skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Oxygen K-edge XANES of germanates investigated using first-principles calculations

Abstract

O K-edge x-ray absorption near-edge structure (XANES) spectra of {alpha}-quartz-type and rutile-type GeO{sub 2} polymorphs and of K{sub 2}Ge{sub 8}O{sub 17} have been analyzed using first-principles plane-wave pseudopotential calculations. XANES spectra have been calculated using supercell including core-hole effects and good agreement with experiment has been obtained. In the the case of GeO{sub 2} polymorphs, local density of empty states has been performed and peaks in the experimental spectra can be assigned to transitions involving hybridization of the O p orbitals with the Ge s, Ge p, Ge sp, and Ge d orbitals. Furthermore, peak positions in the theoretical spectra appear to be correlated with changes in the Ge-O-Ge angle as well as indirectly with the Ge coordination geometry. Analysis of O K-edge XANES spectra for individual O sites in K{sub 2}Ge{sub 8}O{sub 17} shows that oxygens shared between two fivefold Ge atoms or one fourfold and one fivefold Ge atom exhibit subtle shifts to lower energy of the peaks, which have been previously observed in alkali germanate glasses at and above the germanate anomaly.

Authors:
; ;  [1];  [2]
  1. Institut de Mineralogie et de Physique des Milieux Condenses, UMR CNRS 7590, Universite Pierre et Marie Curie, Paris 6, 140 rue de Lourmel, F-75015 Paris (France)
  2. (Canada)
Publication Date:
OSTI Identifier:
20951412
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 18; Other Information: DOI: 10.1103/PhysRevB.75.184205; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; ABSORPTION SPECTRA; ABSORPTION SPECTROSCOPY; GERMANATES; GERMANIUM OXIDES; OXYGEN; PEAKS; POTASSIUM COMPOUNDS; QUARTZ; RUTILE; WAVE PROPAGATION; X RADIATION; X-RAY SPECTRA; X-RAY SPECTROSCOPY

Citation Formats

Cabaret, Delphine, Mauri, Francesco, Henderson, Grant S., and Department of Geology, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1. Oxygen K-edge XANES of germanates investigated using first-principles calculations. United States: N. p., 2007. Web. doi:10.1103/PHYSREVB.75.184205.
Cabaret, Delphine, Mauri, Francesco, Henderson, Grant S., & Department of Geology, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1. Oxygen K-edge XANES of germanates investigated using first-principles calculations. United States. doi:10.1103/PHYSREVB.75.184205.
Cabaret, Delphine, Mauri, Francesco, Henderson, Grant S., and Department of Geology, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1. Tue . "Oxygen K-edge XANES of germanates investigated using first-principles calculations". United States. doi:10.1103/PHYSREVB.75.184205.
@article{osti_20951412,
title = {Oxygen K-edge XANES of germanates investigated using first-principles calculations},
author = {Cabaret, Delphine and Mauri, Francesco and Henderson, Grant S. and Department of Geology, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1},
abstractNote = {O K-edge x-ray absorption near-edge structure (XANES) spectra of {alpha}-quartz-type and rutile-type GeO{sub 2} polymorphs and of K{sub 2}Ge{sub 8}O{sub 17} have been analyzed using first-principles plane-wave pseudopotential calculations. XANES spectra have been calculated using supercell including core-hole effects and good agreement with experiment has been obtained. In the the case of GeO{sub 2} polymorphs, local density of empty states has been performed and peaks in the experimental spectra can be assigned to transitions involving hybridization of the O p orbitals with the Ge s, Ge p, Ge sp, and Ge d orbitals. Furthermore, peak positions in the theoretical spectra appear to be correlated with changes in the Ge-O-Ge angle as well as indirectly with the Ge coordination geometry. Analysis of O K-edge XANES spectra for individual O sites in K{sub 2}Ge{sub 8}O{sub 17} shows that oxygens shared between two fivefold Ge atoms or one fourfold and one fivefold Ge atom exhibit subtle shifts to lower energy of the peaks, which have been previously observed in alkali germanate glasses at and above the germanate anomaly.},
doi = {10.1103/PHYSREVB.75.184205},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 18,
volume = 75,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}
  • X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) spectroscopies are tools in widespread use for providing detailed local atomic structure, oxidation state, and magnetic structure information for materials and organometallic complexes. The analysis of these spectra for transition-metal L-edges is routinely performed on the basis of ligand-field multiplet theory because one- and two-particle mean-field ab initio methods typically cannot describe the multiplet structure. Here we show that multireference configuration interaction (MRCI) calculations can satisfactorily reproduce measured XANES spectra for a range of complex iron oxide materials including hematite and magnetite. MRCI Fe L2,3-edge XANES and XMCD spectramore » of Fe(II)O6, Fe(III)O6, and Fe(III)O4 in magnetite are found to be in very good qualitative agreement with experiment and multiplet calculations. Point-charge embedding and small distortions of the first-shell oxygen ligands have only small effects. Oxygen K-edge XANES/XMCD spectra for magnetite investigated by a real-space Green’s function approach complete the very good qualitative agreement with experiment. Material-specific differences in local coordination and site symmetry are well reproduced, making the approach useful for assigning spectral features to specific oxidation states and coordination environments.« less
  • We report an ab initio study of the mechanical stability of platinum nitride (PtN), in four different crystal structures, the rock salt (rs-PtN), zinc-blende (zb-PtN), cooperite, and a face-centered orthorhombic phase. Of these phases only the rs-PtN phase is found to be stable and has the highest bulk modulus B=284 GPa. Its electronic density of states shows no band gap making it metallic. The zb-PtN phase does not stabilize or harden by the nitrogen vacancies investigated in this study. Therefore, the experimental observation of super hardness in PtN remains a puzzle.
  • Strontium titanate exhibits two phase transitions at 5 GPa and 14 GPa. We use X-ray absorption Ti K pre-edge structure as a probe of the local atomic structure of SrTiO3 under pressure. The pre-edge is characterized by four main features labeled A, B, C1 and C2. Above 5 GPa, the intensity of peak B is decreased while that of the double feature C1-C2 is increased. By increasing the pressure above 14 GPa, peak A shifts towards lower energy and of peak C1 towards higher energy. While the first phase transformation is known to be a transition from the cubic phasemore » to a tetragonal one, the second phase transformation leads to a crystal structure not yet identified. To analyze these spectral modifications, full-potential first principles simulations of Ti K pre-edge are performed. The calculations provide a good agreement with experiments and permits the identification of the four features in terms of orbital hybridization. Trial crystal structures are proposed in order to account for the pre-edge modifications observed under pressure.« less
  • Organic carbon (OC) stability in tropical soils is strongly interlinked with multivalent cation interaction and mineral association. Low molecular weight organic acids (LMWOAs) represent the readily biodegradable OC. Therefore, investigating retention mechanisms of LMWOAs in mineral-cation-LMWOAs systems is critical to understanding soil C cycling. Given the general acidic conditions and dominance of kaolinite in tropical soils, we investigated the retention mechanisms of citric acid (CA) in kaolinite-Fe(III)-CA systems with various Fe/CA molar ratios at pH ~3.5 using Fe K-edge EXAFS and L- 3,2-edge XANES techniques. With Fe/CA molar ratios >2, the formed ferrihydrite mainly contributed to CA retention through adsorptionmore » and/or coprecipitation. With Fe/CA molar ratios from 2 to 0.5, ternary complexation of CA to kaolinite via a five-coordinated Fe(III) bridge retained higher CA than ferrihydrite-induced adsorption and/or coprecipitation. With Fe/CA molar ratios ≤ 0.5, kaolinite-Fe(III)-citrate complexation preferentially occurred, but less CA was retained than via outer-sphere kaolinite-CA complexation. This study highlighted the significant impact of varied Fe/CA molar ratios on CA retention mechanisms in kaolinite-Fe(III)-CA systems under acidic conditions, and clearly showed the important contribution of Fe-bridged ternary complexation on CA retention. In conclusion, these findings will enhance our understanding of the dynamics of CA and other LMWOAs in tropical soils.« less