A number of samples with the nominal formula Y 0.4( Ba x Sr 1−x)0.6 Cu O 3, Y 0.5( Ba x Sr 1−x)0.5 CuO 3 and Y 1.2 ( Ba x Sr 1−x)0.8 CuO 4 have been made. It is found that for x=0 the samples show no superconductivity but for x>0.008 samples do show superconductivity, and for x=0.008, 0.005 the samples have high normal resistivity and no resistive transition but show diamagnetism at about 70k. The structure analysis find a smaller distortion in the the sample Y 0.5( Ba 0.01 Sr 0.99)0.5 CuO 3 than that in YBa 2 Cu 3 O 9−y. The relation between superconductivity and the ionic radius is discussed.
A normal-superconducting-normal transition has been observed resistively in the granular BaPbo 7581p 2503 compound, while the compound remains diamagnetic to the lowest temperature investigated. This has been attributed to the decoupling of the superconducting grains at low temperature caused by the reduction of charge carriers in the grain barriers, in good agreement with the theory.
The composition dependence of superconductivity and crystal structure in La ( Ba 1−x Ca x)2 Cu 3 O 7−y system was determined by the resistivity measurements and X-ray diffraction analysis. The superconducting transition temperature is raised with the increase of Ca content till x=0.6, at which the zero resistance temperature of the sample is 81.5 K. In the meanwhile, the crystal structure of the sample changed from tetragonal (x=0) to orthorhombic structure (x=0.2, 0.4, 0.6). With further increase of Ca content, the superconductivity decrease for the sample of x=0.8 with mixed phases including the orthorhombic oxygen-deficient perovskite-like (ODP) structure and no superconducting transition is found at 4.2 K for the sample of x=1 without the ODP structure. A possible explanation of these experimental results is given.
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