INTERACTION BETWEEN POINT DEFECTS IN NONSTOICHIOMETRIC COMPOUNDS

The variation in thermodynamic activity as a function of nonstoichiometry was derived for binary compounds exhibiting large deviations from stoichiometry. The assumptions were made that only one type of point defect is present in high concentrations, and that there are pair-wise interactions among the randomly distributed defects. It is shown that comparisons of experimentally determined activities with the theoretically derived relations may be used to deduce the type of point defect which is predominantly responsible for the nonstoichiometry, and to determine the free energy of interaction between the defects. Experimental hydrogen activities in yttrium and cerium hydrides, and thorium activities in thorium monocarbide are analyzed in this manner. © 1969.