Buckled crystalline structure of mixed ionic salts

Frenkel, Anatoly I.; Stern, E. A.; Voronel, A.; Qian, Mingxin; Newville, Matthew

doi:10.1103/physrevlett.71.3485

Cited by 57 publications

(49 citation statements)

References 13 publications

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“…Although experimental phases and amplitudes can be favorable over theoretical phases for the first one or two SS shells, 21 naturally they cannot be employed for EXAFS fits out to distances larger than ∼3.0 Å depending on the structure. Several applications of FEFF phases and amplitudes to "real" systems have been reported where all significant scattering paths with an amplitude weight of more than ∼3% out to distances of ∼6 Å were included in the analysis, confirming the reliability of theoretical EXAFS calculations [22][23][24][25] (here "real" refers to systems other than pure metals).…”

Section: Resultsmentioning

confidence: 79%

Multiple-Scattering EXAFS Analysis of Tetraalkylammonium Manganese Oxide Colloids

et al. 1999

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X-ray absorption spectroscopy at the Mn K edge was employed to elucidate the structure of colloidal tetraalkylammonium (TAA) manganese oxides in sols and gels obtained by different preparation and heat treatment procedures. Two series of colloidal TAA MnO x prepared with tetrapropylammonium (TPA) and tetraethylammonium (TEA) cations were studied. Several manganese oxides, birnessite, and feitknechtite were also measured and served as model compounds for structural refinements. Near edge structure (XANES) analysis revealed different average valences of the colloidal systems. As synthesized and heat-treated, TAA colloids exhibited an average valence of 3.6-3.7, whereas gelled TAA colloids showed a lower average valence of ∼3.5. Extended absorption fine structure (EXAFS) analysis was carried out to distances of ∼6.0 Å around the central Mn atom using theoretical backscattering phases and amplitudes calculated from the ab initio FEFF code. All multiple-scattering (MS) paths with a weight of 2% and more with respect to the main Fourier transform peak were included in the refinement. It is found that, except for gelled TAA samples, no significant amount of corner-shared MnO 6 units was detected in the colloidal systems. Theoretical EXAFS phases and amplitudes were derived for a monoclinic birnessite MnO x layer structure consisting of edgeshared MnO 6 octahedra. EXAFS refinements utilizing these phases and amplitudes resulted in good agreement with experimental data. Differences in the refined scattering shell distances between the TPA and TEA series suggest a structure influencing effect of the two ammonium ions. Bond angles between neighboring MnO 6 octahedra were determined from the amplitude dependence of a collinear Mn-Mn-Mn MS path on deviations from 180°("focusing effect"). On the basis of the bond angles, and with use of the average valence to define the distribution of tri-and tetravalent manganese in the MnO x layers, three distinct 2D structures are proposed: one for birnessite, one for TAA sols, and one for TAA gels.

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Section: Resultsmentioning

confidence: 79%

Multiple-Scattering EXAFS Analysis of Tetraalkylammonium Manganese Oxide Colloids

et al. 1999

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“…The details of the techniques using these x-ray spectroscopy methods to study local structure of materials can be found in Refs. [25][26][27][28][29][30][31][32]. XANES experiments ͑beamline X11A at NSLS͒ were mainly focused on the Ti K edge to examine its possible off-center displacement while the EXAFS data were collected for all three cations ͑K edge of Cu, Ti at beamline X11A and Ca at beamline X15B, NSLS͒ to measure the cation short-range order.…”

Section: B Synchrotron X-ray Diffractionmentioning

confidence: 99%

Nanoscale disorder and local electronic properties ofCaCu3Ti4O12: An integrated study of electron, neutron, and x-ray diffraction, x-ray absorption fine struct

Zheng

Frenkel

et al. 2010

Phys. Rev. B

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We report a combined experimental and theoretical study of CaCu 3 Ti 4 O 12 . Based on our experimental observations of nanoscale regions of Ca-Cu antisite defects in part of the structure, we carried out densityfunctional theory ͑DFT͒ calculations that suggest a possible electronic mechanism to explain the gigantic dielectric response in this material. The defects are evident in atomically resolved transmission electron microscopy measurements, with supporting evidence from a quantitative analysis of the electron diffraction and DFT which suggests that such defects are reasonable on energetic grounds. To establish the extent of the defects, bulk average measurements of the local structure were carried out: extended x-ray absorption fine structure ͑EXAFS͒, atomic pair-distribution function analysis of neutron powder-diffraction data, and singlecrystal x-ray crystallography. The EXAFS data are consistent with the presence of the nanoclustered defects with an estimate of less than 10% of the sample being disordered while the neutron powder-diffraction experiments place an upper of ϳ5% on the proportion of the sample in the defective state. Because of the difficulty of quantifying nanoscale defects at such low levels, further work will be required to establish that this mechanism is operative in CaCu 3 Ti 4 O 12 but it presents a nontraditional plausible avenue for understanding colossal dielectric behavior.

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“…A recently published synchrotron X-ray diffraction study 11 12,17 . In the current work, we report results obtained by extending the X-ray absorption measurements to include the complete range of solid solutions.…”

Section: Introductionmentioning

confidence: 99%

Evolution of the local structure at the phase transition in CeO2-Gd2O3solid solutions

et al. 2013

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We investigated the local environment of the Ce and Gd ions in one of the most important oxygen ion conductors, the CeO 2 -Gd 2 O 3 solid solution, using L III edge extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray absorption near edge spectroscopy (XANES). The average Gd-O distance, as deduced by EXAFS, decreases gradually with increasing Gd content, whereas a sharp decrease in the average Ce-O distance occurs at 25 mol% Gd, accompanying the appearance of structural features characteristic of double fluorite symmetry. An abrupt change in the local environment of Ce, rather than of Gd, is also supported by the XANES spectra. Efforts at stabilizing the oxygen conducting Fm-3m phase in CeO 2 -Gd 2 O 3 solid solutions should therefore concentrate on tailoring the local environment of the Ce ion. We further suggest that our data may provide an explanation for the recently discovered giant electrostriction effect in Ce 0 . 8 Gd 0 . 2 O 1.9 . Since this composition is at the limit of stability of the fluorite phase, local distortions in Ce 0 . 8 Gd 0 . 2 O 1.9 may be modulated by an external electric field more readily than those of the other solid solutions.

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Buckled crystalline structure of mixed ionic salts

Cited by 57 publications

References 13 publications

Multiple-Scattering EXAFS Analysis of Tetraalkylammonium Manganese Oxide Colloids

Multiple-Scattering EXAFS Analysis of Tetraalkylammonium Manganese Oxide Colloids

Nanoscale disorder and local electronic properties ofCaCu3Ti4O12: An integrated study of electron, neutron, and x-ray diffraction, x-ray absorption fine struct

Evolution of the local structure at the phase transition in CeO2-Gd2O3solid solutions

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