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College Park, Maryland      June 6 - 10 , 2004

W2-C2 (2:00 PM): Crystal structure of NaxCoO2 (x from 1 to 0.3) at room temperature

Q. Huang (NIST Center for Neutron Research), M.L. Foo (Department of Chemistry, Princeton University, Princeton NJ), J.W. Lynn (NIST Center for Neutron Research), H.W. Zandbergen (National Centre for High Resolution Electron Microscopy, Technical University Delft, The Netherland), B. Toby (NIST Center for Neutron Research), R.J. Cava (Department of Chemistry, Princeton University, Princeton NJ)

The crystal structure of NaxCoO2 (x from 1 to 0.3) has been studied using the neutron powder diffraction technique. The structure consists of layers of edge-shared CoO6 octahedra in a triangular lattice (hexagonal lattice aH~2.85 and cH~10.8 ), with Na ions occupying ordered or disordered positions in the interleaving planes that form by four different Na ions order/disorder configurations. For x=1 the Na ions are completely ordered and fully occupy the 2d (2/3, 1/3, 1/4) site of a P63/mmc symmetry. At x=0.5 the Na ions occupy the 2a and 2b sites of Pnmm symmetry (ao~1.73aH, bo~2aH, co ~ cH), forming zigzag chains. In the range of x between 1 and 0.75, the Na ions randomly occupy the 2b(0, 0, ) and 2c(2/3, 1/3, 1/4) sites of P63/mmc symmetry and the occupancy at the 2c site increases with x increasing. For x between 0.75 and 0.5 and between 0.5 and 0.3, the Na randomly occupy the 2b(0, 0, ) and 6h(2x, x, ) sites in P63/mmc and the occupancy at the 6h site decreases with decreasing x. Structural parameters as a function of x indicate slope changes at x=0.75.

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