MHz band impedance analysis of oxide superconductors [YBCO]

Oxide superconductors were investigated by measuring their MHz band impedances. Impedance measurements were performed at 77 K and room temperature. With increase of frequency, impedance at 77 K increased from zero values at 100 kHz. The impedance locus had almost the same form as that for measurements at room temperature, except its starting point. As the density of the specimen increases, the impedance locus changes its form and moves in the clockwise direction. An equivalent circuit is proposed. By a close examination of frequency characteristics at room temperature, a singular frequency was observed which corresponds to the pinning frequency at 77 K. It is concluded that the proposed complex impedance measurement makes it possible to evaluate the material density and the critical current density of oxide superconductors at room temperature