AURIVILLIUS PHASES (Bi₂O₂)(A_n-1B_nO_3n+1) (n = 1 - 8)

Bi₂WO₆ single crystals
 

Numerous Aurivillius phases are layered perovskite like compounds with constant (ordinary phases) or alternating (mixed layer phases, intergrowths) number of "perovskite" layers (n = 1 - 8) between layers of Bi₂O₂.

Ferroelectric and oxide-ion conductive properties of single-layer phases, such as Bi₂WO₆, Bi₂MoO₆, Bi₂VO_5.5, and intergrowths Bi₆Ti₃WO₁₈ and Bi₁₀Ti₃W₃O₃₀ were investigated. At first time it was found that Bi₂WO₆ exhibit high ionic conductivity caused by fast migration of oxygen anions. The complex polymorphism of Bi₂WO₆ and Bi₂MoO₆ was refined (see a scheme below).

Solid solutions in Bi₂WO₆ - Bi₂VO_5.5, Bi₂MoO₆ - Bi₂VO_5.5 and Bi₂GeO₅ - Bi₂VO_5.5 were investigated with aim to make better oxide conductive properties. Phase transition peculiarities in the above compounds have been also studied.

Special attention was given to study of polymorphism and properties of mixed layer compound Bi₁₀Ti₃W₃O₃₀ with high anionic conductivity (~10^-2 Ohm^-1cm^-1 at 800^oC).

The general question of symmetry and its changes at ferroelectric phase transitions have been analyzed for the first time.

Conductivity temperature dependences for different Aurivillius phases

Schemes of the phase transitions for (1) Bi₂MoO₆ and (2) Bi₂WO₆ with summary concerning phase structures:
(a) – the structure has been solved experimentally and space group is well-known (F. Theobald et al.,1984; D.J. Buttrey et al.,1994; R.W. Wolfe et al., 1969, N.A. McDowell et al., 2006; and many other authors 1965 - present time);
(b) – the structure has not been solved experimentally, space group have been predicted in theory (A.D. Rae, 1991);
(c) – the structure has not been solved, point group have been proposed based on properties of the compounds.

 

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15. V.I. Voronkova, E.P. Kharitonova, O.G. Rudnitskaya. Refinement of Bi₂WO₆ and Bi₂MoO₆ polymorphism // Journal of Alloys and Compounds. 2009. in press.