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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on FeWO4 by Materials Project

FeWO4 is zeta iron carbide-derived structured and crystallizes in the monoclinic P2/c space group. The structure is three-dimensional. W6+ is bonded to six O2- atoms to form distorted WO6 octahedra that share corners with eight equivalent FeO6 octahedra and edges with two equivalent WO6 octahedra. The corner-sharing octahedra tilt angles range from 44–54°. There are a spread of W–O bond distances ranging from 1.84–2.13 Å. Fe2+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with eight equivalent WO6 octahedra and edges with two equivalent FeO6 octahedra. The corner-sharing octahedra tilt angles range from 44–54°. There are a spread of Fe–O bond distances ranging from 2.13–2.19 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent W6+ and one Fe2+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one W6+ and two equivalent Fe2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Synthesis and composition control of epitaxial FeWO4 thin films using pulsed laser deposition

We report the growth of epitaxial FeWO4 thin films on c-plane sapphire via pulsed laser deposition using a Fe 2 O 3 /WO 3 target ablated in an O 2 atmosphere. At a constant O 2 pressure of 1 mTorr, x-ray diffraction (XRD) confirms FeWO 4 as the major crystalline phase for substrate temperatures from 500 to 800 °C. As temperature increases, x-ray fluorescence (XRF) shows the Fe/W ratio remains nearly constant at 0.90 ± 0.02, while x-ray photoelectron spectroscopy (XPS) shows Fe 3+ to Fe 2+ conversion increases from 20% to 35%. Morphological analysis reveals phase separation, likely of amorphous Fe 3+ oxide from crystalline FeWO 4 , increasing with Fe 3+ conversion. This is attributed to an O-rich laser ablated flux, where conversion is driven by the Arrhenius temperature dependence of Fe 3+ → Fe 2+ reduction on the film surface. At a constant substrate temperature of 750 °C, XRD confirms FeWO 4 formation for O 2 pressures from 0.5 to 10 mTorr. As pressure increases, XRF shows the Fe/W ratio decreases from 0.98 to 0.70, while XPS shows Fe 3+ conversion rises from 15% to 70%. Morphology shows phase separation decreasing with increasing Fe 3+ conversion. This is attributed to scattering, where higher O 2 pressure makes the laser ablated flux O-deficient relative to Fe and W, facilitating Fe 2+ formation. Films with Fe 3+ conversion above ∼30% and Fe/W ratios from 0.86 to 0.96 exhibit FeWO 4 optical and electronic properties suitable for photoanode applications.

36 MATERIALS SCIENCE↗