Metals lattice spacings

It is often difficult to represent inorganic compounds with the usual structure models because these structures are based on complex crystals space groups), aggregates, or metal lattices. Therefore, these compounds are represented by individual polyhedral coordination of the ligands such as the octahedron or tetrahedron Figure 2-124d). 

Pearson, W. B., 1967, " Handbook of Lattice Spacings and Structures of Metals and Alloys", Pergamon Press, Oxford. 

LaNis has the CaCu, structure, space group P6/mmm [26] the hexagonal metal lattice is shown in Fig. 4. The crystal structure of LaNi5D7 has been determined 127, 28] and is illustrated in Fig. 5. There are three types of interstitial D sites La2Ni4 tetrahedra, and NiA tetrahedra. The unit cell is doubled along the oaxis because of the formation of a superlattice which is a consequence of long-range correlations between occupied and unoccupied... 

Electrocrystallization with M B( 5135)4 under the same conditions leads to the single crystals of alkali-metal salts M C5q(T33F)j, (x 0.4, y 2.2) with M = Na, Li, K, Cs. They are isomorphic and crystallize with hexagonal unit-cells. In contrast to the PPN-salt the Na salt with the structure NaQ39C5o(THF)2 2 shows metallic properties [85, 86]. The resistivity of this compound was measured to be 50 S cm at room temperature and about 1000 S cm at 100 K. The lattice spacing of about 9.9 A at room temperature indicates a direct Cjq-Cjq interaction, which could explain the salt s metallic character. 

W. P. Pearson, Handbook of Lattice Spacing and Structure of Metals (Pergamon, New York, 1967), Vol. 2. 

Figure 5.13. In situ atomic-resolution ETEM image of Pt/titania catalyst (a) finely dispersed Pt particles (b) in situ real-time dynamic activation in hydrogen imaged at 300 C. The 0.23 nm (111) atomic lattice spacings are clearly resolved in the Pt metal particle, P and (c) the same particle imaged at 450 C, also in H2. SMSI deactivation with a growth of a Ti-oxide overlayer (C), and the development of nanoscale single-crystal clusters of Pt, with atomic resolution (arrowed). (After Gai 1998.)...

For much of the discussion in this chapter, the BOA is assumed valid so that the bond making/breaking is simply described by motion of nuclei on a multidimensional ground state PES. For example, dissociation of a molecule from the gas phase is described as motion on the PES from a region of phase space where the molecule is far from the surface to one with the adsorbed atoms on the surface. Conversely, the time-reversed process of associative desorption is described as motion on the PES from a region of phase space with the adsorbed atoms on the surface to one where the intact molecule is far from the surface. For diatomic dissociation/associative desorption, this PES is given as V(Z, R, X, Y, ft, cp, < ), where Z is the distance of the diatomic to the surface, R is the distance between atoms in the molecule, X and Y are the location of the center of mass of the molecule within the surface unit cell, ft and cp are the orientation of the diatomic relative to the surface normal and represent the thermal distortions of the hh metal lattice atom... 

Numerous studies with low-energy electron diffraction (LEED) revealed that most of the clean surfaces of the platinum group metals exhibit an atomic arrangement that is identical to that expected from an undistorted termination of the bulk. Variations of the vertical lattice spacings between the topmost atomic layers are very small, if present at all (66). Exceptions are, however, found with the (100) and (110) planes of Ir and Pt. The clean and thermodynamically stable structures of the Pt(100) (67-69) and Ir(100) (70, 71) surfaces were found to reconstruct and to exhibit 5 x 1-LEED patterns. A plausible explanation (72) is that in these cases the topmost atomic layer forms a hexagonal arrangement, similar to that within the (111)... 

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