We propose to investigate low lying phonon branches in Nd2NiO4+x crystals with different content of excess oxygen atoms. This compound is part of the RE2MO4+x family of overstoichiometric oxides with RE=(La, Nd, Pr), and M=(Cu, Ni, Co), which are promising candidates to moderate-temperature oxygen ion conduction devices, such as electrolytes in solid oxide fuel cells (SOFC) or sensor devices. Especially, we want to show that low (room) temperature oxygen mobility is depending on structural instabilities directly coupled to the existence (or not) of low energy phonon modes. If verified, this approach will generalize the phonon assisted diffusion mechanism we proposed for the Brownmillerite family, and more importantly it will imply a new approach to conceptualize low temperature oxygen ion conductors. We have already performed detailed lattice dynamical calculations and would like to bench-mark our results with measurements on the high-flux thermal spectrometer IN8.