内田 寛

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.

Study Design. An experimental study, in which spinal fusion in rats was conducted using a hydroxyapatite fiber mesh (HAM) as a carrier for recombinant human bone morphogenetic protein (rhBMP)-2. Objectives. To study the usefulness of the HAM as a carrier and seek the possibility of clinical application in spinal fusion. Summary of Background Data. Several biomaterials have been used as a carrier for BMP to achieve spine fusion, however, to our knowledge, the most effective carrier has not been established. Methods. In experiment No. 1, HAMs and the controls (commercially available hydroxyapatite ceramic body), loaded with rhBMP-2, were immersed in phosphate-buffered saline to evaluate the time course of the release of rhBMP-2. In experiment No. 2, posterolateral fusion was conducted in rats using HAM and the control loaded with rhBMP-2. The fusion status was evaluated radiologically and histologically after surgery. Results. In experiment No. 1, HAMs released a larger amount of rhBMP-2 for up to 28 days than the controls (49.5% vs 7.8%). In experiment No. 2, the fusion rate was significantly higher in the HAM group (> 80%) than in the control group (20%). Dense new bone formed close to the spine, and the HAMs were markedly absorbed compared with the controls. Conclusion. HAM provided more solid fusion mass than the control, suggesting that HAM is an efficient carrier for BMP.

Nd-substituted Bi4Ti3O12 (BNT) polycrystalline thin films with preferred a-/b-axes orientations were grown on sputter-grown IrO2(101)) layers by chemical solution deposition method. After optimizing the heat treatment conditions, insulating characters and ferroelectric properties in 250-nm-thick BNT thin films with a-/b-axes orientations were investigated at room temperature. Low leakage current density of J = 10(-7)similar to 10(-8) A/cm(2) at 100 kV/cm and fair value of remnant polarization (2P(tau) = 31 mu C/cm(2) at 400 kV/cm) were measured even though the Bi2O2 blocking layer aligned parallel to the film normal.

The electrical properties of perovskite-based ferroelectric films were improved by ion modification using rare-earth cations. Thin films of rare-earth-modified lead zirconate titanate [Pb(Zr,Ti)O-3] were fabricated on (111)Pt/Ti/SiO2/(100)Si substrates by a chemical solution deposition technique. The substitution of volatile cations in the simple-perovskite oxides, such as Pb2+ in Pb(Zr,Ti)O-3 films, enhanced the insulating properties of the film. The crystal anisotropy of the Pb(Zr,Ti)O-3 film could be controlled by varying the species and the amount of replacing cations to enhance the spontaneous polarization. Thus, ion modification using Dy3+ cation could enhance the remanent polarization of Pb(ZrTi)O-3 film consequently.

Thin films of titanium oxide (TiO2) were synthesized from Titanium diisopropoxide bis(dipivaloylmethanate) [Ti(O-i-Pr)(2)(dpm)(2)] as a source material using supercritical carbon dioxide (CO2) fluid. Flat films with a uniform microstructure were fabricated on SiO2/(100)Si substrates at a fluid pressure of 8.0 MPa, while granular particles were deposited on the film surface at a fluid pressure of 10.0 MPa. TiO2 films fabricated in supercritical CO2 atmosphere at 10.0 MPa were crystalline at the reaction temperature of 100 degrees C, which was significantly lower than those in the conventional film-deposition techniques.

Bismuth ferrite (BiFeO3) thin films were fabricated by depositing sol-gel solutions oil Pt/Ti/SiO2/Si(100) structures. X-ray diffraction (XRD) showed that a polycrystalline phase and also a small fraction of a secondary phase. Bi2Fe4O9, were present in the film. The nonperovskite secondary phase decreased with increasing thickness, which showed the influence of volume effects on the film. Improved leakage current density and enhanced polarization in BiFeO3 films were observed. A 400-nm-thick film showed a leakage current on the order of 10(-8) A/cm(2) at room temperature. The remanent polarization was approximately 90 mu C/cm(2) at 80K and the piezoelectric coefficient d(33) was approximately 50pm/V.

Spontaneous polarization can be enhanced by increasing the crystal anisotropy of tetragonal Pb(Zr,Ti)O-3 [PZT] lattice by Zr and Ti-site substitution with Dy3+ cations. Spontaneous polarization (P-s) in epitaxial film of 2% Dy3+-substituted tetragonal Pb(Zr0.40Ti0.60)O-3 [Dy-PZT] was compared with that of nonsubstituted Pb(Zr0.40Ti0.60)O-3 [PZT] to investigate intrinsic contribution of the Dy3+ substituion to the P-s improvement. Epitaxial thin films of PZT and Dy-PZT with (111) orientations were grown on (111)(c)SrRuO3//(111)Pt//(100)YSZ//(100)Si substrates by chemical solution deposition. The saturated polarization values of PZT and Dy-PZT films with (111) orientation were 41 and 48 mu C/cm(2), respectively. The estimated P-s values of PZT and Dy-PZT films from the saturation polarization values were 71 and 84 mu C/cm(2), respectively. The P-s value of this PZT was in good agreement with previous reports. The increase in P-s of the epitaxial Dy3+-substituted PZT film is attributed to the enhancement of the crystal anisotropy, i.e., tetragonality, of the tetragonal PZT lattice. This shows that the enhancement of the ferroelectricity of the tetragonal PZT films can be achieved by ion substitution, just as it can in Bi4Ti3O12-based film. (C) 2005 American Institute of Physics.

Rare-earth-substituted lead zirconate titanate thin films were synthesized to improve the ferroelectric properties of lead zirconate titanate through the enhancement of its crystal anisotropy. Thin films of Pb(1.00-(3x/2))RE(x)(Zr(0.4)Ti(0.60))O(3) [RE-PZT(A)] and Pb(1.00)RE(x)(Zr(0.40)Ti(0.60))(1-(3x/4))O(3) [RE-PZT(B)] with RE = La or Dy were deposited on (111)Pt/Ti/SiO(2)/(100)Si substrates by chemical solution deposition (CSD). Rare-earth-substitution did not affect the crystal orientation of the PZT-based films where the PZT(111) plane was oriented along the surface-normal direction. Dy(3+) substitution based on Dy-PZT(B) up to x = 0.02 enhanced the crystal anisotropy (c/a) and remanent polarization (P(r)) of PZT films simultaneously, while both c/a and P(r) values of Dy-PZT(A) decreased as x increased continuously. On the other hand, La(3+) substitution degraded the ferroelectric properties gradually in both the case of La-PZT(A) and (B). The Dy(3+) ion could be substituted for a B-site in a PZT crystal preferentially, and that promoted the crystal anisotropy and the ferroelectric properties of PZT films.

Bi1.5Zn1.0Nb1.5O7 (BZN) epitaxial thin films were prepared on (111)Pt // (001)Al2O3 substrates at 500 degrees C by metal organic chemical vapor deposition (MOCVD). The electrical properties of the as-deposited films were investigated by comparing them with those of the (111)-one-axis-oriented films prepared on (111)Pt/TiO2/SiO2/(100)Si substrates for making a Pt/BZN/Pt capacitor structure. The relative dielectric constant of the epitaxial film was almost the same as that of the one-axisoriented one, but its changes with frequency dependence and tan 6 were smaller than those of the one-axis-oriented one.

Epitaxial (110)(Bi4-xNdx)Ti3O12 (x=0-0.73) films with a variety of neodymium content were grown by metal-organic chemical-vapor deposition, and the effects of neodymium content and site occupancy on spontaneous polarization along the a axis were systematically investigated. Raman spectra revealed that the neodymium is selectively substituted for the bismuth (A site) in the pseudoperovskite layer up to x=0.45; however, with further increasing neodymium content, neodymium is also incorporated into other bismuth sites in the (Bi2O2)(2+) layer. The neodymium substitution led to a continuous decrease in the Curie temperature. The saturated coercive field showed slight dependency on the neodymium content, while the remanent polarization significantly improved to a maximum of 34 mu C/cm(2) at x=0.35. The estimated value of the spontaneous polarization for the epitaxial films with x=0.26-0.45 exceeded 50 mu C/cm(2), i.e., the reported value for pure Bi4Ti3O12 single crystal, but markedly decreased at x=0.73. The degraded spontaneous polarization appeared to be associated with the site occupancy of the neodymium at the two different kinds of bismuth sites. (c) 2005 American Institute of Physics.

Crystal growth from a supersaturated NaCl aqueous solution has been studied by molecular dynamics (MD) simulation. The model was similar to the one previously applied by us for a NaCl melt. 168Na(+), 168Cl(-) and 192H(2)O were set up in a basic cell in the following way: four layers of a NaCl seed crystal were disposed with the (100) plane of 32(Na++Cl-) in contact with a supersaturated NaCl aqueous solution consisting of 40(Na++Cl-) and 192H(2)O. The solution was first equilibrated in contact with the 'frozen' crystal. Two-dimensional periodical conditions were imposed in the directions along the interface. In the direction normal to the interface, the aqueous solution is directly open to vacuum. Only one combination of pair potentials among the five different combinations of inter atomic potentials studied led to crystallization of NaCl. Thus, it strongly depends on the pair potentials used whether a crystal grows from its aqueous solution. After the equilibration run, a run longer than 2 ns was performed. Crystals gradually grew as clusters in the solution, but not uniformly on the seed crystal, which is in contrast to the growth from a NaCl melt. (c) 2004 Published by Elsevier B.V.

The spontaneous polarization (P-s) values of Pb(Zr,Ti)O-3 (PZT) and Bi4Ti3O12-based ferroelectrics were compared based on data obtained from epitaxially-grown films. These two materials are the most promising candidates for use in ferroelectric random access memory (FeRAM). The P-s of tetragonal Pb(Zr0.35Ti0.65)O-3 films was estimated to be about 90 mu C/cm(2) based on data from perfectly (001)-oriented, polar-axis-oriented films. On the other hand, the P-s value of (Bi3.5Nd0.5)Ti3O12 was estimated to be 56-58 mu C/cm(2) based on data from (100)/(010)-, (110)-, and (104)/(014)-oriented epitaxial films. This value is the largest yet reported for bismuth layer-structured ferroelectrics. For both systems, the P-s value generally increased with increasing Curie temperature (T-c). However, it decreased when the T-c became very high and approached the values for PbTiO3 and Bi4Ti3O12. This decrease is attributed to pinning of the domain motion in the bulk. On the other hand, the obtained one-axis film, which is essential to diminish the cell-to-cell property distribution, had a (100)/(001) and (111) orientations for Pb(Zr0.35Ti0.65O3 films, or a (001) orientation for (Bi3.5Nb0.5)Ti3O12 films. Based on our findings, we expect the maximum remanent polarization (P-t) values to be almost the same for both materials. (c) 2005 Elsevier B.V. All rights reserved.

Decomposition of a wood block in sub- and supercritical water was studied by directly observing the change in the size and shape of the wood block in a flow-type reaction cell through sapphire windows attached to the cell. Quantitative kinetic analysis was performed for "hinoki" (a coniferous tree, Chamaecyparis obtusa) as a typical wood sample at a temperature of 523-703 K and a pressure of 10-25 MPa. The phenomenological rate of the size shrink could be analyzed on the basis of two first-order reaction terms. Together with the measurements of the emission of total organic carbons (TOC), it was concluded that the wood block shrank with emitting TOC, and then it shrank at a smaller rate with emitting much smaller amounts of TOC. In the subcritical region, the phenomenological first-order rate constant for the initial shrink increased with the reaction temperature and approximately obeyed the Arrhenius equation with an activation energy of ca. 120 kJ mol(-1). However, the rate constant decreased suddenly near the critical point and again increased with the temperature at the higher temperatures. The phenomenological kinetics was apparently determined by a certain chemical reaction. When the decomposition reaction was assumed to be proton-catalyzed, probably hydrolysis, the rapid change in the vicinity of the critical point was reasonably understood by taking into account the remarkable decrease of the ionic product.

A novel technique for the deposition of oxide thin films using supercritical carbon dioxide (CO(2)) fluid was proposed for the large-scale circuit integration on a silicon (Si) substrate at a low temperature. Thin films of titanium oxide (TiO(2)) as a model material were fabricated from organometallic Ti(Oi-Pr)(2)(dpm)(2) source on (100)Si substrates in supercritical CO, fluid. The film deposition was accomplished using a flow-type supercritical fluid deposition apparatus designed on the basis of metalorganic chemical vapor deposition (MOCVD) systems. Flat films were fabricated on (100)Si substrates at a faster source delivery (fluid flow rate: 2.0-10.0cm(3)/min), while granular deposits owing to homogeneous nucleation in the bulk supercritical CO(2) fluid appeared on the substrates at a slower source delivery (fluid flow rate: 1.0cm(3)/min). The amount of TiO(2) deposited decreased gradually with increasing the temperature of CO, fluid, which would be related to the change in the density of CO(2) fluid. The crystalline TiO(2) film was deposited on the (100)Si substrate at a substrate temperature of 80-120 degrees C and fluid temperature/pressure of 40 degrees C/8.0 MPa, at which the decomposition of organometallic Ti(Oi-Pr)(2)(dpm)(2) source was accomplished. These results indicated that the supercrifical CO(2) deposition technique is suitable for the large-scale circuit integration on Si substrates.

Influences of the B-site substitution using Dy3+ ion on the crystal structure and ferroelectric properties of lead zirconate titanate (PZT) films were investigated. Dy3+-substituted PZT films with nominal chemical compositions of Pb1.00Dyx(Zr0.40Ti0.60)(1-(3x/4))O-3 (x = 0 similar to 0.06) were fabricated by a chemical solution deposition (CSD). Polycrystalline PZT films with preferential orientation of (111)PZT were obtained on (111)Pt/TiO2/SiO2/(100)Si substrates, while epitaxially-grown (111)PZT films were fabricated on (111)SrRuO3//(111)Pt//(100)YSZ//(100)Si substrate. Ratio of PZT lattice parameters (c/a), which corresponds to its crystal anisotropy, was enhanced by the Dy3+-substitution with x = 0.02. Spontaneous polarization (P-s) of Dy3+-substituted PZT film (x = 0.02) along polar [001] axis of PZT lattice was estimated from saturation polarization (P-sat) value of the epitaxially-grown (111)PZT film on (111)SrRuO3//(111)Pt//(100)YSZ//(100)Si to be 84 mu C/cm(2) that was significantly larger than that of non-substituted PZT (= 71 mu C/cm(2)). We concluded that the enhancement of P-s value could be achieved by the Dy3+-substitution that promoted the crystal anisotropy of PZT lattice.

Rare-earth-substituted tetragonal lead zirconate titanate thin films were synthesized for improving the ferroelectric property of conventional lead zirconate titanate. Thin films of Pb1.00REx(Zr0.4Ti0.60)(1-(3x/4))O-3 (x = 0.02, RE = Y, Dy, Er and Yb) were deposited on (111)Pt/Ti/SiO2/(100)Si substrates by a chemical solution deposition (CSD). B-site substitution using rare-earth cations described above enhanced the crystal anisotropy, i.e., ratio of PZT lattice parameters c/a. Remanent polarization (P-r) of PZT film was enhanced by Y3+-, Dy3+- and Er3+-substitution from 20 mu C/cm(2) Up to 26, 25 and 26 mu C/cm(2) respectively, while ion substitution using Yb3+ degraded the P-r value down to 16 mu C/cm(2). These films had similar coercive fields (E-c) of around 100 kV/cm. Improving the ferroelectric property of PZT film by rare-earth-substitution would be ascribed to the enhancement of the crystal anisotropy. We concluded that ion substitution using some rare-earth cations, such as Y3+, Dy3+ or Er3+, is one of promising technique for improving the ferroelectric property of PZT film.

Bi4-xNdxTi3O12 (BNT, x = 0.25, 0.5, 0.75) thin films with in-plane c-axis orientations were grown on IrO2/Si from solution route and their electrical properties were studied. The remanent polarization exhibited a broad peak against x with the maximum value of 2P(r)= 47 mu C/cm(2) at x = 0.5. The orthorhombic lattice parameters and Curie temperature T-C were measured for BNT powders prepared from the same coating solutions. Both orthorhombic anisotropy a/b and T-C monotonically decreased with increasing x. Irrespective of x, leakage current density J < 1.5 x 10(-7) A/cm(2) under 100 kV/cm was observed by optimizing film growth temperature T-G = 700 degrees C, even though the Bi2O2 blocking layers aligned perpendicular to the film.

Ion modification techniques for improving the insulating and ferroelectric properties of BiFeO3 (13170) thin films are reported. Rare-earth-substituted BFO films with chemical compositions of Bi1.00-xRExFe1.00O3 [RE = La and Nd] were fabricated on (111)Pt/TiO2/SiO2/(100)Si substrates using a chemical solution deposition technique. Well-saturated P-E curves were obtained for La3+ and Nd3+-substituted BFO films, while the curve of a nonsubstituted BFO film was distorted due to the leakage current. Remanent polarization (P-r) values measured at 10 K were respectively 44 and 51 mu C/cm(2), for La3+- and Nd3+-substituted BFO films, which are significantly superior to conventional Pb-free ferroelectrics.

Relaxor-type ferroelectric Pb(Zn1/3Nb2/3)O-3 [PZN] films were prepared on (100), (110), (11 l)SrTiO3 and MgO substrates by metalorganic chemical vapor deposition (MOCVD). The dependences of the constituent phase of the deposited films on the sequence of gas introduction in the MOCVD and on the kinds of substrates and the orientation of the substrates were investigated systematically. Compared with continuous and pulsed sequences of source gas introduction, an alternative sequence of source gas introduction of the Pb and Zn + Nb, named alternative MOCVD, produces a higher phase purity of perovskite for film deposited on (100)MgO substrates. In addition, the phase-pure perovskite PZN film was first grown on (110) and (111)MgO substrates. This is due to the relatively smaller lattice mismatch between the perovskite PZN and the substrate than that between an impurity phase, pyrochlore, and substrates that exists when films are deposited on these substrates. This is the first reported deposition of the pyrochlore-free phase-pure epitaxial PZN films.

BiFeO 3 (BFO) thin films were fabricated by depositing sol-gel solutions on Pt/Ti/SiO 2 /Si (100) structures. The crystalline BFO phase was observed after 5-min- and 15-min-annealing for films formed using stoichemistric and 5% Bi-excess sol-gel solutions, respectively. Only Bi 2 Fe 4 O 9 were observed as the secondary phase during deposition and the fraction of secondary phase depended upon the annealing temperature as well as the annealing atmosphere. The leakage current density in the range of 10 -7 A/cm 2 was obtained after optimizing process conditions for stoichemistric BFO chemical solution. The remanent polarization of around 40 mu C/cm 2 was observed at 600 kV/cm applied field at room temperature, although the hysteresis loop was degraded by leakage current.

Dysprosium (Dy3+) -substituted lead zirconate titanate (PDZT) thin films were synthesized in order to improve the ferroelectric properties of lead zirconate titanate (PZT) films by crystal anisotropy enhancement. Thin films of Pb1.00-(3x/2)Dyx(Zr0.40Ti0.60)O-3 (A-PDZT) and Pb1.00Dyx(Zr0.40Ti0.60)(1-(3x/4))O-3 (B-PDZT) were deposited on (111)Pt/Ti/ SiO2/(100)Si substrates by chemical solution deposition (CSD). The ferroelectric properties of A- and B-PDZT thin films were compared with those of a non-substituted PZT film. Dy3+-substitution based on B-PDZT (x = 0.02) enhanced the tetragonality of PZT film, which increased the P-r value of B-PDZT from 20 muC/cm(2) up to 25 muC/cm(2). On the other hand, both the c/a ratio and Pr value of the A-PDZT film decreased with increasing x continuously. These results suggest that the ferroelectric property was enhanced by the Dy3+-substitution for B-site in PZT crystal.

Porous hydroxyapatite (HAp) ceramics possessing well-controlled porosities and pore sizes were developed by firing apatite-fiber compacts mixed with carbon beads and agar. The total porosities could be controlled in the range from 40 to 85% by varying compaction pressure (20-40 MPa), firing temperature (1000-1300degreesC) and carbon/HAp ratio (0/10-10/10 (w/w)). Most of the pores were regarded as open pores. The pore sizes were mainly affected by the carbon-bead diameter (5, 20 or 150 mum) and partly by the compaction pressure and the firing temperature. The pore sizes of the porous HAp ceramics derived from the carbon beads of 150 mum in diameter were distributed in the two separate ranges of several micrometers and more than 100 mum. (C) 2004 Kluwer Academic Publishers.

Ferroelectric properties of La3+-substituted bismuth titanate (BLT) films were modified by Ti-site substitution using higher-valence ions than the Ti4+ ion. Thin films of V5+-, W6+-, Zr4+- and nonsubstituted BLT, i.e., (Bi3.24La0.75)(Ti2.97V0.03)O-12 (BLTV), (Bi3.23La0.75)(Ti2.97W0.03)O-12 (BLTW), (Bi3.25La0.75)(Ti2.97Zr0.03)O-12 (BLTZ) and (Bi3.25La0.75)Ti3.00O12, respectively, were fabricated on (111)Pt/Ti/SiO2/(100)Si substrates by chemical solution deposition; These films consisted of isotropic granular structures without a preferred crystal orientation. Remanent polarizations (P-r) of the BLTV and BLTW films (13 and 12 muC/cm(2), respectively) were larger than those of the BLT and BLTZ films (8 and 9 muC/cm(2), respectively), while those films had similar coercive fields (E-c) of approximately 120 kV/cm. BLTV and BLTW films also had lower leakage current densities (approximately 10(-8) A/cm(2) at 100 kV/cm) than that of BLT film (approximately 10(-6) A/cm(2) at 100 kV/cm). As no obvious difference was found in the crystal orientation or the microstructure, the enhancement of the Pr value and suppression of the leakage current density could be achieved on a BLT film by the charge compensation using higher-valence ions than the Ti4+ ion.

(100)/(010)- and (110)-oriented neodymium-substituted Bi4Ti3O12 films were grown by metalorganic chemical vapor deposition on (101) and (001)RuO2 layers with a rutile structure. Epitaxial growth of the films with an in-plane c-axis orientation was confirmed by several X-ray diffraction measurements. Large remanent polarizations of 31 and 34 muC/cm(2) were observed for the (100)/(010)- and (110)-oriented films, respectively. On the basis of the volume fractions of (100)- and (010)-oriented crystal estimated for the (100)/(010)-oriented film by X-ray diffraction, the spontaneous polarization of neodymium-substituted Bi4Ti3O12 along the a-axis was estimated to be 58 muC/cm(2) from both kinds of epitaxial films.

The biological properties of using two kinds of cells, MC3t3-E1 of an osteoblastic cell line and the rat bone-marrow cell (RBMC) as mesenchymal stem cell model were discussed. The HAp fiber was synthesized via a homogeneous precipitation method using urea. The HAp fiber was mixed with the spherical carbon beads having a diameter of ∼ 150 μm in the mixed solvent. The single HAp phase was present in the S0, S1000, and S2000 scaffolds with porosity of 95% over. The results show that the high porosity and large pore size fulfilled by S2000 could provide an excellent environment for enhancing bone marrow cell activity.

To gain a deep insight into the contribution of Nd-substitution, we have investigated structural phase transition behavior in Bi4-xNdxTi3O12 (BNT) powders derived from chemical solutions. Differential thermal analysis and thermo-gravimetry (DTA-TG) and X-ray diffraction (XRD) studies indicated that the para- and ferroelectric transition temperature (Curie temperature, T-c) continuously decreased with increasing x. The XRD studies also showed that continuous decrease in lattice anisotropy (a/b, orthorhombicity) with the increase of x. Considering the close relationship with T-c, a/b and spontaneous polarization P-s in displacive ferroelectrics, Nd-substitution may not enhance the intrinsic P-s in Bi4Ti3O12 (BIT). For direct evaluation of P-s upon Nd-substitution, synthesis route to polar-axis-orientated BNT films was investigated.

Thin films of calcium-strontium bismuth titanate (Ca1-xSrx)Bi4Ti4O15 solid solution were fabricated on (111)Pt/Ti/SiO2/(100)Si substrates by a chemical-solution deposition (CSD) technique. These films had x = 0-1.00 and consisted of a polycrystalline structure with random orientation of the bismuth layer-structured ferroelectric (BLSF) crystal (m = 4). The relative dielectric constants of (Ca1-xSrx)Bi4Ti4O15 films were enhanced from 40 to 220 with increasing x; these values did not vary significantly with changes in the measuring frequency and the bias field. The temperature coefficient of the relative dielectric constant at around room temperature became larger with increasing x from 0 to 1.00; the change in the dielectric constant of these film between 30-100degreesC increased from 2% to 15%.

Lead-free ferroelectric Bi4Ti3O12 (BIT) thin films were modified by the cosubstitution of Sr2+ for Bi3+ and of Nb5+ for Ti4+ by spin-coating and decomposition of chemical solutions of metal-alkoxide materials (the nominal compositions of Bi4-xSrxTi3-xNbxO12 (BSTN) are x = 0.5, 1.0, 1.5). Single-phase thin films with a BIT-type structure were crystallized above 550°C. At room temperature, the ferroelectric and dielectric properties were found to be Pr = 10 μC/cm2, Ec = 100 kV/cm, εr = 300, and tan δ < 5% for x = 0.5 after annealing at 650°C. The films with x = 1.0 and 1.5 did not exhibit ferroelectric hysteresis behavior because of the decrease in Curie temperature (Tc) below room temperature. The x dependence of of Tc was studied by considering the soft mode behavior in Raman scattering spectra and the Tc values were 400, -25, and -220°C for x = 0.5, 1.0, and 1.5, respectively. The cosubstitution by Sr2+ and Nb5+ is effective for reducing ferroelectric interaction between electrical dipoles leading to a large shift in Tc. Because of its high solubility of Sr2+ and Nb5+ and efficiency for shifting Tc, the BSTN system may find a novel application as a dielectric material rather than as a ferroelectric material.

Lead-free ferroelectric Bi4Ti3O12 (BIT) thin films were modified by the cosubstitution of Sr2+ for Bi3+ and of Nb5+ for Ti4+ by spin-coating and decomposition of chemical solutions of metal-alkoxide materials (the nominal compositions of Bi4-xSrxTi3-xNbxO12 (BSTN) are $x=0.5$, 1.0, 1.5). Single-phase thin films with a BIT-type structure were crystallized above 550°C. At room temperature, the ferroelectric and dielectric properties were found to be $P_{\text{r } }=10$ μC/cm2, $E_{\text{c } }=100$ kV/cm, $\varepsilon_{\text{r } }=300$, and $\tan\delta<5$% for $x=0.5$ after annealing at 650°C. The films with $x=1.0$ and 1.5 did not exhibit ferroelectric hysteresis behavior because of the decrease in Curie temperature ($T_{\text{c } }$) below room temperature. The $x$ dependence of $T_{\text{c } }$ was studied by considering the soft mode behavior in Raman scattering spectra and the $T_{\text{c } }$ values were 400, $-25$, and $-220$°C for $x=0.5$, 1.0, and 1.5, respectively. The cosubstitution by Sr2+ and Nb5+ is effective for reducing ferroelectric interaction between electrical dipoles leading to a large shift in $T_{\text{c } }$. Because of its high solubility of Sr2+ and Nb5+ and efficiency for shifting $T_{\text{c } }$, the BSTN system may find a novel application as a dielectric material rather than as a ferroelectric material.

Crystal growth from supercooled CaCl2 melt has been studied by molecular dynamics (MD) simulation; the crystal has a distorted rutile type. The MD model was similar to that previously applied for NaCl. The Busing-type pair potentials the parameters of which were presented by Umesaki and Iwamoto were employed. The cases were studied that the initial interfaces between crystal and melt were the (001), (100) and (110) planes. The crystal grew only in the (001) case by MD of a nanosecond order, presumably because on every plane parallel to the (001) plane the charge neutrality is maintained. The maximum growth rate at about 100 K below the melting point was about 1 m/s, which is lower than that of NaCl-type structured crystals such as NaCl and MgO by about two orders of magnitude. The relatively slow rate may be due mainly to easy generation of the defects of this crystal which consists of ions with a ratio of one cation to two anions. The very small volume expansion on melting (0.5 %) inherent in CaCl2 seems not to play a special role on the growth rate. (C) 2003 Elsevier Science B.V. All rights reserved.

Bismuth titanate (Bi4Ti3O12; BIT) -based ferroelectric thin films fabricated from a view point of "the site-engineering technique" have been expected to improve the fatal disadvant of a ferroelectric BIT film i.e., its low spontaneous polarization; here, Bi- and Ti-site ions in the BIT crystal are cosubstituted by lanthanoid ions and cations with a higher charge valence, respectively. In the present study, we have mainly focused on Ti-site substitution of bismuth titanate (Bi4Ti3O12; BIT)-based thin films using some ions with higher charge valences (V5+, Nb5+, Ta5+ and W6+; in this study) to enhance the ferroelectric properties of those materials. The BIT-based films with various chemical compositions were fabricated on a (111)Pt/Ti/SiO2/(100)Si substrate by a chemical solution deposition method. Ti-site substitution of BIT films by the higher-valent ions, Bi-3.99(Ti2.97V0.03)O-12, Bi-3.99(Ti2.97Nb0.03)O-12,O- Bi-3.99(Ti-2.Ta-97(0.03)) O-12 and Bi-3.98(Ti2.97W0.03)O-12,O- reduced the leakage current density of BIT films from similar to 10(-6) down to similar to 10(-7) A/cm(2) at an applied field of 50 kV/cm, while the substitution by the same-valent cation, e.g. Bi-4.00(Ti2.97Zr0.03)O-12, did not affect the behavior of leakage current. Whereas polarization (P) - electrical field (E) hysteresis loops of non-substituted and Zr-substituted BIT films were distorted due to the leakage current, non-distorted P-E loops were obtained at V5+-, Nb5+-, Ta5+- and W6+-substituted BIT films. Also, Ti-site substitutionwas effective for improving the ferroelectric properties in lanthanoid-substituted BIT films. In the case of La3+-substituted BIT films (BLT), remanent polarization (P-r) of V5+- and W6+-substituted BLT films, (Bi3.24La0.75)(Ti2.97V0.03)O-12 and (Bi3.23La0.75)(Ti2.97W0.03)O-12 (13 and 12 muC/cm(2), respectively), were larger than those of Zr4+- and non-substituted BLT films, (Bi3.25La0.75)(Ti2.97Zr0.03)O-12 and (Bi3.25La0.75)(Ti-3.00)O-12 (8 and 9 muC/cm(2,) respectively), while those films had similar coercive field (E-c) of approximately 120 kV/cm. Also in the case of Nd3+-substituted BIT film (BNT), P-r and E-c values of V5+-substituted BNT film, (Bi3.24Nd0.75)(Ti2.98V0.02)O-12, were 37 muC/cm(2) and 119 kV/cm, respectively, which were comparable with those of conventional Pb-based ferroelectrics such as lead zirconate titanate, Pb(Zr,Ti)O-3. We concluded that enhancement of the P-r value was achieved by the charge compensation of oxygen vacancies in BIT-based ferroelectrics using higher-valent cations than Ti4+ ion whereas no obvious differences were found in the crystal orientation and or microstructure of these films.

Ferroelectric properties of ion-cosubstituted BIT thin films, (Bi(4.00-y)Ln(y))(4-delta) (Ti3.00-xXx)(3)O-12 (BLnTX), with various lanthanoid (Ln: e.g., La3+ , Nd3+ , Pr3+ , Sm3+) and higher-valent ions (X: e.g., V5+ , Nb5+ , Ta5+ , W6+) were investigated to determine the optimum condition of the ion-cosubstitution. Ion-substituted BIT films were fabricated on (111)Pt/Ti/SiO2 /(100)Si substrates using a chemical solution deposition (CSD) technique. In the case of Bi-site substitution, Pr3+ , Nd3+ and Sm3+ -substituted BIT films (BPT, BNT and BST) had larger remanent polarization ( P r ) values than that of conventional La3+ -substituted BIT film (BLT). Especially, P-r and E-c values of (Bi3.50Nd0.50)Ti3.00O12 film were measured to be 32 muC/cm(2) and 126 kV/ cm, respectively. On the other hand, Ti-site substitution by higher-valent cations degraded the large leakage current density of the BIT film from similar to10 -6 down to similar to10(-7) A/cm(2). V-substituted (Bi3.50Nd0.50)Ti3.00O12 films, i.e., Nd3+/V5+ -cosubstituted BIT films (BNTV), had larger P r values than that of non-substituted (Bi3.50Nd0.50)Ti3.00O12 film. (Bi-3.49 Nd-0.50)(Ti2.97V0.03)O-12 film possessed P-r and E-c values of 37 muC/cm(2) and 119 kV/cm respectively, which were comparable with those of conventional Pb-based ferroelectric thin films like lead zirconate titanate, Pb(Zr,Ti)O-3.

HAp films with good adhesive property were formed by a simple surface treatment utilizing an enzyme reaction of urea with urease. The resulting coating layer consisted of carbonate-containing HAp with poor crystallinity. The in vitro evaluation using osteoblastic cells showed that HAp-coated Ti substrate had a good cellular response, such as cell proliferation and differentiation into osteoblast. From the results of in vivo evaluation using rabbit models, the HAp-coated Ti substrate directly bonded to bones to form. large amount of new bone around implant. It has been found from both the in vitro and in vivo evaluations that the present HAp-coated Ti substrate has excellent biocompatibility.

Novel scaffolds have been developed from single-crystal apatite fibres synthesized by a homogeneous precipitation method using urea. The resulting apatite fibre scaffolds have large pores with diameters of 110-250 mum and high porosities of 98-99%. The scaffolds were biologically evaluated using two kinds of cells, osteoblast cells (MC3T3-E1) and rat bone marrow cells. In both cases, the cells cultured in the scaffolds showed excellent cellular response, such as good cell proliferation and enhanced differentiation into osteoblasts. We conclude that such scaffolds with high porosity and large pore size may be effective as the matrix of tissue engineered structures in order to promote regeneration of bone.

Lanthanoid (M3+ La3+, Pr3+, Nd3+ and Sm3+)-substituted and lanthanoid/vanadium (V5+)-cosubstituted bismuth titanate thin films were fabricated on (11])Pt/Ti/SiO2/(100)Si substrates by a chemical solution deposition (CSD) technique. All the films consisted of a polycrystalline structure with random crystal orientation. Pr3+, Nd3+ and Sm3+-substituted BIT films [BPT, BNT and BST] had larger remanent polarization (P-r) values than that of conventional La3+-substituted BIT film [BLT]; furthermore, the Pr value of the BNT film was higher than those of the BPT and BST films. On the other hand, no significant difference in the coercive field (E-c) value was found among those films. P-r and E-c values of the BNT film with y = 0.50 in (Bi4.00-y, Nd-y)Ti3.00O12 were measured to be 32 muC/cm(2) and 126 kV/cm, respectively. V5+-substitution varied the P-r value of the lanthanoid-substituted BIT films without changing the in E, value. The P, value of the BNT film with y = 0.50 was improved up to 37 muC/cm(2) by V5+-substitution of x = 0.02 in (Bi4.00-y, Nd-y)(1-(x/12)) (Ti3.00-x, V-x)O-12 [BNTV]. Ferroelectric properties of the Pb-free polycrystalline BNT and BNTV films are comparable to those of conventional Pb-based ferroelectric films such as lead zirconate titanate [PZT] films. [DOI: 10.1143/JJAP.41.6820]

Thin films of Nd3+-substituted bismuth titanate, (Bi4.00-y,Nd-y)Ti3.00O12 (BNT), Nd3+/V5+-cosubstituted bismuth titanate, (Bi4.00-y,Nd-y)(Ti3.00-xVx)O-12 (BNTV), and La3+-substituted bismuth titanate, (Bi-3.25,La-0.75)Ti3.00O12 (BLT) were fabricated on the (111)Pt/Ti/SiO2/(100)Si substrates by a chemical solution deposition technique. These films possessed random-oriented polycrystalline structure. The BNT film had larger remnant polarization (P-r) than the BLT film; P-r and coercive field (E-c) of the BNT film with y=0.50 were 32 muC/cm2 and 126 kV/cm, respectively. Furthermore, V5+ substitution improved the P-r value of the BNT film up to 37 muC/cm2 (BNTV film; y=0.50, x=0.02), while the BNTV film had an E-c value of approximately 119 kV/cm which was similar to that of the BNT film. Ferroelectric properties of the Pb-free polycrystalline BNT and BNTV films are comparable with those of conventional Pb-based ferroelectric films like a lead zirconate titanate. (C) 2002 American Institute of Physics.

By molecular dynamics(MD) simulation crystal growth from supercooled MgO melt has been studied, whose crystal has an NaCl type. The model was similar to that previously applied for NaCl, Crystal growth of the melt on the crystal layers has been studied; 1400 or 1800 ions were disposed in an MD basic cell. The Gilbert-Ida-type pair potentials whose parameters were presented by Kawamura and Akarnatsu were employed, with which the melting point simulated in a three-dimensional space was 2670 K, while the experimental m.p. is 3099 K. The cases were studied that the initial interfaces between crystalline and melt were the (100), (110) and (111) planes; crystal grew in the [100], &lt;100&gt; and [111] directions, respectively. For the (100) system the growth rate was studied at various temperatures and found to possess a maximum(ca. 90ms(-1))at about 2300K. The mean square displacements on the x-y plane and in the z-direction were calculated. The overall profile of the growth feature of MgO is very similar to that of NaCl. (C) 2002 Elsevier Science B.V. All rights reserved.

The effect of rare-earth oxide addition (1-5 mass% of Ln(2)O(3) addition; Ln = Y, La, Nd, Sm, Gd, Dy, Er, and Yb) on the properties of hot-pressed (1550 degreesC, 90 min, 31 MPa) magnesium silicon nitride (MgSiN2) compact (ceramic) has been investigated. The role of rare-earth oxide addition on the relative density was classified as follows: (i) Positive effect (Y2O3, La2O3, and Yb2O3 addition), (ii) no appreciable effect (Nd2O3 and Er2O3 addition), and (iii) negative effect (Sm2O3, Gd2O3, and Dy2O3 addition). The grain sizes of the MgSiN2 ceramics with rare-earth oxide addition were almost comparable to or slightly smaller than those of the pure MgSiN2 ceramic. The average Vickers hardness of the MgSiN2 ceramic with 1 mass% of Y2O3 addition showed the highest value (21.5 GPa) amongst the MgSiN2 ceramics with rare-earth oxide addition. The thermal conductivity of the MgSiN2 ceramic had a maximum for the case of 1 mass% of Yb2O3 addition (26.6 W(.)m(-1.)K(-1)) and was believed to be the highest value so far reported for MgSiN2 ceramic. It was concluded that the relative density and Vickers hardness were best enhanced through the use of Y2O3 addition, whereas the addition of Yb2O3 was most suitable for enhancing the thermal conductivity. (C) 2002 Elsevier Science Ltd. All rights reserved.

Bismuth titanate (Bi4Ti3O12; BIT)-based ferroelectric materials are proposed from the view of the "Site-engineering", where the Bi-site ions are substituted by lanthanoid ions (La3+ and Nd3+) and Ti-site ions by other ions with higher charge valence (V5+). In the present study, influences of vanadium (V) - substitution for (Bi,M)(4)Ti3O12 thin films [M = lanthanoid] on the ferroelectric properties are evaluated. V-substituted (Bi,M)(4)Ti3O12 films have been fabricated using a chemical solution deposition (CSD) technique on the (111)Pt/Ti/SiO2/(100)Si substrate. Remnant polarization of (Bi,La)(4)Ti3O12 and (Bi,Nd)(4)Ti3O12 films has been improved by the V-substitution independent of the coercive field. The processing temperature of BLT and BNT films could also be lowered by the V-substitution.