Cubic closest packed lattice

The cubic closest-packed lattice is shown in Figure 7.1(b), and can also be described as a face-centred cubic arrangement in which there is an atom at the centre of each of the six faces of the basic cubic of eight atoms. The coordination number of any particular atom in a cubic closest packed lattice is 12. Considering an atom in one of the face centres of the diagram in Figure 7.1(b), there are four atoms at the corners of... 

Where the lithium ions fit best will be determined by their size relative to the iodide ions. Note from above that there are two types of interstices in a closest packed structure. These represent tetrahedral (f) and octahedral (o) holes because the coordination of a small ion fitted into them is either tetrahedral or octahedral (see Fig. 4.12). The octahedral holes are considerably larger than the tetrahedral holes and can accommodate larger cations without severe distortion of the structure. In lithium iodide the lithium ions fit into the octahedral holes in a cubic closest packed lattice of iodide ions. The resulting structure is the same as found in sodium chloride and is face-centered (note that face-centered cubic and cubic closest packed describe the same lattice). 

Alloys of lead and thallium have a structure based upon cubic closest packing from 0 to about 87-5 atomic percent thallium. The variation of the lattice constant with composition gives strong indication that ordered structures PbTl, and PbTl, exist. In the intermediate ranges, solid solutions of the types Pb(Pb,Tl)a and Pb(Pb,Tl)TlB exist. Interpretation of interatomic distances indicates that thallium atoms present in low concentration in lead assume the same valence as lead, about 2-14, and that the valence of thallium increases with increase in the mole fraction of thallium present, having the same value, about 2-50, in PbTls and PbTl, as in pure thallium. A theory of the structure of the alloys is presented which explains the observed phase diagram,... 

Figure 7.1 Three common crystal lattices adopted by elements (a) body-centred cubic packing, (b) cubic closest packed (or face-centred cubic) and (c) hexagonal closest packed...

Many pure metals and noble gases adopt the cubic closest packing (ccp) structure of identical spheres, which is based on a face-centered cubic (fee) lattice in space group O- Fm3m. The atomic coordinates and equivalent points of this space group are listed in Table 10.1.1. These data are taken from International Tables for Crystallography, Vol. A. 

The three cubic lattices simple cubic (SCC) (not used in nature), body-centered cubic (BCC), and face-centered cubic (FCC = cubic closest-packed = CCP). 

---