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J R Dahn - One of the best experts on this subject based on the ideXlab platform.
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in situ 119sn Mossbauer Effect study of the reaction of lithium with si using a sn probe
Journal of The Electrochemical Society, 2009Co-Authors: A J Smith, R A Dunlap, R J Sanderson, T D Hatchard, J R DahnAbstract:The reaction of lithium with amorphous Si was studied by 119 Sn Mossbauer Effect spectroscopy using small amounts of Sn as probe atoms. Two powder samples, amolphous-Si 87 Sn 13 and amolphous-Si 93 Sn 7 , were prepared by magnetron sputtering and investigated using in situ and ex situ Mossbauer spectroscopy. There are two gently sloping plateaus in the voltage vs capacity of Li/Si cells whose origin has never been explained. There is a clear step between these plateaus at ∼2.3 Li atoms per Si atom, or Li 2.3 Si. The step between the plateaus is found to correlate with dramatic changes in the Mossbauer Effect spectra with x in Li x Si at x ≈ 2.3, which suggest the step occurs at the point when each Si atom is surrounded only by Li atom first neighbors. The changes in the Mossbauer spectra during the delithiation of the Li/Si-Sn cells also give clues about electrode failure mechanisms.
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a Mossbauer Effect and x ray diffraction investigation of ti sn intermetallic compounds i equilibrium phases
Journal of Alloys and Compounds, 2003Co-Authors: J W Obrien, R A Dunlap, J R DahnAbstract:Abstract A thorough X-ray diffraction and Mossbauer Effect investigation of Ti3Sn, Ti2Sn, Ti5Sn3, Ti6Sn5, and Ti2Sn3 phases in the Ti–Sn binary system has been made. The compounds were verified to have the same crystal structures as those reported in the literature. This work presents the first reported 119Sn Mossbauer Effect spectroscopy data on Ti3Sn, Ti2Sn, Ti5Sn3, and Ti6Sn5. The room temperature center shifts (relative to CaSnO3) and quadrupole splittings have been determined for each of the phases by fitting model spectra to the observed data. These results are important for the interpretation of Mossbauer Effect measurements on high capacity Sn-based electrode materials for Li-ion batteries.
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a Mossbauer Effect and x ray diffraction investigation of ti sn intermetallic compounds ii nanostructured phases prepared by ball milling with al2o3 and tin
Journal of Alloys and Compounds, 2003Co-Authors: J W Obrien, R A Dunlap, J R DahnAbstract:A thorough X-ray diffraction and 119Sn Mossbauer Effect investigation of Ti3Sn, Ti2Sn, Ti5Sn3, Ti6Sn5, and Ti2Sn3 phases ball milled with Al2O3 and TiN has been made. The starting compounds were verified to have the same crystal structures as those reported in the literature. X-ray diffraction data showed a decrease in grain size of the Ti–Sn phase with increased milling time and no interactions between the Ti–Sn phase and the Al2O3 or TiN. The two samples with the highest Sn concentrations (Ti2Sn3 and Ti5Sn6) were observed to precipitate elemental Sn when ball milled. This Sn precipitation was observed qualitatively by X-ray diffraction patterns and quantitatively by site populations reported in the Mossbauer spectroscopy data.
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in situ 119sn Mossbauer Effect studies of the reaction of lithium with sno and sno 0 25 b2o3 0 25 p2o5 glass
Electrochimica Acta, 1999Co-Authors: Ian A Courtney, R A Dunlap, J R DahnAbstract:Abstract The electrochemical reaction of lithium with SnO and with SnO:0.25 B 2 O 3 :0.25 P 2 O 5 glass was studied in-situ using 119 Sn Mossbauer Effect spectroscopy in electrochemical cells equipped with beryllium windows. The experiments confirm our previous work that showed that the first two lithium atoms per formula unit react with the oxygen bonded to tin, forming clusters of tin metal and Li 2 O. As further lithium is added, the tin clusters alloy with lithium. The alloy reactions are easily observed in Mossbauer spectroscopy, even in SnO:0.25 B 2 O 3 :0.25 P 2 O 5 glass, where X-ray diffraction did not discern the Li–Sn alloy phases well. Most interesting, however, is the dramatic variation of the total Mossbauer absorption intensity as a function of the amount of lithium that has reacted with the electrode. Since the number of tin atoms in the sample is constant as the lithium content changes, such intensity variations can only be caused by changes in the fraction of Sn atoms undergoing recoil-free absorption. The recoil-free fraction depends on the mean square displacement of the tin atoms from their equilibrium positions. This, in turn, depends on the size of the grains of the Li–Sn alloys and upon the nature of the bonding in the alloy phases, as reflected in their Debye temperatures or in their melting points.
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a Mossbauer Effect investigation of the li sn system
Journal of Alloys and Compounds, 1999Co-Authors: R A Dunlap, D A Small, D D Macneil, M N Obrovac, J R DahnAbstract:Abstract A thorough Mossbauer Effect investigation of all the phases in the Li–Sn binary phase diagram has been made. The compounds studied were verified to have the same crystal structures as those reported in the literature. The center shifts (relative to CaSnO 3 ), quadrupole splittings, number of Sn sites and their abundance have been determined for each of the phases by fitting model spectra to the observed data. The observed spectra show mean center shifts near 2.4 mm/s for the Sn-rich phases (Sn, Li 2 Sn 5 and LiSn) and mean center shifts between 2.1 and 1.8 mm/s for the Li-rich phases (Li 7 Sn 3 , Li 5 Sn 2 , Li 13 Sn 5 , Li 7 Sn 2 and Li 22 Sn 5 ). These results are important for the interpretation of Mossbauer Effect measurements on high capacity Sn-based electrode materials for Li-ion batteries.
R A Dunlap - One of the best experts on this subject based on the ideXlab platform.
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investigation of the reversible sodiation of sn foil by ex situ x ray diffractometry and Mossbauer Effect spectroscopy
Journal of Alloys and Compounds, 2014Co-Authors: R A Dunlap, M N ObrovacAbstract:Abstract The reversible sodiation of Sn foil was investigated using ex-situ X-ray diffractometry (XRD) and Mossbauer Effect spectroscopy. The measured voltage profile indicated that the sodiation process of Sn foil proceeded in three stages. Ex-situ XRD patterns demonstrated that Na4Sn4, Na5Sn2 and Na15Sn4 phases were formed at the end of each discharge plateau. Na5Sn2, Na4Sn4 and β-Sn were formed at the end of each charge plateau. Three single-phase alloys, Na4Sn4, Na9Sn4 and Na15Sn4, were prepared by annealing stoichiometric ratios of Na and Sn. The Mossbauer spectra of ex-situ samples at the end of each discharge plateau were collected and compared with the Mossbauer spectra of the three single phase alloys. The measured parameters for the Mossbauer Effect spectra were consistent with an analysis of the crystal structures. The center shift became less positive with an increase of the sodium content in Na–Sn phases and this was shown to be a useful indicator of the degree of sodiation of Sn electrodes.
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in situ 119sn Mossbauer Effect study of the reaction of lithium with si using a sn probe
Journal of The Electrochemical Society, 2009Co-Authors: A J Smith, R A Dunlap, R J Sanderson, T D Hatchard, J R DahnAbstract:The reaction of lithium with amorphous Si was studied by 119 Sn Mossbauer Effect spectroscopy using small amounts of Sn as probe atoms. Two powder samples, amolphous-Si 87 Sn 13 and amolphous-Si 93 Sn 7 , were prepared by magnetron sputtering and investigated using in situ and ex situ Mossbauer spectroscopy. There are two gently sloping plateaus in the voltage vs capacity of Li/Si cells whose origin has never been explained. There is a clear step between these plateaus at ∼2.3 Li atoms per Si atom, or Li 2.3 Si. The step between the plateaus is found to correlate with dramatic changes in the Mossbauer Effect spectra with x in Li x Si at x ≈ 2.3, which suggest the step occurs at the point when each Si atom is surrounded only by Li atom first neighbors. The changes in the Mossbauer spectra during the delithiation of the Li/Si-Sn cells also give clues about electrode failure mechanisms.
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a Mossbauer Effect study of structural ordering in rapidly quenched fe ga alloys
Journal of Magnetism and Magnetic Materials, 2006Co-Authors: R A Dunlap, Joshua D Mcgraw, S P FarrellAbstract:Samples of Fe100−xGax (x=8.3, 17.9, 20.5 and 23.3) were prepared by rapid solidification from the melt using a single Cu roller. X-ray diffraction studies of all samples showed them to be single phase with the disordered BCC structure. No evidence of superlattice reflections from D03 ordering was observed for any of the samples. Room-temperature 57Fe Mossbauer Effect spectra indicated that all samples were ferromagnetically ordered. Spectra were fit to distributions of hyperfine fields. The x=8.3 sample showed a hyperfine field distribution that was single peaked and indicated a reasonably random distribution of local Fe environments. The x=17.9 and 20.5 samples showed hyperfine field distributions that were bimodal and indicated two distinct local Fe environments. The x=23.3 sample showed three distinct field components. It is suggested that the x=8.3, 17.9 and 20.5 alloys are primarily a disordered BCC phase. The x=8.3 alloy shows a small amount of short-range Ga–Ga pairing, while this short-range pairing is significantly greater in the x=17.9 and 20.5 alloys. The three field components in the x=23.3 alloy correspond well to the two sites associated with the D03 phase and a third component corresponding to a remaining L12 phase suggesting the presence of at least short-range D03 clustering in this alloy.
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Mossbauer Effect studies of fe100 xgax films prepared by combinatorial methods
Journal of Physics: Condensed Matter, 2006Co-Authors: R A Dunlap, N C Deschamps, R E Mar, S P FarrellAbstract:Magnetostrictive Fe100−xGax alloys over the composition range 0 20, the Mossbauer Effect results suggest the presence of short range D03 type order. This persists up to the maximum Ga content studied here (x = 36), although there is no evidence to support the formation of long range D03 structural order in any of the films prepared in this study.
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a Mossbauer Effect investigation of superparamagnetic behavior in ball milled mn zn ferrites
Journal of Alloys and Compounds, 2004Co-Authors: R A Dunlap, J W Obrien, A Alghamdi, S J PenneyAbstract:Abstract Nanostructured Mn 1− x Zn x Fe 2 O 4 , with x =0.4, 0.5, 0.6 and 0.7, were prepared by ball milling and were investigated using X-ray diffraction and 57 Fe Mossbauer Effect methods. Nanocrystallite grain size has been determined from X-ray linewidths to be around 70 A. 57 Fe Mossbauer Effect spectra of all samples showed a combination of a ferromagnetic component and a superparamagnetic component. Low-temperature Mossbauer measurements confirmed the identity of the superparamagnetic component and provided mean grain sizes consistent with the X-ray results.
J W Obrien - One of the best experts on this subject based on the ideXlab platform.
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a Mossbauer Effect investigation of superparamagnetic behavior in ball milled mn zn ferrites
Journal of Alloys and Compounds, 2004Co-Authors: R A Dunlap, J W Obrien, A Alghamdi, S J PenneyAbstract:Abstract Nanostructured Mn 1− x Zn x Fe 2 O 4 , with x =0.4, 0.5, 0.6 and 0.7, were prepared by ball milling and were investigated using X-ray diffraction and 57 Fe Mossbauer Effect methods. Nanocrystallite grain size has been determined from X-ray linewidths to be around 70 A. 57 Fe Mossbauer Effect spectra of all samples showed a combination of a ferromagnetic component and a superparamagnetic component. Low-temperature Mossbauer measurements confirmed the identity of the superparamagnetic component and provided mean grain sizes consistent with the X-ray results.
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a Mossbauer Effect and x ray diffraction investigation of ti sn intermetallic compounds i equilibrium phases
Journal of Alloys and Compounds, 2003Co-Authors: J W Obrien, R A Dunlap, J R DahnAbstract:Abstract A thorough X-ray diffraction and Mossbauer Effect investigation of Ti3Sn, Ti2Sn, Ti5Sn3, Ti6Sn5, and Ti2Sn3 phases in the Ti–Sn binary system has been made. The compounds were verified to have the same crystal structures as those reported in the literature. This work presents the first reported 119Sn Mossbauer Effect spectroscopy data on Ti3Sn, Ti2Sn, Ti5Sn3, and Ti6Sn5. The room temperature center shifts (relative to CaSnO3) and quadrupole splittings have been determined for each of the phases by fitting model spectra to the observed data. These results are important for the interpretation of Mossbauer Effect measurements on high capacity Sn-based electrode materials for Li-ion batteries.
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a Mossbauer Effect and x ray diffraction investigation of ti sn intermetallic compounds ii nanostructured phases prepared by ball milling with al2o3 and tin
Journal of Alloys and Compounds, 2003Co-Authors: J W Obrien, R A Dunlap, J R DahnAbstract:A thorough X-ray diffraction and 119Sn Mossbauer Effect investigation of Ti3Sn, Ti2Sn, Ti5Sn3, Ti6Sn5, and Ti2Sn3 phases ball milled with Al2O3 and TiN has been made. The starting compounds were verified to have the same crystal structures as those reported in the literature. X-ray diffraction data showed a decrease in grain size of the Ti–Sn phase with increased milling time and no interactions between the Ti–Sn phase and the Al2O3 or TiN. The two samples with the highest Sn concentrations (Ti2Sn3 and Ti5Sn6) were observed to precipitate elemental Sn when ball milled. This Sn precipitation was observed qualitatively by X-ray diffraction patterns and quantitatively by site populations reported in the Mossbauer spectroscopy data.
Hans Frauenfelder - One of the best experts on this subject based on the ideXlab platform.
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dynamics and the free energy landscape of proteins explored with the Mossbauer Effect and quasi elastic neutron scattering
Journal of Physical Chemistry B, 2013Co-Authors: Hans Frauenfelder, Robert D Young, Paul W FenimoreAbstract:The Mossbauer Effect and quasi-elastic neutron scattering (QENS) from hydrated proteins yield sharp elastic lines that are accompanied by broad wings. Conventionally, the elastic line and the broad wings are treated as separate phenomena. We show that there is no separation; the entire spectrum consists of Lorentzians with the natural line width. In protein crystals, the shifts of the individual lines from the elastic center above about 150 K are caused by beta fluctuations in the hydration shell. Vibrations cause shifts in the entire temperature range but are best seen below about 150 K. We construct a microscopic model for the dynamics that is based on a random walk of the proteins in their free-energy landscape. The model yields approximate values for the steps in the energy landscape. Remarkably, the quantum electrodynamic concept of gamma rays is needed to justify the model.
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Mössbauer Effect in proteins.
Physical review letters, 2011Co-Authors: Robert D Young, Hans Frauenfelder, Paul W FenimoreAbstract:In proteins, the Mossbauer Effect and neutron scattering show a broad line and a rapid increase of the conformational mean-square displacement above about 180 K. The increase, dubbed the "dynamical transition," is controversial. We introduce a new interpretation of the Mossbauer Effect in proteins and demonstrate that no dynamical transition is required. The increase in the mean-square displacement and the broad line are caused by fluctuations in the protein's hydration shell. Using the dielectric spectrum of these fluctuations, we predict the shape of the Mossbauer spectrum from 80 to 295 K with one dimensionless coefficient.
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The Mössbauer Effect and biological physics
Hyperfine Interactions, 1994Co-Authors: Hans FrauenfelderAbstract:A few remarks about the early days of the Mossbauer Effect will show how much the field has changed in thirty-five years. Some speculations about the future of physics indicate that complex systems will form a major field. Proteins may be the simplest systems that show true complexity; studies of their properties may keep not only biologists and biochemists, but also physicists, occupied for many years to come. The Mossbauer Effect has made, and will continue to make, major contributions to structural and dynamic investigations of proteins. The ultimate goal is a quantitative theory of complex systems.
Paul W Fenimore - One of the best experts on this subject based on the ideXlab platform.
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dynamics and the free energy landscape of proteins explored with the Mossbauer Effect and quasi elastic neutron scattering
Journal of Physical Chemistry B, 2013Co-Authors: Hans Frauenfelder, Robert D Young, Paul W FenimoreAbstract:The Mossbauer Effect and quasi-elastic neutron scattering (QENS) from hydrated proteins yield sharp elastic lines that are accompanied by broad wings. Conventionally, the elastic line and the broad wings are treated as separate phenomena. We show that there is no separation; the entire spectrum consists of Lorentzians with the natural line width. In protein crystals, the shifts of the individual lines from the elastic center above about 150 K are caused by beta fluctuations in the hydration shell. Vibrations cause shifts in the entire temperature range but are best seen below about 150 K. We construct a microscopic model for the dynamics that is based on a random walk of the proteins in their free-energy landscape. The model yields approximate values for the steps in the energy landscape. Remarkably, the quantum electrodynamic concept of gamma rays is needed to justify the model.
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Mössbauer Effect in proteins.
Physical review letters, 2011Co-Authors: Robert D Young, Hans Frauenfelder, Paul W FenimoreAbstract:In proteins, the Mossbauer Effect and neutron scattering show a broad line and a rapid increase of the conformational mean-square displacement above about 180 K. The increase, dubbed the "dynamical transition," is controversial. We introduce a new interpretation of the Mossbauer Effect in proteins and demonstrate that no dynamical transition is required. The increase in the mean-square displacement and the broad line are caused by fluctuations in the protein's hydration shell. Using the dielectric spectrum of these fluctuations, we predict the shape of the Mossbauer spectrum from 80 to 295 K with one dimensionless coefficient.