A comparison of the phenomenological diffusion coefficients

The derivations above give the following interrelation of the three phenomenological oxygen diffusion coefficients (see Eqs. (6.47), (6.54), see Fig. 6.20) 

These relationships will be generalized later for the presence of several charge carriers and, in particular, for the occurrence of association reactions. 

It is worth emphasizing once again that in contrast to and D the chemical diffusion coefficient is first of all addressing the (small) ensemble of (rapid) defects and secondly is made up of ionic and electronic contributions. In other words It is enhanced with respect to Dq /v on account of the drag effect of the electrons, while Do YVq itself is usually much larger than and D because of the concentration effect. Thus, it is not correct to ascribe the ratio D /D (instead of D /Doj /Vq) solely to an acceleration by the electrons as is frequently done. In the case of a 

It is certainly illuminating in this latter case in which it is only the ionic jump process that is relevant for the chemical diffusion, to derive and D using chemical kinetics. Let us consider the jump of an ion (at x) into a vacancy (at x = x+Ax) 

In the chemical diffusion experiment the value of Cv is variable, while Co2- can be regarded as being approximately constantSince k = k = k it follows that 

---