Takuya Hoshina

Tokyo Institute of Technology

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Co-Authors

Takaaki Tsurumi

Tokyo Institute of Technology

219

Hiroaki Takeda

Saitama University

125

Hirofumi Kakemoto

University of Yamanashi

Satoshi Wada

University of Yamanashi

Hiroaki Yasuno

Tokyo Institute of Technology

Masatomo Yashima

Tokyo Institute of Technology

Sou Yasuhara

Tokyo Institute of Technology

Yoshihiro Kuroiwa

Hiroshima University

Manabu Hagiwara

Keio University

Takashi Teranishi

Okayama University

Cooperative Institutions

Tokyo Institute of Technology

350

Tokyo University of Science

199

Tohoku University

184

The University of Tokyo

154

Nagoya University

148

National Institute of Advanced Industrial Science and Technology

129

National Institute for Materials Science

112

Nihon University

Saitama University

American Ceramic Society

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Phase stability and ferroelectricity in HfO2–Y2O3 nanolaminate films

Journal of the Ceramic Society of Japan (2024)

T. Kitahara Sou Yasuhara Takuya Hoshina

HfO2-based ferroelectrics have attracted much attention as key materials for silicon process compatible ferroelectric memories. The ferroelectric phase of HfO2-based materials is a metastable orthorhombic phase whose potential for stabilization by chemical doping with various elements has been investigated. Recently, it was reported that a nanolaminate film composed of HfO2 and ZrO2 films have a ferroelectric phase. However, the stabilization mechanism of the ferroelectric phase is not completely understood. In this study, HfO2–Y2O3 nanolaminate films were fabricated by pulsed laser deposition (PLD) and investigated the ferroelectricity of HfO2–Y2O3 nanolaminate thin films. HfO2–Y2O3 nanolaminate films, where Y2O3 is a paraelectric material, provide greater internal stress compared to HfO2–ZrO2 nanolaminate films. The crystal structure of HfO2–Y2O3 nanolaminate films was evaluated by X-ray diffraction (XRD) and high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) measurements. The results of the HAADF-STEM observations revealed that the orthorhombic phase is stabilized by applying internal stress into HfO2 in the nanolaminate film with Y2O3. The ferroelectricity of HfO2–Y2O3 nanolaminate films was elucidated by carrying out piezoelectric response microscopy (PFM). The coercive electric field value shows a dependence on the thickness of each layer. We demonstrated the importance of the stress engineering in HfO2 ferroelectricity, as it serves not only to stabilize the ferroelectric properties but also to regulate the coercive field.

Orthorhombic crystal system

Pulsed Laser Deposition

10.2109/jcersj2.23206

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Growth and characterization of strontium-substituted Ca2Al2SiO7 piezoelectric single crystals

Journal of the Ceramic Society of Japan (2016)

Hiroaki Takeda Kyohei Yoshida Hiroki Okudera Kheirreddine Lebbou Takuya Hoshina

We report the effect of Sr substitution on the structural, electrical, and mechanical properties of Ca2Al2SiO7 (CAS) piezoelectric single crystals for high-temperature pressure sensors. Single crystals of Sr-substituted CAS (Sr-CAS) with a nominal chemical composition of CaSrAl2SiO7 were grown by using the Czochralski technique. The single-crystal X-ray structure analysis revealed that Sr atoms were placed in the Ca decahedral sites, which decreased the polyhedral distortion slightly. The piezoelectric modulus d′31 and electrical resistivity of Sr-CAS measured at 23°C were slightly lower than those of CAS, but still sufficient for the satisfactory performance of the produced sensors. The rupture strength of the Sr-CAS crystal was 230 MPa, 1.2 times higher than that of a CAS crystal. The obtained results suggest that Sr-CAS crystals can be candidate materials for high-temperature pressure sensors.

Crystal (programming language)

10.2109/jcersj2.16206

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Doping effect of Nb on ionic polarization of SrTiO3

Journal of the Ceramic Society of Japan (2019)

Junji Nishiyama Kazuki Kanehara Hiroaki Takeda Takaaki Tsurumi Takuya Hoshina

THz dielectric spectra of Nb-doped SrTiO3 single crystals were measured using the far-infrared spectroscopic ellipsometer to understand the doping effect of Nb on ionic polarization. The frequency of the Slater transverse optical (TO) mode increased with the doping amount of Nb, meaning the decrease in the ionic polarization by Nb doping. From the change in the Slater TO mode frequency, it was estimated that the ionic polarizability of 1% Nb-doped SrTiO3 was 10.4% lower than that of undoped SrTiO3. This result suggested that the intrinsic permittivity of Nb-doped SrTiO3 is lower than that of that of undoped SrTiO3. First principles calculations revealed that the Nb 4d-orbitals contributes to the covalency between B-site cations and O ions, however, the covalency is suppressed due to the electron carrier doping. The doped electrons causes the decrease in the long-range Coulomb force and the increase in short-range elastic force, and therefore the ionic polarizability is decreased by Nb doping.

Ellipsometry

10.2109/jcersj2.19031

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Citations (10)

Preparation of Barium Titanate Nanoparticles Using Nano-Sized Oxalate and Deposition of their Nanoparticle Dense Films

Key engineering materials (2007)

Satoshi Wada Michiyasu Nishiyama Aki Yazawa Takuya Hoshina Hirofumi Kakemoto

Barium titanate

Deposition

Barium

10.4028/www.scientific.net/kem.350.39

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Citations (3)

TAS1553, a novel class of RNR inhibitor, has robust antitumor activity in murine syngeneic tumor models as a single agent and in combination with anti-PD-1 checkpoint inhibitor

European Journal of Cancer (2020)

Hiroto Fukushima Tanaka Sayaka Y. Wakako Takuya Hoshina Ueda Hiroyuki

Ribonucleotide reductase

10.1016/s0959-8049(20)31232-6

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Deterioration of Luminescence Efficiency of ZnS Phosphors Due to Surface Oxidation by Thermal Decomposition of Ammonium Dichromate

Journal of The Electrochemical Society (1979)

K. Ohno Takuya Hoshina

Cathodoluminescence efficiency of phosphors are deteriorated when they are subjected to heat‐treatment with ammonium dichromate (ADC) as is the case in the manufacturing process of color picture tubes. Luminescence efficiency loss of and phosphors is related to formed on the phosphor particle surface by thermal decomposition of ADC. The loss is determined from a relation between observed efficiency and diffuse reflectance. Formation of 0.1 weight percent (w/o) of , for example, causes 12 and 6% of the efficiency loss for and , respectively, under the excitation of a 10 kV electron beam.

Cathodoluminescence

Quantum Efficiency

10.1149/1.2128837

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Citations (9)

Control of Mesoscopic Particle Structure in Barium Titanate Nanoparticles and their Dielectric Properties

Key engineering materials (2007)

Kayo Takizawa Takuya Hoshina Hirofumi Kakemoto Takaaki Tsurumi Yoshihiro Kuroiwa

Barium titanate (BaTiO3) fine particles were prepared using the 2-step thermal decomposition method of barium titanyl oxalate. At the 2nd step of this method, the intermediate compound (Ba2Ti2O5·CO3) was decomposed into BaTiO3 and CO2 under various degrees of vacuum pressure. As a result, the particle size of prepared BaTiO3 nanoparticles decreased with decreasing pressure. Moreover, the dielectric constants of these BaTiO3 nanoparticles were measured using the powder dielectric measurement method using slurry. The dielectric constant of BaTiO3 nanoparticles increased with decreasing pressure at the same particle size. It is considered that mesoscopic particle structure controlled by vacuum pressure is important for the dielectric properties of BaTiO3 nanoparticles.

Barium titanate

Mesoscopic physics

Particle (ecology)

Barium

10.4028/www.scientific.net/kem.350.59

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Citations (2)

Contents

Journal of the Ceramic Society of Japan (2014)

Hiroki Moriwake Yūki Ichikawa Yuuki Kitanaka Takeshi Oguchi Yuji Noguchi

10.2109/jcersj2.122.c6-1

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Possibility of ferroelectric bismuth and nitrogen co-doped barium titanate

Journal of the Ceramic Society of Japan (2020)

Takahiro Yamada Hiroaki Takeda Takaaki Tsurumi Takuya Hoshina

The possibility of bismuth (Bi) and nitrogen (N) co-doped barium titanate (BaTiO3) as a ferroelectric material was investigated by calculation and experiment. From first principles calculations, it was found that Bi and N co-doped BaTiO3 has a higher spontaneous polarization than undoped BaTiO3 since dopant Bi and N ions contribute to the enhancement of covalent interactions between cations and anions. Because it was revealed that the ferroelectricity of BaTiO3 can be improved by co-doping of Bi and N, we demonstrated the synthesis of (Ba,Bi)Ti(O,N)3. Single phase oxynitride (Ba,Bi)Ti(O,N)3 powder was fabricated by annealing (Ba,Bi)TiO3 in NH3 gas. The tetragonal distortion of (Ba,Bi)Ti(O,N)3 was smaller than that of BaTiO3, which may be due to A-site and O-site vacancies in the perovskite lattice introduced during NH3 annealing.

Barium titanate

Bismuth titanate

Tetragonal crystal system

Bismuth

Bismuth ferrite

10.2109/jcersj2.20020

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Citations (3)

Ultrawide range dielectric spectroscopy of BaTiO3-based perovskite dielectrics

Applied Physics Letters (2007)

Takaaki Tsurumi Jingze Li Takuya Hoshina Hirofumi Kakemoto M. Nakada

Ultrawide range dielectric spectra from the kilohertz to terahertz range of BaTiO3 (BT), Ba(Zr0.25Ti0.75)O3 (BZT), (Ba0.6Sr0.4)TiO3 (BST), and SrTiO3 ceramics were presented by analyzing dielectric permittivity and IR reflectivity data. It was found that the permittivity of the ST was determined only by the ionic polarization while that of the BT was determined by the ionic polarization as well as the dipole polarization due to the domain contribution. The high permittivity of the BZT ceramics was attributed to the dipole polarization of polar nanoregions in the relaxors. The dipole and ionic polarizations overlapped in the BST.

10.1063/1.2804570

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Citations (126)