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See detailCombined Mossbauer Spectral and Density Functional Theory Determination of the Magnetic Easy-Axis in Two High-Spin Iron(II) 2-Pyrazinecarboxylate Complexes
Long, G. J.; Tanase, S.; Remacle, Françoise ULg et al

in Inorganic Chemistry (2009), 48(17), 8173-8179

A combination of density functional theory (DFT) calculations and Mossbauer spectroscopy has been used to determine that the magnetic easy-axis is coincident with its crystallographic c-axis in [Fe(pca)(2 ... [more ▼]

A combination of density functional theory (DFT) calculations and Mossbauer spectroscopy has been used to determine that the magnetic easy-axis is coincident with its crystallographic c-axis in [Fe(pca)(2)(py)(2)]center dot py, where pac is the 2-pyrazinecarboxylate ligand. This easy-axis bisects the approximately axial O-Fe-O coordination axes of molecules adjacent to each other along the b-axis. In {[Fe(pca)(2)(H2O)]center dot H2O}(n) the easy magnetic axis is not coincident with any of its crystallographic axes nor with the Fe-O(water) coordination axis, but is coincident with one of the Fe center dot center dot center dot Fe axes in the crystal structure. The DFT calculations, which use the B3LYP functional and the 6-311 + +G(d,p) basis set, yield s-electron probability densities and electric field gradient tensors for the iron(II) ion that are in excellent agreement with the observed iron-57 Mossbauer spectral isomer shifts and quadrupole interactions. The gas phase results are very similar for calculations based either on the X-ray structures of the two complexes or on their optimized structures; the optimized structures indicate that the iron to ligand bond distances increase in the absence of any solid-state lattice interactions. The results of a normal coordinate vibrational mode analysis of the two optimized structures are compared with the observed infrared spectra. [less ▲]

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See detailEinstein oscillators that impede thermal transport
Hermann, Raphaël ULg; Grandjean, Fernande ULg; Long, G. J.

in American Journal of Physics (2005), 73(2), 110-118

The Einstein model of a solid usually lacks a clear illustration in introductory solid-state physics courses because most solids are much better described by the Debye model. Filled antimony skutterudites ... [more ▼]

The Einstein model of a solid usually lacks a clear illustration in introductory solid-state physics courses because most solids are much better described by the Debye model. Filled antimony skutterudites, materials that have recently attracted much attention because of their potential for thermoelectric applications, provide a canonical illustration of the Einstein model. The filling atoms are loosely bound in the atomic cage formed by their neighbors, and hence their description as independent harmonic oscillators is adequate. Simple models for the heat capacity and thermal conductivity of a solid are introduced, with emphasis on the density of vibrational states. These models are used in conjunction with experimental results obtained from heat capacity and inelastic neutron scattering measurements to demonstrate the applicability of the concept of the Einstein oscillator to the filling guests in antimony skutterudites. The importance of these Einstein oscillators for impeding thermal transport is discussed and some simple problems involving the heat capacity, thermal conductivity, and inelastic neutron scattering are proposed. (C) 2005 American Association of Physics Teachers. [less ▲]

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See detailNeutron and nuclear inelastic scattering study of the Einstein oscillators in Ba-, Sr-, and Eu-filled germanium clathrates
Hermann, Raphaël ULg; Schweika, W.; Leupold, O. et al

in Physical Review b (2005), 72(17),

Inelastic neutron scattering measurements on Ba8Ga16Ge30 and Sr8Ga16Ge30 indicate the presence of soft local modes with Einstein oscillator energies of 4.9 +/- 0.1 and 4.4 +/- 0.1 meV, modes which are ... [more ▼]

Inelastic neutron scattering measurements on Ba8Ga16Ge30 and Sr8Ga16Ge30 indicate the presence of soft local modes with Einstein oscillator energies of 4.9 +/- 0.1 and 4.4 +/- 0.1 meV, modes which are associated with the lowest "rattling" mode of the Ba(B) and Sr(B) guests, respectively. Nuclear inelastic scattering measurements on Eu8Ga16Ge30 yield Einstein oscillator energies of between 3.0 +/- 0.3 and 7.5 +/- 1.2 meV for the different modes of the Eu guests. Further, the resonant character of the measurements on Eu8Ga16Ge30 reveals, without question, that neither of the Eu guests exhibit any vibrational modes above 9 meV. [less ▲]

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See detailStrongly decoupled europium and iron vibrational modes in filled skutterudites
Long, G. J.; Hermann, Raphaël ULg; Grandjean, Fernande ULg et al

in Physical Review b (2005), 71(14),

The europium partial vibrational density of states (DOS) in EuFe4Sb12 and the iron partial vibrational DOS in both EuFe4Sb12 and (CeFe4Sb12)-Fe-57 have been obtained by nuclear inelastic scattering. The ... [more ▼]

The europium partial vibrational density of states (DOS) in EuFe4Sb12 and the iron partial vibrational DOS in both EuFe4Sb12 and (CeFe4Sb12)-Fe-57 have been obtained by nuclear inelastic scattering. The results reveal the strong independence of the iron and rare-earth vibrational modes. The cage filling europium only participates significantly to the low-energy local vibrational modes. The force constants have been obtained from the measured probability of nuclear absorption. The energies of the peaks in the europium and iron DOS are in excellent agreement with the calculated DOS in LaFe4Sb12. The results indicate that nuclear inelastic scattering is the technique of choice for the study of the localized vibrational modes in thermoelectric "phonon glass" materials. [less ▲]

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See detailA Mossbauer spectral study of some iron nitride-based nanocomposites prepared by ball milling
Grandjean, Fernande ULg; Hermann, Raphaël ULg; Long, G. J. et al

in Journal of Magnetism & Magnetic Materials (2005), 292

Powder mixtures of (FeyN)(x) and (Al2O3)(1-x) or (SiO2)(1-x) with x = 0.2 and 0.6 and y = 3.8 have been ball milled for 4, 8, 16, 32, 64, and 128 h and their magnetic properties and Mossbauer spectra have ... [more ▼]

Powder mixtures of (FeyN)(x) and (Al2O3)(1-x) or (SiO2)(1-x) with x = 0.2 and 0.6 and y = 3.8 have been ball milled for 4, 8, 16, 32, 64, and 128 h and their magnetic properties and Mossbauer spectra have been measured. The 5 and 295 K saturation magnetizations decrease with increasing milling time as a result of decreasing particle sizes. Fits with the Langevin function of the field dependence of the magnetization yield particle sizes that are slightly smaller than those determined from a Scherrer analysis of the broadening of the X-ray diffraction peaks. The Mossbauer spectra have been fit with a distribution of hyperfine fields between 0 and 40 T and the peaks in the distribution assigned to the different iron nitride phases present in the nanocomposites. This analysis of the Mossbauer spectra indicates that the gamma'-Fe4N phase present in FeyN is transformed into epsilon-Fe3+xN and alpha-iron by the milling process. The weighted average field decreases and the weighted average isomer shift increases with milling time, as expected for the simultaneous effects of size reduction, the above phase transformation, and mixing with the oxides. A peak in the hyperfine field distribution at 4 T indicates the presence of small superparamagnetic particles, a presence which is also confirmed by the temperature dependence of the Mossbauer spectra and the failure of the magnetization to saturate even at applied fields of 5.5T. (c) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailComplex magnetic ordering in Eu3InP3: A new rare earth metal zintl compound
Jiang, J.; Payne, A. C.; Olmstead, M. M. et al

in Inorganic Chemistry (2005), 44(7), 2189-2197

Eu(3)lnP(3) has been prepared as large single crystals with an indium flux reaction. The structure of the new compound is isotypic to Sr(3)lnP(3) and crystallizes in the orthorhombic space group Pnma with ... [more ▼]

Eu(3)lnP(3) has been prepared as large single crystals with an indium flux reaction. The structure of the new compound is isotypic to Sr(3)lnP(3) and crystallizes in the orthorhombic space group Pnma with unit cell dimensions of a = 12.6517(15) angstrom, b = 4.2683(5) angstrom, and c = 13.5643(14) angstrom (Z = 4, T = 140 K, R1 = 0.0404, wR2 = 0,0971 for all data). The structure consists of one-dimensional chains of corner-shared distorted [InP2P2/2](6-) tetrahedra separated by rows of Eu2+ ions. Two of the three crystallographically distinct europium sites have a short Eu(1)-Eu(2) distance of 3.5954(7) angstrom, which yields Eu-Eu dimers. The Eu-P bond distances range from 2.974(2) to 3.166(2) angstrom. The temperature dependence of the conductivity indicates that Eu(3)lnP(3) is a small band gap semiconductor. Both magnetization and Eu-151 Mossbauer spectral measurements indicate that the europium in Eu(3)lnP(3) is divalent and that at least two magnetic transitions occur. Magnetization studies reveal magnetic transitions at 14, 10.4, and similar to 5 K. These transitions are also observed in heat capacity studies of Eu(3)lnP(3). The Mossbauer spectra indicate that the two europium sites are ordered at 12 K and that all three europium sites are ordered at 8 K. [less ▲]

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