Transport critical current and magnetization measurements of melt-processed YBa2Cu3O(7-x)
This paper reports on the magnetic field dependence of the transport critical current and dc magnetic susceptibility measurements on YBa2Cu3O(7-x) superconductors formed by melt-solid reactions at 950 C between Ba-Cu-O (or Tb-Ba-cu-O) and solid nonstoichiometric Y-Ba-Cu oxide. Four-probe dc critical current measurements at 77, 64, and 4.2 K show strong depression of the critical current density with increasing magnetic field, in agreement with a model of weakly linked superconducting regions. Diamagnetic shielding and Meissner flux expulsion measurements in the temperature range 10-300 K show about one-third volume fraction of perfect superconductivity. Both shielding and flux expulsion were observed to be approximately temperature independent below 60 K, indicating strong coupling between the grains throughout the entire volume below this temperature.