The influence of Ca doping on the crystal structure and superconductivity of orthorhombic

The changes of the chemical structure of and of the superconducting transition temperature associated with Ca doping have been investigated by means of neutron and x-ray powder diffraction, oxygen content determination and magnetic susceptibility measurements. In this work, we were able to show that the depression of superconductivity in Ca-substituted orthorhombic is related to essential structural changes. Using the cation - oxygen distances obtained by neutron diffraction at 1.5 K we calculated the bond valence sums of the cations. This allows us to estimate the charge distribution within the structure and yields a direct correlation between structural changes induced by Ca doping and . Our results show clearly that Ca doping leads to an overdoping of which cannot be reached by oxygen non-stoichiometry alone.