Search

Monoclinic Y$_{0.7}$Er$_{0.3}$Fe$_2$D$_{4.2}$ compound exhibits unusual magnetic properties with different field induced magnetic transitions. The deuteride is ferrimagnetic at low temperature and the Er and Fe sublattices present magnetic transitions at different temperatures. The Er moments are ordered below T$_{Er}$=55 K, whereas the Fe moments remain ferromagnetically coupled up to T$_{M0}$ = 66 K. At T$_{M0}$ the Fe moments display a sharp ferromagnetic-antiferromagnetic transition (FM-AFM) through an itinerant electron metamagnetic (IEM) behaviour very sensitive to any volume change. Y$_{0.7}$Er$_{0.3}$Fe$_2$D$_{4.2}$ becomes paramagnetic above T$_N$=125 K. The pressure dependence of T$_{Er}$ and T$_{M0}$ have been extracted from magnetic measurements under hydrostatic pressure up to 0.49 GPa. Both temperatures decrease linearly upon applied pressure with dT$_{Er}$/dP=-126 and dTM0/dP=-140 K.GPa$^{-1}$ for a field of B=0.03 T. Both magnetic Er and ferromagnetic Fe order disappear at P=0.44(4) GPa. However, under a larger applied field B=5 T, dT$_{M0}$/dP=-156 K.GPa$^{-1}$ whereas dT$_{Er}$/dP=-134 K.GPa$^{-1}$ showing a weaker sensitivity to pressure and magnetic field. At 2 K the decrease of the saturation magnetization under pressure can be attributed to a reduction of the mean Er moment due to canting and/or crystal field effect. Above T$_{M0}$ the magnetization curves display a metamagnetic behaviour from AFM to FM state, which is also very sensitive to the applied pressure. The transition field B$_{trans}$, which increases linearly upon heating, is shifted to lower temperature upon applied pressure with dT=-17 K between 0 and 0.11 GPa. These results show a strong decoupling of the Er and Fe magnetic sublattices versus temperature, applied field and pressure., 24 pages, 10 figures, 1 tables

In this chapter, a theoretical study relying on the thermal modelling of a Curie wheel, used for the conversion of low-grade waste heat into electrical power, is presented. It allows understanding the thermal behaviour of a Curie wheel operating in steady state in order to optimise its design. To this end, a stationary one-dimensional analytical thermal model, based on a Lagrangian approach, was developed. It allows determining the local distribution over time of the temperature in the magnetocaloric material exposed to a periodic sinusoidal heat source. Thanks to this model, the effects of different parameters (nature of the magnetocaloric material, nature and temperature of the fluid) were determined and analysed.

International audience; By implementing X-ray absorption spectroscopy among other techniques, ytterbium was inferred to display a valence of 2 in the thermoelectric YbyCo4Sb12 skutterudites (0.10 ≤ y ≤ 0.20). Consequently, the correlation PF(A 3+) < PF(A 2+) < PF(A 1+) between the valence of the filler atom and the power factor (PF) could be established in a generic set of AyCo4Sb12 skutterudites (A = filler atom and electron donor). By grinding the YbyCo4Sb12 samples under inert atmosphere prior to densification by Spark Plasma Sintering, no spurious oxidation of Yb occurred, conversely to what happens when grinding in air. This led to the effective ytterbium concentration being strictly equal to the nominal one, up to the solubility limit determined to be ylim = 0.41 ± 0.02 mol / formula unit when the YbyCo4Sb12 compounds are synthesized at 1073 K. The maximum PF = 4.2 mW m-1 K-2 at 300 K is reached in Yb0.15Co4Sb12, for the first time at the theoretically predicted electron concentration nopt = 1.8 ± 0.2 × 10 20 cm-3 , thus evidencing the optimization of this compound. Finally, Yb0.15Co4Sb12 also displays the best thermoelectric properties in the series, with a figure of merit ZTmax = 1.4 and PF = 5.5 mW m-1 K-2 at 750 K.

The weak itinerant magnetic properties of A

La(Fe,Co,Si)\(_{13}\) compounds exhibit a giant magnetocaloric effect, and they are considered as a good magnetocaloric working substance for an environmentally friendly cooling technique. The insertion of light elements (H, C) is used to improve the Curie temperature near room temperature for magnetic refrigeration applications. We have developed a method combining high energy ball milling with a subsequent short annealing treatment to obtain a single phase compounds. Moreover, one single step of reactive spark plasma sintering was used. The insertion of H atoms was carried out using a Sievert apparatus and the carbon atom was inserted by solid/solid reaction. Structural and magnetic results were carried out by neutron diffraction and Mossbauer spectroscopy. The misunderstanding on interstitial site is clarified. The magnetovolumic effect on the Curie temperature is explained by the combination of the structural and magnetic properties.

This chapter provides the electrochemical properties of AB2 laves phase compounds relevant for hydrogen storage.

This chapter contains tabular compilation of thermodynamic properties of AB2 laves phase compounds relevant for hydrogen storage.

In this chapter the synthesis and crystal structure of A6B23 phase intermetallic compounds are discussed in detail.

This chapter provides the thermodynamic properties of A6B23 compounds relevant for hydrogen storage.

This chapter gives an introduction to the methods and materials that can be used for hydrogen storage.

This chapter gives overview to the experimental and theoretical study of thermodynamic properties of metal hydride compounds. The theoretical calculations of enthalpy of formation is also discussed in detail.

This chapter contains tabular compilation of thermodynamic and kinetic properties of Mg-based compounds.

This chapter gives an introduction to Mg-based metal hydrides for hydrogen storage applications.

This chapter discusses the methods to determine the structural properties of hydrides that are being considered for hydrogen storage application.

This chapter provides an introduction to hydrides of binary and pseudo-binary intermetallic compounds.

In this chapter the synthesis and crystal structure of A6B23 phase hydrides and deuterides are discussed in detail

In this chapter the synthesis and crystal structure of AB2 laves phase hydrides and deuterides are discussed in detail.

In this chapter the synthesis and crystal structure of AB2 laves phase intermetallic compounds are discussed in detail.

This chapter consists of tabular compilation of cell parameter, cell volume and atomic position of Mg-based compounds.

This chapter provides an overview of electrochemical properties of hydrogen storage materials.

This chapters provides an overview to the synthesis of hydrogen storage materials such as intermetallics, metal-hydrides, complex hydrides, carbon and nanocarbon compounds. The preparation methods of these materials are also discussed in detail.

This chapter provides an overview to A6B23 phase metal hydrides that can be used for hydrogen storage.

This chapter provides an overview to AB2 laves phase metal hydrides that can be used for hydrogen storage.

In this paper, the magnetocaloric effect (MCE) of LaFe13−xSi x compounds with 1.2 ≤ x ≤ 2.2 has been investigated. For this purpose, the magnetization dependence on the temperature and magnetic field were measured. Magnetic entropy change (−ΔSM) allowing estimation of the MCE was determined based on thermodynamic Maxwell’s relation. The experimental results show that TC increases with the Si content, whereas the magnetic entropy variation decreases. A large magnetic entropy change has been observed. The maximum $(-\Delta \mathrm {S}_{\mathrm {M}}^{\text {max}})$ of LaFe10.8Si2.2 occurring close to TC = 240 K is about 2.3 Jkg−1 K−1 for an applied field change of 0–2 T. In addition, a magnetocaloric effect of LaFe13−xSi x compounds (x = 1.2 and 1.6) has been also carried out using phenomenological model. Dependence of the magnetization on temperature variation for LaFe13−xSi x compounds (x = 1.2 and 1.6) in different applied magnetic fields was simulated. The values of maximum entropy change, full width at half maximum, and relative cooling power (RCP) for the LaFe11.8Si1.2 and LaFe11.4Si1.6 compounds in different applied magnetic fields were calculated.

International audience; A theoretical study relying on the thermal modelling of a Curie wheel, used for the conversion of low-grade waste heat into electrical power, is presented in this paper. It allows understanding the thermal behaviour of a Curie wheel operating in steady state in order to optimise its design. To this end, a stationary one-dimensional analytical thermal model, based on a Lagrangian approach, was developed. It allows determining the local distribution over time of the temperature in the magnetocaloric material exposed to a periodic sinusoidal heat source. Thanks to this model, the effects of different parameters (nature of the magnetocaloric material, nature and temperature of the fluid) were highlighted and studied.

The magnetic properties of LaNi 3.55 Mn 0.4 Al 0.3 Co 0.75− x Fe x compounds ( x =0, 0.35) and their changes as a function of electrochemical cycles have been studied using magnetization measurements in temperature range 10⩽ T ⩽300 K and in a magnetic field H ⩽2 T. It has been shown that there is an increase of the magnetization with the number of cycles which is due to the precipitation of (Ni, Co, Fe) superparamagnetic clusters on its surface. The fit of the magnetization curves with the Langevin function, allowed us to determine the size and the amount of superparamagnetic clusters, versus cycle numbers.

In this paper a new electrocatalytic hydrogenation process is reported based on the use of LaNi5 electrodes. The charge/discharge of hydrogen within the intermetallic compound through cyclic voltammetry experiments was observed using a powder microelectrode in classical aqueous KOH medium, as well as in other buffered aqueous or hydro-organic media. Most voltammograms are modified in the presence of unsaturated compounds, which indicates that a hydrogenation reaction occurs. Electrocatalytic hydrogenation on a preparative scale was carried out with three unsaturated compounds taken as models (methyl vinyl ketone, 1-decene, 5-hexen-2-one) and it was found that only the CC bond is hydrogenated with Faradaic efficiencies up to 100%.

The 3 He produced by the tritium disintegration induces the formation of structural and microstructural defects in Pd and LaNi5 tritides which change their thermodynamic properties. The larger change of the thermodynamic properties of LaNi5 intermetallic compound compared to that of palladium with ageing time is related to a larger increase of the local disorder measured by EXAFS. These distinct behaviours can be explained by the formation of different kinds of defects.

In this work are presented results on the structural, magnetic, and magnetocaloric properties of the Y0.9Gd0.1Fe2D4.2 compound in which TM0 is shifted from 84 K to 110 K because of Gd influence. Magnetization measurements have been performed with a magnetic field up to 310 kOe in the 4.2–300 K temperature range with special attention paid near TM0. The spontaneous magnetization at 4.2 K (3.2 μB/mol) is smaller than for YFe2D4.2 (3.7 μB/mol), showing the contribution of Gd moments. Above 110 K, metamagnetic field-induced transitions are observed: the transition field HTR increases linearly with T. These transitions exist up to 170 K. The influence of both cell volume change and Gd magnetic contribution are finally discussed in comparison with other deuterides.

Cobalticinium and ferricinium cations have been intercalated at room temperature into the lamellar structure of V 2 O 5 gels. In both cases an almost constant basal d-spacing is observed, about 13.2 A whatever the counterion used. The basic V 2 O 5 ribbon structure is not modified upon intercalation, but noticeable improvement of the order along the ribbon packing direction is obtained, especially with Co(C 5 H 5 ) + 2 . The 4.4 A increase in the basal d-spacing and its high temperature evolution allow to deduce that cyclopentadienyl rings interpenetrate the V 2 O 5 ribbons presumably in the usual perpendicular position. Water is involved in the intercalation mechanism which is likely of the exchange type rather than of the redox type. Intercalate formula is approximately V 2 O 5 , 0.4 Fe(C 5 H 5 ) 2 , x H 2 O (with x 5 H 5 ) + 2 intercalate, are still stable beyond 200°C. Such a high thermal stability is quite remarkable.

Recently a number of studies have demonstrated that intermetallic compounds may be used as the precursors of new metallic catalysts (1,2). Intermetallics of the LaNi5 series, extensively studied for hydrogen storage, exhibit an appreciable activity in catalytic reactions, particularly in carbon monoxyde or hydrocarbon hydrogenation. The nickel substitution by another transition element implies a significant variation of catalytic properties (3,4).

RNi2 Laves phases (R = La, Ce) absorb easily hydrogen up to 4.4 H/mole at room temperature and atmospheric pressure. But X ray diffraction patterns show no diffraction lines. Such a result has already been mentioned by several authors (1–6) for ternary rare-earth and transition metal hydrides. The absence of diffraction lines can be interpreted by the formation of an amorphous compound or by segregation into microcrystalline particles of RHx and Ni or RNiy (y > 2) (7). The first case would be very interesting since it would provide a new way to prepare amorphous compounds. But until now few studies have been presented on these non crystalline hydrides, except by SAMWER et al (8, 9). These authors have shown that Zr3Rh become amorphous by hydriding the intermetallic compound at 180 C and atmospheric pressure. They have found the same structural and physical properties for the hydrides prepared from amorphous and crystalline Zr3Rh.

Intermetal1ic compounds, such as LaCo5, have been used as active and selective catalysts in chemical reaction involving (CO,H2) mixtures. The general understanding regarding these catalysts is that the observed activation is associated with a partial transformation of the intermetallic component into a metal-support system. The macroscopic study of LaCo3 by use of synchrotron radiation absorption measurements (EXAFS and XANES data analysis) largely support this hypothesis. In this work, the microscopic structure of these catalysts has been studied by HRAEM.