Na4V2(PO4)3 R3c 8.94302 (10) Generally, Na + insertion in the NASICON structure increases the a parameter and decreases the c parameter (in hexagonal axes). When the Na(1) site is depopulated, the c parameter increases mainly due to an increasing repulsion between parallel O3 triangular faces of the MO6 octahedra through the Na(1) site, as less screened by the Na + ions. In the case of NaxV2(PO4)3, the distances between adjacent VO6 octahedra through the Na(1)