NaxMO2 layered oxides are being investigated as potential cathodes for Na-ion batteries. These systems present a variety of structures that are classified in terms of the Na local environment. P2 (prismatic) phases are widely believed to display better overall electrochemical behaviour than the O3-ones (octahedral). However, a direct test of the effect of the difference in structure upon electrochemical performance was hindered by the fact that, for a given sysytem, P2 and O3 phases could only be obtained in different x ranges. We have, for the first time, prepared both P2 and O3 phases of the same composition in the system Nax(Fe,Mn)O2, which allows us to test what the efffect is of the different structure on the behaviour of the system. Here, we intend to probe Na diffusion in both phases to get direct information of the effect of the different local environment on Na moobility.