X-ray scattering factors of oxygen and sulfur ions: an<i>ab</i><i>initio</i>Hartree–Fock calculation

Azavant, P.; Lichanot, Albert

doi:10.1107/s0108767392006342

Cited by 34 publications

(21 citation statements)

References 6 publications

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“…2 for Na2S (BSI). The electron charge-density maps of Li2S are similar and have been given already in our previous work (Azavant & Lichanot, 1993). Figs.…”

Section: Electronic Structuresupporting

confidence: 59%

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Ab initio Hartree–Fock study of lithium and sodium sulfides: electronic and scattering properties

Azavant¹,

Lichanot²,

Rérat³

et al. 1994

Acta Crystallogr Sect B

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The electronic structure of lithium sulfide and sodium sulfide in the solid state is established at the Hartree-Fock level, as implemented in the CRYSTAL program. Two all-electron basis sets are adopted for each compound. Mulliken analysis, band structure, density of states and electron charge density are studied: these exhibit the highly ionic character of both compounds; this seems rather surprising because of the weak electronegativity and large polarizability of the sulfur. Form factors of the sulfur are deduced from the structure factors and analysed in order to show the deformations of this anion in the crystal environment. Finally, electron momentum density and Compton profiles confirm the almost fully ionic character of the compounds and prove the quality of the calculated wavefunctions.

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“…2 for Na2S (BSI). The electron charge-density maps of Li2S are similar and have been given already in our previous work (Azavant & Lichanot, 1993). Figs.…”

Section: Electronic Structuresupporting

confidence: 59%

“…A preliminary study (Azavant & Lichanot, 1993) has shown that Li2S has a highly ionic character, as in Li20 and Na20. This result seems rather surprising: indeed, it is customary to think that sulfur leads to less ionic bonds than oxygen (Shannon, 1981) because of its weaker electronegativity and larger polarizability.…”

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confidence: 99%

Ab initio Hartree–Fock study of lithium and sodium sulfides: electronic and scattering properties

Azavant¹,

Lichanot²,

Rérat³

et al. 1994

Acta Crystallogr Sect B

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“…All refinements were performed using the SHELXTL crystallographic software Azavant and Lichanot (1993) were used for oxygen. The weighting scheme was based on counting statistics.…”

Section: Experimental Methodsmentioning

confidence: 99%

Fe-rich and As-bearing vesuvianite and wiluite from Kozlov, Czech Republic

Groat

Evans

Cempírek

et al. 2013

American Mineralogist

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Green vesuvianite crystals occur with garnet and calcite in a hand specimen from the Nedvědice marble near Kozlov (near Štěpánov nad Svratkou, Svratka Crystalline Complex) in the Czech Republic. The average electron microprobe composition of the vesuvianite shows 12.10 wt% Fe 2 O 3 (4.66 Fe pfu), 2.77 wt% B 2 O 3 (2.45 B pfu), 1.71 wt% As 2 O 5 (0.46 As pfu), and 1.40 wt% F (2.26 F pfu). The Fe concentration is the highest ever recorded for a vesuvianite-group mineral. The boron contents are extremely variable and two of the five compositions show more than the 2.50 B pfu needed for wiluite, and the average is only slightly less than this. The crystal structure [a = 15.7250(4), c = 11.7736(3) Å] was refined in space group P4/nnc to an R 1 value of 0.0221. The site refinement and Mössbauer spectroscopy results show Fe 2+ substituting for Ca at the X3 site and filling the Y1 position, and Fe 3+ substituting for Al at the Y3 position. Most of the Fe (70% from the site refinements and 78% from the Mössbauer interpretation) is ferric. The main effect of the high-Fe concentration is to increase the mean Y3-O distance to an unusually large 2.018 Å. Boron occurs at the T1 site, where it is coordinated by oxygen atoms at two O7B and two O11 positions, and at the T2 sites where it is coordinated by O atoms at one O10 and two O12A sites. When the nearby X3 site contains Fe, the T2 position is either vacant or [3]-coordinated by some combination involving an O10 site and two O12B positions, in which case the B atom is likely offset from the T2 site to reduce the B-O12B distance.Fluorine and OH occupy the O11 positions when there is a vacancy at the adjacent T1 position. Pentavalent As substitutes for Si at the Z2 site and Al at the Y2 site. The P4/nnc symmetry indicates that this vesuvianite formed at high temperatures (400-800 °C) and the predominance of Fe 3+ and As 5+ suggests under oxidizing conditions.The results showing Fe at three different sites with three different coordinations attests to the flexibility of the vesuvianite crystal structure. The incorporation of As at two different sites in the structure shows that rock-forming silicate minerals such as vesuvianite can be a reservoir for this heavy element.

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“…Data were refined by full-matrix least squares on F 2 with the program package SHELXL-93. We used ionic scattering factors for cations from the International Tables for X-ray Crystallography (Ibers and Hamilton 1974) and ionic scattering factors for O 2-from Azavant and Lichanot (1993). Anisotropic displacement parameters for all atoms were refined independently.…”

Section: Structure Refinementsmentioning

confidence: 99%

Rare-earth elements in synthetic zircon: Part 2. A single-crystal X-ray study of xenotime substitution

Finch

Hanchar

Hoskin

et al. 2001

American Mineralogist

129

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Zircon crystals synthesized in a Li-Mo oxide melt and doped with trivalent lanthanides and Y (REE), both with and without P, were examined by single-crystal X-ray diffraction (XRD). REE are incorporated into the Zr site in the zircon structure, and some Zr appears to be displaced to the Si site. Crystals doped with middle REE (MREE, Sm to Dy) and Y, plus P follow the xenotime substitution (REE 3+ + P 5+ = Zr 4+ + Si 4+ ) rather closely, whereas crystals doped with heavy REE (HREE, Er to Lu) deviate from the xenotime substitution, having REE:P atomic ratios significantly greater than one. Xenotime substitution requires that P 5+ replace Si 4+ , but this substitution becomes limited by strain at the Si site in HREE-doped crystals. As Si sites become saturated with P 5+ , additional charge balance in synthetic zircon crystals may be provided by Mo 6+ and Li + from the flux entering interstitial sites, accounting for an additional 0.3 to 0.6 at% HREE beyond that balanced by P 5+ ions. Heavy REE are more compatible in the zircon structure than are LREE and MREE, and HREE substitution is ultimately limited by the inability of the zircon structure to further accommodate charge-compensating elements. Thus the limit on REE concentrations in zircon is not a simple function of REE 3+ ionic radii but depends in a complex way on structural strain at Zr and Si sites, which act together to limit REE and P incorporation. The mechanisms that limit the coupled xenotime substitution change from LREE to HREE. This change means that REE fractionation in zircon may vary according to the availability of charge-compensating elements. REE partition coefficients between zircon and melt must also depend in part on the availability of charge-compensating elements and their compatibility in the zircon structure.

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X-ray scattering factors of oxygen and sulfur ions: anabinitioHartree–Fock calculation

Cited by 34 publications

References 6 publications

Ab initio Hartree–Fock study of lithium and sodium sulfides: electronic and scattering properties

Ab initio Hartree–Fock study of lithium and sodium sulfides: electronic and scattering properties

Fe-rich and As-bearing vesuvianite and wiluite from Kozlov, Czech Republic

Rare-earth elements in synthetic zircon: Part 2. A single-crystal X-ray study of xenotime substitution

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