Crystal chemistry and magnetic properties of layered metal oxides possessing the K2NiF4 or related structures

There is increasing interest in recent years in the structural chemistry and properties of layered metal oxides possessing the K2NiF4 or related structures. Many new oxides of this structure exhibiting novel properties are being reported from time to time in the literature. The crystal chemistry of the oxides of the general formula A2BO4 with particular reference to the stability of the K2NiF4 structure and the relations between the different structures exhibited by this family of oxides is discussed. Non-stoichiometry in these oxides is another aspect of interest discussed in the article. While K2NiF4 itself is a well-known two-dimensional antiferromagnet, oxides of this structure with a variety of magnetic properties are examined in some detail. Besides the ternary A2BO4 oxides, the structure and magnetic properties of complex oxides, where the A or/and the B ions are partly substituted by other cations, is discussed. Some of the problems related to this family of oxides that are worth investigating are indicated. Much of the discussion in this article would have relevance in understanding the structure and properties of layered materials.