This application is concerned with the defect chemistry and stability of Pr2NiO4+d, a highly disordered energy material whose crystal structure is still subject to controversy. This material exhibits high oxide¿ion conductivity and is largely investigated owing to its potential use as cathode in SOFC. A detailed analysis of neutron data collected on heating in the reactivity cell under O2 flow will allow monitoring the structural behavior (phase transition, evolution of the modulation, decomposition) in correlation with the oxygen defects. By considering both the time-averaged structure (Rietveld refinements) and total scattering (PDF-RMC modeling) we aim to tackle the structural issues to make reliable correlations with physical properties. We request Polaris, optimized for study of highly disordered systems by PDF.We request 4 days beam time for this study in SOFC operando conditions.