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

Abstract

Superconducting volume fraction ( f g) 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 f g decrease with increasing ac field amplitude ( H m) for both systems and it is higher in EuBCO system than in BSCCO system. Further, f g shows much steeper decrease in EuBCO system than in BSCCO system. Moreover, the values of f g are found to be more sensitive to the values [ T m/ T c( χ)] rather than T m values ( T m is the temperature at the peak of χ ″ and T c( χ) is the onset temperature of diamagnetism). The same behavior for f g 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 f g and critical current density J c, and indicate that the values of J c are controlled by f g variation in this class of materials.