ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Vibronic Polarization in the Electronic Spectra of Gillespite, a Mineral Containing Iron(II) in Square-Planar Coordination (1966)
    s.l. : American Chemical Society
    Inorganic chemistry 5 (1966), S. 1268-1272 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic50041a043
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    On the occurrence and stability of divalent chromium in olivines included in diamonds (1975)
    Springer
    Contributions to mineralogy and petrology 51 (1975), S. 213-221 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Olivine inclusions in diamonds from kimberlites originating from the deep Upper Mantle contain significant amounts of chromium. It has been suggested that divalent chromium occurs in these olivines. This hypothesis is supported by recent Mössbauer and electronic spectral measurements at high pressures, which demonstrate that pressure-induced reduction takes place in compounds and minerals initially containing Fe3+, Mn3+, and Cu2+ ions. The process is facilitated at high temperatures. Low oxidation states of other metals such as Cr(II) are expected to be stabilized under the very high pressures and elevated temperature conditions in the Mantle. Since Cr2+ ions are susceptible to the Jahn-Teller effect, they are predicted by crystal field theory to be stabilized in certain distorted coordination sites, such as the olivine Ml site, all three sites of the β-spinel phase, and the 7-coordinated site of the strontium plumbate structure-type. The Cr2+ ions in olivines are stabilized in kimberlites intruded into the Crust by the high confining pressures in the diamond inclusions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00372081
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Crystal structural features of the olivine → spinel transition (1978)
    Springer
    Physics and chemistry of minerals 2 (1978), S. 177-197 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Comparisons of structural features of olivine (α phase), spinel (γ phase), and the modified spinel (β phase) lead to predictions of possible mechanisms for the olivine → spinel transitions. In the olivine structure, rigid tetrahedral edges and shared octahedral edges form columns of corner-sharing trigonal dipyramids parallel to the a axis. These rigid columns are separated by weaker, unshared octahedral edges which may be stretched to reduce cation-cation repulsion. As a result, olivine has a relatively loose structure and is stable at low pressure. At elevated pressure, olivine transforms to the more compact spinel structure, in which the rigid tetrahedral edges and shared octahedral edges form a three dimensional network instead of aligned columns. These structural differences explain how compressibility and thermal expansion may be taken up mainly by octahedral sites in olivine, but are evenly distributed over both octahedral and tetrahedral sites in spinel. Because the closest packings of oxygens and interstitial cation distributions differ between olivine (h.c.p.) and spinel (c.c.p.), the olivine structure may have to disintegrate during its transformation to spinel, so that the olivine → spinel transition involves processes of nucleation and growth. The migration of atoms across the olivine-spinel interface is thus a complicated process of random walk without a definite path. In the β phase → spinel transition, however, the diffusion of cations may follow a definite path in restricted regions because oxygen closest packings and cation distributions are similar in the two structures. If the oxygen packing remains intact during the β → γ transition, the transformation will be an intracrystalline process leading to domain structure in the spinel product.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00308172
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Mössbauer spectra of kyanite, aquamarine, and cordierite showing intervalence charge transfer (1977)
    Springer
    Physics and chemistry of minerals 1 (1977), S. 301-311 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The blue colors of several minerals and gems, including aquamarine (beryl, Be3Al2Si6O18) and cordierite (Al3(Mg, Fe)2Si5AlO18), have been attributed to charge transfer (CT) between adjacent Fe2+ and Fe3+ cations, while Fe2+→Ti4+ CT has been proposed for blue kyanites (Al2SiO5). Such assignments were based on chemical analyses and on polarization-dependent absorption bands measured in visible-region spectra. We have attempted to characterize the Fe cations in each of these minerals by Mössbauer spectroscopy (MS). In blue kyanites, significant amounts of both Fe2+ and Fe3+ were detected with MS, indicating that Fe2+→Fe3+ CT, Fe2+→Ti4+ CT, and Fe2+ and Fe3+ crystal field transitions each could contribute to the electronic spectra. In aquamarines, coexisting Fe2+ and Fe3+ ions were resolved by MS, supporting our assignment of the broad, relatively weak band at 16,100 cm−1 in E∥c spectra to Fe2+→Fe3+ CT between Fe cations replacing Al3+ ions 4.6Å apart along c. A band at 17,500 cm−1 in E⊥c spectra of cordierite is generally assigned to Fe2+ (oct)→Fe3+ (tet) CT between cations only 2.74 Å apart. However, no Fe3+ ions were detected in the MS at 293K of several blue cordierites showing the 17,500 cm−1 band and reported to contain Fe3+. A quadrupole doublet with parameters consistent with tetrahedral Fe3+ appears in 77K MS, but the Fe3+/Fe2+ ratios from MS are much smaller than values from chemical analysis. These results sound a cautionary note when correlating Mössbauer and chemically determined Fe3+/Fe2+ ratios for minerals exhibiting Fe2+→Fe3+ CT.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00307569
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    The effect of crystal field stabilization on the olivine→spinel transition in the system Mg2SiO4 - Fe2SiO4 (1978)
    Springer
    Physics and chemistry of minerals 2 (1978), S. 349-364 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Crystal field stabilization (CFS) plays a significant role in determining equilibrium phase boundaries in olivine→spinel transformations involving transition-metal cations, including Fe2+ which is a major constituent of the upper mantle. Previous calculations for Fe2SiO4 ignored pressure and temperature dependencies of crystal field stabilization enthalpies (CFSE) and the electronic configurational entropy (S CFS). We have calculated free energy changes (ΔG CFS) due to differences of crystal field splittings between Fe2SiO4 spinel and fayalite from: ΔG CFS=−ΔCFSE−TΔS CFS, as functions of P and T, for different energy splittings of t 2g orbital levels of Fe2+ in spinel. The results indicate that ΔG CFS is always negative, suggesting that CFS always promotes the olivine→spinel transition in Fe2SiO4, and expands the stability field of spinel at the expense of olivine. Because of crystal field effects, transition pressures for olivine→spinel transformations in compositions (Mg1−x Fe x )2SiO4 are lowered by approximately 50x kbar, which is equivalent to having raised the olivine→spinel boundary in the upper mantle by about 15 km.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00307577
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Polarized absorption spectra of single crystals of lunar pyroxenes and olivines (1972)
    Springer
    Earth, moon and planets 4 (1972), S. 93-102 
    Details
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Measurements have been made of the polarized absorption spectra (360-2200 nm.) of compositionally zoned pyroxene minerals in rocks 10045, 10047 and 10058 and olivines in rocks 10020 and 10022. Specimens in the form of petrographic thin sections were mounted on polarizing microscopes equipped with three-axis universal stage attachments and inserted into a Cary 17 spectrophotometer. The Apollo 11 pyroxenes with relatively high Ti/Fe ratios were chosen initially to investigate the presence of crystal field spectra of Fe2+ and Ti3+ ions in the minerals. Broad intense bands at about 1000 and 2100 nm. arise from spin-allowed, polarization-dependent transitions in Fe2+ ions in pyroxenes. Several weak sharp peaks occur in the visible region. Peaks at 402, 425, 505, 550 and 585 nm. represent spin-forbidden transitions in Fe2+ ions, while broader bands at 460–470 nm. and 650–660 nm. are attributed to Ti3+ ions. Charge transfer bands, which in terrestrial pyroxenes often extend into the visible region, are displaced to shorter wavelengths in lunar pyroxenes. This feature correlates with the absence of Fe3+ ions in these minerals. The magnitudes of the intensity ratios: band 465 nm. (Ti3+) to band 1000 nm. (Fe2+) are similar to Ti/Fe ratios from lunar pyroxene bulk chemical analyses, suggesting that an appreciable amount of titanium occurs as Ti3+ ions in the lunar pyroxenes. The 505 nm. spin-forbidden peak in Fe2+, together with absorption at 465 nm. by Ti3+, contribute to the pink or pale reddish-brown colors of lunar pyroxenes in transmitted lights. The absorption spectral measurements not only provide information on the redox behavior and crystal chemistry of lunar pyroxenes, but also form a basis for interpreting spectral reflectivity properties of lunar rocks and the Moon's surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00562917
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Nanophase mixed-valence iron minerals in meteorites identified by cryogenic Mössbauer spectroscopy (1994)
    Springer
    Hyperfine interactions 91 (1994), S. 571-576 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Determination of oxidation states and the crystal chemistry of iron-bearing minerals in carbonaceous chondrites by Mössbauer spectroscopy is complicated by thermally-induced electron-hopping in cronstedtite, superparamagnetism of hydrous ferric oxides and ill-defined contributions from an incommensurate layered iron sulfide phase believed to be tochilinite. Mössbauer spectra measurements at 30 K of several terrestrial cronstedtite and tochilinite specimens have enables modal proportions of these minerals, as well as Fe3+/Fe2+ ratios, to be determined quantitatively in a suite of CM-type meteorites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02064572
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Mineral Mössbauer spectroscopy: Correlations between chemical shift and quadrupole splitting parameters (1994)
    Springer
    Hyperfine interactions 91 (1994), S. 739-745 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The variety of coordination numbers, symmetries, distortions and ligand environments in thermally-stable iron-bearing minerals provide wide ranges of chemical shift (δ) and quadrupole splitting (δ) parameters, which serve to characterize the crystal chemistries and site occupancies of Fe2+ and Fe3+ ions in minerals of terrestrial and extraterrestrial origins. Correlations between ferrous and ferric chemical shifts enable thermally-induced electron delocalization behavior in mixed-valence Fe2+-Fe3+ minerals to be identified, while chemical shift versus quadrupole splitting correlations serve to identify nanophase ferric oxides and oxyhydroxides in oxidized minerals and in meteorites subjected to aqueous oxidation before and after they arrived on Earth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02064600
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    facet.materialart.
    Unknown
    Polarized absorption spectra of single crystals of lunar pyroxenes and olivines (1972)
    Springer
    Details
    Publication Date: 1972-04-01
    Print ISSN: 0027-0903
    Topics: Geosciences , Physics
    Published by Springer
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 10
    facet.materialart.
    Unknown
    Vibronic Polarization in the Electronic Spectra of Gillespite, a Mineral Containing Iron(II) in Square-Planar Coordination (1966)
    American Chemical Society
    Details
    Publication Date: 1966-07-01
    Print ISSN: 0020-1669
    Electronic ISSN: 1520-510X
    Topics: Chemistry and Pharmacology
    Published by American Chemical Society
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...