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Jiro Abe,Masafumi Kobune,Tetsuo Yazawa 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
High-density (Bi0:5Na0:5TiO3)0:94(BaTiO3)0:06 (BNBT-6) ceramics were fabricated under varying oxygen partial pressure conditions to develop useful lead-free piezoelectric materials with high mechanical quality factors (Qm). In uence of oxygen partial pressure-controlled sintering on physical properties of BNBT-6 ceramics was investigated. A liquid phase occurred in the sample sintered under logP(O2) = 3.50 atm because part of the Bi, a highly volatile element, evaporated from the sample surface during sintering. The mechanical quality factor, Qm, for the radial vibration mode exhibited a maximum (= 270) at logP(O2) = 3.50 atm that was 1.4 times as large as that of the sample sintered at logP(O2) = 0.12 atm. The temperature coecients of resonant and antiresonant frequencies (TCFfr1 and TCFfa1) of the BNBT-6 sample sintered under logP(O2) = 3.50 atm were almost constant: TCFfr1 = 465 ppm/C for the fundamental resonant frequency and TCFfa1 = 381 ppm/C for the fundamental antiresonant frequency. The current technology produces a substantial improvement in Qm characteristics without lowering other piezoelectric parameters, such as relative permittivity, "r, and electromechanical coupling factors, kp and kt, and can be expected to extend the selectivity of electrode materials used in multilayer ceramic actuators.
Jiro Abe,Hiroshi Masumoto,Kazuya Kitada,Masafumi Kobune,Takashi Goto,Tetsuo Yazawa 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
High-density (1.x)(Na0.5K0.5)NbO3-xLiTaO3 [(1.x)NKN.xLT] ceramics with x = 0 . 0.2 were successfully fabricated by spark-plasma sintering (SPS). The effect of SPS on the microstructure and the piezoelectric properties of the fabricated NKN-LT ceramics are discussed and compared with those of the same NKN-LT ceramics prepared by conventional mixed-oxide ceramic processing. The morphotropic phase boundary (MPB) between the orthorhombic and tetragonal phases for the NKN-LT series was found to be in the vicinity of x = 0.06 . 0.08. The MPB was shifted to the slightly LT-rich side of that previously reported by excess addition of 2.5 mol% K2CO3. The dielectric, ferroelectric and piezoelectric properties of the NKN-LT ceramics fabricated by using the SPS process were excellent compared to those for the conventionally prepared sample. The values of "T 33/"0, kp and Pr were 1.9, 1.4 and 2.3 times larger than the values for the conventionally prepared sample, respectively. These improvements in the ferroelectric and piezoelectric properties of the present ceramics are shown to originate from both the slight excess addition of K2CO3 and the particle orientation imparted by SPS.
Toru Yamaji,Hideto Tada,Koji Fukushima,Msafumi Kobune,Tetsuo Yazawa 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Bismuth lanthanum titanate (BLT) films with compositions of (1-x)Bi3.25La0.75Ti3O12 + xBi2O3, where x = 0.28 . 0.36, were successfully deposited on Pt(111)/SiO2/Si(100) substrates by rf-magnetron sputtering using a powder target. All the BLT films were confirmed to have a single-phase bismuth-layer perovskite structure without the presence of a secondary phase. The x = 0.28 and 0.30 BLT films exhibited rounded grain morphologies with an average grain size of approximately 320 nm. On the other hand, BLT films with excess Bi2O3 of x 0.32 had significantly enhanced grain growth, exhibiting oval grain morphologies with an average grain size of approximately 500 nm × 200 nm. From the results for the J . E characteristics, the x = 0.30 BLT films showed the highest electrical insulation. The x = 0.30 BLT film also showed the best hysteresis loop shape with a remanent polarization of 2Pr = 31 μC/cm2 and a coercive field of 2Ec = 170 kV/cm. Measurements of the fatigue characteristics showed that all the samples exhibited nearly fatigue-free behavior that resisted degradation even after 1 × 1010 cycles.C
Akihiro Tamura,Masafumi Kobune,Kazuki Imagawa,Hisashi Oshima,Yusuke Daiko,Atsushi Mineshige,Tetsuo Yazawa,Hiroshi Nishioka,Hironori Fujisawa,Masaru Shimizu,Hideshi Yamaguchi,Koichiro Honda 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
3.0-mm-thick a- and b-axis-oriented (Bi_(3.25)Nd_(0.75))Ti_3O_(12) (BNT-0.75) films were fabricated on conductive Nb:TiO_2(101) (Nb = 0, 0.048, 0.46, 0.79 mass%) single crystal substrates by high-temperature sputtering. A BNT films grown on undoped TiO_2 substrates have no orientation, whereas BNT films deposited on Nb:TiO_2 substrates with 0.46-0.79 mass% Nb show strong (h00/0k0) diffractions and grow with a heteroepitaxial relationship to the underlying Nb:TiO_2 substrates. The BNT-0.75 film deposited on Nb:TiO_2(101) substrate with 0.79 mass% Nb was indicated the peculiar shape of approximately 100-150-nm-thick nanoplates. We speculate that the driving force for producing a plate-like structure for BNT films is attributed to the large anisotropy of linear expansion coefficients for Bi_4Ti_3O12, and the comparatively small lattice matching between Nb:TiO_2 substrate and BNT film.
Masafumi Kobune,Hisashi Oshima,Akihiro Tamura,Kazuki Imagawa,Yusuke Daiko,Atsushi Mineshige,Tetsuo Yazawa,Hitoshi Morioka,Keisuke Saito,Hideshi Yamaguchi,Koichiro Honda 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
a- and b-axis-oriented (Bi_(3.25)Nd_(0.75))Ti_3O_(12) films, 3.0 mm thick, were fabricated on conductive IrO_2(101)/Al_2O_3(012) and Nb:TiO_2(101) [Nb = 0, 0.05 and 0.79 mass%] substrates by high-temperature sputtering. A BNT film grown on an IrO_2(101)/Al_2O_3(012) substrate had a low crystallinity (2.83˚), a low degree of a- and b-axis orientations [a_((h00/0k0)) = 49.2%] and a dense microstructure that a- and b-axis-oriented crystals existed locally in the film, while a BNT film grown on Nb:TiO_2(101) substrate with 0.79 mass% Nb showed a high crystallinity (0.57˚), a high a_((h00/0k0)) (99.9%) and a porous microstructure that was comprised of many nanoplate-like crystals. It is shown that the BNT film grew with a heteroepitaxial relationship to the underlying Nb:TiO_2 substrate has a symmetric loop shape, with a remanent polarization (2P_r) of 29 mC/cm^2 and a coercive field (2E_c) of 297 kV/cm.
SEIGO ITO,TAKUROU N. MURAKAMI,SHAIK M. ZAKEERUDDIN,SUSUMU KAYAMA,MICHAEL GR€ ATZEL,Tetsuo Yazawa,MASAO MIZUNO 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2014 NANO Vol.9 No.5
Di®erent-sized nanocrystalline-TiO 2 particles have been used for the optimization of photovoltaice®ects of dye-sensitized solar cells (DSCs) using an ionic-liquid (IL) electrolyte. Ru dye (Z907)was used for the IL-DSC optimization. The TiO 2 nanoparticle sizes and the thickness of nano-crystalline-TiO 2 electrodes ranged from 13 nm to 81 nm and 2 ? m to 23 ? m, respectively. Theparticle size of the nanocrystalline TiO 2 ¯lm greatly a®ected the photovoltaic characteristics,particularly for the IL electrolyte due to limitation of the photocurrent by I?/I?3-di®usion. Theoptimized electrode for IL-DSC had a 15 ? m thickness using a 27 nm diameter of nanocrystalline-TiO 2 particles. In order to characterize the e®ect of the TiO 2 particle size on the photovoltaice®ects of IL-DSCs, a scanning electron micrograph (surface and cross section of nanoparticles),BET speci¯c surface area analysis, pore-size distribution analysis, photocurrent transient measurements, haze spectroscopy, photovoltaic measurements, incident-photon-to-currentconversion e±ciency spectroscopy and impedance measurement have been used.
Hideto Tada,Masafumi Kobune,Koji Fukushima,Hisashi Oshima,Daisuke Horit,Akihiro Tamura,Yusuke Daiko,Atsushi Mineshige,Tetsuo Yazawa,Hironori Fujisawa,Masaru Shimizu,Hideshi Yamaguchi,Koichiro Honda 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
The structural characteristics, the mechanism of crystal growth, and the ferroelectric properties of partially Sm-substituted perovskite bismuth-samarium-nickel-titanate [(Bi1−xSmx)(Ni0.5Ti0.5)- O3; BSNT, x = 0− 0.9] thin films deposited on Pt(100)/MgO(100) substrates by rf sputtering have been investigated using X-ray diffraction, transmission electron microscope, and polarization - electric field hysteresis loop measurements. The fabricated BSNT samples with x≥0.6 were confirmed to have a single-phase perovskite structure. Of the four samples (x = 0.6 0.7, 0.8, and 0.9) with a single-phase perovskite structure, the c-axis-oriented epitaxial BSNT film with x = 0.9 exhibited the best hysteresis loop, with a remanent polarization of 2 μC/cm2 and a coercive field of 100 kV/cm. The structural characteristics, the mechanism of crystal growth, and the ferroelectric properties of partially Sm-substituted perovskite bismuth-samarium-nickel-titanate [(Bi1−xSmx)(Ni0.5Ti0.5)- O3; BSNT, x = 0− 0.9] thin films deposited on Pt(100)/MgO(100) substrates by rf sputtering have been investigated using X-ray diffraction, transmission electron microscope, and polarization - electric field hysteresis loop measurements. The fabricated BSNT samples with x≥0.6 were confirmed to have a single-phase perovskite structure. Of the four samples (x = 0.6 0.7, 0.8, and 0.9) with a single-phase perovskite structure, the c-axis-oriented epitaxial BSNT film with x = 0.9 exhibited the best hysteresis loop, with a remanent polarization of 2 μC/cm2 and a coercive field of 100 kV/cm.