Rare-earth phosphides preparation

The present chapter consists of two main sections, presenting data about binary and ternary rare-earth phosphides, respectively. Section 1 deals with material on phase diagrams of R-P systems, the crystal structures of all known binary phosphides, their chemical properties, and methods of preparation. Section 2 contains similar information on ternary rare-earth phosphides, and additionally includes systematized data on physical properties and the valence state of lanthanoid atoms. 

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. 

The first part of this section is concerned with the crystal structures of ternary and quaternary phosphides and the isothermal sections of ternary systems. Systems R-M-P are considered in order of increasing atomic number of rare earth and then transition metal. The crystallographic characteristics of the phosphides are listed in tables. For phosphide structures which have been refined by single-crystal methods, atomic parameters and if-values are given. Compounds in each system are considered in order of increasing phosphorus and then rare-earth content. A separate column in the table indicates the method used for preparing the phosphide. 

Kuz ma and Chykhrij present a systematic and encyclopedic discussion of the phosphides of the binary, ternary and quaternary rare earths. Their coverage includes preparation, phase diagrams, structure, as well as chemical and physical properties. The crystallochemical regularities, the nature of the interaction between components in ternary systems, and structural relationships also constitute important aspects of this review. 

In view of the highly versatile reactivity of the (P4R4) and (P4HR4) ions and the rareness of investigations on early transition metals, future work should now be centred on the exploration of different synthetic routes for the preparation of early transition metal or rare earth metal ohgophosphanides as well as on the thermal decomposition of known complexes in order to find novel synthetic procedures for the preparation of binary metal phosphides. 

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