On the absence of superconductivity in Ln_2-xCe_xCuO₄

Although electron-doped superconductivity is readily achieved in Ln_2-xCe_xCuO₄ 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 Gd_2-xCe_xCuO₄ is responsible for the suppression of superconductivity needs to be clarified. A systematic investigation of the Ln_2-xCe_xCuO₄ phases reveal that the absence of superconductivity in Gd_2-xCe_xCuO₄ 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-xCe_xCuO₄ phases-which do not have weak ferromagnetism-support this assertion. © 1994.