Cubic dose packing

Tetrahedral and octahedral interstitial holes are formed by the spaces left when anions pack in a cubic dose-packed array, (a) Which hole can accommodate the larger ions (b) What is the size ratio of the largest metal cation that can occupy an octahedral hole to the largest that can occupy the tetrahedral hole while maintaining the close-packed nature of the anion lattice (c) If half the tetrahedral holes are occupied, what will the chemical formula of the compound M. Ay be, where M represents the cations and A the anions ... 

Consider a metallic element that crystallizes in a cubic dose-packed lattice. The edge length a of the unit cell is 408 pm. If dose-packed layers are deposited on a flat surface so that the depth of the metal deposited is 0.125 mm, how many close-packed layers are present ... 

Our language is rather casual here. The crystal structure of copper is of the cubic dose-packed (cep) type and, because there is only one type of atom, this is ecprivalent to the face-centered cubic (fee) structure for this special case. Although not every F-centered crystal structure belonging to the cubic system (e.g.. Si or NaQ) can be considered dosely packed, the simplified notion cep = fee is so ubiquitous in the literature that we also use it in this book. 

Magnetite structure is an inverse spinel with a face center cubic unit based on 32 O2- ions with a regularly cubic dose packed along the [111] direction. There are eight formula units per unit cell. Magnetite differs from other iron oxides in that it contains both divalent and trivalent iron. Its formula is written as Fe > [Fe Fe in]04and the brackets denote octahedral sites, tetrahedral Fe spans are directed antiparallel to octahedral Fe 3+ and Fe 2+ spins so... 

The single duster shown in Figure 3-31b consists of 17 rows of cubic dose packed palladium atoms and corresponds exactly to a cutout of the lattice of... 

These results agree well with electrochemical experiments. If dichloromethane solutions of different Msj dusters are contacted to Pt electrodes to which 20 V dc is applied, the duster molecules are degraded as a result of the contact with the electrodes. [109] Polarization effects may be the reason for the decomposition. Electrophoresis is observed without any indication of duster decomposition if the platinum electrodes dip into water layers covering the organic phase in a U-tube. The black, thermodynamically unstable microcrystalline products formed on the Pt surfaces have been identified by X-ray powder diffraction to be novel [(Mi3)J metal modifications. The results from the diffraction experiments indicate a structure consisting of cubic dose packed M13 dusters which are linked via their triangular faces to form a kind of pseudo dose packed structure with M13 dusters as building blocks. 

Flgwe S-L Part of a cubic dose packed lattice. The conventional fee unit cell (right side) and edge and comer condensed octa-hedia (left side) are drawn. 

The elements xenon and gold both have solid-state struc-CQ hires consisting of cubic dose-packed arrangements of... 

FIGURE 4 Crystal structures exhibited by the rare earth elements, (a) Hexagonal dose packed (hep), (b) cubic dose packed (cep), (c) double hexagonal close packed (dhep), and (d) the complex structure of Sm. [From Gschneider, K. A., Jr. (1961). Crystallography of the rare-earth metals. In The Rare Earths (F. H. Spedding and A. H. Daane,... 

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