FeWO₄ Single Crystals: Structure, Oxidation States, and Magnetic and Transport Properties

Abstract

Synthetic crystals of the ferberite FeWO4 have been grown by the chemical transport reaction starting from a polycrystalline sample of this phase. Magnetic susceptibility measurements showed an antiferromagnetic Néel temperature of T N = 75 K. The anisotropy in the magnetic susceptibility can be ascribed to the magnetocrystalline anisotropy of the Fe2+ ion, the oxidation state of which was confirmed by X-ray absorption spectroscopy. While X-ray photoemission analysis indicated that all W ions are in the expected 6+ charge state, the dielectric permittivity of the FeWO4 crystals was found to be leaky, hindering changes at T N to be detected. Subsequent thermoelectric power measurements suggested the presence of about 1.5% Fe3+. X-ray diffraction experiments confirmed the basic crystal structure of the wolframite type and revealed some structural disorder in the 1% range. Transmission electron microscopy allowed us to unveil the occurrence of stacking faults attributed to the similarity of the atomic environment of the Fe and W species.

Electronic, Vibrational, and Structural Properties of the Natural Mineral Ferberite (FeWO4): A High-Pressure Study

“…Experimentally, we have determined the band gap energy by means of a Tauc analysis (see the inset of Figure ); therefore, the reported value should be assumed as the lower limit value of E g . We obtained E g = 2.00(5) eV, which is between the previously reported values. ,− This means that the calculated band gap energy is slightly underestimated, but the underestimation, 0.2 eV, is within typical differences between DFT and experiments. , However, this does not affect the determination of the pressure dependence of E g . In Figure , we present the electronic density of states, which shows that Fe states are the main contributors to the top of the valence band and hybridized W and O orbitals dominate the bottom of the conduction band.…”

“…Such a minimal concentration of impurities is not expected to affect the properties studied in this work. Optical absorption and Raman experiments were performed on 40 μm × 40 μm × 10 μm platelets oriented perpendicular to the cleavage plane (010) . The color of the crystals was dark brown in transmitted light.…”

“… The magnetism is dominated by partially filled 3d orbitals of the divalent A cations . In addition to interesting magnetic properties, wolframites, such as FeWO 4 , have been used to develop supercapacitors and photocatalytic and photoluminescent materials. − FeWO 4 can be used for the cheap and environmentally friendly production of ammonia and for applications in phase-change optical recording devices . Therefore, accurate knowledge of the physical properties of this material is essential for its technological applications.…”

“…FeWO 4 is one of the less studied AWO 4 wolframites . Curiously, most studies on this material have focused on nanoparticles, , with single crystals mainly synthesized to characterize their magnetic properties . FeWO 4 showed an antiferromagnetic behavior at low temperatures with a Néel temperature of 75 K .…”

Recent progress in the development of tin tungstate (α-SnWO4) photoanodes for solar water oxidation

“…34,35 Both cations in FeWO 4 and CuWO 4 are coordinated octahedrally forming a wolframite or distorted-wolframite structure. 36,37 Finally, although FeVO 4 contains FeO 6 and VO 4 polyhedra like α-SnWO 4 , it also contains distorted FeO 5 trigonal bipyramids resulting in a triclinic crystal structure. 38,39 Therefore, any correlations between the structure and the photoactivity are not necessarily obvious.…”