When it comes to the number of Na + in the Na(1) and Na(2) sites per formula unit (Table ), our findings establish that the Na(1) site is almost fully occupied in all compositions except for Na3V2(PO4)3 as the occupancy factor of Na(1) site is 0.679 (14). For the Na(2) site, when the Na + content changes from x=4 to 1 in NaxV2(PO4)3, the occupancy factor gradually decreases from almost 100 % down to ~0 %. This evidence appears in good agreement with the computational analysis on Na(1) and Na(2) sites at room temperature. Other NASICON-type materials also show similar trends, i.e. the Na(1) site tends to keep its high occupancies while the Na(2) site is populated or depopulated depending on the compositions. Overall, the refined total number of Na + per formula unit shows very good agreement with the expected compositions.