Am Doping in Copper-Oxide Superconducting Systems

Abstract

ABSTRACTThe effect of Am doping on the physical properties of three superconducting systems (RBa2Cu3O7, Pb2Sr2R1−xCaxCu3O8 and R2−xMxCuO4) have been studied using x-ray diffraction, x-ray absorption spectroscopy (XAS) and magnetic susceptibility experiments. Am is incorporated into all three systems as the tetravalent ion and superconductivity is not observed in any of the resultant compounds. The absence of superconductivity in Pb2Sr2Am0.5Ca0.5Cu3O8 is attributed to the transfer of charge from Am to the Cu-O planes. Systems that cannot incorporate a tetravalent ion, notably AmBa2Cu3O7 and Am2CuO4, do not form. Although Pr1.85Am0.15CuO4 forms with similar structure to Pr1.85Ce0.15CuO4, and Am like Ce is tetravalent, it is not superconducting. We argue that the absence of superconductivity in the Am doped Pr compound it is due to the hybridization of radially-extended f orbitals on the magnetic Am4+ ion with the Cu-O band states.