Papers by Author: Yuji Noguchi

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Authors: Atsushi Kitamura, Choul Woo Lee, Yuji Noguchi, Masaru Miyayama
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Authors: Sho Yoshimura, Yuji Noguchi, Masaru Miyayama
Abstract: Large Bi0.5Na0.5TiO3 (BNT) single crystals with 10 mm × 10 mm × 5 mm were successfully grown by a flux method using BNT powder and the mixed flux composed of Bi2O3 and NaF. Dielectric measurements show a dielectric-permittivity peak at 310°C, which is the result of the gradual phase transition from rhombohedral (R3c) to tetragonal (P4bm) structure. Electric-field induced strain measurements along [100]C reveal that the effective piezoelectric strain constant (d33 *) was estimated to be 130 pm/V in a multidomain state.
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Authors: Shunsuke Teranishi, Yuji Noguchi, Masaru Miyayama
Abstract: 0.999Bi0.5Na0.5TiO3-0.001BaTiO3 (BNT-0.1%BT) single crystals with a maximum size of 1×1×1 mm3 were successfully grown by a flux method using BNT-6%BT powder and Bi2O3 as a flux. The crystals showed a remanent polarization of 33 μC/cm2 and coercive electric field of 40 kV/cm along [100]Cubic. Electric-field induced strain measurements along [100]Cubic revealed an effective piezoelectric strain constant d33 * of 80 pm/V.
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Authors: Mariko Ikezaki, Yuji Noguchi, Keiichi Katayama, Masaru Miyayama
Abstract: Superlattice-structured Bi4Ti3O12- PbBi4Ti4O15 single crystals were grown, and their properties of polarization hysteresis and leakage current along the a axis were investigated. Oxidation annealing led to a marked increase in leakage current, while annealing in N2 atmosphere yielded a marked decrease in leakage current at room temperature. These results show that electron hole is the dominant carrier for the leakage current. A well-saturated polarization hysteresis with a remanent polarization of 41 μC/cm2 was observed, which is suggested to originate from the peculiar ferroelectric displacement of Bi in the Bi2O2 layers.
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Authors: Yoichi Kizaki, Yuji Noguchi, Masaru Miyayama
Abstract: Single crystals of K0.47Na0.53NbO3 (KNN) and Mn-substituted KNN (Mn-KNN, K0.53Na0.47Mn0.004Nb0.996Oy) were grown by a flux method, and the influence of lattice defects on the polarization and leakage current properties was investigated. As-grown KNN did not show an apparent polarization hysteresis loop due to its large leakage current (~10-3 A/cm2). The substitution of 0.4%-Mn at the Nb site and subsequent annealing under a moderate oxidative condition were effective in suppressing the leakage current of KNN crystals. 0.4%-Mn-KNN annealed at 1100°C in air exhibited a low leakage current (~10-8 A/cm2), a relatively large remanent polarization of 40 μC/cm2 and a coercive field of 12 kV/cm at 25°C. The oxidation of Mn and Nb ions during annealing in air is found to play an essential role in the low leakage current of Mn-KNN.
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Authors: Minoru Tamada, Yuji Noguchi, Masaru Miyayama
Abstract: Single crystals of PbTiO3 (PT) were grown by a self flux method, and effects of lattice defects on the leakage current properties were investigated. While PT crystals annealed in air at 700 oC showed a leakage current density of the order of 10-5 A/cm2, annealing under a high oxygen partial pressure of 35 MPa increased leakage current density to 10-4 A/cm2. The increase in leakage current by the oxidation treatment provides direct evidence that electron hole is a detrimental carrier for the leakage current property of PT at room temperature. The vacancies of Pb are suggested to act as an electron acceptor for generating electron holes.
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Authors: Yuuki Kitanaka, Yuji Noguchi, Masaru Miyayama
Abstract: Polarization switching and domain dynamics in unpoled and poled crystals of bismuth titanate by applying electric field along the crystallographic c axis were investigated through polarization measurements and domain observations by optical microscope and piezoelectric force microscope. Poled crystals showed a well-saturated polarization hysteresis with a remanent polarization of 4.4 μC/cm2 and a coercive field of 4.7 kV/cm. Domain observations reveal that lenticular domain acts as an initial nucleus during polarization switching. The sidewise motion of the lenticular-domain walls and resultant single domain state were easily established for the poled crystals, while the lenticular domains observed in unpoled crystals were clamped even though a high electric field was applied to them.
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Authors: Hidekazu Hara, Yuji Noguchi, Masaru Miyayama
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Authors: Yuji Noguchi, Masaru Miyayama
Abstract: Crystal structures of Bi4Ti3O12 ferroelectrics have been investigated by high-temperature neutron powder diffraction study. The ferroelectricity in Bi4Ti3O12 is shown to originate from the in-plane displacement of TiO6 octahedra with respect to heavy Bi ions, and that the off-center Ti displacement in the octahedra plays a minor role. Bond valence analysis shows that the underbonding of Bi with the adjacent oxide ions at the perovskite A site in high-temperature paraelectric state plays an essential role in the ferroelectric phase transition in the Bi4Ti3O12 system.
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