Iron-Doped Sodium-Vanadium Fluorophosphates: Na3V2- yO2- yFey(PO4)2F1+ y (y < 0.3)

Verónica Palomares; Amaia Iturrondobeitia; Paula Sanchez-Fontecoba; Damian Goonetilleke; Neeraj Sharma; Luis Lezama; Teófilo Rojo

doi:10.1021/acs.inorgchem.9b03111

Iron-Doped Sodium-Vanadium Fluorophosphates: Na₃V_{2- y}O_{2- y}Fe_y(PO₄)₂F_{1+ y} (y < 0.3)

Inorg Chem. 2020 Jan 6;59(1):854-862. doi: 10.1021/acs.inorgchem.9b03111. Epub 2019 Dec 16.

Authors

Verónica Palomares^{1

2}, Amaia Iturrondobeitia¹, Paula Sanchez-Fontecoba¹, Damian Goonetilleke³, Neeraj Sharma³, Luis Lezama¹, Teófilo Rojo^{1

4}

Affiliations

¹ Inorganic Chemistry Department, Science and Technology Faculty , University of the Basque Country, UPV/EHU , P.O. Box 644, 48080 Bilbao , Spain.
² BCMaterials , Building Martina Casiano, Third Floor, UPV/EHU Science Park, B° Sarriena s/n , 48940 Leioa , Spain.
³ School of Chemistry , University of New South Wales Australia , Sydney , New South Wales 2052 , Australia.
⁴ CIC ENERGIGUNE, Parque Tecnológico de Álava , Albert Einstein 48, ED. CIC , 01510 Miñano , Spain.

PMID: 31840984
DOI: 10.1021/acs.inorgchem.9b03111

Abstract

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 Na₃V_2-yO_2-yFe_y(PO₄)₂F_1+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 Fe³⁺ 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 Na₃V₂O_1.6(PO₄)₂F_1.4, which could be related to the existence of both iron dopant and V³⁺ in the phase.