Some Hexagonal Structures

Spin-only moments would give /z = l/z5 and 0hb, respectively. Since the spins are in the (111) plane (303), a contribution to the ferrimagnetic moment should come from a canted-spin configuration. Orbital contributions to the g factor must also be playing a role, especially in the case of Co2+. It was pointed out in the discussion on rock salt structures that Co2+ in CoO carries an atomic moment of 3.7hb rather than the spin-only value of 3.0/z, and that this moment can be accounted for quantitatively if orbital considerations are included. 

The magnetic order follows from the coupling rules. Since the 

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Here, as in other branches of inorganic chemistry, interatomic distances show a considerable variation and, although some correlation with bond order is possible, attempts to do so should be regarded with caution.For metals with close-packed structures, the coordination number of any atom is 12 for cubic or hexagonal structures, and 14 (8 plus 6 more neighbors at about 15% further away) for body-centered cubic structures. In general, this number exceeds the number of electrons per atom available for metal-metal bond formation and precludes the formation of localized, two-electron bonds between metal atoms. Bond orders of less than 1 are therefore commonly recorded. For metal clusters, it is necessary to consider the variety of ways in which valence electrons may be utilized in chemical bonding within the Mm... 

In the schemes of Fig. 7.10, typical sections of a few adjacent cells of this structure are shown these are also compared with those of a number of related hexagonal structures, some of which are described in the following paragraphs. Notice that important filled-up derivatives can be considered among the ordered structures derived from Mg. Typical examples are the hP4-NiAs type with occupied octahedral holes and the wurtzite (hP4-ZnS) type with one set of occupied tetrahedral holes. 

The structures of the compounds AMeFs are closely related to each other and can be derived from the well known perovskite structure. Therefore they may be generalizing referred to as fluoroperovskites, although some deformations of the cubic perovskite t e may occxir orthorhombic, tetragonal and hexagonal structures have been observed in ternary fluorides, in addition to the basic cubic type. 

The particles formed are in most cases spherical, although rods, ellipsoids, platelets, and hexagonal structures have also been produced. Solids composed of spherical particles are as a rule amorphous, while those of other morphologies are crystalline. In general, aging times of 2 h at approximately 100°C were sufficient to produce the desired results however, in some instances much longer times were necessary to complete the precipitation process. 

Some phenolic compounds can form flat hexagonal structures with the aromatic rings facing outward, and linked by hydrogen bonds. The internal space thus formed contains solvent. Such compounds are called inclusion compounds or clathrates. An example is dianin (2.14), which can form clathrates in more than 50 different solvents. 

Some of the best hard magnetic materials are those with a hexagonal structure. In these there are only two possible domains, differing by 180°. Table 18.5 lists the maximum BH product for several alloys. Cheap permanent magnets can be made by aligning fine iron powder in a magnetic field while it is being bonded by rubber or a polymer. 

The lamellar—.hexagonal transformation of Zr02 is likely to be initiated first by the removal of some of the surfactant species, followed by the curling of the surfactant bilayer in order to minimize the surface/interface energy as shown in Fig. 4(a) and (b).13,15 The curled bilayers transform to cylindrical rods to further minimize the surface energy as shown in Fig. 4(c) and the cylindrical rods assemble to give the ordered hexagonal structure shown in Fig. 4(d). In order to examine... 

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