Combined NMR and X-ray diffraction study of structural aspects, dynamics and charge ordering mechanism in LixVOPO4.2H2O intercalation compounds

Abstract

We carried out a detailed investigation of the local ordering and dynamics of the lithium intercalation in paramagnetic LixVOPO4.2H2O (with 0 < x ≤ 1) materials. This question was addressed using a combination of X-ray diffraction, 31 P and 7 Li MAS NMR experiments. We first studied the structure of the fully ordered end-member of the series, Li1VOPO4.2H2O, revisiting the X-ray single crystal diffraction data on the basis of the information provided by 31 P MAS NMR. We then carried out 7 Li MAS and exchange NMR experiments and 31 P MAS experiments on the polycrystalline powders obtained after partial lithium insertion in VOPO4.2H2O phases. These experiments evidenced an unexpected ageing of the material related with lithium dynamics between the VOPO4 layers and a V 4+ /V 5+ charge ordering mechanism within the layers.