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Dresden 2006 – wissenschaftliches Programm

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MM: Metall- und Materialphysik

MM 19: Electronic Properties I

MM 19.5: Vortrag

Dienstag, 28. März 2006, 17:30–17:45, IFW B

Structural and Electronic properties of the Layered Na0.46CoO2 — •Dimitri Argyriou1, L.C. Chapon2, C. Milne1, O. Prokhnenko1, and P.G. Radaelli21Hahn-Meitner-Institut, Glienicker Str. 100, Berlin D-14109, Germany — 2ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, UK

The onset of antiferromagnetic ordering coupled to a sharp rise in the resistivity of Na0.5CoO2 has recently been taken as evidence of charge ordering in this half doped cobaltate[1]. We have used neutron powder diffraction to investigate the lattice response to this charge and magnetic ordering using high resolution powder diffraction from 2 till 600K. Our sample is a little off the ideal composition x=0.46, but shows the identical transitions at Tco=52K and at 87K, as other single crystal sample of nominal x=0.5 composition. We find that the orthorhombic structure of Na0. 46CoO2 (Pnmm) is stable from 460K to 2K, even below the charge ordering transition at 50K. At room temperature we can clearly identify two Co sites which are distinguishable from their octahedral distortions. One site, labeled Co(1) is at the center of a CoO6 octahedron that shows an octahedral distortion 5 times larger than the octahedron centered in the Co(2) site. The average bondlength for both Co sites is essentially the same, 1.890Å, suggesting the same bond-valence. With lowering temperatures below Tco, we find no anomalies in Co-O bondlengths or octahedral distortion parameters, suggesting that the sharp increase in the resistivity at 50K may arise from an effect other than charge ordering. [1] M.L. Foo, et al. Phys. Rev. Lett. 92, 247001 (2004).

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