Rare-earth phosphides crystal structure

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. 

The reported data on the formation of binary rare-earth phosphides and their crystal structure provides an opportunity to make some generalizations. The data about compositions and structure types of all known binary rare-earth phosphides are listed in table 16. 

Known scandium phosphides contain 50 or less at.% of phosphorus and in this w they differ in principle from other rare-earth phosphides. The crystal structures of scandium phosphides (except ScP) are characterized by a trigonal-prismatic coordination of phosphorus atoms. They are more closely related to the structures of the IVa transition-metal (Zr and Hf) phosphides than with the other rare-earth phosphides. 

The peculiarities of a number of STs of ternary rare-earth phosphides require a critical examination of the data on their crystal structure. A great number of them are determined by the powder method which does not permit distinction between such small structure details. 

Figure 20 Crystal structures of various ternary and quaternary phosphide oxides of the alkaline earth, rare earth, and actinoid metals. Alkaline earth (rare earth, actinoid), transition metal, phosphorus, and oxygen atoms are drawn as large light grey, medium grey, filled, and open circles, respectively. Some relevant coordination polyhedra around the oxygen atoms and the transition metal-phosphorus bonds are emphasized...

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, Yu.B., Ya.F. Lomnitskaya, S.V Oryshchyn, O.N. Il nitskaya and S.I. Chykhrij, 1989, New phosphides with transition and rare earth metals and their crystal structures, in Collected Abstracts XI Int. Conf on Phosphorus Chemistry, Tallinn, 1989, Vol. 2, ed. M. Veiderma (Academy of Sciences of Estonian SSR, Tallinn) p. 57. 

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