Crystals closest packed structures

A FIGURE 11.48 Hetagonal Closest Packing Crystal Structure The unit cell is outhned in bold. 

HGURE 11.56 Closest-Packed Crystal Structures in Metals Nickel crystallizes in the cubic closest-packed structure. Zinc crystallizes in the hexagonal closest-packed structure. 

The lattice energy based on the Born model of a crystal is still frequently used in simulations [14]. Applications include defect formation and migration in ionic solids [44,45],phase transitions [46,47] and, in particular, crystal structure prediction whether in a systematic way [38] or from a SA or GA approach [ 1,48]. For modelling closest-packed ionic structures with interatomic force fields, typically only the total lattice energy (per unit cell) created by the two body potential,... 

The Au(lll) face, which is the closest packed fee structure, is known to have the lowest surface energy among all possible fee crystal faces. The clean Au( 111) face surface was first approximated to be a /3 X >/3.R30° unit cell. A model with a uniaxially contracted top hexagonal layer was proposed and a charge-density-wave (CDW) structure was also proposed as an explanation of the LEED observations. ... 

The structure of crystals can be investigated by the electron-diffraction method as well as by the x-ray-diffraction method. The electron-diffraction method has been especially useful in studying the strueture of very thin films on the surface of a crystal. For example, it has been shown that when argon is adsorbed on a clean face of nickel crystal the argon atoms occupy only one-quarter of the positions formed by triangles of nickel atoms (in the octahedral face of the cubic closest-packed crystal Figure 2-7). The structure of very thin films of metal oxide that are formed on the surface of metals, and that protect them against further corrosion, has been studied by this method. 

A FIGURE 23.8 Octahedral Holes in Closest-Packed Crystals Octahedral holes are found in a closest-packed stmcture. The octahedral hole is surrounded by six of the atoms in the closest-packed structure. 

When D = 300 or 350 nm, all the PSMSs were also trapped within the dimple on the patterned substrate as shown in Fig. 28e [L = 2.1 pm and P = 4.0pm] and f[L = 1.0pm and P = 2.0pm]. No PSMSs were left on the terrace within the observed SEM images. PSMS colloidal crystal formed in the dimple is defined as the dimension of the dimple, which took cubic-closest packed (cep) structure. The facet, (100) plane, is evidently parallel to the substrate surface. In other words, the present dimple may act as a template to produce PSMS colloidal crystals, the nucleation and growth of which would be confined and conttolled by the four sidewalls inside the dimples [ 132,133]. Namely, the deposition process of PSMSs on patterned substrate... 

In any crystal structure, the close-packed or closest-packed planes are the lowest energy planes. On all other planes, the density of atoms is lower, and the interatomic distance and the energy of the plane are greater. Contrary to intuitive expectations, the diameter of the largest holes or interstices between atoms in the close-packed f.c.c. structure is considerably greater than the diameter of the largest interstices between atoms in the non-close-packed b.c.c. structure. 

I shall take the simple view that most metal oxide structures are derivatives of a closest packed 02 lattice with the metal ions occupying tetrahedral or octahedral holes in a manner which is principally determined by size, charge (and hence stoichiometry) and d configuration (Jj). The presence of d electrons can lead to pronounced crystal field effects or metal-metal bonding. The latter can lead to clustering of metal atoms within the lattice with large distortions from idealized (ionic) geometries. 

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