Rare Earth Atoms Research Articles

Adsorption of Lanthanide Atoms on Graphene: Similar, Yet Different

Many theoretical studies address the interaction of different atoms with graphene; however, the relevant information on the adsorption of the lanthanide species remains limited and controversial, creating a gap in this important area of graphene chemistry and physics. By employing periodic density functional theory calculations, we provide the key theoretical information for the entire series from lanthanum to lutetium interacting with defect-free graphene, including the interaction strength and distances, charge and spin of the lanthanide atoms, and comparative features of the density of states. The central lanthanides Gd, Tb, and Dy exhibit the strongest bonding and shortest distances. The positive charge acquired by the lanthanide atoms varies insignificantly, with the exception of Yb and Lu with a filled 4f shell. The spin increases from La to Tb and then decreases sharply, achieving minimal values for Tm, Yb, and Lu. Interaction with graphene influences even the deeper 5s and 5p shells.

First-principles calculations to study the metal-insulator transition of Al and Be doped RNiO3 (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er)

Rare earth nickelates (RNO) have been extensively studied in the past decades because of the metal-insulator phase transition. It was reported that the phase transition of RNO could be regulated with the electrons introduced by Li and H doping, but little is known about the multi-electrons (such as Be, Al) doping of RNO. In this paper, we applied the first-principles calculations to investigate the electronic structures, interstitial formation energies, migration behaviors and optical properties of Be and Al doped RNO. Results show that RNO would undergo a metal-insulator phase transition when the Be and Al doping concentrations respectively reach 50% and 25%. In addition, the migration of Be and Al along the [001] direction of RNO shows that as the radius of rare earth atoms decreases, the migration barrier generally shows a decreasing trend. As for optical properties, the absorption coefficient and reflectivity decrease in Be and Al doped RNO over the entire range of visible and infrared light. Generally, the transmissivity of RNO can be greatly improved by doping 50% of Be and Al.

Effect of impurities on the Raman spectra of spray-coated β-Ga2O3 thin films

Here, the incorporation of impurities into doped thin β-Ga2O3 films was studied by Raman spectroscopy, and a simple spring model was employed to estimate the impurity concentration from the impurity-modified frequencies of first-order phonon modes. β-Ga2O3 thin film samples were prepared using the spray-coating technique. As impurities, we used rare earth atoms (Er, Sm, and Gd) as well as Mg, Al, and Zn, with the nominal impurity concentrations varying from 0.5% up to 5.0%. As the impurities are expected to predominantly occupy Ga sites in the β-Ga2O3 lattice, heavier and lighter atoms than Ga should have a pronounced influence on Ga-related lattice vibrations. Therefore, in the Raman spectra of the thin films measured using 325-nm excitation, the impurity-induced shifts of the frequencies of vibrations involving Ga and O atoms were employed to estimate the impurity concentration. In addition, a high-impurity concentration can cause the formation of impurity-related oxides, as it is clearly visible for Zn. Besides, the Raman spectra with Mg as the impurity show that Mg most probably occupies interstitial rather than substitutional sites as the Raman modes do not shift with respect to the impurity concentration.

A combined first- and second-order optimization method for improving convergence of Hartree–Fock and Kohn–Sham calculations

In this work, we investigate the optimization of Hartree-Fock (HF) orbitals with our recently proposed combined first- and second-order (SO-SCI) method, which was originally developed for multi-configuration self-consistent field (MCSCF) and complete active space SCF (CASSCF) calculations. In MCSCF/CASSCF, it unites a second-order optimization of the active orbitals with a Fock-based first-order treatment of the remaining closed-virtual orbital rotations. In the case of the single-determinant wavefunctions, the active space is replaced by a preselected "second-order domain," and all rotations involving orbitals in this subspace are treated at second-order. The method has been implemented for spin-restricted and spin-unrestricted Hartree-Fock (RHF, UHF), configuration-averaged Hartree-Fock (CAHF), as well as Kohn-Sham (KS) density functional theory (RKS, UKS). For each of these cases, various choices of the second-order domain have been tested, and appropriate defaults are proposed. The performance of the method is demonstrated for several transition metal complexes. It is shown that the SO-SCI optimization provides faster and more robust convergence than the standard SCF procedure but requires, in many cases, even less computation time. In difficult cases, the SO-SCI method not only speeds up convergence but also avoids convergence to saddle-points. Furthermore, it helps to find spin-symmetry broken solutions in the cases of UHF or UKS. In the case of CAHF, convergence can also be significantly improved as compared to a previous SCF implementation. This is particularly important for multi-center cases with two or more equal heavy atoms. The performance is demonstrated for various two-center complexes with different lanthanide atoms.

Competing dynamical and lattice instabilities in RVO4 rare-earth vanadium oxides under high pressure

Zircon-type ${R\mathrm{VO}}_{4}$ compounds (where R = rare-earth atom) constitute a family of ternary oxides which are abundant in both nature and the industrial field. Their structural systematics upon compression has been widely studied. According to the observed systematics, the high-pressure crystal structure is determined by the rare-earth cation size. Nonetheless, the mechanisms involved in the phase transitions remain relatively unexplored. Thus, we gathered the experimental data reported in the literature and compared it to our ab initio calculations, including not only enthalpy, but also the frequency of lattice modes and the value of elastic constants. Our study reveals systematic trends, where high-pressure phases appear only if they are thermodynamically stable and are always preceded by a mechanical or dynamical instability, which counteracts the effects of kinetic barriers in the zircon-to-monazite or -scheelite phase transition, respectively.

Structure and Chemical Bonding in Medium-Size Boron Clusters Doped with Praseodymium.

After reports of unusually low oxidation states of lanthanide elements in Ln-B clusters and their inverse sandwich geometrical topologies, the interest shifted from boride clusters doped with transition metal (TM) elements to the boride clusters doped with lanthanide atoms. In this work, the results obtained by a combined approach consisting of CALYPSO structure predictions and density functional theory (DFT) calculations for the neutral and anionic PrBn series, n = 7-16, are reported. A close agreement between our calculated vertical detachment energies and experimental data supports the accuracy of the results obtained. Contrary to the medium-size TM-doped medium boron clusters, which prefer three types of structural configurations, all lowest-energy states of the medium-size Pr-doped boron clusters have half-sandwich geometries. An interesting structural evolution pattern was found for both neutral and anionic PrBn clusters at n = 7, 10, 13, and 16, which includes quasi-planar B7 units half-sandwiching the Pr atom. Unusual oxidation numbers of +2 and +1 were found for the Pr atom in the PrB7- and PrB8- anions, respectively. Chemical bonding analysis for the neutral PrB7 and PrB13 clusters revealed that their high stability stems from interactions between Pr 5d and B 2p orbitals. A stable tubular-shaped PrB30 cluster is proposed as a promising building block for boron-based nanotubes.

Magnetic properties of a capped kagome molecule with 60 quantum spins

We compute ground-state properties of the isotropic, antiferromagnetic Heisenberg model on the sodalite cage geometry. This is a 60-spin spherical molecule with 24 vertex-sharing tetrahedra which can be regarded as a molecular analogue of a capped kagome lattice and which has been synthesized with high-spin rare-earth atoms. Here, we focus on the S=1/2S=1/2 case where quantum effects are strongest. We employ the SU(2)-symmetric density-matrix renormalization group (DMRG). We find a threefold degenerate ground state that breaks the spatial symmetry and that splits up the molecule into three large parts which are almost decoupled from each other. This stands in sharp contrast to the behaviour of most known spherical molecules. On a methodological level, the disconnection leads to ``glassy dynamics’’ within the DMRG that cannot be targeted via standard techniques. In the presence of finite magnetic fields, we find broad magnetization plateaus at 4/5, 3/5, and 1/5 of the saturation, which one can understand in terms of localized magnons, singlets, and doublets which are again nearly decoupled from each other. At the saturation field, the zero-point entropy is S=\ln(182)\approx 5.2S=ln(182)≈5.2 in units of the Boltzmann constant.

Electronic and Magnetic Properties of The Graphene/RE/Ni(111) (RE: La, Yb) Intercalation‐Like Interfaces: A DFT Analysis

AbstractThe effect of the rare‐earth (RE) metals (La and Yb) intercalation on the electronic and magnetic properties of the graphene/Ni(111) interface is studied using state‐of‐the‐art density functional theory calculations. In both systems, the intercalation of RE leads to the dramatic decrease of the magnetic moments of the Ni‐interface atoms and to the negligible moments of C‐atoms in a graphene layer, compared to the parent graphene/Ni(111) system. At the same time, the significant ‐doping of graphene together with a band‐gap opening is observed in both cases of the RE intercalation with a position of the graphene Dirac point reaching eV. Also the large density of states is found in the vicinity of the Fermi level () along the direction for the graphene‐derived states which can be attributed to the joint effect of the intercalated RE and interface Ni atoms. These factors – increased density of states at and absence of magnetism of C‐atoms in a graphene layer – indicate the possibility of the observation of the superconductive state in graphene in the considered RE‐based systems, which is important for the understanding of these and other electronics effects in the graphene‐based systems.

Ordered CaCu5-type phases REPd2Zn3 (RE = Y, La–Nd, Sm, Gd–Dy)

Abstract The ternary intermetallic phases REPd2Zn3 (RE = Y, La–Nd, Sm, Gd–Dy) were synthesized from the elements by induction melting in sealed niobium ampoules followed by annealing. The CaCu5-type samples (space group P6/mmm) were characterized through Guinier powder patterns. The structures of YPd2Zn3 (a = 523.91(4), c = 430.88(3) pm, wR2 = 0.0570, 96 F 2 values, 9 variables) and NdPd2Zn3 (a = 535.08(7), c = 427.81(6) pm, wR2 = 0.0217, 123 F 2 values, 9 variables) were refined from single-crystal X-ray diffractometer data. The zinc atoms form Kagome layers in AA stacking which leave trigonal prismatic voids for the palladium and hexagonal prismatic voids for the rare earth atoms. The Zn–Zn distances within the Kagome network of YPd2Zn3 are 262 pm and the Pd–Zn distances in the Pd@Zn6 trigonal prisms are 263 pm.

Structural and luminescence characterization of europium-doped niobium germanate glasses and glass-ceramics: Novel insights from 93Nb solid-state NMR spectroscopy

A thorough understanding of network former roles in optical glasses and glass-ceramics, as well as structural environments of luminescent rare-earth atoms, is paramount to assessing their suitability and effectiveness as components for fully-optical integrated devices. The present contribution sheds light on the overall poorly understood structural role of Nb2O5 in oxide glasses and offers a rationale for the luminescence changes concomitant to the heat-treatment induced glass-to-crystal transition in niobium germanate glasses. To this end, results from 93Nb nuclear magnetic resonance (NMR), Raman, and Eu3+ ion based luminescence spectroscopies as well as 3D micromanufacturing are reported for glasses and glass-ceramics in system (89.9-x)GeO2-xNb2O5-10K2O-0.1Eu2O3. Thanks to very-fast 93Nb magic-angle spinning (MAS) and a novel excitation scheme for Triple-quantum (TQ)MAS solid-state NMR spectroscopy distinct Nb(OGe)6-y(ONb)y species were identified for the first time: at low Nb concentrations structural units with rather low y-values are formed, reaching down to isolated Nb(OGe)6 units – next to units bearing non-bridging oxygen atoms; at intermediate Nb contents and beyond, structural units with increasingly higher y-values up to Nb(ONb)6 are found, resembling the local environments found in crystalline Nb2O5. After the glass-to-crystal transition the Nb local environment maintains a high degree of disorder while some residual glass remains. Moreover, photoluminescence spectroscopy of the europium probes suggests the rare-earth ions are preferentially incorporated into high y-value Nb(OGe)6-y(ONb)y polyhedra based on spectral features such as the phonon sideband, the 5D0 → 7F2/7F1 ratio, and split 4f bands. Finally, femtosecond laser microfabrication of waveguides was successful in the presented europium-doped niobium germanate glasses, making them promising candidates for further studies as photonic devices.

Critical current density in granular REBa2Cu3O7-δ superconductors with different interlayer magnetic coupling

Current-voltage (IV) characteristics of REBa2Cu3O7-δ have been used to extract critical current density (JcG and Jc) using an electric field (E) criterion below the onset critical temperature (Tc). By changing the intrinsic magnetic moment via four different rare earth (RE) atoms the interlayer coupling between superconducting planes is modified strongly. Variations of granular critical current density (JcG (T)) and total critical current density (Jc) are used to extract an exponent which we propose to be important to understand the nature of the vortex pinning by distributed magnetic moments. Also the effect of the grain boundary angles on pinning exponents extracted from both Jc (T) and JcG (T) has been discussed.

2D paddle wheel lanthanide metal-organic framework: Synthesis, structure and exploration of catalytic N-arylation reaction

Novel lanthanide based two-dimensional metal–organic framework (MOF) compound [Dy(NDC)(NO3)(DMA)2]n (1) [H2NDC = 2,6-naphthalenedicarboxylic acid and DMA = N,N-dimethylacetamide] has been synthesized through solvothermal route and structurally characterized. Structural analysis reveals that compound is crystallized in the orthorhombic crystal system with space group Pbca. MOF features “paddle-wheel” (PW) core building units which are constructed via carboxylato oxygen coordinated to lanthanide atoms. Remaining coordination sites of the octa-coordinated metal center are occupied by oxygen atoms of DMA and NO3− ions. Paddle-wheel cores of 1 are interconnected to each other to give rise to layered network structure. The morphology of the MOFs as well as different types of weak interactions possessed by the framework have been assessed using Hirshfeld surface analysis and fingerprint plots have been drawn to understand various interactions. Notably, compound 1 can efficiently catalyze the N-arylation reaction heterogeneously.

Theoretical insights into the effects of RE doping on the structural, electronic, and optical properties of magnesium clusters

Doping of magnesium-based materials with the rare earth (RE) elements allows one to adjust or modify the structures and properties of the materials. In the present work, the structural, electronic, and optical properties of the global minima Mgn (n = 2–10) and MgnX (X = Sc, Y, La, Nd, Gd, n = 1–9) clusters have been examined using the density functional theory (DFT) and the time-dependent DFT. The identified structures show that the RE atoms tend to occupy the center of the surface of the geometries, which enhances their structural stability. Further analyses on average bonding energies, the second-order differences in energy, and HOMO–LUMO gaps indicate that the Mg3Nd cluster is more stable than others. The excellent stability of this cluster is caused by the strong Nd 4f and Mg 2p interactions through the analyses of molecular orbitals. The natural population analyses imply that the electron transfers mainly occur among the s-p-d orbitals in MgnX (X = Sc, Y, La) clusters and the s-d-f orbitals in MgnX (X = Nd, Gd). In addition, the results of the excited-state calculations reveal that the absorption spectra of all MgnX clusters emerge red-shift phenomena compared with that of Mgn, and the absorbance strongest resonances of Mg4X clusters concentrate at visible light region (about 600 nm).

Synthesis and characterisation of η6-arene(halogenidoaluminato)-lanthanoid(II) and alkaline earth(II) complexes

η6-Arene(iodidoaluminato)lanthanoid(II) complexes, {[Ln(η6-C6H5Me)(AlI4)2]}n [Ln = Sm, 1, Eu, 2, Yb, 3; C6H5Me = toluene] have been prepared by reactions of in situ generated aluminium triiodide with the corresponding lanthanoid metals and 1,2-diiodoethane in toluene (molar ratio: 2:1:1). Compounds 1–3 are polymeric and the lanthanoid(II) atom of 1 and 2 is coordinated by an η6–arene and three chelating κ (I, I′) tetraiodidoaluminate ligands, two of which are also bridging (LnI2AlI2Ln) and one is terminal. 3 is coordinated by an η6–arene, one terminal chelating κ (I, I′) and one chelating and bridging (YbI2AlI2Yb) tetraiodidoaluminate ligand, and one monodentate tetraiodidoaluminate ligand, which is also bridging (YbIAl(I)I2Yb). These are the first X-ray crystal structures of arene(tetrakisiodidoaluminato)lanthanoid(II) complexes. The first reported alkaline earth(II) (η6–arene)iodidoaluminate complexes, namely [Ca(η6-C6H5Me)(AlI4)2]n (4), {[Sr(η6-C6H5Me)(AlI4)2]n·nPhMe} (5), [Ba(η6-C6H5Me)2(AlI4)2] (6), [Ca(η6-C6H3Me3-1,3,5)(AlI4)2]n (7) and {[Sr(η6-C6H3Me3-1,3,5)(AlI4)2]n·0.5n(PhMe3)} (8) have also been obtained in an arene (toluene or mesitylene) solution by a similar method. Complex 4 is isocoordinate with 3, and 5 is isomorphous with 2. Complex 7 has eight coordinate Ca similar to 4, and complex 8 has nine coordinate Sr as in 5. Mononuclear ten coordinate complex 6 is the first example of a monomeric η6–arene sandwich complex of barium. The EuII bromidoaluminate complex {[Eu(η6-C6H5Me)(AlBr4)2]n·0.5nPhMe} (9) has been prepared from Eu metal, AlBr3, and BrCH2CH2Br in toluene and has a unit cell similar to 8 despite the different metal and arene.

Rare earth praseodymium-based single atom catalyst for high performance CO2 reduction reaction

Rare earth single-atom catalysts (SACs) can be used to obtain atomically dispersed species on supports to provide the maximum number of well-defined active sites, which would subsequently maximize the utilizationof rare earth metals. However, the design and synthesis of SACs are mostly based on transition metals, and rare earth SACs have been rarely explored. Herein, we report a rare earth praseodymium SAC dispersed on a porous carbon substrate by utilizing the cascade anchoring strategy, with a metal loading of up to 5.07 wt%. This praseodymium SAC exhibits excellent catalytic performance for the electrochemical CO2 reduction reaction (CO2RR) and achieves high selectivity for CO, with a faradaic efficiency (FECO) of up to 93% at a low potential of −0.43 V vs RHE. Experiments and theoretical calculations confirm that the isolated praseodymium atoms on the substrate are critical for improving the CO2RR performance of the material.

Nanotubes from the Misfit Layered Compound (SmS)1.19TaS2: Atomic Structure, Charge Transfer, and Electrical Properties.

Misfit layered compounds (MLCs) MX-TX2, where M, T = metal atoms and X = S, Se, or Te, and their nanotubes are of significant interest due to their rich chemistry and unique quasi-1D structure. In particular, LnX-TX2 (Ln = rare-earth atom) constitute a relatively large family of MLCs, from which nanotubes have been synthesized. The properties of MLCs can be tuned by the chemical and structural interplay between LnX and TX2 sublayers and alloying of each of the Ln, T, and X elements. In order to engineer them to gain desirable performance, a detailed understanding of their complex structure is indispensable. MLC nanotubes are a relative newcomer and offer new opportunities. In particular, like WS2 nanotubes before, the confinement of the free carriers in these quasi-1D nanostructures and their chiral nature offer intriguing physical behavior. High-resolution transmission electron microscopy in conjunction with a focused ion beam are engaged to study SmS-TaS2 nanotubes and their cross-sections at the atomic scale. The atomic resolution images distinctly reveal that Ta is in trigonal prismatic coordination with S atoms in a hexagonal structure. Furthermore, the position of the sulfur atoms in both the SmS and the TaS2 sublattices is revealed. X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and X-ray absorption spectroscopy are carried out. These analyses conclude that charge transfer from the Sm to the Ta atoms leads to filling of the Ta 5dz2 level, which is confirmed by density functional theory (DFT) calculations. Transport measurements show that the nanotubes are semimetallic with resistivities in the range of 10–4 Ω·cm at room temperature, and magnetic susceptibility measurements show a superconducting transition at 4 K.

Effect of lanthanide fission product concentrations on the mechanical properties of UO2: A first principle based study

The fission products generated from UO2 during the nuclear fission process alters the mechanical properties of the nuclear fuel. The effect of fission atom substitution in UO2 is a requisite for the safe operation of nuclear reactors. The lanthanide atoms contribute significantly to the mixture of fission products generated. Therefore, in this work, we investigate the effect of lanthanum (La), promethium (Pm), and dysprosium (Dy) doping on mechanical properties of UO2. Further, the relation between doping concentration and different mechanical properties are derived by varying the La, Pm and Dy substitution in UO2. All the calculations are performed with density functional theory with Hubbard U corrections in the DFT + U formalism. Mechanical properties such as bulk, Young’s and shear modulus of UO2 change with the amount of dopant atom in the fuel. The results obtained from our calculations show good agreement with available experimental and theoretical findings. Thus, the present study validates the relationship between fission atom substitution and mechanical properties of UO2, which will help to understand the fuel performance at reactor conditions.

η6‐Arene(halogenidoaluminato)lanthanoid(III) Complexes: Synthesis, Characterization and Catalytic Activity for Isoprene Polymerization

Abstractη6‐Arene(iodido‐/bromido‐aluminato)lanthanoid(III) complexes, [Ln(η6‐C6H5Me)(AlI4)3] [Ln=La (1), Ce (2), Nd (3), (Gd) (4); C6H5Me=toluene], [Ln(η6‐C6H3Me3‐1,3,5)(AlI4)3] [Ln=La (5), Ce (6), Pr (7), Nd (8), Sm (9), Gd (10); C6H3Me3‐1,3,5=mesitylene], and [Ln(η6‐C6H5Me)(AlBr4)3] [Ln=La (11), Nd (12), Sm (13)] were prepared by reactions of aluminium triiodide or aluminium tribromide with the corresponding lanthanoid metals and 1,2‐diiodoethane or 1,2‐dibromoethane in an arene (toluene or mesitylene) solution (molar ratio : 6 : 2 : 3). The first X‐ray crystal structures of arene(iodidoaluminato)lanthanoid(III) complexes are reported. The lanthanoid atom is coordinated by an η6‐arene and three chelating κ(I, I′)‐tetraiodidoaluminato ligands. The tetrabromidoaluminate complexes have similar structures. The precatalyst 3 was treated with AlR3 (R=Me or iBu) to give [Nd(η6‐C6H5Me)(AlI3R)3] species in situ, which were then tested for catalytic activity towards isoprene polymerization. Although the resulting polyisoprene had a desirable high cis‐1,4 content, the catalyst performance was well below known best performing systems and indicates that iodidoaluminates are the least favorable of the halogenidoaluminatolanthanoid(III) complexes.

Laser-induced thermal source for cold atoms

We demonstrate a simple and compact approach to laser cool and trap atoms based on laser-induced thermal ablation (LITA) of a pure solid granule. A rapid thermalisation of the granule leads to a fast recovery of the ultra-high vacuum condition required for a long trapping lifetime of the cold gas. We give a proof-of-concept of the technique, performing a magneto-optical trap on the 461 nm ^1S_0rightarrow ,^1P_1 transition of strontium. We get up to 3.5 million of cold strontium-88 atoms with a trapping lifetime of more than 4 s. The lifetime is limited by the pressure of the strontium-free residual background vapour. We also implement an original configuration of permanent magnets to create the quadruple magnetic field of the magneto-optical trap. The LITA technique can be generalized to other atomic elements such as transition metals and lanthanide atoms, and shows a strong potential for applications in quantum technologies ranging from quantum computing to precision measurements such as outdoor inertial sensing.

Simulating two-dimensional dynamics within a large-size atomic spin

Encoding a dimension in the internal degree of freedom of an atom provides an interesting tool for quantum simulation, facilitating the realization of artificial gauge fields. We propose an extension of the synthetic dimension toolbox, making it possible to encode two dimensions within a large atomic spin. The protocol combines first- and second-order spin couplings, such that the spin projection $m$ and the remainder $r=m$ (mod 3) of its Euclidian division by 3 act as orthogonal coordinates on a synthetic cylinder. It is suited for an implementation with lanthanide atoms, which feature a large electronic spin and narrow optical transitions for applying the required spin couplings. This method is useful for simulating geometries with periodic boundary conditions, and engineering various types of topological systems evolving in high dimensions.