PuNi3 Type Research Articles

Competition effect of light and heavy rare earth in Pr1-xGdxCo3 compounds with large coercivity and exchange bias

The effect of Gd doping on the structure and magnetic properties of PrCo3 compound was systematically studied, and a large zero-field cooling exchange bias effect at room temperature was observed. The results show that Pr1-xGdxCo3 (x = 0.0–1.0) series ribbons samples retains the rhombohedral structure of PuNi3 type. The addition of Gd element linearly reduce the lattice constant. Large coercivity strengthening and zero-field cooling exchange bias effect were stable below Curie temperature. At 10 K, the abnormal minimum saturation magnetization MS occurs at the critical point xc = 0.6, which corresponds to the maximum critical field, and the pinning effect is the strongest. At the same time, the maximum critical field is accompanied by the strongest exchange bias field, up to 14.92 kOe, showing a large unidirectional anisotropy. The coercivity HC is also improved by pinning effect, reaching a maximum of 23.17 kOe at the critical point xh = 0.5. Due to the influence of HEB, the actual coercivity HC1 was as high as 36.23 kOe. The mechanism of these phenomena was explained specifically in this paper. This work provides a novel idea for the development of permanent magnet materials and exchange bias materials.

Structural and high-field magnetic properties of Laves phase RFe2-H hydrides

The crystal structure and magnetic properties of the multicomponent compounds (Tb1−xYx)0.8Sm0.2Fe2Hz (x = 0, 0.2, 0.4, 0.6, 0.8, 1; z = 0 and 3.7) are investigated. The compounds crystallize in the MgCu2 type of structure. While the parent compounds Tb0.8Sm0.2Fe2 and Y0.8Sm0.2Fe2 are single phase, we detect 5%–8% of a second phase with a crystal structure of the PuNi3 type (space group R3m) in the alloys with 0.2 ≤ x < 0.8. Hydrogen absorption does not change the space group of the (Tb,Y,Sm)Fe2 compounds but boosts significantly the lattice parameter a. A large volume change of ΔV/V ∼ 28% upon hydrogen absorption is observed. By applying high magnetic fields up to 58 T, we observed rotations of the magnetic sublattices and hence we were able to determine the critical transition fields, H, from the ferrimagnetic to the ferromagnetic state and the inter-sublattice exchange parameter λ. The magnetic compensation occurs at x ≈ 0.6 and 0.2 in (Tb1−xYx)0.8Sm0.2Fe2Hz at z = 0 and 3.7, respectively. While maintaining the collinear magnetic structure, the phenomenon of compensation in hydrides should be observed at x ≈ 0.4.

La2MgNi7.5Co1.5 Hydrogen Storage Alloy Prepared by the Magnetic Field Assisted Sintering

La2MgNi7.5Co1.5 hydrogen storage alloy was prepared by magnetic field assisted sintering method. The phase structure and hydrogen absorption properties of the alloy were systematically studied by means of isothermal constant volume method, XRD, SEM, EDS and HPDSC etc. The results showed that the main phase is PuNi3 type structure of (La, Mg) (Ni, Co)3. The impure phase La (Ni, Co)5 decreased firstly and increased later with the magnetic field increased. Addition of Co can improve the hydrogen absorption and desorption properties of the alloy obviously, the maximum hydrogen storage capacity reached 1.538 wt.%. The dehydrogenation DSC curve of the alloy has a multimodal characteristics. The magnetic field changed hydrogen desorption thermal behavior of (La, Mg)(Ni, Co)3 phase significantly. The alloy after activation showed excellent hydrogen absorption and desorption kinetics performance.

Phase equilibria in the Nd–Mg–Co system at 300 and 500 °C, crystal structure and hydrogenation behavior of selected compounds

The isothermal sections of the Nd–Mg–Co phase diagram at 300 and 500 °C have been constructed on the basis of X-ray diffraction (XRD), Wavelength Dispersive Spectrometry (WDS) and Electron Probe Micro Analyzer (EPMA) analysis. The existence of two ternary compounds Nd4Mg3Co2 (own structure type) and Nd4MgCo (Gd4RhIn type) was confirmed. The latter has homogeneity range defined as Nd4-xMg1+xCo with 0 ≤ x ≤ 0.2 at 300 °С and 0 ≤ x ≤ 0.3 at 500 °С. Four new ternary compounds were identified in this work: Nd23-xMg4+xCo7 (Pr23Mg4Ir7 type; −1.5 ≤ x ≤ 0.1 at 300 °С and −0.6 ≤ x ≤ 0.3 at 500 °С); NdMg2Co9 (YIn2Ni9 type), ∼Nd77Mg14Co9 (cubic) and ∼Nd56Mg6Co38 (unknown crystal structure). Two binary compounds, NdCo2 and NdCo3, were found to dissolve significant amount of Mg with the formation of substitutional solid solutions Nd1-xMgxCo2 (MgCu2 type; x ≤ 0.1 at 300 °С and x ≤ 0.15 at 500 °C) and Nd1-xMgxCo3 (PuNi3 type; x ≤ 0.33 at 300 °С and x ≤ 0.5 at 500 °C), respectively. The Nd4Mg3Co2, Nd4-xMg1+xCo, Nd23-xMg4+xCo7 and Nd1-xMgxCo2 compounds irreversibly absorb hydrogen at room temperature and pressure 1–10 bar to form crystalline or amorphous hydrides with hydrogen content 1.6–2.1 wt. %. Hydrogen thermal desorption from these hydrides in vacuum results in their disproportionation with formation of binary NdH2 hydride. The Nd1-xMgxCo3 (0 ≤ x ≤ 0.5) alloys reversibly absorb up to 1.3 wt. % of hydrogen. NdMg2Co9 compound has small hydrogenation capacity, absorbing only 0.5 wt. % at room temperature and hydrogen pressure 185 bar.

Novel Ho(Ni0.8Co0.2)3 nanoflakes produced by high energy ball – milling

The morphology and magnetic properties of bulk crystalline and ball – milled Ho(Ni0.8Co0.2)3 intermetallic compounds were studied. The influence of the duration of the high energy ball - milling (HEBM) for the final size of particles and crystallites was confirmed by a variety of complementary measurement methods. The crystallization of all studied specimens in the PuNi3 type of crystal structure was confirmed. The presence of an amorphous phase was evidenced at the final stage of pulverization. The influence of different grinding times is reflected in the variation of morphology and magnetism of as-milled powders. An emergence of nanoflakes having nanoflower-like morphology was found at the end of HEBM process. Furthermore, a slight variation of magnetic parameter was observed. Potential coating of the nanoflakes by Ni/Co oxides was demonstrated by XPS investigations.

Characterization of HoCo3 nanoflakes synthesized via high energy ball – milling

The microstructure and magnetic properties of bulk crystalline and ball – milled binary HoCo3 intermetallic compounds were studied. The presence of PuNi3 type of crystal phase was confirmed in all investigated specimens. The emergence of a partly amorphous phase was demonstrated at the end of grinding process. The influence of the applied high energy ball – milling parameters on the microstructure was investigated. The influence of the increased milling time on the final size of particles and crystallites was characterized by a variety of complementary measurement methods. The fabrication of nanoflakes and agglomerates for long pulverization times was demonstrated. Furthermore, the non-linear dependence of the saturation magnetization, coercivity and remanence driven by high energy ball – milling was evidenced. The enhancement of the coercivity for a low milling time was shown. A quantitative analysis of the XPS spectra over ion etching indicates the formation of Co oxides on the nanoflakes surface.

Evolution of morphology and magnetism of Ho(Fe0.5Co0.5)3 intermetallic nanopowders synthesized by HEBM

The morphology and magnetic properties of bulk and ball – milled Ho(Fe0.5Co0.5)3 intermetallic compounds were studied. The influence of the high energy ball – milling (HEBM) duration for the final size of particles and crystallites was confirmed by a variety of complementary measurement methods. The presence of the main PuNi3 type of crystal phase was confirmed for crystalline and as – milled samples. The emergence of a partly amorphous phase was confirmed at the end of pulverization (t = 80 h). The synthesis of nanostructured flakes with a thickness of less than 100 nm after applying HEBM for various time periods was confirmed. Additionally, the formation of agglomerates for the prolonged pulverization was evidenced. The non – linear variation of magnetic parameters across milling was observed. Furthermore, a slight exchange bias and deformation of hysteresis loops for as – milled powders was noticed. A quantitative analysis of XPS spectra at the end of grinding process indicates the probable coating of flakes by Fe/Co oxides the amount of which varies over ion etching.

Application of HEBM for obtaining Ho(Ni0.5Co0.5)3 nanoflakes

The morphology and magnetic properties of bulk and ball – milled Ho(Ni0.5Co0.5)3 intermetallic compounds were studied. The presence of PuNi3 type of crystal phase was confirmed in crystalline as well as powdered samples. The emergence of a partly amorphous phase was confirmed at the end of pulverization. The applying of the high energy ball - milling (HEBM) method for various grinding time is reflected in the fabrication of nanostructured flakes with a thickness of less than 100 nm. The formation of agglomerates for the prolonged pulverization was demonstrated. The influence of the increased milling time for the final size of particles and crystallites was confirmed by a variety of complementary measurement methods. Furthermore, the enhanced coercivity (HC), non-linear dependence of remanence (MR) and emergence of MR/MS ratio higher than 0.5 driven by HEBM was evidenced. A quantitative analysis of XPS spectra indicates the formation of Ni/Co oxides on the nanoflakes surface, which was subsequently reduced over ion etching.

Phase-structural transformations in a metal hydride battery anode La1.5Nd0.5MgNi9 alloy and its electrochemical performance

This work was aimed at in situ studies of the phase-structural transformations in an Mg- and Nd-modified LaNi3 intermetallic having a bulk composition La1.5Nd0.5MgNi9, as related to its performance as battery anode material in the Ni-Metal Hydride batteries. The interactions in the La1.5Nd0.5MgNi9 system were studied by in situ neutron diffraction in a temperature range 300–1248 K. Two alternative processes of preparation of the alloy were studied: (a) Synthesis from a mixture of the powders La0.75Nd0.25Ni5 + La0.75Nd0.25MgNi4; and (b) annealing of the alloy prepared by induction melting. Various transformations take place in the samples on heating, leading to the formation of four new phases, all with the stacking structures of the intermetallic alloys having three variable ratios (RE + Mg)/Ni, 1:3, 2:7 and 5:19. Further to (La0.75Nd0.25)2MgNi9 with a rhombohedral PuNi3 type, there were formed (La0.75Nd0.25)3MgNi14 with a rhombohedral Gd2Co7 structure and two polymorphic modifications of (La0.75Nd0.25)4MgNi19 compound, a high temperature hexagonal Pr5Co19 type and a low temperature rhombohedral Ce5Co19 type. In every case the unit cell parameters showed shrinking as compared to the La-based analogues. Nd substitution for La in La2MgNi9 promotes the formation of a more homogeneous alloy, with a predominant formation of the target AB3 intermetallic.Properly homogenized La1.5Nd0.5MgNi9 alloy shows a more flat and longer plateau, both in the course of hydrogen absorption–desorption and under electrochemical charge–discharge. An apparent hydrogen diffusion coefficient in alloy bulk appears to be higher as compared to Nd-free alloy, contributing to a better reversibility under a high-rate operation at high discharge current densities, while maintaining a good cycle stability.

The isothermal section phase diagram of the Sm-Fe-Ni ternary system at 800 °C

Isothermal section at 800 °C of the ternary Sm-Fe-Ni system was established in the whole concentration range, by means of powder X-ray diffraction and scanning electron microscopyenergy dispersive X-ray spectroscopy (SEM/EDS). All measured compositions and unit-cell refinements were performed at room temperature from quenched samples annealed at 800 °C for one week. Ten binary compounds and α(Fe1−x Nix) (Im−3m-W type structure) have been confirmed.The SmNi5−xFex (P6/mmm-CaCu5 type structure) was found to have a solubility range from 0 to 50 at% Fe. The maximum solubility at 800 °C of Fe in Sm2Ni7−xFex (P63/mmc-Ce2Ni7 type structure), SmNi3−xFex (R3¯m-PuNi3 type structure) and SmNi2−xFex (Fd−3m-MgCu2 type structure) are about 2.7 at% Fe, 40 at% Fe and 6.66 at% Fe, respectively. The homogeneity domain of Sm2Fe17−xNix (R3¯m-Th2 Zn17 type structure) ranges from 0 to 21.05 at% Ni. The XRD and the SEM/EDS analysis show that there are no solubility of Fe in the Sm2 Ni17, Sm5Ni19 and SmNi. The same analysis show that there are no solubility of Ni in the SmFe2 and SmFe3 and no ternary compound was found in all ternary alloy samples. The addition of Ni in the Sm-Fe system did not stabilize the ThMn12 type structure.

Synthesis of nanostructured Ho(Ni0.5Fe0.5)3 compound via ball-milling

The morphology and magnetic properties of the crystalline and ball-milled Ho(Ni0.5Fe0.5)3 intermetallic compounds are studied. The presence of PuNi3 type of crystal structure was confirmed in crystalline as well as powdered samples. The emergence of a partly amorphous phase was confirmed at the end of the pulverization process. The use of the ball-milling method for various grinding time is reflected in the fabrication of nanostructured flakes, with a thickness of less than 100nm. Prolonged milling favors an assemblage of as-prepared nanopowder. The increase of pulverization time leads to the reduction in crystallites sizes confirmed by a variety of complementary measurement methods. Moreover, the increase in comminution duration results in the enhancement of the coercivity (HC), non-linear dependence of remanence (Mr) and emergence of Mr./MS ratio to values higher than 0.5. A quantitative analysis of XPS spectra shows an increase of Fe concentration versus sputtering which is in coincidence with magnetic measurements.

Study of the magnetic and electronic properties of nanocrystalline PrCo3 by neutron powder diffraction and density functional theory

Nanocrystalline PrCo3 powder has been synthesized by high-energy milling and was subsequently annealed from 873 to 1273 K for 30 min to optimize the extrinsic properties. The structure and magnetic properties of the nanocrystalline PrCo3 have been investigated by means of x-ray and neutron diffraction as well as magnetization measurements. All compounds crystallize in the same PuNi3 type structure, with grain sizes between 28 and 47 nm. As the annealing temperature increases, a maximum coercive field of 12 kOe at 300 K (55 kOe at 10 K) was obtained by annealing at 1023 K for a grain size of 35 nm. The refinement of the neutron powder diffraction patterns (NPD) of PrCo3 from 1.8 to 300 K shows an expansion of the parameter a and a contraction of the parameter c, leading to a decrease of the ratio c/a. The evolution of the Co and Pr magnetic sublattices measured by NPD indicates that this compound is a highly anisotropic uniaxial ferromagnet with the easy magnetization axis parallel to . This experimental study has been completed by a theoretical investigation of the electronic structure of the PrCox (x = 2, 3 and 5) compounds. Band structure calculations with collinear spin polarization were performed by using the local approximation of the density functional theory scheme implemented in the projector-augmented wave method. The electronic structure of PrCo3 compound in both directions of spin shows that the majority of occupied states are dominated by the 3d states of Co, with a strong electronic charge transfer from Pr to Co. The PrCo3 electronic structure can be explained by a superimposition of those of PrCo2 and PrCo5, as expected from its crystal structure. The magnetic anisotropy has been confirmed for PrCo3, as a non-collinear spin calculation with the polarization along the c axis is shown to be more stable than with the polarization in the () plane.

New CeMgCo4 and Ce2MgCo9 compounds: Hydrogenation properties and crystal structure of hydrides

Two new ternary intermetallic compounds, CeMgCo4 (C15b pseudo-Laves phase, MgCu4Sn type) and Ce2MgCo9 (substitution derivative of PuNi3 type) were synthesized by mechanical alloying method. The structural and hydrogenation properties of these compounds were studied by X-ray diffraction and Pressure–Composition–Temperature measurements. Both compounds absorb hydrogen at room temperature and pressures below 10MPa forming hydrides with maximum compositions CeMgCo4H6 and Ce2MgCo9H12. Single plateau behavior was observed in P–C isotherm during hydrogen absorption/desorption by Ce2MgCo9 alloy. The CeMgCo4–H2 system is characterized by the presence of two absorption/desorption plateaus corresponding to formation of β-CeMgCo4H4 and γ-CeMgCo4H6 hydride phases. The structure of β-hydride CeMgCo4H(D)4 was determined from X-ray and neutron powder diffraction data. In this structure initial cubic symmetry of CeMgCo4 is preserved and hydrogen atoms fill only one type of interstitial sites, triangular MgCo2 faces. These positions are occupied by 70% and form octahedron around Mg atom with Mg–D bond distances 1.84Å.

Crystal structure and magnetic properties of V-doped YCo 2 and YCo 3 and their hydrides

Pseudo-binary YCo 3− x V x and YCo 2− x V x ( x = 0.1 and 0.2) phases have been investigated for the influence of V-doping on the crystal structure and magnetic properties of YCo 3 (PuNi 3-type, space group R 3 ¯ m ) and YCo 2 (MgCu 2-type, space group F d 3 ¯ m ) and their hydrides. All substituted solid solutions preserve the structure of the binary parent compounds. The lattice parameters increase with increasing V content. All investigated compounds and solid solutions can easily absorb hydrogen up to 3.2–3.9 at.H/f.u. at room temperature at 0.1–0.12 MPa pressure without amorphization. YCo 3 and solid solutions YCo 3− x V x show ferrimagnetic behaviour where Co/V substitution reduces T c from 301 K of YCo 3 to 225 K in YCo 2.8V 0.2. Hydrogenation causes complex antiferromagnetism below 200 K in the γ-phase hydrides with a reduced mean 3d-moment at low temperatures. Substitution of Co by V induces weak ferromagnetism in the archetypical itinerant electron metamagnet YCo 2 with Curie temperatures of 175 K and 110 K and a mean 3d-moment of 0.14 μ B and 0.07 μ B at 6 T and 2.5 K for x = 0.1 and x = 0.2, respectively. Hydrogen absorption enhances the mean 3d-moment slightly but reduces the ordering temperature to below 30 K in the corresponding β-phase hydrides. A ferromagnetic background occurs in all YCo 2 and YCo 3 based hydrides persisting up to above room temperature which is of different origin but appears to be not an intrinsic property of these hydrides.

Magnetic properties and structure of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi2Mn x (0 ≤ x ≤ 1.5)

Crystal structure, magnetization, coercive force, magnetic susceptibility, and anisotropic magnetostriction of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi2Mn x (0 ≤ x ≤ 1.5) have been studied. The samples with x ≤ 1 have an fcc structure, whereas TbNi2Mn1.25 has a rhombohedral structure of the PuNi3 type. It has been found that the magnetic ordering temperature increases sharply when manganese is added. As the Mn concentration grows, the magnetization and the magnetostriction decrease monotonically, while the coercive force increases. The experimental data obtained have been interpreted on the assumption that a partial substitution of manganese for terbium in TbNi2Mn x leads to local distortions of the crystal field acting on Tb ions, to the appearance of a local uniaxial random anisotropy, and to the formation of a noncollinear magnetic structure in the terbium sublattice.

Structural investigation and electrochemical properties of La 5− xCa xMg 2Ni 23 ( x = 0, 1, 2 and 3) hydrogen storage alloys

The structures and electrochemical properties of the La 5− x Ca x Mg 2Ni 23 ( x = 0, 1, 2 and 3) alloys were investigated. It was found that the La 5Mg 2Ni 23 alloy consists of Ce 2Ni 7-type, Gd 2Co 7-type, LaNi 5, Pr 5Co 19-type, Ce 5Co 19-type and LaMgNi 4 phases. Ca substitution for La is favorable for the formation of the PuNi 3-type phase. The Ca-substituted La 5− x Ca x Mg 2Ni 23 alloys are composed of PuNi 3-type, Gd 2Co 7-type and CaCu 5-type phases, except for the La 2Ca 3Mg 2Ni 23 alloy additionally containing 4 wt.% of Ni. Among these alloys, the La 3Ca 2Mg 2Ni 23 alloy has a highest discharge capacity (404.2 mAh/g) and a best high-rate dischargeability (HRD 600 = 61.6%) due to the optimum Ca content and the highest abundance of the PuNi 3-type and Gd 2Co 7-type phases.

Directional metal–hydrogen bonding in interstitial hydrides. III. Structural study of ErCo 3D x (0⩽ x⩽4.3)

The ErCo 3–D 2 system has been studied by in situ neutron powder diffraction (NPD) at 60 °C and 0–16 bar deuterium pressure. Two deuteride phases were identified, β-ErCo 3D 1.07−1.38 and γ-ErCo 3D 3.7−4.3. They were structurally characterized at the compositions β-ErCo 3D 1.37 and γ-ErCo 3D 3.7 by high-resolution neutron and synchrotron powder diffraction. In contrast to the analogous nickel systems RNi 3–D 2 ( R=Er, Ho; see part I, J. Alloys and Compds. 404–406 (2005) 89–94, and part II, J. Alloys and Compds. 2005, in press), their structures preserve the symmetry of the parent alloy (PuNi 3-type, space group R-3 m). Deuterium occupies mainly AB 2 building blocks in the β-phase, and AB 2 and AB 5 building blocks in the γ-phase. In the AB 2 building blocks cobalt is surrounded by an average of 3.8 ( β-ErCo 3D 1.37) and 4.4 D-atoms ( γ-ErCo 3D 3.7) in disordered distorted octahedral configurations (point symmetry −3), in contrast to nickel that is surrounded by ∼3 ( β 1- and β 2- RNi 3D x , R=Er, Ho) and ∼4 ( γ-ErNi 3D 3.7) D-atoms in disordered trigonal (pyramidal) and tetrahedral configurations, respectively (point symmetry 3). These results indicate that the D-atom distributions in this homologous series depend on the nature of the transition element rather than on geometric factors, and that directional bonding effects similar to those in non-metallic complex transition metal hydrides also prevail in metallic interstitial metal hydrides.

Effect of annealing treatment on structure and electrochemical properties of La 0.67Mg 0.33Ni 2.5Co 0.5 alloy electrodes

La 0.67Mg 0.33Ni 2.5Co 0.5 alloys were prepared by induction melting followed by different annealing treatments (1023, 1073, 1123 and 1173 K) for 24 h. Alloy structure and electrochemical properties of different annealed alloys have been studied systematically by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical experiments. Alloy structure analyses show that all of the alloys consisted of complex phases such as (La, Mg)(Ni, Co) 3 phase (PuNi 3-type, SG: R-3 m), (La, Mg) 2(Ni, Co) 7 phase (Ce 2Ni 7-type, SG: P6 3/mmc), LaMg(Ni, Co) 4 phase (MgCu 4Sn-type, SG: F-4 3 m) and La(Ni, Co) 5 phase (CaCu 5-type, SG:P6/mmm). One thousand one hundred and twenty-three kelvin benefited formation of (La, Mg)(Ni, Co) 3 phase best. Main phase in alloy became (La, Mg) 2(Ni, Co) 7 phase at 1173 K annealing treatment. Electrochemical experiments show that absorption/desorption plateau became flatter and wider after annealing treatment, that all of the alloy electrodes exhibited good activation characteristics, that annealing treatment improved discharge capacities of alloy electrodes from 315 mAh g −1 (as-cast) to 402.5 mAh g −1 (1173 K). At the same time, cyclic stability of alloy electrodes was also improved with rise of annealing temperature, especially for alloy electrode (S 70 = 92.9%) with main phase (La, Mg) 2(Ni, Co) 7 at 1173 K. As (La, Mg)(Ni, Co) 3 phase in alloys increased, high rate dischargeability characteristics were deteriorated. However, alloy electrode with main phase (La, Mg) 2(Ni, Co) 7 exhibited the best kinetic characteristics. All experiments imply that alloy electrode with main phase (La, Mg) 2(Ni, Co) 7 possessed excellent overall electrochemical properties.

Crystallographic and hydriding properties of the system La 1− xCe xY 2Ni 9 ( xCe=0, 0.5 and 1)

The structural properties of the system La 1− x Ce x Y 2Ni 9 with x Ce=0, 0.5 and 1 have been investigated by electron probe microanalysis, powder X-ray diffraction and absorption spectroscopy. The compound LaY 2Ni 9 adopts a rhombohedral structure of PuNi 3-type ( R-3 m space group, Z=3). It can be described as an intergrowth between RM 5 (Haücke phase) and RM 2 (Laves phase) type structures. Among the two available crystallographic sites for R atoms, lanthanum occupies preferentially the site 3 a leading to a partially ordered ternary compound. Substitution by cerium involves anisotropic variations of the cell parameter with a decrease of a and an increase of c leading to an overall cell volume reduction. Increasing cerium content does not induce any symmetry change but leads to a statistical distribution of the rare earths over the two sites 3 a and 6 c involving an evolution toward a pseudo-binary compound. This behavior is related to the intermediate valence state of cerium observed by X-ray absorption spectroscopy. The hydriding properties of the two compounds LaY 2Ni 9 and CeY 2Ni 9 are described in relation with their crystallographic structure.

Hydrogen absorption characteristics in the Tb1−xZrxFe3 (x=0.1, 0.2, 0.3) system

The hydrogen absorption pressure-composition-isotherms of the PuNi3 type rhombohedral Tb1−xZrxFe3 (x=0.1, 0.2, 0.3) alloys are investigated by Sievert’s apparatus, in the temperature and pressure ranges 75≤T(°C)≤150 and 0.1≤P(bar)≤25, respectively, with a view to study the dependence of hydrogen solubility and the plateau pressure on Zr content. The P-C isotherms show the presence of a single plateau region in the temperature and pressure ranges studied and it is found that the plateau pressure at any given temperature increases with increase of Zr content along with a reduction in the hydrogen capacity. The absorption of hydrogen is accompanied by a maximum of 17.4% expansion in the unit cell volume of the host material without any change in PuNi3 type structure as evidenced by the X-ray diffraction studies on the alloy– hydrides. The presence of single and two phase regions as seen in the P-C isotherms are confirmed from the powder X-ray diffractogram of the alloy–hydrides with appropriate hydrogen concentration. The powder X-ray diffractograms on the alloy–hydrides with maximum hydrogen concentration further show the absence of hydrogen induced amorphization (H1A) upon hydrogenation.