Single-crystal neutron-diffraction structures of reduced and oxygenated ${\mathrm{Nd}}_{2-x}{\mathrm{Ce}}_x\mathrm{Cu}{\mathrm{O}}_y$

The structures of single crystals of oxygenated and reduced ($T_c=24\mathrm{}$ K) ${\mathrm{Nd}}_{1.85}{\mathrm{Ce}}_{0.15}\mathrm{Cu}{\mathrm{O}}_y$ ($y\approx 4$) were examined by neutron diffraction. Although refinements of various models including interstitial oxygen atoms was inconclusive, Fourier maps of the oxygenated crystal exhibit peaks at the apical O(3) oxygen site. This peak is almost entirely absent in the superconducting reduced crystal. These results are consistent with results from a previous study of oxygenated and reduced ${\mathrm{Nd}}_2\mathrm{Cu}{\mathrm{O}}_y$.