All solid-state sodium ion batteries are potential low-cost alternatives to lithium ion batteries, especially for static and large-scale energy storage systems. The shift from liquid to solid electrolytes also promises major gains in battery safety. The critical challenge for all solid-state batteries is the lack of high conductivity electrolytes. In order to improve existing materials and develop new ones, we require not only a detailed knowledge of the structural properties of these materials, but also of the conduction mechanisms at the atomic scale. The proposed experiment aims to investigate the atomic scale conduction mechanisms by means of quasielastic neutron scattering in promising solid-state electrolytes based on Na3PS4 and elucidate the influence different doping strategies (i.e. the introduction of Na vacancies vs. Na interstitials) onto the Na diffusion process.