[en] Seven solid phases including three metastable phases of (CH3)3CNH3NO3 were revealed by differential thermal analysis in the temperature range between 80 K and the melting point (418 K), and cationic dynamics in each phase was studied by use of 1H-NMR techniques. The highest-temperature solid phase obtainable above 412 K was found to be an ionic plastic phase, where the cations perform rapid translational self-diffusion and overall rotation about their center of gravity