Measurement of local changes in oxygen concentration of YBa 2Cu 3O y using electron diffraction

Abstract

The local changes in oxygen concentration of high T c superconductor YBa 2Cu 3O y (Y123) were determined through three electron diffraction techniques, where y denotes the oxygen fraction in the unit cell. (1) Using the relationship between oxygen concentration and lattice parameters, a local change in y was measured from selected area electron diffraction patterns. The results show that the oxygen concentration is lower near a grain boundary compared with a central region of the grain in a sintered sample. The relative accuracy of y and the spatial resolution in this measurement is ±1.5% and several hundreds nm, respectively. (2) A local change in y was detected by comparing measured zone axis critical voltages with theoretical values. A value of y is lower in the vicinity of Y 2BaCuO 5 (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 determined by quantitative analysis of rocking curves from convergent-beam electron diffraction patterns. The value of y decreases by 3% after electron irradiation for 300 s at 200 kV. The accuracy of y is ±0.5% and the spatial resolution is several nm when imaging plates were used in an energy-filtering transmission electron microscope with a field emission gun.