MAGNETIC-FIELD DEPENDENCE OF THE TRANSPORT CRITICAL CURRENT-DENSITY IN MELT-TEXTURED BI-SR-CA-CU-O HIGH-TC SUPERCONDUCTORS

The transport critical current densities (J(c)) in magnetic fields up to 14 T at 4.2 K have been measured on melt-textured Bi-Sr-Ca-Cu-O samples on MgO substrates. The samples were multiphase with partial alignment of the grains. J(c) values of 1.58 x 10(4) A/cm2, 1.13 x 10(4) A/cm2 and 8.2 x 10(3) A/cm2 were obtained in magnetic fields B = 0 T, 1 T and 14 T, respectively. The magnetic field dependence of J(c) was relatively flat in fields higher than 1 T. The flux pinning force density increased monotonically in the whole range of fields. The shape of the current-voltage characteristics has been examined and shown to follow approximately a power-law behaviour E approximately J(n) in the range of E-values of 10(-4) - 10(-1) V/m with n almost-equal-to 30. Preliminary results of J(c)(B,T) measurements at higher temperatures are presented.