Spatial localization of holes in La<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CuO<Subscript>4</Subscript>

The parameters of the tensor of the electric field gradient (EFG) in cation sites of the La_{2 ? x} Sr _x CuO₄ lattice have been determined by the method of emission Mössbauer spectroscopy on ⁵⁷Co(^57m Fe), ⁶⁷Cu(⁶⁷Zn), ⁶⁷Ga(⁶⁷Zn), and ¹⁵⁵Eu(¹⁵⁵Gd) isotopes. There is no quantitative agreement between the calculated (the pointcharge model) and experimental values of the main component of the tensor EFG V _zz , which is explained by the absence of the reliable data on the Sternheimer coefficients for Fe³⁺, Zn²⁺, and Gd³⁺ ions. Based on the comparison of the calculated and experimental dependences of V _zz on x it was shown that the holes appearing during the substitution of La³⁺ for Sr²⁺ are localized preferably on the oxygen atoms that are in the same plane as the copper atoms, which is in agreement with the model discussed in the literature and assumes that the mechanism responsible for the high-temperature superconductivity of solid solutions La_{2 ? x} Sr _x CuO₄ is the interaction between the conductivity electrons and two-atomic two-electron centers with negative correlation energy.     

Charge states of atoms in ceramic superconductors HgBa2Ca n − 1Cu n O2n + 2, Tl2Ba2Ca n − 1Cu n O2n + 4, and Bi2Sr2Ca n − 1Cu n O2n + 4 (n = 1–3)

The parameters of the electric-field-gradient tensor for copper sites in the HgBa₂Ca _{n ? 1}Cu _n O_{2n + 2}, Tl₂Ba₂Ca _{n ? 1}Cu _n O_{2n + 4}, and Bi₂Sr₂Ca _{n ? 1}Cu _n O_{2n + 4} (n = 1–3) lattices have been determined using ⁶⁷Cu(⁶⁷Zn) Mössbauer emission spectroscopy and calculated in the framework of the point-charge approximation. The agreement between the experimental and calculated parameters has been achieved under the assumption that the holes formed as a result of the decrease in the oxidation state of a part of the mercury, thallium, or bismuth atoms are distributed over the oxygen sites in the Cu-O or adjacent planes. It has been demonstrated that the oxidation state of cations can be controlled in high-temperature superconducting ceramic materials.     

Hyperfine interactions of copper ions in the structure of high-temperature superconductors

Emission Mössbauer ⁶¹Cu(⁶¹Ni) spectra of simple MgO, NiO, Cu₂O, CuO oxides and superconducting La_{2 ? x} Sr _x CuO₄, Nd_{2 ? x} Ce _x CuO, and YBa₂Cu₃O_{7 ? x} copper metal oxides have been measured. It has been shown that emission Mössbauer spectroscopy on isotopes ⁶¹Cu(⁶¹Ni) makes it possible to determine the parameters of the electric gradient field tensor and magnetic field values in the copper sites of lattices of high-temperature superconductors and related materials.     

Sites occupancy preference of Bi3+ and white light emission through co‐doped Sm3+ in LiGd5P2O8

Bi³⁺, Sm³⁺‐activated LiGd₅P₂O₈ (LGPO) phosphors were prepared through high‐temperature solid‐state method. In LGPO host, there are 5 types of Gd crystallographic sites, named as Gd(1)/Gd(2)/Gd(3)/Gd(4), and Gd(5). Bi³⁺‐activated LGPO phosphors exhibit 1 broad excitation band from 250 to 320 nm centered at 293 nm and a broad asymmetric emission band ranging from 350 to 600 nm with the maximum value approximately at 409 nm. It can be concluded from dual‐emission spectra that Bi³⁺ may occupy 2 Gd sites and an obvious spectral blue‐shift appeared with increasing Bi³⁺ content, which is caused by the intensity of crystal field of Bi³⁺ is decreased. Notably, through the calculation of each Gd‐O chemical parameter, the environmental factor (h_e) value of each Gd site can be obtained and it can be further inferred that 2 emission bands centered at 409/461 nm are ascribed to Bi³⁺ ions which occupies Gd(3) and Gd(4) sites, respectively. Energy transfer from Bi³⁺ to Sm³⁺ ions in Bi³⁺/Sm³⁺ co‐doped LGPO samples occurred and it realizes the color‐tunable emission from cyan to yellow including white‐light emission, through controlling Sm³⁺ content. Moreover, energy transfer mechanism between Bi³⁺ and Sm³⁺ ions is verified to be dipole‐dipole interaction by analyzing the spectroscopic experimental results and the critical distance between them is calculated to be 8.22 Å by concentration quenching method. Finally, it is illustrated that Bi³⁺ and Sm³⁺ co‐doped LGPO phosphors will be a promising candidate for n‐UV chip pumped w‐LEDs.     

Gd(III) based MRI contrast agents: improved physical meaning in a combined analysis of EPR and NMR data?

A new global analysis of EPR, ¹⁷O NMR relaxation and chemical shift and ¹H NMRD profiles with physically meaningful parameters for [Gd(DOTA)(H₂O)]⁻ and for [Gd(DTPA)(H₂O)]²⁻ in aqueous solution is presented (DOTA=1,4,7,10-tetraaza-1,4,7,10-tetrakis(carboxymethyl)-cyclododecane; DTPA=diethylenetriamine-N,N,N^′,N″,N″-pentaacetic acid). The recent developments of an improved EPR relaxation theory, the inclusion of the internal motion of the bound water molecule are the principal modifications. Furthermore the better knowledge of the quadrupolar coupling constant of the bound water molecule, the neglect of the outer-sphere contribution to the chemical shift and the consideration of different isomers for the DOTA complex allowed for an improved analysis. The water exchange and parameters of rotational motion are only slightly changed. Comparison of the contributions of static zero-field-splitting shows that a more symmetric environment of the Gd(III) ion should lead to slower electron spin relaxation, a feature which can become important if all other parameters (rotational correlation time and water exchange rate) are optimised. In the actual stage the improved combined analysis of Gd(III) poly(amino carboxylate) is limited by the approximations of Redfield’s relaxation theory, i.e., very low frequency NMRD-data and slowly tumbling complexes cannot be analysed with the method presented.     

SYNERGISTIC SOLVENT EXTRACTION OF LANTHANIDES WITH MIXTURES OF 1-PHENYL-3-METHYL-4-BENZOYL-PYRAZOL-5-ONE AND ALIQUAT 336

The solvent extraction of Pr(III),Gd(III) and Yb(III) With 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one (HP) and Aliquat 336(QCl) in CCl₄.C₆H₆ and CHCl₃, has been studied.The composition of the extracted species has been determined as LnP₄ ^?.Q⁺ (Ln=Pr,Gd and Yb).The values of the equilibrium constants have been calculated. The extraction mechanism has been discussed.     

Improving the spin entropy by suppressing Co4+ concentration in thermoelectric Ca3Co4O9+δ

We report the effects of rare earth Gd doping on the spin entropy in Ca₃Co₄O_9+δ. Magnetothermopower is found to be strongly magnetic-field dependent and increases upon Gd doping, revealing that Gd doping can improve the spin entropy of Ca₃Co₄O_9+δ. X-ray photoemission spectroscopy (XPS) results allow us to determine the decrease in Co⁴⁺ concentration induced by Gd doping. Our results confirm that the spin-entropy enhancement originates from the decrease of Co⁴⁺ concentration. The present study suggests that we can improve the spin entropy by suppressing Co⁴⁺ concentration in layered cobalt oxides.     

Highly uniform Gd(OH)3 and Gd2O3:Eu hexagram-like microcrystals: glucose-assisted hydrothermal synthesis,growth mechanism and luminescence property

Monodispersed and uniform Gd(OH)₃ microcrystals with novel hexagram-like morphology have been successfully prepared through a simple and green hydrothermal process with the assistance of glucose. The results of control experiments revealed that the glucose concentration in the reaction system was an important factor, which affected the morphology of the Gd(OH)₃ microcrystals significantly. On the basis of time-dependent experiments, the growth mechanism of the Gd(OH)₃ hexagrams was discussed. Furthermore, the Gd₂O₃ and Eu³⁺-doped Gd₂O₃ hexagram-like microcrystals, inheriting the Gd(OH)₃ precursors' morphology, were obtained during a direct annealing process in air. The corresponding Gd₂O₃:Eu³⁺ hexagram-like microcrystals exhibit strong red emission pertaining to the ⁵D₀→⁷F₂ transition of the Eu³⁺ ions under UV light, which have potential applications in novel optoelectronic devices.     

INFLUENCE OF THE AMMONIUM SALT ANION ON THE SYNERGISTIC SOLVENT EXTRACTION OF LANTHANIDES WITH MIXTURES OF THENOYLTRDJLUOROACETONE AND TRIDECYLAMINE

ABSTRACT

The synergistic solvent extraction of Pr, Gd and Yb with mixtures of thenoyltnfluoroacetone ( HTTA) and primary ammonium salt ( tridecylammonium chloride or perchlorate, TDAH( C1, CI0) in dHhas been studied. The composition of the extracted species have been determined as Ln( TTA)₃ TDAHA( A= CI or CIO⁴ ) The values of the equilibrium constant K_{T. s} have been calculated. The influence of the ammonium salt anion on the extraction process has been discussed. The separation factors of the pairs Gd/ Pr and Yb/ Gd have been determined.     

Doped effect of Gd and Y elements on corrosion resistance of ZrO2 in CMAS melt: First-principles and experimental study

The effects of Gd and Y doping on the corrosion resistance of ZrO₂ in CMAS (CaO, MgO, Al₂O₃, SiO₂) melts were investigated via first-principle calculations and experimental investigations. It is found that, although Gd₂Zr₂O₇ with single Gd-doped ZrO₂ has the lowest cohesive energy E_cohesive and formation enthalpy H_formation, YSZ(Gd) exhibits the lowest chemical activity with Y and Gd composite doping. The small Griffith’s rupture work (W = −3.498 J m⁻²) is beneficial to the flow of the CMAS melt on the YSZ(Gd) surface. Furthermore, the low Fermi energy and low O and Y electronegativities cause the weakest chemical activity. Additionally, the diffusion coefficients of Y, Zr, and O elements are also decreased through Gd-doping in YSZ. EDS investigations also demonstrate that the CMAS/YSZ(Gd) has the smallest reaction depth (6.65 μm) and the lowest elements penetration ability. Thus, the best corrosion resistance is originated from Y and Gd composite doping in YSZ(Gd) TBCs.     

Analysis of the Parameters of the Mössbauer Spectra and the Spectra of Nuclear Quadrupole Resonance of the Superconducting Ceramic YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript>

The parameters of the Mössbauer spectra on ⁶⁷Cu(⁶⁷Zn), ⁶⁷Ga(⁶⁷Zn) isotopes, and the data of nuclear quadrupole resonance on an ¹⁷O isotope are anlayzed, and the lattice gradient of the electric field for the crystal lattice YBa₂Cu₃O₇ is calculated. It is shown that these parameters correspond to the model when the hole is predominantly in the sublattice of the oxygen chain.     

Synthesis,characterization, thermal constant and relaxation of gadolinium(III), iron(III) and manganese(II) chelates of diethylenetriamine-bis-inositol-N,N′,N″-triacetic acid

The reaction of the bicyclic anhydride of diethylenetraiamine-pentaacetic acid (DTPAA) with inositol gave diethylenetriamine-inositol-biester-N,N^′,N″-triacetic acid (DTPA-BI) (1). (1) was characterized by FAB-MS, ¹HNMR, IR and elemental analysis. Its chelates of Gd(III), Fe(III) and Mn(II) holding promise of magnetic resonance imaging (MRI) were synthesized. Gd(III) complex was obtained from Gd₂O₃ and the acid form of (1). Thermodynamic stability constant and relaxation of Gd(III) complex with DTPA-BI were determined. The spin–lattice relaxivity (R₁=5.6 l mmol⁻¹ s⁻¹) of chelate was slightly larger than that of [GdDTPA]²⁻. The results showed that the complex is a prospective MRI agent, although thermodynamic stability constant of DTPA-BI K_[GdDTPA-BI]⁻=10^18.2 was a little less than that of [GdDTPA]²⁻ (K_[GdDTPA]²⁻=10^20.73).     

First observation of 5DJ (J=1, 2, 3) emission transitions in Eu3+-activated rare-earth antimony garnet R3Sb5O12 (R=Y,Gd, La)

R_2.9Eu_0.1Sb₅O₁₂ (R=Y, Gd, La) polycrystalline powders were prepared by solid-state reaction and characterized by X-ray powder diffraction (XRD), photoluminescence, decay lifetimes, and CIE color coordinates. The phosphors can be efficiently excited by UV-light and presents the emission covering the entire visible spectrum. Except for the commonly reported ⁵D₀–⁷F_0,1,2,3,4 transitions of Eu³⁺ ions in R_2.9Eu_0.1Sb₅O₁₂ (R=Y, La), higher ⁵D_1,2,3 states present stronger emission lines. This produces white emission in the single-phased phosphor, whereas R_2.9Eu_0.1Sb₅O₁₂ (R=Gd) shows orange emission due to the absence of ⁵D_3,2 transitions. The emission mechanism from the high-energy levels of ⁵D_1,2,3 Eu³⁺ ion in R_2.9Eu_0.1Sb₅O₁₂ (R=Y, Gd, La) phosphors is also discussed.     

Hydrothermal synthesis of uniform Fe-doped Gd(OH)3 nanorods and their magnetic properties: Phase conversion from paramagnetism to ferromagnetism

High quality pure and Fe-doped Gd(OH)₃ nanorods were fabricated through a template-free hydrothermal method for the first time. Analysis of XRD indicates that Fe³⁺ was incorporating in the interstitial sites rather than occupying the substitutional sites, forming pure hexagonal structure of Gd(OH)₃ without any other impurity phase. TEM characterizations show that all the samples perform uniform rod-like morphologies with similar diameter and length, which suggests that the Fe doping has little influence on the morphologies of samples. ICP and XPS spectra suggest that the dopant Fe³⁺ is incorporated into the inner body sites, not on the surface of nanorods. Magnetic studies show that the magnetic phase can be converted from paramagnetism to room-temperature ferromagnetism by doping Fe³⁺ ions into the Gd(OH)₃ nanorods. The saturation magnetization (Ms) is sensitive to the amount of Fe dopants, and the Ms for Fe_0.03Gd_0.97(OH)₃ nanorods reaches the maximum value of 0.184 emu/g. It is considered that the ferromagnetic ordering is possibly originated from the exchange interaction of Fe³⁺ through the oxygen vacancies, leading to the formation of point defect-mediated bound magnetic polarons (BMPs). Ruling out the affect of morphologies and secondary magnetic phase on the magnetic properties, the ferromagnetic ordering in uniform Fe-doped Gd(OH)₃ nanorods, in which the dopant Fe³⁺ is incorporated into the inner body sites of nanorods, are of great importance to deeply understand the rare earth-based DMS/DMD systems and have potential applications in spintronic devices.     

Turbulence level significance of the coalescence-dispersion rate parameter

The random coalescence-and-dispersion (C–D) models for non-ideal mixing in reactors involve a rate parameter, I, which is the frequency of the coalescence and dispersion events divided by the available number of coalescence sites per unit residence time, where residence time is a measure of reactor size. An approximate relationship between I and hydrodynamic parameters has been found by carefully comparing C–D computations, where I varies with location, with actual measurements of the turbulent energy dissipation rate, ε, and the turbulence length scale, L_s, in a tubular reactor. At each location I was determined such that the calculated conversion of a second-order reaction matched the measured conversion. The relationship found was: I≈ 1333(ε/L_s²)^{$\text{1}\text{3}$}(^?τ/N) where L_s, is the length scale of segregation, ε has dimensions of velocity squared per unit time, and (^?τN) is the residence time divided by the number of coalescence sites.The relationship above was applied to the C–D modeling of a semi-batch reactor with a consecutive-competitive reaction. The resulting yields and selectivities under the various conditions of the experimental data were very close to experimental results.     

Dielectric spectroscopy and magnetometry investigation of Gd-doped strontium titanate ceramics

Structural, dielectric and magnetic properties of dense Gd-doped strontium titanate ceramics prepared by the conventional mixed oxide method are studied. Lattice parameter is found to decrease linearly in the Sr_1-1.5xGd _xTiO₃ system, confirming the incorporation of Gd onto the Sr site of the perovskite lattice of strontium titanate up to x = 0.05. Real and imaginary parts of the dielectric permittivity of Sr_1-1.5xGd _xTiO₃ ceramics exhibit a relaxation between 100 Hz and 1 MHz in the temperature range of 17–26 K, slightly shifting to higher temperatures with increasing Gd content. Such dielectric behaviour is attributed to the relaxation of individual dipoles formed by off-centre displacement of Gd³⁺ ions on Sr sites in a highly polarizable lattice of strontium titanate. Other dielectric relaxations observed in Sr_1-1.5xGd _xTiO₃ from 125 to 300 K are attributed to the oxygen vacancy related mechanisms. No magnetic anomaly but paramagnetic behaviour is observed for Sr_1-1.5xGd _xTiO₃ ceramics, indicating an absence of the magnetic order and hence magnetoelectric coupling.     

Gold-silver alloy nanoshells: a new candidate for nanotherapeutics and diagnostics

We have developed novel gold-silver alloy nanoshells as magnetic resonance imaging (MRI) dual T₁ (positive) and T₂ (negative) contrast agents as an alternative to typical gadolinium (Gd)-based contrast agents. Specifically, we have doped iron oxide nanoparticles with Gd ions and sequestered the ions within the core by coating the nanoparticles with an alloy of gold and silver. Thus, these nanoparticles are very innovative and have the potential to overcome toxicities related to renal clearance of contrast agents such as nephrogenic systemic fibrosis. The morphology of the attained nanoparticles was characterized by XRD which demonstrated the successful incorporation of Gd(III) ions into the structure of the magnetite, with no major alterations of the spinel structure, as well as the growth of the gold-silver alloy shells. This was supported by TEM, ICP-AES, and SEM/EDS data. The nanoshells showed a saturation magnetization of 38 emu/g because of the presence of Gd ions within the crystalline structure with r₁ and r₂ values of 0.0119 and 0.9229 mL mg^-1 s^-1, respectively (Au:Ag alloy = 1:1). T₁- and T₂-weighted images of the nanoshells showed that these agents can both increase the surrounding water proton signals in the T₁-weighted image and reduce the signal in T₂-weighted images. The as-synthesized nanoparticles exhibited strong absorption in the range of 600-800 nm, their optical properties being strongly dependent upon the thickness of the gold-silver alloy shell. Thus, these nanoshells have the potential to be utilized for tumor cell ablation because of their absorption as well as an imaging agent.     

Studies on electrode kinetics of mixed ligand complexes of Co(II) in dimethyl formamide at dme

Mixed ligand complexes of Co(II) with pyridines and halide and pseudohalide have been synthesised. The reduction of synthesised complexes at dropping mercury electrode in various percentage of dimethyl formamide have been studied. The reduction is diffusion controlled. Slope values indicate the reduction to be irreversible. Kinetic parameters (K_s, K^o_f and α_n) have been calculated by Matsuda and Koutecky's method. K_s value was found to be in order 10^?4 cm. The effect of temperature and various composition of dmf have been investigated. At higher temperature the reduction becomes less irreversible.     

Fabrication of reduced Graphene Oxide supported Gd3+ doped V2O5 nanorod arrays for superior photocatalytic and antibacterial activities

In the current report, pure V₂O₅, a series of Gd doped V₂O₅ (1 wt%, 3 wt%, 5 wt% and 10 wt%) and graphene integrated Gd–V₂O₅ photocatalysts have been prepared using a facile wet chemical approach. The effect of Gd⁺³ ions substitution and RGO support on V₂O₅ was studied by the different analytical techniques. X-ray diffraction (XRD) results showed the orthorhombic crystal structure of synthesized samples with crystallize size in range of 22–35 nm. Morphological analysis showed nanorods and nanorod arrays like appearance of V₂O₅, Gd–V₂O₅ and GdV-₂O₅/RGO, respectively. Gd–V₂O₅ and Gd–V₂O₅/RGO exhibited enhanced optical response in the visible region along with decrease in the band gap values for Gd doped V₂O₅ samples. BET surface area of Gd–V₂O₅ and Gd- V₂O₅/RGO was calculated as 12.39 g/m² and 15.35 g/m² that was found to be higher than pristine V₂O₅. To study the photocatalytic activity of synthesized photocatalysts, methylene blue (MB) was chosen as model pollutant. Among the Gd doped V₂O₅ samples, highest photocatalytic activity (45.62%) was achieved by optimal concentration of 5 wt% Gd–V₂O₅ that is accredited to effective separation of electron-hole pairs. While Gd–V₂O₅/RGO showed 2.1 times higher dye removal (97.12%) than unsupported Gd–V₂O₅, under the visible light irradiation. The significantly high photocatalytic activity of Gd–V₂O₅/RGO is due to the synergistic effect aroused by combined action of Gd⁺³ ions doping and advantageous properties of highly conductive and large surfaced graphene. Recycling experiments for V₂O₅ derivatives showed good stability and recyclability of photocatalysts. Additionally, Gd–V₂O₅/RGO was found to be more potential anti-bacterial agent than V₂O₅ and Gd–V₂O₅.     

The limiting diffusion current value on a macroscopically inhomogeneous electrode

The limiting diffusion current I_dN to an electrode in the form of system of alternating active and inactive sites has been calculated. It is shown that I_dN = I⁰_dπ(N,θ). Here I⁰_d is the limiting diffusion current to the same electrode with an all-active surface. The correction factor π(N,θ) depends on the degree of the surface activity θ and on the distribution of active sites N along the surface. The factor π(N,θ) does not depend on the intensity of stirring of electrolyte solution.