Changes in the electronic structure of lithium cobaltites Li1+xCoO2(0 less than or equal to x less than or equal to 0.1) during chemical deintercalation were studied by X-ray diffraction; IR, X-ray photoelectron, and diffuse reflectance electron spectroscopy; and magnetic measurements. Acid treatment was shown to cause the partial removal of lithium from the oxide structure and the appearance of delocalized electrons in the system. The electronic state of cobalt ions did not change significantly, whereas oxygen ions were oxidized (O-2 --> O-). Structural defects in delithiated oxides had the same nature as in the initial superstoichiometric oxides; these structural defects were low-coordinate oxygen ions in the O- state. The structure of oxides containing excess lithium was stabler during chemical deintercalation. The magnetic properties of delithiated oxides were determined by (Co3+-O-) exchange-coupled pairs.

X-ray, IRS, XPS, EDRS and magnetic measurements were used to study Li1+xCoO2 (0 < x greater than or equal to 0.1) samples prepared by conventional ceramic method. It was shown that nonstoichiometric Li1+xCoO2 are characterized by homogeneous crystal structure with statistically distributed vacancies in the cobalt and oxygen layers and the increased Co-O bond covalency. The excess lithium results not in the reduction of Co3+ ions, but in the appearance of a new state of oxygen ions different from cell oxide, with higher value of binding energy (BE), i.e. with smaller electronic density. Acid treatment of Li1+xCoO2 leads to the appearance of delocalized (itinerant) electrons. The electronic state of cobalt ions does not change noticeably whereas the additional oxygen state increases significantly, thus, evidencing that oxygen ions do compensate for the charge upon chemical delithiation. The structure of nonstoichiometric samples appeared to be more stable upon this process. (C) 2003 Elsevier Science B.V. All rights reserved.

Li1+xCoO2 (0 less than or equal to x less than or equal to 0.1) samples prepared by the traditional ceramic technique were studied by X-ray diffraction, IR spectroscopy, X-ray photoelectron spectroscopy, diffuse reflectance electron spectroscopy, and magnetic measurements. The superstoichiometric oxides had a uniform crystal structure with statistically distributed vacancies in cobalt layers and an enhanced covalence of Co-O bonds. Excess lithium caused the appearance of a new oxygen state (O-) different from the oxide state (O2-) rather than the reduction of Co3+ ions to Co2+. The appearance of oxygen ions with an unusually low electron density was directly related to the formation of oxygen positions with a decreased coordination number; the magnetic properties of Li1+xCoO2 were governed by exchange-coupled (Co3+-O-) pairs.

Monophasic NaxNbO2 (x = 0.5 - 0.6), T-c approximate to 4.1 K was prepared by solid state reaction between Na3NbO4 and Nb. X-ray powder diffraction data from a monophasic sample were used for a refinement of the structure of Na0.5NbO2 (R(p) = 7.4 % and R(I) = 5.3 %), using the Rietveld method. At low x-values a closely related second phase can occur. Rietveld refinement using X-ray powder diffraction data showed this phase to be isostructural with NaNbO2 but with the chemical formula Na0.1NbO2. Transmission electron microscopy studies of NaxNbO2 and LixNbO2 revealed the presence of superstructures in some crystallites. The electron diffraction patterns resemble to some extent those reported for transformations among tantalum chalcogenides.