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Journal Articles

Incommensurately modulated crystal structure of $$alpha$$'(O'3)-type sodium cobalt oxide Na$$_{x}$$CoO$$_{2}$$ (${it x}$ $$sim$$ 0.78)

Miyazaki, Yuzuru*; Igawa, Naoki; Yubuta, Kunio*

Acta Crystallographica Section B; Structural Science, Crystal Engineering and Materials (Internet), 77(3), p.371 - 377, 2021/06

 Times Cited Count:0 Percentile:0.02(Chemistry, Multidisciplinary)

Crystal structure of $$alpha$$'(O'3)-type layered sodium cobalt oxide Na$$_{x}$$CoO$$_{2}$$ (${it x}$ $$sim$$ 0.78) was analyzed using the (3+1)-dimensional superspace approach to the neutron diffraction data. The crystal structure is described based on the superspace group ${it C}$2 = ${it m}$(${it p}$0${it q}$)00, wherein the positions of Na atoms are most significantly modulated in the monoclinic ${it a}$-direction to form an ordered arrangement. Such a positional modulation causes a quasi-periodic shift of Na atoms from the centers of the NaO$$_{6}$$ polyhedra between undulated CoO$$_{2}$$ sheets, changing the form of the NaO$$_{6}$$ polyhedron from an octahedral coordination (O) to a trigonal prismatic one (P). Where the Na atoms are most significantly shifted, the neighboring Na atoms are located at almost touching distances and yielding Na-deficient sites. As a result, a typical sequence of NaO$$_{6}$$ octahedra with -O-O-O-P-$${it V}$$$$_{mathrm Na}$$-P- along the a-axis is realized.

Journal Articles

Chemical-pressure-induced point defects enable low thermal conductivity for Mg$$_{2}$$Sn and Mg$$_{2}$$Si single crystals

Saito, Wataru*; Hayashi, Kei*; Huang, Z.*; Sugimoto, Kazuya*; Oyama, Kenji*; Happo, Naohisa*; Harada, Masahide; Oikawa, Kenichi; Inamura, Yasuhiro; Hayashi, Koichi*; et al.

ACS Applied Energy Materials (Internet), 4(5), p.5123 - 5131, 2021/05

 Times Cited Count:0 Percentile:0(Chemistry, Physical)

Journal Articles

Preparation, thermoelectric properties, and crystal structure of boron-doped Mg$$_{2}$$Si single crystals

Hayashi, Kei*; Saito, Wataru*; Sugimoto, Kazuya*; Oyama, Kenji*; Hayashi, Koichi*; Happo, Naohisa*; Harada, Masahide; Oikawa, Kenichi; Inamura, Yasuhiro; Miyazaki, Yuzuru*

AIP Advances (Internet), 10(3), p.035115_1 - 035115_7, 2020/03

 Times Cited Count:5 Percentile:68.88(Nanoscience & Nanotechnology)

Journal Articles

Quantum-mechanical tunneling in the H$$_{2}$$ elimination from 2,3-dimethylbutane cation: (CH$$_{3}$$)$$_{2}$$CHCH(CH$$_{3}$$)$$_{2+}$$$$rightarrow$$(CH$$_{3}$$)$$_{2}$$C=C(CH$$_{3}$$)$$_{2+}$$+H$$_{2}$$; An ab initio molecular orbital study

Kurosaki, Yuzuru*; Takayanagi, Toshiyuki; Miyazaki, Tetsuro*

Journal of Molecular Structure; THEOCHEM, 452, p.209 - 218, 1998/00

no abstracts in English

Oral presentation

Modulated structure of $$alpha$$'-Na$$_{x}$$CoO$$_{2}$$

Miyazaki, Yuzuru*; Igawa, Naoki; Yubuta, Kunio*; Kajitani, Tsuyoshi*

no journal, , 

The crystal structure of polycrystalline $$alpha$$'-Na$$_{x}$$CoO$$_{2}$$ has been determined by means of the (3+1)-dimensional superspace group approach using the neutron powder diffraction and Rietveld analysis method. Na site in the$$alpha$$'-Na$$_{x}$$CoO$$_{2}$$ is modulated along ${it a}$- and ${it c}$-axes and periodic vacancy sites are existed. It was founded that the octahedrons and prisms of NaO are combined along ${it a}$-axis and that the CoO$$_{2}$$ layers are modulated along ${it c}$-axis.

Oral presentation

Crystal structure and thermoelectric properties of Ba$$_{x}$$CoO$$_{2}$$ synthesized by means of ion-exchange method

Igarashi, Dai*; Miyazaki, Yuzuru*; Yubuta, Kunio*; Igawa, Naoki; Kajitani, Tsuyoshi*

no journal, , 

The crystal structures of polycrystalline ${it A}$ $$_{x}$$CoO$$_{2}$$ (${it A}$=Ca, Sr, Ba) have been determined by the neutron powder diffraction and the electron diffraction studies. In the profile of the Ba$$_{0.35}$$CoO$$_{2}$$, the 002 peak was shifted to lower diffraction angle compared with those of other samples, and the diffraction peak attributed to the superlattice structure was appeared between 002 and 004 peaks. The relationship between the crystal structures and thermoelectrical properties will be discussed in the presentation.

Oral presentation

Effect of cation-ordering on thermoelectric properties in layered cobaltates

Igarashi, Dai*; Miyazaki, Yuzuru*; Yubuta, Kunio*; Igawa, Naoki; Kajitani, Tsuyoshi*

no journal, , 

Layered cobaltates ${it A$_{x}$}$CoO$$_{2}$$ (A = Na, Ca, Sr, Ba) were prepared, and those cation orderings on thermoelectric properties were investigated. It was appeared that those samples had a (3+1) dimensional complexed crystal structure with the cation-disordering on the A layer to the Co$$_{2}$$ layer.

Oral presentation

Modulated crystal structure of layered cobaltate $$alpha$$'-Na$$_{x}$$CoO$$_{2}$$ (${it x}$ $$sim$$ 0.75)

Miyazaki, Yuzuru*; Igawa, Naoki; Yubuta, Kunio*

no journal, , 

The crystal structure of a polycrystalline sample of $$alpha$$'(O1)-type Na$$_{x}$$CoO$$_{2}$$ (${it x}$ $$sim$$ 0.75) has been determined by means of the (3+1)-dimensional superspace group approach using powder neutron diffraction. The structural parameters were refined with a superspace group of ${it C}$2/${it m}$(${it p}$0${it q}$)00. The positional modulation of Na atoms along the ${it a}$-axis is most significant; the ${it x}$ coordinate approaches +0.18 at ${it x}$ $$sim$$ 0.32, while it is negatively shifted to -0.18 at ${it x}$ $$sim$$ 0.68. For both extreme cases, the ${it x}$ position of Na atoms is deviated $$sim$$ 0.9 ${AA}$ from (0,1/2, 1/2), nearly touching neighboring.

Oral presentation

Modulated crystal structure and physical properties of $$alpha$$'-Na$$_{x}$$CoO$$_{2}$$

Miyazaki, Yuzuru*; Yubuta, Kunio*; Igawa, Naoki

no journal, , 

The crystal structure of polycrystalline samples of $$alpha$$'-Na$$_{x}$$CoO$$_{2}$$ (O1-type) has been determined by means of the (3+1)-dimensional superspace group approach using neutron diffraction data. The precise structural modulation including an undulated arrangement of the CoO$$_{2}$$ conduction sheets has been revealed. Due to the cooperative shift of the Na atoms in the crystallographic a-axis, the coordination polyhedron of NaO$$_{6}$$ changes from prismatic to octahedral site by site. A large positive Seebeck coefficient and a reasonably low electrical resistivity imply that the compound exhibits better thermoelectric performance than that of the $$gamma$$-NaxCoO$$_{2}$$ (P2-type) phase at lower temperatures below 300 K.

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