Near Stoichiometry Electronic Defects

As the partial pressure of X2 falls away from that at the stoichiometric point, anion vacancies and electrons would be expected to be more favored than cation vacancies and holes, as before  

Suppose that 1017 m-3 of vacancies, and double that number of electrons, is produced by the change in partial pressure. The change in the concentration of electrons will be negligible, from 1 x 10 m to 1.002 x 10 m. The concentration of vacancies will change appreciably, from 1 x 1016 m-3 to 1 x 1017 m 3. 

As above, suppose that 1017 m-3 of vacancies, and double that number of holes, is produced by the change in partial pressure. The concentration of vacancies will 

In both of these regimes it is more reasonable to approximate the electroneutrality Eq. (7.12) by 

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When referring to the defect structures in Figure 10.3c or 10.4b and the corresponding conductivity isotherms in Figures 10.6a and b, for the undoped and acceptor-doped BaTi03 8, respectively, the defects in the majority must be Vo compensated by the acceptors A c, whether they are extrinsic (i.e., Al xi) or not. Thus, oxide ions (0 ) and electrons (e ) may be taken as the most mobile charged components in this near-stoichiometry regime. 

When referring to the defect structure in the near-stoichiometry regime, 2[Vd ] w [At] in Figure 10.3c or 10.4b, the ionic conductivity is due to Vo , and essentially is independent of oxygen activity. The variation of the total conductivity in Figure 10.6a and b is, therefore, attributed to that of the partial electronic conductivity,... 

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