But, and that is the big advantage, we can apply the mass action law directly to the reactions in the Schottky notation. This is not directly obvious. Theoretically , however, you can introduce one more vacancy or one more interstitial into a crystal with a given concentration of each and look at the change of the free enthalpy, i.e. the chemical potential of the species under consideration. We will see how this works later. There is a simple recipe for doing this.
Lets first look at an example and the generalize.
Consider the Frenkel disorder in AgCl . Now all we have to do is to write down the corresponding Schottky notation and identify the terms in brackets with the Schottky structure elements. Do not confuse it with a symbol for concentration. Consider charges and check for electroneutrality. If the sum of all charges is not zero, search for mistakes and if there are none, throw in holes or electrons, as your system provides.