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Titre du document / Document title

Crystal structure of an open-tunnel oxide α-MnO2 analyzed by Rietveld refinements and MEM-based pattern fitting

Auteur(s) / Author(s)

KIJIMA Norihito (1) ; IKEDA Takuji (2) ; OIKAWA Kenichi (3) ; IZUMI Fujio (2) ; YOSHIMURA Yuji (1) ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

(1) National Institute of Advanced Industrial Science and Technolgoy, Tsubuka Central 5. 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, JAPON
(2) Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, JAPON
(3) Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Naka, Ibaraki 319-1195, JAPON

Résumé / Abstract

The crystal structure of an open-tunnel oxide, α-MnO2, free from any large stabilizing cations was analyzed by Rietveld refinement and whole-pattern fitting based on the maximum-entropy method (MEM). Rietveld refinement from neutron powder diffraction data for a partially deuterated specimen of MnO2.0.1(D0.34H0.66)2O showed it to have a hollandite-type structure (tetragonal; space group I4/m; a = 9.777(2) and c = 2.8548(5) Å; Z = 8; Rwp = 4.56%, Rp = 3.67%, RB = 1.52%, and RF = 0.77%; S = 1.23). The bond valence sum of Mn was calculated at +4.04. The quadratic elongation and bond angle variance for the MnO6 octahedron proved that its distortion is relatively small even if small H2O molecules are contained in tunnels instead of large stabilizing cations. Electron-density distribution (EDD) in MnO2.0.15H2O was visualized by MEM-based pattern fitting from both synchrotron and conventional X-ray powder diffraction data. The resulting EDD images showed that the inner effective diameters of a cage in α-MnO2 are about 2.6 Å for a bottleneck on the (002) plane and about 4.8 Å for an inner space on the (001) plane. Thus, H2O molecules (2.2 Å) can be trapped in the narrow tunnels of α-MnO2, whereas N2 molecules (4.3 Å) cannot penetrate the tunnel cavity. Elongation of electron densities for tunnel water along the tunnel direction was observed in the EDD images. Further, to obtain a reasonable isotropic atomic displacement parameter for the O3 site in the tunnel cavity, O3 had to be split into two pieces at the 4e site in the Rietveld refinement from the neutron diffraction data. These findings provide evidence that H2O molecules are not only vibrating markedly but also highly disordered, particularly along the [001] direction, near the center of the cage.

Revue / Journal Title

Journal of solid state chemistry    ISSN  0022-4596   CODEN JSSCBI 

Source / Source

2004, vol. 177, no4-5, pp. 1258-1267 [10 page(s) (article)] (45 ref.)

Langue / Language

Anglais

Editeur / Publisher

Elsevier, Amsterdam, PAYS-BAS  (1969) (Revue)

Mots-clés anglais / English Keywords

Transition element compounds

;

Inorganic compounds

;

Hollandite structure

;

Tetragonal lattices

;

Binary compounds

;

Manganese oxides

;

Precipitation

;

Deuteration

;

Scanning electron microscopy

;

Electron density

;

XRD

;

Neutron diffraction

;

Patterning

;

Maximum entropy methods

;

Refinement

;

Crystal structure

;

Experimental study

;

Mots-clés français / French Keywords

Métal transition composé

;

Composé minéral

;

Structure hollandite

;

Mn O

;

MnO2

;

Réseau quadratique

;

Composé binaire

;

Manganèse oxyde

;

Précipitation

;

Deutération

;

Microscopie électronique balayage

;

Densité électron

;

Diffraction RX

;

Diffraction neutron

;

Formation motif

;

Méthode entropie maximum

;

Affinement

;

Structure cristalline

;

Etude expérimentale

;

Mots-clés espagnols / Spanish Keywords

Afinamiento

;

Mots-clés d'auteur / Author Keywords

α-MnO2

;

Hollandite-type structure

;

Neutron powder diffraction

;

X-ray powder diffraction

;

Rietveld analysis

;

Maximum-entropy method

;

Electron-density distribution

;

Localisation / Location

INIST-CNRS, Cote INIST : 14677, 35400011150498.0260

Nº notice refdoc (ud4) : 15597757



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