Local structure around Ce in the Nd <InlineEquation ID="Equ1"> <EquationSource Format="TEX">$\mathsf{_{2-x}}$</EquationSource> </InlineEquation>Ce<InlineEquation ID="Equ2"> <EquationSource Format="TEX">$\mathsf{_{x}}$</EquationSource> </InlineEquation>CuO <InlineEquation ID="Equ3"> <EquationSource Format="TEX">$\mathsf{_{4\pm \delta}}$</EquationSource> </InlineEquation> superconductor probed by ...
The local structure around the Ce substitutional defects has been investigated by Ce and Nd K-edge EXAFS on Nd<Subscript>2-x </Subscript>Ce<Subscript> x </Subscript>CuO <InlineEquation ID="Equ4"> <EquationSource Format="TEX">$_{4\pm \delta}$</EquationSource> </InlineEquation> samples with different dopant concentrations (x=0.05, 0.10, 0.15 and 0.20) and oxygen amounts. The lattice distortion around the Ce <InlineEquation ID="Equ5"> <EquationSource Format="TEX">$_{\rm Nd}^\bullet$</EquationSource> </InlineEquation> can be described as a shrinkage of the oxygen cuboid along the z crystallographic direction. Moreover, the CuO<Subscript>4</Subscript> planes become corrugated. The lattice distortion is well localized and is largely independent of temperature and Ce and oxygen content. EXAFS measurements made at the Nd-K edge indicate that the local chemical environment of Nd is not distorted. The difference electron density maps, obtained from low temperature single crystal X-ray diffraction data, revealed three strong positive residuals which have been ascribed to cerium (at 0, 0, <InlineEquation ID="Equ6"> <EquationSource Format="TEX">$z\cong 0.41$</EquationSource> </InlineEquation>) and to two non equivalent oxygen apical positions O3 (at 0, 0, <InlineEquation ID="Equ7"> <EquationSource Format="TEX">$z\cong 0.19$</EquationSource> </InlineEquation>) and O4 (at 0, 0 <InlineEquation ID="Equ8"> <EquationSource Format="TEX">$z\cong 0.24$</EquationSource> </InlineEquation>). The electron population of O4 site, which is closer to cerium (<InlineEquation ID="Equ9"> <EquationSource Format="TEX">$d_{\rm Ce-O4}=1.96$</EquationSource> </InlineEquation> Å), is 3-4 times the O3 one. Copyright Springer-Verlag Berlin/Heidelberg 2004
