posted on 2015-09-08, 00:00authored byJean-Noël Chotard, Gwenaëlle Rousse, Rénald David, Olivier Mentré, Matthieu Courty, Christian Masquelier
The crystal structure of the NASICON
Na3V2(PO4)3 phase (NVP)
has been investigated as
a function of temperature. Combining laboratory and synchrotron X-ray
powder diffraction with single crystal X-ray diffraction, we demonstrate
the presence of four polymorphs of NVP from 30 to 225 °C. While
the high temperature γ-NVP crystallizes in the classical rhombohedral
cell (S.G. R3̅c, a = 8.73382(4) Å, c = 21.91438(17) Å),
the low temperature α-NVP undergoes a monoclinic distortion
(S.G. C2/c, a =
15.1244(6) Å, b = 8.7287(3) Å, c = 21.6143(8) Å, β = 90.163(2)°) together
with an ordering of the Na atoms. In the middle temperature range,
two incommensurate modulated structures (β- and β′-NVP)
are also reported for the first time.