Structural refinement of [Y1-xCax]SrBaCu2.80(PO4)(0.20)O-y

[Y1-xCax]SrBaCu2.80(PO4)(0.20)O-y samples with 0.10 less than or equal to x less than or equal to 0.40 were synthesized using the solid state reaction technique. X-ray diffraction patterns show that all the compounds crystall ized into a 123 tetragonal structure. The analyses of the structure with Ri etveld refinement were made using a model that contain one Cu(2) in a four coordination and not in five coordination as the other 123 tetragonal struc tures. This fact permits that the T,increases with Ca concentration. All sa mples are superconductors as reported previously. (C) 2001 Elsevier Science B.V. All rights reserved.