화학공학소재연구정보센터
Inorganic Chemistry, Vol.59, No.1, 854-862, 2020
Iron-Doped Sodium-Vanadium Fluorophosphates: Na3V2-yO2-yFey(PO4)(2)F1+y (y < 0.3)
The sodium-vanadium fluorophosphate family has been actively investigated recently, but few examples tackle chemical doping or the substitution of vanadium. This work presents a series of iron-doped compounds Na3V2-yO2-yFey(PO4)(2) F1+y (y < 0.3) prepared by hydrothermal synthesis with low iron content. The amount of iron in the structure is confirmed by X-ray and neutron powder diffraction, electronic paramagnetic resonance, magnetic susceptibility measurements, and solid-state nuclear magnetic resonance (ssNMR). The degree of vanadium substitution, together with the solubility limit for iron in sodium- vanadium fluorophosphates, has been calculated by ssNMR and magnetic susceptibility measurements to be y = 0.3 based on the synthetic route used here. The introduction of small amounts of Fe' to the structure leads to the reduction of a fraction of V4+ to V3+, and the voltage profiles do not change with the introduction of iron to the structure. In situ synchrotron X-ray diffraction demonstrates that the electrochemical-structural changes during charge and discharge are very similar to those observed in the V3+/V4+ mixed-valent Na3V2O1.6(PO4)(2) F-1.4 , which could be related to the existence of both iron dopant and V3+ in the phase.