Unit cell rock salt lattice

Not all ionic compounds crystallize in the same way as rock salt. Figure 10 shows the lattice of CsGl in which each positive ion is not surrounded by six, but by eight Cl- ions. The smallest unit, or unit cell of the crystal, is a cube in which the Cs+ ions occupy the corners,... 

X (units of lattice constant) Figu re 8.20 Charge density difference [LSDA + U] - LSDA (U = S.leN) for bulk NiO taken through a (100) plane of the rock salt cubic unit cell, centered on a Ni ion. Taken from ref [113]. 

The rock-salt or halite structure is one of the most simple and well-known structures, with many halides and oxides showing a similar arrangement. A three-dimensional picture and projection of the structure is shown in Figure 1.14. All the octahedral holes created by the ions are filled, creating a ratio of 4Na 4Cl by atom/hole counting. This is characteristic of all face-centred cubic lattices four formula units e.g. 4NaCl) are present in the unit cell. 

In high radiation fields, the spinel crystal structure has been shown to change. The structure, while still cubic, becomes disordered with a reduction in lattice parameter. The disordered rock-salt structure has a smaller unit cell reflecting the more random occupation of the octahedral sites by both trivalent and divalent ions. Increased radiation damage results in the formation of completely amorphous spinels. Radial distribution functions (g(r)) of these amorphous phases have Al-0 and Mg-O radial distances that are different from equivalent crystalline phases. The Al-0 distance in the amorphous form is reduced from Al-O of 0.194nm in the crystalline phase to 0.18nm in the amorphous phase, while the Mg-O distance is increased (0.19nm in the crystal to 0.21 nm in the amorphous phase). Differences between the Al-O distances of crystalline and amorphous phases are a characteristic of both calcium and rare earth aluminates. 

MgO has the rock salt structure which implies that the ions touch along the side of the unit cell. Refer to Fig. 3.1a. The lattice parameter = 2/-Mg + 2/q = 2(126 + 86) = 424 pm. 

There are four lattice points in the face-centred unit cell, and the motif is one sodium atom at (0,0,0) and one chlorine atom at (5,5,5). In this structure, called the halite, rock salt or sodium chloride... 

The sodium chloride (NaCl also called the rock salt structure) and zinc blende (ZnS) structures are based on a face-centered cubic lattice. In both structures the anions sit on the lattice points that lie on the corners and faces of the unit cell, but the two-atom motif is slightly different for the two structures. In NaCl the Na ions are displaced from the CF ions along the edge of the unit cell, whereas in ZnS the Zn ions are displaced from the ions along the body diagonal of the unit cell. This difference leads to different coordination numbers. In sodium chloride, each cation and each anion are surrounded by six ions of the opposite type, leading to an octahedral coordination environment. In zinc blende, each cation and... 

Double perovskites are described by the general formula A2B B"06 5, and can be interpreted as a doubling of the regular perovskite ABOa.s- The elements on the B site are different from those on the B" site, and the two sites alternate to form a sublattice with a rock-salt structure. In a perfectly ordered lattice, every B ion would be coordinated by six perovskite unit cells with B" ions and vice versa. This is illustrated in Fig. 3.16 for Sr2MgMo06 g (SMMO) the Mo ion (green) is surrounded by 6 Mg ions (red). The ordering is caused by large differences in the... 

As previously described, FeO is an oxygen excessive (Fe defect) non-stoichiometric iron oxide (Fei xO), which shows the rock-salt type face center cubic structure (fee). The unit cell of Fei xO are constituted from four Fei xO molecules, where there are eight tetrahedral interspaces A site) and four octahedral interspaces B sites) with 0 closely packing onto NaCl-type cubic lattices. 

Sodium chloride, or rock salt, is one of the most commonly encountered structures. As previously noted, its radius ratio is consistent with sodium cations occupying octahedral holes in the ccp lattice of chloride anions. Figure 7.21a shows the ABCABC layer structure of chlorides, which is consistent with an fee unit cell. The sodium ions are shown in the octahedral holes in both the center of the unit cell and at... 

The three ionic lattices, rock-salt, cesium chloride and zincblende, which we have discussed in this chapter, are called bipartite lattices, because they include two equivalent sites per unit cell which can be occupied by the different ions, so that each ion type is completely surrounded by the other. Describe the corresponding bipartite... 

Perhaps the most common AX crystal structure is the sodium chloride (NaCl), or rock salt, type. The coordination number for both cations and anions is 6, and therefore the cation-anion radius ratio is between approximately 0.414 and 0.732. A unit cell for this crystal structure (Figure 12.2) is generated from an FCC arrangement of anions with one cation situated at the cube center and one at the center of each of the 12 cube edges. An equivalent crystal structure results from a face-centered arrangement of cations. Thus, the rock salt crystal structure may be thought of as two interpenetrating FCC lattices—one composed of the cations, the other of anions. Some common ceramic materials that form with this crystal structure are NaCl, MgO, MnS, LiF, and FeO. 

Alkali halides with the rock salt structure may be cleaved perfectly only along the (001) plane. The ideal unrelaxed (001) surface has a square unit cell, is nonpolar, and is characterized by layers containing both, cations and anions. The distance d between subsequent layers is half the bulk lattice constant The possible deviations of the real surface from the ideally truncated bulk structure are illustrated in... 

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