BaAl4 type related structures

The crystal chemistry of the phosphide oxides discussed above is closely related to the structural slabs of the well-known BaZn2P2 type (isolated P ) /BaAl4 type (P2 pairs) and related compounds. This is different for the phosphide halide structures. Some relevant structures of the phosphide halides are presented in Figure 21 and a list is given in Table 9. These structures contain isolated phosphorus atoms, P2 pairs, or one-dimensional spirals like in the structure of elemental selenium. 

Structure types of antimonides with structures related to BaAl4 type structure... 

The ThCfjSij-type, a BaAl4-type derivative, shown in fig. 50a, is the most frequent structure type found in R-T-B, R-T-Si and R-T-Ge systems. It is also found with phosphides and related compounds. For a recent literature survey see Jeitschko and Jaberg (1980). 

The LaNi, (iGa(i structure, shown in fig. 85, can be interpreted as an intergrowth of BaAVtype and Cap2-type slabs with the nickel sites in the centre in one of two Cap2-type slabs only partially occupied. The structure is closely related to the 8591 Ce2NiGaio structure, shown in fig. 52a, but has a BaAl4-type slab which is only half as thick. These intergrowth structures are discussed in detail with 8050 CeNi2Si2. 

In the review by Kanatzidis et al. (2005), the preparation by the tin-flux method is mentioned also for several ternary phosphides and polyphosphides of rare-earth and transition metals. Typically the components (R metal, T metal, P and Sn in an atomic ratio of about 1 4 20 50) in sealed silica tubes were slowly heated, to avoid violent reactions, up to 800°C, annealed at that temperature for 1 week and slowly (2 K/h) cooled to ambient temperature. The tin-rich matrix was dissolved in diluted hydrochloric acid. The authors described the preparation of compounds corresponding for instance to the formula MeT4P12 (Me = heavy rare-earth metals and Th and U, T = Fe, Ru, etc.) and to the series of phases MeT2P2 (Me is a lanthanide or an actinide and T a late transition metal) having a structure related to the BaAl4 or ThCr2Si2 types. 

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