Abstract
This paper is concerned with the systematics of recently derived exact forms of the Nernst-Einstein relation and other relations among the d.c. ionic conductivity, the chemical diffusivity and the tracer diffusivity in unary, binary, and ambipolar diffusion systems. In addition, the cross coefficients in the phenomenological theory are interpreted with the aid of kinetic Ising-like models as solved by Monte Carlo methods. This leads to a consistent understanding of diffusion processes in discrete hopping models unfettered by approximations.