Revised structure of Bi₃TiNbO₉

Structure refinement of commensurately modulated bismuth tungstate, Bi2WO6

“…1). Recently we have re-refined the crystal structures of Bi4Ti3012 (Rae, Thompson, Withers & Willis, 1990) and Bi3TiNbO9 (Thompson, Rae, Withers & Craig, 1991). Careful analysis using improved data sets and a modulated structure approach for these two commensurate structures produced structural models substantially different from those previously reported (Dorrian, Newnham, Smith & Kay, 1971;Wolfe, Newnham, Smith & Kay, 1971).…”

“…As in our recent refinements of Bi4Ti3Oi2 (Rae, Thompson, Withers & Willis, 1990) and Bi3TiNbO9 (Thompson, Rae, Withers & Craig, 1991) we have calculated apparent valences (AV's) to confirm the chemical plausibility of the refined structure and to help understand the driving force underlying the various observed displacive modes (Table 8).…”

“…The reflections allowed to contribute to the of the observed satellite reflections and a knowledge of the displacive modulations in the closely related BiaTi3012 (Rae, Thompson, Withers & Willis, 1990) and Bi3TiNbO9 (Thompson, Rae, Withers & Craig, 1991) structures, the most likely explanation is an intergrowth of a majority P2~ab structure and a minority B1 a 1 structure. This choice of space-group options and the implicit displacement-mode description is discussed in more detail later.…”

Structure refinement of commensurately modulated bismuth strontium tantalate, Bi2SrTa2O9

“…In recent years the room-temperature crystal structures of the ferroelectric Aurivillius phases, Bi4Ti30~2 (Rae, Thompson, Withers & Willis, 1990), Bi3TiNbO9 (Thompson, Rae, Withers & Craig, 1991) and Bi2WO6 (Rae, Thompson & Withers, 1991) have been re-refined from single-crystal X-ray diffraction data using a modulated structure approach. Their room-temperature structures can be described in terms of relatively small amplitude, displacive pertubations from a high-symmetry parent structure (space-group symmetry 14/mmm, ap = b e = 3.85/~, p = perovskite).…”

Antiferroelectric modulations in Sb2WO6 and Sb2MoO6

“…Given the previously demonstrated usefulness of a modulation wave approach in describing and refining the structures of Aurivillius phases , 1992Thompson, Rae, Withers & Craig, 1991), it was decided to re-examine the reported unit cell and space-group symmetry of Sb2WO6 via an electron diffraction study. Electron diffraction has a proven ability to observe weak features of reciprocal space often missed via conventional X-ray diffraction procedures and, in this case, led to the observation of previously unobserved G + ½(111)* satellite reflections.…”