Rare Earth Atoms Research Articles

First-Principles Investigation of Point Defects on the Thermal Conductivity and Mechanical Properties of Aluminum at Room Temperature

The effects of point defects on the mechanical and thermal conductivity of aluminum at room temperature have been investigated based on the first-principles calculations combined with the Boltzmann equation and the Debye model. The calculated results showed the equilibrium lattice constants a0 of all REAl are larger than that of Al, and the defective formation energy Ef of all REAl is lower than that of VAl. Both a0 and Ef increase from Sc to La and then decrease linearly to Lu. The effects of solute atoms on the mechanical properties of the Al matrix were further calculated, and compared with Al, it is found that the REAl defects decrease the elastic constant Cij, Cauchy pressure C12–C44, bulk modulus B, shear modulus G, Young’s modulus E, B/G and Poisson’s ratio ν of Al, except for C44 of REAl (RE = La-Nd). With the increase of atomic number, the C11 and E of Al-containing REAl decrease from Sc to La and then slowly increase to Lu, whereas C12, C44, B, and G have little change. Meanwhile, the values of C12–C44 and B/G of Al-containing REAl increase from Sc to Ce, and it slightly change after Ce, while ν is nearly unchanged. All defects containing Al present nonuniform and ductility. Finally, the effects of rare earth (RE) atoms on the thermal conductivity (TC) of Al alloys have been investigated based on the first-principles calculations. The reduction of TC of Al alloys by RE solute atoms REAl is much greater than that by the L12 Al3RE phase with the same concentration of RE, which is in good agreement with the experiments. With the RE atomic number increasing, the total TC κ of the Al-RE solid solution decreases from Sc to La firstly and then increases linearly to Lu. Moreover, the decrement of TC Δκ of the Al matrix by early REAl (RE = La-Sm) is larger than that by VAl, while the later REAl (RE = Gd-Lu) shows the opposite influence.

The electronic, magnetic and optical properties of GaN monolayer doped with rare-earth elements

Structural, electronic, magnetic, and optical properties of rare earth (RE) metal element doped GaN monolayers are investigated using density functional theory, where RE = Nd, Sm, Eu, Gd, and Er. The introduction of RE atoms causes structural deformation of the GaN monolayer. The induced local magnetic moments are observed to be 4.00, 6.00, 7.00, 8.00, and 2.00 μB in Nd, Sm, Eu, Gd, and Er adsorbed GaN monolayers, respectively, while the values are 3.00, 5.00, 6.00, 7.00, and 3.00 μB in the substitution of Ga atoms. When Nd, Gd and Er adsorbed in GaN monolayer Fermi levels are shifted to the conduction band leading to metallicity, while in the case of Sm and Eu adsorption impurity states are found near the Fermi level. On the contrary, Eu, Gd and Er substitution of Ga atoms leads to the Fermi energy level being shifted below the VBM. In the Nd and Eu substitution system, the f-state is found near the Fermi level and the Nd-f state crosses the Fermi level. Optical absorption, transmission and refraction coefficients show that the addition of RE atoms can significantly enhance the prospects of GAN monolayers in visible as well as infrared applications. This research provides an outlook for the development of GaN monolayer-based optoelectronic as well as spintronics devices.

Embedding oxophilic rare-earth single atom in platinum nanoclusters for efficient hydrogen electro-oxidation

Designing Pt-based electrocatalysts with high catalytic activity and CO tolerance is challenging but extremely desirable for alkaline hydrogen oxidation reaction. Herein we report the design of a series of single-atom lanthanide (La, Ce, Pr, Nd, and Lu)-embedded ultrasmall Pt nanoclusters for efficient alkaline hydrogen electro-oxidation catalysis based on vapor filling and spatially confined reduction/growth of metal species. Mechanism studies reveal that oxophilic single-atom lanthanide species in Pt nanoclusters can serve as the Lewis acid site for selective OH- adsorption and regulate the binding strength of intermediates on Pt sites, which promotes the kinetics of hydrogen oxidation and CO oxidation by accelerating the combination of OH− and *H/*CO in kinetics and thermodynamics, endowing the electrocatalyst with up to 14.3-times higher mass activity than commercial Pt/C and enhanced CO tolerance. This work may shed light on the design of metal nanocluster-based electrocatalysts for energy conversion.

Enhanced magnetic anisotropy induced by praseodymium ferromagnetic order and anomalous transport properties in PrMn2Ge2 single crystals

Anisotropic magnetization and anomalous electrical transport properties of flux-grown $\mathrm{Pr}{\mathrm{Mn}}_{2}{\mathrm{Ge}}_{2}$ single crystals were investigated. The grown crystals exhibit strong magnetic anisotropy with easy magnetization along the $c$ axis. Linear magnetoresistance (MR) and a conventional anomalous Hall effect (AHE) are observed for $H\text{//}c$ and $I\text{//}b$ in contrast to a nonlinear positive MR and a large planar topological Hall effect (PTHE) observed for $H\text{//}a$ and $I\text{//}b$. The anisotropy of the magnetic and electrical transport properties is increased as temperature decreases because magnetic ordering of Pr atoms brings about an increase of the saturation magnetic field of nonlinear MR and the critical field for the maximum values of PTHE. A scaling analysis using the Tian-Ye-Jin model suggests that the AHE in this compound has a larger intrinsic contribution compared to the extrinsic contribution. The nonlinear positive MRs are attributed to the field-induced nontrivial spin textures. The PTHE is related to the real-space skyrmionic bubbles and the noncoplanar spin texture with nonzero spin chirality. These results demonstrate a magnetic field induced anisotropic magnetoresistance and Hall resistivity and its tunability by the ferromagnetic ordering of rare earth atoms in conical-ordered magnets.

Two-Dimensional Lattices with Lanthanoids, Anilato Ligands and Formamide

Here, we illustrate the use of formamide (fma) and anilato-type ligands to build two-dimensional lattices with lanthanoids. Thus, we describe the synthesis and crystal structure of four lattices formulated as [Ln2(C6O4X2)3(fma)6]·6fma with Ln/X = La/Cl (1), La/Br (2), Eu/Cl (3), and Eu/Br (4), where C6O4X22− = dianion of 3,6-disubstituted-2,5-dihydroxy-1,4-benzoquinone with X = Cl (chloranilato) and X = Br (bromanilato). Single crystal X-ray analysis shows that the four compounds crystallize in the triclinic P-1 space group and present two-dimensional, very distorted hexagonal lattices with the lanthanoids ions in the vertex coordinated by three anilato ligands forming the sides of the distorted hexagons that appear as rectangles. The rectangles are disposed parallel to their long sides in a brick wall fashion. The nona-coordination of the lanthanoids is completed by three formamide molecules. These layered compounds include three additional formamide molecules per lanthanoid atom, located in the interlayer space inside the channels formed by the eclipsed packing of the layers. We discuss the differences observed among these compounds due to the change of the lanthanoid ion (La and Eu) and of the substituent group X in the anilato ligand (Cl and Br).

Characterization of friction and wear of phenolic resin matrix composites reinforced by bamboo fibers of alkaline and LaCl3 treatment

Mechanical and tribological properties of phenolic resin matrix composites reinforced by bamboo fibers, which were pre-treated with sodium hydroxide (NaOH) and post-treated with lanthanum chloride (LaCl3), were characterized by hardness, impact, microscratch tests, friction and wear testers, and thermogravimetric analysis. Bamboo fibers before and after modification were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Hemicellulose and lignin of bamboo fibers can be dissolved by alkaline or NaOH treatment, resulting in a rough surface. The high coordination number of rare earth atoms in LaCl3 solution enhanced the formation of chemical bonds between the hydroxyl groups of bamboo fibers and the oxygen-containing groups on the molecular chain of phenolic resin. The hardness and impact strength of the composites both firstly increased and then decreased with an increase in LaCl3 concentration or soaking duration in LaCl3 solution. Tribological performance (e.g. high-temperature friction coefficient, wear rate, thermogravimetric loss, crack propagation) of phenolic resin matrix composites was significantly improved by the treated bamboo fibers. The optimum mechanical and tribological properties of bamboo fiber-reinforced phenolic resin matrix composites were achieved under the conditions of LaCl3 concentration of 10% and soaking duration of 30 min.

Heteroatom-Driven Coordination Fields Altering Single Cerium Atom Sites for Efficient Oxygen Reduction Reaction.

For current single-atom catalysts (SACs), modulating the coordination environments of rare-earth (RE) single atoms with complex electronic orbital and flexible chemical states is still limited. Herein, cerium (Ce) SAs supported on a P, S, and N co-doped hollow carbon substrate (Ce SAs/PSNC) for the oxygen reduction reaction (ORR) are reported. The as-prepared Ce SAs/PSNC possesses a half-wave potential of 0.90V, a turnover frequency value of 52.2s-1 at 0.85V, and excellent stability for the ORR, which exceeds the commercial Pt/C and most recent SACs. Ce SAs/PSNC-based liquid zinc-air batteries (ZABs) exhibit a high and stable open-circuit voltage of 1.49V and a maximum power density of 212mWcm-2 . As the catalyst of the air cathode, it also displays remarkable performance in flexible electronic devices. Theoretical calculations reveal that the introduction of S and P sites induces significant electronic modulations to the Ce SA active sites. The P and S dopings promote the electroactivity of Ce SAs and improve the overall site-to-site electron transfer within the Ce SAs/PSNC. This work offers a unique perspective for modulating RE-based SACs in a complex coordination environment toward superior electrocatalysis and broad applications in energy conversion and storage devices.

Magnetic Dilution as a Direct Method for Detecting and Evaluation of Exchange Interactions between Rare Earth Elements in Oxide Systems

This work is devoted to the study of exchange interactions between rare earth atoms in the LaAlO3 matrix. Using the magnetic dilution method, the study of concentration and temperature dependences of magnetic susceptibility and effective magnetic moments of diluted solid solutions the magnetic characteristics of single rare earth atoms and the character of superexchange between them are described—antiferromagnetic at low concentrations, and for samarium, predominantly ferromagnetic within greater clusters as the concentration increases. The development of superexchange is similar to the exchange between d-elements in the same matrix.

Improving CO2-to-C2+ Product Electroreduction Efficiency via Atomic Lanthanide Dopant-Induced Tensile-Strained CuOx Catalysts

Cu is a promising electrocatalyst in CO2 reduction reaction (CO2RR) to high-value C2+ products. However, as important C-C coupling active sites, the Cu+ species is usually unstable under reduction conditions. How atomic dopants affect the performance of Cu-based catalysts is interesting to be studied. Herein, we first calculated the difference between the thermodynamic limiting potentials of CO2RR and the hydrogen evolution reaction, as well as the *CO binding energy over Cu2O doped with different metals, and the results indicated that doping atomic Gd into Cu2O could improve the performance of the catalyst effectively. On the basis of the theoretical study, we designed Gd1/CuOx catalysts. The distinctive electronic structure and large ion radii of Gd not only keep the Cu+ species stable during the reaction but also induce tensile strain in Gd1/CuOx, resulting in excellent performance of the catalysts for electroreduction of CO2 to C2+ products. The Faradic efficiency of C2+ products could reach 81.4% with a C2+ product partial current density of 444.3 mA cm-2 at -0.8 V vs a reversible hydrogen electrode. Detailed experimental and theoretical studies revealed that Gd doping enhanced CO2 activation on the catalyst, stabilized the key intermediate O*CCO, and reduced the energy barrier of the C-C coupling reaction.

Asymmetry effects on the phases of RKKY-coupled two-impurity Kondo systems

In a related work [arXiv:2106.07519] we have shown that in the two-impurity Anderson (2iA) model with two hosts coupled by spin exchange in the most symmetric case there are either two phase transitions or none. The phases comprise the conventional Kondo and RKKY regimes and a novel one, interpreted as a Kondo-stabilized, metallic quantum spin liquid (QSL). Here we analyze how various types of asymmetry affect this picture. We demonstrate that the transitions are robust against the coupling and particle-hole asymmetries, provided charge transfer is forbidden. This holds true despite the scattering phase shift at each impurity taking non-universal values. Finally, for an extended model including charge transfer between the hosts and a small Coulomb interaction at the host sites directly coupled to impurities, we show that the presence of charge transfer changes the phase transitions into crossovers. Provided the inter-host hopping is sufficiently small, this leads to qualitatively the same physics at non-zero temperature. The relevance of this model for rare-earth atoms in a metallic host is discussed and potential experimental setups for observing our findings are proposed.

Strong Bending Distortion of a Supercoronene Graphene Model upon Adsorption of Lanthanide Atoms

Numerous applications of graphene involve quasi-infinite sheets, as well as finite structures with edges, pores, graphene quantum dots, etc. In theoretical studies of adsorption of diverse chemical species, including single atoms, molecules, cations, and anions, graphene usually behaves as a very rigid planar structure. However, we found that when adsorbing lanthanide atoms, finite size structures, represented by the widely used supercoronene model, can undergo considerable distortion, and the degree of distortion depends on the number of unpaired electrons, reaching a maximum for Gd (eight unpaired electrons). Lanthanides closely approach the supercoronene surface and increase the interaction energy. Extrapolating to real-world systems, one can expect the existence and magnitude of lanthanide-induced distortion to depend on the size of graphene structures. Quasi-infinite or very large graphene sheets are too rigid to undergo such bending, but it becomes tangible for graphene quantum dots and for atom adsorption closer to graphene edges.

Probing rare earth segregation in steels

The challenge of characterizing the precise sites of rare earth (RE) atoms has limited our understanding of microalloying and the design of RE steels with superior performance in recent decades. Electron microscopy with near-atomic resolution can be used to identify RE retention or trapping in alloys but fails to provide reliable results in steel due to the extremely low solid solubility of RE atoms. Here, we probed the segregation and clustering of RE atoms by identifying the location of RE oxides via the in situ oxidation of these extremely active atoms in dendritic regions, ultimately providing direct visualization of the distribution of RE atoms. First-principles calculations confirmed that dendritic interfaces can serve as trapping sites for solute RE atoms. These findings effectively solve the problems caused by the use of traditional techniques to characterize RE atoms in steels and provide the first evidence for a solid solution of RE atoms.

Engineering high-coordinated cerium single-atom sites on carbon nitride nanosheets for efficient photocatalytic amine oxidation and water splitting into hydrogen

Developing highly-active rare-earth single atom photocatalysts have attracted extensive attention due to their excellent catalytic properties. Herein, we prepared a single-atom Ce-SA-C3N4 catalyst composed of atomically dispersed rare-earth cerium (Ce) on C3N4 nanosheets by the pyrolysis of cerium-incorporated layered precursor. The atomic distribution and high-coordinated environment of Ce sites were disclosed by aberration-corrected scanning transmission electron microscopy, electron energy-loss spectra, X-ray absorption spectroscopy, and theoretical calculations. In Ce-SA-C3N4, Ce single atoms are coordinated by four N atoms and six O atoms (Ce-N4/O6). The cooperation of single-atom Ce-N4/O6 active sites in C3N4 nanosheets tunes the electronic structure and the surface trap states, resulting in accelerated charge transfer/separation and extended lifetime of photoinduced electrons. Meanwhile, the high-coordinated Ce-N4/O6 active sites could promote the production of superoxide radicals (•O2−) and C = N bond, thus, the optimized single-atom Ce-SA-C3N4 photocatalyst exhibits highly efficient photocatalytic oxidation of amines under visible light irradiation. Furthermore, the fabricated single-atom Ce-SA-C3N4 photocatalysts are applied to split water into hydrogen, producing the maximum hydrogen yield of 33.5 mmol h−1 g−1. The apparent quantum efficiency for hydrogen evolution achieves 32.6% at 420 nm. This study provides a guideline for rationally designing efficient high-coordinated rare-earth single-atom active sites for efficient solar energy conversion and utilization.

Electronic and magnetic behaviors of lanthanide atoms intercalated G/MoS2 heterostructures: A first-principles study

A two-dimensional vertical heterostructure is constructed by placing graphene (G) above MoS2 monolayer via the first-principles methods. The influences of lanthanide (Ln) atoms, including La, Ce, Pr, Nd, Pm, Sm, and Eu intercalated in the interlayer of G/MoS2 heterojunction are studied. The adsorption energies show that these lanthanide atoms can stably adsorb in the G/MoS2 heterojunction. The electronic and magnetic properties of G/MoS2 heterostructure can be modulated by intercalary lanthanide atoms. After intercalating Ln atoms, the band gap of G/MoS2 heterostructure transforms semiconductor to a metal. The considered systems are magnetic except for the La@G/MoS2 heterostructure. These results reveal that the Ln@G/MoS2 systems are potential application in the development of magnetic nanostructures.

Accurate Determination of the Bandgap Energy of the Rare-Earth Niobate Series.

We report diffuse reflectivity measurements in InNbO4, ScNbO4, YNbO4, and eight rare-earth niobates. A comparison with established values of the bandgap of InNbO4 and ScNbO4 shows that Tauc plot analysis gives erroneous estimates of the bandgap energy. Conversely, accurate results are obtained considering excitonic contributions using the Elliot-Toyozawa model. The bandgaps are 3.25 eV for CeNbO4, 4.35 eV for LaNbO4, 4.5 eV for YNbO4, and 4.73-4.93 eV for SmNbO4, EuNbO4, GdNbO4, DyNbO4, HoNbO4, and YbNbO4. The fact that the bandgap energy is affected little by the rare-earth substitution from SmNbO4 to YbNbO4 and the fact that they have the largest bandgap are a consequence of the fact that the band structure near the Fermi level originates mainly from Nb 4d and O 2p orbitals. YNbO4, CeVO4, and LaNbO4 have smaller bandgaps because of the contribution from rare-earth atom 4d, 5d, or 4f orbitals to the states near the Fermi level.

Insight into the structural and magnetic properties of RECo12B6 (RE = Ce, Pr, Nd) compounds: A combined experimental and theoretical investigation

Rare earth (RE) based RE-TM-X (TM = transition metal elements; X = P-block elements) materials have received continuous attention due to the exhibition of various intriguing magnetic functional characteristics. In this work, a combined experimental and theoretical investigation has been conducted in detail for RECo12B6 (RE = Ce, Pr, Nd) compounds with regard to their structural and magnetic properties, particularly the magnetocaloric effect and magnetic phase transition (MPT). All of the present RECo12B6 compounds are found to crystalize in the SrNi12B6-type structure and with a ferrimagnetic ground state, which is confirmed by density functional theory calculations and magnetization measurements. The magnetic moments of RE atoms and Co atoms tend to be in antiparallel alignment, and the MPT of these materials originates primarily from the spin-polarized 3d electrons of the Co atoms, which can be greatly affected by the 4f electrons of RE atoms. Considerable magnetocaloric effects have been observed around its own TC of 130, 157, and 160 K, for CeCo12B6, PrCo12B6, and NdCo12B6, respectively, which is related to a typical second-order MPT. The corresponding maximum magnetic entropy change and relative cooling power values,with field changes of 0–70 kOe, are determined to be 2.54, 2.84, and 2.77 J/kg K and 116.8, 156.2, and 155.1 J/kg, respectively. The MPT properties of present RECo12B6 compounds were studied in further detail by critical analysis using the modified Arrott Plot and Kouvel-Fisher methods, which can be explained within the frame of the 3D Heisenberg model with short-range magnetic interaction.

Topological Dirac semimetal BaAuSb

Dirac semimetals feature Dirac cones with topologically nontrivial states in the bulk that are protected by crystalline symmetries. They attract considerable attention due to rich quantum states and properties of interest, such as high Fermi velocities, mobility, and small effective masses. Here, we show that a ternary intermetallic BaAuSb crystal hosts both trivial and nontrivial topological Dirac states in the bulk. The nontrivial Fermi-surface pocket at the Brillouin zone center is characterized with only a few hundredths of a bare electron mass and with very high mobility. All parts of the Fermi surface detected by quantum oscillations, topologically trivial or nontrivial, have carriers with unusually high Fermi velocities and small masses. These conducting states may be coupled with magnetic moments in materials where Ba is replaced by magnetic rare-earth atoms.

Erbium and thulium on MgO(100)/Ag(100) as candidates for single atom qubits

Lanthanide atoms on surfaces are prospective platforms for realizing atomic-scale quantum logic units. Here, the authors combine scanning tunneling microscopy, x-ray magnetic circular dichroism, density functional theory, and atomic multiplet calculations to identify the quantum level structure of erbium and thulium atoms on MgO(100)/Ag(100), and to estimate their performance as spin qubits. Their analysis reveals that both atoms have a ground state that is suitable to perform efficient quantum coherent operations.

Controlling the electronic and magnetic properties of ZnO monolayer by rare-earth atoms substitutional doping

In this article, the structural, electronic, and magnetic properties of rare-earth (RE) atoms substitutional doping in the ZnO monolayer have been studied by DFT + U. The relaxed structures of RE-doped (RE = La, Ce, Pr, Nd, Pm, Sm and Eu) ZnO monolayer present a distortion of the environment while the calculated formation energies reveal that the substitutional doping of considered rare-earth atoms in ZnO monolayer are possible. The results show that the local spin magnetic moments of La-, Ce-, Pr-, Nd-, Pm-, Sm-, and Eu-doped systems are 0, 1.26, 3.06, −4.05, 5.06, 6.06, 7.08 μB, respectively, which are proportional to the number of spin-parallel 4f electrons. The electronic structure calculations reveal that the La-doped system becomes conductor, while other doping systems are still semiconductors. These results suggest that ZnO monolayer with rare-earth substitutional doping systems have potential values in spintronic applications and the development of magnetic nanostructures.

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.