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  • 1
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    A semi-quantitative approach to derive the electric field gradient, applied to synthetic fayalite, {alpha}-Fe2SiO4: a reappraisal (2012)
    Schweizerbart
    Details
    Publication Date: 2012-09-01
    Description: Experimental and calculated structure factors from a previous synchrotron diffraction measurement on synthetic fayalite have been converted by an inverse Fourier transformation to difference electron (deformation) densities (DED). These were processed in a revised 3D-display program giving hyperareas of DED floating in space around the iron positions M1 and M2 within the fayalite unit-cell and spanning a cluster size of 6 and 4 Å, respectively. These relatively wide limits are due to the different site symmetries and had been proposed by earlier DFT (density functional theory) calculations. From the different hyperareas the supposed charges were integrated in space and processed to electric field gradients (EFG) on M1 and M2 using a point-charge model. The two EFGs were compared with respect to the system of crystallographic axes with those obtained from published single-crystal Mössbauer measurements (experimental EFGs), yielding excellent agreement within ±5° and surpassing even the DFT results. This study reports the procedure and the conditions of success of the underlying semi-quantitative method, which is halfway between theory (DFT) and experiment (diffractometry) and is promising valuable results on many other compounds. The term "nanoscope" for the graphical representation may be justified due to its high spatial resolution.
    Print ISSN: 0935-1221
    Electronic ISSN: 1617-4011
    Topics: Geosciences
    Published by Schweizerbart
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  • 2
    Electronic Resource
    Electronic Resource
    Antiferromagnetism in synthetic olivines
    Amsterdam : Elsevier
    Journal of Magnetism and Magnetic Materials 54-57 (1986), S. 1005-1006 
    Details
    ISSN: 0304-8853
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0304-8853(86)90355-0
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Crystal field magnetic anisotropy of La(Pr)Sn"3
    Amsterdam : Elsevier
    Physica B+C 107 (1981), S. 63-64 
    Details
    ISSN: 0378-4363
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0378-4363(81)90338-7
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    A combined temperature dependent57Fe Mössbauer and single crystal X-ray diffraction study of synthetic almandine: evidence for the Gol'danskii-Karyagin effect (1992)
    Springer
    Physics and chemistry of minerals 19 (1992), S. 121-126 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Synthetic almandine garnet, Fe3Al2Si3O12, has been studied by temperature — dependent single crystal X-ray diffraction and57Fe Mössbauer spectroscopy. The Fe2+ doublet in almandine is characterized by a small asymmetry between the high and low-velocity peaks that decreases in magnitude with decreasing temperature from 420 to 15 K. The X-ray results show that the Fe2+ cation is dynamically disordered with an anisotropic motion within the eight-coordinated site in garnet. The magnitudes of the X-ray determined mean-square-vibrational amplitudes of this motion parallel,x ∥, and perpendicular,x ⊥, to the principle axes of the electric field gradient give a calculated angular dependence of the electric quadrupole interaction of theI 1/2 toI 3/2 transitions that agree with the experimentally measured peak ratios. This is the first recognition of anisotropic recoil free fraction of57Fe in silicates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00198609
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  • 5
    Electronic Resource
    Electronic Resource
    Powder- and single crystal Mössbauer spectroscopy on synthetic fayalite (1995)
    Springer
    Physics and chemistry of minerals 22 (1995), S. 259-267 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Mössbauer measurements on synthetic iron orthosilicate Fe2SiO4 (fayalite) were carried out in the antiferromagnetic spin state below T N ≃65 K. The Mössbauer parameters isomer shift δ, inner magnetic field H(0), angle Θ between H(0) and the z-component of the electric field gradient (efg), quadrupole splitting QS and asymmetry parameter η were determined as a function of temperature. These parameters could be attributed to the two crystallographic sites M1 and M2. The smaller isomer shift on M1 with respect to M2 displays the more covalent character of the Fe-O bond on M1, which is supported by previous neutron diffraction experiments. H(0) shows a Brillouin-type behaviour with different fields on the two crystallographic sites (stronger on M1) and a small discontinuity at T = 23 K which corresponds with previous magnetic measurements. The quadrupole splitting is equal on both sites within error bars, in agreement with previous theoretical results and in contradiction to previous Mössbauer refinements published elsewhere. Single crystal Mössbauer spectroscopy revealed the orientation of the crystallographic c-axis (Pnma) with respect to the axes of the efg. A second parameter set which also holds true for the powder refinement yields the angle between c and H(0) on M1 to be temperature-dependent in quantitative agreement with previous neutron diffraction results and solves an old discrepancy discussed elsewhere. On M2, the angle between c and H(0) is found to be much smaller than 90° in contradiction to symmetry requirements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202259
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic properties of the clinopyroxenes aegirine and hedenbergite: a magnetic susceptibility study on single crystals (1997)
    Springer
    Physics and chemistry of minerals 24 (1997), S. 294-300 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  Two natural clinopyroxene single crystals were investigated, an aegirine-augite (AEG) and a magnesian hedenbergite (HED). Both samples were carefully characterized by electron microprobe, X-ray diffraction, and Mössbauer spectroscopy. Magnetic susceptibility measurements of powdered samples reveal low temperature antiferromagnetic coupling and Curie-Weiss behaviour with T N =7.5(5) K, Θ P =−19(1) K for AEG, and T N =31(1) K, Θ P =+21(1) K for HED, respectively. Low temperature Mössbauer spectra exhibit relaxation phenomena. Magnetic susceptibility measurements of the single crystals show the direction of the magnetic moments to be lying within the a/c plane for both samples: 50(±2)° from a and 57(±2)° from c in AEG, and 45(±2)° from a and 60(±2)° from c in HED, respectively. The antiferromagnetic interchain interaction competes with the ferromagnetic intrachain interaction in both pyroxenes. In the magnesian hedenbergite a field induced magnetic transition is found. Its dependence on temperature, magnetic field and crystallographic direction is investigated and described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050041
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  • 7
    Electronic Resource
    Electronic Resource
    Vorträge über Tonbildung bei Musikinstrument und Sprache (1950)
    Springer
    Naturwissenschaften 37 (1950), S. 302-308 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00630900
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Crystallographic phase transition and valence fluctuation in synthetic mn-bearing ilvaite CaFe2+ 2-x Mn2+ xFe3+ [Si2O7/O/(OH)] (1992)
    Springer
    Physics and chemistry of minerals 18 (1992), S. 491-496 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The dependence of the electronic and the crystallographic structure on temperature of synthetic Mnbearing ilvaites CaFe2+ 2-xMn2+ xFe3+ [Si2O7/O/OH] with 0≤x≤0.19 has been investigated. The change of the electronic structure was studied by 57Fe Mössbauer spectroscopy. The spectra show an increasing valence fluctuation rate between Fe2+ and Fe3+ in the double chain of edge-sharing octahedra with increasing temperature resulting in a mixed valent state of iron. The valence fluctuation rate is distinctly increased by the Mnsubstitution. The temperature of the crystallographic phase transition T x as studied by a high temperature Guinier method is distinctly lowered by the Mn-substitution (x = 0.0, T x=390K; x = 0.12, T x =370K; x = 0.19, T x=295K). The reasons for this behaviour are discussed in terms of Fe2 +, Fe3 + cation order-disorder, electronic relaxation rate, and relaxation of the lattice. In the monoclinic phase there is electron hopping between Fe2 +, Fe3 + pairs whereas in the orthorhombic phase there is extended electron delocalization via a narrow, d-band mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00205263
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  • 9
    Electronic Resource
    Electronic Resource
    Single crystal Mössbauer spectroscopy on the three principal sections of a synthetic fayalite sample in the antiferromagnetic state (1996)
    Springer
    Physics and chemistry of minerals 23 (1996), S. 432-438 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The present work reports Mössbauer investigations for several temperatures below T N on fayalite single crystal sections cut perpendicularly to the crystallographic a and b-axis (Pnma). The previously detected correspondence between the c-component of the magnetic moment on M1 from neutron diffraction and our own Mössbauer measurements published elsewhere are confirmed for the other principal sections to a large extent. Small humps in the angular dependence of two components of the internal magnetic field H(0) on T below T=23 K are in good agreement with magnetometric and calorimetric data published elsewhere; a reinterpretation of single reflection neutron data has been possible by our results. Moreover, the axes of the electric field gradient (efg) are oriented within the crystallographic axes for the M1-site at low temperatures. The violation of symmetry on the M2 position as a result of our previous investigations could be confirmed for the section ⊥ a, but not with respect to b. A possible explanation in terms of saturation effects of large line intensities at the expense of the small ones is given in the context.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202029
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  • 10
    Electronic Resource
    Electronic Resource
    A time-minimizing hybrid method for fitting complex Mössbauer spectra (1999)
    Springer
    Physics and chemistry of minerals 27 (1999), S. 34-40 
    Details
    ISSN: 1432-2021
    Keywords: Key words Fitting of Mössbauer spectra ; Genetic algorithm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The present study includes results of the application of a program consisting of a genetic algorithm routine and a conventional refinement part (“hybrid method”) for the evaluation of Mössbauer spectra published elsewhere. It is shown that the saving of total evaluation time compared with conventional refinement routines is very high due to the rapid finding of adequate starting parameters. Contrary to a recently published work on a similar topic our algorithm provides solutions of the combined interaction Hamiltonian with a minimum of conventional input data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050237
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