Connecting ionic and thermal diffusion. The results presented above have the surprising observation that the thermal conductivity of Ag + argyrodites is seemingly independent of ionic transport as the diffuson-based thermal conductivity does not change significantly, while the changes in ion transport (based on Nernst-Einstein diffusion coefficients, Supplemental Note 4) are large across the same temperature range (Figure a). To comprehend the underlying differences of thermal and ionic transport one can examine the number of Ag + ions participating in the respective processes. While all Ag + vibrational modes (and with that all Ag + ions) contribute to thermal transport at high temperatures (e.g., Figure e), the instantaneous fraction of mobile Ag + participating in ionic transport is given by the Boltzmann distribution,