INVESTIGATION OF A SINGLE-CRYSTAL YBCO SUPERCONDUCTOR BY MICRO-RES TECHNIQUE

The stoichiometry of a single crystal (1.5 x 1.3 x 0.075 mm(3)) of YBC O superconductor was investigated using Rutherford Backscattering Spec trometry (RBS). Initially a 2 MeV alpha-macrobeam of approximate to 2 mm diameter was used encompassing the entire crystal. The macrobeam-RB S spectrum had an unusual shape, indicating lateral and/or depth nonun iformity in the crystal, and could not be ana lyzed to obtain stoichio metric information. SEM micrographs revealed a small crystal overgrowt h (0.34 x 0.34 x 0.1 mm(3)) protruding out of the main crystal, with a n uneven interface between the two parts. An alpha-microbcam of 80 mu m resolution was then used to investigate each of the three regions se parately. The microbeam-RBS spectra from the main crystal and the smal ler crystal overgrowth could be fitted reasonably well with RUMP simul ation assuming lateral and depth uniformity, both yielding a stoichiom etry of Y1Ba1.8Cu3O6.7/Au-0.08 (Au being a contaminant). This is close to the ideal stoichiometry of Y1Ba2Cu3O6.9.