Modeling and Rietveld-Refinement of the Crystal Structure of Bi4Ta2O11Based on That of Bi7Ta3O18

✍ Scribed by Christopher D Ling; John G Thompson; Ray L Withers; Siegbert Schmid

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 309 KB
• Volume: 142
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1998.7980

✦ Synopsis

A P1 model for the crystal structure of Bi 4 Ta 2 O 11 has been proposed based on units from the P1 crystal structure of Bi 7 Ta 3 O 38 . The model was found to be plausible in terms of bond valence sums. When refined via the Rietveld method using X-ray (synchrotron) and neutron powder diffraction data, the final structure had greatly improved bond valence sums. The metal atom array approximates fluorite-type with regular ''step'' defects on (h k 0) planes (perpendicular to [1 1 1] fluorite ). Regular TaO 6 octahedra form corner-connected columns. Bismuth atoms are in high coordination environments similar to those found in fluorite-type. Bi 7 Ta 3 O 18 and Bi 4 Ta 2 O 11 are discussed in terms of their structural relationships to one another, to adjacent phases in the Bi 2 O 3 -Ta 2 O 5 system, and to structures proposed by earlier authors based on an archetypal fluorite-type substructure.