Interplay of disorder and antiferromagnetism in TlFe1.6+(Se1−xSx )2 probed by neutron scattering

International audienceThe effect of selenium substitution by sulphur on the structural and physical properties of antiferromagnetic TlFe1.6+δSe2 has been investigated via neutron, x-ray and electron diffraction, and transport measurements. The 5 sqrt(a)× 5sqrt(a)×c super-cell related to the iron vacancy ordering found in the pure TlFe1.6Se2 selenide is also present in the S-doped TlFe1.6+δ(Se1−xSx)2 compounds. Neutron scattering experiments show the occurrence of the same long range magnetic ordering in the whole series i.e. the 'block checkerboard' antiferromagnetic structure. In particular, this is the first detailed study where the crystal structure and the 5 a× 5 a antiferromagnetic structure is characterized by neutron powder diffraction for the pure TlFe1.6+δS2 sulphide over a large temperature range. We demonstrate the strong correlation between occupancies of the crystallographic iron sites, the level of iron vacancy ordering and the occurrence of block antiferromagnetism in the sulphur series. Introducing S into the Se sites also increases the Fe content in TlFe1.6+δ(Se1−xSx)2 which in turn leads to the disappearance of the Fe vacancy ordering at x = 0.5 ± 0.15. However, by reducing the nominal Fe content, the same 5 a× 5 a×c vacancy ordering and antiferromagnetic order can be recovered also in the pure TlFe1.6+δS2 sulphide with a simultaneous reduction in the Néel temperature from 435 K in the selenide TlFe1.75Se2 to 330 K in the sulphide TlFe1.5S2. The magnetic moment remains high at low temperature throughout the full substitution range, which contributes to the absence of superconductivity in these compounds

Room-temperature tuning of magnetic anisotropy in samarium-thulium orthoferrites

Rare-earth orthoferrites (RFeO3) provide a flexible playground for magnetic materials design, combining the magnetic properties arising from complex interactions between R3+ and Fe3+ cations within the robust framework of the perovskite structure. The most important magnetic property common to most orthoferrites is a spin reorientation transition in which the magnetic moments of Fe3+ cations rotate with respect to a crystallographic axis. SmFeO3 is unique among orthoferrites due to its high-temperature spin reorientation. It is possible to tune the spin reorientation transition to occur at room temperature by replacing Sm with Tm in the Sm0.70Tm0.30FeO3 perovskite. In this study, we show how small changes in composition in the Sm1-xTmxFeO3 (x=0.30-0.50) series provide a high degree of control over the magnetic properties. This work also offers a rather unusual look into the magnetic structure of a samarium-based perovskite by means of neutron powder diffraction, which was made possible by using Sm152. The combination of these results and magnetization measurements allowed the construction of the magnetic phase diagram of the series.Fil: Bolletta, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Cuello, Gabriel Julio. Institut Laue Langevin; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Nassif, Vivian. Universite Grenoble Alpes; FranciaFil: Suard, Emmanuelle. Institut Laue Langevin; FranciaFil: Kurbakov, Alexander I.. No especifíca;Fil: Maignan, Antoine. No especifíca;Fil: Martin, Christine. No especifíca;Fil: Carbonio, Raul Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Effect of the isoelectronic substitution of Sb for As on the magnetic and structural properties of LaFe(As1−xSbx)O

International audienceThe antiferromagnetic (AFM) order and structural distortion in the LaFe(As1−xSbx)O system have been investigated by neutron powder diffraction and physical properties measurements. Polycrystalline samples of LaFe(As1−xSbx)O (x < 0.5) were prepared using solid state synthesis at ambient and high pressure. We find that the isoelectronic substitution of Sb for As decreases the structural and magnetic transition temperatures, but, contrary to the effects of phosphorus substitution, superconductivity is not induced. Instead a slight increase in the Fe-magnetic moment is observed

Magnetic Structure of SmCo 5 from 5 K to the Curie Temperature

International audienc

Hydrogen Storage Properties of a New Ti-V-Cr-Zr-Nb High Entropy Alloy

International audienceWe are reporting the synthesis, the physicochemical, and the hydrogen sorption properties of a novel bcc high entropy alloy Ti0.30V0.25Cr0.10Zr0.10Nb0.25. At room temperature, the alloy rapidly absorbs hydrogen reaching a capacity of 2.0 H/M (3.0 wt.%) and forming a dihydride with fcc structure, as confirmed by both synchrotron X-ray diffraction and neutron diffraction. The absorption Pressure–Composition Isotherms corroborated with synchrotron X-ray diffraction prove that the reaction with hydrogen occurs within two steps, i.e., bcc alloy → bcc monohydride → fcc dihydride. The thermodynamic parameters calculated for the second step transformation evidence the formation of a stable dihydride with ΔHabs = −75 kJ/molH2. The phase transition during hydrogen/deuterium desorption was investigated by in situ synchrotron X-ray and neutron diffraction confirming a reversible reaction with hydrogen. Furthermore, the cycling properties show a decrease of the capacity over the first cycles followed by a stabilization at 2.44 wt.%, whereas the absorption kinetics improve after the first cycle reaching full capacity after only 30 s at room temperatur

Magnetic Structure of SmCo₅ from 5 K to the Curie Temperature

The crystal and magnetic structure of SmCo₅ is determined by neutron powder diffraction between 5 K and the Curie temperature. In order to overcome the enormous neutron absorption of samarium, a ¹⁵⁴Sm isotopically enriched sample was used. The ordered magnetic moments of both crystallographically distinct cobalt atoms are not significantly different over the whole temperature range. They decrease from 2.2 μ_B at 5 K to about 0.6 μ_B at 1029 K. Samarium’s ordered magnetic moment decreases from 1.0 μ_B at 5 K, runs through a minimum of 0.2 μ_B around 650 K, and becomes larger than cobalt’s ordered magnetic moment above 950 K. No sign or orientation change of the samarium and cobalt ordered magnetic moments is found between the Curie temperature and 5 K. SmCo₅ is thus a ferromagnet and does not switch to a ferrimagnetic state as discussed in the literature

Hydrogen Sorption Properties of a Novel Refractory Ti-V-Zr-Nb-Mo High Entropy Alloy

International audienceHigh entropy alloys belong to a new and promising class of functional materials for solid-state hydrogen storage. In this context, a novel single-phase body centered cubic (bcc) high entropy alloy Ti0.30V0.25Zr0.10Nb0.25Mo0.10 was prepared. The physicochemical and hydrogen sorption properties have been determined by both laboratory and large-scale facilities. This alloy can quickly absorb hydrogen up to 2.0 H/M (2.8 wt.%) at room temperature and forms a face centered cubic (fcc) hydride, as proven by synchrotron X-ray diffraction. The Pressure–Composition Isotherm and in situ neutron diffraction during hydrogen/deuterium desorption reaction suggest that the alloy experiences a reversible single step phase transition (bcc↔fcc). PDF analysis from X-ray total scattering data points out that the hydride phase possesses an average fcc structure with random atoms distribution and small lattice distortion. Despite an initial small fading of the capacity, the alloy withstands 20 absorption/desorption cycling without phase decomposition, as demonstrated by kinetic measurements coupled with X-ray diffraction and microstructural study by SEM-EDS. Moreover, the complete hydrogen absorption occurs in less than 30 s at room temperature and the kinetic improves during cyclin

High temperature neutron powder diffraction study of the Cu12Sb4S13 and Cu4Sn7S16 phases

International audienceTernary copper-contg. sulfides Cu12Sb4S13 and Cu4Sn7S16 have attracted considerable interest since few years due to their high-efficiency conversion as absorbers for solar energy and promising thermoelec. materials. We report therein on the decompn. study of Cu12Sb4S13 and Cu4Sn7S16 phases using high temp. in situ neutron powder diffraction. Our results obtained at a heating rate of 2.5 K/min indicate that: (i) Cu12Sb4S13 decomps. above ≈792 K into Cu3SbS3, and (ii) Cu4Sn7S16 decomps. above ≈891 K into Sn2S3 and a copper-rich sulfide phase of sphalerite ZnS-type structure with an assumed Cu3SnS4 stoichiometry. Both phase decompns. are assocd. to a sulfur volatilization. While the results on Cu12Sb4S13 are in fair agreement with recent published data, the decompn. behavior of Cu4Sn7S16 differs from other studies in terms of decompn. temp., thermal stability and products of reaction. Finally, the crystal structure refinements from neutron powder diffraction data are reported and discussed for the Cu4Sn7S16 and tetrahedrite Cu12Sb4S13 phases at 300 K, and for the high temp. form of skinnerite Cu3SbS3 at 843 K

High temperature neutron powder diffraction study of the Cu12Sb4S13 and Cu4Sn7S16 phases

International audienceTernary copper-contg. sulfides Cu12Sb4S13 and Cu4Sn7S16 have attracted considerable interest since few years due to their high-efficiency conversion as absorbers for solar energy and promising thermoelec. materials. We report therein on the decompn. study of Cu12Sb4S13 and Cu4Sn7S16 phases using high temp. in situ neutron powder diffraction. Our results obtained at a heating rate of 2.5 K/min indicate that: (i) Cu12Sb4S13 decomps. above ≈792 K into Cu3SbS3, and (ii) Cu4Sn7S16 decomps. above ≈891 K into Sn2S3 and a copper-rich sulfide phase of sphalerite ZnS-type structure with an assumed Cu3SnS4 stoichiometry. Both phase decompns. are assocd. to a sulfur volatilization. While the results on Cu12Sb4S13 are in fair agreement with recent published data, the decompn. behavior of Cu4Sn7S16 differs from other studies in terms of decompn. temp., thermal stability and products of reaction. Finally, the crystal structure refinements from neutron powder diffraction data are reported and discussed for the Cu4Sn7S16 and tetrahedrite Cu12Sb4S13 phases at 300 K, and for the high temp. form of skinnerite Cu3SbS3 at 843 K

How 10 at% Al Addition in the Ti-V-Zr-Nb High-Entropy Alloy Changes Hydrogen Sorption Properties

International audienceAl0.10Ti0.30V0.25Zr0.10Nb0.25 was prepared to evaluate the effect of 10% aluminum into the previously reported quaternary alloy, Ti0.325V0.275Zr0.125Nb0.275. The as-cast quinary alloy formed a single-phase body centered cubic solid solution and transformed into a body centered tetragonal after hydrogenation. The alloy had a storage capacity of 1.6 H/M (2.6 wt.%) with fast absorption kinetics at room temperature, reaching full capacity within the first 10 min. The major improvements of Al addition (10%) were related to the desorption and cycling properties of the material. The temperature for hydrogen release was significantly decreased by around 100 °C, and the quinary alloy showed superior cycling stability and higher reversible storage capacity than its quaternary counterpart, 94% and 85% of their respective initial capacity, after 20 hydrogenation cycles without phase decomposition