Study of the impact of HgO addition and low-field magnetic relaxation behaviour in granular high-T-c superconductors

A series of high-T-c, superconductors have been prepared with the HgO addit ion/substitution. Significant improvement in the T-conset as well as T-c0 w as observed in all the cases. Substitution of Hg at the Sr site and Ba site in the case of (Bi, Pb)Sr-Ca-Cu-O and Y-Ba-Cu-O systems, respectively over a range 0.01-0.6 at % helps in constructing an entire spectrum: improvemen t of T-c0 up to 0.4 at % in the case of Bi-system and up to 0.03 at % in th e case of Y123 system and slight drop in T-c thereafter. Such improvement i s the result of abundant supply of highly reactive nascent oxygen all throu gh the bulk. HgO decomposes and provides oxygen which helps in maintaining proper oxygen stoichiometry throughout the bulk. No Hg or Hg-based impure p hases were observed in the X-ray diffraction spectra. Low-field (10-100 Oe) magnetic relaxation studies reveal faster relaxation of the Intergranular critical state in the case of silver added samples as the grain boundary co upling energy E-J becomes quite uniform across the entire bulk which leads to smaller flux pinning energy. The distribution of the pinning energy is e valuated from the observed relaxation pattern and is found to be narrower i n the case of silver added samples. It was also observed that the transport J(c) similar to exp[-Delta T-c/T-c0] and the flux pinning energy U similar to AT(c), where Delta T-c is the transition width and is a measure of the inhomogeneity within the sample. Such relationships may help in devising a strategy for achieving high J(c), high II yet low Delta T-c. Silver additio n turns out to be an effective tool in tailoring the sample properties depe nding on requirement.