Structural studies on Er1− xCaxBa2Cu3O7− δ: oxygen vacancies in Cu O2 planes

Abstract

In the Er 1− x Ca x Ba 2 Cu 3 O 7− δ system, 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 with increasing x. Both, the buckling [Cu(2)O(2)Cu(2)] angle and the planar Cu(2)O(2) distance in CuO2 planes increase with increasing x. Increased Cu(2)O(2) bond distance indicates a slight decrease in p-type hole carriers in CuO2 planes. With increasing x, oxygen vacancies are created in CuO2 planes, which along with increased buckling angle, may be partly responsible for T c suppression in this system.