X-ray photoelectron spectroscopic study of non-stoichiometric nickel and nickel-copper spinel manganites

Abstract : The surface of non-stoichiometric nickel and nickel-copper spinel manganites has been investigated by X-ray Photoelectron Spectroscopy (XPS). The oxidation states of the nickel, copper and manganese cations present on the surface of the samples were determined from the analysis of the M 2p(3/2) core levels (M=Ni, Cu, Mn). In particular both Cu2+ and Cu+ were evidenced in the determined from the analysis of the M 2p(3/2) core levels (M=Ni, Cu, Mn). In particular, both Cu structure whereas only bivalent nickel was observed. The partial substitution of manganese by copper led to a chemical shift towards lower binding energy in the Ni 2p(3/2) region, which was explained by the displacement of some Ni2+ cations from tetrahedral to octahedral sites of the spinel structure. Finally, the surface atomic ratios Ni/Mn for nickel manganites, Ni/(Mn+Cu) and Cu/(Mn+Ni) for nickel-copper manganites, determined from XPS data, were compared to the ratios corresponding to the bulk composition. This study shows in all cases a nickel enrichment at the surface which is not affected by the copper content of the oxide. On the contrary, the ratio Cu/(Mn+Ni) was found to be lower than the corresponding bulk value.
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C. Drouet, C. Laberty, J.L.G. Fierro, Pierre Alphonse, Abel Rousset. X-ray photoelectron spectroscopic study of non-stoichiometric nickel and nickel-copper spinel manganites. International Journal of Inorganic Materials, Elsevier, 2000, vol. 2, pp. 419-426. ⟨10.1016/S1466-6049(00)00047-7⟩. ⟨hal-00997764⟩

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