Lanthanum Atoms Research Articles

Gradient distribution of cations in rhabdophane La0.27Y0.73PO4·nH2O nanoparticles

The structure of gradient rhabdophane nanoparticles of variable composition (La,Y)PO4·nH2O obtained by precipitation is considered. According to the data of HAADF TEM and EDX mapping using the Abel inversion procedure, it was shown that there is an inhomogeneous distribution of yttrium and lanthanum atoms in the particles from the central part to the periphery. At the same time, the nominal composition of both individual nanoparticles and the entire sample meets the value specified during synthesis within the error of the method – La0.27Y0.73PO4·nH2O. According to SAXS data, it was determined that in the particles of (La,Y)PO4·nH2O, there is a redistribution of scattering densities, which is caused by an increase in the fraction of YPO4 in the peripheral region of the particles. The observed effect of the distribution of cations over the particle made it possible to determine the size of the gradient layer, which reaches 50 % of the total particle size.

Electrochemical Performance of Niobium MXenes with Lanthanum.

MXenes are the newest class of two-dimensional nanomaterials characterized by large surface area, high conductivity, and hydrophilicity. To further improve their performance for use in energy storage devices, heteroatoms or functional groups can be inserted into the Mxenes' structure increasing their stability. This work proposes insertion of lanthanum atoms into niobium-MXene (Nb-MX/La) that was characterized in terms of morphogy, structure, and electrochemical behavior. The addition of La to the Nb-MXene structure was essential to increase the spacing between the layers, improving the interaction with the electrolyte and enabling charge/discharge cycling in a higher potential window and at higher current densities. Nb-MX/La achieved a specific capacitance of up to 157 mF cm-2, a specific capacity of 42 mAh cm-2 at 250 mV s-1, a specific power of 37.5 mW cm-2, and a specific energy of 14.1 mWh cm-2 after 1000 charge/discharge cycles at 50 mA cm-2.

The Mixed‐Anion Compound La2S2(CN2)

AbstractThe new binary metal carbodiimide La2S2(CN2) was synthesized via a solid‐state metathesis reaction. The crystal structure was solved and refined on the basis of single‐crystal X‐ray diffraction data with space group C2/m. The structure is represented by a layered arrangement, based on alternating layers of lanthanum, sulfide, and carbodiimide units. A close resemblance of the structure with that of La2O2C2 is discussed, as well as the less‐common coordination number seven of the lanthanum atom.

Spectral Investigations of 60S Bioactive Glass Modified with La and Y Ions.

The changes in the atomic structure and in the network of bonds between oxide tetrahedra in 60S bioactive glass upon modification of its structure by yttrium and lanthanum atoms were investigated via XPS, FTIR, and NMR spectroscopy methods. The presence of nanostructure in the samples of 60S bioactive glass modified with yttrium and lanthanum was demonstrated. The formation of a bioinert core of 60S bioactive glass nanoparticles with the subsequent formation of a biocompatible layer is facilitated by the redistribution of electron density when oxygen bridge bonds are broken, PO4 and SiO4 tetrahedra are fragmented in the polymer matrix, and isolated nanoclusters are formed. Given the fact that during the interaction with the extracellular matrix, the breakdown of covalent bonds -O-Si-O-P- is more energetically costly than the rapid ionic exchange of network modifiers Ca2+ (Y3+, La3+) and the leaching of isolated nanoclusters into the surrounding physiological environment, it is argued that modification of 60S bioactive glass with yttrium or lanthanum can accelerate bioactive ionic processes in the extracellular matrix.

Orbital-overlap-driven hybridization in 3d-transition metal perovskite oxides LaMO3 (M = Ti-Ni) and La2CuO4

The wide tunability of strongly correlated transition metal (TM) oxides stems from their complex electronic properties and the coupled degrees of freedom. Among the perovskite oxides family, LaMO3 (M = Ti-Ni) allows an M-dependent systematic study of the electronic structure within the same-structure-family motif. While most of the studies have been focusing on the 3d TMs and oxygen sites, the role of the rare-earth site has been far less explored. In this work, we use resonant inelastic X-ray scattering (RIXS) at the lanthanum N4,5 edges and density functional theory (DFT) to investigate the hybridization mechanisms in LaMO3. We link the spatial-overlap-driven hybridization to energetic-overlap-driven hybridization by comparing the RIXS chemical shifts and the DFT band widths. The scope is extended to highly covalent Ruddlesden-Popper perovskite La2CuO4 by intercalating lanthanum atoms to rock-salt layers. Our work evidences an observable contribution of localized lanthanum 5p and 4f orbitals in the band structure.

First-principles analysis of the local atomic environment in calcium lanthanum sulfide ceramics

Density functional theory is utilized to investigate the energetics and mechanisms of sulfur loss across different stoichiometries of La2S3:CaS ceramics. These atomistic results reveal that the local atomic environment around each sulfur atom, consisting of six cation sites, can be used to predict the vacancy formation energy of the atom. Three nominal compositions are considered, 50:50, 65:35, and 90:10 La2S3:CaS, for two different atomic configurations, La2S3-like and La3S4-like. Relations were developed utilizing multivariable linear models. It is shown that the number of cation vacancies and lanthanum atoms in the local environment are among the most important factors in determining the energetics of a sulfur vacancy. Bader charge analysis reveals this is related to the degree of localization of charge change around the vacancy site and how close to the preferred oxidation states the lanthanum is. Results also suggest that while defect-free La2S3-like structures are energetically favorable, once a critical vacancy content is reached, the La3S4-like structure becomes the lower energy structure, which agrees qualitatively with recent experimental observations. This has important implications on how defect content and stoichiometry in this system are related. These findings also provide useful guidance on how these materials might best be processed.

THE EFFECT OF BARIUM SUBSTITUTION WITH COMBINATIONS OF RARE EARTH ON PERMANENT MAGNETIC SURFACE MORPHOLOGY BASED ON BARIUM HEXAFERRITE

The development of hard magnets today is progressing very rapidly. Developing hard magnets based on rare earth metals becomes a severe problem when the raw materials are not readily available. The chosen solution is to replace oxide-based permanent magnets with small amounts of rare earth metals substituted to improve their magnetic properties. This study synthesized a permanent magnet oxide based on barium hexaferrite doped with lanthanum and cerium atoms. In the synthesis of this material, a mechanical wet milling technique is used to obtain a single-phase permanent magnetic Ba1-β-γLaβCeγFe12O19 system with composition (β = 0 - 0.5 and γ = 0 - 0.1). The precursors are weighted according to their stoichiometric composition. Each mixed composition was milled by high energy milling (PW 1000 in the mixer/mill) at a milling speed of 1000 rpm using steel balls with an average diameter of 12 mm. Grinding conditions included a ball-to-powder weight ratio of 2:1, milling time 5 hours, then compacted with 7000 Psi pressure and sintered at 1200oC for 2 hours. The surface morphology and microstructure of the resulting sample particles were observed using scanning electron microscopy (SEM) with the SEM JEOL JED 305 brand. The characterization results show that the particles are hexagonally homogeneous in shape with particle sizes in the range of 1000-2000 nm for β = 0 and γ = 0 (without doping). In general, the four samples with varying concentrations of doping ions La3+ and Ce4+ showed homogeneous hexagonal structures but smaller particle sizes than pure barium hexaferrite. The sample particle sizes ranged from 500-1000 nm for β = 0.02 and 300-1000 nm for β = 0.04.

High-temperature superconductivity in La4H23 below 100 GPa

High-temperature superconductivity has been observed in binary hydrides such as LaH10 at pressures close to 180GPa, whereby hydrogen cagelike structures have been identified as a common motif beneficial for high critical temperatures Tc. Efforts are now focused on finding hydride high-temperature superconductors at lower pressures. We present evidence for high-temperature superconductivity in binary La4H23 at a pressure of P=95GPa, with A15-type arrangement of the lanthanum atoms in the type-I clathrate structure. We synthesize La4H23 from a lanthanum film capped with a palladium catalyst promoting the dissociation of hydrogen. In resistance measurements, we observe superconductivity with a transition temperature Tc∼90K. The A15-type lanthanum sublattice is identified in x-ray diffraction on the same sample, in agreement with previous x-ray diffraction and structure prediction studies. Our study reinforces the favorability of cagelike networks of the hydrogen lattice for high-temperature superconductivity. Published by the American Physical Society 2024

Synthesis of Garnet-type Solid Electrolyte for All-Solid-State Battery Application

The Ga-doped Li7La3Zr2O12 (LLZO) Solid State Electrolyte (SSE) has been synthesized via solid-state reaction. The structural study of the SSE was conducted with the help of X-ray diffraction and the Rietveld method. The SSE crystallizes in the Li6.25Ga0.15La2.90Zr2O12 phase with cubic space group number 220 and unit cell parameter 13.02081 Å, and La2Zr2O7 impurity phase with cubic space group number 227 and unit cell parameter 10.79475 Å. Obtained lattice planes in the refinement were confirmed with the help of TEM. The core of the Li-ion migration channel has been defined as the loop formed by the Li32, Li1, Li2, and Li22 sites with minimal Li...Li distance and occupational disorganization of the Ga-doped LLZO SSE. The electron density plots of the Li6.25Ga0.15La2.90Zr2O12 phase have shown maximum distribution of electrons inside the unit cell for lanthanum atoms. XPS confirmed the presence of all the precursors i.e., Li, La, Zr, Ga, and O in the synthesized compound. The elemental composition was confirmed with the help of EDX. In the direct current charge-discharge behavior of the Li symmetric cell no voltage breakdown was observed even at 6 mAcm‑2 current density and after 400 charge/discharge cycles for over 200 hours.

(Digital Presentation) Crystal Structure Study of Ga-Substituted Li7La3Zr2O12 solid State Electrolyte with the Help of Rietveld Refinement

The Ga-doped Li7La3Zr2O12 (LLZO) Solid State Electrolyte (SSE) has been looked into with the help of X-ray diffraction and its structure has been successfully refined by the Rietveld method. The SSE crystallizes in the Li6.25Ga0.15La2.90Zr2O12 phase with cubic space group number 220 and unit cell parameter 13.02081 Å, and La2Zr2O7 phase with cubic space group number 227 and unit cell parameter 10.79475 Å. With 113 total reflections, the structural parameters of both the phases conversed to Rp = 13.5, Rexp = 14.16, Rwp = 18.5 and the goodness of fit i.e., χ2 was obtained as 1.74. The core of the Li-ion migration channel has been defined as the loop formed by the Li32, Li1, Li2, and Li22 sites with minimal Li...Li distance and occupational disordering of the Ga-doped LLZO SSE. The electron density plots of Li6.25Ga0.15La2.90Zr2O12 phase has shown maximum distribution of electrons inside the unit cell for lanthanum atoms. XPS confirmed the presence of all the precursors in the synthesized compound. Figure 1

MODIFICATION OF LANTHANUM OXIDE La<sub>2</sub>O<sub>3</sub> ON THE STRUCTURE OF SUPRASTRUCTURAL UNITS IN ALKALI BORATS

It shows a significant change in structurally sensitive properties in the experiment of modifying a melt (or glass) of the B2O3–Na2O system with lanthanum oxide La2O3 with the destruction of superstructural units when lanthanum atoms hit, since small additions of rare earth metal oxides lead to a significant change in the properties of alkali borate melts. Molecular models of some of the superstructural units, the structure and properties of which were calculated by semi-empirical quantum chemical methods with MNDO and PM7 parameters: as a result of the optimization procedure, both methods lead to models that are qualitatively close, but differ in bond lengths, and practically the same value of heat of formation. The superstructural unit of the considered type is preserved, while its characteristics change: the volume occupied by it increases, the newly formed bond is less strong and its ionic degree is greater.

Synthesis and Stabilization of Crystal Hydrate Modification SrSO4⋅0.5H2O

A method has been developed for the synthesis of the metastable trigonal modification SrSO4⋅0.5H2O, isostructural to the well-known CaSO4⋅0.5H2O modification (space group P3121). Frozen solutions of NaCl in water have been proposed as a precursor in the crystallization of SrSO4⋅0.5H2O. The SrSO4⋅0.5H2O structure can be stabilized by isovalent substitution of calcium ions for strontium ions or by aliovalent substitution of potassium and lanthanum ions for strontium ions. The compound of composition K0.25La0.25Sr0.5(SO4)⋅0.5H2O has been synthesized as an example of the stabilized SrSO4⋅0.5H2O modification. The unit cell parameters have been determined and refined. A model of the structure of SrSO4⋅0.5H2O with a statistical distribution of potassium, lanthanum, and strontium atoms over the positions of Ca atoms in the well-known СаSO4⋅0.5H2O structure has been proposed.

Effect of lanthanum on thermal and mechanical properties of modified polyvinyl chloride film

Polyvinyl chloride (PVC) hybrid film containing cerium, tin and folic acid modified nano titanium dioxide is a new functional material with good compatibility, light resistance and heat resistance. In this work, the PVC hybrid film was prepared by replacing cerium with lanthanum. The hybrid film was characterized by thermogravimetric infrared spectroscopy, dynamic mechanical analysis, atomic force microscopy, x-ray photoelectron spectroscopy, scanning electron microscopy, tensile strength and thermal aging. The results show that the initial thermal stability of the hybrid film containing lanthanum is slightly higher than that of the control sample (conversion α < 1.9%). For the same gaseous component plasticizer, the peak intensity of the ester based infrared characteristic group is higher than that of the hybrid film containing lanthanum, indicating that the intermolecular force between lanthanum and plasticizer is greater than that of cerium. In the range of 350 °C–575 °C and the wave number range of 2850–3100 cm−1, the peak height of the lanthanum containing film is significantly higher than that of the control sample, which may be due to the difference of the outer layer electrons. The peak intensity of O and C atoms on the surface of the hybrid film containing lanthanum is significantly lower than that of the control sample, indicating that the surface relative concentration of lanthanum atoms is lower than that of cerium atoms. The surface roughness RMS of the hybrid film containing lanthanum is significantly lower than that of the organic tin film, which is the result of the attraction between folic acid modified TiO2, lanthanum and tin and the carbon chlorine bond in PVC. It has the function of a potential ultrafiltration membrane. In addition, the hybrid film containing 1phr lanthanum shows good energy storage modulus and low temperature resistance. The prepared hybrid film shows the characteristics of a potential multi-functional material.

The Effect of La3+ on the Methylene Blue Dye Removal Capacity of the La/ZnTiO3 Photocatalyst, a DFT Study.

Theoretically, lanthanum can bond with surface oxygens of ZnTiO3 to form La-O-Ti bonds, resulting in the change of both the band structure and the electron state of the surface. To verify this statement, DFT calculations were performed using a model with a dispersed lanthanum atom on the surface (101) of ZnTiO3. The negative heat segmentation values obtained suggest that the incorporation of La on the surface of ZnTiO3 is thermodynamically stable. The bandgap energy value of La/ZnTiO3 (2.92 eV) was lower than that of ZnTiO3 (3.16 eV). TDOS showed that the conduction band (CB) and the valence band (VB) energy levels of La/ZnTiO3 are denser than those of ZnTiO3 due to the participation of hybrid levels composed mainly of O2p and La5d orbitals. From the PDOSs, Bader’s charge analysis, and ELF function, it was established that the La-O bond is polar covalent. MB adsorption on La/ZnTiO3 (−200 kJ/mol) was more favorable than on ZnTiO3 (−85 kJ/mol). From the evidence of this study, it is proposed that the MB molecule first is adsorbed on the surface of La/ZnTiO3, and then the electrons in the VB of La/ZnTiO3 are photoexcited to hybrid levels, and finally, the MB molecule oxidizes into smaller molecules.

Partial re-investigation of the ternary diagram La2O3 – Nb2O5 – CaO, synthesis and characterization of the Ca2La3Nb3O14 and Ca8La8Nb14.4□1.6O56 compounds

This paper focuses on the synthesis and the structure determination of two previously reported compounds of unknown structure - Ca0.96La1.56Nb1.48O7 and Ca1.16La1.26Nb1.56O7 - as well as the investigation of the center of the ternary phase diagram La2O3 – Nb2O5 – CaO. The samples are prepared by the conventional solid state ceramic route. Structure determination is performed by using microscopy electron diffraction, X-ray and neutron powder diffraction data. The formulas of the two compounds are found to be Ca2La3Nb3O14 and Ca8La8Nb14.4□1.6O56, respectively, where the symbol □ denotes cationic vacancies. Ca2La3Nb3O14 crystallizes in the rhombohedral space group R 3¯ m (No.166) (Z ​= ​3) with the cell parameters a ​= ​7.6525(2) (Å) and c ​= ​18.2981(5) (Å). Ca8La8Nb14.4□1.6O56 crystallizes in the cubic space group Fd 3¯ m (No.227) (a ​= ​10.6111(1) (Å), Z ​= ​1). In both structures, Calcium and Lanthanum atoms are randomly distributed on the appropriate crystallographic sites. Both compounds belong to the Pyrochlore family A2B2X7. Their conduction properties are studied with complex impedance spectroscopy.The central region of the ternary diagram La2O3 – Nb2O5 – CaO, investigated using Rietveld refinements on X-ray diffraction data, is found to be composed of 8 zones which are in agreement with Gibbs rules from a thermodynamic point of view.

Optimal alloying in hydrides: Reaching room-temperature superconductivity in LaH10

Doping represents one of the most promising avenues for optimizing superconductors, such as high-pressure conventional superconductors with record-breaking critical temperatures. In this work, we perform an extensive search for substitutional dopants in ${\mathrm{LaH}}_{10}$, looking for elements that enhance its electronic structure. In total, 70 elements were investigated as possible substitutions of La-sites at doping ratio of 12.5% under high pressure. To accelerate the screening of the ternary phases, our protocol to scan the chemical space is 1) to be constrained to highly symmetric patterns of hydrogen atoms, 2) focusing on phases with compact basis of lanthanum atoms (minimize enthalpy) and 3) to choose candidate dopants that preserve the van Hove singularity around the Fermi level. We found Ca as the best candidate dopants, which shift the van Hove singularity and increase the electronic DOS at the Fermi level. By using harmonic-level phonon calculations and performing first-principles calculation of ${T}_{\mathrm{c}}$, Ca-doped ${\mathrm{LaH}}_{10}$ shows ${T}_{\mathrm{c}}$ which is 15% higher than the one of ${\mathrm{LaH}}_{10}$. It provides a promising route to reach room-temperature superconductivity in pressurized hydrides by doping.

Dinitrogen fixation mediated by lanthanum hydride

Dinitrogen fixation is one of the key reactions in chemistry, which is closely associated with food, environment, and energy. It has been recently recognized that the hydride materials containing negatively charged hydrogen (H‾) show promises for N2 fixation and hydrogenation to ammonia. Herein, we report that rare earth metal hydrides such as lanthanum hydride can also fix N2 either by heating to 200 °C or ball milling under ambient N2 pressure and temperature. The N2 fixation by lanthanum hydride may proceed via an intermediate lanthanum hydride-nitride (La-H-N) structure to form the final lanthanum nitride product. The hydride ion functions as an electron donor, which provides electrons for N2 activation possibly mediated by the lanthanum atoms. It is observed that N–H bond is not formed during the N2 fixation process, which is distinctly different from the alkali or alkaline earth metal hydrides. The hydrolysis of La-H-N to ammonia is feasible using water as the hydrogen source. These results provide new insights into the nitrogen fixation by hydride materials and more efforts are needed for the development of rare earth metal-based catalysts and/or nitrogen carriers for ammonia synthesis processes.

New odd-parity energy levels of the neutral lanthanum atom

The discovery of 22 new energy levels of the La atom, having odd parity, is reported. These levels were derived from an analysis of unclassified spectral lines found either in optogalvanic spectra and/or Fourier transform spectra. The reliability of results obtained from the combination principle of Ritz was verified by hyperfine structure investigations. Further three new odd-parity levels of the first La ion are found. For two already known odd-parity levels substantial changes, concerning total angular momentum and hyperfine structure constants A, must be made.

Valence band structure and charge distribution in the layered lanthanide-doped CuCr0.99Ln0.01S2 (Ln\u2009=\u2009La, Ce) solid solutions

The comprehensive study of the electronic density distribution of CuCr0.99Ln0.01S2 (Ln = La, Ce) solid solutions was carried out using both X-ray photoelectron and emission spectroscopy. It was found that cationic substitution of chromium with lanthanum or cerium atoms does not significantly affect the atomic charges of the matrix elements (Cu, Cr, S) in the lanthanide-doped solid solutions. The copper atoms in the composition of CuCrS2-matrix and the lanthanide-doped solid solutions were found to be in the monovalent state. The chromium and lanthanide atoms were found to be in the trivalent state. This fact indicates the isovalent cationic substitution character. The sulfur atoms were found to be in the divalent state. The near-surface layers contain the additional oxidation forms of sulfur (S0, S4+, S6+) and copper (Cu2+) atoms. The detailed analysis of the valence band structure using DFT calculations has shown that partial DOS distribution character of the matrix elements is preserved after the cationic substitution. The experimental valence band spectra structure of CuCrS2-matrix and CuCr0.99Ln0.01S2 is determined by the occupied copper d-states contribution. The contribution of the lanthanide states in the valence band structure is lower in comparison with those for the matrix elements. The major contribution of the lanthanide states was found to be mainly localized near the conduction band bottom.

Theoretical Investigation on Rare Earth Elements of Y, Nd and La Atoms’ Adsorption on the Kaolinite (001) and (001¯) Surfaces

With the growing demand of rare earth elements, the recovery of rare earth elements is a major issue for researchers in related fields. Adsorption technology is one of the most effective and popular recovery methods. Therefore, the adsorption mechanism of Yttrium (Y), Neodymium (Nd), and Lanthanum (La) atoms on the kaolinite (001) and (001¯) surfaces was examined by density functional theory (DFT). The most stable adsorption sites on the kaolinite (001) surface for Y atoms was the bridge site, and the hollow site was the most favorable adsorption site for Nd and La atoms with high adsorption energy. However, the adsorption energies of kaolinite (001¯) surface sites for Y, Nd, and La atoms were much lower than the (001) surface sites, indicating that the adsorption capability of the hydroxylated (001) surface is stronger. The effects of coverage on adsorption position, energy, and structures were entirely investigated on top, bridge, and hollow sites of the kaolinite (001) surface from 0.11 to 1.0 monolayers (ML). The adsorption energy of Y, Nd, and La atoms on three kinds of sites increased with increasing of the coverage implied the stronger capability of surface adsorption. The recovery capability of kaolinite for the rare earth atoms was in the order of La &gt; Nd &gt; Y. The changes in the atomic structure, charge density, and electron density of states for Y, Nd, and La/kaolinite (001) before and after adsorption were also analyzed in depth.