Résumé
The structure of the fully ordered R-Na3Ti2(PO4)3 NASICON compound was elucidated using highquality single-crystal data. The cation/vacancy distribution forms a homogeneous 3D arrangement and could represent the absolute cationic ordering available in the full Na3M2(PO4)3 series, as verified for M = Fe. For M = Ti, the reversible Rfγ transition was observed at 85 C, leading to the standard disordered R3c γ model. Through JPDF analysis, the most probable Na+ zigzag M(2) M(1) diffusion scheme was directly deduced using our accurate crystallographic data.