Perovskite-related layered oxides

Fig. 16.2 Idealized structures of some perovskite-related layered oxides and their fluoride relatives.2)...

Table 16.3 Perovskite-Related Layered Oxides Studied for Photocatalysis... 

Table 10. Perovskite-related layered oxides studied for photocatalysis.

Perovskite-related Oxides.—The perovskite-related oxides have been studied extensively in recent years because of the large variety of device applications for which these materials are suited. The interaction between structure, properties, and stoicheiometry is significant at all levels, but here we will discuss only the narrow areas where intergrowth is a dominant structural feature. We will not, therefore, consider solid solutions typified by the Pb(Zr Tii )03 ferroelectrics, and neither will we discuss the structurally complex but stoicheiometric phases related to hexagonal BaTiOj, which includes BaNiOj, which has a simple two-layer repeat in the c-direc-tion, the nine layer BaRuOj, the twelve layer Ba4Re2CoOj2, and the twenty-four layer Sr5Re20ig phase. The crystal chemistry of these phases is treated in detail by Muller and Roy. The materials we shall discuss are the two series of phases A B 0 +2 and A + B 02n+, and the bismuth titanates. Some of the anion deficient perovskites, ABO -x, will be considered in Section 5. 

Lamellar perovskites of the general formula MI(A 1B 03 +i) are also known and have been tried as catalysts for reactions such as oxidative coupling of methane. [Barrault et al. (1992)]. One example of this type is CsCa2Nb3Oi0 which consists of blocks built up from three perovskite layers interleaved with Cs+ cations. Other perovskite-related structures have been discussed by Baran (1990). 

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. 

More recently efforts have been directed towards the development of perovskite related cathode materials, particularly those of the K2Nip4 structure type [2,3], Fig. 1. These oxides consist of alternating layers of ABO3 and AO (rock salt) and have been demonstrated to accommodate a significant oxygen non-stoichiometry. 

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