CA DOPED YBCO ON THE BA SITE

The effect of partial nominal replacement of Ba with Ca on the propert ies of the YBa2Cu3O6+delta superconductor varies with the concentratio n of Ca. For nominal concentrations in Ca up to 50% a two phase system is formed: the known superconducting phase Y1-yCayBa2Cu3O6+delta and a new, non superconducting phase of composition Y1.14Ca1.58Cu3.27O6.45 . The x-ray diffraction pattern of this new phase matches the Bragg pe aks, as well as the commensurate and incommensurate peaks of a partial ly indexed pattern of the phase Y2-xCa2+xCu5O10. For nominal Ca concen trations 40 and 50%, microprobe analysis shows that the superconductin g phase becomes a mixture of Y1-yCayBa2Cu3O6+delta and YBa1.8Ca0.2Cu3O 6.5, where Ca enters the structure in the Ba site. The microraman spec tra indicate a small substitution of Ba by Ca, while the new phase sho ws novel characteristics.