Gadolinium Atoms Research Articles

On how Doping with Atoms of Gadolinium and Scandium affects the Surface Structure of Silicon

The experimental team has developed a technology of step-by-step low-temperature diffusion doping of gadolinium and scandium into silicon that allows the clusters of impurity atoms to be uniformly distributed throughout the entire bulk of the silicon material. It was shown that, unlike the samples obtained under the high-temperature diffusion doping technology, in the samples obtained under the novel technology the team had detected any surface erosion or formation of alloys and silicide in the near-surface region. The authors have revealed increased thermostability and radiation resistance of silicon samples dotted with clusters of impurity atoms of gadolinium and scandium. The authors have conducted comprehensive studies by using the techniques of tagged atoms, autoradiography, measurement of conductivity and Hall effect, isothermal relaxation of capacitance and current of diffusion, solubility, and electrophysical properties of scandium in silicon under various doping conditions and for a wide temperature range (1100 ÷ 1250 0С). Diffusion parameters, solubility and acceptor nature of scandium in silicon as well as thermal stability of silicon doped with gadolinium and scandium impurity atoms have been established.

Features of cluster ion treatment of the surface of KGd(WO<sub>4</sub>)<sub>2</sub>:Nd single crystal

The features of the surface treatment of single crystals of potassium gadolinium tungstate doped with neodymium ions with low- and high-energy cluster argon ions are considered. Two radically different treatment modes were used: low-energy for more efficient surface smoothing and high-energy for more efficient target etching. Using atomic force microscopy, the topography of the target surface was analyzed before and after cluster ion treatment. Treatment in a low-energy mode was shown to smooth out irregularities on the target surface formed by chemical-mechanical polishing at an etching depth of less than 100 nm. The root-mean-square roughness and maximum height difference of the initial and treated surfaces of potassium gadolinium tungstate doped with neodymium ions were compared. Survey X-ray photoelectron spectra of the initial surface of a KGd(WO4)2:Nd single crystal and after the cluster ion treatment in different modes are presented. The intensities of the potassium and gadolinium peaks were shown to decrease after cluster ion treatment in both modes. A significant decrease in the concentration of potassium atoms in the subsurface layer of the target is explained by the predominant sputtering of potassium as a lighter chemical element. The mutual decrease in the concentrations of gadolinium and potassium atoms can be explained by the weak bonds of these atoms in the lattice of the KGd(WO4)2:Nd single crystal.

Structure, morphology and functional characteristics of Gd2Ti2O7 nanocrystals formed under various annealing conditions

This article is devoted to the study of the processes of formation and growth of nanocrystals with the pyrochlore structure in the TiO2-Gd2O3 system. A mixture of an aqueous solution of gadolinium nitrate and a solution of titanium isopropoxide with polyethylene glycol in isopropyl alcohol was evaporated to a gel state, and then it was heat-treated using a one- or two-stage scheme. The study showed that the material being formed has a trabecular structure with a developed system of macropores. The use of the two-stage roasting method allows a uniform distribution of titanium and gadolinium atoms in the sample. Gadolinium titanate with a pyrochlore structure, which is formed using an aggregation mechanism at a temperature T = 700 °C from an X-ray amorphous precursor, is a variable composition compound. It has been shown that in terms of obtaining a monophasic product, the possibility of varying the size of nanocrystals, and defects in the pyrochlore structure, the most promising heat treatment mode is synthesis in the temperature range of 750–900 °C. In this case, the possibility of controlling the above characteristics of Gd2Ti2O7 nanoparticles can be implemented by varying the ratio of titanium- and gadolinium-containing precursors in the initial mixture, the duration of the isothermal exposure process.

Electronic structures and molecular dynamics of gadolinium-doped FAPbI3 perovskite crystals

The additive effect of a gadolinium ion into a formamidinium lead iodide (FAPbI3) perovskite crystal on electronic structures and molecular dynamics was investigated for improving photovoltaic performance with stability. The electronic structures, band structure, partial density of state, and molecular dynamics were determined by first-principles calculation. The band distribution and charge transfer between the 5d orbital of the gadolinium atom, the 5p orbital of the iodine atom, and the 6p orbital of the lead atom promoted the carrier generation and diffusion related to short-circuit current density. The enthalpy and kinetic energy prompted stabilization of the gadolinium-doped crystal with a slight distortion of coordination structure, as compared with the decomposition of the FAPbI3 crystal. Diffusion coefficients of iodine and lead ions in the FAPbI3 crystal with defect were increased, predicting decomposition. The gadolinium-doped FAPbI3 perovskite crystal has great potential for applications in photovoltaic devices by improving photovoltaic performance.

Magnetic susceptibility La<sub><sub>1-0.397</sub><sub><i>x</i></sub></sub>Gd<sub><sub>0.067</sub><sub><i>x</i></sub></sub>Ca<sub><sub>0.33</sub><sub><i>x</i></sub></sub>Mn<sub><i>х</i></sub>Al<sub><sub>1-</sub><sub><i>х</i></sub></sub>O<sub>3 </sub>solid solutions

Solid solutions of lanthanum manganites with perovskite structure containing calcium and gadolinium atoms were studied by the method of magnetic dilution. The obtained magnetic characteristics and the character of their temperature changes point to a clustering of magnetic atoms in the perovskite structure. A comparison of the solid solutions under study with La1- y Gd y AlO3 testifies for gadolinium atoms taking part in the exchange interactions in the La1-0.397 х Gd0.067 х Ca0.33 х Mn х Al1- х O3 solid solutions.

Electronic and optical properties of quaternary selenides for optoelectronic applications: Insights from DFT+U‐computations

AbstractThe optical properties, electronic charge density, electronic structure of the new layered selenides materials, BaGdCuSe3, CsUCuSe3, CsZrCuSe3, and CsGdZnSe3 compounds have been calculated by using the full potential and linear augmented plane wave (FP‐LAPW) methods as applied in the WIEN2k package, which is based on the density functional theory. The ALnMSe3 compound's structure of these was (A = Cs, Ba; Ln = Zr, Gd, U; M = Cu, Zn) is composed of (n = 1, 2) layers, which might be separated by A atoms. It is to be observed that there is strong hybridization between the s, p, and d states of Zr, Gd, and Cu atoms. Around the gadolinium atom, the charge density contours are completely circular, but the Gadolinium “Gd” atom shows an ionic nature. To calculate the refractive index, we used Kramer's Kronig correlations with the imaginary part dielectric function. The decrease in the refractive index is due to the lack of probability for direct excitation of the electrons, resulting in a loss of energy. The value of the static refractive index for all reference compounds is about 1.75–2.25, which is indication that the material used in optoelectronic devices.

Influence of intercalated Gd atoms on graphene-4H-SiC(0001) properties

In this work, the influence of intercalated gadolinium (Gd) atoms on graphene-4H-SiC(0001) properties are presented, using X-ray photoelectron spectroscopy, low energy electron diffraction and density functional theory calculations. Detailed analysis, ranging from adsorption to temperature induced intercalation under the graphene, of the chemical composition, surface structures, charge transfer and changes in the graphene band structure is performed. The investigation is carried out for various initial Gd film thicknesses and temperature of annealing, which allows to obtain and observe interactions between elements in the subsequent stages of intercalation. Calculations show that the deeper Gd is placed into the substrate the more energetically favourable configuration is obtained, which indicates the possibility of intercalation process to occur. Moreover, intercalated Gd strongly affects the electronic properties of both graphene and buffer layer. Simultaneously, experiment results show that Gd induces n-type doping in graphene. Additionally, temperature induced intercalation causes the buffer layer decoupling and transformation into new graphene one. The presence of gadolinium at the graphene-SiC interface results also in chemical shifts to the lower binding energy range and follows the trend in which the more gadolinium intercalates the higher shift is observed.

Immobilization of boronic acid derivative onto the magnetic Gd-containing composites

Aiming to develop new magnetic materials for neutron shielding applications, B- and Gd-containing magnetic nanoparticles were synthesized. Following bottom-up synthetic approach, core-shell Fe 3 O 4/Gd 2 O 3 nanocomposite particles were synthesized at the first stage. In the next stage, magnetic core-shell particles were modified with amino groups followed by grafting onto their surface of the boronic acid derivative. Such a multifunctional material, containing both boron (B) and gadolinium (Gd) atoms is a promising candidate for developing films and membranes, strongly interacting with neutrons. Due to the presence of boronic acids and bound to the indicator (Alizarin Red S), the material can induce color changes while immersed in sugar-containing solutions. Such a feature enables a possibility to estimate the number of boron atoms left after interaction with neutrons, thus allowing to check composite neutron-capture recourse.

A New Generation of Ultrasmall Nanoparticles Inducing Sensitization to Irradiation and Copper Depletion to Overcome Radioresistant and Invasive Cancers

An emerging target to overcome cancer resistance to treatments is copper, which is upregulated in a wide variety of tumors and may be associated with cancer progression and metastases. The aim of this study was to develop a multimodal ultrasmall nanoparticle, CuPRiX, based on the clinical AGuIX nanoparticle made of the polysiloxane matrix on which gadolinium chelates are grafted. Such hybrid nanoparticles allow: (i) a localized depletion of copper in tumors to prevent tumor cell dissemination and metastasis formation and (ii) an increased sensitivity of the tumor to radiotherapy (RT) due to the presence of high Z gadolinium (Gd) atoms. CuPRiX nanoparticles are obtained by controlled acidification of AGuIX nanoparticles. They were evaluated in vitro on two cancer cell lines (lung and head and neck) using the scratch-wound assay and clonogenic cell survival assay. They were able to reduce cell migration and invasion and displayed radiosensitizing properties.

Electrical and magnetic properties of intercalated compounds in the Gd-=SUB=-x-=/SUB=-NbSe-=SUB=-2-=/SUB=- system (0≤ x≤0.33)

The electrical and magnetic properties were measured on polycrystalline samples of niobium diselenide intercalated with gadolinium atoms. The dependences of the electrical resistance on temperature point to a predominantly phonon scattering mechanism for charge carriers, while the concentration dependences are determined by increasing scattering by interstitial atoms. The magnetic properties of GdxNbSe2 (0≤ x≤0.33) were studied in the temperature range of 2-350 K and in the range of magnetic fields up to 70 kOe. Based on the results of studies of magnetic susceptibility and magnetization, the possibility of the existence of antiferromagnetic interactions in the studied compounds and the phenomenon of spin reorientation in a magnetic field are shown. The observed decrease in the effective magnetic moment of gadolinium ions with an increase with their concentration is discussed in terms of a possible intramolecular exchange. Keywords: niobium diselenide, gadolinium, intercalation, electrical resistance, magnetization, effective magnetic moment.

Электрические и магнитные свойства интеркалированных соединений в системе Gd-=SUB=-x-=/SUB=-NbSe-=SUB=-2-=/SUB=- (0 ≤ x≤0.33)

The electrical and magnetic properties were measured on polycrystalline samples of niobium diselenide intercalated with gadolinium atoms. The dependences of the electrical resistance on temperature point to a predominantly phonon scattering mechanism for charge carriers, while the concentration dependences are determined by increasing scattering by interstitial atoms. The magnetic properties of GdxNbSe2 (0≤x≤0.33) were studied in the temperature range of 2–350 K and in the range of magnetic fields up to 70 kOe. Based on the results of studies of magnetic susceptibility and magnetization, the possibility of the existence of antiferromagnetic interactions in the studied compounds and the phenomenon of spin reorientation in a magnetic field are shown. The observed decrease in the effective magnetic moment of gadolinium ions with an increase with their concentration is discussed in terms of a possible intramolecular exchange.

Magnetization of silicene via coverage with gadolinium: Effects of thickness, symmetry, strain, and coverage

When covered by gadolinium (Gd) atoms, silicene, a freestanding monolayer of Si atoms in a honeycomb network, remains stable above the room temperature and becomes a two-dimensional (2D) ferromagnetic semiconductor, despite the antiferromagnetic ground state of three-dimensional bulk ${\mathrm{GdSi}}_{2}$ crystal. In thin ${\mathrm{GdSi}}_{2}$ multilayers, even if magnetic moments are ordered parallel in the same Gd atomic planes, they are antiparallel between nearest Gd planes; hence they exhibit a ferrimagnetic behavior. In contrast, a freestanding ${\mathrm{Gd}}_{2}{\mathrm{Si}}_{2}$ monolayer constructed by covering silicene from both sides by Gd atoms is a stable antiferromagnetic metal due to the mirror symmetry. While multilayers covered by Gd from both sides having an odd number of Gd planes have a ferrimagneticlike ground state, even-numbered ones have antiferromagnetic ground state, but none of them is ferromagnetic. Silicon atoms intervening between Gd planes are responsible for these intriguing magnetic orders conforming with the recent experiments performed on Si(111) surface. Additionally, the magnetic states of these 2D gadolinium disilicide monolayers can be monitored by applied tensile strain and by the coverage/decoration of Gd. These predictions obtained by using first-principles, spin-polarized, density functional theory calculations combined with Monte Carlo simulations herald that C, B, Si, Ge, Sn, and their compounds functionalized by rare-earth atoms can lead to novel nanostructures in 2D spintronics.

Review of the influence of copper and chromium substitution on crystal structure, magnetic properties and magnetocaloric effect of GdFe2−x(Cu, Cr)x (x = 0, 0.1, 0.15 and 0.2) intermetallic compounds

The iron-based compounds GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) were synthesized successfully by means of arc-melting and annealing at 800 °C for one week. The structural, magnetic and magnetocaloric properties of these intermetallic compounds were investigated systematically in detail using X-ray powder diffraction (XRD) analysis, Scanning electron microscopy (SEM) equipped with Energy dispersive X-ray spectroscopy (EDS), and magnetic measurements. The Rietveld analysis of X-ray diffraction patterns proves that GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) compounds crystallize in the cubic laves phase MgCu2-type structure with the Fd3̄m space group. Gadolinium and iron atoms statistically occupy the 8a and 16d sites respectively. Moreover, copper and chromium atoms substitute the iron atoms at site 8a in the MgCu2-type structure. The temperature dependence of magnetization studied in a broad temperature range reveals that all compounds exhibit a ferromagnetic-paramagnetic transition at Curie temperature (TC). We find that the substitution of iron by copper and chromium leads to a decrease in the magnetic ordering transition temperature. The Arrott plots of all our samples show the occurrence of a second-order phase transition. Besides, the performance of magnetocaloric effect (MCE) for GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) compounds was evaluated by the magnetic entropy change (ΔSM) and the related Relative Cooling Power (RCP). In the vicinity of TC, the ΔSM reached a maximum value of 0.79 J/kg.K, 1.2 J/kg.K, 1.4 J/kg.K and 2.5 J/kg.K, while the RCP was found to be 13.2 J/kg, 21.6 J/kg, 31.7 J/kg and 44.3 J/kg, respectively for GdFe2−xCux (x = 0, 0.1, 0.15 and 0.2) compounds. Furthermore, the GdFe2−xCrx (x = 0.1, 0.15 and 2) compounds show ΔSM values of about 0.9 J/kg.K, 1.3 J/kg.K and 1.8 J/kg.K, and RCP values of 14.8 J/kg, 25.4 J/kg and 36.8 J/kg respectively, under a field change of 1.56 T. Through these results, the GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) compounds can be an attractive materials for use in magnetic refrigeration and heat pumping technology above room temperature.

Computational Modelling of Ceria-Based Solid Oxide Fuel Cell Electrolyte Materials

The significant advances in materials development for solid oxide fuel cells (SOFCs) and modelling techniques have challenged researchers to develop streamlined methodologies aiming at faster and more reliable fabrication of highly efficient cells. Instead of adopting a trial-and-error technique to discover the optimal composition of fuel cell component materials, alternative tools and techniques should be developed for predicting the likely best compositions in a cost-effective and timely manner. Many formulations have been studied for application as SOFC electrolytes over the years and doubly-doped ceria materials have been of considerable recent interest.Here, a simulation methodology to calculate the lattice parameter and the oxygen ion migration energy of ceria-based electrolyte formulations was developed, and the results were analysed and benchmarked against corresponding results obtained experimentally in order to verify the efficacy of the simulation methodology. To this end, a supercell consisting of 2 x 2 x 2 ceria unit cells doubly-doped with samarium and gadolinium was modelled and simulated using molecular mechanics force field methods using the CP2K computational chemistry suite. Two compositional series were modelled with the general formula Ce32-(x+y)SmxGdyO64-(x+y)/2 where x and y are the number of samarium and gadolinium dopant atoms per supercell respectively. The first compositional series, Series One, had equal amounts of dopants but different total dopant concentration with values of x = y = 1, 2, 8, or 16. Series Two had a fixed total dopant concentration (x + y = 8) but different amounts of each dopant in each structure such that x had integer values from 0 to 8 (x = 0 ... 8) and y = 8 - x. Moreover, two doping strategies were simulated for each compositional series depending on how the dopant atoms and resulting vacancies were distributed throughout the crystal. The first doping strategy places one dopant atom in two or more of the eight minicubes comprising the 2 x 2 x 2 supercell for Series One structures and, for Series Two structures, one dopant atom is placed in each minicube starting with one gadolinium atom in each minicube and then progressively replacing one gadolinium atom with one samarium atom in each of the subsequent structures of this series until there is one samarium atom in each minicube. The second doping strategy places the dopants exclusively in the four minicubes that let the dopants be as far as possible from each other. In all cases, the oxygen vacancies are chosen to be the nearest neighbours, i.e., in the nearest lattice positions, to the dopant atoms.For each structure, the lattice parameter was calculated using a cell optimisation technique utilizing the conjugate gradient method where the soft particle mesh Ewald (SPME) sums method and the DIPole Polarizable Ion Model (DIPPIM) for the long- and short-range potentials respectively. To estimate the activation energies associated with hopping of an oxygen ion from a specific site to a neighbouring site in the structures studied, the following steps were applied: The positions of the dopant atoms in the pure crystal were assigned.The at a distance within 3.0 Å was generated.The climbing image nudged elastic band (CI-NEB) method was applied to determine all the activation barriers of the doped crystal.The average energy barrier was calculated. The results obtained for the lattice parameter were comparable to those observed experimentally and exhibited the same linear trends satisfying Vegard's law, albeit the trend for the fixed dopant concentration series had a slight negative slope. Simulation-derived values of the activation energy showed the same trends as those observed experimentally. The simulations also produced transition state curves showing the saddle point and energy minima for each structure; information that could not be obtained experimentally and that can shed some light on the mechanism of ionic conduction. It was found that the position of oxygen vacancies within the crystal structure play a key role in determining the activation energy of ion hopping, and that the different patterns of doping do not affect the overall trends in lattice parameter and activation energy. They do however produce different patterns in the energy profiles contributing to the energy barriers to ion hopping within the crystal structure.This work demonstrates that computational simulations of SOFC electrolyte materials provide results comparable with those obtained experimentally and could also provide insights into the mechanisms of ionic conduction. The incongruence of the computational and experimental results was attributed to the limitations of the molecular mechanics force field methodology utilised, with the expectation that an ab initio density functional theory (DFT) calculation would yield closer conformance. Figure 1

Synthesis, Crystal Structures of Gadolinium(III) and Erbium(III) Complexes Derived from Pyridine-2,6-Dicarboxylic Acid and Fluorescent Sensing of Picric Acid

Two new complexes of gadolinium(III) and erbium(III) with pyridine-2,6-dicarboxylic acid (H2Pydc),{Na3[Gd(Pydc)3]·2H2O}n (I) and [Er(HPydc)3]·10H2O (II), were prepared and their crystal structures were determined by X-ray crystallography (CIF files CCDC nos. 940633 (I) and 872068 (II)). The gadolinium atom in I is nine-coordinate (GdN3O6) and exhibits a tricapped trigonal prismatic geometry having 14 triangular faces. The Pydc ligand adopts chelating and, μ3- and μ5-bridging coordination modes. The 1D chains are further joined by Na atoms to generate a 3D coordination polymer. The structure is additionally stabilized by H-bonding. The Erbium polyhedron in II is also a tricapped trigonal prism (ErN3O6). The HPydc anions in II behave as tridentate chelating ligands. The complex molecules are connected to each other through hydrogen bonding interactions to form a three-dimensional network. Fluorescence titration experiments for complex II displayed highly sensitive fluorescence quenching efficiency of 98.3% against picric acid.

Analysis of physical dose enhancement in nano-scale for nanoparticle-based radiation therapy: a Cluster and endothelial cell model

Objective(s): One major difficulty of conventional radiotherapy is the lack of selectivity between the tumor and the organs at risk. In nanoparticle aided radiotherapy, heavy elements are present at higher concentrations in the tumor than normal tissues. This study aimed to model the characteristics of secondary electrons generated from the interaction of clusters comprised of five different nanoparticles including Gold, Gadolinium, Iridium, Bismuth, and Hafnium atoms with low energy x-rays (similar to brachytherapy sources in terms of energy) as a function of nanoparticle size and beam energy. Materials and Methods: To better evaluate the contributions of secondary electrons in energy deposition, and also to develop a framework in analyzing further measurements in the future, we attempted to enhance and promote existing mathematical models for energy deposition in endothelial cells by nanoparticle-enhanced radiotherapy. Also, the MCNPX Monte Carlo code was used to model the identical geometry and the dose enhancement factor was calculated for all types of simulated nano-clusters.Results: Our results showed that for our model consist of a nano-cluster and an endothelial cell the DEF significantly depends on the energy of photons and L- and K-edge binding energy of the atoms inside the nano-cluster. However, for Gd at the energy 60 keV, a higher dose enhancement factor was seen.Conclusion: It can be concluded that the mathematical model considers the DEF variation with photon energy and the effect of NP type is considered in DEF calculations. However, the MC method has indicated very high sensitivity to photon energy, and NP type compared to the mathematical method.

Local coordination numbers of up to 19 in gadolinium-tin alloy nanoclusters.

A combined approach based on quantum-chemical calculations and molecular beam experiments demonstrates that in isolated nanoalloy clusters of type GdSnN, a total number of N = 19 tin atoms can be arranged around a central gadolinium atom. While the formation of the first coordination shell is incomplete for clusters with less than 15 tin atoms, the second coordination sphere starts to form for cluster sizes of more than 20 tin atoms. The magnetic properties of the clusters reveal that the tin atoms not only provide a hollow cage for Gd but also are chemically bound to the central atom. The calculated spin densities imply that an electron transfer from Gd to the tin cage takes place, which is similar to what is observed for endohedral metallofullerenes. However, the measured electric dipole moments indicate that in contrast to metallofullerenes, the Gd atom is located close to the center of the tin cage.

Gadolinium ion bonding on the surface of carboxylated detonation nanodiamond in terms of magnetochemistry and density functional theory

Gadolinium ions (Gd3+) can be fixed on the surface of 5-nm detonation nanodiamonds with terminal carboxyl and/or hydroxyl surface groups. Magnetization curves measured below the temperature of liquid helium at normal pressure give the amount of Gd3+ ions of about 18 per a 5-nm nanodiamond particle. The corresponding 2D surface density of ions is smaller than that obtained by density functional theory for a single gadolinium atom fixed on the surface of (111) diamond slab with 36 surface carbon sites with up-standing s-bonds by a factor of 2.

A quantum chemical study of endometallofullerenes: Gd@C70, Gd@C82, Gd@C84, and Gd@C90

Quantum chemical (U)PBE0 method is used to investigate the endometallofullerenes Gd@C70, Gd@C82, Gd@C84, and Gd@C90 for different spin states. The equilibrium structural parameters, IR spectra, the chemical bond energies, the electron affinity and vertical ionization potentials are calculated. The analysis of the electron and spin populations of the atomic orbitals in gadolinium endocomplexes was carried out. For all considered configurations, the calculations predict the polarizability depression and a high value of the magnetic moment. The endocomplex has the same high value of multi-electron spin as the free gadolinium atom, that characterizes its significant magnetic properties.

Large Carbon Clusters with Entrapped Gadolinium Atoms

Gadolinium metallofullerenes have long shown promise as potential MRI contrast agents. The ability to entrap up to three gadolinium atoms permits a high concentration of metal content per fullerene cage. The protective carbon cage prevents the escape of otherwise toxic free Gd ion. In this presentation, we will discuss purification strategies to isolate gadolinium clusters entrapped within larger carbon cages (C96-C120). We have recently isolated a series of fullertubes, which consist of a nanotube belt of carbons with fullerene endcaps. It is unknown if the entrapped Gd atoms are inside fullerene or fullertube cages.