Oxygen-ordering and ac-susceptibility in polycrystalline YBa2Cu3O7−δ (δ=0.15∼0.67)

Abstract

A perfect shielding behavior has been observed by ac-susceptibility measurement in a wide oxygen-deficiency range of YBa2Cu3O7−gd (δ=0.15∼0.67) and the measurement indicated the existence of a bulk superconducting phase (ortho.II) with Tc∼60K at δ∼0.5. The ortho.II superconductivity was very sensitive to the magnetic field. A detailed ac-susceptibility measurement was conducted on the quenched polycrystalline ortho.II samples with a range of measuring magnetic field. The ac-susceptibility of the ortho.II was found to be suppressed to a constant value; about 70% of the perfect one by the magnetic field of a few oersteds. Heat-treatments at low temperatures in an encapsulated condition did not alter the essential feature. The field sensitive nature of the ortho.II susceptibility was related to the weakly coupled Josephson link through ortho.II grain boundaries.