The structural parameters of a fully oxidized, superconducting sample and a deoxidized, non-superconducting sample of Nd1.32Sr0.41Ce0.27CuO4 - y were refined by Rietveld analysis of TOF neutron powder diffraction data. No appreciable structural differences were found between the two samples. Its structure consists of K2NiF4- and Nd2CuO4-type units stacked alternately along the c-axis. Ce4+ ions, whose oxidation state was confirmed by XPS, occupy an eight-coordinate site together with Nd3+ ions in the Nd2CuO4 units. On the other hand, a nine-coordinate site in the K2NiF4 units is filled with Nd3+ and Sr2+ ions. Each Cu atom is coordinated to five oxide ions in a distorted square-pyramidal configuration. O(2) atoms at the apical positions of the CuO5 pyramids are displaced from an ideal 2c site to an 8j site with lower symmetry, which is mainly caused by the occupation of the same nine-coordinate site by Nd3+ and Sr2+ ions. The occupation factors of site O(2) were refined to be ca. 0.23, giving the 4 - y value of ≈3.92. The formal charge of Cu, +1.98, suggests that this superconductor has an unhomogeneous domain structure in which oxygen-rich superconducting regions and oxygen-poor non-superconducting regions coexist within each particle.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering