Solution and refinement of the crystal structure of Bi7Ta3O18

• Published in: Acta crystallographica. Section B, Structural science Vol. 55; no. 2; pp. 157 - 164
• Main Authors: Ling, Christopher D., Schmid, Siegbert, Withers, Ray L., Thompson, John G., Ishizawa, Nobuo, Kishimoto, Shunji
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01-04-1999; Blackwell
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Inorganic compounds; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Water, oxides, hydroxides, peroxides; Inorganic compounds; Ternary compounds; Transition element compounds; Tantalum oxides; Bismuth oxides; XRD; Experimental study; Synchrotron radiation; Crystal structure
• ISSN: 0108-7681; 1600-5740
• DOI: 10.1107/S0108768198011148

The structure of heptabismuth tritantalum octadecaoxide, Bi7Ta3O18, has been solved and refined using single‐crystal X‐ray diffraction data collected at a synchrotron source in conjunction with unit‐cell and symmetry information derived from electron diffraction. The space‐group symmetry is triclinic C1 but is very close to monoclinic C2/m. A twin component observed during data collection was successfully modelled in the refinement. The C2/m prototype fitted all the Rietveld‐refinable features of a medium‐resolution neutron powder diffraction pattern. The metal‐atom array is approximately face‐centred cubic (fluorite type), punctuated by regularly spaced displacement faults perpendicular to the [111]fluorite direction every 2.5 fluorite unit cells. The metal‐atom populations and O‐atom positions are fully ordered. The Ta5+ cations are octahedrally coordinated, with TaO6 octahedra forming columns. The remaining O atoms occupy distorted fluorite positions. The Bi3+ cations occupy octahedral, square pyramidal or trigonal prismatic sites within the O‐atom array; strain in the latter coordination environment appears to be responsible for the lowering of symmetry from monoclinic to triclinic.