a b s t r a c t Pyrochlore-type H 3 OSbTeO 6 is a remarkable proton conductor exhibiting an outstanding electrical conductivity even at ambient temperature. It consists of a three-dimensional interconnected (Sb,Te)O 6 framework, built from randomly distributed corner-shared SbO 6 and TeO 6 octahedra, forming large cages in which the H 3 O þ ions are located. The dynamics of the caged species has been investigated by temperature-dependent neutron diffraction, quasielastic neutron scattering, and NMR experiments. Three types of motion may be discerned, namely, stochastic rotations of the H 3 O group around its 3-fold axis, jumps between four equivalent positions within the cage, and long-range inter-cage translational diffusion. The onset of ionic conductivity is clearly reflected by structural changes. Details of the complex diffusion mechanism are given.