Depending on the thermal history of the sample, Na3V2(PO4)3 can crystallize either in the monoclinic α or β form at room temperature (the reversible phase transition occurring very close to room temperature with about 10° of hysteresis). In the present study, the crystal structure was refined with the monoclinic β phase since the (111) reflection at 6.74° (λ=0.8266 Å) was not observed, while it is allowed in the α (i.e., Na + ordered) phase, as