Papers by Author: Masaru Miyayama

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Authors: Atsushi Kitamura, Choul Woo Lee, Yuji Noguchi, Masaru Miyayama
Authors: Hiroaki Onozuka, Yuuki Kitanaka, Yuji Noguchi, Masaru Miyayama
Abstract: A single crystal of ferroelectric 0.88(Bi,Na)TiO30.12BaTiO3 (BNTBT) solid solution with tetragonal P4mm structure was grown by the top-seeded solution growth (TSSG) method at a high oxygen pressure (PO2) of 0.9 MPa. The crystals grown by the high-PO2 TSSG method exhibited a large remanent polarization (Pr) of 54 μC/cm2, which leads to a spontaneous polarization of 54 μC/cm2. The large Pr compared with that of crystals grown at PO2 = 0.1 MPa is suggested to originate from a low oxygen vacancy concentration for the crystals grown at a higher PO2. The high-PO2 TSSG method was demonstrated to be effective for obtaining BNTBT crystals with superior polarization and piezoelectric properties.
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.
Authors: Akifumi Morishita, Yuuki Kitanaka, Makoto Izumi, Yuji Noguchi, Masaru Miyayama
Abstract: Single crystals of x (Bi0.5K0.5)TiO3-(1-x)(Bi0.5Na0.5)TiO3 (BKT-BNT) solid solution were grown by a flux method, and their ferroelectric properties were investigated along [100]cubic (the cubic notation). While the flux growth soaked at 1250 °C led to the crystals with a composition of x less than 0.14, the crystals with x of 0.45 were obtained by decreasing soaking temperature to 1150 °C. The crystals of BKT-BNT (x = 0.45) exhibited a relatively large remanent polarization of 39  C/cm2 and a low coercive field of 23 kV/cm.
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.
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.
Authors: Ayuko Matsunaga, Yuuki Kitanaka, Ryotaro Inoue, Yuji Noguchi, Masaru Miyayama, Kenji Itaka
Abstract: High-quality La0.84Sr0.16Ga0.26Mg0.74O3-δ (LSGM) epitaxial thin films were successfully grown on (100)-SrTiO3 (STO) substrates at a temperature of 800 °C by a pulsed laser deposition (PLD) method with KrF excimer laser pulses at an ozone pressure of 1.3 × 103 Pa. X-ray diffraction rocking curve measurements showed that the LSGM films had a full-width at half-maximum (FWHM) value of 0.11 °for out-of-plane 002 reflection, which was smaller than that reported for LaGaO3 films grown by atomic layer deposition methods (0.18 o). The reciprocal spaces mapping of 103 refraction showed that the LSGM films had a slightly larger lattice parameter a (out-of-plane) of 0.393 nm than a// (in-plane) of 0.391 nm.
Authors: Takaaki Fukushima, Shinya Suzuki, Masaru Miyayama
Abstract: Lithium-ion conducting properties were investigated for a layered perovskite oxide Li2SrTa2O7 (LST) and defect-controlled LST, synthesized via solid state reactions. The ionic conductivities of A-site solid solutions Li2[Sr-(La2/3□1/3)-(La1/2Li1/2)]Ta2O7 (□ denotes vacancy.) suggested that lithium ions migrate in the Li-layer. The conductivity of Li-deficient (Li2-z□z)(LazSr1-z)Ta2O7 increased dramatically from 4.2 × 10-6 S cm-1 (z = 0, LST) to 1.6 × 10-3 S cm-1 (z = 0.2) at 400°C with increasing Li-vacancy concentration. This result obviously indicates that the conductivity of LST originate from the Li migration through vacancies in the Li-layer.
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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