Superlattice structures in solid solution of high-T-c YBa2Cu3O7-delta and (Pb,Cu)Sr-2(Ca,Y)Cu2O7-delta superconductors

A complete solid solution range exists between the systems YBa2Cu3O7-delta and (Pb,Cu)Sr-2(Ca,Y)Cu2O7-delta has been found with general stoichiometry (Pb0.75xCu1-0.75x)(Sr2xBa2-2x)(Ca0.5xY1-0.5x)Cu2O7-delta. Energy dispersive spectrometry and X-ray diffraction identified that a true solid solution e xists. Superlattice structures observed by electron diffraction across the solid solution range have a modulation range have a modulation periods alon g a* which can be varied by altering both the compositional parameter x and the overall oxygen content. The existence of these superlattices infers th at the solid solution is non-random and therefore thermodynamically non-ide al. The superconducting transition temperatures, T-c across the solid solut ion range are also strongly dependent on the composition, x, but no direct relationship with the modulation period has been established. From these st udies it may be concluded that the solid solution between known superconduc tors is possible, although involving some partial ordering of the lattice, but ordering of cations in the rock-salt to charge reservoir layer is not a significant factor in determining the superconducting properities, which d epend more closely on the overall composition and hence on the ability of t he charge reservoir layer to transfer charge to the superconducting layers. (C) 2001 Elsevier Science Ltd. All rights reserved.