Of ternary stannides

Structure types of ternary stannides obtained by inserting a third component into the structure of binary... 

Structures of ternary stannides with the structures of binary compounds or their superstructures... 

Structure types of ternary stannides wich consist of fragments of other structures ... 

The phase equilibria of the Sc-M-Sn (where M = Ru, Rh, Pd, Os, Ir, or Pt) systems are not known. One or two ternary compounds have been synthesized in each of the systems. These data are shown in table 21. Espinosa et al. (1982) reported on the tetragonal ternary compounds of a tentative composition ScMi.jSns.e (M=Ru, Rh, Ir) giving their pseudocubic cell parameters (table 21). Probably, these compounds are isotypic with Er5 j Rh6Sni8+ found by Hodeau andMarezio (1984), however, additional investigations are necessary to determine the proper composition and structure of these stannides. Two and three different crystal structure types have been reported for ScPdSn and ScPtSn, respectively (see table 21). This might be an indication for a polymophism of these compounds. 

Interconnection of the structure types of stannides with the other types 4. Properties of the ternary stannides... 

In this survey the stannides containing rare earths are discussed in the following sequence the systems investigated, the composition and crystallographic data of the compounds, and results of the research on the magnetic and transport properties. An attempt is made to find some regularities in the crystal chemistry and physical properties of the ternary stannides. 

The ternary systems R-M-Sn have not been studied completely. The majority of systems has been investigated by Skolozdra and co-authors (Skolozdra 1993). In other studies only individual alloys were investigated with the aim of finding new compounds. The phase diagrams are described below. One section of the review of Gladyshevsky et al. (1990) has been dedicated to the description of the ternary rare-earth-tin systems and the ternary stannides. 

The isothermal section of the phase diagram of the Sc-Cu-Sn system at 673 K was constructed (Kotur and Derkach 1994). The system is characterized by the existence of three ternary stannides ScCu4Sn, ScCuSn and Sc6CuSn2. The crystal structure was studied for ScCu4Sn and ScCuSn. The homogeneity range of the ternary compounds is small. 

As we have seen from the previous part, the structures of the stannides are connected in some way with the structures of other groups of compounds. Analysis shows, that the structures of the ternary stannides can be divided into three main groups. The first group contains the stannides obtained by an insertion of the third component in the structure of binary compounds. These types are presented in table 6. 

The stannides with the structures of the binary compounds and their superstructures form the second group (table 7). The formation of the superstructures of the ternary stannides is connected with the change of the number of the components and ordered placement of their atoms in Wyckoff sites which are occupied in the binary compounds by one component. In most cases, M and Sn are the ordered atoms, and only in the superstructures of the TiAs type (RPt2Sn stannides) and CrasCg (phases III) do the R and Sn atoms order. The structure of the RNi2Sn (MnCu2Al type) compound can be considered as both a phase of insertion and as a superstructure. 

The magnetic and transport properties of the ternary stannides have not been investigated to any great extent. Of these, the magnetic properties have been more completely... 

The resistivities of the ternary stannides have different values and temperature dependences because of the variety of their composition and crystal structures. Skolozdra (1993) classified the stannides by their resistivity behaviours from the curvature of the p(T) function in the range 80-360 K. A tendency that stannides with large M contents have a bigger curvature has been found. A comparison of the influence of different metals (Fe, Co, Ni, Cu) on curvature indicated that as the transition of M from iron to copper occurs, the curvature of the p(f) function decreases and all practically studied copper stannides have a linear p(T) dependence. 

It follows from eq. (3) that the thermopower must change linearly with the temperature. In most ternary stannides the dependence S T) is complex. Analysis carried out by Skolozdra (1993) shows that the deviations from linearity mainly correlate with the ones in the p(T) dependence and are caused by the same type of mechanisms of the electron scattering. The main causes of the anomalous 5(T) are the peculiarities of the structure of the electron band spectrum in the region of the Fermi level, a strong electron-phonon interaction, and the presence of a statistical distribution of atoms in the crystal structure. 

So far more than 180 rare earth-transition metal-plumbides have been reported. They crystallize with 23 different structure types. Apart from the few lead rich plumbides with YbsRlpSnis and related structures, only plumbides with 33 at% or even lower lead content have been reported. Some ternary systems exhibit large liquidus ranges in the lead rich regions at 870 °C. Through phase analytical investigations at lower temperatures one will certainly get access to new lead rich phases. In view of the more than 500 and 850 rare earth-transition metal-stannides and indides, respectively, the lead based systems certainly have a great potential for many more phases to be discovered. 

Only YbAgPb and La4Ni3Pb4 show peculiar structure types, which have first been observed for a plumbide. All other plumbides exhibit relatively simple structure types, which have been observed also for silicides, germanides, stannides, gallides, or indides. We expect that lead characteristic structures will form in the lead rich parts of the ternary systems, similar to the gallium and indium based phase diagrams. 

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