A Powder Neutron Diffraction Investigation of Structure and Cation Ordering in Ba2+xBi2-xO6-y

✍ Scribed by Kenneth P. Reis; Allan J. Jacobson; Jacqueline M. Nicol

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 473 KB
• Volume: 107
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1993.1367

✦ Synopsis

The structures and cation ordering of several barium bismuth oxide phases, (\mathrm{Ba}{2+x} \mathrm{Bi}{2-} \mathrm{O}{6-x}(x=0.22), (0.28,0.40,0.67)), have been determined at ambient temperature from constant wavelength and timeof-flight neutron powder diffraction data. The end member of the series, (\mathrm{Ba}{2} \mathrm{Bi}(\mathrm{III}) \mathrm{Bi}(\mathrm{V}) \mathrm{O}{6}), has a monoclinic distortion of the simple cubic perovskite structure with an ordered arrangement of the (\mathrm{Bi}^{3+}) and (\mathrm{Bi}^{\mathrm{5t}}) cations on the (B) sites. When additional barium atoms are introduced into the structure, substitution of (\mathrm{Ba}) for (\mathrm{Bi}(I I I)) occurs to give phases with the composition (\mathrm{Ba}{2}\left[\left(\mathrm{Bi}{1-x} \mathrm{Ba}{x}\right) \mathrm{Bi}\right] \mathrm{O}{6}) when (x<0.6). The monoclinic structure at (x=0) changes first to a thombohedral structure and then to cubic as (x) is increased. At (x=\mathbf{0 . 6 7}), the structure remains cubic but the cation distribution changes to give an unusual arrangement, represented by (\mathrm{Ba}{5 / 3} \mathrm{Bi}{1 / 3}[\mathrm{BaBi}(\mathrm{V})] \mathrm{O}{5.67}), with (\mathrm{Bi}^{3+}) cations on the perovskite (A) sites and complete (\mathrm{Ba}^{2+} / \mathrm{Bi}^{5+}) ordering on the (B) sites. 01993 Academic Press, Inc.