内田 寛

PZTを超える新規非鉛圧電体材料を探索するためには、その端成分である正方晶圧電体が重要であるが、これまでの研究はチタン酸バリウム[BaTiO₃]やチタン酸ビスマスカリウム[(Bi,K)TiO₃]等に限定されていた。本研究では、2006年に正方晶強誘電体であることが報告されたコバルト酸ビスマス[BiCoO₃]および亜鉛酸チタン酸ビスマス[Bi(Zn_1/2Ti_1/2)O₃]の2種類のビスマス正方晶強誘電体に注目した。これらのビスマス系正方晶強誘電体は、高温高圧を用いないと作製できないことから、これまで圧電性に着目した研究は未だ多くはない。本研究ではMOCVD法を用いて、BiCoO₃およびBi(Zn_1/2Ti_1/2)O₃を含有するエピタキシャル薄膜を作製した。得られた薄膜について、結晶構造解析と電気特性および圧電特性を調査し、従来の鉛系圧電体膜と比較検討を行うことで、新規圧電体材料の設計指針を検討した。

SrBi4Ti4O15 (SBTi) and CaBi4Ti4O15 (CBTi) dielectric films of Bismuth Layered Structure Dielectrics (BLSD) are prepared on Pt film for constructing stacked-type dielectric capacitors. Compared to perovskite barium titanate family of (Ba,Sr)TiO3 (BST) case, it is observed that the SBTi film keeps a low leakage of 10(-7) A/cm(2) at 250 kV/cm, which is smaller by an order of magnitude than the BST film, even with thinner thickness in the SBTi film. This indicates that the SBTi film is effective for applying to high permittivity capacitor with the barium perovskite oxide family.

Thin films of MBi4Ti4O15 (M = Ca and Sr) with preferential crystal orientation were fabricated using underneath perovskite layers on various substrates. One-axis BLSD films on (100)LaNiO3/(111)Pt/Ti/(100)Si and epitaxial BLSD films on (100)SrRuO3//(100)SrTiO3 were fabricated by chemical solution deposition (CSD). Dielectric constants of the CaBi4Ti4O15 and SrBi4Ti4O15 films on (100)LaNiO3/(111)Pt/Ti/(100)Si were approximately 250, while those on (100)SrRuO3//(100)SrTiO3 were 220, respectively. The temperature coefficients of capacitance (TCCs) of these films were below 10% in atmospheric temperature range between R.T. and 300 degrees C, which is significantly smaller than those of conventional (Ba,Sr)TiO3-based capacitors.

Bi-based perovskite-type oxide materials such as BiFeO3 (BFO) and the related compounds receive much attention and have been developed actively as important candidates for Pb-free ferroelectric / piezoelectric materials instead of toxic Pb-based perovskite oxide materials. Recently, many researches have been reported for thin films of BFO by various film-deposition techniques for actual application of semiconductive devices, microactuators, etc. In this report, we tried preferential crystal growth of BFO films on semiconductive silicon substrates using uniaxial-(100)-oriented LaNiO3 (LNO) buffer layer. BFO films were fabricated via chemical solution deposition (CSD) technique on platinized silicon wafer [(111)Pt/TiO2/(100)Si] and (100)LNO-coated platinized silicon [(100)LNO/(111)Pt/TiO2/(100)Si] substrates. XRD analysis indicated that the films fabricated on (111)Pt/TiO2/(100)Si substrate consisted of randomly-oriented BFO crystal with lower crystallinity and trace amount of the second Bi2Fe4O9 phase. On the other hand, the films on (100)LNO/(111)Pt/TiO2/ (100)Si consisted of uniaxial-(100)-oriented BFO crystal with higher crystallinity. The crystallization temperature these films were 450 and 400°C, respectively. These results suggest that the BFO crystal was grown epitaxially on uniaxial oriented (100)LNO plane which also had perovskite-type crystal structure. Consequently, (100)-oriented BFO films were prepared on Si substrate successfully using (100)LNO buffer layer. © Published under licence by IOP Publishing Ltd.

Perovskite oxides with higher phase transition temperature receive much attention as promising candidates which possess excellent and stable dielectric properties over wide temperature range. In the present research, dense ceramics of Ba-based perovskite oxides of Ba(Cu1/3Nb2/3)O3 (BCN) were fabricated by powder sintering. Mn-substituted BCN (Mn-BCN) ceramics were also fabricated for improving the insulating property of the BCN ceramics. Mn-BCN ceramics were fabricated by powder sintering using fine precursor powders derived from sol-gel solutions. The chemical composition of the precursors were Ba[(Cu1/3Nb2/3)1- yMny]O3 with Mn content of y 0-0.05. The cylindrical compacts of the powders were heat-treated at 1200-1350°C for 1-6 h for sintering. All of Mn-BCN ceramics consisted of perovskite-type crystal structure in tetragonal system at room temperature. The relative density of the pure and Mn-BCN ceramics sintered at 1300°C for 1 h were higher than 90%. The densities were degraded by firing at higher temperature and/or for longer time, owing to the thermal decomposition of the BCN crystalline phase. The Mn-substitution for BCN ceramics resulted in disappearing the dielectric relaxation and suppressing the leakage current conduction. © Published under licence by IOP Publishing Ltd.

Metal oxide electrode have been widely developed for high-performance electric device because they possess some attractive characteristic such as thermal/chemical stabilities and change compensation for oxygen vacancies in interconnected dielectric layers, etc., which is often hardly achieved by convention metal electrodes. As almost all metal oxide electrodes were usually fabricated by some vapour deposition techniques which require large-scale equipments, power, resources and costs, film deposition via solution technique would be worthy for familiarizing the metal oxide electrodes. In this research, thin films of conductive perovskite-type oxides, (La,Sr)CoO3 [LSCO], were fabricated by chemical solution deposition technique. The precursor solution for LSCO was prepared using metal nitrate, acetates, and iso-propoxide and 2-methoxyethanol. The solution was spin-coated on substrates, followed by drying, pyrolysis and RTA-treatment for crystallization at 500-750°C, for 5 min in air. These processes were repeated to obtain desired film thickness. (100)Si and (100)SrTiO3 were used as substrate. XRD analysis indicated that both of LSCO films fabricated on (100)SrTiO3 and (100)Si substrates were crystallized at and above 600°C. The films on (100)SrTiO3 had preferential crystal orientation of (100)LSCO normal to the substrate surface, while random crystal orientation was confirmed for the films on (100)Si. Electrical resistivity of the both films fabricated at 700°C were 6.09 × 10 -5 Ω cm and 1.12 × 10-4 Ω cm, respectively, which is almost same as the LSCO films fabricated by conventional vapour deposition technique. © Published under licence by IOP Publishing Ltd.

Chemical processing using supercritical carbon dioxide fluid (scCO2) was demonstrated for lowering processing temperature of sol-gel-derived metal oxide thin films. The film processing was performed in a hot-wall closed vessel filled with scCO2 fluid. Precursor films of titanium dioxide (TiO2) on soda-glass substrates prepared by sol-gel coating using Ti-alkoxide solution were converted to crystalline TiO2 (anatase) films successfully by the scCO2 treatment at a fluid pressure of 15 MPa and a substrate temperature of 300°C whereas no crystallization was occurred by conventional heat treatment at 400°C. XPS analysis indicated that the interface reaction related to Si element was suppressed successfully by scCO2 treatment at 300°C. These results suggest that the sol-gel synthesis using scCO2 fluid would be a cadidate for low-temperature processing of crystalline oxide films, which is more preferable than conventional techniques based on the heat treatment. © 2011 Ceramic Society of Japan.

Epitaxial (La0.07Sr0.93)SnO3 [LSSO] films were deposited on CaF2 substrates by pulse laser deposition. The (1 0 0)(c) orientation of LSSO films was observed only on (1 1 0)CaF2, whereas (1 1 0), orientation was found on (1 1 1)CaF2 and (1 0 0)CaF2, (0 0 1) polar axis oriented tetragonal Pb(Zr0.35Ti0.65)O-3 films were grown on the fabricated (1 0 0)(c)LSSO vertical bar vertical bar(1 1 0)CaF2 by pulsed metal organic chemical vapor deposition. The (0 0 1)Pb(Zr0.35Ti0.65)O-3 vertical bar vertical bar(1 0 0)cLSSO(1 1 0)CaF2 stack structure exhibited about 70% transparency with an adsorption edge of approximately 330 nm. (C) 2010 Elsevier B.V. All rights reserved.

xBi(Zn1/2Ti1/2)O-3-(1 - x)BiFeO3 films with x=0-0.68 were prepared on (1 0 0)SrTiO3 and (100)(c)SrRuO3 vertical bar vertical bar(100)SrTiO3 substrates by pulsed metalorganic chemical vapor deposition. Effects of the composition, x, on the constituent phases and their electrical properties were systematically investigated. {100}-oriented epitaxial films were ascertained to be grown and three series of peaks with x=0-0.23 (Peak A), x=0.15-0.44 (Peak B) and x=0.23-0.68 (Peak C) were observed. Leakage current density monotonously decreased with increasing x. On the other hand, maximum relative dielectric constant of the films was observed at x=0.20. almost corresponding to the compositional boundary of the x between Peaks A and C. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

The crystal symmetries of epitaxial (1-x)BiFeO3-xBiCoO 3 films (x = 0(0:46) grown on (100)SrTiO3, (110)SrTiO3, and (111)SrTiO3 substrates covered with/without SrRuO3 layers were systematically investigated as a function of film thickness and the crystal orientation of the substrates. Raman analysis was an effective method of crystal symmetry research on epitaxial BiFeO3-BiCoO3 films. Crystal symmetry was changed from being rhombohedral to tetragonal through the mixture of these symmetries with increasing BiCoO3 content irrespective of film thickness and the crystal orientation. However, the constituent phase was strongly depended on film and the crystal orientation of the substrates. The perovskite single phase was observed up to a higher x for the films grown on (100)SrTiO3 substrates than for those grown on (110)SrTiO2and (111)SrTiO3 substrates. On the other hand, the constituent phase of the films grown on (111)SrTiO3 substrates was similar to that of the strain free powders obtained by high-pressure synthesis. © 2010 The Japan Society of Applied Physics.

Epitaxial xBi(Zn1/2Ti1/2)O-3-(1-x)BiFeO3 films were grown on (100)(c)SrRuO3//(100)SrTiO3 substrates by metal organic chemical vapor deposition (MOCVD). The effects of x value on the crystal structure and the electrical properties were investigated. Constituent phase changed from rhombohedral symmetry to two types of tetragonal ones with different unit cell volume and tetragonality. Rhombohedral phase and the tetragonal phase with smaller tetragonality were not ascertained to transform to cubic phase up to 800 degrees C from high temperature XRD results. Relative dielectric constant measured at room temperature showed the maximum value at x = 0.21 near the phase boundary between tetragonal and rhombohedral symmetries. Leakage current became small when the measurement temperature decreased at 80 K and the ferroelectricity monotonously decreased with increasing x values and was not ascertained above 0.26. (C) 2010 The Ceramic Society of Japan. All rights reserved.

Barium titanate (BaTiO3, BT) and strontium titanate (SrTiO3, ST) nanocube particles were prepared by a solvothermal method. The prepared particles were collected by a centrifugal separator. The X-ray diffraction (XRD) measurement and a transmittance electron microscope (TEM) observation confirmed the formation of perovskite BT and ST nanocube particles with sizes of around 17 nm. These nanocube particles were monodistributed in hexane with tri-n-butylphosphine oxide (TBPO) as dispersant, separately, and then, the accumulations composed of the BT and ST nanocubes were built up using a selective catalytic reaction between 3-bromopropylphosphonic acid (BP) and aminomethylphosphonic acid (AM) as smart glue. The TEM observation confirmed that a part of accumulations showed a hetrointerface connection between BT and ST. (C) 2010 The Ceramic Society of Japan. All rights reserved.

We irradiated a glassy carbon electrode in AgNO3 solution using a 532 nm pulsed laser to prepare a silver-activated electrode. The UV-visible spectrum of the solution evidenced the production of Ag particles, and transmission electron microscopic images showed the formation of carbon silver composite on the solid carbon surface. The reduction potential of O-2 measured with the prepared electrode by differential pulse voltammetry shifted positively by 0.05 V in NaClO4 solution, which indicated that the present irradiation procedure effectively activated the glassy carbon electrode.

Highly ordered mesoporous titanium dioxide (titania. TiO(2)) thin films on indium-tin-oxide (ITO) coated glass were prepared via a Pluronic (P123) block copolymer template and a hydrophilic TiO(2) buffer layer. The contraction of the 3D hexagonal array of P123 micelles upon calcination merges the titania domains on the TiO(2) buffer layer to form mesoporous films with a mesochannel diameter of approximately 10 nm and a pore-to-pore distance of 10 nm. The mesoporous titania films on TiO(2)-buffered ITO/glass featured an inverse mesospace with a hexagonally-ordered structure, whereas the films formed without a TiO(2) buffer layer had a disordered microstructure with submicron cracks because of non-uniform water condensation on the hydrophobic ITO/glass surface. The density of the mesoporous film was 83% that of a bulk TiO(2) film. The optical band gap of the mesoporous titania thin film was approximately 3.4 eV, larger than that for nonporous anatase TiO(2) (similar to 3.2 eV), suggesting that the nanoscopic grain size leads to an increase in the band gap due to weak quantum confinement effects. The ability to form highly-ordered mesoporous titania films on electrically conductive and transparent substrates offers the potential for facile fabrication of high surface area semiconductive films with small diffusion lengths for optoelectronics applications. (C) 2009 Elsevier By. All rights reserved.

Barium titanate (BaTiO3, BT) and strontium titanate (SrTiO3, ST) nanocube particles were successfully prepared by a solvothermal method. The prepared particles were collected by a centrifugal separator. The X-ray diffraction (XRD) measurement confirmed the formation of perovskite BT and ST nanoparticles with sizes of around 17 nm while a transmittance electron microscope (TEM) observation revealed formation of cubic-shaped nanoparticles with sharp edge and corner. These nanocube particles were monodistributed in hexane with tri-n-octylphosphine oxide (TOPO) as dispersant, separately, and then, the 2-dimentional checkerboard-structured accumulations composed of the BT and ST nanocubes were built up using DNA base pair such as adenine and thymine as smart glue. TEM observation confirmed that a part of accumulations had a checkerboard-structure.

Barium titanate (BaTiO3, BT) and strontium titanate (SrTiO3, ST) nanocube particles were prepared by a solvothermal method. The prepared particles were collected by a centrifugal separator. The X-ray diffraction (XRD) measurement and a transmittance electron microscope (TEM) observation confirmed the formation of perovskite BT and ST nanocube particles with sizes of around 17 nm. These nanocube particles were monodistributed in hexane with tri-n-butylphosphine oxide (TBPO) as dispersant, separately, and then, the accumulations composed of the BT and ST nanocubes were built up using a selective catalytic reaction between 3-bromopropylphosphonic acid (BP) and aminomethylphosphonic acid (AM) as smart glue. The TEM observation confirmed that a part of accumulations showed a hetrointerface connection between BT and ST.

現在使用されている鉛系材料は正方晶強誘電体のPbTiO₃を端成分としており、非鉛の正方晶強誘電体の材料探索が非鉛圧電体材料探索のkey pointであると考えられている。その候補の一つとして、我々はBi(Zn_1/2Ti_1/2)O₃に着目した。これは、巨大正方晶性(c/a = 1.21)を有しており大体材料として非常に有望であるが、高圧相であるために常圧合成は非常に困難である。我々は常圧相のBiFeO₃との固溶体であるBi(Zn_1/2Ti_1/2)O₃-BiFeO₃をMOCVD法で合成することにより、c/a = 1.22 を有する正方晶性薄膜の作製に成功した[2]。しかし、PbTiO₃(c/a = 1.06)に比べて大きな正方晶性歪を有することにより、高い抗電界による分極反転の困難さが予想される。そこで我々は添加物によって正方晶性歪を制御した。

Thin films of bismuth layer-structured dielectrics (BLSDs), CaBi4Ti4O15, and SrBi4Ti4O15, were prepared by a chemical solution deposition (CSD) technique on various substrates, such as (111)Pt/TiO2/(100)Si, (100)LaNiO3/(111)Pt/TiO2/(100)Si, and (100)SrRuO3 // (100)SrTiO3 substrates. Conductive perovskite oxide LaNiO3 with (100) preferential crystal orientation was introduced into the interface between the BLSD film and the (111)Pt/TiO2/(100)Si substrate to control the crystal orientation of BLSD by lattice matching between pseudo-perovskite blocks in the BLSD crystal and the (100)LaNiO3 plane with the perovskite structure. The (00l) planes of BLSD crystals were preferentially oriented on the substrate surface of the (100)LaNiO3/(111)Pt/TiO2/(100)Si, whereas randomly-oriented BLSD crystals with lower crystallinity were only obtained on the surface of (111)Pt/TiO2/(100)Si substrate. The (001)-oriented BLSD films exhibited the leakage current densities below 10(-7) A/cm(2) at +/- 50 kV/cm, which is significantly lower than those for randomly-oriented films, above 10(-6) A/cm(2), The room-temperature dielectric constants (epsilon(r)) of CaBi4Ti4O15 and SrBi4Ti4O15 thin films on the (100)LaNiO3/(111)Pt/TiO2/(100)Si substrate were both approximately 250, while those on the (100)SrRuO3 // (100)SrTiO3 substrate were approximately 220. The temperature dependence of the capacitances for the CaBi4Ti4O15 and SrBi4Ti4O15 films on the (100)LaNiO3/(111)Pt/TiO2/(100)Si substrate were approximately +17 and +10%, respectively, in the temperature range from 25 to 400 degrees C. These values were slightly larger than those of epitaxial BLSD films, but smaller than those of (Ba,Sr)TiO3 films. (C) 2010 The Japan Society of Applied Physics

Thin films of a bismuth layer-structured dielectric oxides (BLSD), SrBi4Ti4O15, with preferential crystal orientation were prepared by means of chemical solution deposition (CSD) technique on (111)Pt/(100)Si substrate with bottom nucleation layers of conductive perovskite oxides, LaNiO3 and SrRuO3. CSD technique was utilized for the film preparation of SrBi4Ti4O15. These films possessed highly crystal orientation of (001) BLSD planes parallel to the substrate surface. The leakage current densities of the SrBi4Ti4O15 films on (100)SrRuO3//(100)LaNiO3/(111)Pt/Ti/(100)Si and on (100)LaNiO3/(111)Pt/Ti/(100)Si were approximately 10(-6) and 10(-7) A/cm(2) respectively. The dielectric constants of these films in a frequency range of 10(2) - 10(6) Hz were from 310 to 350 and 250 to 260 respectively. The value of capacitance change of these films in the range from 20 to 300 degrees C was about +8 and +5% respectively.

We studied supercritical carbon dioxide fluid deposition of titanium oxide (TiO2) in trench features on Si substrates using a flow-type deposition apparatus from titanium diisopropoxide bis(dipivaloylmethanate), aiming at fabricating conformal films at a relatively low temperature. We investigated the deposition rate and step coverage under a fluid temperature from 40 to 60 degrees C, a pressure from 8.0 to 10.0 MPa, and a substrate temperature from 80 to 120 degrees C. They were dependent on the fluid density, indicating that the solubility difference between the bulk fluid and the neighborhood of the substrate surface plays a decisive role for the deposition. An excellent conformal filling of the trench features was achieved from the fluid of 60 degrees C under 8 MPa on the substrate kept at 80-100 degrees C. The XPS spectra of the deposited film suggested partial formation of TiO2, and the XRD spectra showed the existence of some crystalline TiO2 (anatase). (C) 2009 Elsevier B.V. All rights reserved.

Thin films of CaBi4Ti4O15 and SrBi4Ti4O15 with preferential crystal orientation were prepared by the chemical solution deposition (CSD) technique on a (100)LaNiO3/(111)Pt/(100)Si substrate. The films consisted of a crystalline phase of bismuth-layer-structured dielectric (BLSDs). The (001) planes of a BLSD crystal were preferentially oriented to the surface of the (100)LaNiO3/(111)Pt/(100)Si substrate, which is ascribed to the lattice matching between pseudo perovskite blocks in the BLSD crystal and the (100)LaNiO3 plane with a perovskite structure. Frequent heat treatment for crystallization, i.e., once after each coating, also enhanced the degree of crystallinity and crystal orientation of the BLSD films. The dielectric constants (epsilon(r)) of SrBi4Ti4O15 and CaBi4Ti4O15 thin films were approximately 250 at room temperature. The epsilon(r) values of both films increased with ambient temperature, The variations in capacitance in the temperature range from 25 to 200 degrees C were approximately 3 and 5% respectively, which were significantly smaller than that in the (Ba,Sr)TiO3 thin film. (C) 2009 The Japan Society of Applied Physics

Raman OH stretching frequency shifts in supercritical water and in O-2- or acetone- aqueous solutions near the water critical point were observed to discuss the microscopic solution structure of these fluids. In neat water, the peak frequencies shifted almost linearly to the density except near the critical density. As the temperature approached the critical temperature, the density dependence of the shift became non-linear. This behavior was considered to be due to some microscopic structural non-uniformity caused by the density fluctuation. In the solutions, such non-linear density dependences were decreased, suggesting the decrease in the local density augmentation around water molecules. (c) 2009 Elsevier B.V. All rights reserved.

The shift of the Raman band of nu(1) (SO(4)(2-)) in aqueous alkali (Li, Na and K) and ammonium sulfate solutions was studied over a wide temperature range up to 350 degrees C under 25 MPa. The temperature shift for Li sulfate that was in the direction to low wavenumber was smaller and its dependence on the molality was larger than for the other two alkali sulfates. These trends were discussed based on the solution structure controlled by the cation. The discontinuous change of the spectral position from the solution phase to the solid phase at 390 degrees C was observed during the precipitation progress of Li and Na sulfates. Based on the present experimental results, K(+) cations are suggested to be most adequate among the investigated alkali cations as the neutralizing reagent in supercritical water oxidation (SCWO) process. (C) 2009 Elsevier B.V. All rights reserved.

Effect of annealing temperature on the dielectric properties of Bi1.5Zn1.0Nb1.5O7 films prepared on (111)Pt//(001)Al2O3 and (111)Pt/fused silica substrates by MOCVD was investigated. The tunability and the inverse of the dielectric loss [1/ (tan delta)] increased with increasing annealing temperature. Relative dielectric constant and temperature coefficient of the capacitance (TCC) increased with the crystallinity of the films. On the other hand, (1/tan delta) was independent of the crystallinity of the films, but was dramatically increased by the annealing.

Au nanocrystals stabilized by dodecanethiol were deposited into 100-150 run thick TiO2, films with evenly spaced perpendicular nanopillars and mesochannels oil the order of 10 nm supported oil conducting ITO/glass electrodes. Electrophoretic deposition was used to enhance nanocrystal deposition within the mesoporous TiO2 film. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy dispersive X-ray (EDX), UV-vis spectroscopy, variable-angle spectroscopic ellipsometry (VASE). and scanning Surface potential microscopy (SSPM) were used to characterize the resulting Au nanocrystal/ TiO, composites. Au nanocrystal loadings reached 21 wt % and were not kinetically limited at 10 min, relative to depositions performed for 20 h. Both VASE Measurements of the anisotropy of the imaginary refractive index, k, and X-ray photoelectron spectroscopy (XPS) depth profiling Studies indicate that Au nanocrystals are dispersed within the vertically aligned mesopores and distributed throughout the film. The mean penetration depth of a single nanocrystal penetrating inside the film is described with I model in terms of the electric field and a local deposition rate constant, which is influenced by ligand binding and architecture oil the nanocrystal surface.

When carbon suspended in water was it-radiated repetitively by pulsed laser at 532 nm. the carbon particles were gradually consumed, being accompanied with morphology change. Transmission electron microscopy (TEM) showed formation of seemingly entangled long fibrils and/or thin shells front the particles. In the copresence of silver ions, characteristic plasmon absorption peak appeared and formation of nanosized silver particles was evidenced by TEM. Under the typical fluence of 125 mJ.cm(-2). pulse(-1), the quantum yield of silver reduction was 10(-3).

Thermal strain sensitivity of the dielectric property was investigated for (111)-textured polycrystalline Bi-Zn-Nb-O films. Cubic pyrochlore films with similar crystallinity and the degree of the orientation were obtained on various substrates, and their 111 lattice spacing monotonously increased with the increasing thermal expansion coefficient of the substrates. The dielectric constant at 0 kV/cm and its tunability were almost independent of the residual strain, unlike highly sensitive (Ba(0.5)Sr(0.5))TiO(3) films. This strain independent characteristic of the dielectric property of pyrochlore Bi-Zn-Nb-O film is a big advantage in actual applications. 0 2008 American Institute of Physics.

The specific surface reaction rates of Breasol coal and styrene-divinylbenzene resin particles in sub and supercritical water with O-2 were investigated in the temperature range of 300-450 degrees C at 25MPa by observing the size change using a shadowgraph method. The rates were approximately proportional to the O-2 concentration and non-linearly dependent on the flow rate. The rate obeyed the Arrhenius law at lower temperatures, but became gradually independent on the temperature above 400 degrees C, which indicated that the overall reaction is controlled by a certain mass transfer process at the higher temperatures. Compared with the case of coal and activated carbon, much smaller amount of O-2 is enough to result in the rapid size decrease rate in the resin particle. (c) 2007 Elsevier Ltd. All rights reserved.

Thin films of Bi(Fe1-xScx)O-3 (BFSO) system were fabricated on (111)Pt/TiO2/SiO2/(100)Si substrates by chemical solution deposition to improve the electrical resistivity by substituting electrically unstable Fe3+ cations for stable Sc3+ cations. A single phase of perovskite was obtained in the range of x=0-0.30, in which selective replacement of Fe3+ and Sc3+ was confirmed in x=0-0.15 by using Raman measurement. The leakage current density of the BFSO films was reduced by increasing x. A well-saturated polarization-electric field hysteresis loop was obtained for BFSO films with x=0.15, showing remanent polarization of approximately 35 mu C/cm(2). (C) 2007 American Institute of Physics.

Zinc-substituted lithium tantalate thin films were fabricated for improving the electrical resistivity by compensating the valence of lattice defects in LiTaO3 crystal. The films with the chemical composition of (Li1.00-xZn (x) )TaO3 were fabricated on (111)Pt/TiO2/SiO2/(100)Si substrate by a chemical solution deposition technique using metal-organic precursors. Dense films consisting of a ilumenite-type crystalline phase were deposited by spin coating on the substrates, followed by heat-treatment at 650 degrees C for 5 min in air. The leakage current density of the LiTaO3 film was reduced from approximately 10(-4) to 10(-6) A/cm(2) By substituting Zn2+ ions for Li+ in the LiTaO3 films. Polarization-electric field hysteresis loop was improved significantly by partial substitution of Zn2+ for Li+ ions, which is based on the enhancement of electrical resistivity.

Thin films of Bi-based perovskite ferroelectrics BiFeO3 is recently recognized as strong candidates for alternatives to toxic Pb-based ferroelectrics such as conventional Pb(Zr,Ti)O-3. Authors fabricated BiFeO3 thin films with excellent performance of ferroelectric polarization by ion modification based on sol-gel technique. Some rare-earth ions, such as La3+ or Nd3+, could be substituted for Bi3+ ion in BFO crystal in order to reduce ionic defects in crystal lattices. Electrical resistivity of BiFeO3 films were improved by ion modification of rare-earth elements, as well as other Bi-based ferroelectric films like Bi4Ti3O12. Although crystal anisotropy and phase-transition temperature (Curie temperature) of these materials are generally reduced by the ion modification, it yield fully-saturated polarization (P) - electrical field (E) property to produce enhanced remanent polarization of approximately 50 mu C/cm(2) comparable or superior to conventional Pb(Zr,Ti)03 films. We concluded that the ion modification using rare-earth elements could suppress the ionic defects that caused electrical conduction in BiFeO3 films.

Pb(Zn1/3Nb2/3)O-3 (PZN) thin films were grown by metalorganic chemical vapor deposition (MOCVD). We systematically investigated what effects the supply sequence of source gases used in MOCVD and substrate types and orientations had on the constituent phase. Alternate-MOCVD, in which source materials of the A-site (Pb) and B-site (Zn and Nb) are alternately supplied to create the perovskite structure ABO(3), which efficiently increases the phase purity of the perovskite phase in the PZN-pyrochlore phase mixture. A relatively smaller mismatch between the PZN and the substrate than that between the pyrochlore phase and the substrate also increased the phase purity of the PZN. As a result, single-phase PZN films were successfully grown on (I 10) and (I I I)MgO substrates by alternate-MOCVD. (c) 2006 Elsevier B.V. All rights reserved.

Pb(Mg1/3Nb2/3)O-3 films with film thickness as ranging from 100 to 2000 nm were grown on (100)(c)SrRuO3//(100)SrTiO3 substrates by pulsed metal organic chemical vapor deposition. (100)-oriented epitaxial films were grown regardless of film thickness. The tetragonal symmetry of 100-nm-thick films was found to have changed to an almost cubic symmetry having almost equal out-of-plane and in-plane lattice parameters with increasing film thickness. The room-temperature relative dielectric constant epsilon(r) at 10 kHz increased almost linearly from 630 to 3100 with increasing film thickness, suggesting its strong thickness dependence on epsilon(r), which is different from that observed in the Pb(Zr0.65Ti0.35)O-3 films with a rhombohedral symmetry.

Pb(Mg1/3Nb2/3)O1/3 films with film thickness as ranging from 100 to 2000 nm were grown on (100) cSrRuO33//(100)SrTiO3 substrates by pulsed metal organic chemical vapor deposition. (100)-oriented epitaxial films were grown regardless of film thickness. The tetragonal symmetry of 100-nm-thick films was found to have changed to an almost cubic symmetry having almost equal out-of-plane and in-plane lattice parameters with increasing film thickness. The room-temperature relative dielectric constant Er at 10 kHz increased almost linearly from 630 to 3100 with increasing film thickness, suggesting its strong thickness dependence on Er, which is different from that observed in the Pb(Zr0.65Ti0.35)O3 films with a rhombohedralsymmetry. © 2006 The Japan Society of Applied Physics.

(1 - x)BiFeO3-xBiSCO(3) (x = 0-0.5) thin films were prepared on (111)Pt/TiO2/SiO2/(100)Si substrates by chemical solution deposition, and their crystal structure, leakage current density, and ferroelectric properties were investigated. X-ray diffraction analysis revealed that the single-phase perovskite was obtained for x from 0 to 0.4. The lattice parameter of the a-axis increased monotonically with increasing x, whereas that of the c-axis decreased. The surface of the films became smooth for the increase in x of up to 0.15, and the leakage current density at room temperature decreased to 5.1 x 10(-8) A/cm(2) at 100 kV/cm. Well-saturated polarization and electric field hysteresis loops were obtained for x = 0.15 and 0.3, and the remanent polarization (P-r) and coercive field (E-c) of the films for x = 0.15 and 0.3 were 66 and 70 mu C/cm(2) and 525 and 545kV/cm, respectively.

The effect of site selectivity on the ferroelectric polarization property was investigated in Dy-substituted Pb(Zr0.4Ti0.6)O-3 films prepared on (111)Pt/Ti/SiO2/(100)Si substrates by a chemical solution method. Dy ions were introduced, assuming Pb or Zr and Ti site substitutions in Pb(Zr0.40Ti0.60)O-3 with x ranging from 0 to 0.06. Site occupation was determined by Raman spectroscopy. Dy ions selectively replaced the assumed sites at a low x value; however, these ions interdiffused to opposite sites at a high x value. Remnant polarization was enhanced when Dy ions selectivity substituted the Zr and Ti sites at a low x value, while it was contrarily degraded by Ph site substitution. These results provide useful guidelines for ferroelectric property improvement by ion substitution in Pb(Zr0.4Ti0.6)O-3.

Reaction of a wood block of "hinoki" (a coniferous tree, Chamaecyparis obtusa) was studied in the presence of O-2 in sub- and supercritical water by observing the change in the size and shape of the block in a flow-type reaction cell, to understand the kinetic aspects of the whole reaction progress. The employed temperature was 573-698 K, the pressure was 25 MPa, and the O-2 concentration was 0-3.0 mass%. The phenomenological rate value was evaluated on the basis of the size change. In the subcritical water, O-2 promoted the size decrease rate almost linearly up to its solubility limit. Its temperature dependence was weaker than in the absence of O-2. The recovered amount of total organic carbon was smaller in the presence of O-2 and became richer in organic acids such as formic acid. The reaction rate increased with increasing the flow rate. These results indicated that a certain mass-transfer process was involved in the promotion of the reaction. On the other hand, in the supercritical region, the wood block left an intermediate solid residue after a very rapid initial size decrease. The residue was then gradually consumed. The amount of the residue was dependent on the O-2 concentration. However, the initial size decrease of the wood block in the supercritical water was less affected by the presence of O-2 than that in the subcritical water. The reaction in the presence of O-2 is not affected strongly by the ionic product of water, contrary to the decomposition reaction in the absence of O-2. The understanding of the whole reaction progress of the wood block should help in devising a reasonable technology to utilize the biomass wood.

The influence of ion modification using rare-earth cations on crystal structures, along with the insulating and ferroelectric properties of BiFeO3 (BFO) thin films was investigated. Rare-earth-substituted BFO films with chemical compositions of (Bi1.00-xREx)Fe1.00O3 (x=0-0.15, RE=La and Nd) were fabricated on (111)Pt/TiO2/SiO2/(100)Si substrates using a chemical solution deposition technique. A crystalline phase of rhombohedral BFO was obtained by heat treatment in a N-2 atmosphere at 500 degrees C for 5 min. The crystal anisotropy and the Curie temperature of BFO were degraded continuously with increasing contents of La3+ or Nd3+ cations. Ion modification using La3+ and Nd3+ cations up to x=0.05 lowered the leakage current density of the BFO film at room temperature from approximately 10(-3) down to 10(-6) A/cm(2). A polarization (P)-electrical field (E) hysteresis loop measured at 10 K revealed that the intrinsic remanent polarization of La3+- and Nd3+-substituted BFO films with x=0.05 (44 and 51 mu C/cm(2), respectively) was smaller than that of a nonsubstituted BFO film (79 mu C/cm(2)), which is ascribed to the degradation of crystal anisotropy and the Curie temperature of the BFO crystal. (c) 2006 American Institute of Physics.