The chromium site in doped glassy lithium tetraborate

Kelly, T. D.; Echeverría, Elena; Beniwal, Sumit; Адамів, В.Т.; Bürak, Ya. I.; Enders, Axel; Petrosky, James C.; McClory, John W.; Dowben, Peter A.

doi:10.1016/j.matchemphys.2014.05.021

Cited by 3 publications

(4 citation statements)

References 27 publications

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“…As a result of the doping, there is a slight expansion of the coordination shells (O and B atoms) that surrounded the original Li + atom from approximately 2.0 Å to approximately 2.5 Å, the exact value depending upon the size of the rare earth. The results for rare earth doped borates compare well with expected bonding distances when compared with rare earth coordination number and atomic radii from Shannon [93], the radial distributions functions obtained from X-ray diffraction [55] and consistent with prior EXAFS studies [66,67]. The first coordination shell's distance and coordination number (in the range of 6-8) (amplitude reduction factor fixed at 0.85) compares well with the expectations for a rare earth oxygen coordination environment and occupation of the Li + site.…”

Section: Resultssupporting

confidence: 80%

“…In all cases, the EXAFS is evident up to approximately 6 Å −1 and is similar for the rare earth doped lithium tetraborate samples studied, with only small shifts. The signal-tonoise in the EXAFS spectra deteriorate with wave vectors greater than about 7.5 Å −1 as is expected for glassy samples when the host matrix about the dopant consists primarily of low Z material [55,67]. The energy range available for the various EXAFS spectra is limited by the presence of the L2 edge; hence, higher Z elements have a wider EXAFS energy range.…”

Section: Extended X-ray Absorption Fine Structurementioning

confidence: 81%

“…First, the spectra were analyzed using standard procedures with the IFEFFIT tool suite and FEFF 6 [61][62][63][64][65]. This consisted of isolating the EXAFS signal, converting to k-space, then using the Fourier transform to determine the average coordination number and element-type around the rare earth dopants, as detailed elsewhere for other doped Li 2 B 4 O 7 crystals [66] and glasses [67]. The second method of analysis employed the use of a Latin hyper-cube sampling (LHS) routine and the scattering code FEFF 9 for phase shifts and backscattering amplitudes.…”

Section: Methodsmentioning

confidence: 99%

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Rare earth dopant (Nd, Gd, Dy, and Er) hybridization in lithium tetraborate

et al. 2014

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The four dopants (Nd, Gd, Dy, and Er) substitutionally occupy the Li + sites in lithium tetraborate (Li 2 B 4 O 7 : RE) glasses as determined by analysis of the extended X-ray absorption fine structure. The dopants are coordinated by 6-8 oxygen at a distance of 2.3 to 2.5 Å, depending on the rare earth. The inverse relationship between the RE-O coordination distance and rare earth (RE) atomic number is consistent with the expected lanthanide atomic radial contraction with increased atomic number. Through analysis of the X-ray absorption near edge structure, the rare earth dopants adopt the RE 3+ valence state. There are indications of strong rare earth 5d hybridization with the trigonal and tetrahedral formations of BO 3 and BO 4 based on the determination of the rare earth substitutional Li + site occupancy from the X-ray absorption near edge structure data. The local oxygen disorder around the RE 3+ luminescence centers evident in the structural determination of the various glasses, and the hybridization of the RE 3+ dopants with the host may contribute to the asymmetry evident in the luminescence emission spectral lines. The luminescence emission spectra are indeed characteristic of the expected f-to-f transitions; however, there is an observed asymmetry in some emission lines.

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Section: Resultssupporting

confidence: 80%

Section: Extended X-ray Absorption Fine Structurementioning

confidence: 81%

Section: Methodsmentioning

confidence: 99%

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Rare earth dopant (Nd, Gd, Dy, and Er) hybridization in lithium tetraborate

et al. 2014

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“…In previous EXAFS analyses that fit theoretical models to experimental data, the analysis was difficult and time‐exhaustive, taking weeks if not months . Some difficulties included confirming false minima in the fitting parameter spaces and avoiding experimenter bias in parameter adjustment.…”

Section: Methodsmentioning

confidence: 99%

Analysis of oxygen shell splitting in hydrothermally grown single crystal ThO₂(200)

Kelly

Petrosky

McClory

et al. 2015

Physica Rapid Research Ltrs

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Single crystals of ThO2 have been synthesized using hydrothermal growth and studied using the X‐ray absorption fine structure (XAFS) technique. The extended X‐ray absorption fine structure (EXAFS) has been extracted from the XAFS and analyzed using a novel, computational Latin hypercube sampling method. The methodology not only confirms the expected space group and crystal structure, it also identifies the origin of a previously reported split O shell. Since EXAFS is a local order analysis technique, the O shell splitting is identified as an O atom occupying an interstitial site. This result is significant for examining O2– transport in a ThO2 matrix and corroborating research indicating partial Th 5f occupancy that is similar to hyper‐stoichiometric UO2+x compounds. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

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