Transport in defective ionic materials: from bulk to nanocrystals

This contribution reviews the current state of knowledge of atomic transport in ionic materials, a dominant theme of the EURODIM Conference series for nearly four decades. The early history of the subject is briefly reviewed followed by the important developments that occurred in the early post-WWII period. That work was mainly based on studies of relatively simple binary ionic systems in the form of single crystals and laid the foundation for much of the current knowledge. An overview is given of more recent work on fast-ion conductors where the materials are generally more complex and the aim is to produce good ionic conductors for applications as electrolyte membranes in batteries and fuel cells. This includes the development of computer simulation techniques that are now an almost essential part of any investigation of ionic transport. Finally, a brief summary is given of transport in nanocrystalline ionic materials (nanoionics) where enhanced ionic conduction has been reported with the potential for significantly improved devices.