The challenge is to transfer such a concept to the ion migration in crystalline solids. Typically the binding sites in solids correspond to highly coordinated configuration, for example six-fold coordination in octahedral sites or fourfold coordinated sites in tetrahedral sites, whereas the transition states have a lower coordination, for example a three-fold coordination in spinel materials . Upon doping the spinel material by a very reactive atom, the effect of the dopant might be much stronger at the low coordinated transition state where often also the distances are much smaller than at the high-coordinated binding sites.