Reentrant transport transition in oxide superconductors prepared with a quenching-process

We studied the transport properties of tetragonal CaLaBaCu3Oy, EuSrBaCu3Oy, and GdSrBaCu3Oy samples and of orthorhombic DySrBaCu3Oy samples, which are expected to be isomorphic to YBa2Cu3O7-δ. Samples with various oxygen contents were prepared by changing the annealing temperature or the annealing time in O2 gas and quenching in liquid nitrogen. The transport properties were measured in detail below the usual critical temperature Tc. The reported correlation of Tc with oxygen content was reconfirmed, and the reentrant transition toward a voltage state below Tc was confirmed in the R - T curves and the I-V curves for various measuring currents and temperatures not nobly in CaLaBaCu3Oy but also in GdSrBaCu3Oy and EuSrBaCu3Oy. These phenomena exhibited good reproducibility in several samples prepared by the liquid-nitrogen quenching process. In these phenomena, the inhomogeneous distribution of the Tc value inside the sample due to the inhomogeneous oxygen content seemed to play an important role