Neutron diffraction on Er1-xCaxBa2Cu3O7-δ (0.0≤x≤0.3) system:: possible oxygen vacancies in Cu-O2 planes

In the system Er1-xCaxBa2Cu3O7-delta with x = 0.0 to 0.3, the superconducting transition temperature (T-c), as measured from AC susceptibility, decreases with increasing Ca substitution, x. Detailed analysis of the powder neutron diffraction patterns of these samples shows a decrease in oxygen content with increasing x. The orthorhombic distortion decreases slightly and the c-parameter increases slightly with increasing x. Both, the buckling angle [(Cu(2)-O(2)-Cu(2) angle)] and the planer Cu(2)-O(2) distance in Cu-O-2 planes, increase with increasing x. Increased Cu(2)-O(2) bond distance indicates a slight decrease in p-type hole carriers in Cu-O-2 planes. On comparison with reported results on T-c vs. p-type carriers in high T-c superconducting compounds, it is inferred that decrease in p-type carriers alone cannot account for sharp T-c depression with increasing n in Er1-xCaxBa2Cu3O7-delta system. With increasing x, oxygen vacancies are created in Cu-O-2 planes, which along with increased buckling angle might be partly responsible for T-c suppression in this system. (C) 2000 Elsevier Science B.V. All rights reserved.