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  • Title: Oxygen nonstoichiometry of tetragonal La2-xSr(x)CuO4-δ (x = 0.15-1.2) and in situ XPS studies at elevated temperatures.
    Author: Alyoshin VA, Romanova IP, Mikhailova D, Oswald S, Senyshyn A, Ehrenberg H.
    Journal: J Phys Chem A; 2010 Dec 30; 114(51):13362-9. PubMed ID: 21133400.
    Abstract:
    The peculiarities of oxygen nonstoichiometry (δ) in tetragonal La(2-x)Sr(x)CuO(4-δ) solid solution with x(Sr) = 0.15-1.2 were studied by XRD, NPD, in situ high-temperature XPS, and chemical analysis. Temperature dependences of oxygen nonstoichiometry, δ = δ(T), were obtained for different Sr contents at 1 bar of O(2). Two types of charge compensation during replacement of lanthanum by strontium are discussed: an increase of the average copper oxidation state and a formation of oxygen vacancies. The average copper oxidation state V(Cu) exhibits a maximum of 2.32 at x(Sr) = 0.6, while δ increases with x(Sr). Oxygen vacancies are unambiguously located on the 4c site ({CuO(2)} plane) for compositions with different strontium contents, which electronic state is described by the O 2p core electron peak at about 531 eV. Thermal stability of the solid solution in a vacuum is associated with the extraction of practically the entire oxygen from CuO(2) layers and the formation of Cu(+) at least in the near-surface region. The higher average copper oxidation state after synthesis in the Sr-rich phases in comparison with the Sr-poor compositions prevents oxygen removal and the formation of Cu(+) and, therefore, stabilizes the structure during heating in a vacuum.
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