Anisotropic Upper Critical Fields of Orthorhombic Single Phase YBa2Cu3O7-δ Studied Using Preferentially Oriented Pellets

Anisotropic behavior of the upper critical fields Hc2 studied in as-sintered disk of YBa2Cu3O7-δ and the characterization of the samples by X-ray diffraction analysis are described. Highly oriented samples with c-axis perpendicular to the disk plane show anisotropic behavior of Hc2 for midpoints and isotropic behavior for the offset field Hc2off defined at 1 % points: the slope (-dHc2/dT) for midpoints is 3.8 T/K and 2.6 T/K for the magnetic field parallel and perpendicular to the disk plane, respectively, and the offset field is about 5-6 T at 80 K. An analysis based on a simplified model suggests the anisotropy factor ε of about 0.2 for YBa2Cu3O7-δ. The X-ray powder diffraction combined with Rietveld analysis together with the resistivity measurement show the samples to be single phase with orthorhombic structure and 90 Krange Tc.