Other alkali ion conductors

The best Na +, K +, Rb, and Cs ion conductors all belong to the five families described above. Some other high-conductivity materials are represented in Table 7.2 and Figure 7.17, but descriptions of their structures are omitted here. Only a very specific class of oxide structures with a 3 A translation (types I-XIV in Figure 7.19 [48,49,53,168-187]) will be reviewed briefly. This short distance precludes the location of any atom or ion between two large alkali ions, guaranteeing their free motion in that direction [62]. The freedom may, however, be restricted by impurities, crystal defects (e.g., anions on cation sites [188]) and grain-boundaries in ceramics. 

Many other systems have subsequently been found to display anion conductivity. The electrical conductivity of lead fluoroborate and fluorogermanate glasses is similar to that of the lead fluorosilicate glasses. Calcium fluoroaluminate glasses also conduct by fluorine migration. Fluorophosphate glasses have also proven to be good anionic conductors. All of these systems are free of alkali ions. 

Sprik et al, 1993 Signorini et al, 1990), a typical example being the orientational disorder associated with NH in NH Br. Detailed simulations have been reported on (NaCN),, t(KCN),t and other mixed alkali halides and alkali cyanides. Other systems studied include potassium and calcium nitrate crystals and their mixtures. The transition from the crystalline to the superionic conductor phase in solid electrolytes has also been successfully investigated. Molecular dynamics studies of Agl were carried out by Parrinello, Rahman Vashishta (1983). LijSO has been investigated by molecular dynamics by Impey et al. (1985). Here, the Li ions become mobile at high temperatures. The ions exhibit orientational disorder and the orientational... 

Alkali metals easily lose a valence electron and form an ion with a 1 + charge. They are soft enough to cut with a knife. Sodium, shown in Figure 7-3b, has the consistency of cold butter. Because alkali metals are highly reactive, they are found combined with other elements in nature. Lab samples are stored in oil to prevent a reaction with oxygen in the air. Alkali metals are good conductors of heat and electricity. 

A number of other -alumina related phases have been prepared. In some of these the spinel blocks have an increased thickness, the so-called P, P" and P " phases, while in others, the Na or A1 components have been replaced with similar species. Related structures, such as BaMgAlnOiy doped with Eu +, are widely used as phosphors. Crystal-structure studies on such materials show that the defects present depend sensitively upon both temperature and the constituents of the phase. Large replacement ions, lanthanide or alkali metals, tend to occupy the interlayer regions as interstitial defects, but surprisingly, some also enter the spinel blocks as substitutional defects, in association with oxide ion vacancies. Smaller ions occupy the spinel blocks as substitutional point defects. The delicate balance between oxygen interlayer interstitials and spinel block cation vacancies varies with composition. These defect interactions can often be successfully explored by using simulation techniques. Ordering occurs at lower temperatures see Ionic Conductors). 

The electrolyte—the ionic conductor—which provides the medium for transfer of charge, as ions, inside the cell between the anode and cathode. The electrolyte is typically a liquid, such as water or other solvents, with dissolved salts, acids, or alkalis to impart ionic conductivity. Some batteries use solid electrolytes, which are ionic conductors at the operating temperature of the cell. 

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