Ag katkılı YBa2Cu3O7-X seramik süperiletkeninde uygulanan akım ve manyetik alan tarafından indüklenen zaman etkileri

In this thesis, current-voltage (I ? V) curves with different sweeping rates (dI/dt) of transport current in Ag-doped YBa2Cu3O7-x sample (YBCO/Ag) were investigated. During the measurements, the transport current was cycled up and down. In addition, in measuring the I ? V curves, two different procedures were applied: Standard and reverse procedures. At moderate dissipation levels, we did not observe any difference between these two procedures. This experimental observation suggests that the surface effects are weakened by adding Ag into the superconducting matrix.The time effects were investigated by means of transport relaxation measurements (V ? t curves). At well-defined values of transport current (I), temperature (T) and external magnetic field (H), an abrupt rise in the sample voltage was observed at the early stage of the relaxation process. After reducing the initial current to a finite value, the sample voltage levels off within a very short time. The rapid voltage drops observed in the V ? t curves were attributed to the rapid dynamic reorganization of flux lines traversing the sample edges. These observations were also interpreted as easy suppression of superconducting order parameter due to the presence of Ag. As the transport current was reduced to a finite value, the time evolution of the quenched state YBCO/Ag is quite different from that of undoped YBCO. This difference in the V ? t curves was interpreted in terms of presence of Ag which destroys the order parameter in the whole sample.We also investigated the influence of bi-directional square wave (BSW) current on the evolution of the V ? t curves at different periods (P), temperatures and external magnetic fields. The nonlinear voltage response seen in the V ? t curves to the BSW current with sufficiently short periods or sufficiently low amplitude reflects itself as regular sinusoidal-type voltage oscillations, which were discussed mainly in terms of the dynamic competition between pinning and depinning.Magnetovoltage (V ? H curves) measurements were performed at selected values of the magnitude of transport current (I), temperature (T) and magnetic field-sweep rate (dH/dt) to investigate the intergranular region and weak-link profile. It was observed that there were clockwise (CW) hysteresis effects in the forward region (FR) of V ? H curves, and counterclockwise (CCW) effects in the reverse region (RR).