The Effect of potassium doping on electrical and magnetic properties of YbCO high temperature superconductors

The Effect of Potassium Doping on Electrical and Magnetic Properties of YBCO High Temperature Superconductors In this study, the effect of potassium (K) doping on YBCO (123) high temperature superconductors has been investigated in terms of XRD, electrical resistivity and critical current density measurements. The samples with nominal compositions Y1^2xBa2-o,2XKxCu30y (x=0 and x=0,4) were prepared by solid state reaction method. The superconducting samples were characterized by XRD measurements. It was seen from XRD data that the pure YBCO and K-doped YBCO had orthorombic structure. The electrical resistivity measurements showed that the critical temperature Tc shifted slightly to lower temperature due to K-doping process. This process also decreased the activation energy for thermally activated flux flow (TAFF) and the transport critical current density. The resistive transitions in the magnetic field range of 0-760 mT were performed employing zero field cooling procedure for both samples. The activation energy values for TAFF were obtained from the Arrhenius plot of the resistivity versus temperature curves which were measured under this magnetic field range. The magnetic field dependence of the critical current density was measured at 77 K after zero field cooling when the applied magnetic field was impressed and removed. For the pure YBCO sample, the transport critical current hysteresis was observed in the field increasing and decreasing direction after an excursion of the field to 6 mT. From AC susceptibility measurement, the transition temperature was determined and the temperature dependent critical current density was calculated using Clem model for the pure YBCO sample. It was seen that these values were in agreement with the values of the critical current density obtained from four probe tecnique at 77 K. Key Words: YBCO High Temperature Superconductors, K-doping, Activation Energy, Critical Current, Thermally Activated Flux Flow (TAFF), AC Susceptibility. VI