezoresponse force microscopy (PFM) signal was observed on BaTaO2N crystals in the present study. Reddish crystallites of BaTaO2N of up to 3.1 mu m in size were grown using a BaCN2 flux. Grain growth proceeded through the formation of a Ruddlesden-Popper-type oxynitride from the reaction between BaTaO2N powder and molten BaCN2. Their electrical property was studied using PFM with special care because of the small size of the crystals. They were found to be much more highly insulating than its ceramics. Ferroelectricity with complete phase inversion was observed on an oxynitride perovskite crystal for the first time. A large coercivity of 50-60 V was observed in the measurement. Such ferroelectricity is ascribed to the PNRs induced by the polar linkages between cis-type TaO4N2 octahedra.

Published
2019

32. Synthesis of submicron-sized NiPS3 particles and electrochemical properties as active materials in all-solid-state lithium batteries

Author

Suto, Yusaku, Fujii, Yuta, Miura, Akira, Rosero-Navarro, Nataly Carolina, Higuchi, Mikio, and Tadanaga, Kiyoharu

Subjects
All-solid-state lithium secondary battery, Sulfide
Abstract

Submicron-sized NiPS3 particles were synthesized by heating fine Ni powder ( Li4P2S6 + 2Ni), and this irreversible reaction would reduce the capacity of the cathode. The XANES spectra suggested the oxidation/reduction of Ni during discharge-charge cycles, but the change in the spectra during the cycles was considerably small if one assumed the oxidation/reduction of Ni2+/Ni-0. (C) 2018 The Ceramic Society of Japan. All rights reserved.

Published
2018

33. Red-emission over a wide range of wavelengths at various temperatures from tetragonal BaCN2:Eu2+

Author

Masubuchi, Yuji, Nishitani, Sayaka, Hosono, Akira, Kitagawa, Yuuki, Ueda, Jumpei, Tanabe, Setsuhisa, Yamane, Hisanori, Higuchi, Mikio, and Kikkawa, Shinichi

Abstract

A new polymorph of BaCN2 was obtained via a simple nitridation reaction of BaCO3 under an NH3 flow at 900 1C. The product was analyzed via single crystal X-ray diffraction and infrared spectroscopy, and it was found to have a tetragonal I4/mcm crystal structure (space group no. 140) with a = 0.60249(4) nm and c = 0.71924(5) nm. In this structure, each Ba2+ cation is situated in the square antiprism of N atoms of NCN(2-)anionic groups. Eu2+ doped BaCN2 can be excited by irradiation of blue and green light (from 400 to 550 nm), and it generates an intense red emission peak at 660 nm with a quantum efficiency of 42% in response to 465 nm excitation at room temperature. The peak emission wavelength varies over an extremely wide range of temperature, from 640 nm at 500 K to 680 nm at 80 K, and this red-shift with decreasing temperature is attributed to a unit cell shrinkage that results in significant crystal field splitting of the 5d energy levels of the Eu2+ ions.

Published
2018

37. B2O3 as a new sintering additive for perovskite-type SrTaO2N oxynitride ceramics.

Author

Masubuchi, Yuji, Miyamoto, Daiki, and Higuchi, Mikio

Subjects
SILICON nitride, SINTERING, STEREOLITHOGRAPHY, TRANSMISSION electron microscopy, CERAMICS
Abstract

The development of new sintering processes for ferroelectric perovskite-type oxynitrides is a crucial aspect of realizing practical applications of these materials. The present study examined the sintering of SrTaO2N with B2O3, a new additive. The addition of B2O3 was found to significantly lower the sintering temperature. In addition, observations by transmission electron microscopy showed that the B2O3 combined with SrO to form an amorphous structure that enhances the diffusion of elements during high-temperature sintering. [ABSTRACT FROM AUTHOR]

Published
2022
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47. Scintillation characteristics of Ce : [Gd.sub.2][Si.sub.2][O.sub.7] (Ce 2.5-30 mol%) single crystals prepared by the floating zone method

Author

Kawamura, Sohan, Kaneko, Junichi H., Higuchi, Mikio, Haruna, Jun, Saeki, Shohei, Fujita, Fumiyuki, Homma, Akira, Nishiyama, Shusuke, Ueda, Shunsuke, Kurashige, Kazuhisa, Ishibashi, Hiroyuki, and Furusaka, Michihiro

Subjects
Crystals -- Properties, Gamma rays -- Properties, Gadolinium -- Properties, Diffraction patterns -- Evaluation, Business, Electronics, Electronics and electrical industries
Abstract

Cerium-doped gadolinium pyrosilicate single crystals Ce : [Gd.sub.2][Si.sub.2][O.sub.7] (Ce:GPS) with various Ce concentrations of 2.5-30 mol% with respect to the total rare-earth sites were prepared by the floating zone method. Their scintillation performances were investigated under irradiation of gamma rays of [sup.137]Cs. The Ce concentration dependence of scintillation characteristics and high-performance scintillation characteristics were obtained: 3-6 times greater light output than that of BGO single crystals, rapid decay, and good energy resolutions of 5.1-8.4%. Furthermore, X-ray diffraction patterns of Ce:GPS revealed Ce concentration dependence of the crystal structure of Ce:GPS. Index Terms--Crystal growth, gadolinium compounds, [Gd.sub.2][Si.sub.2][O.sub.7], neutron detectors, radiation detectors, scintillators.

Published
2009

48. Low temperature synthesis of barium oxynitridosilicates using BaCN2 and SiO2.

Author

Masubuchi, Yuji, Sada, Naoki, Kawahara, Yoshiteru, Arai, Kenji, Motohashi, Teruki, and Higuchi, Mikio

Subjects
LOW temperatures, BARIUM, MASS spectrometry, GAS analysis, GAS chromatography
Abstract

Barium oxynitridosilicates, Ba3Si6O12N2 and Ba3Si6O9N4, were obtained from a mixture of BaCN2 and SiO2 at 800 °C, which is several hundred degrees lower than the temperature required in solid state reactions using BaCO3, SiO2 and Si3N4. The low-temperature formation mechanism was investigated by thermogravimetry analysis in conjunction with gas chromatography and mass spectroscopy. The phase ratio between the oxynitridosilicates was controlled by tuning the reaction temperature, duration, and atmosphere. Almost single-phase Ba3Si6O12N2 was obtained by reaction at 800 °C for 15 h under a N2 atmosphere, but the product changed to Ba3Si6O9N4 after 50 h at 800 °C or by heating at 950 °C for 15 h. The photoluminescence properties of Eu-doped products obtained at 800 °C using a mixture of BaCN2 : Eu and SiO2 were investigated. [ABSTRACT FROM AUTHOR]

Published
2021
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