| 1. |
- Abdu, Y. A., et al.
(författare)
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High-temperature cation ordering in olivine : an in situ Mossbauer study of synthetic (Mg0.55Fe0.45)(2) SiO4
- 2008
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540. ; 186:1-3, s. 99-103
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Tidskriftsartikel (refereegranskat)abstract
- High- temperature in situ Mossbauer spectroscopy measurements ( 300 950. C) were done on synthetic olivine of composition ( Mg0.55Fe0.45) 2 SiO4 (= Fa45) in order to study the distribution of Fe2+ over the M1 and M2 octahedral sites. The spectra are fit with two doublets, which are assigned to Fe2+ at the M1 ( smaller splitting) and M2 sites. The Fe2+ site- occupancies at M1 and M2, obtained from the Mossbauer relative areas, suggest that Fe2+ has a slight preference for the M1 site at temperatures below similar to 500. C, with a tendency of disordering around this temperature. At higher temperatures, Fe2+ again prefers to occupy the M1 site, where it shows a considerable order at this site up to 750C. At still higher temperatures, the spectra indicated partial reduction of the Fa- component into metallic iron and the resolution of the doublets was severely deteriorated.
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| 2. |
- Aryal, M. M., et al.
(författare)
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Understanding of nuclear quadrupole interactions of Cl-35, Br-79 and I-129 and binding energies of solid halogens at first-principles level
- 2007
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540. ; 176:1-3, s. 51-57
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the understanding at a first-principles level of the nuclear quadrupole interaction (NQI) parameters of solid chlorine, bromine and iodine as well as the intermolecular binding of these molecules in the solid. The electronic structure investigations that we have carried out to study these properties of the solid halogens are based on the Hartree-Fock Cluster approach using the Roothaan variational procedure with electron correlation effects included using many-body perturbation theory with the empty orbitals used in the perturbation theory investigations for the excited states. The results of our investigations provide good agreement with the measured NQI parameters primarily from the Hartree-Fock one electron wave-functions with many-body effects making minor contributions. The binding (dissociation) energies for the molecules with the solid state environment on the other hand arises from intermolecular many body effects identified as the Van der Waals attraction with one-electron Hartree-Fock contribution being repulsive in nature.
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| 3. |
- Dubey, Archana, et al.
(författare)
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Nuclear quadrupole interactions and electronic structure of BF3 center dot H2O complex
- 2007
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540. ; 176:1-3, s. 45-50
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Tidskriftsartikel (refereegranskat)abstract
- This work deals with first-principles investigation of the electronic structure of the BF3 center dot H2O complex which is important in catalysis of organic reactions and polymerization. The dissociation energy of the BF3 center dot H2O complex and the nuclear quadrupole interaction parameters for the excited nuclear state F-19* (I = 5/2) of the fluorine nuclei have been studied. Our investigation shows that the complexation bond BO between the BF3 and H2O units is strongly influenced by the larger electronegativity of Oxygen as compared to Nitrogen in BF3 center dot NH3. The quadrupole coupling constants of F-19* and the asymmetry parameter are however quite close to those for BF3 center dot NH3. The likely reasons for these features of these two important catalytic systems are suggested.
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| 4. |
- Fedosseev, V. N., et al.
(författare)
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Ionization scheme development at the ISOLDE RILIS
- 2005
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540. ; 162:1-4, s. 15-27
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Tidskriftsartikel (refereegranskat)abstract
- The resonance ionization laser ion source (RILIS) of the ISOLDE on-line isotope separation facility is based on the method of laser step-wise resonance ionization of atoms in a hot metal cavity. The atomic selectivity of the RILIS complements the mass selection process of the ISOLDE separator magnets to provide beams of a chosen isotope with greatly reduced isobaric contamination. Using a system of dye lasers pumped by copper vapour lasers, ion beams of 24 elements have been generated at ISOLDE with ionization efficiencies in the range of 0.5-15%. As part of the ongoing RILIS development off-line resonance ionization spectroscopy studies carried out in 2003 and 2004 have determined the optimal three-step ionization schemes for scandium, antimony, dysprosium and yttrium.
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| 5. |
- Ferrow, Embaie, et al.
(författare)
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Oxidation of pyrite grains: A Mossbauer spectroscopy and mineral magnetism study
- 2005
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 1572-9540 .- 0304-3843. ; 163:1-4, s. 95-108
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Tidskriftsartikel (refereegranskat)abstract
- Fe2+ in pyrite is found in a low-spin d(6) configuration, a necessary condition for diamagnetic and semi-conducting properties of material. The semi-conducting property of pyrite has been studied since the time when pyrite was used as a rectifier in early radios. Pyrite posses the highest possible crystal field stabilisation energy and offers a better altemative as solar material compared to Si- based materials. Unfortunately, pyrite is difficult to study due to its inherent deviation from stoichiometry and its ease of oxidation. Since pyrite and its oxidation products are all Fe-bearing phases, combining Mossbauer spectroscopy with mineral magnetic methods provides enough information to monitor the oxidation of pyrite in air and identify the different phases produced and their relation to different experimental parameters. For mm-sized grain samples, heating FeS2 at temperatures between 450 degrees C and 650 degrees C five different mineral assemblages are identified. FeS2 is oxidized to alpha-Fe2O3 along two separate routes: FeS2 -> FeSO4 -> epsilon-Fe2O3 -> alpha-Fe2O3; and FeS2 -> FeSO4 -> Fe-2 (SO4)(3) -> ss-Fe2O3 -> alpha-Fe2O3.
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| 6. |
- Ferrow, Embaie, et al.
(författare)
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Reaction kinetics and oxidation mechanisms of the conversion of pyrite to ferrous sulphate: A Mossbauer spectroscopy study
- 2005
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 1572-9540 .- 0304-3843. ; 163:1-4, s. 109-119
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Tidskriftsartikel (refereegranskat)abstract
- Pyrite undergoes a series of exothermic reactions during mine roasting to porous hematite. At low temperatures, the first non-refractive phase to form is ferrous sulphate and could be a cheaper alternative to hematite roasting for the mining industry. In this study, pyrite powder is heated in air at temperatures between 200 and 370 degrees C for 1 to 256 h in a temperature and time series. The rate of oxidation of pyrite to ferrous sulphate is modelled by combining the Arrhenius equation with the Weibull function to extract reliable thermodynamic data, including the energy of activation, the frequency factor and the overall order of reaction. From the thermodynamic data obtained, two possible oxidation mechanisms are recognized, depending on the bond dissociation energies of the S-S and Fe-S bonds in pyrite.
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| 7. |
- Häggström, Lennart, et al.
(författare)
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Mössbauer and magnetisation studies of iron oxide nanocrystals
- 2008
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540. ; 183:1-3, s. 49-53
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Tidskriftsartikel (refereegranskat)abstract
- Monodisperse iron oxide nanocrystals have been produced following non-hydrolytic, thermal decomposition routes. Spherically shaped particles with diameter of 4 and 12 nm and cubic shaped particles with an edge length of 9 nm have been studied. The particles have been shown to consist of mainly maghemite. A reduction of the saturation magnetic hyperfine field is observed for the 4 nm particles as compared to the corresponding bulk value. The anisotropy energy determined from the temperature variation of the magnetic hyperfine field was strongly enhanced for the 4 nm particles.
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| 8. |
- Häggström, Lennart, et al.
(författare)
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Structural transformations in lithiated Mn2Sb electrodes probed by Mossbauer spectroscopy and X-ray diffraction
- 2006
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540. ; 167:1-3, s. 759-765
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical reactions of Li with Mn2Sb and small amounts of MnSb have been investigated by Mossbauer spectroscopy and X-ray diffraction. The lithiation transforms initially the MnSb part and later the Mn2Sb part into amorphous LiMnSb. On further lithiation the LiMnSb phase transforms to rather well crystallized Li3Sb. In the X-ray diffraction pattern for the fully lithiated sample extruded nanocrystalline Mn is seen for the first time in these type of electrodes. The first delithiation of Li3Sb results in a mixture of three phases Mn2Sb, MnSb and LiMnSb. After several cycles (charges and discharges) of the electrode the Mn2Sb phase disappears completely.
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| 9. |
- Jeong, Junho, et al.
(författare)
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First-principles study of location of Er3+ ion-relationship to understanding of hyperfine interactions in the optoelectronic erbium-silicon system
- 2007
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540. ; 178:1-3, s. 51-56
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Tidskriftsartikel (refereegranskat)abstract
- The importance of hyperfine interactions in the Erbium-Silicon system is underscored by our first-principles Hartree-Fock Cluster investigations on the location of Erbium in Silicon. Our theoretical studies show that both substitutional and tetrahedral interstitial sites are stable for Er3+ ion with the latter having a larger binding energy. This conclusion is not completely supported by channeling experiments. It is suggested that Mossbauer measurements on Er-166 isotope would be valuable to compare experimental results with theoretical predictions of the hyperfine interactions of both magnetic and quadrupolar types to provide additional information about the location of Er3+.
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| 10. |
- Kamali, Saeed, et al.
(författare)
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Metallurgical behaviour of iron in brass studied using Mössbauer spectroscopy
- 2006
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540. ; 168:1-3, s. 995-999
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Tidskriftsartikel (refereegranskat)abstract
- The behaviour of small amounts of Fe in brass is investigated using Mossbauer spectroscopy. Different samples, made from the same ingot material, but run through different annealing temperatures and duration times and then quenched to room temperature, have different amount of gamma-Fe. The present work shows that a suitable heat treatment can increase the amount of these precipitations and, that a heat treatment at 650 degrees C is the optimal one for having the highest amount of this phase.
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