The structure of Sb2WO6 [Mr = 523.4, triclinic, Fl, a = 11.132(1), b = 9.896 (4), c= 18.482(7) A, a = 90.20(4), 0 = 96.87(8), 7 = 90.21(5)°, Dv = 6.88gem"3, Z = 16, Mo Ka, A = 0.7107 A, fi = 338.5 cm"1, F(0Q0) = 3536] has been refined as an enlarged 2a x 2b x 2c F-centred superstructure of the previously reported structure [Castro, Millan, Enjalbert, Snoeck & Galy (1994). Mat. Res. Bull. 29, 871-879] refined in the space group PI. The re-refinement follows the observation, initially by TEM, of satellite reflections at G ± |(111)*, where G represents a reflection of the PI reciprocal lattice. A final value of 0.040 for /?, = ShH^obsfli)! -l^caic(h)H/Z)hll^obS(h)l was obtained for 3316 merged reflections with /(h) > 3er[/(h)], compared with R = 0.12 for the previous refinement. The refined structure is described in terms of an antiferroelectric modulation of a P12|/al underlying parent structure in the original setting. Twinning of the crystal was successfully modelled in the refinement. Synthesis of the previously unknown phase Sb2MoO6 [Mr = 435.5, triclinic, Fl, a = 10.758(1), b = 9.673(2), c = 17.57(1) A, a = 90.00(5), (i = 96.98(3), 7 = 90.05 (2)°, Z = 16, Dx = 4.97 gem"3] is also reported, along with evidence for its isostructuralism with Sb2WO6.
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