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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 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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See detailLattice instabilities in bulk EuTiO3
Bessas, D.; Rushchanskii, K. Z.; Kachlik, M. et al

in PHYSICAL REVIEW B (2013), 88(14),

The phase purity and the lattice dynamics in bulk EuTiO3 were investigated both microscopically, using x-ray and neutron diffraction, Eu-151-Mossbauer spectroscopy, and Eu-151 nuclear inelastic scattering ... [more ▼]

The phase purity and the lattice dynamics in bulk EuTiO3 were investigated both microscopically, using x-ray and neutron diffraction, Eu-151-Mossbauer spectroscopy, and Eu-151 nuclear inelastic scattering, and macroscopically using calorimetry, resonant ultrasound spectroscopy, and magnetometry. Furthermore, our investigations were corroborated by ab initio theoretical studies. The perovskite symmetry, Pm (3) over barm, is unstable at the M- and R-points of the Brillouin zone. The lattice instabilities are lifted when the structure relaxes in one of the symmetries: I4/mcm, Imma, R (3) over barc with relative relaxation energy around -25 meV. Intimate phase analysis confirmed phase purity of our ceramics. A prominent peak in the Eu specific density of phonon states at 11.5 meV can be modeled in all candidate symmetries. A stiffening on heating around room temperature is indicative of a phase transition similar to the one observed in SrTiO3, however, although previous studies reported the structural phase transition to the tetragonal I4/mcm phase our detailed sample purity analysis and thorough structural studies using complementary techniques did not confirm a direct phase transition. Instead, in the same temperature range, Eu delocalization is observed which might explain the lattice dynamical instabilities. [less ▲]

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See detailStructural diversity in iron oxide nanoparticle assemblies as directed by particle morphology and orientation
Disch, Sabrina; Wetterskog, Erik; Hermann, Raphael ULg et al

in NANOSCALE (2013), 5(9), 3969-3975

The mesostructure of ordered arrays of anisotropic nanoparticles is controlled by a combination of packing constraints and interparticle interactions, two factors that are strongly dependent on the ... [more ▼]

The mesostructure of ordered arrays of anisotropic nanoparticles is controlled by a combination of packing constraints and interparticle interactions, two factors that are strongly dependent on the particle morphology. We have investigated how the degree of truncation of iron oxide nanocubes controls the mesostructure and particle orientation in drop cast mesocrystal arrays. The combination of grazing incidence small-angle X-ray scattering and scanning electron microscopy shows that mesocrystals of highly truncated cubic nanoparticles assemble in an fcc-type mesostructure, similar to arrays formed by iron oxide nanospheres, but with a significantly reduced packing density and displaying two different growth orientations. Strong satellite reflections in the GISAXS pattern indicate a commensurate mesoscopic superstructure that is related to stacking faults in mesocrystals of the anisotropic nanocubes. Our results show how subtle variation in shape anisotropy can induce oriented arrangements of nanoparticles of different structures and also create mesoscopic superstructures of larger periodicity. [less ▲]

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See detailEffects of impurities on the lattice dynamics of nanocrystalline silicon for thermoelectric application
Claudio, Tania; Schierning, Gabi; Theissmann, Ralf et al

in JOURNAL OF MATERIALS SCIENCE (2013), 48(7), 2836-2845

Doped silicon nanoparticles were exposed to air and sintered to form nanocrystalline silicon. The composition, microstructure, and structural defects were investigated with TEM, XRD, and PDF and the ... [more ▼]

Doped silicon nanoparticles were exposed to air and sintered to form nanocrystalline silicon. The composition, microstructure, and structural defects were investigated with TEM, XRD, and PDF and the lattice dynamics was evaluated with measurements of the heat capacity, of the elastic constants with resonant ultrasound spectroscopy and of the density of phonon states (DPS) with inelastic neutron scattering. The results were combined and reveal that the samples contain a large amount of silicon dioxide and exhibit properties that deviate from bulk silicon. Both in the reduced DPS and in the heat capacity a Boson peak at low energies, characteristic of amorphous SiO2, is observed. The thermal conductivity is strongly reduced due to nanostructuration and the incorporation of impurities. [less ▲]

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See detailEffect of pressure, temperature, fluorine doping, and rare earth elements on the phonon density of states of LFeAsO studied by nuclear inelastic scattering
Sergueev, I.; Hermann, Raphael ULg; Bessas, D. et al

in PHYSICAL REVIEW B (2013), 87(6), 064302-9

We have performed systematic studies of the lattice dynamics in LFeAsO (L = La, Ce, Pr, Nd, Sm) in the parent and in the similar to 10% F-doped compounds as a function of pressure and temperature. We have ... [more ▼]

We have performed systematic studies of the lattice dynamics in LFeAsO (L = La, Ce, Pr, Nd, Sm) in the parent and in the similar to 10% F-doped compounds as a function of pressure and temperature. We have found that the modifications in the partial Fe density of phonon states are mainly governed by the Fe-As bond length. The change of this bond length explains the change of the Fe density of phonon states above 25 meV. We further observe anomalies in the behavior of the phonon mode near 16 meV. In the parent phase, this mode softens anomalously upon cooling through the structural phase transition. Upon F doping, this mode hardens indicating a strong electron-phonon coupling. This suggests that the corresponding phonons play an important role in the competition between superconductivity and magnetism in these materials. DOI: 10.1103/PhysRevB.87.064302 [less ▲]

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See detail2D to 3D crossover of the magnetic properties in ordered arrays of iron oxide nanocrystals
Faure, Bertrand; Wetterskog, Erik; Gunnarsson, Klas et al

in NANOSCALE (2013), 5(3), 953-960

The magnetic 2D to 3D crossover behavior of well-ordered arrays of monodomain gamma-Fe2O3 spherical nanoparticles with different thicknesses has been investigated by magnetometry and Monte Carlo (MC ... [more ▼]

The magnetic 2D to 3D crossover behavior of well-ordered arrays of monodomain gamma-Fe2O3 spherical nanoparticles with different thicknesses has been investigated by magnetometry and Monte Carlo (MC) simulations. Using the structural information of the arrays obtained from grazing incidence small-angle X-ray scattering and scanning electron microscopy together with the experimentally determined values for the saturation magnetization and magnetic anisotropy of the nanoparticles, we show that MC simulations can reproduce the thickness-dependent magnetic behavior. The magnetic dipolar particle interactions induce a ferromagnetic coupling that increases in strength with decreasing thickness of the array. The 2D to 3D transition in the magnetic properties is mainly driven by a change in the orientation of the magnetic vortex states with increasing thickness, becoming more isotropic as the thickness of the array increases. Magnetic anisotropy prevents long-range ferromagnetic order from being established at low temperature and the nanoparticle magnetic moments instead freeze along directions defined by the distribution of easy magnetization directions. [less ▲]

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See detailNuclear forward scattering by the 68.7 keV state of 73Ge in CaGeO3 and GeO2
Simon, RE; Sergueev, I; Persson, J et al

in Europhysics Letters [=EPL] (2013), 104

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See detailXe-129 nuclear resonance scattering on solid Xe and Xe-129 clathrate hydrate
Klobes, B.; Desmedt, A.; Sergueev, I. et al

in Europhysics Letters [=EPL] (2013), 103(3), 36001-6

Nuclear inelastic and nuclear forward-scattering experiments utilizing the Xe-129 Mossbauer resonance were performed on solid Xe and enriched Xe-129 clathrate hydrate. The lifetime and energy of the ... [more ▼]

Nuclear inelastic and nuclear forward-scattering experiments utilizing the Xe-129 Mossbauer resonance were performed on solid Xe and enriched Xe-129 clathrate hydrate. The lifetime and energy of the nuclear resonance were determined to be 1.465(72) ns and 39581.30(4) eV, respectively. Nuclear inelastic scattering spectra could be obtained with an instrumental resolution of 0.93(4) meV. Despite low Lamb-Mossbauer factors, Xe specific densities of phonon states were derived for solid Xe and Xe clathrate hydrate. Their reliability was investigated using 1-phonon terms obtained by fixing Lamb-Mossbauer factor values within the applied Fourier-Log decomposition. ABINIT calculations of the density of phonon states in solid Xe supplement the interpretation of the experimental data for fcc Xe and good agreement with published densities of phonon states could be achieved below 4meV. Results for the Xe clathrate hydrate essentially confirm the rattling nature of the Xe guests and indicate that Xe modes do not contribute to lattice dynamics above 6 meV. Copyright (C) EPLA, 2013 [less ▲]

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See detailParamagnetic nanoparticles as potential MRI contrast agents: characterization, NMR relaxation, simulations and theory
Quoc Lam Vuong; Van Doorslaer, Sabine; Bridot, Jean-Luc et al

in MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE (2012), 25(6), 467-478

Paramagnetic nanoparticles, mainly rare earth oxides and hydroxides, have been produced these last few years for use as MRI contrast agents. They could become an interesting alternative to iron oxide ... [more ▼]

Paramagnetic nanoparticles, mainly rare earth oxides and hydroxides, have been produced these last few years for use as MRI contrast agents. They could become an interesting alternative to iron oxide particles. However, their relaxation properties are not well understood. Magnetometry, H-1 and H-2 NMR relaxation results at different magnetic fields and electron paramagnetic resonance are used to investigate the relaxation induced by paramagnetic particles. When combined with computer simulations of transverse relaxation, they allow an accurate description of the relaxation induced by paramagnetic particles. For gadolinium hydroxide particles, both T (1) and T (2) relaxation are due to a chemical exchange of protons between the particle surface and bulk water, called inner sphere relaxation. The inner sphere is also responsible for T (1) relaxation of dysprosium, holmium, terbium and erbium containing particles. However, for these latter compounds, T (2) relaxation is caused by water diffusion in the field inhomogeneities created by the magnetic particle, the outer-sphere relaxation mechanism. The different relaxation behaviors are caused by different electron relaxation times (estimated by electron paramagnetic resonance). These findings may allow tailoring paramagnetic particles: ultrasmall gadolinium oxide and hydroxide particles for T (1) contrast agents, with shapes ensuring the highest surface-to-volume ratio. All the other compounds present interesting T (2) relaxation performance at high fields. These results are in agreement with computer simulations and theoretical predictions of the outer-sphere and static dephasing regime theories. The T (2) efficiency would be optimum for spherical particles of 40-50 nm radius. [less ▲]

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See detailLattice dynamics in Bi2Te3 and Sb2Te3: Te and Sb density of phonon states
Bessas, D.; Sergueev, I.; Wille, H.-C. et al

in PHYSICAL REVIEW B (2012), 86(22), 224301-9

The lattice dynamics in Bi2Te3 and Sb2Te3 were investigated both microscopically and macroscopically using Sb-121 and Te-125 nuclear inelastic scattering, x-ray diffraction, and heat capacity measurements ... [more ▼]

The lattice dynamics in Bi2Te3 and Sb2Te3 were investigated both microscopically and macroscopically using Sb-121 and Te-125 nuclear inelastic scattering, x-ray diffraction, and heat capacity measurements. In combination with earlier inelastic neutron scattering data, the element-specific density of phonon states was obtained for both compounds and phonon polarization analysis was carried out for Bi2Te3. A prominent peak in the Te specific density of phonon states at 13 meV, that involves mainly in-plane vibrations, is mostly unaffected upon substitution of Sb with Bi revealing vibrations with essentially Te character. A significant softening is observed for the density of vibrational states of Bi with respect to Sb, consistently with the mass homology relation in the long-wavelength limit. In order to explain the energy mismatch in the optical phonon region, a similar to 20% force constant softening of the Sb-Te bond with respect to the Bi-Te bond is required. The reduced average speed of sound at 20 K in Bi2Te3, 1.75(1) km/s, compared to Sb2Te3, 1.85(4) km/s, is not only related to the larger mass density but also to a larger Debye level. The observed low lattice thermal conductivity at 295 K, 2.4 Wm(-1)K(-1) for Sb2Te3 and 1.6 Wm(-1)K(-1) for Bi2Te3, cannot be explained by anharmonicity alone given the rather modest Gruneisen parameters, 1.7(1) for Sb2Te3 and 1.5(1) for Bi2Te3, without accounting for the reduced speed of sound and more importantly the low acoustic cutoff energy. [less ▲]

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See detailQuantitative spatial magnetization distribution in iron oxide nanocubes and nanospheres by polarized small-angle neutron scattering
Disch, S.; Wetterskog, E.; Hermann, Raphaël ULg et al

in New Journal of Physics (2012), 14

By means of polarized small-angle neutron scattering, we have resolved the long-standing challenge of determining the magnetization distribution in magnetic nanoparticles in absolute units. The reduced ... [more ▼]

By means of polarized small-angle neutron scattering, we have resolved the long-standing challenge of determining the magnetization distribution in magnetic nanoparticles in absolute units. The reduced magnetization, localized in non-interacting nanoparticles, indicates strongly particle shape-dependent surface spin canting with a 0.3(1) and 0.5(1) nm thick surface shell of reduced magnetization found for similar to 9 nm nanospheres and similar to 8.5 nm nanocubes, respectively. Further, the reduced macroscopic magnetization in nanoparticles results not only from surface spin canting, but also from drastically reduced magnetization inside the uniformly magnetized core as compared to the bulk material. Our microscopic results explain the low macroscopic magnetization commonly found in nanoparticles. [less ▲]

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See detailRoom-temperature MBE deposition, thermoelectric properties, and advanced structural characterization of binary Bi2Te3 and Sb2Te3 thin films
Peranio, N.; Winkler, M.; Bessas, D. et al

in Journal of Alloys & Compounds (2012), 521

Sb2Te3 and Bi2Te3 thin films were grown at room temperature on SiO2 and BaF2 substrates using molecular beam epitaxy. A layer-by-layer growth was achieved such that metallic layers of the elements with 0 ... [more ▼]

Sb2Te3 and Bi2Te3 thin films were grown at room temperature on SiO2 and BaF2 substrates using molecular beam epitaxy. A layer-by-layer growth was achieved such that metallic layers of the elements with 0.2 nm thickness were deposited. The layer structure in the as-deposited films was confirmed by X-ray diffraction and was seen more clearly in Sb2Te3 thin films. Subsequent annealing was done at 250 degrees C for 2 h and produced the Sb2Te3 and Bi2Te3 crystal structure as confirmed by high-energy X-ray diffraction. This preparation process is referred to as nano-alloying and it was demonstrated to yield single-phase thin films of these compounds. In the thin films a significant texture could be identified with the crystal c axis being almost parallel to the growth direction for Sb2Te3 and tilted by about 30 degrees for Bi2Te3 thin films. Inplane transport properties were measured for the annealed films at room temperature. Both films yielded a charge carrier density of about 2.6 x 10(19) cm (3). The Sb2Te3 films were p-type, had a thermopower of +130 mu V K-1, and surprisingly high mobilities of 402 cm(2) V-1 s(-1). The Bi2Te3 films were n-type, showed a thermopower of -153 mu V K-1, and yielded significantly smaller mobilities of 80 cm(2) V-1 s(-1). The chemical composition and microstructure of the films were investigated by transmission electron microscopy (TEM) on cross sections of the thin films. The grain sizes were about 500 nm for the Sb2Te3 and 250 nm for the Bi2Te3 films. In the Bi2Te3 thin film, energy-filtered TEM allowed to image a Bi-rich grain boundary phase, several nanometers thick. This secondary phase explains the poor mobilities of the Bi2Te3 thin film. With these results the high potential of the nano-alloying deposition technique for growing films with a more complex layer architecture is demonstrated. (C) 2012 Elsevier B.V. All rights reserved. [less ▲]

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See detailSb2Te3 and Bi2Te3 Thin Films Grown by Room-Temperature MBE
Aabdin, Z.; Peranio, N.; Winkler, M. et al

in Journal of Electronic Materials (2012), 41(6), 1493-1497

Sb2Te3 and Bi2Te3 thin films were grown on SiO2 and BaF2 substrates at room temperature using molecular beam epitaxy. Metallic layers with thicknesses of 0.2 nm were alternately deposited at room ... [more ▼]

Sb2Te3 and Bi2Te3 thin films were grown on SiO2 and BaF2 substrates at room temperature using molecular beam epitaxy. Metallic layers with thicknesses of 0.2 nm were alternately deposited at room temperature and the films were subsequently annealed at 250A degrees C for 2 h. x-Ray diffraction and energy-filtered transmission electron microscopy (TEM) combined with high-accuracy energy-dispersive x-ray spectrometry revealed stoichiometric films, grain sizes of less than 500 nm, and a texture. High-quality in-plane thermoelectric properties were obtained for Sb2Te3 films at room temperature, i.e., low charge carrier density (2.6 x 10(19) cm(-3)), large thermopower (130 V K-1), large charge carrier mobility (402 cm(2) V-1 s(-1)), and resulting large power factor (29 W cm(-1) K-2). Bi2Te3 films also showed low charge carrier density (2.7 x 10(19) cm(-3)), moderate thermopower (-153 V K-1), but very low charge carrier mobility (80 cm(2) V-1 s(-1)), yielding low power factor (8 W cm(-1) K-2). The low mobilities were attributed to Bi-rich grain boundary phases identified by analytical energy-filtered TEM. [less ▲]

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See detailNanostructure, Excitations, and Thermoelectric Properties of Bi2Te3-Based Nanomaterials
Aabdin, Z.; Peranio, N.; Eibl, O. et al

in Journal of Electronic Materials (2012), 41(6), 1792-1798

The effect of dimensionality and nanostructure on thermoelectric properties in Bi2Te3-based nanomaterials is summarized. Stoichiometric single-crystalline Bi2Te3 nanowires were prepared by potential ... [more ▼]

The effect of dimensionality and nanostructure on thermoelectric properties in Bi2Te3-based nanomaterials is summarized. Stoichiometric single-crystalline Bi2Te3 nanowires were prepared by potential-pulsed electrochemical deposition in a nanostructured Al2O3 matrix, yielding transport in the basal plane. Polycrystalline, textured Sb2Te3 and Bi2Te3 thin films were grown at room temperature using molecular beam epitaxy and subsequently annealed at 250A degrees C. Sb2Te3 films revealed low charge carrier density of 2.6 x 10(19) cm(-3), large thermopower of 130 V K-1, and large charge carrier mobility of 402 cm(2) V-1 s(-1). Bi-2(Te0.91Se0.09)(3) and (Bi0.26Sb0.74)(2)Te-3 nanostructured bulk samples were prepared from as-cast materials by ball milling and subsequent spark plasma sintering, yielding grain sizes of 50 nm and thermal diffusivities reduced by 60\%. Structure, chemical composition, as well as electronic and phononic excitations were investigated by x-ray and electron diffraction, nuclear resonance scattering, and analytical energy-filtered transmission electron microscopy. calculations yielded point defect energies, excitation spectra, and band structure. Mechanisms limiting the thermoelectric figure of merit for Bi2Te3 nanomaterials are discussed. [less ▲]

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See detailElectronic Properties as a Function of Ag/Sb Ratio in Ag1-yPb18Sb1+zTe20 Compounds
Dadda, Jayaram; Mueller, Eckhard; Klobes, Benedikt et al

in Journal of Electronic Materials (2012), 41(8), 2065-2072

In this study efforts have been made to optimize the electronic properties such as the electrical conductivity and Seebeck coefficient of Ag1- (y) Pb18Sb1+ (z) Te-20 (lead-antimony-silver-tellurium, LAST ... [more ▼]

In this study efforts have been made to optimize the electronic properties such as the electrical conductivity and Seebeck coefficient of Ag1- (y) Pb18Sb1+ (z) Te-20 (lead-antimony-silver-tellurium, LAST-18) compounds by systematically varying the Ag and Sb compositions with constant Pb/Te ratio. It was found that increasing the content of Sb relative to Ag raised the charge carrier density (n) and thereby the electrical conductivity and power factor. The results indicate that, for deficient Ag, the excess trivalent Sb atoms occupy divalent Pb sites in the unit cell, increasing the value of n in the system. It was established that the Seebeck coefficient decreases with increasing n indicating a dominant acoustic phonon scattering mechanism in the current alloys. The results demonstrate that the interaction between Ag and Sb atoms plays a major role in determining the electronic properties in the current Ag1-y Pb18Sb1+z Te-20 compounds. [less ▲]

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See detailMicrostructure analyses and thermoelectric properties of Ag1-xPb18Sb1+yTe20
Perlt, S.; Hoeche, Th; Dadda, J. et al

in Journal of Solid State Chemistry (2012), 193(SI), 58-63

This study reports microstructural investigations of long-term annealed 18, x=y=0, hereinafter referred to as AgPb18SbTe20) (Lead-Antimony-Silver-Tellurium, LAST-18) as well as of Ag1-xPb18Sb1+yTe20, i.e ... [more ▼]

This study reports microstructural investigations of long-term annealed 18, x=y=0, hereinafter referred to as AgPb18SbTe20) (Lead-Antimony-Silver-Tellurium, LAST-18) as well as of Ag1-xPb18Sb1+yTe20, i.e. Ag-deficient and Sb-excess LAST-18 (x not equal 0, y not equal 0), respectively. Two different length scales are explored. The micrometer scale was evaluated by SEM to analyze the volume fraction and the number of secondary phases as well as the impact of processing parameters on the homogeneity of bulk samples. For AgPb18SbTe20, site-specific FIB liftout of TEM lamellae from thermoelectrically characterized samples was accomplished to investigate the structure on the nanometer scale. High-resolution TEM and energy-filtered TEM were performed to reveal shape and size distribution of nanoprecipitates, respectively. A hypothesis concerning the structure-property relationship is set out within the frame of a gradient annealing experiment. This study is completed by results dealing with inhomogeneities on the micrometer scale of Ag1-xPb18Sb1+yTe20 and its electronic properties. (C) 2012 Elsevier Inc. All rights reserved. [less ▲]

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