Hi, I am confused about the difference (if there is any?) between the movement of oxygen ions and oxygen vacancies inside the solid oxides. In some literature I find they are taking about the movement of negatively charged oxygen ions inside the metal oxides, while in some other cases it is positively charged oxygen vacancies that move. Is this the same thing? In crystals I imagine the oxygen vacancy as the vacancy of the lattice oxygen atom (for example in the case of SiO2 the missing oxygen atom between the two silicon atoms). Now the oxygen vacancy is a virtual particle and in reality it is always oxygen that moves. So is there any difference between the two (movement of oxygen vacancies and oxygen ions) in terms of mobility or similar? Thanks a lot!