Laves Phase Structure Research Articles

Structural, magnetic, and magnetostrictive properties of Prx(Tb0.27Dy0.73)1‒xFe1.95 polycrystalline

Magnetostriction materials are a significant kind of magnetic functional materials, while RFe2 (R = rare earth) compounds, especially Tb0.27Dy0.73Fe2, with cubic Laves phase structure, are the most famous. In this work, polycrystalline Prx(Tb0.27Dy0.73)1–xFe1.95 (x = 0, 0.05, 0.10, 0.15, 0.2, 0.25) alloys were synthesized to explore the influence of adding Pr on the structural, magnetic and magnetostrictive properties of Tb0.27Dy0.73Fe1.95. The results show that Prx(Tb0.27Dy0.73)1–xFe1.95 alloys can form the C15 Laves phase when x ≤ 0.2. Meanwhile, the samples with a Pr content of up to 0.1 exhibit a higher saturation magnetostriction compared to the Pr-free sample. As the content of Pr in Prx(Tb0.27Dy0.73)1–xFe1.95 rises from 0 to 0.1, the saturation magnetostriction, λs, improves from 1057 ppm to 1147 ppm. The apparent enhancement of the magnetostrictive property of Tb0.27Dy0.73Fe1.95 reveals the great potential of (Pr,Tb,Dy)Fe2 to become a widely-used magnetostriction material. Larger lattice distortion of the material itself leads to an increase in magnetostriction.

Layered composite magnetic refrigerants for hydrogen liquefaction

Many exciting effects resulting from the coupling of magnetic sublattice with a magnetic field, may be exposed by changing the field. One such phenomenon is the magnetocaloric effect, which is characterized by the absorption or emission of heat in response to changes in the external magnetic field. Magnetic refrigeration based on the magnetocaloric effect has emerged as an attractive alternative to conventional cooling technology that relies on gas compression and expansion. It is not only more efficient and environmentally friendly, but it can also be implemented across a broad temperature range, from ultra-low to a few hundred Kelvin temperatures. One of the areas where magnetic cooling can have a significant impact is hydrogen liquefaction. Hydrogen is one of the most promising candidates for clean energy sources, but it must be liquefied to facilitate storage and transportation, which requires cooling it down to ∼20 K. The ideal magnetic refrigerant should exhibit consistent magnetocaloric properties across the entire operating temperature range of a cooler. This paper presents novel three-layer composite magnetic refrigerants that provide a uniform magnetocaloric response over a 30 K temperature range. The selected initial HoNi2, DyNi2, and TbNi2 magnetic intermetallic compounds with a Laves phase structure exhibit large magnetocaloric properties in the temperature range of 13–37 K. The composite composition of 23.56 wt% HoNi2 + 18.21 wt% DyNi2 + 58.23 wt% TbNi2 optimized for 2 T magnetic field change, was determined through numerical approach. The composites are manufactured using spark plasma sintering (SPS) and innovative high-isostatic-pressure (HIP) synthesis. The results of isothermal entropy change derived from magnetization data for a 2 T magnetic field change indicated 4.7 J/kgK (47.2 mJ/cm3K) and 4.4 J/kgK (44.2 mJ/cm3K) in the temperature range of approx. 13–42 K for composites after SPS and SPS + HIP processes, respectively. Despite the sample subjected to HIP showing slightly lower results, the entropy change is nearly uniform over the 30 K temperature range due to enhanced atomic diffusion between neighboring compounds, as confirmed by microscopic studies. Such a uniform magnetocaloric response in ∼30-K temperature range has never been observed before in layered refrigerants. By utilizing the innovative high-isostatic-pressure synthesis technique, we have paved the way to high-performing magnetic composite materials that can be used in cryogenic magnetic coolers operating over a broad temperature span, expanding the possibilities of what can be achieved and laying the foundation for cost-effective, clean hydrogen energy.

Development of Ti–Zr–Mn–Cr-(V–Fe) based alloys for hydrogen feeding system in hydrogen metallurgy application

AB2-type Ti-based hydrogen storage alloys are considered promising candidates for the hydrogen feeding system in hydrogen-metallurgy application. In this work, Ti0·87Zr0.15MnxCr1.75-xV0.25 (x = 1.25–1.5), Ti0·87Zr0·15Mn1·5Cr0.5-y(VFe)y (y = 0.25–0.43) and Ti0.85+zZr0.15Mn1·5Cr0·07(VFe)0.43 (z = 0–0.05) alloys were synthesized using induction levitation melting, where ferrovanadium VFe consists of 80 wt% V and 20 wt% Fe. Subsequently, their microstructures and hydrogen storage performances were systematically investigated. The results demonstrate that all alloy samples exhibit a single C14 Laves phase structure with uniform element distribution. With the increment of Cr/Mn, VFe/Cr ratio, or Ti stoichiometry, the alloys exhibit enhanced hydrogen storage capacity, accompanied by a decrease in hydrogenation equilibrium pressure because of interstitial volume expansion or hydrogen affinity improvement, which is also supported by density functional theory calculations. Considering the application of hydrogen metallurgy, Ti0·86Zr0·15Mn1·5Cr0·07(VFe)0.43 alloy is regarded as a promising candidate, exhibiting a saturated capacity of 2.01 wt% H2, an effective reversible capacity of 1.91 wt% H2, rapid hydrogenation kinetics, excellent cyclic durability and low costs. This work provides valuable insights into the compositional design of hydrogen storage alloys for the hydrogen feeding system in hydrogen metallurgy applications.

Thermodynamic and elastic properties of laves phase AB2-based alloys and their hydrides: A density functional theory (DFT) study

A first-principles method based on the density functional theory (DFT) was employed in conjunction with quasi-harmonic Debye model to investigate the structural, elastic, and thermodynamic properties of a series of AB2-based Laves phases alloys and their hydrides. Simulation results revealed that the studied materials possess the Laves phase structure with lattice parameters comparable to experimental findings. For the first time, to the best of our knowledge, mixing entropy determined using Debye model was used to classify alloys into (Low- Medium-High Entropy Alloys) LEA, MEA and HEA categories rather than the commonly used ideal solution model, which is often inaccurate and ignores the impact of temperature. Lattice analyses of the alloy materials indicated that cell volume increases with the addition of elements, while the enthalpy of hydride formation indicates that hydrogen absorption in these alloys is exothermic and that the 3.00 H/F.U configuration is energetically stable. The alloys and their hydrides are metallic with no band gap at the Fermi level. The thermodynamic properties were studied using the quasi-harmonic Debye model and it was found that Bulk modulus decreases with increasing volume, and the hydrides possess lower bulk modulus compared to their metallic counterparts. Moreover, Debye temperature decreases with the gradual addition of elements, indicating weaker chemical bonds in ternary and other alloys. All hydrides have lower Debye temperature than their parent alloy materials. Finally, The alloys are classified into low-, medium-, and high-entropy alloys based on mixing entropy calculated using the Debye model. TiMn2 is classified as a low-entropy alloy, ZrMn2, Ti0.5Zr0.5Mn2, and Ti0.5Zr0.5MnFe as medium-entropy alloys, and Ti0.5Zr0.5(MnCr)2, Ti0.5Zr0.5Mn2/3Fe2/3Cr2/3, and Ti0.5Zr0.5Mn0.5Fe0.5Cr0.5Ni0.5 as high-entropy alloys.

Structural-regulation of Laves phase high-entropy alloys to catalytically enhance hydrogen desorption from MgH2

Magnesium hydride (MgH2) is a promising hydrogen storage material, but slow hydrogen desorption kinetics and poor cycling stability still limit its development. Catalytic doping was demonstrated to provide effective solution for it. In this work, we develop novel Zr-based high-entropy alloys (HEAs) catalysts with different Laves phase structures to improve the hydrogen storage in MgH2. It was demonstrated that the catalyst grain size, defect density and lattice distortion have a great influence on the performance of HEAs catalysts. Specially, the C15 type Laves phase HEA exhibits a better catalytic effect than that of C14 type. The introduction of HEAs with "hydrogen pump" effect would shift the rate-limiting step of MgH2 hydrogen desorption from two-dimensional nucleation growth to two-dimension phase boundary migration, which makes it exhibit both great better hydrogen desorption kinetics enhanced by nine times and cycling stability with 92 % capacity retention after 30 cycles. This work not only highlights the impact of Laves phase crystal structure regulation on HEAs catalysts, but also provides insights into the design and development of HEAs catalysts to improve the hydrogen storage performance of MgH2.

A New Strategy for the Design of Triple-Phase Eutectic High-Entropy Alloys Based on Infinite Solid Solution and Pseudo-Ternary Method.

Eutectic high-entropy alloys (EHEAs) have combined both high-entropy alloys and eutectic alloy contributions, with excellent castability and high-temperature application potential. Yet, multielement/triple-phase eutectic high-entropy alloy (TEHEA) designs remain puzzling. This work proposed a new strategy based on an infinite solid solution and pseudo-ternary model to reveal the puzzle of TEHEAs. The designed triple-phase eutectic high-entropy alloys (TEHEAs) with more than seven elements were identified as face-centered cubic (FCC), ordered body-centered cubic (B2), and Laves phase structures. In this work, the alloy C showcases outstanding comprehensive mechanical properties, offering a novel avenue for the design of high-performance EHEAs.

Interface Nuclei in the Y-Ag-Zn System: Three Chemical Pressure-Templated Phases with Lamellar Mg2Zn11- and CaPd5+x-Type Domains.

The interface nucleus approach was recently presented as a framework for understanding and predicting the emergence of modular intermetallic phases, i.e., complex structures derived from the assembly of units from simpler parent structures. Here, we present the synthesis and crystal structures of three new modular intermetallics in the Y-Ag-Zn system that support this strategy: YAg2.79Zn2.80 (I), YAg2.44Zn3.17 (II), and YAg2.71Zn2.71 (III). Each of these structures is derived from an intergrowth of slabs of the Mg2Zn11 and CaPd5+x types, with the chief differences being in the thickness and degree of disorder within the CaPd5+x-type domains. The merging of the parent structure domains is facilitated by their sharing a common geometrical unit, a double hexagonal antiprism. The use of this motif as an interface nucleus mirrors its role in another family of structures: an intergrowth series combining the CaCu5 and Laves phase structure types, as in the PuNi3-type phase YNi3. However, there is a key difference between the two series. While in the CaCu5/Laves intergrowths, the interface between the parent structures arises perpendicular to the interface nucleus's unique (hexagonal) axis, in the Mg2Zn11/CaPd5+x-type intergrowths revealed here, the interfaces run parallel to this axis. Using CP analysis of the Mg2Zn11/CaPd5+x-type parent structures, we trace this behavior to the different directions of high-CP compatibility of the interface nuclei in the Mg2Zn11/CaPd5+x and CaCu5/Laves structure type pairs. In this way, the Y(Ag/Zn)5+x phases highlight the role that interface nuclei play in directing the domain morphologies of modular intermetallic phases.

High-pressure high-temperature synthesis of NdRe2.

In this study, we report the synthesis of a new cubic neodymium-rhenium metallic alloy NdRe2 through the utilization of high pressure and laser heating in a diamond anvil cell. NdRe2 crystallizes in the space group with a lattice parameter equal to 7.486 (2) Å and Z = 8at 24 (1) GPa and 2,200 (100) K. It was studied using high-pressure single-crystal X-ray diffraction. The compound crystallizes in the cubic MgCu2 structure type. Its successful synthesis further proves that high-pressure high-temperature conditions can be used to obtain alloys holding a Laves phase structure. Ab initio calculations were done to predict the mechanical properties of the material. We also discuss the usage of extreme conditions to synthesize and study materials present in the nuclear waste.

Optimized hydrogen storage properties of Ti–Zr–Mn–VFe-based alloys by orthogonal experiment for upscaled production

Ti–Mn-based hydrogen storage alloys have been widely developed for hydrogen compressors and storage because of their excellent hydrogen storage properties. However, there is still a need to develop a high-capacity hydrogen storage based on low-cost and large-scale preparation. Herein, cheap VFe80 intermetallic alloy is employed to replace the expensive V, and Ti–Zr–Mn–VFe-based alloys ((Ti1-yZry)1+xMn1.88-z(VFe)z, x = 0, 0.05, 0.1, y = 0.05, 0.1, 0.15, z = 0.34, 0.44, 0.54) with mainly C14 Laves phase structure were designed and prepared to optimize the composition by an orthogonal experiment. According to the orthogonal analysis, it is found that the maximum hydrogen storage capacity and hysteresis factor mainly are controlled by the content of VFe80 in the Ti–Zr–Mn–VFe-based alloys. The over-stoichiometry of A-side governs the plateau slope, and the content of Zr decreases hydrogen plateau pressure. The optimal Ti0.9Zr0.1Mn1.44(VFe)0.44 alloy achieves a revisable hydrogen storage capacity of 1.73 wt% with low plateau hysteresis factor (0.49) and plateau slope factor (0.73) at room temperature, the dehydrogenation enthalpy and entropy values respectively are 33.92 kJ/mol and 120.64 J/(mol∙K), which exhibits the best overall hydrogen storage properties. Furthermore, the optimal alloy was successfully produced on a large scale, which provides empirical value for upscaled production of AB2 Laves-phase hydrogen alloys.

Hydrogen-Stabilized ScYNdGd Medium-Entropy Alloy for Hydrogen Storage.

The research on the functional properties of medium- and high-entropy alloys (MEAs and HEAs) has been in the spotlight recently. Many significant discoveries have been made lately in hydrogen-based economy-related research where these alloys may be utilized in all of its key sectors: water electrolysis, hydrogen storage, and fuel cell applications. Despite the rapid development of MEAs and HEAs with the ability to reversibly absorb hydrogen, the research is limited to transition-metal-based alloys that crystallize in body-centered cubic solid solution or Laves phase structures. To date, no study has been devoted to the hydrogenation of rare-earth-element (REE)-based MEAs or HEAs, as well as to the alloys crystallizing in face-centered-cubic (FCC) or hexagonal-close-packed structures. Here, we elucidate the formation and hydrogen storage properties of REE-based ScYNdGd MEA. More specifically, we present the astounding stabilization of the single-phase FCC structure induced by the hydrogen absorption process. Moreover, the measured unprecedented high storage capacity of 2.5 H/M has been observed after hydrogenation conducted under mild conditions that proceeded without any phase transformation in the material. The studied MEA can be facilely activated, even after a long passivation time. The results of complementary measurements showed that the hydrogen desorption process proceeds in two steps. In the first, hydrogen is released from octahedral interstitial sites at relatively low temperatures. In the second, high-temperature process, it is associated with the desorption of hydrogen atoms stored in tetrahedral sites. The presented results may impact future research of a novel group of REE-based MEAs and HEAs with adaptable hydrogen storage properties and a broad scope of possible applications.

High-Temperature Thermal Stability of Hot Isostatic Pressed Co25.1Cr18.8Fe23.3Ni22.6Ta8.5Al1.7 (at%) Eutectic High-Entropy Alloy

An eutectic high-entropy alloy (EHEA) consisting mainly of a face-centered cubic (FCC) phase and a C14 Laves phase with the compositions of Co25.1Cr18.8Fe23.3Ni22.6Ta8.5Al1.7 (at%) was successfully prepared by hot isostatic pressing. The present EHEA exhibits a skeleton-type Laves phase structure, deviating from typical EHEA structures. After a series of annealing treatments at 1000 °C for different durations (ranging from 0 to 150 h), the Co3Ta phase precipitated after annealing. The mechanical properties measured at 850 °C showed a tensile strength of 441 MPa and an elongation of 3.3%. The results of the high-temperature tests showed that the mechanical properties of this alloy did not change significantly before and after annealing, and its microstructure showed a high degree of stability, which suggests that the material has some potential for use in high-temperature environments.

Magnetism, magnetocaloric and magnetostrictive effects in RCo2 – type (R = Tb, Dy, Ho) laves phase compounds

This work presents the results of a comparative analysis of the thermal, magnetic, magnetocaloric and magnetostrictive properties of the Dy0.42Ho0.42Tb0.16Co2, Dy0.5Ho0.5Co2 and TbCo2 compounds. All studied compounds have the MgCu2-type Laves phase structure at room temperature. Dy0.5Ho0.5Co2 and TbCo2 demonstrate first- and second-order transitions from a paramagnetic state to a magnetically ordered one, respectively. Special attention is given to determining the order of magnetic phase transition in a multicomponent compound with three rare earth elements (Tb,Dy and Ho). Features of the magnetocaloric effect and magnetostriction of (Tb,Dy,Ho)Co2 compounds have been studied in magnetic fields up to 14 T and in wide temperature range (4.2 – 300 K). The joint manifestation of significant magnetocaloric and magnetovolume effects at the Curie temperature can be useful for a variety of technical applications.

Математическое моделирование взаимодействия водорода с многокомпонентными ИМС на основе гексагональных фаз Лавес

To calculate the properties of previously unstudied intermetallic compounds (IMC), a statistical model developed in our laboratory was applied, which uses already known literature data on the thermodynamic parameters of absorption / desorption reactions of hydrogen for intermetallic compositions with the structure of hexagonal Laves phases. For the alloys, hydrogen absorption and desorption isotherms were plotted. Comparison of calculated and experimental data was carried out to assess the correctness of the forecast model.

Magnetocaloric, magnetostrictive and 57Fe Mössbauer studies of the multicomponent (Er,Y,Sm)Fe[formula omitted] compounds

The effect of substitutional 4f-elements on the magnetism of rare-earth compounds RFe2-type with the Laves phase structure is studied to find new multifunctional materials, as well as to define the macro- and microscopic parameters of multicomponent magnets. The crystal structure of (Er,Y,Sm)Fe2 compounds is investigated by X-ray powder diffraction. Detailed information on the magnetic properties of the iron sublattice for multicomponent compounds with three different rare-earth elements is obtained for the first time by means of the 57Fe Mössbauer spectroscopy. The main regularities in the magnitude variation of magnetocaloric effect and magnetostriction (linear, anisotropic and volume) in varying composition of the (Er,Y,Sm)Fe2 compounds are determined.

Stoichiometry and annealing condition on hydrogen capacity of TiCr2-x AB2 alloys

This study presents the effect of stoichiometry and annealing condition on Ti–Cr AB2-type hydrogen storage alloys. Prior to annealing the majority phase of the as-cast alloys was the C14 Laves phase, with separate Ti and Cr phases. Annealing treatment (1273 K/14 d) led to a transition from C14 to C15 Laves phase structure. Both C14 (as-cast) and C15 (annealed) cell size increased with Ti content, up to a ratio (Cr/Ti) of 1.6, due to B-site Ti substitution in the lattice up to a limit. Pressure composition isotherm (PCI) measurements demonstrated alloys containing a greater Ti content had a better maximum hydrogen storage capacity (1.5 vs. 1.03 wt%) and lower plateau pressure (9.4 vs. 15.8 bar) at 253 K. Annealing resulted in a lower storage capacity (1.05 vs. 1.49 wt%), greater plateau pressure (ca. 30 bar) and flatter plateau slope (25 % reduction in plateau slope). Reduction in hydrogen storage capacity of annealed alloys could be due to diffusion of residual Cr in the alloy into the C15 Laves phase during the annealing process, thereby changing the local composition as confirmed through X-ray diffraction (XRD).

Anisotropic magneto-resistivity and magnetocaloric effect in DyAl2

In this study, we experimentally and theoretically investigate the correlation between the anisotropic magnetic resistivity and magnetocaloric effect in DyAl2 single crystals. DyAl2 crystallizes in the C15 Laves phase structure with cubic symmetry. While some earlier studies revealed that the isothermal entropy change in dialuminides follows a similar trend as the electrical resistivity change as a function of temperature and magnetic field, the correlation between anisotropic behavior of these two physical parameters is yet to be explored to the best of our knowledge. To address this gap, we measured electrical resistivity of DyAl2 single crystals along two different directions in zero and applied magnetic fields and compared the experimental results with our theoretical model. For the theoretical analysis, we employed a model Hamiltonian in the mean-field approximation, considering the exchange interaction, Zeeman effect, and crystalline electric field associated with the cubic symmetry. Our findings reveal a significant dependence of DyAl2 resistivity on the direction of the applied magnetic field, in agreement with our theoretical results. These outcomes emphasize the interplay between magnetocaloric effect and magneto-resistivity, underscoring the potential of the magnetocaloric effect as a valuable tool for gaining deeper insights into basic physical properties including electron transport behavior.

Development of AB2-type TiZrCrMnFeCoV intermetallic high-entropy alloy for reversible room-temperature hydrogen storage

Intermetallic high-entropy alloys (HEAs) with C14 Laves phase structure have shown promise as hydrogen storage materials due to their ability to maintain the advantages of the AB2-type hydrogen storage alloys while offering the potential for the improvement of hydrogen storage properties through the use of multi-principal elements. However, some intermetallic HEAs are limited in their ability to scale-up production using the low-cost induction melting method and reversible hydrogen storage at room temperature due to their extremely low equilibrium desorption pressure. In this work, intermetallic HEAs with reversible room-temperature hydrogen storage are designed using an empirical model based on calculation of the electronic and geometrical factors. An orthogonal experiment was conducted to optimize the composition and the optimal (Ti1.3Zr0.7)1.1Cr1.1Mn1.8Fe0.3Co0.4V0.4 HEA with a single C14 Laves phase was found to exhibit the best overall hydrogen performance. It can reversibly store 1.84 wt% hydrogen with a relatively low plateau hysteresis factor (0.71) and slope factor (0.89) at a temperature of 15 °C. The dehydrogenation enthalpy and entropy of the optimal HEA were determined to be 35.0 kJ mol−1 and 115.3 J mol−1 K−1, respectively. To reduce the cost of HEAs, FeV80 was employed to replace the V. It was found that the optimal HEA could be successfully scaled-up for production, and our findings demonstrate the potential of intermetallic HEAs for efficient hydrogen storage.

Magnetocaloric Effect in Rare-Earth Magnetic Materials

Abstract—A study of the magnetocaloric characteristics of rare-earth magnets was carried out. There were studied a systems Gd–H, (Gd,R)Ni–H containing hydrogen (R is a rare earth metal); system RCo2–H with the structure of Laves phases; and systems without hydrogen, such as RTX intermetalic compounds (T = Mn, Fe, Co; X = Si), R2(Fe,T)17 compounds (T = Al), which have a magnetic compensation point and exhibit an alternating magnetocaloric effect (MCE). The MCE was measured by the direct method and calculated indirectly from the field dependences of the magnetization. The main regularities are established and the specific features of the formation of magnetocaloric properties are revealed depending on the composition and structure.

Large magnetocaloric effect in a ternary Laves phase compoundHo2Rh3Ge

Structural and magnetic properties of an intermetallic Ho2Rh3Ge compound have been investigated in this paper. We report the observation of large magnetocaloric effect (MCE) in Ho2Rh3Ge from the characterization of magnetism isotherms. The Rietveld refinement of powder X-ray diffraction revealed that Ho2Rh3Ge crystallizes in a rhombohedral Laves phase structure (space group R3̄m, hR18). It exhibits ferromagnetic order below the Curie temperature TC = 13 K. Around TC, maximum value of entropy change −ΔSm = 25.4 J kg−1 K−1 was observed for a change of magnetic field 0−8 T. The obtained refrigeration capacity (relative cooling power) for a change of magnetic field from 0 8 T is 497(664) J.kg−1. The second–order magnetic phase transition in Ho2Rh3Ge is confirmed from Arrott plots, universal scaling plots of magnetic entropy changes, and also from the field dependence of the magnetic entropy change.

Effects of Mo and Nb on the microstructure and high temperature oxidation behaviors of CoCrFeNi-based high entropy alloys

A series of CoCrFeNi(Mo, Nb) high entropy alloys (HEAs) were prepared using vacuum arc-melting. The effect of Nb and Mo on the microstructure and high temperature anti-oxidation properties of HEAs was investigated. The addition of only Mo was found to not cause formation of new phase, but did increase the lattice distortion. After the addition of Nb, as-prepared CoCrFeNiMo0.2Nb0.1 and CoCrFeNiMo0.2Nb0.2 alloys are characteristic of duplex-phase structures of FCC and Laves, in which the Laves phase is semi-coherent with FCC matrix. Our studies also revealed that the oxidation kinetics of the alloys followed parabolic rate law and the corresponding oxidation rate constants were calculated. Due to the synergistic effects of Mo and Nb, the anti-oxidation properties of HEAs improved significantly. It was also discovered that the new Laves phase containing Mo and Nb at the inner oxidation layer hindered the outward diffusion of active metal cations, ergo improving the oxidation resistance of HEAs. With increase of Nb content, it was further recognized that the layered structure of Laves phase was thinner and denser. Therefore, the oxygen ion diffusion process in the CoCrFeNiMo0.2Nb0.2 alloy can be inhibited effectively by the new formation of duplex-phase structures with undulated Laves phase and FCC matrix.