The Effect of B-Site Cation on Oxygen Diffusivity

3 The Effect of A-Site Cation Vacancies on Oxygen Diffusivity 

In addition to following the isothermal effects, it is also quite important to understand the changes that take place in the observed activation energy for diffusion as a function of the composition. The ease of oxygen ion diffusion in perovskite structure is usually attributed to the value of the apparent aetivation energy estimated from the Arrhenius plots of diffusion coefficient. This apparent activation energy, Ea, however, consists of several terms, as indicated in the following equation  

Here AH , is the enthalpy of vacancy migration, A//y is the enthalpy of vacaney formation, and A//a is the enthalpy of vacancy-dopant association, e.g.  

AHf affects the stoichiometric vacancy concentration whereas AH a affects the mobile vacancy concentration and A// only enters into the vacancy diffusion coefficient. Thus, if we can determine the stoichiometric vacancy concentration (or, more accurately, the mobile vacancy concentration), then we can extract the value of Dv, leading to a value for AHm. 

There are several very interesting implications from this finding. It would 

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