CaCu5-type Structure Research Articles

Phase Formation and Magnetic Properties of (Y1−xSmx)Co5 Melt-Spun Ribbons

Using X-ray diffraction (XRD) and a vibrating sample magnetometer (VSM), the effects of Sm substitution, wheel speed, and annealing temperature on the phase formation and magnetic properties of (Y1−xSmx)Co5 (x = 0.2, 0.3, 0.4, 0.5) melt-spun ribbons were investigated. The results indicate the following: (1) With the increase in Sm substitution, it was found that (Y1−xSmx)Co5 ribbons are entirely composed of the (Y-Sm)Co5 phase with a CaCu5-type structure. Additionally, the coercivity gradually increases, while the remanence and saturation magnetization gradually decrease. (2) As the wheel speed increases, the (Y1−xSmx)Co5 ribbons exhibit an increasing proportion of (Y-Sm)Co5 phase until reaching a speed of 40 m/s, where they are entirely composed of the (Y-Sm)Co5 phase. Magnetic measurements show that the coercivity (Hcj) and remanence (Br) of (Y0.5Sm0.5)Co5 ribbons increase gradually with increasing wheel speed, while saturation magnetization decreases. The variation in magnetic properties is mainly attributed to the formation of nucleation centers for reversed magnetic domain (2:7 and 2:17 phases); (3) (Y0.5Sm0.5)Co5 ribbons are composed of the (Y-Sm)Co5 phase and a small amount of the Sm2Co7 phase after annealing at 550 °C, 600 °C, and 650 °C. Temperature elevation promotes crystallization of the amorphous phase, resulting in a gradual decrease in coercivity, while the remanence and saturation magnetization exhibit an overall increasing trend. Through continuous optimization of the process, favorable magnetic properties were achieved under the conditions of a 0.5 Sm substitution level, a wheel speed of 40 m/s, and an annealing temperature of 550 °C, with a coercivity of 7.98 kOe, remanence of 444 kA/m, and saturation magnetization of 508 kA/m.

Structural and magnetic properties of YNi4-xCoxSi alloys

The transition-metal based alloy system YNi4-xCoxSi shows a second-order ferromagnetic-to-paramagnetic transition near room temperature. Here, the magnetic structure, the magnetocaloric properties and the magnetic anisotropy of YNi4-xCoxSi (x = 0–4) are investigated. For x = 3.5, 3.75 and 4.0 a Curie temperature near room temperature is observed with TC = 250, 283 and 310 K, respectively. In orientated YNi4-xCoxSi powder samples the c axis of the hexagonal crystal structure is found to be the easy magnetic axis, with a large dominant K2 anisotropy constant (K2 >K1 > 0). The magnetic structure and the preferred atomic position for Ni are demonstrated by neutron diffraction measurements. We have found a dramatic decrease in the magnetic moment at the 3g site in the CaCu5-type structure (space group P6/mmm), the saturation magnetization and the Curie temperature with increasing Ni concentration.

Phase, chemical constitution and effective depth of oxide overgrowth and its influence on SmPrCo5 magnetic properties

Ternary Sm-Pr-Co magnets with CaCu5-type hexagonal structure exhibit superior magnetic properties and investigating their oxidation behavior is crucial for assessing their stability under the service conditions. In this regard, here thermal oxidation of sintered SmPrCo5 magnet is carried out by varying the oxidation temperature from 373 to 973 K for 5 hr under atmospheric pressure. Owing to their lower negative Gibbs free energy, rare earth oxides of Sm2O3 and Pr2O3 are found to initially form, making cobalt free from SmPrCo5 lattice. Cobalt is then observed to migrate to the oxide surface, because of the difference in chemical potential between the surface and inner layers, leading to Co3O4 formation. Moreover, here a comprehensive discussion on the occurrences of different oxide phases and their depth distributions in the oxide layer are being made. Finally, a correlation between these oxide phases and the alterations in their magnetic properties is discussed.

Crystal structure of the ternary silicide ErNi4.04Si0.96

Abstract The ternary silicide ErNi4.04Si0.96 was synthesized by arc-melting of stoichiometric quantities of the elements, and its crystal structure has been determined using single-crystal X-ray diffraction data. The compound crystallizes in the CaCu5 structure type: hexagonal space group P6/mmm, Pearson code hP6, Z = 1; a = 4.874(3), c = 3.959(2) Å, V = 81.5(1) Å3; R1 = 0.0239, wR2 = 0.0503, for 67 independent reflections with I > 2σ(I) and eight variables. The erbium and nickel atoms occupy the crystallographic positions 1a and 2c, respectively. The position 3g is occupied by a mixture of Ni and Si atoms. The structure of this silicide represents a packing of bipyramidal units built from nickel and Ni/Si atoms.

Investigation of spin reorientation and magnetocaloric behavior in PrCo[formula omitted]Cu[formula omitted] compounds

In the present work, we have studied the structural and magnetic properties of the compounds PrCo2Cu3, PrCo2.5Cu2.5 and PrCo3Cu2 as well as their spin reorientation transition and magnetocaloric behavior. All three compounds crystallize in the hexagonal CaCu5-type structure. The lattice parameters increase when copper replaces cobalt. The temperature dependence of the magnetization has been determined at low and high temperatures. It revealed that the Curie temperature decreases from ∼ 1000 K to 310 K after the substitution of cobalt by copper (PrCo2Cu3). For the copper-rich compound, a merging of the transition from the planar ferromagnetic state to the axial ferromagnetic one and the transition from the ferromagnetic state to the paramagnetic one is observed. A constant entropy variation is observed over a wide temperature range centered around room temperature. It results from the merging of the entropy measured around the spin reorientation temperature and that measured around Curie temperature.

Influence of Fe on the Hydrogen Storage Properties of LaCeNi Alloys.

LaNi5 intermetallic compounds with a hexagonal CaCu5 type structure can react reversibly with hydrogen. The element substitutions in LaNi5 can significantly change the hydrogenation properties, allowing to tune them to a large extent. It could be very advantageous to partially replace Ni or La with other elements to reduce the cost of this alloy as well as the equilibrium pressure of absorption and desorption. The hydrogen storage properties of ball-milled AB5 alloys containing the elements La, Ce (A-rare elements) and Ni, Fe (B-transition metals) were studied in this paper. Although the substitution of Ni (atomic radius 1.49 Å) with Fe atom (atomic radius 1.56 Å) increased the unit cell volume from 86.4149 to 87.947 5 Å3 of the LaNi5 phase, its hydrogen storage capacity was still close to the value 1.4 wt %. The enthalpy (ΔH) of hydride formation for hydrogen absorption and desorption of the experimental alloys was in the range of 29-32.6 kJ/mol. A very favorable effect of Fe on the sorption properties was found in the significant reduction of the equilibrium pressure of absorption and desorption. These studied experimental Fe-containing alloys were able to store hydrogen at 300 K and with pressure under 0.1 MPa. The fastest sorption kinetics of hydrogen was found in alloys with FeNi phase particles located on the surface of the powder. However, if the FeNi phase was segregated at the grain boundaries, it acted as a barrier limiting the growth of the hydride phase. This led to a decrease of the hydride sorption kinetics.

On Structural and Magnetic Properties of Substituted SmCo5 Materials.

SmCo5 is a well-established material in the permanent magnet industry, a sector which constantly gains market share due to increasing demand but also suffers from criticality of some raw materials. In this work we study the possibility of replacement of Sm with other, more abundant rare earth atoms like Ce-La. These raw materials are usually called "free" rare-earth minerals, appearing as a by-product during mining and processing of other raw materials. Samples with nominal stoichiometry Sm1-xMMxCo5 (x = 0.1-1.0) were prepared in bulk form with conventional metallurgy techniques and their basic structural and magnetic properties were examined. The materials retain the hexagonal CaCu5-type structure while minor fluctuations in unit cell parameters as observed with X-ray diffraction. Incorporation of Ce-La degrade intrinsic magnetic properties, Curie temperature drops from 920 K to 800 K across the series and mass magnetization from 98 Am2/kg to 60 Am2/kg; effects which trade off for the significantly reduced price. Atomistic simulations, implemented based on Density Functional Theory calculations are used in the case of the stoichiometry with x = 0.5 to calculate atomic magnetic moments and provide additional insight in the complex interactions that dominate the magnetic properties of the material.

CRYSTAL STRUCTURE OF THE TmNi5

Сrystal structure of the TmNi5 compound has been investigated by means of X-ray single crystal method (Oxford Diffraction X’calibur four-circle diffractometer, MoKα radiation) for the first time: CaCu5-type structure, Pearson symbol hP6, space group P6/mmm, a = 4.8684(12), c = 3.9541(7) Å, R1 = 0.0529, wR2 = 0.1835 for 80 reflections. Similarly to intermetallic compounds with high transition metal content, atoms in the title structure have rather high coordination numbers: 20 for thulium and 12 for nickel.

Atomically Ordered Pt5La Nanoparticles as Electrocatalysts for the Oxygen Reduction Reaction

In this study, atomically ordered intermetallic Pt5La nanoparticles (NPs) were successfully prepared using a relatively simple wet chemical process. X-ray diffraction measurements were carried out to determine the crystal structures of the prepared catalysts. The transmission electron microscopy results revealed that the Pt5La NPs with a size of 3–15 nm were distributed on the carbon surface. The crystal structure of the Pt–La alloy depended on the annealing temperature. A face-centered cubic-type (i.e., a disordered phase) structure was formed at temperatures less than 700 °C, while a CaCu5-type structure (i.e., an ordered phase) could be formed at 800 °C. The prepared Pt5La NPs exhibited oxygen reduction reaction (ORR) specific (1.39 mA cm–2) and mass (0.657 A mg–1) activities approximately 3.7 and 5.1 times higher than those of commercially available Pt NPs on carbon, respectively. Furthermore, the as-prepared NPs showed enhanced ORR durability. The enhanced ORR activity was evaluated through surface analysis using high-angle annular dark-field scanning transmission electron microscopy and X-ray photoelectron spectroscopy. The significantly enhanced ORR activity of the ordered Pt5La NPs was due to their compressive strain and rich atomic steps. The findings of this study will be helpful in the development of electrocatalysts with high electrochemical activity.

Cost effective modification of SmCo5-type alloys

In the present work we present a preliminary experimental and ab-initio study of a series of compounds with nominal composition Sm1-xMMxCo5-y-zFeyNiz (x = 0 – 0.7; y = 0.5 – 1.5; z = 0.5 – 1). Compounds with MM content up to 50% were successfully synthesized in CaCu5-type structure, retaining uniaxial magnetocrystalline anisotropy. Magnetization values are within the 85 to 50 Am2/kg range, with Ni content playing a significant role in stabilization of the structure at the cost of magnetization weakening. Theoretical calculations predict higher magnetization values, especially in the case of SmCo2.5Fe1.5Ni compound with a value close to that of SmCo5.

Dynamically Staged Phase Transformation Mechanism of Co-Containing Rare Earth-Based Metal Hydrides with Unexpected Hysteresis Amelioration

Solid hydrogen storage and supply systems with high density in a hydrogen refueling station are the critical factor to realize large-scale application of hydrogen energy, and one of the biggest challenges is how to ameliorate the extremely large pressure hysteresis of Ce-rich rare-earth-based metal hydrides. In this work, two series of La–Ce–Ca–Ni–Co alloys with single CaCu5-type structure and uniformly distributed elements were prepared via induction levitation melting. With increasing Co content in La0.3Ce0.5Ca0.2Ni5–xCox (x = 0, 0.5, 1.0, 1.5) alloys, a staged phase transformation occurs, contributing to a significant improvement in the pressure hysteresis without the monotonical sacrifice of dehydrogenation equilibrium pressure. An equilibrium-state thermal analysis method (ETA) is proposed and well verifies the thermodynamical phase transformation processes. Further first-principles calculations indicate that the enhanced charge synergy and increased charge transfer drive the conversion of staged phase transformation from dynamic to thermodynamically stable pathways. Thus, “dynamically staged phase transformation”, nominated as the dynamic realization of thermodynamic staged phase transformation, is more constructive for practical use. Consequently, the optimal composition of La0.25Ce0.55Ca0.2Ni4.5Co0.5 was developed with a saturated hydrogen storage capacity of 1.52 wt %, dehydrogenation equilibrium pressure of 10.68 MPa at 90 °C, and satisfactory cycling durability. The ETA method and composition design concept proposed in this work pave a convenient avenue for wider exploration of high-pressure hydrogen storage alloys.

Ab initio, artificial neural network predictions and experimental synthesis of mischmetal alloying in Sm-Co permanent magnets.

The use of the mischmetal alloy, comprised of La and Ce in 1 : 3 ratio, as a partial substitute for Sm in the CaCu5-type structure is explored, as a means for the search of viable alternatives for permanent magnets that require fewer steps in the rare earth separation processing. The structural and magnetic properties of the introduced stoichiometry, containing 50% less Sm, are compared to the ones of the SmCo5, LaCo5 and CeCo5 binary compounds by means of ab initio simulations. The capability of artificial neural networks to accurately predict the relationship between structure and total magnetization from DFT calculations in the supercell approach that was employed, is also demonstrated. Experimental fabrication and structural and magnetic characterization of the proposed stoichiometry verifies the structural configuration and provides insight for the macroscopic hard magnetic properties of the material. The reduction of magnetic properties was found to be favorable compared to the respective reduction of the raw materials cost, while measurements of the Cure temperature verify that the proposed compound is still suitable for high temperature applications.

Morphological, structural and electrochemical properties of the LaNi4Fe compound elaborated by mechanical alloying

In this paper, we have studied the morphologic, the structural and the electrochemical properties of the LaNi4Fe compound elaborated by mechanical alloying (MA) for two durations 5 and 10 h. These properties are determined by various methods, such as XRD, SEM and galvanostatic cycling. The results show that the LaNi4Fe compound crystallizes in the hexagonal CaCu5 type structure for the two alloying durations 5 and 10 h. The particles obtained by mechanical alloying are in the order of 6 to 7 nm. The chemical microanalysis by EDX shows that the nominal and actual compositions are very close for the two grinding times. The maximum discharge capacity, of 180 and 200 mAh / g respectively for 5h and 10 h, is obtained from the first two cycles, which shows that the activation of nano compounds is easier than that obtained for bulk material obtained by melting since the reaction surface is larger. A decrease in capacity is observed after about thirty cycles: A loss of around 15% of maximum capacity is observed.

Magnetocaloric effect in spin-glass-like GdCu4Mn compound

Materials based on Gd with magnetic frustration may have high magnetocaloric application potential. GdCu4Mn crystallizes in hexagonal CaCu5-type structure with space group P6/mmm (no. 191, Pearson symbol: hP6). Lattice parameters for the polycrystalline sample are equal to a = 5.114(3) Å and c = 4.151(4)Å. Due to structural disorder, namely random distribution of Cu and Mn atoms on 2c and 3g positions, a spin-glass-like behavior is observed in this material at low temperatures. In addition to the standard measurements of DC magnetization and AC magnetic susceptibility, the spin-glass state was confirmed by the memory effect and relaxation behavior. The absence of clear anomalies in the temperature dependencies of specific heat and electrical resistance suggests the lack of long-range magnetic order. For a change in magnetic field from 0 to 5 T, maximum values of the isothermal magnetic entropy change (ΔSm), temperature averaged entropy change (TEC(5)), relative cooling power (RCP), and adiabatic temperature change (ΔTad) at ∼50 K are equal to −1.3(1) J/(kg K), 1.2(1) J/(kg K), 125(1) J/kg, and 0.5(1) K, respectively.

Synthesis, crystal structure and physical properties of the TbCo4.5SixLi0.5-x solid solution

Alloys from the region of existence of the solid solution TbCo4.5SixLi0.5-x were synthesized by arc melting. Quantitative and qualitative composition of alloys and powders of electrode materials was determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The Tb/Co/Si ratio in the samples was confirmed by X-ray fluorescence spectroscopy. The change in cell parameters within the solid solution existence was established by the results of X-ray powder diffraction (TbCo4.5SixLi0.5-x, x = 0.1–0.4: a = 4.9518(5) – 4.9324(3), c = 3.9727(4) – 3.9746(3) Å). The crystal structure of the solid solution was determined by the Rietveld method (CaCu5 structure type, space group P6/mmm). Cobalt atoms are partially replaced by silicon and lithium only in 2c position. The ability of alloys to reversibly absorb hydrogen was studied by the method of electrochemical hydrogenation. Under experimental conditions the amount of deintercalated hydrogen was about 0.19 H/f.u. The change in cell parameters after hydrogenation (volume increases from 83.74(1) to 85.54(6) Å3) and the stability of the electrode in the electrolyte solution was further confirmed by X-ray phase analysis. Measurements of the electrical resistivity of the samples indicated a decrease of resistivity value with a slight increase in the amount of alkali metal in samples.

Three Rh-rich ternary germanides in the Ce–Rh−Ge system

The germanides Ce3Rh11Ge5, Ce6Rh30Ge19.5, and CeRh3Ge2, which are new ternary Rh-rich phases in the Ce–Rh−Ge system, were prepared by reactions of the elements. Their crystal structures were determined by single-crystal and powder X-ray diffraction methods. Ce3Rh11Ge5 adopts the Gd3Ru4Al12-type structure, which represents the fully stoichiometric version of the defect Sc3Ni11Ge4-type structure, in hexagonal space group P63/mmc with Z ​= ​2 and cell parameters a ​= ​8.6964 (12) Å and c ​= ​9.2209 (12) Å. Ce6Rh30Ge19.5 is a filled derivative of the U6Co30Si19-type structure in hexagonal space group P63/m with Z ​= ​2 and cell parameters a ​= ​22.8480 (11) Å and c ​= ​3.9208 (2) Å. CeRh3Ge2 is derived from a symmetry-lowered distortion of the hexagonal CeCo3B2-type (or substitutionally ordered CaCu5-type) structure, and crystallizes in orthorhombic space group Fmmm with Z ​= ​16 and cell parameters a ​= ​7.392 (6) Å, b ​= ​11.341 (9) Å, and c ​= ​19.66 (2) Å. As expected by their Rh-rich compositions, the three compounds exhibit extensive Rh–Rh bonding, but surprisingly, they also show some short Ge–Ge contacts. Analysis of the electron localization functions and Bader charges reveals that charge transfer takes place from Ce to Rh atoms, indicative of a polar character in the bonding in these intermetallic compounds.

Structural stability, magnetic properties and hardness of equiatomic light rare earth-cobalt with CaCu5 type structure before and after adding Y

To explore the existence of single-phase high entropy intermetallic compound (HEIC) by elements randomly occupation at one sublattice, the four intermetallic compounds (Sm1/2Pr1/2)Co5, (Sm1/3Pr1/3Y1/3)Co5 (Sm1/3Pr1/3Nd1/3)Co5 and (Sm1/4Pr1/4Nd1/4Y1/4)Co5 have been synthesized by vacuum arc-melting technology, and their crystal structures, microstructures, magnetic properties, and hardness have been systematically studied. X-ray diffraction confirms that the four intermetallics are single phase with hexagonal CaCu5 type structure. A configuration entropy of 11.56 ​J/(mol·K) is obtained in (Sm1/4Pr1/4Nd1/4Y1/4)Co5. The morphologic images show that grains are refined via adding Y into (Sm1/2Pr1/2)Co5 and (Sm1/3Pr1/3Nd1/3)Co5. These intermetallics are ferromagnetic characteristics and show strong magnetocrystalline anisotropy along c axis at room temperature. Y doping into (Sm1/2Pr1/2)Co5 and (Sm1/3Pr1/3Nd1/3)Co5 induces the enhancements of anisotropy field, maximum energy product and Vickers hardness. The improvements of magnetic properties and hardness might be due to the modulation of lattice parameter ratio (c/a) by yttrium doping.

Structural and magnetic properties of hard magnetic system Ce(Co1-xFex)4.4Cu0.6 (0 ≤ x ≤ 0.19)

The Ce(Co1-xFex)4.4Cu0.6 (0 ≤ x ≤ 0.19) is a composite, hard magnetic system that is based on the CaCu5-type structure (1:5). It shows both, unique magnetic and microstructural features that are essential for permanent magnets, e.g., exceptional squareness of the 2nd. quadrant of the magnetization loops and microstructural features typically needed for pinning. Samples solidified in alumina crucibles are coarse-grained and often clearly faceted and readily align in a magnetic field. X-ray, SEM, and TEM analyses show a 1:5-type single-phase material when quenched from high temperature, which, after heat treatment, transforms into a laminar coherent nanostructure through the formation of a dense array of extended intercalated regions. These extended intercalated regions are comprised of segments of the Ce2Ni7–type structure (2:7) which segregate into various closely related precipitates forming a nanostructure similar to the SmCo5 - Sm2Co17 composites seen in Sm-Co permanent magnets. Based on TEM and Lorentz microscopy of well-aligned single grain particles, the magnetic domains’ reversal mechanism is regulated by anisotropy fluctuations occurring along the easy direction of magnetization and strong exchange interactions between the matrix and defects (e.g.: stacking faults). Lorentz microscopy suggests the domain wall is not physically pinned by the defect, but rather is offset/deflected when it interacts with the defect. The Lorentz and magnetization data suggest that defects cause a bending of the moment away from the c axis inside the grains.

Crystal structure and magnetic properties of Al2NdNi3 studied by experimental and first-principles

The Al2NdNi3 single-phase alloy was prepared by melting stoichiometric Al, Nd, and Ni in the nonconsumable arc furnace filled with argon and then homogenizing annealing at a high temperature. The crystal structure of Al2NdNi3 was analyzed by an X-ray powder diffraction technique, Rietveld refinement analysis, and the first-principles simulation calculation method. The results show that Al2NdNi3 crystallizes in ordered variant of CaCu5-type structure (space group P6/mmm, No. 191, hP6), and the lattice parameters of a ​= ​5.1247 (1) Å, c ​= ​4.0941 (1) Å, Z ​= ​1 and Dcalc ​= ​6.68 ​g/cm3. The temperature-dependent susceptibility data shows field sensitive behaviour of Al2NdNi3 with low temperature transformation of magnetic ordering below ~100 ​K Al2NdNi3 exhibits ferromagnetic properties at low temperatures and has a Curie temperature (Tc) of 253 ​K in field of 50 ​Oe with the saturation magnetic moment (Ms) of 0.25 μB/f.u. in field of 8 ​T and coercivity (Hc) of 0.16 ​T at 2 ​K. The simulation results also show that Al2NdNi3 is a ferromagnet with a spontaneous magnetic moment of 0.28 μB/f.u., and it is believed that the spontaneous magnetization of this alloy originate from the electron spin in the Nd(1a)-4f band.

Significant improvement of electrochemical hydrogenation, corrosion protection and thermal stability of LaNi4·6Zn0.4-xLix (x ≤ 0.2) solid solution phases due to Li-doping

The electrochemical hydrogenation, structure and thermal stability of LaNi4·6Zn0.4-xLix (x ≤ 0.2) intermetallic compounds have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) with WDS/EDX, differential scanning calorimetry (DSC) and electrochemical techniques: potentiodynamic polarization, charge/discharge, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS). The synthesized LaNi4·6Zn0.4-xLix intermetallics are solid solutions on the basis LaNi5 compound with hexagonal CaCu5 structure type. Precise structural studies by single crystal methods revealed that with the increase of lithium content in the phase, the hexagonal unit cell is transformed into a new orthorhombic structure (Cmmm, a = 5.0068 (10), b = 8.6719 (17) Å, c = 3.9952 (8) Å). The LaNi4·6Zn0.4-xLix intermetallics effectively passivate in 6 M KOH over a wide potential range. The presence of lithium in the solid solution phase improves corrosion resistance of LaNi4·6Zn0.4-xLix intermetallics compared to the reference compound (LaNi5). The electrochemical measurements show that LaNi4·6Zn0.4-xLix intermetallic compounds absorb hydrogen, and the highest effectiveness of hydrogen absorption shows LaNi4·6Zn0·2Li0.2 compound with orthorhombic structure. The DSC/TG results indicate greater thermal stability of compounds doped by Zn (LaNi4·6Zn0.4) and Zn/Li (LaNi4·6Zn0·2Li0.2) in compare to LaNi5.