Abstract
Traditionally materials with the fluorite and perovskite structures have dominated the research in the area of oxide ion/proton conducting solid electrolytes. In such cases, the key defects are oxide ion vacancies, and conduction proceeds via a simple vacancy hopping mechanism. In recent years, there has been growing interest in alternative structure types, many of which contain tetrahedral moieties. Forย these new systems, an understanding of the accommodation of defects and the nature of the conduction mechanism is important for the optimisation of their conductivities, as well as to help target related structures that may displayย high oxide ion/proton conduction. Computer modelling studies on a range of systems containing tetrahedralย moieties are presented, including apatiteโtype La~9.33+~~x~Ge~6~O~26+3~~x~~/2~, cuspidineโtype La~4~Ga~2โ~~x~Ti~x~O~9+~~x~~/2~ and La~1โ~~x~Ba~1+~~x~GaO~4โ~~x~~/2~. The type of anion defect (vacancy or interstitial), their location and the factors affecting their incorporation are discussed. In addition, modelling data to help to understand their conduction mechanisms are presented, showing novel aspects including the important role of the tetrahedral moieties in the conduction processes.