Defect Concentration as a Function of Temperature and Pressure

As we have seen, a given enthalpy term can be associated with each defect process (tables 4.2 and 4.3). The defect process generally also involves an entropic term, which may be quantified through 

Because a defect entropy (Ai j), a defect enthalpy and a defect vol- 

The enthalpic term A/7 is the dominant one in equation 4.37 and determines the variation of the defectual concentration with T. For instance, for a Schottky defect we can write 

If we assume, at first approximation, that AHs does not change with T, it is obvious that the increase in defect concentration with T is simply exponential. Table 4.4, for instance, hsts Schottky defect concentrations calculated in this way at various T by Lasaga (1981c) for NaCl and MgO, assuming defect enthalpies of 2.20 and 4.34 eV, respectively. 

The approximation discussed above is in fact rather rough, and there are actually two general cases. 

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