Masafumi Nakaya

Conversion of Anisotropically Phase-Segregated Pd/γ-Fe2O3 Nanoparticles into Exchange-Coupled fct-FePd/α-Fe Nanocomposite Magnets

Exchange-coupled fct-FePd/alpha-Fe nanocomposite magnets were fabricated by converting anisotropically phase-segregated Pd/gamma-Fe2O3 nanoparticles via the interfacial atom diffusion. The magnetically hard fct-FePd phases formed by the interdiffusion between alpha-Fe and fcc-Pd phases nearly preserve their sizes at the nanometer scale because they are surrounded by the alpha-Fe matrix. The VSM measurements reveal that the exchange coupling between the soft and hard phases has been realized.

One-step solvothermal synthesis of cubic-shaped ITO nanoparticles precisely controlled in size and shape and their electrical resistivity

Highly crystalline cubic-shaped ITO nanoparticles with narrow size distribution were successfully prepared through a one-step process from a mixed ethylene glycol solution of indium and tin salts. The present paper is focused on the detailed study on their solvothermal synthesis, in particular, the effect of process variables on the size and shape. In the present system with using glycol as a solvent, it was observed that the direct formation of ITO nanoparticles occurred from the dissolution–recrystallisation of the amorphous-like indium hydroxides initially formed as precursors. The mean size of the ITO nanoparticles was controlled from 15.1 to 43.5 nm by changing the initial NaOH concentration. The high resolution transmission electron microscopic and the Fourier transform (FT) analyses showed that the as-prepared nanoparticles have single-crystalline structure and were bound by a {200} plane. In addition, judging from the FT image, Sn ions in the cubic crystal structure of In2O3 were substituted homogeneously to form stable oxygen defects. The effect of particle size and morphology on the resistivity of the resultant powder was found to be distinct. Namely, the lower resistivity of well-crystallized cubic-shaped nanoparticles with the larger size, compared with the finer particles with random shape, was due to the lower interparticle resistivity because of the face-to-face contact for the former, but point-to-point contact for the latter.

Hydrothermal synthesis of BaZrO3 fine particles controlled in size and shape and fluorescence behavior by europium doping

Monodispersed barium zirconate (BaZrO3) fine particles with high crystallinity have been synthesized by hydrothermal reactions using barium hydroxide and a Zr–triethanolamine complex. The particle shape was controlled by changing initial Ba2+ and Zr4+ concentrations, and sphere-, rhombic dodecahedral-, and flower-shaped BaZrO3 fine particles were obtained. On the other hand, the particle mean size of the BaZrO3 microspheres was precisely controlled by the addition of NaOH into the precursor solutions. By Eu-doping, the present BaZrO3 synthesis was also applied to investigate the effect of size and shape on the fluorescence properties of BaZrO3 for its use as a phosphor. The asymmetric ratio of the photoluminescence intensity of the resulting Eu-doped BaZrO3 powders suggested that the particles obtained by the present method had a basically single crystalline structure.

Hydrothermal synthesis of size- and shape-controlled CaTiO3 fine particles and their photocatalytic activity

Calcium titanate fine particles controlled precisely in size and morphology were synthesized by an optimized hydrothermal method. Their photocatalytic activity was evaluated as the effect of the particle morphology, that is, the exposed surface. The size and morphology were successfully controlled with aging temperature and alternative use of Ti-sources, such as a TiO2 dispersion and titanium–triethanolamine complex. The photocatalytic activity of the CaTiO3 fine particles was measured by the evolution amount of H2 from a methanolic aqueous solution and the decomposition of acetic acid in water. As a result, rod-like particles showed the highest photocatalytic activity for H2 evolution. On the other hand, cubic-shaped particles exhibited a higher activity for the decomposition of acetic acid. Judging from electron diffraction images, both the cubic and rod-like particles were bound by {110} and {001} facets, but the rate of the {110} faces of the rod-like particles was much more than that of the cubic ones. The proper selection of the particle shape, outer surface is one of the key factors for the photocatalytic activity.

Size Control of Magnetite Nanoparticles in Excess Ligands as a Function of Reaction Temperature and Time

The novel synthesis of monodisperse magnetite Fe3O4 nanoparticles of varying sizes using a solventless synthetic method was developed. Iron salt was treated in excess oleylamine and oleic acid as ligands. The effect of the reaction temperature and time on the particle size was investigated and the particle sizes were easily tuned from 5.3 to 20.4 nm by changing the reaction temperature and time.

Precursor Effect on Hydrothermal Synthesis of Sodium Potassium Niobate Fine Particles and Their Piezoelectric Properties

Controlled synthesis of sodium potassium niobate (NaxK1-xNbO3: NKN) fine particles with different K/Na ratios was successfully achieved by the two-step hydrothermal reaction at 100 °C for 24 h and 200–250 °C for 3 h using niobium pentachloride as a soluble precursor. As a result of the effect of the K/Na ratio in the starting solution, NKN particles with an orthorhombic sodium niobate were formed in the NaOH/KOH ratios from 10/8 to 7/11. When the NaOH/KOH ratio was adjusted to 10/8, cubic-shaped particles were obtained, and the mean particle size with the size distribution was 3.0±1.2 µm. In contrast, by aging at 250 °C, NKN particles with orthorhombic potassium niobate crystal structure were obtained in the NaOH/KOH ratios from 5/13 to 1/17. Furthermore, monodispersed and octahedral-shaped NKN fine particles with a tetragonal crystal structure were formed as a single phase at 200 °C with the NaOH/KOH ratio of 6/12. The octahedral-shaped particles had a hierarchical built-up structure of cubic-shaped nanoparticles. The sodium and potassium ratio in the NKN crystal structures was further characterized by Rietveld analysis. All the NKN ceramics, prepared starting from the present hydrothermal method, had a highly porous structure. However, these ceramics exhibited high d33 values of ca. 100 pC/N. This result means that the octahedral-shaped NKN particles have high potential as lead-free piezoelectric materials.

Mechanochemically assisted hydrothermal synthesis of Sn-substituted MFI-type silicates

ABSTRACT Substitution of Al atoms in a zeolite framework by catalytic metal atoms has attracted considerable attention because the catalytic behavior can be tuned by the substituted atoms. In the present study, Sn-substituted MFI-type silicates were synthesized using a hydrothermal reaction of an amorphous Si-O-Sn precursor prepared by mechanochemical grinding of SiO2 and Sn(OH)4. The mechanochemical treatment was found to be a key technique for obtaining the amorphous Si-O-Sn precursor, where tetrahedral Sn4+ species were incorporated into the amorphous matrix. The Sn content in the framework of the MFI-type silicates was successfully controlled by the initial HCl/Si molar ratio of the hydrothermal procedures. Optical reflectance measurements revealed that the Sn4+ ions were dispersedly incorporated into the silicate framework while preserving the initial tetrahedrally coordinated species. Infrared results imply that the resulting Sn-substituted MFI-type silicate has Brønsted acid character. Precise control of the Brønsted and Lewis acid properties by Sn doping is a promising approach to the development of novel types of zeolite-based catalytic materials. GRAPHICAL ABSTRACT