Thermal expansion and compressibility in superconducting Na{sub x}CoO{sub 2}{center_dot}4xD{sub 2}O (x{approx_equal}1/3): Evidence for pressure-induced charge redistribution

Journal Article · Thu Dec 01 00:00:00 EST 2005 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.72.2· OSTI ID:20787762

Jorgensen, J D; Avdeev, M; Hinks, D G; Barnes, P W; Short, S ^[1]

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1. Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

We have performed thermal expansion and compressibility measurements on the recently discovered superconducting material Na{sub x}CoO{sub 2}{center_dot}4xD{sub 2}O (x{approx_equal}1/3) using neutron powder diffraction over the temperature range 10-295 K and the pressure range 0-0.6 GPa. Pressure measurements were done in a helium-gas pressure cell. Both the thermal expansion and compressibility are very anisotropic, with the largest effects along the c axis, as would be expected for a layered material with weak hydrogen bonding nominally along the c axis. Near room temperature, the anisotropies of the thermal expansion and compressibility of the hexagonal crystal structure are nearly the same [({delta}c/c)/({delta}a/a){approx_equal}3-4], with a 100 deg. C change in temperature being roughly equivalent to 0.2 GPa pressure. It might be then inferred that changes in atom position parameters are also the same, but this is not the case. While the effects of temperature on the atom positions are essentially what one might expect, the effects of pressure are surprising. With increasing pressure, the thickness of the CoO{sub 2} layer increases, due to the combined effects of an increasing Co-O bond length and changes in the O-Co-O angles of the CoO{sub 6} octahedra. We conclude that this unusual effect results from pressure-induced strengthening of the hydrogen bonding between the Na{sub x}(D{sub 2}O){sub 4x} layers and the CoO{sub 2} layers. The strengthening of these hydrogen bonds requires that charge be moved from elsewhere in the structure; hence, there is a pressure-induced charge redistribution that weakens (lengthens) the Co-O bonds and changes the electronic structure of the superconducting CoO{sub 2} layers.

• OSTI ID: 20787762
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 72, Issue 22; Other Information: DOI: 10.1103/PhysRevB.72.224515; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANISOTROPY
ATOMS
BOND ANGLE
BOND LENGTHS
CHEMICAL BONDS
COBALT OXIDES
COMPRESSIBILITY
CRYSTAL STRUCTURE
ELECTRONIC STRUCTURE
HEAVY WATER
HELIUM
LAYERS
NEUTRON DIFFRACTION
PRESSURE MEASUREMENT
PRESSURE RANGE GIGA PA
SODIUM COMPOUNDS
SUPERCONDUCTORS
THERMAL EXPANSION