The thermodynamics of characteristic defect parameters

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Abstract
The authors discuss the distinction between defect parameters (energies and entropies) defined at constant pressure and those defined at constant lattice parameter or constant volume and draw attention to the relations which exist between these quantities. These relations are important for the comparison of theoretical and experimental values, since the latter are almost invariably obtained from experiment at constant pressure while the basic calculations are most conveniently done at constant volume. They illustrate this importance with detailed calculations for AgCl and in particular show that the enthalpy of Frenkel defect formation at constant pressure, hp, and the corresponding internal energy for defect formation at constant volume, uv, depend in opposite ways upon the temperature. In addition the authors calculate the free volume of defect formation, also as a function of temperature. The agreement between these calculations and experiment is excellent.