AN EXACT AND SIMPLE APPROACH TO LOG-LOG PLOTS FOR DEFECT AND IONIC EQUILIBRIA

An alternative approach to log-log plots for defect equilibria in the solid state and ionic equilibria in solution is presented. The method is based on the strictly monotone character of the functional dependen ce of an externally controlled thermodynamic variable (e.g. the oxygen partial pressure P(O-2) for the defect equilibria in a simple oxide, or a total concentration for the ionic equilibria in solution) on a ch emically relevant compositional variable (such as the electron concent ration n for defect equilibria, or [H3O+] or a free ligand concentrati on for solution equilibria). This functional dependency can be safely inverted. The concentration of all species and the externally controll ed thermodynamic variable can be calculated as a function of the chemi cally relevant compositional variable. The appropriate plots are then obtained using naively a spreadsheet program. This method gives exact results in many more cases than the traditional approach.