The electron oxide superconductors Nd2-xCexCuO4-y have been investigated by X-ray diffraction, XPS, magnetization and resistivity measurements. We found that Ce-ions lie between the 3+ and 4+ valence states, and that sharp changes in various bond-lengths occur near x=0.15 coinciding with the onset of superconductivity. The later has been taken as evidence for electron-transfer to the CuO2-layers. The results and their implications are discussed.
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