Free Energy and Stoichiometry of Oxides

Because the potential developed across a stabilized zirconia electrolyte is simply related to the free energy of the reactions taking place in the surrounding cell, the material can be used to measure the free energy of formation of an oxide. (Details of cells and cell types for this task are outside the scope of this book and only principles will be outlined. For information on these techniques see the Further Reading section at the end of this chapter.) 

If the oxide is a nonstoichiometric phase MO. it will still be able to gain oxygen. The cell will be 

The voltage measured will now appear to drift as the composition range of the nonstoichiometric oxide is crossed. The voltage will become constant above and below the composition range of the oxide. Note that this is closely related to the variation of oxygen partial pressure over a nonstoichiometric oxide (see Sections 7.3, 7.4). 

---