Measurement of local changes in oxygen concentration of YBa2Cu3Oy using electron diffraction

The local changes in oxygen concentration of high T-c superconductor YBa2Cu 3Oy (Y123) were determined through three electron diffraction techniques, w here y denotes the oxygen fraction in the unit cell. (1) Using the relation ship between oxygen concentration and lattice parameters, a local change in y was measured from selected area electron diffraction patterns. The resul ts show that the oxygen concentration is lower near a grain boundary compar ed with a central region of the grain in a sintered sample. The relative ac curacy of y and the spatial resolution in this measurement is +/-1.5% and s everal hundreds nm, respectively. (2) A local change in y was detected by c omparing measured zone axis critical voltages with theoretical values. A va lue of y is lower in the vicinity of Y2BaCuO5 (Y211) particles in a sample prepared by the quench and melt-growth method. The accuracy of y is +/-0.67 % and the spatial resolution is 20-50 nm. (3) A change in y was also determ ined by quantitative analysis of rocking curves from convergent-beam electr on diffraction patterns. The value of y decreases by 3% after electron irra diation for 300 s at 200 kV. The accuracy of y is +/-0.5% and the spatial r esolution is several nm when imaging plates were used in an energy-filterin g transmission electron microscope with a field emission gun. (C) 2000 Else vier Science B.V. All. rights reserved.