Bonding in alpha-quartz (SiO2): A view of the unoccupied states
-
Laurence A.J. Garvie
,
Peter Rez
Abstract
High-resolution core-loss and low-loss spectra of α-quartz were acquired by electron energyloss spectroscopy (EELS) with a transmission electron microscope (TEM). Spectra contain the Si L1, L2,3, K, and O K core-loss edges, and the surface and bulk low-loss spectra. The core-loss edges represent the atom-projected partial densities of states of the excited atoms and provide information on the unoccupied s, p, and d states as a function of energy above the edge onset. The band structure and total density of states were calculated for α-quartz using a self-consistent pseudopotential method. Projected local densities of Si and O s, p, and d states (LDOS) were calculated and compared with the EELS core-loss edges. These LDOS successfully reproduce the dominant Si and O core-loss edge shapes up to ca. 15 eV above the conduction-band onset. In addition, the calculations provide evidence for considerable charge transfer from Si to O and suggest a marked ionicity of the Si-O bond. The experimental and calculated data indicate that O 2p-Si d π-type bonding is minimal. The low-loss spectra exhibit four peaks that are assigned to transitions from maxima in the valence-band density of states to the conduction band. A band gap of 9.65 eV is measured from the low-loss spectrum. The structures of the surface low-loss spectrum are reproduced by the joint density of states derived from the band-structure calculation. This study provides a detailed description of the unoccupied DOS of α-quartz by comparing the core-loss edges and low-loss spectrum, on a relative energy scale and relating the spectral features to the atom- and angular-momentum-resolved components of a pseudopotential band-structure calculation.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Th-Pb ion-microprobe dating of allanite
- Zircon U-Pb SHRIMP dating of a Neoproterozoic overprint in Paleoproterozoic granitic-gneissic terranes, southern Brazil
- Radioluminescence and thermoluminescence of rare earth element and phosphorus-doped zircon
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- Experimental study of Cr incorporation in pargasite
- The mechanism of charge compensation in Cu-Fe-PGE thiospinels from the Penikat layered intrusion, Finland
- Crystal chemistry of the axinite-group minerals: A multi-analytical approach
- A transmission electron microscope investigation of the C2/c→ P21/c phase transition in clinopyroxenes along the diopside-enstatite (CaMgSi2O6-Mg2Si2O6) join
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- Compression mechanism of brucite: An investigation by structural refinement under pressure
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- A new uranyl phosphate chain in the structure of parsonsite
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- The crystal structure of philolithite, a trellis-like open framework based on cubic closestpacking of anions
- XPS study of reductive dissolution of birnessite by H2SeO3 with constraints on reaction mechanism
- Structure of H-exchanged hexagonal birnessite and its mechanism of formation from Na-rich monoclinic buserite at low pH
- Anisotropic peak broadening analysis of a biogenic soil greigite (Fe3S4) with Rietveld analysis and single peak fitting
- Serrabrancaite, MnPO4 · H2O, a new mineral from the Alto Serra Branca pegmatite, Pedra Lavrada, Paraiba, Brazil
- Synchrotron XPS evidence for Fe2+-S and Fe3+-S surface species on pyrite fracture-surfaces, and their 3D electronic states
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