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Iono-Covalent Solids

Hundreds of inorganic structure types are known. UnfoiTunately, it is only possible to present a limited number of them here. The strucmres of several nonmolecular solids that are of historical or pedagogical significance, or which are presently of significant technological interest have been chosen for description however, a large number of omissions is inevitable. There are examples of ionic, covalent, and metallic compounds that exist for almost every stmcture type. Thus, the common practice of classifying the stmcture types themselves as ionic, covalent, or metallic is not followed in this text. It should also be noted that many stmcture types are common to both iono-covalent and intermetallic compounds. [Pg.127]

Other AZ stmcture types include cesium chloride, CsCl (Fig. 3.11) two polymorphs of zinc sulfide-wurtzite and zinc blende and NiAs. Although these stmcture t) pes are [Pg.127]

The other polymorph of ZnS is wurtzite (Fig. 3.13). The zinc atoms are tetrahedrally coordinated as in zinc blende, but the anions in wurtzite form an HCP-hke array instead of a CCP-like array. Indeed, the wurtzite structure is often thought of as an HCP-like array of anions with one-half the tetrahedral sites occupied by Zn cations. Hence, the [Pg.128]

The wurtzite structure is adopted by most of the remaining compounds comprised of elements from the same groups as zinc blende, but which do not take the zinc blende strucmre, for example, AIN, InN, CdSe. The strucmre seems to be able to accommodate larger electronegativity differences between the constiment atoms, as in BeO, GaN, and ZnO. For these more ionic compounds, the wurtzite unit cell must be more stable than that of zinc blende, to an extent governed by the specific bonding forces in each case. [Pg.129]

In contrast to wurtzite, the structure of nickel arsenide, NiAs (Fig. 3.14a), contains vacant tetrahedral sites but a completely occupied set of octahedral sites. In NiAs, the [Pg.129]


Under the proper circumstances, most soft chemical processes can allow ready manipulation of the ionic component of many nonmolecular materials. Indeed, the solid-state literature has seen an enormous growth in the number of reports, wherein the utility of these synthetic strategies are exploited. However, these methods typically leave the covalent framework of iono-covalent strucmres intact. It would be extremely desirable to exercise kinetic control over the entire strucmre of a solid, thereby maximizing the ability to tune its properties. [Pg.166]

The word ceramics is derived from the Greek keramos, meaning solid materials obtained from the firing of clays. According to a broader modern definition, ceramics are either crystalline or amorphous solid materials involving only ionic, covalent, or iono-covalent chemical bonds between metallic and nonmetallic elements. Well-known examples are silica and silicates, alumina, magnesia, calcia, titania, and zirconia. Despite the fact that, historically, oxides and silicates have been of prominent importance among ceramic materials, modern ceramics also include borides, carbides, silicides, nitrides, phosphides, and sulfides. [Pg.593]


See other pages where Iono-Covalent Solids is mentioned: [Pg.44]    [Pg.94]    [Pg.97]    [Pg.815]   


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Covalent solids

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