AC Inductive Measurement of Intergrain and Intragrain Currents in High-Tc Oxide Superconductors

Bulk intergrain current and closed intragrain current in sintered Y-Ba-Cu-O superconductors were measured at 77 K by using an ac inductive method. These currents can be separated because of the large difference in penetrating rates of the magnetic flux into specimens with respect to the ac field amplitude. The obtained intergrain current density agreed approximately with critical current density measured resistively. The closed intragrain current density amounted to 4.3×108 A/m2 at B=0.5 T and decreased gradually with increasing magnetic field. The present results show that the ac inductive measurement is one of the available nondestructive methods to characterize sintered oxide specimens.