Hyperfine electric field gradient tensors at Fe2+ sites in octahedral layers: Toward understanding oriented single-crystal Mössbauer spectroscopy measurements of micas
-
R. James Evans
and
Michael Grodzicki
Abstract
In this first systematic, theoretical study of the complete electric field gradient (EFG) tensor of 57Fe Mössbauer spectroscopy as a function of chemistry and local structural distortion using electronic structure calculations, local EFG tensors were calculated at the central Fe2+ sites in clusters of seven octahedra, where the neighbor octahedra were populated with a mixture of Mg2+ and Al3+ cations. The independent parameters of the EFG tensor.particularly the principal value VZZ, the asymmetry parameter η, and the direction of the principal axis with regards to the octahedral sheet.were examined in detail as functions of octahedral flattening for each of the thirteen possible configurations of cations. We demonstrate that the argument that the EFG tensor at a particular site is largely determined by the point group symmetry of the corresponding crystallographic site is not correct. We find that in clusters with monoclinic or triclinic local point group symmetry, the value of VZZ changes discontinuously from positive to negative as flattening increases. The principal axis changes from being in the plane of the octahedral sheet to being normal to it at this discontinuity, and the value of η reaches a maximum and begins to decline. This discontinuous behavior is caused by the continuous change of the EFG eigenvalues as the Fe(3d) character of the highest occupied spin-down orbital evolves with flattening. Taking EFG tensor results from all clusters, and using probabilities for the occurrence of each possible cation configuration in a chemically disordered octahedral sheet of a given bulk composition, we simulate averages and distributions of η, principal axis angles, and quadrupole splittings. While the value of η is broadly distributed from zero to one at all flattening angles and bulk compositions, there are two distinct populations of principal axes, normal to and in-plane with the octahedral sheet, as has been observed experimentally. We find these in-plane and normal populations of principal axes correspond exactly to populations with positive and negative values of VZZ, respectively. Histograms representing quadrupole splitting distributions (QSDs) show features found in experimental QSDs, such as a constant high edge, a variable low edge, and a QSD width that changes dramatically with flattening. These results represent the first predictions relating average structural parameters, as would be obtained by X-ray diffraction, to characteristics of the Fe2+ QSD, as obtained by 57Fe Mössbauer spectroscopy, in a chemically disordered material.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Presidential Address To The Mineralogical Society Of Amrica, Boston, November 6, 2001: Some Precambrian Banded Iron-Formations (BiIFs) From Around The World: Their Age, Geologic Setting, Mineralogy, Metamorphism, Geochemistry, And Origin
- Effects of high pressure and high temperature on cation ordering in magnesioferrite, MgFe2O4, using in situ synchrotron X-ray powder diffraction up to 1430 K and 6 GPa
- Raman spectroscopy and vibrational analyses of albite: From 25 °C through the melting temperature
- A new occurrence of xitieshanite [Fe3+(SO4)Cl⋅6H2O] crystals in acid-mine seepways, Green Valley, Vigo County, Indiana, U.S.A.
- Effect of A-site cation radius on ordering of BX6 octahedra in (K,Na)MgF3 perovskite
- Crystal chemistry of NaMgF3 perovskite at high pressure and temperature
- Hyperfine electric field gradient tensors at Fe2+ sites in octahedral layers: Toward understanding oriented single-crystal Mössbauer spectroscopy measurements of micas
- Does the bazhenovite structure really contain a thiosulfate group? A structural and spectroscopic study of a sample from the type locality
- Light-induced degradation dynamics in realgar: in situ structural investigation using single-crystal X-ray diffraction study and X-ray photoelectron spectroscopy
- Absolute quantification by powder X-ray diffraction of complex mixtures of crystalline and amorphous phases for applications in the Earth sciences
- Detrital illite crystals identified from crystallite thickness measurements in siliciclastic sediments
- High-temperature density of lanthanide-bearing Na-silicate melts: Partial molar volumes for Ce2O3, Pr2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, and Yb2O3
- Coupled dichotomies of apatite and fluid composition during contact metamorphism of siliceous carbonate rocks
- The effect of zoned garnet on metapelite pseudosection topology and calculated metamorphic P-T paths
- Low-pressure and low-temperature K-bearing kosmochloric diopside from the Osayama serpentinite mélange, SW Japan
- Dehydration of natural stilbite: An in situ FTIR study
- Structural changes accompanying the phase transformation between leadhillite and susannite: A structural study by means of in situ high-temperature single-crystal X-ray diffraction
- Optic properties of centimeter-sized crystals determined in air with the spindle stage using EXCALIBRW
- Zoltaiite, a new barium-vanadium nesosubsilicate mineral from British Columbia: Description and crystal structure
- Mn-tourmaline from island of Elba (Italy): Crystal chemistry
- Letter: An infrared study of carbon-oxygen bonding in magnesite to 60 GPa
- Letter: Metals in quartz-hosted melt inclusions: Natural facts and experimental artifacts
- Letter: A high-pressure phase transition of calcite-III
- Letter: Experimental observation of an interface-controlled pseudomorphic replacement reaction in a natural crystalline pyrochlore
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