The effect of potassium doping on resistive transitions and transport critical current of bulk YBCO high- $T_c$ superconductors

Özet

We report on observations of the effect of potassium in YBCO (123) high tem­perature superconductors with nominal composition $Y_{1-0,2x} Ba_{2-0.2x} K_x Cu_3 O_y$. The electrical resistivity measurements show that the critical temperature $T_c$ (R=0) shifted slightly to lower temparature due to the K doping process. This process also decreases the transport critical current density and the activation energy for ther­mally activated flux flow. The magnetic field dependence of $j_c$ was measured at 77 K after zero field cooling (ZFC) when the applied magnetic field is impressed (ZFCV) and removed (ZFCD). The results are discussed in terms of "return" magnetic flux density associated with the magnetization of the grains. Activation energy was de­termined from the Arrhenius resistivity plot versus temperature curve. The XRD patterns are also presented for sample characterization.