Electronic conduction and non-stoichiometry

The main interest of ionic conductors or solid electrolytes in comparison with liquid electrolytes lies in the enormous difference in mobility of ionic species of opposite charge. In the former, this difference is generally more than ten orders of magnitude. Electronic conductivity can be a serious 

The electronic properties of crystalline materials are described in terms 

Intrinsic and extrinsic defects do not play the same role. With the latter, impurities determine the electron (hole) concentration in the conduction (valence) band. A very important practical case occurs when non-stoichiometry depends on the atomic exchange between a crystal and the surrounding medium, usually gas. A simple binary non-stoichiometric compound for instance, is an intrinsic semiconductor or dielectric 

Under these conditions, the composition change may be described by Kroger s quasi-chemical equations (see Chapter 3). 

The ionization of defects can take place but is not described here (see reference 1 for detailed analysis). 

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