Ccp structures

Austenitic steels retain the ccp structure right down to room temperature. For this reason these steels cannot be hardened by quenching. 

Both palladium and platinum are shiny, silvery metals (with ccp structures), easily drawn and worked when pure. Palladium has the lower melting and boiling points (1552 and 3141°C, respectively) the corresponding figures... 

To calculate the fraction of occupied space in a close-packed structure, we considei a ccp structure, e can use the radius of the atoms to find the volume of the cube and ow muc o t at volume is taken up by atoms. First, we look at how the cube is built rom t e atoms. In Fig. 5.29, we see that the corners of the cubes are at the centers of etg t atoms, n y 1/8 of each corner atom projects into the cube, so the corner atoms collectively contribute 8xi/S=1 atom to the cube. There is half an atom on each of t e six aces, so the atoms on each face contribute 6 X 1/2 = 3 atoms, giving four... 

FIGURE 5.30 The lot ations of (a) tetrahedral and (b) octahedral holes Note that both types of holes are defined by two neighboring close-packed layers, so they are present with equal abundance in both hep and ccp structures. 

The differing malleabilities of metals can be traced to their crystal structures. The crystal structure of a metal typically has slip planes, which are planes of atoms that under stress may slip or slide relative to one another. The slip planes of a ccp structure are the close-packed planes, and careful inspection of a unit cell shows that there are eight sets of slip planes in different directions. As a result, metals with cubic close-packed structures, such as copper, are malleable they can be easily bent, flattened, or pounded into shape. In contrast, a hexagonal close-packed structure has only one set of slip planes, and metals with hexagonal close packing, such as zinc or cadmium, tend to be relatively brittle. 

All noble gases except helium crystallize with ccp structures at very low temperatures. Find an equation relating the atomic radius to the density of a ccp solid of given molar mass and apply it to deduce the atomic radius of each of the following noble gases, given the density of each (in g-cm ) Ne, 1.20 Ar, 1.40 Kr, 2.16 Xe, 2.83 Rn, 4.4 (estimated). 

Metals with bcc structures, such as tungsten, are not close packed. Therefore, their densities would be greater if they were to change to a ccp structure (under pressure, for instance). 

The tetragonal distortion of the ccp structure also leads to the bcc structure. 

Cubed compound, in PVC siding manufacture, 25 685 Cube lattice, 8 114t Cubic boron nitride, 1 8 4 654 grinding wheels, 1 21 hardness in various scales, l 3t physical properties of, 4 653t Cubic close-packed (CCP) structure, of spinel ferrites, 11 60 Cubic ferrites, 11 55-57 Cubic geometry, for metal coordination numbers, 7 574, 575t. See also Cubic structure Cubic symmetry Cubic silsesquioxanes (CSS), 13 539 Cubic structure, of ferroelectric crystals, 11 94-95, 96 Cubic symmetry, 8 114t Cubitron sol-gel abrasives, 1 7 Cucurbituril inclusion compounds,... 

Intensive effort has been devoted to the optimization of CCP structures for improved fluorescence output of CCP-based FRET assays. The inherent optoelectronic properties of CCPs make PET one of the most detrimental processes for FRET. Before considering the parameters in the Forster equation, it is of primary concern to reduce the probability of PET. As the competition between FRET and PET is mainly determined by the energy level alignment between donor and acceptor, it can be minimized by careful choice of CCP and C. A series of cationic poly(fluorene-co-phenylene) (PFP) derivatives (IBr, 9, 10 and 11, chemical structures in Scheme 8) was synthesized to fine-tune the donor/acceptor energy levels for improved FRET [70]. FI or Tex Red (TR) labeled ssDNAg (5 -ATC TTG ACT ATG TGG GTG CT-3 ) were chosen as the energy acceptor. The emission spectra of IBr, 9, 10 and 11 are similar in shape with emission maxima at 415, 410, 414 and 410 nm, respectively. The overlap between the emission of these polymers and the absorption of FI or TR is thus similar. Their electrochemical properties were determined by cyclic voltammetry experiments. The calculated HOMO and LUMO... 

CCP close-packed structures,or pillars are placed between the layers to provide the stabilization. We reported on compounds KMn02 i o,i84 (VO)j-Mn02, which are examples of such pillared structures. The former is stable to spinel formation at low current densities, and the latter shows excellent stability but poor rate capability. The groups of Dahn and Doeff among others have pursued non-ccp structures by looking at tunnel structures such as... 

The simplest of the cubic structures is the primitive cubic structure. This is built by placing square layers like the one shown in Figure 1.1 (a), directly on top of one another. Figure 1.9(a) illustrates this, and you can see in Figure 1.9(b) that each atom sits at the corner of a cube. The coordination number of an atom in this structure is six. The majority of metals have one of the three basic structures hep, cep, or bcc. Polonium alone adopts the primitive structure. The distribution of the packing types among the most stable forms of the metals at 298 K is shown in Figure 1.10. As we noted earlier, a very few metals have a mixed hcp/ccp structure of a more complex type. The structures of the actinides tend to be rather complex and are not included. 

Draw a projection of a unit cell for both the hep and ccp structures, seen perpendicular to the close-packed layers (i.e., assume that the close-packed layer is the ab plane, draw in the v and / coordinates of the atoms in their correct positions and mark the third coordinate zas a fraction of the corresponding repeat distance c). 

Next we discuss the micro-twin structure derived from a CCP lattice. Using the hexagonal expression, the CCP structure is composed of layer stacking... ABCABC. .. along the Ch(, -axis (= The ortho-hexagonal... 

The nohle gases and most metals crystallize in either the hep or the ccp structure as would be expected for neutral atoms. The alkali metals, barium, and a few transition metals crystallize In the body-centered cubic system, though the reasons for this choice are unknown. 

However, many particles contained layered defects resulting in ABC stacking that signified the presence of polytypic intergrowths of the cubic close-packed (cep) structure (Figure 5). The phase having this ccp structure was designated STAC-1 and discussed in the next section. 

In the second arrangement, the spheres of the third layer lie in the dips of the second layer that do not lie directly over the atoms of the first layer (Fig. 5.25). If we call this third layer C, the resulting structure has an ABCABC. . . pattern of layers to give a cubic close-packed structure (ccp). The name comes from the fact that the atoms in a ccp structure form a cubic pattern (Fig. 5.26). The coordination number is also 12 each sphere has three nearest neighbors in the layer below, six in its own layer and three in the layer above. Aluminum, copper, silver, and gold are examples of metals that crystallize in this way. 

Figure 3.2 (a) A tetrahedral site in a close-packed structure. Orientation of tetrahedra in adjacent layers for (b) hep and (c) ccp structures. 

There are many variations of the 3 4PTOT structure based on a ccp structure or P PgPc- The full sequence is P/ Tg OcT PgTc OaT, P(... 

Tj,0/jTf.. The O layers are in a ccp sequence (CABC...) and the T layers have a ccp sequence (for T+BG4. .. and for T ABCBecause each P layer has two close T layers (e.g., T PgTc) and each O layer has two close T layers (e.g., T OgTc) with exactly the same relationships, we can reverse designations of P and O layers. This is true for ccp, but not for hep. The full 3 4PTOT ccp structure is shown in Figure 3.8. Note the equivalence of P and O layers, exactly as for NaCl. We could also reverse the roles of pairs of T layers (T+ and T ) with the roles of P and O together. The first T layer above a P layer is T+, and this becomes O and T becomes P. P and O layers become T layers ... 

Figure 3.8. The ccp structure of P layers with all layers labeled.

Here we have briefly considered the structures for various combinations of P, T, and O layers. All patterns for ccp structures are shown in Figure 3.12. The face-centered cube is the same as the cubic close-packed structure. The two names stress particular features. The unit cell of a ccp structure is fee. The packing direction, the direction of stacking the close-packed layers, is along the body diagonals of the cube. The packing direction is vertical in Figures 3.6, 3.7, and 3.8. 

Not all of these patterns are encountered for hep structures because there are strong interactions between O sites because they are all in C positions without shielding. There is also strong interaction between close adjacent T layers preventing full occupancy of both T layers for hep. These problems are avoided for ccp structures because P, O, and T sites are staggered at A, B, and C positions. 

The 3P (ccp) structure is centrosymmetric, and there are three equivalent packing directions along the cubic diagonals. The six neighbors of an atom in any close-packed layer for 2P (hep) or 3P (ccp) are at the corners of a centrosymmetric hexagon. For hep, the six neighbors in... 

A possible mechanism for the conversion of a ccp structure to bcc for a metal involves compression. Metals are more compressible than solids such as salts, and metals are much more malleable and ductile than most other solids. In Figure 4.4, on the left side, we view a ccp structure parallel to the packing layers. The ccp structure is viewed from an angle so that A, B, and C positions are staggered. No attempt has been made to distinguish the distance of the atoms in each layer from the viewer. As drawn the distances from the viewer are shortest for A and longest for C (this is an arbitrary choice of sites one could choose C positions closer than either A or B). In the figure the layers are compressed so that layers are converted as follows ... 

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