Neutron diffraction on Er1-xCaxBa2Cu3O7-delta (0.0 <= x <= 0.3) system: possible oxygen vacancies in Cu-O-2 planes

In the system Er1-xCaxBa2Cu3O7-delta with x = 0.0 to 0.3, the superconducti ng transition temperature (T-c), as measured from AC susceptibility, decrea ses with increasing Ca substitution, x. Detailed analysis of the powder neu tron diffraction patterns of these samples shows a decrease in oxygen conte nt with increasing x. The orthorhombic distortion decreases slightly and th e c-parameter increases slightly with increasing x. Both, the buckling angl e [(Cu(2)-O(2)-Cu(2) angle)] and the planer Cu(2)-O(2) distance in Cu-O-2 p lanes, increase with increasing x. Increased Cu(2)-O(2) bond distance indic ates a slight decrease in p-type hole carriers in Cu-O-2 planes. On compari son with reported results on T-c vs. p-type carriers in high T-c supercondu cting compounds, it is inferred that decrease in p-type carriers alone cann ot account for sharp T-c depression with increasing n in Er1-xCaxBa2Cu3O7-d elta system. With increasing x, oxygen vacancies are created in Cu-O-2 plan es, which along with increased buckling angle might be partly responsible f or T-c suppression in this system. (C) 2000 Elsevier Science B.V. All right s reserved.