Phase Aurivillius

If the A layers in the above series are replaced by a layer of composition Bi202, a series of phases is formed called Aurivillius phases, with a general formula (Bi202)(A 1B 03 +i), where A is a large cation, B a medium-sized cation, and the index n mns from 1 to oo. The structure of the Bi202 layer is similar to that of... 

Figure 4-30 Idealized structures of the Aurivillius phases viewed along [110] (a) Bi4Ti3Oi2, n 3. anc] (b) Bi5TiNbWOi5, ordered n = 1 n = 2. The shaded squares represent Ti06 or (Ti Nb W)Os octahedra and the shaded circles Bi atoms. B represents Ti, Nb, W.

Ruddleston-Popper phases and Aurivillius phases both contain slabs of structure similar to that of ... 

Withers, R. L., Thompson, J. G., and Rae, A. D. (1991). The crystal chemistry underlying ferroelectrieity ini Bi4Ti30i2 and related Aurivillius phases. 

Another group of materials that has displayed high oxide ion conductivity is based upon a layered bismuth perovskite-based structure, first reported by Aurivillius in 1949 [90-92], The so-called Aurivillius phases are chemically expressed normally as Bi2A B 03 +3 [82], where A is a large 12-coordinated cation and B a small 6-coordinated cation. The structure is formed by n perovskite-like layers, (A 1B 03n+1)2, sandwiched between bismuth-oxygen fluorite-type sheets, (Bi/) 2 [93,94],... 

As described in Section 8.2.6, along with YSZ, mixed oxygen-ion, and electron-conducting oxides with a perovskite-type structure, the so-called Aurivillius phase and pyrochlore materials are fundamentally used for the production of a variety of high-temperature electrochemical devices [50-58],... 

Fig. 10. High-resolution electron micrograph of a (3,4) intergrowth structure involving the Aurivillius phases Bi4Ti30I2 (n = 3) and...

Plate 12 Disordered intergrowth of Aurivillius phases as illustrated in the case of Bi,Ti3Fe50i- (from ref 91... 

Unresolved complexity is found in the defect stmctures of the Bi and T1 containing superconducting oxides (see Superconductivity). These compounds, closely related to the Aurivillius phases described above, form restricted homologous series, with formulae TlBa2Ca iCu 02 +3, Tl2Ba2Ca iCu 02 +4 and Bi2Ba2Ca iCu 02 +4 with n =... 

There is little doubt that many materials that at present are described as containing ordered arrays of point or extended defects will be successfully described as notionally defect-free modulated structures. For example, the intergrowth Aurivillius phases, described as containing extended planar defects, have recently been described compactly as modulated structures. " The same formalism has been applied to hexagonal perovskite structures and superconducting copper oxides. Others will certainly follow. 

In some layered compounds, electric charge separation between the layers may destabilize the structures AurivilUus phases [Bi202] [B lM 03, l] " are examples. If oxygen vacancies are introduced into an Aurivillius phase, a stepped superstructure may form to release the charge separation and, probably, reduce the number of oxygen vacancies. For example, Bi2WO,5 is a well known n = I member of the family of Aurivillius phases. The unit cell consists of fluorite-like [Bi202] and... 

A further variation results from a combination of the above-described structures with those of the tetragonal PbO-type structure. A typical example of the resulting class of compounds., referred to as Aurivillius phases, is Bi2Nb205F, where the bismuth atoms combine with the oxygen atoms to form a highly altered polymeric network (28). Other examples of both ordered and disordered intergrowth phenomena from Aurivillius phases have been given by Rao et al. (24). 

Compounds Containing Perovskite Layers. A second class of layered oxides have structures related to the three-dimensional perovskite lattice and include the Auriv-illius phases, the Ruddlesden-Popper phases and the Dion-Jacobson phases. The general composition can be written Ma[A iB 03 +i] where A is an alkaline or rare earth metal, and B is niobium or titanium. In the Aurivillius phases = Bi2 02 +, whereas M is an alkali metal cation in the ion-exchangeable Ruddlesden-Popper a = 2) and Dion-Jacobson a = 1) phases. The relationships between the three structure types is shown in Figure 14. The intercalation chemistry of the Dion - Jacobson phases was the first to be studied. 

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