  There is a growing interest in the development of functional metal oxides
with mixed ionic electronic conduction for their application in different
strategic fields. In particular, ionic transport-related phenomena are of
primary importance in energy transformation and storage devices, such as solid
oxides fuel cells (SOFC) or batteries. Traditionally, the main issue that
hindered a wide spread of solid state electrochemical devices is the slow ionic
conduction and the reduced number of families of materials with pure ionic
conductivity able to play the role of the electrolyte. This is due to the low
mobility of the ionic charge carriers and their mechanical and coulombic
interactions with their host crystal structures. For relatively big and charged
ions, e.g. O2- or Na+, the low ionic conductivity imposes operating at high
temperatures, which is incompatible with some applications such as portable
electronics.
