Key Engineering Materials Vol. 350

Abstract: We realized morphology control of ZnO crystals and prepared ZnO particles with variety of shapes such as hexagonal, ellipse, two large needles with small needles and multi-needles. The morphology control was achieved by the control of super saturation degree of aqueous solutions. All of the particles showed X-ray diffraction of single ZnO phase. The control of crystal growth and particle morphology in this system would contribute to the development of future crystalline materials and devices.

Abstract: To fabricate porous and thick alumina films, we prepared an aqueous alumina hydroxide sol containing trehalose. The alumina films were deposited by dip-coating technique on glass substrates and heating at 500 °C. The maximum thickness of the film obtained by one-run dip-coating using the sol containing trehalose was over 1000 nm. The film was an aggregate of alumina particles with a diameter of 20-40 nm and pores were interstices between the particles. The porosity of alumina film can be controlled in the range of 48-65 % by changing trehalose concentration in the dip-coating solution.

Abstract: Barium titanate nanoparticle (BT-NP) suspensions were prepared by dispersing sol-gel-derived BT-NPs in ethylene glycol monomethyl ether (EGMME) under sonication. When an electric field was applied, a part of the BT-NPs in a suspension was deposited on the cathode by electrophoretically deposition and most of the rest of the BT-NPs settled down towards the bottom of a container. The concentration of BT-NPs in the lower part of the container (Cbottom) increased with time until the Cbottom reached a specific concentration (threshold concentration) at which sedimentation of BT-NPs start to occur. The threshold concentration of the nanoparticles sedimentation gave a significant influence upon the aspect of a BT-NPs deposit formed on the cathode.

Abstract: We have demonstrated a fabrication procedure for spin-electronic devices by using two-dimentional titania nanosheets. Magneto-optical Kerr measurements demonstrate that Co-substituted titania nanosheets (Ti0.8Co0.2O2) act as nanoscale ferromagnetic layers at room temperature, and their multilayer-assemblies exhibit robust magnetic circular dichroism (104–105 deg/cm) near the absorption edge at 260 nm, an operating wavelength being the shortest attained so far. The availability of ferromagnetic nanostructures and their molecule-level assembly allow the rational design and construction of high-efficiency magneto-optical devices by forming superlattices.

Abstract: Vertically aligned carbon nanotubes (CNTs) were grown on a stainless steel substrate (SUS304) by resistance-heating method in alcohols containing homogeneously dissolved cobaltocene Co(C5H5)2 as a catalyst source. Straight-chain primary alcohols, 1,2-ethanediol and cyclohexanol were used as carbon sources to examine the effects of the molecular structures on the morphology of the aligned CNTs. Methanol brought the best purity and alignment of CNTs of all the alcohols. The CNTs from 1,2-ethanediol was worse in the purity than those from ethanol with the same number of carbon atoms. The CNTs from cyclohexanol had a better purity than those from 1-hexanol. Distinctive features of this method are simple, low cost and a one-step process involving none of vacuum processes and catalyst preparation processes.

Abstract: Aligned carbon nanotube arrays (CNTAs) were readily synthesized by a resistance heating method on a substrate of commercially available stainless steel which has more plentiful availability than the wafers of Si and quarts. The catalyst was supported on the substrate by dip coating with a methanol solution of M(C5H5)2(M=Co,Fe), and the substrate was electrically heated at 800oC in methanol. Highly aligned CNTAs were grown from the catalyst prepared from 0.02 M Co(C5H5)2 methanol solution. The alignment was influenced by the concentration and the kind of M(C5H5)2.

Abstract: The series of partially Al-substituted lithium manganese oxides were prepared by spray pyrolysis process from spray solutions with citric acid and ethylene glycol. The as-prepared particles obtained from spray solution with citric acid and ethylene glycol turned to fine-sized LiMn(12- x)/6Alx/6O4(0.05≤x≤2) particles with regular morphology after post-annealing. The discharge capacities of the particles post-annealed at temperature of 800oC changed from 128 to 84 mAh/g when the x of the LiMn(12-x)/6Alx/6O4 particles was changed from 0 to 2. The Al-doped LiMn2O4 fine particles prepared by spray pyrolysis from spray solution with citric acid and ethylene glycol had good cycle properties.

Abstract: We synthesized barium titanate (BaTiO3) nanoparticles by sol-gel process and investigated their crystallization behavior using differential scanning calorimetry and X-ray diffraction. BaTiO3 nanoparticles with various degrees of crystallinity were obtained by adjusting synthesis conditions. Under aging conditions that do not allow dealcholization reaction to complete, many hydroxyl ligands remain in as-synthesized BaTiO3 nanoparticles, resulting in the formation of voids or defects in the nanoparticles after calcination. It is essential to use high concentration alkoxides precursor solutions for producing BaTiO3 nanoparticles with high crystallinity at low temperature.

Abstract: BaTiO3 nano-sized powders were successfully prepared by spray pyrolysis using multiphase plasma under the air atmosphere. The particles characteristics of BaTiO3 nano-sized powders were studied by SEM and XRD. The effect of volume of arc plasma and precursor solution on the formation of BaTiO3 nano-sized powders was investigated. The use of Ba-Ti complex precursor solution derived from lactic acid led to formation of tetragonal BaTiO3 nano-sized powders with 140 nm size. As for BaTiO3 ceramics, the effect of sintering temperature on relative density and the temperature dependence of dielectric properties were investigated.