Hexagonal closest packing hep

The crystal structure of many pure metals adopts the hep of identical spheres, which has a primitive hexagonal lattice in space group D h - Pbi/mmc. There are two atoms in the hexagonal unit cell with coordinates (0,0,0) and(f,i,i). 

Positions of interstices in the hep structure (a) octahedral interstices, (b) tetrahedral interstices. 

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The aba arrangement has the hexagonal unit cell shown in Fig. 16.14, and the resulting structure is called the hexagonal closest packed (hep) structure. The abc arrangement has a face-centered cubic unit cell, as shown in Fig. 16.15 on page 779, and the resulting structure is called the cubic closest packed (ccp) structure. Note that in the hep structure the spheres in every other layer occupy the same vertical position (ababab. . . ), while in the ccp structure the spheres in every fourth layer occupy the same vertical position (abcabca. . . ). A characteristic of both structures is that each sphere has 12 equivalent nearest... 

Hess s law in going from a particular set of reactants to a particular set of products, the enthalpy change is the same whether the reaction takes place in one step or in a series of steps in summary, enthalpy is a state function. (9.5) Heterogeneous equilibrium an equilibrium involving reactants and/or products in more than one phase. (6.5) Hexagonal closest packed (hep) structure a structure composed of closest packed spheres with an ababab arrangement of layers the unit cell is hexagonal. (16.4)... 

Hexagonal closest packed (hep) structure a structure composed of closest packed spheres with an ababab arrangement of layers the unit cell is hexagonal. (10.4)... 

In the hexagonal closest packed (hep) arrangement, shown in Figure 5.3c, the coordination consists of six atoms in the same plane as the atom under consideration plus three atoms from both of the adjacent planes, making a total of 12. 

The aba arrangement has the hexagonal unit cell shown in Fig. 10.14, and the resulting structure is called the hexagonal closest packed (hep) structure. The abc arrangement has a face-centered cubic unit cell, as shown in Fig. 10.15, and the resulting structure is... 

There are two possibilities for C, the third layer (Fig. 12-39a). In one arrangement, called hexagonal closest packed (hep), all the tetrahedral holes are covered. Layer C is identical to layer A, and the structure begins to repeat itself. In the other arrangement, called cubic closest packed, all the octahedral holes are covered. The spheres in layer C (blue) are out of line with those in layer A. Only when the fourth layer is added does the structure begin to repeat itself. 

A FIGURE 12-41 The hexagonal closest packed (hep) crystal structure... 

Crystal Structures— Some crystal structures can be described in terms of the packing of spheres. Depending on the way in which the spheres are packed, different unit cells are obtained (Fig. 12-37). The hexagonal unit cell is obtained with hexagonal closest packed (hep)... 

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