Model-independent structure factors from powder X-ray diffraction: a novel approach

Straasø, Tine; Dippel, Ann‐Christin; Becker, Jacob; Als‐Nielsen, J.

doi:10.1107/s1600577513028269

Cited by 5 publications

(4 citation statements)

References 21 publications

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“…Another method is to remove all air scattering by performing the diffraction measurements in vacuum. Recently, the first version of the AVID was reported (Straasø et al, 2013(Straasø et al, , 2014. By performing PXRD in vacuum, the external background signal can, in the absence of fluorescence, be limited to (i) scattering from the sample container, which can be measured individually and subtracted, (ii) Compton scattering from the sample, and (iii) thermal diffuse scattering, which can be minimized by carrying out data collection at low temperature (Wahlberg, Bindzus, Christensen et al, 2016).…”

Section: Diffraction In Vacuummentioning

confidence: 99%

Accurate charge densities from powder X-ray diffraction – a new version of the Aarhus vacuum imaging-plate diffractometer

Tolborg

Jørgensen

Christensen

et al. 2017

Acta Crystallogr B Struct Sci Cryst Eng Mater

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In recent years powder X-ray diffraction has proven to be a valuable alternative to single-crystal X-ray diffraction for determining electron-density distributions in high-symmetry inorganic materials, including subtle deformation in the core electron density. This was made possible by performing diffraction measurements in vacuum using high-energy X-rays at a synchrotron-radiation facility. Here we present a new version of our custom-built in-vacuum powder diffractometer with the sample-to-detector distance increased by a factor of four. In practice this is found to give a reduction in instrumental peak broadening by approximately a factor of three and a large improvement in signal-to-background ratio compared to the previous instrument. Structure factors of silicon at room temperature are extracted using a combined multipole-Rietveld procedure and compared with ab initio calculations and the results from the previous diffractometer. Despite some remaining issues regarding peak asymmetry, the new diffractometer yields structure factors of comparable accuracy to the previous diffractometer at low angles and improved accuracy at high angles. The high quality of the structure factors is further assessed by modelling of core electron deformation with results in good agreement with previous investigations.

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Section: Diffraction In Vacuummentioning

confidence: 99%

Accurate charge densities from powder X-ray diffraction – a new version of the Aarhus vacuum imaging-plate diffractometer

Tolborg

Jørgensen

Christensen

et al. 2017

Acta Crystallogr B Struct Sci Cryst Eng Mater

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“…For a simple high-symmetry crystal like copper (space group Fm3m) only complete overlap of reflections presents a challenge. Multiple methods exist to extract the Bragg intensities from the powder pattern (Pawley, 1981;LeBail et al, 1988;Straasø et al, 2014), but in the current study we chose model-dependent Rietveld refinement (Rietveld, 1969). Partitioning the peak according to the relative magnitude of the model structure factors solves the problem of the overlapping reflections.…”

Section: Extraction Of Structure Factorsmentioning

confidence: 99%

Low-temperature powder X-ray diffraction measurements in vacuum: analysis of the thermal displacement of copper

et al. 2016

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A serious limitation of the all‐in‐vacuum diffractometer reported by Straasø, Dippel, Becker & Als‐Nielsen [J. Synchrotron Rad. (2014), 21, 119–126] has so far been the inability to cool samples to near‐cryogenic temperatures during measurement. The problem is solved by placing the sample in a jet of helium gas cooled by liquid nitrogen. The resulting temperature change is quantified by determining the change in unit‐cell parameter and atomic displacement parameter of copper. The cooling proved successful, with a resulting temperature of ∼95 (3) K. The measured powder X‐ray diffraction data are of superb quality and high resolution [up to sinθ/λ = 2.2 Å−1], permitting an extensive modelling of the thermal displacement. The anharmonic displacement of copper was modelled by a Gram–Charlier expansion of the temperature factor. As expected, the corresponding probability distribution function shows an increased probability away from neighbouring atoms and a decreased probability towards them.

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“…The experiments were performed at the PETRA III synchrotron radiation source at DESY Hamburg, Germany (High Resolution Powder Diffraction, P02.1). 9 Synchrotron radiation with an energy of 60 keV (corresponding to λ = 0.207 Å) was used. Diffraction patterns were collected in Debye-Scherrer-geometry with a PerkinElmer XRD 1621 area detector.…”

Section: Powder X-ray Diffraction ( Powder Xrd)mentioning

confidence: 99%

Formation of a Eu(iii) borate solid species from a weak Eu(iii) borate complex in aqueous solution

et al. 2014

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In the presence of polyborates (detected by (11)B-NMR) the formation of a weak Eu(III) borate complex (lg β11 ~ 2, estimated) was observed by time-resolved laser-induced fluorescence spectroscopy (TRLFS). This complex is a precursor for the formation of a solid Eu(III) borate species. The formation of this solid in solution was investigated by TRLFS as a function of the total boron concentration: the lower the total boron concentration, the slower is the solid formation. The solid Eu(III) borate was characterized by IR spectroscopy, powder XRD and solid-state TRLFS. The determination of the europium to boron ratio portends the existence of pentaborate units in the amorphous solid.

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Model-independent structure factors from powder X-ray diffraction: a novel approach

Cited by 5 publications

References 21 publications

Accurate charge densities from powder X-ray diffraction – a new version of the Aarhus vacuum imaging-plate diffractometer

Accurate charge densities from powder X-ray diffraction – a new version of the Aarhus vacuum imaging-plate diffractometer

Low-temperature powder X-ray diffraction measurements in vacuum: analysis of the thermal displacement of copper

Formation of a Eu(iii) borate solid species from a weak Eu(iii) borate complex in aqueous solution

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