Core-exciton absorption in the FKabsorption spectra of 3dtransition-metal fluorides

Nakai, S.; Kawata, A.; Ohashi, Masanao; Kitamura, Michihide; Sugiura, Chikara; Mitsuishi, Tsutomu; Maezawa, H.

doi:10.1103/physrevb.37.10895

Cited by 32 publications

(21 citation statements)

References 25 publications

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“…The peak at the absorption threshold of La 2 CuO 4 reflects the O 2p-Cu 3d hybridization and originates upon excitation to the Upper Hubbard Band (UHB) of predominantly 3d x 2 −y 2 character in this material 26 . Such p-d hybridized peaks have also been observed in F K-XAS of several 3d metal fluorides [35][36][37] . The sharp peak marked by the arrow in F K-XAS on AgF 2 , therefore represents excitations in to Ag 4d orbitals via hybridization with F 2p, reflecting the narrow UHB in AgF 2 14 .…”

Section: Resultssupporting

confidence: 52%

Charge Transfer and $dd$ excitations in AgF$_{2}$

Bachar,

Koteras,

Gawraczynski

et al. 2021

Preprint

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Charge transfer (CT) insulators are the parent phase of a large group of today's unconventional high temperature superconductors. Here we study experimentally the interband excitations of the electronic structure of a CT insulator in the form of silver fluoride, AgF2, which has been proposed as an excellent analogue of oxocuprates. Optical conductivity and resonant inelastic X-Ray scattering (RIXS) on AgF2 polycrystalline sample show a close similarity with that being measured on undoped La2CuO4 while the former show a larger CT gap of approximately 3.4 eV, d − d excitations are nearly at the same energy in both materials. DFT and exact computations in a small cluster show that AgF2 is more covalent than cuprates despite having a larger fundamental gap. In addition, our computations show that AgF2 is at the verge of a charge transfer instability. The overall resemblance of our data on AgF2 to those published before on its cuprate equivalent La2CuO4 suggests that the underlying CT insulator physics is the same, while AgF2 could also benefit from a proximity to a charge density wave phase as in BaBiO3. Therefore, our work provides a compelling support to the future use of fluoroargentates for the growth of novel high-temperature superconductors.

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Section: Resultssupporting

confidence: 52%

Charge Transfer and $dd$ excitations in AgF$_{2}$

Bachar,

Koteras,

Gawraczynski

et al. 2021

Preprint

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“…41 In addition, the L 3 /L 2 intensity ratio and energy position of L 3 and L 2 lines are also strongly dependent on the d-band occupancy and therefore on the oxidation state of the transition element. 10,40,42 In this study, we have measured this L 3 /L 2 ratio to determine the Fe valence state during lithiation and delithiation processes. Details on the L 3 and L 2 measurement methodology and Fe valence calibration can be found elsewhere.…”

Section: Electron Diffraction and Stem/eels Resultsmentioning

confidence: 99%

Structural phase transformation and Fe valence evolution in FeOxF2−x/C nanocomposite electrodes during lithiation and de-lithiation processes

Sina

Nam

et al. 2013

J. Mater. Chem. A

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In this study, the structural changes of FeO x F 2Àx /C during the first discharge and recharge cycles were studied by ex situ electron microscopy techniques including annular dark field scanning transmission electron microscopy (DF-STEM) imaging, selected area electron diffraction (SAED) and electron energy loss spectroscopy (EELS) as well as by in situ X-ray absorption spectroscopy (XAS). The evolution of the valence state of Fe was determined by combined EELS using the Fe-L edge and XAS using the Fe-K edge. The results of this investigation show that the conversion reaction path during 1 st lithiation is very different from the re-conversion path during 1 st delithiation. During lithiation, intercalation is first observed followed by conversion into a lithiated rocksalt (Li-Fe-O-F) structure, and metallic Fe and LiF phases. During delithiation, the rocksalt phase does not disappear, but co-exists with an amorphous (rutile type) phase formed initially by the reaction of LiF and Fe. However, a de-intercalation stage is still observed at the end of reconversion similar to a single phase process despite the coexistence of these two (rocksalt and amorphous) phases.

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“…These observed spectra showed similar spectral profiles as earlier experiments. 12,14) The most intense peak, peak E, appeared at the threshold, 687.8 eV, in the case of ZnF 2 , while only weak peak, peak A, was shown there and second peak, peak B, was the most intense one in the spectrum of MgF 2 . In order to interpret these differences in observed NEXAFS spectra between MgF 2 and ZnF 2 , we performed the first principles DFT calculations.…”

Section: Resultsmentioning

confidence: 99%

“…12,13) Those of the 3d transition metal difluorides with the rutile type of structure have been also investigated. [14][15][16][17] However their theoretical calculations have provided only qualitative reproductions of the experimental data. Therefore, in the present study, the first principles calculations using the Density Functional Theory (DFT) have been carried out for MgF 2 and ZnF 2 and compared with the experimental NEXAFS spectra of MgF 2 and ZnF 2 at F K-edge.…”

Section: Introductionmentioning

confidence: 99%

First Principles Study of Core-hole Effect on Fluorine K-edge X-ray Absorption Spectra of MgF2 and ZnF2

et al. 2004

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First principles calculations have been carried out to investigate the core-hole effects on the theoretical fine structures of the X-ray absorption spectra of MgF 2 and ZnF 2 at F K-edge. Significant differences are found between the calculated spectral fine structures with and without core-holes. Experimental profiles of the near-edge X-ray absorption fine structures are well reproduced by the theoretical ones when the core-hole effect is introduced. The dependence of supercell size on the theoretical fine structures is also examined.

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Core-exciton absorption in the FKabsorption spectra of 3dtransition-metal fluorides

Cited by 32 publications

References 25 publications

Charge Transfer and $dd$ excitations in AgF$_{2}$

Charge Transfer and $dd$ excitations in AgF$_{2}$

Structural phase transformation and Fe valence evolution in FeOxF2−x/C nanocomposite electrodes during lithiation and de-lithiation processes

First Principles Study of Core-hole Effect on Fluorine K-edge X-ray Absorption Spectra of MgF<SUB>2</SUB> and ZnF<SUB>2</SUB>

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