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300 results on '"Kan, Daisuke"'

101. Overpotential-Induced Introduction of Oxygen Vacancy in La0.67Sr0.33MnO3 Surface and Its Impact on Oxygen Reduction Reaction Catalytic Activity in Alkaline Solution

Author

Kan, Daisuke, primary, Orikasa, Yuki, additional, Nitta, Kiyofumi, additional, Tanida, Hajime, additional, Kurosaki, Ryo, additional, Nishimura, Tomoe, additional, Sasaki, Takahiro, additional, Guo, Haichuan, additional, Ozaki, Yusuke, additional, Uchimoto, Yoshiharu, additional, and Shimakawa, Yuichi, additional

Published
2016
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107. Research Update: Interface-engineered oxygen octahedral tilts in perovskite oxide heterostructures

Author

40378881, 50186491, 20372550, Kan, Daisuke, Aso, Ryotaro, Kurata, Hiroki, Shimakawa, Yuichi, 40378881, 50186491, 20372550, Kan, Daisuke, Aso, Ryotaro, Kurata, Hiroki, and Shimakawa, Yuichi

Abstract

Interface engineering of structural distortions is a key for exploring the functional properties of oxide heterostructures and superlattices. In this paper, we report on our comprehensive investigations of oxygen octahedral distortions at the heterointerface between perovskite oxides SrRuO3 and BaTiO3 on GdScO3 substrates and of the influences of the interfacially engineered distortions on the magneto-transport properties of the SrRuO3 layer. Our state-of-the-art annular bright-field imaging in aberration-corrected scanning transmission electron microscopy revealed that the RuO6 octahedral distortions in the SrRuO3 layer have strong dependence on the stacking order of the SrRuO3 and BaTiO3 layers on the substrate. This can be attributed to the difference in the interfacial octahedral connections. We also found that the stacking order of the oxide layers has a strong impact on the magneto-transport properties, allowing for control of the magnetic anisotropy of the SrRuO3 layer through interface engineering. Our results demonstrate the significance of the interface engineering of the octahedral distortions on the structural and physical properties of perovskite oxides.

Published
2015

108. Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films

Author

40378881, 70365691, 20372550, Hirai, Kei, Kan, Daisuke, Ichikawa, Noriya, Mibu, Ko, Yoda, Yoshitaka, Andreeva, Marina, Shimakawa, Yuichi, 40378881, 70365691, 20372550, Hirai, Kei, Kan, Daisuke, Ichikawa, Noriya, Mibu, Ko, Yoda, Yoshitaka, Andreeva, Marina, and Shimakawa, Yuichi

Abstract

Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550 K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620 K is ascribed to charge disproportionation of Fe 3.66+ into Fe 4+ and Fe 3+, associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality.

Published
2015

109. Nanoscale oxygen ion dynamics in SrFeO2.5+δ epitaxial thin films.

Author

Heo, Yooun, Kan, Daisuke, and Shimakawa, Yuichi

Subjects
*TRANSITION metal oxides, *OXIDES, *OXIDATION-reduction reaction, *THIN films, *FERRITES
Abstract

A variety of functional properties in transition metal oxides are often underpinned by oxygen vacancies. While the oxygen vacancy concentration and arrangements are well-known to have strong influence on the physical properties of oxides, the oxygen dynamics in oxides—including oxygen ion incorporation and movements during redox reactions—remain elusive. Performing conductive AFM studies of epitaxial thin films of oxygen-deficient SrFeO2.5 treated by air-annealing at various temperatures, we observe oxidation-induced enhancement of local electronic conduction on the higher terraces near the outer step edges at which oxygen ions are preferably incorporated and diffuse into the films. We also show that the local conduction can be reversibly controlled by electric-field-induced redox reactions at room temperature. These results highlight the importance of the nanoscale oxygen dynamics in redox reactions in SrFeO2.5 films. [ABSTRACT FROM AUTHOR]

Published
2018
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124. Atomic level observation of octahedral distortions at the perovskite oxide heterointerface.

Author

40378881, 20372550, 50186491, Aso, Ryotaro, Kan, Daisuke, Shimakawa, Yuichi, Kurata, Hiroki, 40378881, 20372550, 50186491, Aso, Ryotaro, Kan, Daisuke, Shimakawa, Yuichi, and Kurata, Hiroki

Abstract

For perovskite oxides, ABO3, slight octahedral distortions have close links to functional properties. While perovskite oxide heterostructures offer a good platform for controlling functionalities, atomistic understanding of octahedral distortion at the interface has been a challenge as it requires precise measurements of the oxygen atomic positions. Here we demonstrate an approach to clarify distortions at an atomic level using annular bright-field imaging in aberration-corrected scanning transmission electron microscopy, which provides precise mappings of cation and oxygen atomic positions from distortion-minimized images. This technique revealed significant distortions of RuO6 and ScO6 octahedra at the heterointerface between a SrRuO3 film and a GdScO3 substrate. We also found that structural mismatch was relieved within only four unit cells near the interface by shifting the oxygen atomic positions to accommodate octahedral tilt angle mismatch. The present results underscore the critical role of the oxygen atom in the octahedral connectivity at the perovskite oxide heterointerface.

Published
2013

126. Neutron Diffraction Investigations of Magnetism in BiFeO3 Epitaxial Films

Author

CALIFORNIA INST OF TECH PASADENA, Ratcliff, II, William, Kan, Daisuke, Chen, Wangchun, Watson, Shannon, Chi, Songxue, Erwin, Ross, McIntyre, Garry J, Capelli, Sylvia C, Takeuchi, Ichiro, CALIFORNIA INST OF TECH PASADENA, Ratcliff, II, William, Kan, Daisuke, Chen, Wangchun, Watson, Shannon, Chi, Songxue, Erwin, Ross, McIntyre, Garry J, Capelli, Sylvia C, and Takeuchi, Ichiro

Abstract

The recovery of a modulated magnetic structure in epitaxial BiFeO3 thin films as revealed by neutron diffraction is reported. The magnetic structure in thin films is found to strongly depend on substrate orientation. The substrate orientation causes different strain-relaxation processes resulting in different thin-film crystal structures. The (110) oriented film with a monoclinic structural phase has a single-domain modulated magnetic structure where the magnetic moment lies in the HHL plane. For the (111) oriented film that has a rhombohedral structure, a modulated structure superimposed on the G-type antiferromagnetic order is found. These results indicate that slight structural modifications in the BiFeO3 thin film cause drastic changes in the magnetic structure., Published in the Journal of Advanced Functional Materials, v21 n9 p1567-1574, 2011.

Published
2011

134. Resistive switching properties of epitaxial BaTiO3−δ thin films tuned by after-growth oxygen cooling pressure.

Author

Heo, Yooun, Kan, Daisuke, Shimakawa, Yuichi, and Seidel, Jan

Abstract

BaTiO3−δ, i.e. oxygen-deficient barium titanate (BaTiO3), thin films grown on GdScO3(110) substrates with SrRuO3 conductive electrodes by pulsed laser deposition are studied by X-ray diffraction and conductive AFM to characterize their structure and nanoscale electronic properties. Bias- and time-dependent resistive switching measurements reveal a strong dependence on the oxygen vacancy concentration, which can be tuned by after-growth oxygen cooling conditions of thin films. The results indicate that the resistive switching properties of BaTiO3−δ can be enhanced by controlling oxygen deficiency and provide new insight for potential non-volatile resistive random-access memory (RRAM) applications. [ABSTRACT FROM AUTHOR]

Published
2016
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