Binary structures copper

A large number of binary AB compounds formed by elements of groups IIIA and VA or IIA and VIA (the so-called III-V and II-VI compounds) also fcrystallize in diamond-like structures. Among the I-VII compounds, copper (I) halides and Agl crystallize in this structure. Unlike in diamond, the bonds in such binary compounds are not entirely covalent because of the difference in electronegativity between the constituent atoms. This can be understood in terms of the fractional ionic character or ionicity of bonds in these crystals. 

A wide range of structural motifs are found for the copper-triad xanthates, ranging from monomeric species to layer structures. This variety of structures can be ascribed to the flexible coordination modes adopted by the xanthate ligands in this group, in particular for the copper and silver xanthates. However, there is a dearth of binary xanthate structures with only two available for copper and one each for silver and gold. The paucity of data can be ascribed directly to the inability to obtain suitable crystals for structure determination. Phosphine adducts are known for all three elements of this group and in the case of both copper and silver, mixed-metal species are also known. 

When the a phase, i.e, the primary solid solution, has only a limited range of stability, other intermediate phases are formed. At particular concentrations of the second component a transformation from one crystal structure to another takes place. In a large number of binary systems, e.g. Gu-Au, Cu-Al, Cu-Sn, a transition from the cubic close packed structure of copper to a body centred cubic structure ()3 phase) occurs at a particular concentration. The phase is stable over a particular range of concentration and at higher concentrations is generally converted to the y-phase which has a complex structure, followed by the e and >) phases which are... 

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