Neutron-diffraction study of NdBa2Cu3O7+x with x=0.06 and 0.18

Abstract

Two samples of $\mathrm{Nd}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7+x}$ with zero-resistance transition temperatures of 85 K ($x=0.06\mathrm{}$) and 90 K ($x=0.18\mathrm{}$), respectively, were studied by using neutron-diffraction powder profile analysis. The compounds crystallize in the same orthorhombic, oxygen-deficient perovskite structure with space group Pmmm, in which both $1e (0,\frac{1}{2},0)$ and $1b (\frac{1}{2},0,0)$ sites are occupied partially by oxygen atoms, with a majority of atoms being located in the $1e$ sites. The final refinements converge to weighted profile $R$ factors, $R_{\mathrm{WP}}$, of 7.05% and 7.58% for the 90- and 85-K samples, respectively. The significant differences between the two samples are the oxygen content and the regular changes of all the Cu-O bond distances in the structures.