Synchrotron X-ray study of orthorhombic Rb(3)Ta(5)O(14) with a modified pyrochlore structure.
The structure of a new orthorhombic trirubidium pentatantalum oxide (Rb(3)Ta(5)O(14)) phase with Pnma symmetry was identified from a half sphere of synchrotron X-ray data measured at a wavelength of 0.85 A. This notionally linked TaO(6) octahedral structure broadly consists of three different modifications of the pyrochlore ring motif with layer stacking normal to (205) planes. Successive pyrochlore layers do not simply stack normal to these planes but are offset along the [100] axis. An unusual aspect of this structure is the occurrence of TaO(5) trigonal bipyramids in structurally complex regions where the modified pyrochlore rings connect.
Synchrotron X-ray study of ortho­rhombic Rb3Ta5O14 with a modified pyrochlore structure
The structure of a new orthorhombic trirubidium pentatantalum oxide (Rb3Ta5O14) phase with Pnma symmetry was identified from a half sphere of synchrotron X-ray data measured at a wavelength of 0.85 A. This notionally linked TaO6 octahedral structure broadly consists of three different modifications of the pyrochlore ring motif with layer stacking normal to (205) planes. Successive pyrochlore layers do not simply stack normal to these planes but are offset along the [100] axis. An unusual aspect of this structure is the occurrence of TaO5 trigonal bipyramids in structurally complex regions where the modified pyrochlore rings connect.
Crystal structures of some niobium and tantalum oxides. VIII. The 5Rb2O:14.6Ta2O5 phase—A tunnel structure
Abstract Rb10Ta29.20O78 crystallizes in the hexagonal system with unit-cell dimensions (from single-crystal data) a = 7.503(4)A, c = 36.348(4)A, and space group P6 3 mmc , z = 1 . The structure was solved using three-dimensional Patterson and Fourier techniques. Of the 666 unique reflections measured by counter techniques, 515 with I ⩾ 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.057 (Rω = 0.039). The structure of Rb10Ta29.20O78 consists of layers of corner-sharing groups of six edge-shared octahedra separated by layers of single octahedra and double hexagonal tungsten bronze-like layers, these layers being perpendicular to the hexagonal c-axis. Nine-coordinate tricapped trigonal prismatic sites between the hexagonal tungsten bronze-like layers are partially occupied by Ta(V) ions.