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Okayama-shi, Japan

Kano J.,Okayama University | Kano J.,Japan Science and Technology Agency | Okamoto T.,Okayama University | Okamoto T.,Denso Corporation | And 11 more authors.
Japanese Journal of Applied Physics

Various types of iron oxides loaded on ferroelectric BaTiO3 and nonferroelectric ZrO2 supports have been studied by 57Fe Mössbauer spectroscopy to investigate the valence instability of iron oxides affected by ferroelectric polarization fluctuation. Although the iron oxide loaded on ZrO2 shows a typical reduction process at high vacuum and high temperature, the iron oxide loaded on BaTiO3 shows an opposite process, i.e., iron oxide oxidization. We propose the dynamics of band structures of ferroelectrics in the paraelectric phase to understand this phenomenon. The oscillation of band bending causes electron transfer from an iron oxide to a ferroelectric support. This result suggests that the surface charges of ferroelectrics are useful in developing new functional materials with metal compounds. © 2014 The Japan Society of Applied Physics. Source

Fujii E.,Industrial Technology Center Of Okayama Prefecture | Kawabata K.,Industrial Technology Center Of Okayama Prefecture | Nakazaki Y.,Nano Cube Japan Co. | Tanizawa Y.,Nano Cube Japan Co. | And 3 more authors.
Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi/Journal of the Ceramic Society of Japan

A flow-micro-reactor system was employed to fabricate hydroxyapatite (HAp) in order to mimic the interface between calcium and phosphate solutions on a wet chemical procedure. The mixing ratioof calcium nitrate tetrahydrate and diammonium hydrogenphosphate solution was set to the stoichiometric atomic ratio HAp, 1.67, whilepH value of the product suspension was varied from 6.4 to 10.0. The product morphology was changed from nano-sheet type to nano-particle type via nano-rod one, while theirsize was decreased from 100-500 nm to 50 nm. All as-prepared samples, irrespective of pH value of the resultant suspension, consisted of HAp, predominant phase, octacalcium phosphate (OCP), and dicalcium phosphate dihydrate (DCPD) or dicalcium phosphate anhydrate (DCPA). A batch system using the same solutions yielded very similar results, which confirmed that the reactions inthismicro-reactor well reproduced a large-scalemixing system. Calcining sample obtained from pH 6.4 suspension for 2h at lower temperatures (<400°C) lead to decomposition of DCPD, DCPA, and OCP. Trace tricalcium phosphate (TCP) appeared on calcination above 400°C. HAp remained the predominant phase throughout the process. After calcination at 600°C, no other phases than HAp and TCP were present in the product. The analyzed ratioCa/P (1.38) implied that those crystalline phases were highly Ca-deficient, and that amorphous calcium phosphates were involved in both as-prepared and calcined sample pH 6.4. ©2011 The Ceramic Society of Japan. All rights reserved. Source

Okamoto T.,Denso Corporation | Okamoto T.,Okayama University | Kano J.,Okayama University | Nakamura S.,Teikyo University | And 8 more authors.
Hyperfine Interactions

57Fe Mössbauer spectroscopy was performed on two types of Fe oxide nanoparticles supported on a typical ferroelectric, BaTiO3. It was found that the valence state of FeO nanoparticles changed to a mixed 2+/3+ state at high temperature where BaTiO3 shows paraelectric behaviour. We attribute this phenomenon to the fluctuation of electric dipoles which realizes carrier injection into the Fe oxides. This is the first report which discusses a dynamical valence state of transition metal oxides supported on ferroelectrics. © 2012 Springer Science+Business Media Dordrecht. Source

Fujii E.,Industrial Technology Center Of Okayama Prefecture | Kawabata K.,Industrial Technology Center Of Okayama Prefecture | Nakazaki Y.,Nano Cube Japan Co. | Tanizawa Y.,Nano Cube Japan Co. | And 4 more authors.
Ceramic Transactions

A micro-chemical process was applied to prepare nanometer-size hydroxy apatite (HA) particles with various shapes and sizes so as to provide high surface activities, where solutions of reagent-grade calcium nitrate tetrahydrate and diammonium hydrogen phosphate were introduced in a micro reactor. The particles were characterized by X-ray diffractometry, transmission electron microscopy, or inductively coupled plasma photometry. Particle size and shape were dependent on not only pH and concentration of the mixing solutions but also the flow rate. Dilute solutions containing 3 mM Ca(II) and 5 mM P(V) yielded spherical HA particles, whose average particle size increased from about 3 nm to 40 nm as the flow rate increased from 0.3 to 3 ml·min -1, where pH and the temperature of the reaction system were respectively maintained at 10 and at 40°C. Concentrated solutions with 50 mM Ca(II) and 30 mM P(V) yielded rectangular plate-like HA particles, 300 nm long and 50 nm wide, when pH was kept at 8, while agglomerations of smaller HA particles of about 20-50 nm were obtained when pH was kept at 10. Source

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