K2NiF4 type

Galasso and Darby [220] prepared and investigated the oxyfluoride K2NbC>3F, which has crystal structure similar to K2Ta02F and crystallizes in a K2NiF4 type structure. The structure of the compound consists of infinite layers of octahedrons, Nb04F2, that are oriented perpendicular to the c axis, as shown in Fig. 34. 

MX4 layer of vertex-sharing octahedra, and the packing of such layers in the K2NiF4 type. The packing in SnF4 is obtained by leaving out the K+ ions and shifting the layers towards each other in such a way that every octahedron apex of one layer comes to be between four apexes of the next layer... 

The ternary fluorides M2HgF4 (M = Rb, Cs), obtained by heating the alkali-metal fluorides MF with Hg2F2 under carefully controlled conditions, crystallize in the well-known K2NiF4 type, with octahedra sharing four corners to form layers lDC2[I IgF2F4/2]2 and the cations M+ embedded between these layers.350... 

The structure of La2Cu04 (K2NiF4-type) is illustrated in Figure 4 and is represented by the following scheme ... 

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... 

Mn04 (M = Pr - Gd) have the K2NiF4-type structure. Included in the second group is EuMA104 (M = La- Gd), in which the Eu2+ and M3+ ions coexist in identical sites. 

Ferromagnetic Fluorides Derived from the K2NiF4 Type. 108... 

Table 5. Magnetic parameters of K2NiF4-type compounds...

Both symmetry and unit cell constants are similar to the corresponding values of K2NiF4 type compounds, as is shown in Table II. Indeed, we have found that a reasonable structure can be derived for Sr2Pd03 which is closely related to the K2NiF4 structure. In this proposed structure, the space group D2h25-Zmmm is assumed and the atoms are placed as follows ... 

The structure can be considered as an orthorhombically distorted K2NiF4 type, from which of the oxygens have been removed in an ordered way. If these missing oxygens are inserted—2 O in (2d), +... 

It was further difficult to derive the antiferromagnetic state in the case of transition metal oxides like Cu oxides. One of typical Cu oxides is La2Cu04, in the K2NiF4-type crystal structure, we displayed in Figure 5.10. The Cu oxide of... 

Tetragonal li/mm). Perovskite layers of K2NiF4 type, each [MnCl6] sharing four corners in plane Orthorhombic Pbam). Edge-sharing chains of [MnCl6]... 

Figure 21 (a) K2NiF4-type layer structure (b) K3N12F7 or Rud-dlesden-Poppertype structure... 

Preparation of Superconductive Ceramics 17.3.10.2. High Temperature Superconductors 17.3.10.2.1. K2NiF4-Type Cuprates. 

The most often found types of mixed oxides are perovskites (RBO3), K2NiF4-type oxides (R2BO4), R 1 B C>2 +1 ( = 2 or 3), lamellar perovskites, pyrochlores, spinels, and oxide solid solutions. Perovskite oxides are, by far, the most commonly used oxides. Therefore, this chapter will reflect this situation by putting more emphasis on this type of materials. Within this section the structure, preparation methods and general characteristics of the mixed oxides will be discussed. Note that R stands for rare-earth elements while A includes all types of elements. 

Let us review first the state of the art concerning nitric oxide decomposition. In the last 10 years the search for NO decomposition catalysts sharply increased in an effort to comply with more severe regulations which reduce the allowed emission level of this contaminant. Particularly during the 1990s quite a few papers have been published concerning the use of different rare-earth-containing perovskites and K2NiF4-type mixed oxides. Ni, Cu and Co are the most commonly used transition metals. 

Figure 23 Unit cell of Sr2Ti04 (K2NIF4 type) at right. Unit ceU of 873X1207...

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