Abstract
Dense, high-refractive index, ultra-hard, wide-gap polymorphs of SiO2, recently discovered orthorhombic seifertite (space group 60 Pbcn), and earlier characterized tetragonal stishovite (space group 136 P42/mnm) and monoclinic coesite (space group 15 C2/c) were studied using advanced methods of electronic structure calculations involving full-potential linearized augmented plane wave density functional theoretical method (FP-LAPW-DFT) with spin polarization, orbital-dependent potentials, and modified Becke-Johnson potential (mBJ) for accurate account of the band gaps. Although these calculations yield an excellent account of many properties, we here focus on quantitative aspects of optical absorption and selection rules therein. Specifically, the valence-to-conduction band transition in seifertite is symmetry-allowed, and is symmetry-forbidden in stishovite and coesite. Theory is compared with published experimental data, and explanation is provided for weak pre-edge optical absorption in stishovite. Electronic structure and calculated properties of stishovite are also compared with those of the isostructural rutile TiO2. Effective masses are calculated from the energy dispersion curves E(k) at the valence band maximum for holes and conduction band minimum for electrons. In addition, we propose that splitting of the O2p valence-band in coesite and also observed in α-quartz is a general feature of polymorphs with tetrahedrally coordinated Si, in contrast with continuous valence bands in those with octahedral SiO6 units such as seifertite and stishovite. Based on quantitative results obtained from the BVA theory, this difference originates from a high degree of covalence in the tetrahedral polymorphs as opposed to high iconicity in octahedral polymorphs.
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- The American Mineralogist at 100 years, and a mineralogy renaissance
- At the blurry edge of mineralogy
- Mineral evolution and Earth history
- Franciscan geologic history constrained by tectonic/olistostromal high-grade metamafic blocks in the iconic California Mesozoic-Cenozoic accretionary complex
- The rapid expansion of environmental mineralogy in unconventional ways: Beyond the accepted definition of a mineral, the latest technology, and using nature as our guide
- Microelectronic junctions in arsenian pyrite due to impurity and mixed sulfide heterogeneity
- The structure of water-saturated carbonate melts
- In-situ measurements of fluorine and chlorine speciation and partitioning between melts and aqueous fluids in the Na2O-Al2O3-SiO2-H2O system
- High-pressure high-temperature transitions in MgCr2O4 and crystal structures of new Mg2Cr2O5 and post-spinel MgCr2O4 phases with implications for ultrahigh-pressure chromitites in ophiolites
- Mid-infrared emission spectroscopy and visible/near-infrared reflectance spectroscopy of Fe-sulfate minerals
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- Applications of Hirshfeld surfaces to mineralogy: An example of alumohydrocalcite, and the classification of the dundasite group minerals
- Optical absorption anisotropy of high-density, wide-gap, high-hardness SiO2 polymorphs seifertite, stishovite, and coesite
- The system Na2CO3-FeCO3 at 6 GPa and its relation to the system Na2CO3-FeCO3-MgCO3
- Chlorine-hydroxyl diffusion in pargasitic amphibole
- The use of cation-cation and anion-anion bonds to augment the bond-valence model
- AIM analysis and the form of the bond-valence equation
- Atomistic simulation on mixing thermodynamics of calcite-smithsonite solid solutions
- Combined geochemistry and geochronology constrains coupled subduction of oceanic and continental crust in the Huwan shear zone, central China
- Near-infrared investigation of folding sepiolite
- First-principles study of sulfur isotope fractionation in pyrite-type disulfides
- Tetrataenite in terrestrial rock
- Thermo-compression of pyrope-grossular garnet solid solutions: Non-linear compositional dependence
- Phase relationships in the system K2CO3-CaCO3 at 6 GPa and 900–1450 °C
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