Anion interstitial current

Figure 21 indicates the anion interstitial currents through the layers. The coordinate system is chosen to be the same as that already utilized for cation interstitial diffusion, namely that illustrated in Fig. 18. Because all anion interstitials originate at the oxygen interface, the anion interstitial currents decrease in magnitude in the order i + 1, i, i — 1,. . . , as noted in Fig. 21. The difference current Jf(ai) — J VI serves to increase the thickness...

The c/ vi is thus not an oxygen anion interstitial current, but is introduced merely to cast the growth equation for layer N into a form analogous to that for the inner layer growth. The N is determined by eqn. (229). 

Fig. 2. Field-controlled oxide growth, (a) Surface and interfacial charges (b) Cation interstitial (ci) and anion interstitial (ai) currents.

Fig. 8. Schematic diagrams of concentration profiles and the associated particle currents, (a) Cation interstitials or anion vacancies [(dC/dx)<0] and positively directed particle currents ( 0). (b) Cation vacancies or anion interstitials [(dC/dx) > 0] and negatively directed particle currents (J< 0).

Since local space-charge neutrality does not hold at the oxide interfaces, the above expression for the current is restricted to the interior zone [28] where local space charge neutrality has been found [46] to be a good approximation. This is illustrated for the case of cation vacancy (or anion interstitial) and electron-hole diffusion by Fig. 17. Thus, the domain of validity is not 0 but instead is 5 < [Pg.75]

Fig. 21. One of the interior oxide layers labeled i in a sandwich array of multilayered oxides growing by anion interstitial (ai) diffusion illustrated with the relative magnitudes of the negatively directed particle currents through layer i and the adjacent layers i — 1 and i + 1.

The conductivity of anhydrous acridizinium (benzo[ lquinolizinium) bromide in the form of void-free plates has been reported to be 1.2 fl-1 cm- at 90 °C (68JA3120). It was believed that most of the current was carried by bromide ion either interstitially or through anion... 

For strongly ionic solids where cation and anion sizes are comparable, e.g. NaCf, KBr, etc., Schottky defects will predominate and both transport numbers and are greater than zero t = 0, no current is carried by electron migration). When the size of the cation is considerably smaller than the anion, eg. AgBr, AgCf, etc., Frenkel defects occur and the interstitial cations are the dominant current carriers 1). 

The steady-state thickness of the barrier layer (and also possibly of the outer layer) varies linearly with the applied voltage. The logarithm of the current is also found to vary linearly with voltage, with a positive, finite slope being predicted, and observed, if the barrier layer is a cation conductor (e.g. NiO/Ni)). On the other hand, ln Iss) vs. V has a zero slope if the barrier layer is an interstitial cation conductor (ZnO/Zn) or an anion conductor (WO3/W), but only if no change in oxidation state occurs upon the ejection of a cation from, or dissolution of, the barrier layer. 

The changes in the film material with the current density, field, and temperature at which the films are made (in dilute, aqueous solution) and the changes which occur on subsequent annealing at temperatures of up to 200 C or so, represent large proportional changes in the concentration of mobile ions, that is, according to the usual theory, in the concentration of defects (interstitial metal ions and anion and cation vacancies). However, the absolute variations in terms of numbers of defects are probably small. Thus the variations in properties, which are not directly functions of defect concentrations, such as refractive index and density, are of the order of 1 %— not large for ordinary formation conditions—whereas the variations in those properties, such as ionic conductivity, electronic conductivity, and rate of dissolution in which are directly dependent on the concentra-... 

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