Peak effect in NdBa2Cu3O7-δ superconductor and related Raman spectra

A peak effect of the critical current density was observed for all NdBa2Cu3O7-delta(Nd123) samples prepared by the solid-state reaction method in atmospheres containing different oxygen concentrations. The peak position (field value) and its critical current density value measured at 30, 50, and 71 K depend strongly on the sintering time, and on the oxygen concentration in the sintering atmosphere. The synthesized samples have a high critical temperature T-c of about 96 K and a DeltaT(c)[= T(0.9rho(onset)) - T(0.1rho(onset)),rho(onset) is the normal-state resistivity] lower than 2 K. It implies that the samples are of single superconducting phase without oxygen deficiency. Macro-Raman and micro-Raman spectra were recorded at room temperature for all samples. New modes, supposed to be related with disorder in chain layers, were observed. The disorder is assumed to be induced by a substitution of magnetic Nd3+ ions into the Ba2+ sites in the Nd123 lattice, and is considered to be a main cause of the obtained peak effect. (C) 2003 Elsevier Science B.V. All rights reserved.