Papers by Author: Takashi Goto

Abstract: Ba²TiO₄ and Ba₄Ti₁₃O₃₀ Thick Films Were Prepared by Laser Chemical Vapor Deposition Using Ba- and Ti-Dipivaloylmethanate Precursors. Single-Phase Ba₂TiO₄ Thick Films Were Obtained at 845–946 K and Ba/Ti Source Molar Ratio 2.4. Single-Phase Ba₄Ti₁₃O₃₀ Films Were Obtained at 944–1011 K and Ba/Ti Source Molar Ratio 0.38. Ba₂TiO₄ Thick Films Consisted of Truncated Grains, while Ba4ti13o30 Thick Films Had Shellfish-Like Grains. Ba₂TiO₄ and Ba₄Ti₁₃O₃₀ Thick Films Showed a Columnar Growth and their Deposition Rates Were 72 and 132 μm h⁻¹, Respectively.

Abstract: B-Axis-Oriented Bati2o5 Nanopillars Were Prepared on (100) Mgo Single Crystal Substrate by Laser Chemical Vapor Deposition Using Ba and Ti Dipivaloylmethanate Precursors. B-Axis-Oriented Bati2o5 Nanopillars Were Approximately 250–400 Nm in Width and 2.5 μm in Height. Deposition Rate of Bati2o5 Nanopillar Arrays Was about 75 μm H−1.

Abstract: Α-Al₂O₃ Films Were Prepared by Laser Chemical Vapor Deposition and the Effects of Precursor Evaporation Temperature (T_vap) and Oxygen Gas Flow Rate (FRo) on Phase and Orientation of Al₂o₃ Films Were Investigated. at T_vap = 413 K, (100)-Oriented α-Al₂O₃ and θ-Al₂O₃ Were Codeposited. the Amount of θ-Al₂O₃ Increased with Increasing FRo. at T_vap = 433–443 K, α-Al₂O₃ Films Showed a (001) Orientation. (100)- and (001)-Oriented α-Al₂O₃ Films Had a Rectangular- and Hexagonal-Shaped Grains, Respectively, and Showed a Columnar in Cross Section. Grain Size of (100)- and (001)-Oriented α-Al₂O₃ Films Decreased from 10 to 2 μm with Increasing FRo from 0.085 to 0.85 Pa m³ s⁻¹. Deposition Rate Increased from 100 to 300 μm h⁻¹ with Increasing T_vap from 413 to 443 K.

Abstract: MgO substituted polycrystalline BaTi₂O₅ (BT₂), Ba_1-xMgxTi₂O5 (BMT₂), was prepared by a floating zone method (FZ-melting). The dielectric property of BMT₂ was investigated by_{Subscript text} an AC impedance method. At x = 0.005 MgO, the permittivity (r) showed the maximum value of 5800 for FZ-melted specimens. The Curie temperature (T_c) decreased with increasing x and the permittivity showed a flat peak at x ≥ 0.03. Second phases of BaTiO₃, Ba₆Ti17O40 and Ba4MgTi11O27 were identified in polycrystalline BMT2. BaTiO3 and Ba6Ti17O40 could be due to the decomposition of BT2 at high temperatures.

Abstract: c-axis-oriented YBa2Cu3O7- films were prepared by laser chemical vapor deposition (laser CVD) using Y(DPM)3, Ba(DPM)2/Ba(TMOD)2 and Cu(DPM)2 as precursors with enhancement by a continuous wave Nd:YAG laser. YBa2Cu3O7- film almost in a single phase and that with different second phases of BaCuO2, CuBaO2, BaY2O4, CuYO2, Y2O3 and CuO were obtained by varying evaporation temperature of precursors. Ternary phase diagram as a function of evaporation amount of three precursors were obtained. The deposition rate of the c-axis-oriented YBCO film was 60 µmh-1, about 60–600 times higher than those of conventional CVD.

Abstract: Transparent La2Zr2O7 with cubic pyrochlore structure was first fabricated by reactive spark plasma sintering using commercially available La2O3 and ZrO2 powders. Single phase of pyrochlore La2Zr2O7 was obtained at a sintering temperature of 1673 K and sintering pressure at 100 MPa for 2.7 ks. The La2Zr2O7 sintered body had a uniform grain size of 1.5 m and exhibited 68% transmittance in the wavelength range of 4–6 m.

Abstract: The oxidation tests of the ZrB2-15vol.%SiC composite were carried out at 1673-1923 K under a low partial pressure of oxygen. Cross sections of the oxidized samples were studied using WDS. The reaction layer consists of ZrO2 and SiO2 at 1673 K. The SiO2 protective layer is formed on the surface. No apparent SiC depleted layer is observed. SiC depletion seems to occur at 1923 K and only the ZrO2 phase exists at the reaction layer. The passive oxidation occurs at 1673 K, whereas the active oxidation at 1923 K. The mass changes are quantitatively discussed by introducing a new emprical equation. The ZrB2-30 vol.%SiC composite is also discussed briefly.

Abstract: First of all, the as-cast microstructures of Mo-rich Mo-Si-B ternary alloys were investigated around the triple junction point of the primary Mo solid solution, Mo5SiB2 and Mo2B in this work, based on the liquidus projections of the Mo-Si-B system which have been reported in earlier studies. Subsequently, their microstructural evolution through heat treatment was investigated. Since Mo2B crystallizes out during solidification into a primary or secondary phase even though the alloy composition lies in the triangle of Mo-Mo5SiB2-Mo3Si in the Mo-Si-B equilibrium phase diagram, the as-cast microstructures include the non-equilibrated Mo2B in wide compositional ranges. However, Mo2B was completely decomposed during heat treatment at 1800 °C for 24 h and this contributed to the development of homogeneous, fine microstructures. On the other hand, since Mo2B was not decomposed perfectly during 24 h of 1600 °C heat treatment, as-cast microstructures largely remained. Therefore, it is realized that the heat treatment at 1800 °C is necessary to obtain well-developed microstructures of Mo-Si-B alloys.

Abstract: Nearly stoichiometric TiN_x films were deposited on Al₂O₃ substrates by laser enhanced chemical vapor deposition (CVD) with tetrakis (diethylamido) titanium (TDEAT) and ammonia as the source materials. Emphases were given on the effects of laser power (P_L) and pre-heating temperature (T_pre) on the composition and deposition rate of TiN_x films. Single phase of TiN_x films with columnar cross section were obtained. The ratio of N to Ti in TiN_x films increased with increasing P_L and was close to stoichiometric at P_L > 150 W. The deposition rate of TiN_x films with a depositing area of 300 mm² was about 18-90 µm/h, which decreased with increasing P_L and T_pre.

Abstract: Oxyapatite, amorphous calcium phosphate, and double-layered calcium phosphate coating films were fabricated on mirror-polished commercially pure titanium (CP Ti) and blasted Ti-6Al-4V alloy substrates by radiofrequency (RF) magnetron sputtering; the properties of these films were evaluated in vivo and in vitro. The bonding strength between the calcium phosphate films and the Ti substrates was higher than 50 MPa. This value is higher than the bonding strength reported in the case of plasma-sprayed calcium phosphate coating films fabricated on Ti substrates. The removal torque of screw-type blasted Ti-6Al-4V alloy implants in the femurs of Japanese white rabbits increased with the duration of implantation, and the removal torque values of the coated implants was observed to be higher than those of the non-coated implants. In vitro and in vivo studies indicate that coating Ti implants with calcium phosphate films using RF magnetron sputtering is effective in improving the bone compatibility of Ti implants. Finally, the factors that should be considered in fabricating biomedical coating films were discussed.