Lattice, coordination layer

Fig. 103. a. Principle of the Weissenborg moving-film goniometer, arranged for recording equatorial layer by normal-beam method, b. Determination of reciprocal lattice coordinates for. pots on equatorial layer. 

Sliding between concentric multiwalled carbon nanotubes presents a simple geometry, which restricts interlayer motion to a single (axial) direction with a fixed interlayer orientation of stiff, smooth layers. Each layer in a concentric multiwalled carbon nanotube is indexed by two integers (n, m) that give the circumference in graphitic lattice coordinates. The difference in radii between successive layers frustrates the circumferential interlayer registry. The axial... 

In molecular lattices, chain lattices and layer structures the coordination numbers are found to be increased by applying sufficient pressure, and at very high pressure a highly coordinated metallic packing is obtained. For example phosphoms is converted into a structure in which its homologous element, antimony, is stable at ordinary pressure (16). 

The Fourier transform of the y-th TS unit layer, Gj(HK.Lr), is two-dimensionally periodic and the reciprocal lattice coordinate in the direction lacking periodicity is not restricted to integral values but is a real variable, labeled Lr. In Equation (22), Gj plays a role analogous to that of the atomic scattering factor in the expression of the structure factor. 

Vermiculite is a hydrous, silicate mineral, which exfoliates greatly when heated sufficiently. The structure of vermiculite consists of 2 tetrahedral sheets for every one octahedral sheet. It has medium shrink-swell capacity with limited expansion. The cation exchange capacity is high in the range of 100-150 meq/100 g. The structure of typical vermiculite contains a central octahedrally-coordinated layer of Mg ions, which lies between two inwardly pointing sheets of silicate tetrahedra. These silicate layers are normally separated by two sheets of interlayer water molecules. Complete removal of water molecules leads to 9.02 A lattice. These layers are electrically neutral and interlayer cations occupy only about one-third of the available sites. The cohesion between the layers is typically weak [10]. 

In Ay B compounds like As2Se3, sp hybridization is present in both As and Se. The As2Se3 lattice combines the 3-fold pyramid coordination of the nearest Se neighbours of the As atoms with the 2-fold angular coordination of the nearest As neighbours of the Se atoms in a single lattice with layer structure (Figure 2.17). 

Since at a generation time of 20 min about 500 S-layer subunits have to be produced per second to keep the bacterial cell surface completely covered with an S-layer lattice, S-layer protein expression must be very efficient and regulatory circuits are necessary to ensure that its synthesis is coordinated with cell growth. Actually, most S-layer protein mRNAs have a long leader sequence and an exceptionally high stability [51,52]. In addition, two or even more promot-... 

Lateral density fluctuations are mostly confined to the adsorbed water layer. The lateral density distributions are conveniently characterized by scatter plots of oxygen coordinates in the surface plane. Fig. 6 shows such scatter plots of water molecules in the first (left) and second layer (right) near the Hg(l 11) surface. Here, a dot is plotted at the oxygen atom position at intervals of 0.1 ps. In the first layer, the oxygen distribution clearly shows the structure of the substrate lattice. In the second layer, the distribution is almost isotropic. In the first layer, the oxygen motion is predominantly oscillatory rather than diffusive. The self-diffusion coefficient in the adsorbate layer is strongly reduced compared to the second or third layer [127]. The data in Fig. 6 are qualitatively similar to those obtained in the group of Berkowitz and coworkers [62,128-130]. These authors compared the structure near Pt(lOO) and Pt(lll) in detail and also noted that the motion of water in the first layer is oscillatory about equilibrium positions and thus characteristic of a solid phase, while the motion in the second layer has more... 

The structure of AICI3 is similarly revealing. The crystalline solid has a layer lattice with 6-coordinate Al but at the mp 192.4° the stmcture changes to a 4-coordinate molecular dimer Al2Clg as a result there is a dramatic increase in volume (by 85%) and an even more dramatic drop in electrical conductivity almost to zero. The mp therefore represents a substantial change in the nature of the bonding. The covalently bonded... 

The predominantly ionic alkali metal sulfides M2S (Li, Na, K, Rb, Cs) adopt the antifluorite structure (p. 118) in which each S atom is surrounded by a cube of 8 M and each M by a tetrahedron of S. The alkaline earth sulfides MS (Mg, Ca, Sr, Ba) adopt the NaCl-type 6 6 structure (p. 242) as do many other monosulfides of rather less basic metals (M = Pb, Mn, La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Th, U, Pu). However, many metals in the later transition element groups show substantial trends to increasing covalency leading either to lower coordination numbers or to layer-lattice structures. Thus MS (Be, Zn, Cd, Hg) adopt the 4 4 zinc blende structure (p. 1210) and ZnS, CdS and MnS also crystallize in the 4 4 wurtzite modification (p. 1210). In both of these structures both M and S are tetrahedrally coordinated, whereas PtS, which also has 4 4... 

All three metals form a wide variety of binary chalcogenides which frequently differ both in stoichiometry and in structure from the oxides. Many have complex structures which are not easily described, and detailed discussion is therefore inappropriate. The various sulfide phases are listed in Table 22.4 phases approximating to the stoichiometry MS have the NiAs-type structure (p. 556) whereas MS2 have layer lattices related to M0S2 (p. 1018), Cdl2, or CdCl2 (p. 1212). Sometimes complex layer-sequences occur in which the 6-coordinate metal atom is alternatively octahedral and trigonal prismatic. Most of the phases exhibit... 

The telluride halides crystallize in monoclinic lattices, but only In-TeBr and InTel are isotypic 162). InTeCl forms a layer type of structure, as do InSCl and its analogs, but, owing to the size of the Te atom and the enhanced covalency of the In-Te bond, only a coordination number of 4 for indium is realized. The structure is built up of strongly distorted, InTesraCli/j tetrahedra that share the corners and edges occupied by Te atoms. The Cl atoms are coordinated to one tetrahedron each, and do not take part in the layer formation 324, 325). 

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