Stoichiometric oxygen content in NaxCoO2

Abstract

The crystal structure and oxygen stoichiometry in two-layer Na0.74CoO2 and Na0.38CoO2 at room temperature are analyzed by powder neutron diffraction. Two sets of diffraction data for each sample, taken at different incident neutron wavelengths, lambda=1.1968 Angstroms and lambda=1.5403 Angstroms, are analyzed simultaneously by the Rietveld method, allowing for the independent refinement of all structural parameters. The fractional oxygen site occupancies are found to be 1.01(1) for Na0.74CoO2 and 0.99(2) for Na0.38CoO2 respectively. These results indicate that the oxygen content of these phases is stoichiometric to a precision of 1 to 2%, and therefore the formal cobalt oxidation state is determined solely by the sodium content. The analysis also reveals that both types of sodium ions in the structure are in off-center distorted trigonal prismatic geometry.

15 pages, 2 tables, 3 figures

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Cited by in corpus (5)

• Electronic phase diagram of the layered cobalt oxide system, LixCoO2 (0.0 <= x <= 1.0)
• Searching for Stable Na-ordered Phases in Single Crystal Samples of gamma-NaxCoO2
• Electronic Correlations in CoO2, the Parent Compound of Triangular Cobaltates
• Theoretical analysis of oxygen vacancies in layered sodium cobaltate Na_xCoO_{2-δ}
• Tuning Co valence state in cobalt oxyhydrate superconductor by post reduction