Dresden 2011 – wissenschaftliches Programm
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KR: Fachgruppe Kristallographie
KR 6: Poster: Crystallography in Materials Science
KR 6.5: Poster
Mittwoch, 16. März 2011, 15:00–17:30, P1
Oxygen nonstoichiometry of tetragonal La2-xSrxCuO4-δ (x = 0.15 - 1.2) and in situ XPS studies at elevated temperatures — •Daria Mikhailova1, Vladimir Alyoshin2, Steffen Oswald1, and Helmut Ehrenberg1 — 1IFW Dresden, Helmholtzstr. 20 01069 Dresden, Deutschland — 2Moskauer Staatliche Lomonossov Universität, Vorobyovy Gory, 119992, Moscow, Russia
The peculiarities of oxygen nonstoichiometry (δ) in tetragonal La2-xSrxCuO4-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 O2. Two types of charge compensation during replacement of lanthanum by strontium are discussed: an increase of the average copper oxidation state or 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 ({CuO2}-plane) for compositions with different strontium contents, which electronic state is described by the O2p core electron peak at about 531 eV. Thermal stability of the solid solution in vacuum is associated with the extraction of practically the entire oxygen from CuO2-layers and the formation of Cu+ at least in the surface-near 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 vacuum.