Heat Treatment Effects on the Superconductivity and Crystal Structure of Nd_1.85Ce_0.15CuO₄Studied Using a Single Crystal

Abstract

We performed systematic post-growth heat treatments on sizable single crystals of Nd 1.85 Ce 0.15 CuO 4 . The superconducting transition temperature, T c , and its distribution in the sample are both sensitive to details of the heat treatment and sample size. With refinement of the heat treatment conditions we have succeeded in preparing two distinct superconducting samples in which T c equals 18 K and 25 K under identical Ce-concentrations. Neutron scattering experiments initially observed nonmagnetic superstructure peaks at (π,π) only in the reduced superconducting phase. Atomic displacement in this structure is different from that induced by in-plane rotation of CuO 4 squares as previously reported for Gd 2- x Ce x CuO 4 . A possible relationship between atomic displacements and superconductivity and the role of reduced heat treatments are discussed from the viewpoint of carrier localization.