Function Of Gd Concentration Research Articles

Analyzing the grain‐boundary resistance of oxide‐ion conducting electrolytes: Poisson‐Cahn vs Poisson‐Boltzmann theories

AbstractThe diminished conductivity of pristine grain boundaries in oxide‐ion conducting electrolytes, such as (Ce,Gd)O2 and (Zr,Y)O2, is widely interpreted with the Mott‐Schottky space‐charge model, or less frequently, with the Gouy‐Chapman space‐charge model. Although routinely applied to the entire compositional range of solid solutions, from dilute to concentrated, these models, being based on the Poisson‐Boltzmann formalism, are limited in their range of validity to dilute solutions of point defects. Analyzing the grain‐boundary properties of concentrated solid solutions with such models is expected to lead to errors and inconsistencies. In this study, we employ Poisson‐Cahn theory to analyze literature data for the grain‐boundary resistance of CeO2‐Gd2O3 materials as a function of Gd concentration. Poisson‐Cahn theory combines the Cahn‐Hilliard theory of inhomogeneous systems with the Poisson equation of electrostatics and it is valid over the entire compositional range. We treat the realistic case of a restricted equilibrium: Gd accumulation profiles are frozen‐in from sintering temperatures, while the oxygen‐vacancy distributions are in equilibrium at sintering and (much lower) measurement temperatures. Data for the grain‐boundary resistance are also analyzed with the standard analytical expressions from the Mott‐Schottky and Gouy‐Chapman models. Outside the domain of their validity, these expressions are found to perform poorly. In general, we emphasize the importance of treating the interfacial properties of concentrated solid solutions with physically appropriate theories.

Damping-like spin-orbit-torque-induced magnetization dynamics in ferrimagnets based on Landau-Lifshitz-Bloch equation

A theoretical model based on the Landau-Lifshitz-Bloch equation is developed to study the effect of damping-like spin-orbit torque in ferrimagnets, which can capture many experimental findings. For example, the sample changes from Gd to FeCo dominate by increasing temperature, the damping-like spin-orbit torque has a peak at the magnetization compensation temperature, and angular-momentum compensation temperature increases as a function of Gd concentration. In contrast to the ferromagnet system, the switching trajectory in ferrimagnets is found to be precession free. The two sublattices are not always collinear, which produce a large exchange field affecting the magnetization dynamics. The study of material composition shows the existence of an oscillation region at intermediate current density, induced by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert model, our developed model based on the Landau-Lifshitz-Bloch equation enables the systematic study of the spin-torque effect and the evaluation of ferrimagnet-based devices.

Photoluminescence properties of Gd:ZnO nano phosphor

Gd (0.1, 0.5, 1.0 mol%) doped ZnO nano phosphor, prepared by wet chemical method followed by sintering in air at 700 °C, was characterized by XRD, EDX, SEM, and photoluminescence techniques. EDX confirmed the doping of Gd in ZnO, while XRD patterns showed that the ZnO wurtzite crystal structure remained unchanged on doping. Nanostructure nature of the prepared samples was confirmed from XRD data as well as from SEM images. The photoluminescence in visible region (400–700 nm) was observed when excited with 280, 300, 345, 395, and 460 nm radiation from a Xe lamp. The observed emission when excited with 280, 300, and 345 nm radiation shows concentration quenching, which could be explained in terms of 4f–4f transitions of Gd3+. The intensity of this emission is maximum for 0.5 mol% Gd:ZnO when excited by 300 nm. The chromaticity coordinates of this emission are x = 0.31 and y = 0.32 indicating its potential for the realization of optical sources/displays. On the other hand the emission excited by 395 and 460 nm radiation consists of relatively sharp peaks in blue, green and red regions. This emission is better explained in terms of the defects in ZnO. However, marginal increase in the intensity of this emission with the increase in the concentration of Gd shows the increase in defect density with Gd doping. (a) Integrated PL intensity as a function of Gd concentration (b) Chromaticity color coordinates x = 0.31 and y = 0.32

Growth and optical properties of (Y1−xGdx)3Al5O12:Ce single crystal phosphors for high-brightness neutral white LEDs and LDs

(Y1−xGdx)3Al5O12:Ce ((Y,Gd)3Al5O12:Ce) single crystal phosphors (SCPs) were successfully grown using the Czochralski method. The Gd segregation coefficient was determined. The lattice spacing, absorption and emission properties were systematically investigated as a function of Gd concentration in a wide temperature range. Gd incorporation red-shifts the SCP emission so that neutral white with correlated color temperatures in the range of 4098–6594 K can be achieved in conjunction with a blue light-emitting diode (LED). SCPs demonstrate high conversion efficiency (>90% above 150 °C) and better thermal stability compared to analogous ceramic powders. Additionally, SCPs are compatible with resin-free packaging, overcoming drawbacks associated with powder encapsulants. Therefore, (Y,Gd)3Al5O12:Ce SCPs are promising candidates for high-brightness neutral white sources based on intense blue LEDs and laser diodes.

Monte Carlo study of radiation dose enhancement by gadolinium in megavoltage and high dose rate radiotherapy.

MRI is often used in tumor localization for radiotherapy treatment planning, with gadolinium (Gd)-containing materials often introduced as a contrast agent. Motexafin gadolinium is a novel radiosensitizer currently being studied in clinical trials. The nanoparticle technologies can target tumors with high concentration of high-Z materials. This Monte Carlo study is the first detailed quantitative investigation of high-Z material Gd-induced dose enhancement in megavoltage external beam photon therapy. BEAMnrc, a radiotherapy Monte Carlo simulation package, was used to calculate dose enhancement as a function of Gd concentration. Published phase space files for the TrueBeam flattening filter free (FFF) and conventional flattened 6MV photon beams were used. High dose rate (HDR) brachytherapy with Ir-192 source was also investigated as a reference. The energy spectra difference caused a dose enhancement difference between the two beams. Since the Ir-192 photons have lower energy yet, the photoelectric effect in the presence of Gd leads to even higher dose enhancement in HDR. At depth of 1.8 cm, the percent mean dose enhancement for the FFF beam was 0.38±0.12, 1.39±0.21, 2.51±0.34, 3.59±0.26, and 4.59±0.34 for Gd concentrations of 1, 5, 10, 15, and 20 mg/mL, respectively. The corresponding values for the flattened beam were 0.09±0.14, 0.50±0.28, 1.19±0.29, 1.68±0.39, and 2.34±0.24. For Ir-192 with direct contact, the enhanced were 0.50±0.14, 2.79±0.17, 5.49±0.12, 8.19±0.14, and 10.80±0.13. Gd-containing materials used in MRI as contrast agents can also potentially serve as radiosensitizers in radiotherapy. This study demonstrates that Gd can be used to enhance radiation dose in target volumes not only in HDR brachytherapy, but also in 6 MV FFF external beam radiotherapy, but higher than the currently used clinical concentration (>5 mg/mL) would be needed.

Preparation and study of thermoelectric properties of fine grains Gd x Zn1−x O

GdxZn1−xO nanosize powders (nominal x = 0–0.03) were prepared by using a modified-Pechini method. We observed a clear diminution of the grain-size with an increase in the gadolinium nominal concentration (down to 25 nm for x = 0.003). Attempts to substitute larger Gd amount (x = 0.05) on the Zn site were unsuccessful. The powders were densified into dense pellets using spark plasma sintering (SPS). A second phase, Gd2O3, was evidenced after the SPS step for Gd fractions as low as x = 0.008. We studied the temperature-dependent thermoelectric properties and the best properties at room temperature were observed for x = 0.002–0.003, with an electrical resistivity (ρ) of about 5.9 × 10−3 (Ω cm) and a Seebeck coefficient (S) of −164 µV K−1, corresponding to a power factor (S2/ρ) of 0.46 mW K−2 m−1. Hall effect measurements were carried out and the obtained results were consistent with the Seebeck coefficient and electrical resistivity evolution, in function of Gd concentration.

Efficiency of ultrafast laser-induced demagnetization in GdxFe100−x−yCoyalloys

Laser-induced ultrafast demagnetization in ferrimagnetic Gd${}_{x}$Fe${}_{100\ensuremath{-}x\ensuremath{-}y}$Co${}_{y}$ thin films was studied experimentally as a function of Gd concentration ($x=18$, 22, 24, 30%, and $y\ensuremath{\approx}9$--10%), pump fluence, and sample temperature. The results showed that the conditions for full demagnetization at the ultrafast time scale in Gd${}_{x}$Fe${}_{100\ensuremath{-}x\ensuremath{-}y}$Co${}_{y}$ thin metal films are easily achieved below the magnetization compensation point (${T}_{M}$) and, furthermore, when the ratio between Gd and Fe concentrations is not too large. Consequently, the ultrafast demagnetization strongly depends on the initial temperature of these alloys compared to their ${T}_{M}$. These results provide further insight into the unconventional ultrafast dynamics of multisublattice metallic magnets.

STRUCTURAL PHASE DIAGRAM FOR THE THERMAL CONTROLLED DISTORTION BY Gd IONS IN THE (Nd1-yGdy)1.85Ce0.15CuO4 HTS SYSTEM

The influence of partial substitution of Nd by Gd on the temperature dependence of the lattice parameters of the optimal doped Nd 1.85 Ce 0.15 CuO 4n-type superconductor (maximum value of Tc) was studied by using X-ray diffraction measurements function of temperature. The transition from the structural normal phase (I4/mmm) to the distortion phase (Acam) was evidenced above y = 0.65 Gd substitution level in ( Nd 1-y Gd y)1.85 Ce 0.15 CuO 4. The structural phase transition temperature TI-A from undistorted phase to the distorted phase changes function of Gd concentration. The structural phase diagram for thermal controlled distortion by Gd ions, TI-A = f(y) was obtained, and compared by the superconducting phase diagram Tc(y).

Indirect detection of lung perfusion using susceptibility‐based hyperpolarized gas imaging

To address the problem of inadequate signal-to-noise ratio (SNR) encountered in lung perfusion magnetic resonance imaging (MRI) by developing an indirect detection based on the strong hyperpolarized (HP) gas signal. Our model is based on detecting the effects of gadolinium (Gd) flowing through lung capillaries by recording the phase of the nearby alveolar HP gas. In a HP gas 3He phantom we imaged gas phases before and after removing tubes containing paramagnetic solution away from the phantom. We also imaged HP gas phases in pig lungs before and after injection of Gd. Finally, parenchymal spin phase in excised lungs was measured as a function of Gd concentration. In the phantom, the differential phase map displayed a pattern characteristic of a susceptibility-induced dipole field, showing the possibility of an indirect detection. In vivo, the differential phase map showed homogeneous appearance, as expected for uniform perfusion in healthy lungs. Ex vivo, the parenchymal spin phases were shown to depend linearly on Gd concentration. Our method should allow indirect perfusion (Q) and direct ventilation (V) to be assessed simultaneously, thus allowing for diagnosis of V/Q mismatches. The linear dependency of parenchymal spin phase vs. Gd concentration may allow for quantification of lung perfusion.

Magnetic properties of Pr 1− xGd xMn 2Ge 2 compounds

The structure and magnetic properties of the Pr 1− x Gd x Mn 2Ge 2 (0.0≤ x≤1.0) compounds have been investigated by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC) techniques and AC magnetic susceptibility measurements. All compounds crystallize in the ThCr 2Si 2-type structure with the space group I4/ mmm. The lattice constants and the unit cell volume obey Vegard’s law. Samples in this alloy system exhibit a crossover from ferromagnetic ordering for PrMn 2Ge 2 to antiferromagnetic ordering for GdMn 2Ge 2 as a function of Gd concentration x. At low temperatures, the rare earth sublattice also orders and reconfigures the ordering in the Mn sublattice. The results are summarized in the x– T magnetic phase diagram.

Basal plane magnetostruction and anisotropy of (Tb 0.5Dy 0.5) xGd 100− x single crystals

The effect of adding Gd to the binary alloy Tb 0.5Dy 0.5 has been studied via magnetostriction and differential scanning calorimetry measurements for concentrations of Gd of 40 and 60%. The two lowest-order magnetostriction constants were determined, as was the basal plane anisotropy. We report the anisotropy compensation temperaures as a function of Gd concentration, as well as the Curie and Néel temperatures, where present. These data are examined in conjunction with previous data taken on alloys with Gd concentrations of 0 and 20%.

ESR of gadolinium in CeSi2, LaSi2and GdSi2

Electron spin resonance of gasolinium has been observed in the intermediate-valence compound CeSi2 and in non-magnetic LaSi2. A Korringa-type relaxation occurs; the slope of the linewidth against temperature curve is correlated with the variations of Delta g as a function of Gd concentration. Once the bottleneck effects have disappeared the Korringa slope for Gd:CeSi2 is found smaller than that for Gd:LaSi2. These results have some similarity to previous results obtained on CePd3; a possible explanation could be the occurrence of a hybridisation gap at low temperature in CeSi2.

Correlation between electron spin resonance and superconductivity in Gd xB 1−xRu 2 (B=Th, Ce, La)

Correlation between EPR and superconductivity in Gd x B 1− x Ru 2 (B=Th, Ce, La) enables us to interpret the behavior of the superconducting transition temperature as a function of Gd concentration in these cubic intermetallic compounds.

The growth and laser characteristics of yttrium-gadolinium-aluminium garnet single crystals

It is shown that optically transparent garnet single crystals can be grown from Y 3Al 5O 12 (YAG) melts containing up to 30 mol.% Gd 3Al 5O 12(GdAG). The presence of Gd expands the YAG lattice and allows more Nd 3+ to be incorporated for a given concentration in the melt i.e. the distribution coefficient is increased. A comparison of pulsed laser measurements on Nd 3+ YGdAG and Nd 3+ YAG rods has shown that in spite of an increased Nd 3+ concentration in the mixed garnet, other factors, in particular the broad linewidth, make it less desirable as a host lattice. The phase diagram between YAG and GdAG has been partially determined. Measurements have also been made of absorption coefficient and absorption and fluorescent linewidths as a function of Gd concentration.