X-ray and Electron Diffraction Study of a Precipitation Phase in Nd_1.85Ce_0.15CuO_4+<i>y</i> Single Crystal

Abstract

X-ray diffraction measurements have been performed to investigate a crystal structure of a precipitation phase in oxygen-reduced Nd 1.85 Ce 0.15 CuO 4+ 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) 2 O 3 , which is distorted tetragonally by the surrounding NCCO phase. The averaged grain size of the precipitation phase exceeds 200 Å parallel to the CuO 2 plane of the parent NCCO, while the size along layered direction is short-ranged (∼30 Å). The grain thickness along layered direction is strongly correlated with the homogeneity of superconducting state. The volume fraction of the (Nd,Ce) 2 O 3 phase is about 2%. We also performed electron diffraction as well as microscopy experiment, which confirms that the (Nd,Ce) 2 O 3 phase segregate from the parent NCCO phase and exists as an epitaxial layer along the c -axis.