Synchrotron X-ray Single-Crystal Structure Analysis of Partially-Disordered Tb3RuO7

Nagoya Institute of Technology* ANBF**
â—‹Tsuyoshi Suwa* Nobuo Ishizawa* James R. Hester**

A series of Ln3MO7 crystals composed of trivalent lanthanide (Ln) and pentavalent transition metal (M=Ru, Os) oxides is structurally characterized by the presence of infinite single chains of corner-linked MO6 octahedra embedded in the matrix of Ln and O atoms. This series has attracted attention because of its interesting electrical and magnetic properties. The series shows a polymorphism. A noncentrosymmetric orthorhombic P21nb modification has been recently found in addition to the centrosymmetric Cmcm. The present study revealed that the Tb3RuO7 crystals grown from the SrCl2-Ru2O5-Tb2O3 system form the P21nb structure with partially disordered Tb positions. Single-crystal diffraction data were collected using synchrotron X-rays of 0.6886Å at the Photon Factory, Tsukuba. Presence of residual electrons near Tb5 in the figure (2 e/Å3 intervals, 2.1x2.1 Å2 section perpendicular to a) suggested a positional disorder of the atom. The least-squares refinement, assuming split atom sites for Tb5 and Tb6, yielded a final RF value of 0.017 for 7559 independent reflections. Nine and five percents of Tb atoms are slightly displaced from the regular Tb5 and Tb6 positions by 0.323(5) and 0.395(6) Å, respectively.