The two-channel model additionally allows for a spectral analysis of the thermal conductivity of both channels (Figure ). The contributions from the phonon gas channel arise from the lowest frequency modes below 1 THz, while the spectral thermal conductivity of the diffusonchannel is extended over the whole frequency range. Note that the spectral thermal conductivity is not expected to be zero at zero frequency but is an apparent artifact of uniform q-meshing. Here, the minimal contributions of the high-frequency vibrations, dominated by M = Si, Ge and Sn (see Figure ), explain why no significant changes to the thermal transport are observed in the solid-solutions. Nevertheless, at temperatures relevant for ion transport, the Ag + vibrations have predominantly diffuson-like character.