[en] By using the chemical and electrochemical properties of plutonium chlorides in the equimolar mixture CaCl₂ NaCl at 550 deg. C determined by electrochemical methods, a potential-oxo-acidity diagram has been established. This diagram summarizes the properties of plutonium compounds in the melt. In considering the americium thermodynamical data, a potential-oxo-acidity diagram has been calculated at 550 deg. C. Those diagrams allow us to predict operating conditions for americium and plutonium separation process (selected chlorination or precipitation by gaseous mixtures). (authors)