Low X2 Partial Pressures Ionic Defects

As the pressure diminishes far below that of the stoichiometric point, the number of metal vacancies and holes will continue to fall and the electroneutrality equation chosen, Eq. (7.16), will no longer be representative. A more appropriate form of the electroneutrality equation for the low-pressure region ignores the minority defects, which are now metal vacancies and holes, to give 

This is substituted into Eqs. (7.7)-(7.10) to derive the defect concentrations relevant to the low partial pressure region. 

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