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See detailThermoelectric properties of the unfilled skutterudite FeSb3 from first-principles and Seebeck local probes
Lemal, Sébastien ULg; Nguyen, Ngoc; de Boor, Johannes et al

in Physical Review. B, Condensed Matter and Materials Physics (2015)

Using a combination of first-principles calculations and experimental transport measurements, we study the electronic and magnetic structure of the unfilled skutterudite FeSb3. We employ the hybrid ... [more ▼]

Using a combination of first-principles calculations and experimental transport measurements, we study the electronic and magnetic structure of the unfilled skutterudite FeSb3. We employ the hybrid functional approach for exchange-correlation. The ground state is determined to be anti-ferromagnetic with an atomic magnetic moment of 1.6 uB/Fe. The Néel temperature Tn is estimated at 6 K, in agreement with experiments which found a paramagnetic state down to 10 K. The ground state is semiconducting, with a small electronic gap of 33 meV, also consistent with previous experiments on films. Charge carrier concentrations are estimated from Hall resistance measurements. The Seebeck coefficient is measured and mapped using a scanning probe at room temperature that yields an average value of 38.6 uV/K, slightly lower than the theoretical result. The theoretical conductivity is analyzed as a function of temperature and concentration of charge carriers. [less ▲]

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See detailHighly dispersed iron xerogel catalysts for p-nitrophenol degradation by photo-Fenton effects
Mahy, Julien ULg; Tasseroul, Ludivine ULg; Zubiaur, Anthony ULg et al

in Microporous and Mesoporous Materials (2014), 197

Several iron xerogel catalysts were synthesized by hydrolysis and condensation of tetraethoxysilane (TEOS) and 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) which is able to form a chelate with iron ... [more ▼]

Several iron xerogel catalysts were synthesized by hydrolysis and condensation of tetraethoxysilane (TEOS) and 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) which is able to form a chelate with iron ions. The EDAS/TEOS ratio strongly influences the texture of xerogel catalysts. The specific surface area and the micro- and mesoporous volume increase with this ratio. It seems that EDAS plays a nucleating agent role for silica particles and allows to anchor Fe-based moieties inside the silica network. Iron oxide nanoparticles of diameter 1-1.5 nm and Fe3+ ions result, encapsulated in silica particles with sizes of about 10-30 nm in diameter. The iron species was determined by Mössbauer spectroscopy and magnetometry measurements and only Fe3+ species were observed in xerogel catalysts. The Fenton and photo-Fenton effect of these catalysts were evaluated on the degradation of p-nitrophenol in aqueous media under different conditions. Results show that in the presence of H2O2, iron xerogel catalysts present a photo-Fenton effect, reaching 99 % of degradation after 24 h. [less ▲]

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See detailHighly dispersed iron xerogel catalysts for p-nitrophenol degradation by photo-Fenton effects
Mahy, Julien ULg; Tasseroul, Ludivine ULg; Zubiaur, Anthony ULg et al

Poster (2014, July)

Since the beginning of the industrial era, the various human activities have increased steadily, leading to a rapid technological development and a high population growth. Thus, the expansion of the ... [more ▼]

Since the beginning of the industrial era, the various human activities have increased steadily, leading to a rapid technological development and a high population growth. Thus, the expansion of the industry has heavily polluted the atmosphere, soil and water with negative consequences for humans and environment [1]. To decrease this pollution, it exists various treatment methods: chemical, physical and biological [2,3]. Among all these methods, a recent way of treatment is the degradation of pollutants in soils or waters by Fenton and photo-Fenton reactions [3] which use H2O2, iron-based compounds and UV light. In this way, several Fe2O3/SiO2 xerogel catalysts were synthesized by cogelation method by hydrolysis and condensation of tetraethoxysilane (TEOS) and 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) which is able to form a chelate with iron ions [4]. Five samples were synthesized: four samples with different percentage of iron (0.5, 1, 1.5 and 2.5 theoretical wt% confirmed by ICP-AES measurements), and a sample of pure silica. TEM pictures, nitrogen adsorption-desorption and mercury porosimetry measurements have established that EDAS plays a role of nucleating agent of silica particles [5,6] and allows to anchor iron particles inside silica network [4]. Indeed, it results iron nanoparticles of diameter 1-1.5 nm encapsulated in silica particles with sizes of about 10-30 nm in diameter. The species of iron was determined by Mössbauer spectroscopy and only Fe3+ ions were observed in xerogel catalysts. Then, the Fenton and photo-Fenton effect of these catalysts were evaluated on the degradation of p-nitrophenol (PNP) in aqueous medium in different conditions. Results show that Fe2O3/SiO2 xerogels present a photo-Fenton effect with H2O2, reaching with a sample 99 % of degradation after 24 h. [1] M. A. Khan, A. M. Ghouri, Environmental pollution: its effects on life and its remedies, Journal of Arts, Science & Commerce (Vol. 2), 2011, pg 276-285. [2] M. S. Kuyukina , I. B. Ivshina, Biology of rhodococcus: chapter 9, Springer, 2010, pg 232-256. [3] J. J. Pignatello, E. Oliveros, A. MacKay, Advanced Oxidation Processes for Organic Contaminant Destruction Based on the Fenton Reaction and Related Chemistry, Critical Reviews in Environmental Science and Technology (Vol. 36), 2006, pg 1-84. [4] B. Heinrichs, L. Rebbouh, J.W. Geus, S. Lambert, H.C.L. Abbenhuis, F. Grandjean, G.J. Long, J.-P. Pirard, R.A. van Santen, Iron (III) species dispersed in porous silica through sol-gel chemistry, Journal of Non-Crystalline Solids (Vol. 354), 2008, pg 665-672. [5] S. Lambert, C. Alié, J.-P. Pirard, B. Heinrichs, Study of textural properties and nucleation phenomenon in Pd/SiO2 , Ag/SiO2 and Cu/SiO2 cogelled xerogel catalysts, Journal of Non-Crystalline Solids (Vol. 342), 2004, pg 70-81. [6] B. Heinrichs, S. Lambert , N. Job , J.-P. Pirard, in "Catalyst Preparation: Science and Engineering, J. R. Regalbuto (Ed.)", CRC Press, Taylor & Francis Group, Boca Raton, 2007, p. 163-208. [less ▲]

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See detailLattice dynamics in intermetallic Mg2Ge and Mg2Si
Bessas, D.; Simon, R. E.; Friese, K. et al

in Journal of Physics : Condensed Matter (2014), 26(48),

The lattice dynamics of polycrystalline Mg2Ge and Mg2Si are compared using both microscopic and macroscopic measurements as well as theoretical calculations. The volume thermal expansion coefficient ... [more ▼]

The lattice dynamics of polycrystalline Mg2Ge and Mg2Si are compared using both microscopic and macroscopic measurements as well as theoretical calculations. The volume thermal expansion coefficient between 200 and 300K was found to be 4.37(5)•10-5K-1 in Mg2Ge, compared to 3.69(5)•10-5K-1 in Mg2Si. Inelastic neutron scattering measurements yield densities of phonon states which are in line with theoretical calculations. The microscopic data were corroborated with macroscopic calorimetry measurements and provide quantified values for anharmonicity. The estimated macroscopic Grneisen parameter is, γMg 2Si=1.17(5) and γMg 2Ge=1.46(5) at 295K, in excellent agreement with Raman scattering data. Although the element specific mean force constants are practically the same, in Mg2Ge and Mg2Si, a mass homology relation alone cannot reproduce the difference in the partial densities of vibrational states in these compounds and differences in elemental bonding should be taken into account. © 2014 IOP Publishing Ltd. [less ▲]

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See detailInterpenetrated (8,3)-c and (10,3)-b metal-organic frameworks based on {FeIII 3} and {FeIII 2CoII} pivalate spin clusters
Botezat, O.; Van Leusen, J.; Kravtsov, V. C. et al

in Crystal Growth & Design (2014), 14(9), 4721-4728

Two new magnetic cluster-based 3D coordination polymers consisting of μ3-oxo-centered cationic homometallic [FeIII 3O(O2CCMe3)6]+ or neutral heterometallic [FeIII 2CoIIO(O 2CCMe3)6] coordination clusters ... [more ▼]

Two new magnetic cluster-based 3D coordination polymers consisting of μ3-oxo-centered cationic homometallic [FeIII 3O(O2CCMe3)6]+ or neutral heterometallic [FeIII 2CoIIO(O 2CCMe3)6] coordination clusters bridged by different N,N′-donor ligands into three-dimensional networks of {[Fe 3O(O2CCMe3)6(4,4′-bpy) 1.5](OH)·0.75(CH2Cl2)·x(H 2O)}n (1, x ≤ 8) and {[Fe2CoO(O 2CCMe3)6(bpe)0.5(pyz)]}n (2) (where 4,4′-bpy = 4,4′-bipyridine; bpe = 1,2′-bis(4- pyridyl)ethylene; pyz = pyrazine) have been prepared under solvothermal conditions. Single-crystal X-ray diffraction studies reveal the existence of a 6-fold interpenetrated network with rare (8,3)-c (etc) topology for 1 and a 3-fold interpenetrated network with (10,3)-b (ths) topology for 2. The interpenetration effectively results in very low BET surface areas, and the compounds have to be regarded as nonporous. Magnetic studies of 1 and 2 point to both ferro- and antiferromagnetic intra- and intercluster exchange interactions between the isotropic FeIII and the strongly anisotropic Co II spin centers. 57Fe Mössbauer spectroscopy confirms the uniform ferric (+III) valence state in both 1 and 2, and low-temperature data for 1 point toward distinct hyperfine fields for the Fe sites. © 2014 American Chemical Society. [less ▲]

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See detailSpin excitations in cubic maghemite nanoparticles studied by time-of-flight neutron spectroscopy
Disch, S.; Hermann, Raphaël ULg; Wetterskog, E. et al

in Physical Review. B, Condensed Matter and Materials Physics (2014), 89(6),

We have determined the field dependence of collective magnetic excitations in iron oxide nanoparticles of cubic shape with 8.42(2) nm edge length and a narrow log normal size distribution of 8.2(2)% using ... [more ▼]

We have determined the field dependence of collective magnetic excitations in iron oxide nanoparticles of cubic shape with 8.42(2) nm edge length and a narrow log normal size distribution of 8.2(2)% using time-of-flight neutron spectroscopy. The energy dependence of the uniform precession modes was investigated up to 5 T applied field and yields a Landé factor g=2.05(2) as expected for maghemite (γ-Fe2O3) nanoparticles. A large effective anisotropy field of BA,eff=0.45(16) T was determined, in excellent agreement with macroscopic measurements. This anisotropy is attributed to enhanced shape anisotropy in these monodisperse cubic nanoparticles. The combination of our results with macroscopic magnetization information provides a consistent view of the energy scales of superparamagnetic relaxation and collective magnetic excitations in magnetic nanoparticles. © 2014 American Physical Society. [less ▲]

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See detailEvolution of phase segregation and eutectic structures in AgPb 18SbTe20
Dadda, J.; Müller, E.; Perlt, S. et al

in Physica Status Solidi A. Applications and Materials Science (2014), 211(6), 1276-1281

The evolution of phase segregation in stoichiometric quenched AgPb mSbTe2+m (m = 18, Lead-Antimony-Silver-Tellurium - LAST-18) compounds was studied starting from the known pseudo-binary diagrams among ... [more ▼]

The evolution of phase segregation in stoichiometric quenched AgPb mSbTe2+m (m = 18, Lead-Antimony-Silver-Tellurium - LAST-18) compounds was studied starting from the known pseudo-binary diagrams among Ag2Te, PbTe, Sb2Te3 and AgSbTe 2. The compositions of secondary phases indicate that liquid phase during cooling, even under quenching conditions, follows mainly the liquidus line on the 2PbTe-Ag0.45Sb0.55Te1.05 quasi-binary section of the phase diagram until it reaches a critical point (18 mol.% of 2PbTe) and then turns to Ag2Te- and Sb2Te 3-rich sides of quasi-ternary system. This has led to the formation of various secondary phases at various stages during the solidification, whose microstructural features and morphology strongly depend upon their chemical composition. Moreover, during solidification the local compositional fluctuations of liquid phase in combination with the shift of liquid composition towards Sb-rich side of the phase diagram resulted in the development of eutectic microstructures in some regions of LAST-18 matrix phase. This suggests there exists a miscibility gap and eutectic point below 600 C on the 2PbTe-Ag0.45Sb0.55Te1.05 boundary line. These eutectic lamellar structures with a cumulative composition close to LAST-3 are on the 200-500 nm length scales and possess thermal conductivity of 0.55-0.65 W/m K at room temperature. The low thermal conductivity of lamellar eutectic structures was later confirmed on bulk samples using laser flash analysis, where the samples were synthesized by quenching and annealing. The results clearly demonstrate that one can engineer the microstructures in LAST compounds by selecting the appropriate initial composition from quasi PbTe-Ag 2Te-Sb2Te3 ternary phase diagram to lower the thermal conductivity further. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. [less ▲]

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See detailNuclear probes for battery materials investigations: Mössbauer spectroscopy, nuclear scattering, and neutron scattering
Hermann, Raphaël ULg; Mahmoud, A.; Brisbois, Magali ULg et al

in Proceedings of 2014 International Renewable and Sustainable Energy Conference, IRSEC 2014 (2014)

Selected examples of application of Mössbauer spectroscopy, nuclear resonance scattering of synchrotron radiation, and neutron scattering to battery and related materials research are presented. The ... [more ▼]

Selected examples of application of Mössbauer spectroscopy, nuclear resonance scattering of synchrotron radiation, and neutron scattering to battery and related materials research are presented. The charms of Mössbauer spectroscopy as a technique for screening materials, for detailed structure investigations, and for in situ measurements are illustrated. New developments of nuclear resonance scattering for isotopes with 30-90 keV resonant energy are presented. Structural, diffusive and dynamic studies utilizing neutron scattering are exemplified. © 2014 IEEE. [less ▲]

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See detailEnhanced Debye level in nano Zn1+xSb, FeSb2, and NiSb: Nuclear inelastic spectroscopy on121 Sb
Claudio, T.; Bessas, D.; Birke, C. S. et al

in Physica Status Solidi B. Basic Research (2014), 251(5), 919-923

The121 Sb partial density of phonon states (DPS) in nanopowder antimonides were obtained with nuclear inelastic scattering on Zn1+xSb, FeSb2, and NiSb prepared by a wet chemistry route. The DPS is ... [more ▼]

The121 Sb partial density of phonon states (DPS) in nanopowder antimonides were obtained with nuclear inelastic scattering on Zn1+xSb, FeSb2, and NiSb prepared by a wet chemistry route. The DPS is compared with the bulk counterpart. An increase of the Debye level indicative of a decrease of the isothermal speed of sound is systematically observed. This observation reveals that the decrease in speed of sound observed in nanostructured thermoelectric materials is not restricted to sintered nanocomposites. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. [less ▲]

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See detailThermal transport in nanoscale semiconductors
Nielsch, K.; Schierning, G.; Hermann, Raphaël ULg et al

in Semiconductor Science and Technology (2014), 29(12),

[No abstract available]

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See detailNanocrystalline silicon: Lattice dynamics and enhanced thermoelectric properties
Claudio, T.; Stein, N.; Stroppa, D. G. et al

in Physical Chemistry Chemical Physics (2014), 16(47), 25701-25709

Silicon has several advantages when compared to other thermoelectric materials, but until recently it was not used for thermoelectric applications due to its high thermal conductivity, 156 W K-1 m-1 at ... [more ▼]

Silicon has several advantages when compared to other thermoelectric materials, but until recently it was not used for thermoelectric applications due to its high thermal conductivity, 156 W K-1 m-1 at room temperature. Nanostructuration as means to decrease thermal transport through enhanced phonon scattering has been a subject of many studies. In this work we have evaluated the effects of nanostructuration on the lattice dynamics of bulk nanocrystalline doped silicon. The samples were prepared by gas phase synthesis, followed by current and pressure assisted sintering. The heat capacity, density of phonons states, and elastic constants were measured, which all reveal a significant, ≈25%, reduction in the speed of sound. The samples present a significantly decreased lattice thermal conductivity, ≈25 W K-1 m-1, which, combined with a very high carrier mobility, results in a dimensionless figure of merit with a competitive value that peaks at ZT ≈ 0.57 at 973°C. Due to its easily scalable and extremely low-cost production process, nanocrystalline Si prepared by gas phase synthesis followed by sintering could become the material of choice for high temperature thermoelectric generators. © the Owner Societies 2014. [less ▲]

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See detail121Sb and125Te nuclear inelastic scattering in Sb2Te3under high pressure
Simon, R. E.; Sergueev, I.; Kantor, I. et al

in Semiconductor Science and Technology (2014), 29(12),

We investigated the lattice dynamics of Sb2Te3 under high pressure using 121Sb and 125Te nuclear inelastic scattering of synchrotron radiation. We measured the room temperature 121Sb and 125Te inelastic ... [more ▼]

We investigated the lattice dynamics of Sb2Te3 under high pressure using 121Sb and 125Te nuclear inelastic scattering of synchrotron radiation. We measured the room temperature 121Sb and 125Te inelastic spectra at 15(1) GPa and 77(3) GPa and extracted the Te and Sb element specific density of phonon states of δ-Sb2Te3 at 77(3) GPa. X-ray diffraction confirms the sample to be in the cubic δ-Sb2Te3 phase with space group Im3m and lattice constant a = 3.268(4) A˚. The total density of phonon states of δ-Sb2Te3 strongly resembles the one of amorphous GeSb2Te4, suggesting the presence of covalent bonding in contrast to the resonance bonding in α-Sb2Te3. From the density of phonon states of δ-Sb2Te3 a mean speed of sound of 2.61(6) km s-1 and Debye temperatures of 278(10) K for Te and 296(10) K for Sb were determined. © 2014 IOP Publishing Ltd. [less ▲]

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See detailNuclear forward scattering of synchrotron radiation by Ru 99
Bessas, D.; Merkel, D. G.; Chumakov, A. I. et al

in Physical Review Letters (2014), 113(14),

We measured nuclear forward scattering spectra utilizing the Ru99 transition, 89.571(3) keV, with a notably mixed E2/M1 multipolarity. The extension of the standard evaluation routines to include mixed ... [more ▼]

We measured nuclear forward scattering spectra utilizing the Ru99 transition, 89.571(3) keV, with a notably mixed E2/M1 multipolarity. The extension of the standard evaluation routines to include mixed multipolarity allows us to extract electric and magnetic hyperfine interactions from Ru99-containing compounds. This paves the way for several other high-energy Mössbauer transitions, E∼90keV. The high energy of such transitions allows for operando nuclear forward scattering studies in real devices. © 2014 American Physical Society. [less ▲]

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See detailMagnetism and lattice dynamics of FeNCN compared to FeO
Herlitschke, M.; Tchougréeff, A. L.; Soudackov, A. V. et al

in New Journal of Chemistry (2014), 38(10), 4670-4677

Three-dimensional non-oxidic extended frameworks offer the possibility to design novel materials with unique properties, which can be different from their oxide analogues. Here, we present first ... [more ▼]

Three-dimensional non-oxidic extended frameworks offer the possibility to design novel materials with unique properties, which can be different from their oxide analogues. Here, we present first experimental results concerning unusual magnetic properties of FeNCN, investigated using Mössbauer spectroscopy and magnetometry between 5 and 380 K. This study reveals an unconventional behaviour of the magnetic parameters below the Néel temperature of 350 K, i.e., the hyperfine field on iron decreases with decreasing temperature. At room temperature, quadrupole and hyperfine magnetic field interaction energies are comparable in magnitude, which leads to a rare five-line absorption spectrum. We suggest that these features in the hyperfine field are caused by the combination of a small Fermi contact term and a temperature-dependent contribution from the orbital momentum and the dipole term. One additional spectral component is observed, which exhibits a magnetic relaxation behaviour and slows down at low temperatures to yield a sextet. The magnetometry data suggest that the antiferromagnetic FeNCN is rich in structural distortions, which results in a splitting of the field-cooled and zero-field-cooled curves. The lattice dynamics of FeNCN were investigated using nuclear inelastic scattering. The comparison of the obtained data with literature data of iron monoxide reveals very similar iron phonon modes with a small softening and a slightly reduced sound velocity. This journal is © the Partner Organisations 2014. [less ▲]

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See detailRole of disorder in the thermodynamics and atomic dynamics of glasses
Chumakov, A. I.; Monaco, G.; Fontana, A. et al

in Physical Review Letters (2014), 112(2),

We measured the density of vibrational states (DOS) and the specific heat of various glassy and crystalline polymorphs of SiO2. The typical (ambient) glass shows a well-known excess of specific heat ... [more ▼]

We measured the density of vibrational states (DOS) and the specific heat of various glassy and crystalline polymorphs of SiO2. The typical (ambient) glass shows a well-known excess of specific heat relative to the typical crystal (α-quartz). This, however, holds when comparing a lower-density glass to a higher-density crystal. For glassy and crystalline polymorphs with matched densities, the DOS of the glass appears as the smoothed counterpart of the DOS of the corresponding crystal; it reveals the same number of the excess states relative to the Debye model, the same number of all states in the low-energy region, and it provides the same specific heat. This shows that glasses have higher specific heat than crystals not due to disorder, but because the typical glass has lower density than the typical crystal. © 2014 American Physical Society. [less ▲]

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See detailQuadrupole splitting and isomer shifts in Te oxides investigated using nuclear forward scattering
Klobes, B.; Barrier, N.; Vertruyen, Bénédicte ULg et al

in Hyperfine Interactions (2014), 226(1-3), 713-719

Nuclear forward scattering by 125Te is a viable alternative to conventional 125Te Mössbauer spectroscopy avoiding all source related issues. Using reference compounds with known hyperfine parameters and ... [more ▼]

Nuclear forward scattering by 125Te is a viable alternative to conventional 125Te Mössbauer spectroscopy avoiding all source related issues. Using reference compounds with known hyperfine parameters and Te oxides exhibiting stereochemically active lone pairs, we show that nuclear forward scattering by 125Te can be reliably used to extract quadrupole splitting energy and relative isomer shift. The rough correlation between Te-Ocoordination and quadrupole splitting energy as put forward by Takeda and Greenwood (J. Chem. Soc. Dalton, 2207, 1975), is corroborated by the presented results. © 2014 Springer Science+Business Media Dordrecht. [less ▲]

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See detailComparison of functionalized carbon nanofibers and multi-walled carbon nanotubes as supports for Fe-Co nanoparticles
Vidick, Deborah; Herlitschke, Marcus; Poleunis, Claude et al

in Journal of Materials Chemistry A (2013), 1(6), 2050-2063

Multi-walled carbon nanotubes (MWCNT) and nanofibers (CNF) have been functionalized at their surfaces with chelating phosphine (PPh2) and ammonium (NMe3+) groups, as anchoring sites for metal complexes ... [more ▼]

Multi-walled carbon nanotubes (MWCNT) and nanofibers (CNF) have been functionalized at their surfaces with chelating phosphine (PPh2) and ammonium (NMe3+) groups, as anchoring sites for metal complexes. The surface functionalization has been monitored by XPS, elemental analyses, N-2 physisorption and/or SEM surface morphology analysis at each step. Bimetallic Fe-Co nanoparticles from two different starting cluster complexes, [HFeCo3(CO)(12)] (1) and (NEt4)[FeCo3(CO)(12)] (2), have been deposited onto the surfaces of the functionalized MWCNT and CNF as well as their pristine forms for comparison. The samples have been fully characterized before and after thermal treatment. The obtained nanoparticles were shown by TEM to be better dispersed and of smaller size on functionalized than on pristine supports. Magnetic characterization revealed blocked superparamagnetic Fe-Co nanoparticles together with paramagnetic ions on CNF as well as MWCNT. [less ▲]

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See detailLattice dynamics and structure of GeTe, SnTe and PbTe
Pereira, Paula Bauer; Sergueev, Ilya; Gorsse, Stephane et al

in PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS (2013), 250(7), 1300-1307

The lattice dynamics in the IV-VI compounds GeTe, SnTe and PbTe were studied by Te-125 and Sn-119 nuclear inelastic scattering and the obtained partial density of phonon states were compared with ... [more ▼]

The lattice dynamics in the IV-VI compounds GeTe, SnTe and PbTe were studied by Te-125 and Sn-119 nuclear inelastic scattering and the obtained partial density of phonon states were compared with published theoretical calculations. The phase purity and structure were characterized by high energy X-ray diffraction. The effect of the atomic arrangement, rhombohedral for GeTe and cubic for SnTe and PbTe, is visible in the density of phonon states. Vibrational properties are found to be in good agreement with available calculated data and the softer character of the NaCl-type structures in comparison with the rhombohedral GeTe is confirmed. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [less ▲]

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See detailPhonon spectroscopy in a Bi2Te3 nanowire array
Bessas, Dimitrios; Toellner, William; Aabdin, Zainul et al

in NANOSCALE (2013), 5(21), 10629-10635

The lattice dynamics in an array of 56 nm diameter Bi2Te3 nanowires embedded in a self-ordered amorphous alumina membrane were investigated microscopically using Te-125 nuclear inelastic scattering. The ... [more ▼]

The lattice dynamics in an array of 56 nm diameter Bi2Te3 nanowires embedded in a self-ordered amorphous alumina membrane were investigated microscopically using Te-125 nuclear inelastic scattering. The element specific density of phonon states is measured on nanowires in two perpendicular orientations and the speed of sound is extracted. Combined high energy synchrotron radiation diffraction and transmission electron microscopy was carried out on the same sample and the crystallinity was investigated. The nanowires grow almost perpendicular to the c-axis, partly with twinning. The average speed of sound in the 56 nm diameter Bi2Te3 nanowires is similar to 7% smaller with respect to bulk Bi2Te3 and a decrease in the macroscopic lattice thermal conductivity by similar to 13% due to nanostructuration and to the reduced speed of sound is predicted. [less ▲]

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