Oxides perovskite layered compounds

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. 

Ti,Nb)-0, and La-deficient La2-02 layers (Fig. 6.7(a)). Two-dimensional lithium cation conduction has also been reported in the orthorhombic layered perovskite-type compound Lao.62Lio.i6Ti03 [55], in which the Li cation exists and migrates only near the La-deficient La2-02 layer. This work has thus revealed that oxide ion diffusion in an ionic conductor with a double perovskite structure is two dimensional. 

Thus, today Ruddlesden-Popper phases include complex oxides eontaining metals from groups 1,2, 13, 14 and 15 as well as transition (d- and 4f-) elements. The general formula of such oxides can be written as A0(AB03)n, where A means alkaline, alkali earth or rare earth element, while B is d-element, Al, Ga, In, Pb or Bi. This formula shows the main structural feature of this class of the layered perovskite-like eompoimds, that is the intergrowth of the perovskite blocks AMO3 (P) and rock salt blocks AO (RS) in a consequence -Pn-RS-Pn-RS-. In case of n = 00 the perovskite structure itself is obtained. Pigure 1 shows schematically the structure of the Ruddlesden-Popper phases (n=3) as eompared to the other types of the layered perovskite-like compounds. 

The general formulation of these oxides, (ACuOg.x)m(AO)n, reflects for each of them the number m of copper layers which form each perovskite slab, and the number n of AO layers which form each rock salt-type slab (the AO layers which lie at the boundary of the perovskite slabs and rock salt type slabs can only be counted as for 1/2). Thus all these oxides (2-34) can be represented by the symbol [m,n] in which m,n will be integral numbers. In most of these oxides one observes for one compound only one m and n value, corresponding to single intergrowths. 

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