ON THE ABSENCE OF SUPERCONDUCTIVITY IN GD2-XCEXCUO4

Although electron-doped superconductivity is readily achieved in Ln2-xCeCuO4 for Ln = (La, Nd), Pr, Nd, Sm, and Eu, the Ln = Gd member remains to be a notable exception in the series. Whether or not the weak ferromagnetism observed in Gd2-xCexCuO4 is responsible for the suppression of superconductivity needs to be clarified. A systematic investigation of the Ln2-xCexCuO4 phases reveal that the absence of superconductivity in Gd2-xCeCuO4 is due to an inability, arising from a smaller lattice parameter, to achieve (i) the required electron concentration and (ii) a uniform oxygen coordination around the Cu atoms, and not necessarily due to the weak ferromagnetism. The difficulties to achieve bulk superconductivity in (La, Gd)2-xCexCuO4 phases-which do not have weak ferromagnetism - support this assertion.