Plumbides

In view of the lack of a simple valence relation between the atoms, complex atom-groups may be formed in sodium cadmide in a way similar to the formation of Pt>2- ions in a solution of sodium plumbide, NaPb2, in liquid ammonia,9 preventing a simplicity of structure. 

General characteristics of alloys such as those presented in Fig. 3.3 have been discussed by Fassler and Hoffmann (1999) in a paper dedicated to valence compounds at the border of intermetallics (alkali and alkaline earth metal stannides and plumbides) . Examples showing gradual transition from valence compounds to intermetallic phases and new possibilities for structural mechanisms and bonding for Sn and Pb have been discussed. Structural relationships with Zintl phases (see Chapter 4) containing discrete and linked polyhedra have been considered. See 3.12 for a few remarks on the relationships between liquid and amorphous glassy alloys. 

Alkali metal plumbides, characteristics, 2, 25 Alkali metal salts, into Ge—Group 15 element bond compounds, 3, 733... 

While the systems with the 3p, 4p, and 5p main group elements have been investigated in detail, less information is available for the thallides, plumbides, and bismuthides. This is largely due to synthesis problems, since these elements... 

Herein we review the crystal chemistry, physical properties and structure-property relationships of known plumbides in the R-T-Pb systems. The latter have not been investigated as detailed as the tin based systems. So far, the studies mainly focussed on the 3d transition metals. 

A method that has so far only scarcely been used for the synthesis of the RxTyPbz plumbides is the lead flux. The latter has successfully been used for the growth of phosphide crystals (Kanatzidis et al., 2005). This technique has certainly a great potential, especially for lead-rich R TyPbz compounds. 

The Nd-Ag-Pb phase diagram has only been studied for the 0-33 at% Nd range at 870 K (Salamakha et al., 1996). Only the equiatomic plumbide NdAgPb has been reported. Similar behavior has been observed for the Nd-Zn-Pb system at 870 K (Salamakha et al., 1999a). Both systems reveal a liquidus range in the lead rich region at 870 K. Probably the isothermal sections at lower temperatures will reveal the existence of lead rich compounds. 

There is a distinct difference for these fifteen plumbide systems when compared with the stannide systems (Skolozdra, 1997). This difference becomes already evident when looking at the binary Ni-Sn(Pb) and Cu-Sn(Pb) systems (Massalski, 1986). While binary stannides like NigSn, Ni3Sn2/ NiSn, Ni3Sn4, Cu3Sn,... 

CuioSn3, and Cu6Sn5 (Villars and Calvert, 1991,1997) exist, no binary nickel and copper plumbides are known. This fact is transferred to the ternary R-Ni(Cu)-Pb systems. The plumbides systems contain fewer ternary compounds when compared to the stannide ones. To give an example, 15 stannides have been reported for the Gd-Ni-Sn system (Skolozdra, 1997), while only five plumbides exist in the related system with lead (Gulay, 2003b). This empirical rule is observed for many other ternary systems. 

In the following section we list and discuss the crystal chemical data of many RxTyPbz plumbides. The basic crystallographic data, lattice parameters, space... 

Table 1 lists the lattice parameters of the RxTyPbz plumbides in the order of the periodic table, i.e. from the yttrium to the lutetium compounds. For each compound also the structure type is listed. 

TABLE 1 Crystallographic data for ternary rare-earth transition metal-plumbides. If listed in the literature, standard deviations are given in parentheses... 

There exists also a lower symmetry variant, the CaLiSn type, space group P3ml, where also the B layer is puckered (Figure 15). So far, no rare earth containing compound has been observed with this structure type, however, this arrangement is realized for the plumbide CaAgPb (Merlo et al., 1996). 

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