Structure of the Crystal B Phase

As with the hexatic B phase, the molecules are hexagonally close-packed, with the hexagonal packing array extending to infinity in three dimensions. However, the crystal B phase can show some variations in the inter-layer stacking, and mono-, hi-, and tri-layer unit cells can be obtained [44] (see Fig. 8). For example, as the layers are hexagonally close-packed, the layer structuring of the crystal B phase can either  

Examples of AAAA, ABABAB and ABCABC stacking structures are shown in Fig. 9. In addition, transitions between different packing structures can occur with respect to temperature. In a real sample, however, no enthalpy effects can be detected despite the fact that there are symmetry changes occurring with such transitions. 

as with the hexatic B phase, the mesophase has long range bond orientational order [3]. The bond orientational order takes the form of a hexagonal packing net that has the same orientation on passing from layer to layer and extends to infinity within the layer. Therefore, the crystal packing structure and the bond orientational order are identical (Fig. 8). 

The crystal B phase can be easily distinguished from the hexatic B phase by comparison of their respective X-ray diffraction patterns. The X-ray diffraction pattern for the hexatic B phase shows diffuse scattering, whereas in a well-aligned crystal B phase the scattering profile is sharpened into resolution limited diffraction spots [3]. Interestingly, the results obtained from X-ray studies of crystal B phases suggest that the molecules 

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Figure 8. Structure of the crystal B phase showing ABC packing.

Fig. 17 The solid-state photopolymerization reaction of DSP (shown at top), (a) Crystal structure of the polymeric product phase obtained directly from the solid-state photopolymerization reaction of DSP, viewed along the i)-axis (for clarity, only half the unit cell is shown along the direction of view), and (b) overlay of the monomer (green) and polymer (orange) in their crystal structures...

Fig. 18 (a) The solution-state reaction to produce cis-[CoBr(NH3)(en)2]Br2 (denoted 2). (b) Crystal structure of the new racemic phase of 2 viewed nearly along the c-axis, showing the straight and helical chains that run along the ti-axis and b-axis respectively (Co, red Br, green N, blue C, grey). Hydrogen atoms are omitted for clarity... 

Figure 31 (a) Electron micrograph of a crystal of an intergrowth tungsten bronze phase in the K.WOa system. The structure consists of slabs of WOs-like structure five octahedra wide separated by strips of the hexagonal tungsten bronze type, (b) A drawing of the idealized structure of the crystal in (a)... 

Steiner, T., Hnfried, H. and Saenger, W. (1993) Jumping crystals X-ray structures of the three crystalline phases of ( ) -3,4- Di- O-acetyl-1,2,5,6-tetra- O-benzyl-myo-inositol. Acta Crystallogr. B, 49, 708-718. 

The smectic phase of this homolog has a rhombohedral structure (36) and possesses a significantly higher degree of order than the crystal-B phase of CCH-4 (39). A 2 1 mixture of CCH-2 and CCH-4 ( EB ) forms a very useful room-temperature nematic phase (25-54°C), and a smectic phase which is similar to that of pure C(2H-2 between 10-25°C (39). In some studies (yide infra) we have also used a 16 mol% solution of cyclohexane in CCH-2 ( EC ) as a model isotropic solvent in experiments conducted at SO C. 

We re-derive the CTR structure factor for a 3D semi-infinite crystal to show its rodlike character explicitly. We assume an orthogonal bulk crystal structure with lattice parameters a, b, c) where the surface is defined by the a-b plane (Fig. 6A). The lattice vectors are oriented so that Q = [(A, Qy, Qz] = [(2 / ) , (2 / ) , (2 / ) ], where H, , and L are the surface Miller indices. If the structure of the crystal is assumed to be identical for every unit cell in the crystal (including all surface layers), then the sum in Equation (14) can be rewritten so that the structure factor of the whole crystal is expressed as the unit cell structure factor, Fuc, multiplied by the phase factors that translate the unit cell structure factor to each and every unit cell in the crystal, both laterally within the surface plane, and vertically into the crystal. In this case,... 

On the crystal structures of the gold-richest phases in the systems Potassium-Gold and Rubidium-Gold (in German), Ch. J. Raub and V. B. Compton, Zeitschrift fur anorganische und allgemeine Chemie, 1964, 332, 5. 

Figure 6.4 Crystal structure of ar-tetragonal boron. This was originally thought to be B50 (4Bi2 + 2B) but is now known to be either B50C2 or B50N2 in which the 2C (or 2N) occupy the 2(b) positions the remaining 2B are distributed statistically at other vacant sites in the lattice. Note that this reformulation solves three problems which attended the description of the or-tetragonal phase as a crystalline modification of pure B ...

The crystal structures of the borides of the rare earth metals (M g) are describedand phase equilibria in ternary and higher order systems containing rare earths and B, including information on structures, magnetic and electrical properties as well as low-T phase equilibria, are available. Phase equilibria and crystal structure in binary and ternary systems containing an actinide metal and B are... 

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