Effect of hydrogen on high Tc granular superconductors: Observation of percolating behaviour

• Published in: Solid state communications 1988-06, Vol.66 (11), p.1157-1160
• Main Authors: Nicolas, M., Daou, J.N., Vedel, I., Vajda, P., Burger, J.P., Lesueur, J., Dumoulin, L.
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Occurrence, potential candidates; Physics; Superconductivity
• ISSN: 0038-1098; 1879-2766
• DOI: 10.1016/0038-1098(88)91123-4

MBa 2 Cu 3 O 7 H χ compounds (with M = Y, Er, Eu, and x ⩽ 0.38) have been prepared by absorption of hydrogen around 200°C, without modification of the oxygen content. We observe first a noticeable increase of the normal state resistivity and a change of the slope ( dϱ/ dT) while there is only a small decrease of T c , the corresponding resistive transition remaining sharp. At the same time, we observe a large decrease of the a.c. Meissner effect, an increase of the magnetic transition width and a decrease of the magnetic hysteresis measured up to static applied fields H ⩽ 6 kGauss. The resistive and magnetic data can be qualitatively interpreted in terms of a two-phase model with the occurence of a poorly conducting or insulating hydride phase. We propose also that the percolative morphology of both phases and the Josephson type coupling between intergrain and intragrain defects play an important role. Anomalously high T c values ( T c > 95 K) which correlate with an increase of the contact resistance have also been observed on one sample.