Oxygen concentration of Eu sub 1 Ba sub 2 Cu sub 3 O sub 7 minus x in vacuum: An atom probe study

Atom Probe mass analysis, at 85 K, using a wide-angle instrument was used to measure the oxygen content and metallic stoichiometry of the near-surface region of the superconducting ceramic oxide Eu{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} ({ital x}{approx equal}0.1) after vacuum exposure at room temperature. Routine specimen preparation, handling, and field-ion imaging produced a specimen which had already lost oxygen such that its measured surface oxygen content corresponded to {ital x}=0.73 and the metallic stoichiometry of the surface was not the expected 1:2:3 but was enhanced in Ba and Eu. The specimen was subsequently exposed to vacuum for up to 80 h at room temperature and no additional loss of oxygen was detected. It was concluded that either (1) a stoichiometric low-oxygen surface also would not have lost oxygen or (2) the nonstoichiometric layer forms a barrier for subsequent oxygen loss.