3 Diffusion in fast-ion conducting solids

This chapter discusses classification of fast-ion conductors followed by discussion on experimental techniques employed for studying diffusion in fast-ion conductors and the use of the recorded data. The techniques are tracer techniques, indirect nuclear methods and electrical conductivity. Fluorite-structured fast-ion conductors have attracted interest from both academic and technological viewpoints. The structural simplicity has made them the ideal test-bed for theoretical models of fast-ion conduction. Fast-ion conductors present a number of experimental problems when accurate diffusion data are required and these problems are discussed for each of the techniques. The most useful literature data on ionic transport are those which report diffusion coefficients as a function of temperature in well-defined samples, fit the results to an Arrhenius law and record the data in the form of a pre-exponential factor, D0 (in m2 s-1) and an activation enthalpy, Q (in kJ mol-1).