Crystal structure and elementary properties of NaxCoO2 (x=0.32, 0.51, 0.6, 0.75, and 0.92) in the three-layer NaCoO2 family

L Viciu, Jan-Willem G Bos, H W Zandbergen, Q. Huang, M. L. Foo, S. Ishiwata, A P Ramirez, M Lee, N P Ong, R J Cava

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Abstract

The crystal structures of NaxCoO2 phases based on three-layer NaCoO2, with x=0.32, 0.51, 0.60, 0.75, and 0.92, determined by powder neutron diffraction, are reported. The structures have triangular CoO2 layers interleaved by sodium ions, and evolve with variation in Na content in a more complex way than has been observed in the two-layer NaxCoO2 system. The phases with highest and lowest Na content studied (x=0.92 and 0.32) are trigonal, with three CoO2 layers per cell and octahedral Na ion coordination. The intermediate compositions have monoclinic structures. The x=0.75 compound has one CoO2 layer per cell, with Na in octahedral coordination and an incommensurate superlattice. The x=0.6 and 0.51 phases are also single layer, but the Na is found in trigonal prismatic coordination. The magnetic behavior of the phases is similar to that observed in the two-layer system. Both the susceptibility and the electronic contribution to the specific heat are largest for x=0.6.

Original languageEnglish
Article number174104
Number of pages10
JournalPhysical Review B: Condensed Matter and Materials Physics
Volume73
Issue number17
DOIs
Publication statusPublished - 1 May 2006

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