Ordering oscillation of local composition in melt-processed REBa2Cu3O7-δ superconductors (RE: Sm, Eu, Gd)

High quality melt-processed GdBa2Cu3O7-delta, (Sm0.5Eu0.5)Ba2Cu3O7-delta and (Sm0.33Eu0.33Gd0.33)Ba2Cu3O7-delta single domains were grown in air and the microstructural origin of their distinguished superconducting performance was investigated by a transmission electron microscope equipped with energy-dispersive spectroscopy. A periodic array of the chemical composition with tens of micrometer correlation was unveiled due to the spatial oscillation of RE (RE: Sm, Eu, and Gd) and Ba around the stoichiometric ratio with a nanometer scale wavelength. For (Sm0.5Eu0.5)Ba2Cu3O7-delta, the temperature dependence of the reversible magnetic moment at certain fields showed two kinks. The first transition followed three-dimensional scaling and yielded dB(c2)/dT=1.98 T/K, corresponding to thermal fluctuation of the bulk superconductivity while the second displayed a linear temperature function with slightly lower T-c than bulk T-c and a slope of 0.6 T/K. This may indicate a field-induced pinning scenario with low T-c stripes. (C) 2003 American Institute of Physics.