NaCl crystal structure

We may recall that in the NaCl crystal structure each positive ion is surrounded by six negative ions, while each negative ion is surrounded by six positives as a result the crystal can be broken up into its component ions only if work is done equal to the crystal energy. In a dilute solution wc find a tendency toward a somewhat similar situation each positive ion is surrounded by a cloud of negative charge, while at the same time each negative ion is surrounded by a cloud of positive charge ... 

Thus, in cubic oxyfluorides of niobium and tantalum with rock-salt (NaCl) crystal structures, the formation and extinction of spontaneous polarization occurs due to polar ordering or disordering of Li+ - Nb5+(Ta5+) dipoles. 

Figure 5.18.1 The NaCl crystal structure consisting of two interpenetrating face-centered cubic lattices. The face-centered cubic arrangement of sodium cations (the smaller spheres) is readily apparent with the larger spheres (representing chloride anions) filling what are known as the octahedral holes of the lattice. Calcium oxide also crystallizes in the sodium chloride structure.

The calculation of M for a three-dimensional array is much more complicated, and depends on the structure of the array. For the particular case of the face-centered-cubic NaCl crystal structure, its value is M = 1.747, whereas, for the body-centered-cubic CsCl structure, it is M = 1.763. 

Figure 9.2 is schematic diagram of the crystal structure of most of the alkali halides, letting the black circles represent the positive metal ions (Li, Na, K, Rb, and Cs), and the gray circles represent the negative halide ions (F, Cl, Br, and I).The ions lie on two interpenetrating face-centered-cubic lattices. Of the 20 alkali halides, 17 have the NaCl crystal structure of Figure 9.1. The other three (CsCl, CsBr, and Csl) have the cesium chloride structure where the ions lie on two interpenetrating body-centered-cubic lattices (Figure 9.3). The plastic deformation on the primary glide planes for the two structures is quite different.

Figure 9.7 Schematic diagram of the vicinity of a divalent impurity in the NaCl crystal structure.

The prototype hard metals are the compounds of six of the transition metals Ti, Zr, and Hf, as well as V, Nb, and Ta. Their carbides all have the NaCl crystal structure, as do their nitrides except for Ta. The NaCi structure consists of close-packed planes of metal atoms stacked in the fee pattern with the metalloids (C, N) located in the octahedral holes. The borides have the A1B2 structure in which close-packed planes of metal atoms are stacked in the simple hexagonal pattern with all of the trigonal prismatic holes occupied by boron atoms. Thus the structures are based on the highest possible atomic packing densities consistent with the atomic sizes. 

Nitrides are closely related to carbides. Several of them have the same NaCl crystal structure, and similar lattice parameters. Also, the carbide and nitride of the same metal are mutually soluble. Their hardnesses are similar. 

If you examine the NaCl crystal structure closely, you will see that each Ch is surrounded by 6 Na, and each Na is surrounded by 6 Cl . The regular, repetitive structure has a high degree of order and low entropy low disorder. 

MgO has the NaCl crystal structure 23,24 each magnesium ion is coordinated by six O2 ions and each 02 by six Mg2+. The structure of a-Al203 consists of close-packed sheets of 02 ions stacked in the sequence A-B-A-B, forming a hexagonal close-packed array of anions.25 The cations are located in two-thirds of the octahedral sites. The structure of a-Al203 results in coordination numbers of 6 and 4 for the cation and the anion, respectively.25... 

LiBr has a density of 3.464 g/caf and the NaCl crystal structure. Calculate the interionic distance and compare your answer with the value from the sum of the ionic radii found in Appendix B-1. 

Consider the compound semiconductor and TE material PbTe with the relatively simple NaCl crystal structure. A complete understanding of the mechanisms that result in low k for PbTe continues to be investigated [70]. 

Figure 2.9 I Two different representations of the NaCl crystal structure are shown. In each case, the green spheres represent chlorine anions, and the gray spheres denote sodium cations. The view on the left emphasizes the positions of the ions, and that on the right better illustrates their relative sizes. In a macroscopic salt crystal, additional ions would simply extend this stmcture, repeating the same alternating pattern.

Lanthanide compounds with the NaCl crystal structure... 

Figure 12.2 A unit cell for the rock salt, or sodium chloride (NaCl), crystal structure.

Show that the minimum cation-to-anion radius ratio for a coordination number of 6 is 0.414. Hint Use the NaCl crystal structure in Figure 12.2, and assume that anions and cations are just touching along cube edges and across face diagonals.)... 

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