Читать книгу Solid State Chemistry and its Applications - Anthony R. West - Страница 66

The anti‐perovskites have the inverse of the expected cation–anion distribution. In these: X sites contain large atoms such as alkaline earth and rare earth elements; the octahedral B sites contain anions or small atomic species; a range of metallic elements or larger halogens occupy the A sites. However, it is difficult to give a description of a typical anti‐perovskite material. Some are best regarded as interstitial alloys, such as Fe₃NPt in which N occupies octahedral sites within the cubic close packed Fe₃Pt lattice. Others have metallic elements on the A sites and have properties and bonding that are intermediate between ionic and metallic, such as BiNCa₃, SnNNd₃ and MgCNi₃. Another group is a range of oxy‐compounds such as Na₃OCl, K₃OBr, Ag₃IS, Ca₃NAs and Cs₃OAu. Most have undistorted cubic structures analogous to SrTiO₃, but distorted structures also occur.