Oxygen Pressure Dependence and Electronic Conductivity

As an example, the normally stoichiometric insulator SrTiOj can readily be made into an oxygen-deficient form SrTiOj by heating in a vacuum. The loss of oxygen can be written in defect terms as 

The number of oxygen vacancies will be proportional to the partial pressure of oxygen as 

A consequence of the presence of oxygen vacancies results in the appearance of a balancing population of electrons (Equation (5.2)), which will give rise to electronic (n-type) conductivity. Within the limits of the point defect equUibrium model, the electronic conductivity will be proportional to the number of electrons and the partial pressure of oxygen as 

Under conditions where this point defect equilibrium accurately reflects the situation, electron n-type conductivity is possible due to the hopping of electrons from Fe to Fe . The electronic conductivity will depend upon the amount of Fe present. This will depend upon the partial pressure of oxygen and can be derived from the equilibrium constant equation as 

However, the production of oxygen vacancies may also encourage oxygen ion conduction, and the total conductivity of a material may have several components, oxide ion, electron or hole contributions. These more complex situations are discussed in the following section. 

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