TRANSPORT-PROPERTIES OF YBA2-XLAYCU3ON HIGH-TEMPERATURE SUPERCONDUCTORS

The lattice parameters of the defect and La(III) substituted YBa2-xLay Cu3On (0.05 less-than-or-equal-to x less-than-or-equal-to 0.4,0 less-t han-or-equal-to y less-than-or-equal-to 0.2) superconductors prepared in presence of the K2CO3 flux indicate substitution of La(III) on Ba(I I) sites and intercalation of oxygen on 0(5) sites. This is manifested by a lowering of T(c) values. The presence of metastable phases with a sharp drop in resistivity around 200 K, which have been reported by Suzuki et al. (1989) for samples of similar composition, was not confi rmed. The conductivity measurements show an increase of resistivity ab ove 673 K, which is a consequence of gradual deoxygenation and the los s of metallic character. The full reversibility of this process in the bulk sample is modified by the oxygen diffusion into the sample.