Evidence of a cubic iron sub-lattice in t-CuFe2O4 demonstrated by X-ray Absorption Fine Structure

Caddeo, Francesco; Loche, Danilo; Casula, Maria Francesca; Corrias, Anna

doi:10.1038/s41598-017-19045-8

Cited by 49 publications

(32 citation statements)

References 47 publications

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“…Figure 2d,e shows the Fourier transformed (FT) curves of Cu and Fe K-edge EXAFS spectra, respectively. For the Cu K-edge FT curves, the first peak at 1.45 Å originates from the Cu−O bond, 47,49 and the second peak at 2.57 Å is ascribed to the bonds of Cu−Fe and Cu−Cu with both cations occupying the octahedral sites. 47,49 The CuFe 2 O 4 (flame) elicits a higher intensity for the first peak (Cu−O bond), while the CuFe 2 O 4 (furnace) has a higher intensity for the second peak (Cu−Fe and Cu−Cu bonds).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Rapid Flame-Annealed CuFe₂O₄ as Efficient Photocathode for Photoelectrochemical Hydrogen Production

Park

Baek

Zhang

et al. 2019

ACS Sustainable Chem. Eng.

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Copper ferrite (CuFe 2 O 4) possesses an indirect bandgap in the range of 1.54−1.95 eV. It is used as an attractive p-type photocathode in photo-electrochemical (PEC) water splitting, and theoretically it can yield a maximum photocurrent density of ∼27 mA/cm 2 and a maximum solar-to-hydrogen conversion efficiency of ∼33%. To date, only a few reports have been published on CuFe 2 O 4 photocathodes with very low-photocurrent densities, with a maximum value of 0.4 mA/cm 2 at 0.4 V vs RHE. Herein, we prepared a CuFe 2 O 4 photocathode on FTO glass with the sol−gel method followed by either high-temperature flame annealing or furnace annealing. We found that the flame-annealed CuFe 2 O 4 photocathode generated a photocurrent density of 1.82 mA/cm 2 at 0.4 V vs RHE that is approximately 3.5 times higher than the furnace-annealed CuFe 2 O 4 (0.52 mA/cm 2). This photocurrent density is also higher than those of all the reported CuFe 2 O 4 photocathodes, and any Cu containing ternary oxide (Cu−M−O, M: Fe, Bi, V, and Nb) photocathode (0.1−1.3 mA/cm 2 at 0.4 V vs RHE). An improved PEC performance of the flame-annealed CuFe 2 O 4 photocathode is elicited owing to the beneficial effects of flame annealing on the physical, optical, and electrical properties of CuFe 2 O 4. Flame annealing enhances the light absorption property of the CuFe 2 O 4 photocathode by slightly reducing the bandgap, and by forming a thicker film with increased porosity. Flame annealing also reduces the oxygen vacancy concentration in CuFe 2 O 4 , thus facilitating charge transport and interfacial charge transfer processes. Moreover, flame annealing requires only 16 min, which is much shorter than the time required for furnace annealing (∼9 h). These results demonstrate that flame annealing is a rapid and effective means for fabricating metal oxide photoelectrodes with an enhanced PEC water splitting performance.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Rapid Flame-Annealed CuFe₂O₄ as Efficient Photocathode for Photoelectrochemical Hydrogen Production

Park

Baek

Zhang

et al. 2019

ACS Sustainable Chem. Eng.

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“…Moreover, despite the theoretical spinel consists on a cubic structure, CuFe 2 O 4 can be present in two different structures: (i) tetragonal (space group I4 1 /amd) which is stable at low temperatures, and (ii) cubic (space group Fd3m) which appears above 700K (427°C). The formation of the tetragonal phase is attributed to the Jahn-Teller effect 16,17 , which arises from the distortion of one of the axis of the octahedrons (leading to a crystal symmetry reduction) [17][18][19] caused by the Cu 2+ (3d 9 ) ions migrations to the S T 16,18,20 . For d 4 and d 9 transition-metal ions, a spontaneous degeneration of the orbits of the neighbouring atoms -leading to a distortion from the regular octahedron -may decrease the electrostatic repulsion and thus increase the stabilization energy 18,21 .…”

Section: Introductionmentioning

confidence: 99%

Influence of the Synthesis Route in Obtaining the Cubic or Tetragonal Copper Ferrite Phases

Rosa

Segarra

2020

Inorg. Chem.

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In this work, magnetic copper ferrite nanoparticles are synthesized by polymer-assisted sol-gel and co-precipitation methods. The obtained purity and particle size reach values of 96 % and 94 nm, respectively. Evident differences in the crystal structure have been found in the synthesized nanoparticles. A tetragonal structure is formed by the sol-gel method, while the cubic form is obtained when the co-precipitation approach is used. This work provides an experimental evidence of the formation of both phases by using the same reactants and thermal conditions, and only modifying the technical procedure. The formation and stability of each phase is analysed by temperature dependent measurements, and the observed crystal structure differences are used to propose a potential fundamental explanation to our observations based on a difference on the cations' distribution and the Jahn-Teller distortion. Moreover, different copper ferrite purity and particle sizes are found when using each of the methods. The spherical shape of the particles and their tendency to sinter forming micrometric clusters are observed by electron microscopy. Finally, the divergence in magnetization between the samples prepared by each method support our argument about the different cations' distribution and open the door to a wide range of different technological applications for these materials.

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“…The systems, where it can be observed, include single crystals [4][5][6][7] , thin films 8 , non-organic and organic molecules [9][10][11] , and even biomolecules [12][13][14][15] . The JTE approach is used for description of properties of functional materials, such as semiconductors [16][17][18] , magnetic materials 5,6,[19][20][21] , superconductors 22 , optical materials 10,18 , and multiferroics 4,17,23,24 . In crystals, the JTE can manifest itself local or uniform.…”

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confidence: 99%

Sub-lattice of Jahn-Teller centers in hexaferrite crystal

Гудков

Сарычев

Жерлицын

et al. 2020

Sci Rep

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A novel type of sub-lattice of the Jahn-teller (Jt) centers was arranged in ti-doped barium hexaferrite Bafe 12 o 19. In the un-doped crystal all iron ions, sitting in five different crystallographic positions, are fe 3+ in the high-spin configuration (S = 5/2) and have a non-degenerate ground state. We show that the electron-donor ti substitution converts the ions to fe 2+ predominantly in tetrahedral coordination, resulting in doubly-degenerate states subject to the ⊗ E e problem of the JT effect. The arranged JT complexes, Fe 2+ o 4 , their adiabatic potential energy, non-linear and quantum dynamics, have been studied by means of ultrasound and terahertz-infrared spectroscopies. the Jt complexes are sensitive to external stress and applied magnetic field. For that reason, the properties of the doped crystal can be controlled by the amount and state of the Jt complexes.

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Evidence of a cubic iron sub-lattice in t-CuFe2O4 demonstrated by X-ray Absorption Fine Structure

Cited by 49 publications

References 47 publications

Rapid Flame-Annealed CuFe₂O₄ as Efficient Photocathode for Photoelectrochemical Hydrogen Production

Rapid Flame-Annealed CuFe₂O₄ as Efficient Photocathode for Photoelectrochemical Hydrogen Production

Influence of the Synthesis Route in Obtaining the Cubic or Tetragonal Copper Ferrite Phases

Sub-lattice of Jahn-Teller centers in hexaferrite crystal

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Evidence of a cubic iron sub-lattice in t-CuFe2O4 demonstrated by X-ray Absorption Fine Structure

Cited by 49 publications

References 47 publications

Rapid Flame-Annealed CuFe2O4 as Efficient Photocathode for Photoelectrochemical Hydrogen Production

Rapid Flame-Annealed CuFe2O4 as Efficient Photocathode for Photoelectrochemical Hydrogen Production

Influence of the Synthesis Route in Obtaining the Cubic or Tetragonal Copper Ferrite Phases

Sub-lattice of Jahn-Teller centers in hexaferrite crystal

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Product

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Rapid Flame-Annealed CuFe₂O₄ as Efficient Photocathode for Photoelectrochemical Hydrogen Production

Rapid Flame-Annealed CuFe₂O₄ as Efficient Photocathode for Photoelectrochemical Hydrogen Production