Correlation between superconducting volume fraction and critical current density in copper oxide superconducting systems

Superconducting volume fraction (fg) is calculated from the data of real and imaginary components (χ',χ'') of ac susceptibility measurements versus temperature based on EuBCO and BSCCO systems. It is found that the values of fg decrease with increasing ac field amplitude (Hm) for both systems and it is higher in EuBCO system than in BSCCO system. Further, fg shows much steeper decrease in EuBCO system than in BSCCO system. Moreover, the values of fg are found to be more sensitive to the values [Tm/Tc(χ)] rather than Tm values (Tm is the temperature at the peak of χ'' and Tc(χ) is the onset temperature of diamagnetism). The same behavior for fg is obtained for both systems by using Ravi expression [Physica C 295 (1998) 277]. Another various parameters such as decoupling field, London penetration depth and average grain size are also calculated and discussed for both systems. On the other hand, our results show a reverse correlation between both fg and critical current density Jc, and indicate that the values of Jc are controlled by fg variation in this class of materials