Effect of oxygen stoichiometry on superconducting transition broadening under a magnetic field in YBa2Cu3Ox

Resistivity as a function of temperature has been measured in magnetic fields up to 12 T for YBa2Cu3Ox samples with oxygen concentration ranging from x=6.55 to 6.98. It has been observed that the oxygen concentration has a strong effect on the broadening behavior of the resistive transition in the magnetic field. The smearing of the transition region is due to a superconductive glassy state which arises from weakly coupled semiconductor-insulator-semiconductor junctions in a magnetic field, where the insulating region is a few angstroms thick twin boundary, and the flux creep model can be used to interpret the shape and the width of the resistive transition. For the well-oxygenated sample (x=6.98), the data yield (dHc2/dT)T=Tc=-25.00 T/K for 90% transition resistivities at different fields, and -0.80 T/K for 10% transition curves. The broadening effect in field is decreased when the oxygen content is lowered to x=6.55 due to reduced thermally activated flux creep effects