Single rock-salt-type layers

Figure 26 (a) Single rock-salt-type layers appear as defects in TlBa2CaCu207. (b) Idealized drawing of the defect. 

Fig. 1. Structure of the oxides La2, A Cu04 (A = Ca, Sr, Ba), an intergrowth of single rock-salt-type layers and single perovskite l ers.

Figure 3 The stmcture of different members of the family of the titanates Sr0(SrTi03)m (a) m = 1, (b) m = 2, (c) m = 3. They correspond to the intergrowth of single SrO rock-salt-type layers with multiple perovskite layers (SrTiOsV.

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. 

Layered cobaltite ( 3300409) presents a misfit structure builtup with alternating single Cdl2-type [Co02]oo layers and triple [CaO-CoO-CaO] rock salt t3qie layers. The proposed structural model for involving a supercell with b 8hi 13 2 is shown in Scheme 5.4. This layered structure enables electrons behave in an anisotropic... 

On the other hand, before and/or after a layer (AX) there may be a layer of type (BX2) or one of type (AX). This last case is possible because (AX) is characteristic of both the perovskite and the rock salt structures and, therefore, is structurally coherent with both (BX2) and (AX). A sequence. .(AX)c o(AX)o c... can consequently substitute the single layer (AX)co, thus increasing the thickness of the rock salt monolayers (AX) present in the structure of perovskite. In this way, we may derive the structure of A2BX4 (K2NiF4 - type) from that of perovskite by substituting each (AX)C 0 in expression (6) with bilayers... 

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