The aim of the experiment is to investigate by means of in situ NPD the structural behavior of two new Mn-rich double perovskites compounds, NdBaCo1.5Mn0.5O5+d and NdBaMn2O5+d in actual anode working conditions (wet hydrogen, 600-1000°C) of Solid Oxide Fuel Cell (SOFC) to get insight into the ordered/disordered nature of the oxygen sublattice and determine the mechanism of oxygen diffusion. It is crucial to check if diffusion in wet hydrogen conditions at high temperature (HT) proceeds in the transition-metal layers as in related cobaltites cathodes LnBaCo2O5+d heated in air. Such experiment on SOFC anode materials has not been performed so far. POLARIS is requested because its high resolution and good statistics allow detection of subtle distortion and afford precise information on the oxygen content and position, essential to unambiguously establish the diffusion mechanism.