Добірка наукової літератури з теми "Rare-earth Based Intermetallic Compunds"

The paper studies the combined effects of rare earth metals such as praseodymium, neodymium and erbium, melting technologies on intermetallic alloy based on nickel aluminide and pure charge materials using 25, 50 and 75 wt. % of waste, the technology of casting single-crystals of crystallographic orientation [001] and their heat treatment combined with hot isostatic pressing (HIP), on mechanical properties and long-term strength at the level of passport data.

This review discusses the properties of candidate compounds for semi-hard and hard magnetic applications. Their general formula is R1−sT5+2s with R = rare earth, T = transition metal and 0≤s≤0.5 and among them, the focus will be on the ThMn12- and Th2Zn17-type structures. Not only will the influence of the structure on the magnetic properties be shown, but also the influence of various R and T elements on the intrinsic magnetic properties will be discussed (R = Y, Pr, Nd, Sm, Gd, … and T = Fe, Co, Si, Al, Ga, Mo, Zr, Cr, Ti, V, …). The influence of the microstructure on the extrinsic magnetic properties of these R–T based intermetallic nanomaterials, prepared by high energy ball milling followed by short annealing, will be also be shown. In addition, the electronic structure studied by DFT will be presented and compared to the results of experimental magnetic measurements as well as the hyperfine parameter determined by Mössbauer spectrometry.

The impact properties of high-pressure die cast Mg-RE alloys were investigated. It was found that, for rare earth contents between 2-4 wt.%, the Mg-La and Mg-Nd alloys performed better than the Mg-Ce alloys in un-notched tests. The notched results appear to be related to the amount of intermetallic. In contrast, the un-notched results indicate that at some compositions the Mg-La alloys out-performed the other alloys when compared to the amount of intermetallic. It was apparent that a lamellar eutectic structure can improve the un-notched impact properties of Mg-RE based alloys even when this is not evidenced in tensile test or notched impact results.

After approximately 30 years of dormancy, the binary, ternary, and multicomponent intermetallic compounds of rare earth metals (R) with the group 14 elements (T) at the R5T4 stoichiometry have become a goldmine for materials science, condensed matter physics, and solid-state chemistry. In addition to providing numerous opportunities to clarify elusive structure-property relationships, the R5T4 compounds may soon be developed into practical materials by exploiting their unique sensitivity toward a variety of chemical and physical triggers. The distinctiveness of this series is in the remarkable flexibility of the chemical bonding between well-defined, self-assembled, subnanometer-thick slabs and the resultant magnetic, transport, and thermodynamic properties of the R5T4 compounds that can be controlled by varying either or both R and T, including mixed rare earth elements on the R-sites and different group 14 (and 13 or 15) elements occupying the T-sites. In addition to chemical means, the interslab interactions are tunable by temperature, pressure, and magnetic field. Presently, a substantial, yet far from complete, body of knowledge exists about the Gd compounds with T = Si and Ge. In contrast, only a little is known about the physics and chemistry of R5T4 alloys with other lanthanides, while compounds with T = Sn and Pb remain virtually unexplored.

Magnetic intermetallic compounds based on rare earth elements and 3d transition metals are widely investigated due to the functionality of their physical properties and their variety of possible applications. In this work, we investigated the features of the electronic structure and magnetic properties of ternary intermetallic compounds based on gadolinium GdMn1-xTixSi, in the framework of the DFT + U method. Analysis of the densities of electronic states and magnetic moments of ions in Ti-doped GdMnSi showed a significant change in the magnetic properties depending on the contents of Mn and Ti. Together with the magnetic moment, an increase in the density of electronic states at the Fermi energy was found in almost all GdMn1-xTixSi compositions, which may indicate a significant change in the transport properties of intermetallic compounds. Together with the expected Curie temperatures above 300 K, the revealed changes in the magnetic characteristics and electronic structure make the GdMn1-xTixSi intermetallic system promising for use in microelectronic applications.

RENi5 (RE: rare earth) based alloys have been extensively evaluated for use as an electrode material for nickel-metal hydride batteries. A variety of alloys have been developed from the prototype intermetallic compound LaNi5. The use of mischmetal as a source of rare earth combined with transition metal and Al substitutions for Ni has caused the evolution of the alloy from a binary compound to one containing eight or more elements. This study evaluated the microstructural features of a complex commercial RENi5 based alloy using scanning and transmission electron microscopy.The alloy was evaluated in the as-cast condition. Its chemistry in at. pct. determined by bulk techniques was 12.1 La, 3.2 Ce, 1.5 Pr, 4.9 Nd, 50.2 Ni, 10.4 Co, 5.3 Mn and 2.0 Al. The as-cast material was of low strength, very brittle and contained a multitude of internal cracks. TEM foils could only be prepared by first embedding pieces of the alloy in epoxy.

Depuis quelques dizaines d’années, l’étude de composés intermétalliques à base des métaux de transition 3d, et d’éléments de terres rares 4f, présente un vif intérêt tant d’un point de vue fondamental qu’appliqué. Les propriétés remarquables de ces matériaux magnétiques proviennent de la présence, dans le même composé, de métaux de transition 3d, caractérisés par un magnétisme itinérant donné par les électrons de la bande externe 3d, et de métaux de terres-rares 4f qui, eux, présentent un magnétisme localisé dû aux électrons de la couche interne 4f. La recherche présentée ici se concentrera sur deux diagrammes des phases ternaires alliant samarium, fer et nickel et l’yttrium, fer et Gallium dans le deuxième système. Ces types d’intermétalliques sont aussi potentiellement caractérisés par un effet magnétocalorique (EMC) défini par le réchauffement ou le refroidissement de ces matériaux magnétiques sous l’application ou la suppression d’un champ magnétique extérieur.Le but de la thèse est la construction des deux diagrammes ternaires qui n’ont jamais été publiés et étudier les propriétés physicochimiques dans les systèmes (Sm,Y)-Fe-(Ni,Ga). Cette recherche aboutira à la détermination des diagrammes ternaires Sm-Fe-Ni et Y-Fe-Ga expérimentales (section isotherme à 800°C) et d’étudier les propriétés structurales de ces composés intermétalliques. Les propriétés magnétiques et magnétocaloriques ont également été étudiées en couplant les analyses magnétiques avec les mesures par diffraction des rayons X et par spectroscopie Mössbauer. Ces travaux ont mis en évidence l’influence importante de la nature et du taux de fer substitué au nickel et au gallium dans les deux systèmes sur les propriétés magnétiques
In recent decades, the study of intermetallic compounds containing 3d transition metals and 4f rare earth elements presents great interest both from a fundamental point of view and in its various applications. The remarkable properties of these magnetic materials come from the presence, in the same compound, of 3d transition metal, characterized by an itinerant magnetism given by the electrons in the 3d external band, and 4f rare-earth which themselves have a localized magnetism due to the electrons of the 4f inner layer. The research presented here will focus on the construction of two ternary phase diagrams combining [Sm-Fe-Ni] in the first system and [Y-Fe-Ga] in the second one. These types of intermetallics are also characterized by a magnetocaloric effect (EMC) defined by the heating or cooling of these magnetic materials under the application or removal of an external magnetic field.The aims of the thesis are the construction of two ternary phase diagrams that have never been published before and the study of the physicochemical properties in the (Sm, Y) -Fe- (Ni, Ga) systems. This research will lead to the determination of experimental ternary phase diagrams Sm-Fe-Ni and Y-Fe-Ga (isothermal section at 800°C) and to study the structural properties of some intermetallic compounds.The magnetic and magnetocaloric properties were also studied by coupling magnetic analysis with the X-ray diffraction and Mössbauer spectroscopy measurements. This work has highlighted the important influence of the nature and rate of iron substituted by nickel and gallium in both systems on the magnetic properties

博士
國立成功大學
物理學系碩博士班
90
The mixed-valence (MV) and heavy-fermion (HF) phenomena in cerium based intermetallic compounds are the subjects of continuous interest for experimental study of their physical behaviors for decades. It is believed that the hybridization of highly correlated 4f electrons with the itinerant conducting electrons should be responsible for both HF and MV behaviors. New ternary intermetallic compounds of type CeTX2 (where T = transition metals and X= Si, Ge) remain a considerable focus. In this work, we studied on this new type of Ce-based system. The thesis mainly consists of three parts. In the first part, we studied on the physical properties of CePdSi2. We examined x-ray diffraction, dc electrical resistivity, dc and ac magnetic susceptibilities, specific heat and the Ce LIII-edge x-ray absorption spectrum of this cerium based ternary compound. Electrical resistivity ρ(T) indicates the presence of Kondo and crystal-field effects. The results of magnetic susceptibility measurements for CePdSi2 exhibit a spin-glass behavior at Tf ~ 5 K and the antiferromagnetism at TN = 2.7 K. The M(t) measurement and magnetic entropy calculation also indicate the presence of spin-glass phase. The specific-heat measurement shows two peaks in C(T), one is at around 2.7 K, another is at ~ 6.8 K. The former is likely due to an antiferromagnetic transition, the latter might be due to the Schottky anomaly with spin-glass contribution. The linear specific-heat coefficient γ of CePdSi2 is 0.348 Jmole-1K-2, which is much larger than those of normal metals. This large γ value might result from Kondo effect, crystal effect and spin-glass magnetism. From these measurements, in additional to an antiferromagnetic Kondo Lattice, this compound might be magnetically classified as a re-entrant spin glass. The second part of this thesis, we worked on the evolution from heavy-fermion to mixed valence behavior in the series CePt1-xIrxSi2. To study the evolution from heavy-fermion to mixed-valence behavior upon substituting Pt for Ir in the ternary intermetallic compound CePtSi2, we carried out the x-ray diffraction, dc electric resistivity, Ce LIII-edge x-ray absorption spectra (XAS), dc susceptibilities, and specific heat measurements in the series CePt1-xIrxSi2 (x = 0, 0.2, 0.4, 0.6, 0.8. 1.0). The results obtained allowed us to suggest that the evolution from heavy-fermion to mixed-valence behavior is likely due to the enhancement of hybridization between the Ce 4f-electron wave function and sp wave function of the adjacent transition metal ion. Besides, it was found that x ~ 0.6 is the borderline region between heavy-fermion and mixed-valence regimes. The last part of this thesis, we studied on the evolution from mixed-valence to anti-ferromagnetic Kondo-Lattice behavior in the series CeNi(Si1-xGex)2, we carried out the x-ray diffraction, dc electric resistivity, Ce LIII-edge x-ray absorption spectra (XAS), dc and ac susceptibilities, and specific heat measurements in the series CeNi(Si1-xGex)2 (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8. 1.0). The results show that CeNiSi2 is a mixed-valence compound. On the other hand, CeNiGe2 is a Kondo-Lattice with an anti-ferromagnetic phase transition at ~ 5.8 K. When we substituted Ge for Si, with an increase in x, there is a discernible tendency towards a increasing in unit-cell volume. The increasing in unit cell volume will decrease the hybridization of Ce 4f electron wave function with the sp wave function of the neighboring transition metal atoms and increase the localization of 4f electrons and finally drive the system from MV behavior to anti-ferromagnetism. The results allowed us to suggest that the evolution from mixed-valence to Kondo-lattice behavior is likely due to the dehybridization between the Ce 4f-electron wave function and sp wave function of the adjacent transition metal ion. Besides, from these measurements, it was found that x = 0 ~ 0.2, the series show basically mixed-valence behavior. When x = 0.8 ~ 1.0, the series show Kondo-Lattice behavior. Between x = 0.4 ~ 0.6, the behaviors of the samples can be characterized as single impurity Kondo effect.

Abstract Neutron absorbers are expected to play an important role in the long-term storage of spent nuclear fuels and nuclear wastes. High neutron absorbing capability, long-term stability, and the capacity to stay with the fuel are important criteria in preventing critical conditions during possible waste package degradation in geological time frames. Existing available neutron absorbing materials are based on boron or boron-10 isotope modifications of austenitic stainless steels or to aluminum based metal matrix composites. Specific rare earths such as gadolinium, samarium, or europium are found to have much higher thermal neutron cross section than boron or boron-10 but have high reactivity which limit their stability and ultimate applicability. In this paper, it is described how it is possible through a nanotechnology approach, to overcome the solubility and stability limitations of conventional materials to allow incorporation of high amounts of boron and rare earths into advanced HVOF coatings. During the development of the NeutraShieldTM Coatings, it was found that high fractions of rare earth elements such as gadolinium along with high concentrations of boron could be dissolved in the liquid melt and then remain soluble in the metallic glass structure. During the transformation of the glass to the nanocomposite structure, the rare earths are found to come out of supersaturated solid solution to form stable nanoscale ternary intermetallic R2Fe14B phases which form in a commensurate fashion and is protected by the highly noble matrix. Abstract only; no full-text paper available.

Samarium cobalt permanent magnets have been widely used for their excellent intrinsic magnetic properties such as very high Curie temperature, high anisotropy fields and most importantly excellent temperature coefficients of induction and coercivity. These materials have continuing industrial interest especially for applications operating at elevated temperatures and in the presence of high demagnetizing fields, such as particle accelerators, high frequency traveling wave tubes (TWTs), servo-motors and automotive and aerospace applications. An area of opportunity for improving performance of SmCo magnets is increasing magnet toughness — resistance to fracture. Like all other sintered rare earth magnetic materials, SmCo magnets are based on intermetallic compounds which are intrinsically brittle and can crack in the course of fabrication, machine work, and installation in the application. Increased toughness would also reduce handling sensitivity of magnetized magnets. For many years, studies on SmCo magnets have been focused on their magnetic properties, but the mechanical characteristics, strengthening and toughening mechanisms have been rarely reported. Understanding the phase and structural transformations induced in the SmCo magnets during the manufacturing process offers insight into potential modifications — chemical or processing-related. In this study, microstructural characterizations of 1:5 and 2:17 Sm-Co magnets were carried out using optical and scanning electron microscopes. In scanning electron microscopy (SEM), backscattered electron imaging and energy dispersive X-ray (EDX) microanalysis were used to investigate different phases and oxides. Finally, crystal structure of the magnets was studied using an X-ray diffractometer (XRD). The study correlates the microstructure characterization with the thermal processing history of different grades of SmCo magnets.