XAS studies of pressure-induced structural and electronic transformations in α-FeOOH

Abstract

Structural and electronic transformation taking place in α-FeOOH goethite have been studied by Fe K-edge x-ray absorption spectroscopy at pressures up to 50 GPa. These studies have shown the symmetrization of FeO6 octahedra coinciding with the Fe3+ high to low spin transition at pressure above ~45 GPa. Our data are in excellent agreement with the results of recent single crystal XRD and Mössbauer spectroscopy studies (Xu et al 2013 Phys. Rev. Lett. 111 175501), supporting the H-bonds symmetrization in iron oxyhydroxide, resulting from the Fe3+ high-to-low spin crossover at above 45 GPa. Our study shows an applicability of the x-ray absorption spectroscopy in a further study of the H-bonds symmetrization phenomenon.

Low‐Spin‐State Hematite with Superior Adsorption of Anionic Contaminations for Water Purification

“…Bulk α‐Fe 2 O 3 and nanosized FM show similar prepeak (1s to 3d transition) at 7115.4 eV, while the obvious change is observed for ultrafine FTMC with the prepeak position shifting toward lower energy of 7114.7 eV ( Figure a), indicating the spin transition from high‐spin Fe(III) to low‐spin state . Meanwhile, the shoulder peak (Figure S7 of the Supporting Information, labeled as A) of FTMC shifts toward higher energy from 7181 eV (bulk α‐Fe 2 O 3 and FM) to 7189 eV and becomes wider, which is correlated to the reduction of FeO bond distances . The EXAFS (extended X‐ray absorption fine structure) R‐space Fourier transform signals of FeFe and FeOFe/FeOO shell weaken gradually from bulk to nanosized, and then ultrafine particles (Figure 2b), confirming the gradually reduced coordination number of the shells.…”

“…[8,12] Meanwhile, the shoulder peak ( Figure S7 of the Supporting Information, labeled as A) of FTMC shifts toward higher energy from 7181 eV (bulk α-Fe 2 O 3 and FM) to 7189 eV and becomes wider, which is correlated to the reduction of FeO bond distances. [13] The EXAFS (extended X-ray absorption fine structure) R-space Fourier transform signals of FeFe and FeOFe/FeOO shell weaken gradually from bulk to nanosized, and then ultrafine particles (Figure 2b the appearance of abundant surface unsaturated coordinated Fe due to the very small particle size. [14] Importantly, the intensity increase of first shell (FeO peak) and the shrinkage of unit cell volume of ultrafine α-Fe 2 O 3 in FTMC are in good agreement with the difference between low-spin and high-pin α-Fe 2 O 3 .…”

Z-scheme charge transfer between a conjugated polymer and α-Fe2O3 for simultaneous photocatalytic H2 evolution and ofloxacin degradation

“…The area labeled A is the pre-peak region which is related to the electronic state and structural environment of Fe. 36 Compared with α-Fe 2 O 3 , the pre-peak of FPD-2 shifts toward lower energy (Fig. 3d), suggesting the transition from the high spin state of Fe III to the low spin state.…”

“…3d), suggesting the transition from the high spin state of Fe III to the low spin state. 36,37 Moreover, the shoulder peak (labeled B in Fig. S4†) in FPD-2 moves toward higher energy and becomes a little bit wider than that of α-Fe 2 O 3 (Fig.…”

Pressure-Induced Mixed Protonic–Electronic to Pure Electronic Conduction Transition in Goethite

“…Iron oxyhydroxide (FeOOH) is among the most common hydrous minerals on the Earth’s surface and in its interior. , At ambient conditions, goethite (α-FeOOH, space group Pnma ) is the most stable and comprises double chains of edge-shared octahedra that form 2 × 1 channels hosting hydrogen bonds . Because a proton-centered symmetrization of hydrogen bonding is expected to present in the high-pressure phase (ε-FeOOH, space group P 2 1 mn ) and the similar structural features have been reported to occur in the high-pressure phase of AlOOH, which is isostructural with ε-FeOOH, the previous high-pressure research studies about goethite mainly focused on the structural stability and the behavior of hydrogen bonds by the methods of X-ray diffraction (XRD), − infrared spectra (IR), Raman spectroscopy, Mössbauer spectroscopy, X-ray absorption spectroscopy, and first-principles calculations. ,,− Although the electrical studies of goethite are very important for us to understand the mantle mineralogy, there are only a few studies on electrical conductivity. Until recently, there have been few reports on the high-pressure electrical conductivity of goethite. ,, Liu et al conducted the electrical impedance and Raman studies on goethite and reported two pressure-induced structural phase transitions at 7 and 20 GPa.…”