X-ray and electron diffraction study of a precipitation phase in Nd1.85Ce0.15CuO4+y single crystal

X-ray diffraction measurements have been performed to investigate a crystal structure of a precipitation phase in oxygen-reduced Nd1.85Ce0.15CuO4+y (NCCO). A detailed structure analysis of the precipitation phase as well as the parent NCCO phase revealed that the precipitation phase is a cubic (Nd, Ce)2O3, which is distorted tetragonally by the surrounding NCCO phase. The averaged grain size of the precipitation phase exceeds 200 A parallel to the CuO2 plane of the parent NCCO, while the size along layered direction is short-ranged (∼30 A). The grain thickness along layered direction is strongly correlated with the homogeneity of superconducting state. The volume fraction of the (Nd, Ce)2O3 phase is about 2%. We also performed electron diffraction as well as microscopy experiment, which confirms that the (Nd, Ce)2O3 phase segregate from the parent NCCO phase and exists as an epitaxial layer along the c-axis. (author)