High resolution characterization of structural inhomogeneities in YBa2Cu3O7−δ crystals with sharp superconducting transitions

Abstract

Structural inhomogeneities in two single crystals of YBa2Cu3O7−δ are characterized using high resolution x-ray diffraction. Results of these analyses show a distribution in the c-axis lattice parameters. These are interpreted as evidence of a distribution in oxygen content. Values of 7−δ range from 6.71 to 7.00 in one crystal and from 6.80 to 6.99 in the other. Nevertheless, the measured superconducting transition widths for both crystals are less than 0.5 K, as determined by ac susceptibility. When examined with conventional x-ray diffraction techniques, both crystals also appeared to be free of gross defects, but high resolution rocking curves reveal variations in defect density. These results suggest that crystals presumed to be homogeneous based on narrow superconducting transition widths or conventional x-ray diffractometry, may not be. Therefore, crystals found to exhibit exotic physical properties should be carefully examined for the presence of structural anomalies. If such defects are present, the experimental results may be attributed to sample imperfections, rather than intrinsic phenomena.