Gd Oxides Research Articles

Microstructural characterization of gadolinium-rich phases in titanium alloys

This study explores the microstructural characteristics of gadolinium (Gd)-rich phases in titanium (Ti) alloys through comprehensive electron microscopy analysis. The Ti alloys were produced using plasma arc melting and subsequently hot-forged. Elaborate material characterization, including scanning electron microscopy, electron backscatter diffraction, and energy dispersive spectroscopy, revealed the formation of round or angular Gd oxides and elongated Gd-rich grains within the alloy. High-magnification transmission electron microscopy and X-ray diffraction confirmed the presence of the FCC-type γ-Gd phase, influenced by the oxygen intake during casting, coexisting with Gd2O3 due to their similar crystal structures. The study also observed internal twins in the Gd grains, potentially delaying the transformation to the stable α-Gd phase. The significant mechanical property differences between the Gd-rich phases and the Ti matrix caused defects at phase interfaces during hot processing, weakening the Gd phase. This work enhances the understanding of Gd phase formation and its implications on the mechanical properties of Ti–Gd alloys.

Self‐Assembled Colloidal Photonic Structures for Directional Radioluminescence of Gd and Ta Oxide Scintillators

AbstractRadiation detection is being revolutionized by integrating photonic elements into scintillators. In this study, a scalable and cost‐effective method is proposed to achieve tuneable emission enhancement across the visible spectrum by colloidal self‐assembly of photonic crystals on scintillator surfaces. This concept is demonstrated for Eu3+/Tb3+‐doped Gd and Ta oxides. Widely available and affordable colloidal nanospheres of SiO2 or polymethyl methacrylate are self‐assembled on these scintillators. The size of the nanospheres is carefully optimized to match the desired emission lines of Eu3+/Tb3+. The result is homogeneous and closely‐packed structures with clear photonic bandgap in the visible range. Under X‐ray excitation, the scintillators covered with the photonic layers exhibit enhanced light extraction in the direction perpendicular to the surface, compared to isotropic emission in the bare scintillator. Such scintillation directionality, when optically matched with a proper detector, will result in higher efficiency of the overall detection system. Moreover, X‐ray imaging demonstrates an enhancement of 25% in system resolution of the scintillator supplemented with the photonic layer compared to unmodified scintillators. The proposed method is scintillator‐ and nanosphere‐agnostic, thus offering a promising versatile approach for directing the scintillation light toward a photodetector and increasing detection system performance, including high‐resolution imaging applications.

Synergistic effects and electrocatalytic insight of single-phase hexagonal structure as low-temperature solid oxide fuel cell cathode

Enhancing the electrocatalytic activity of the electrode materials, specifically oxygen reduction reaction (ORR), at lower operating temperatures (<600 °C) is the prime rank to realize the commercialization of solid oxide fuel cells (SOFCs) research. Herein, a new hexagonal structure-based cathode material was developed with the co-doping of Gd2O3 and Cr2O3 of parent SrFe12O19 oxide, respectively. At 550‒475 °C, Sr0.90Gd0.10Fe11.90Cr0.10O19 (SFO-10) cathode sample leading to the large peak power density (PPD) of 395 mW/cm2, has appropriate surface oxygen defects (Oβ) up to 17%, as verified by X-ray photoelectron microscopy (XPS). Theoretical calculations reveal that the co-doping of Gd and Cr oxides creates lattice disorder at the hexagonal lattice, which decreases the energy barrier for ion transport and enhances the electrocatalytic characteristics of ORR. Consequently, the SFO-10 cathode shows a favorable ORR activity with the least lower polarization resistance (ASR) at 550 °C with gadolinium-doped ceria (GDC) electrolyte. This work provides a self-assembled single-phase hexagonal cathode to accelerate the low-temperature hindrance of SOFC technology.

Designing gadolinium-transition metals-based perovskite type high entropy oxides with good cryogenic magnetocaloric performances

Cryogenic magnetic cooling based on the principle of the magnetocaloric effects (MCEs) of magnetic solids has been recognized as an alternative cooling technology due to its significant economic and social benefits. Designing novel magnetic materials with good magnetocaloric performance is a prerequisite for practical applications. In this study, three gadolinium-transition metal-based high entropy oxides (HEOs) of Gd(Fe1/4Ni1/4Al1/4Cr1/4)O3, Gd(Fe1/5Ni1/5Al1/5Cr1/5Co1/5)O3, and Gd(Fe1/6Ni1/6Al1/6Cr1/6Co1/6Mn1/6)O3 were designed and systematically characterized regarding their structural and cryogenic magnetic properties. These HEOs were confirmed to crystallize into a single-phase perovskite-type orthorhombic structure with a homogeneous microstructure, reveal a second-order magnetic transition at low temperatures, and exhibit significant cryogenic MCEs. The magnetocaloric performances of the present HEOs, identified by magnetic entropy changes, relative cooling power, and temperature-averaged entropy changes, were comparable with recently reported candidate materials. The present study indicates potential applications for cryogenic magnetic cooling of the present HEOs and provides meaningful clues for designing and exploring HEOs with good cryogenic magnetocaloric performances.

Structure, magnetic properties and cryogenic magnetocaloric performances of perovskite-type Gd(4TM0.25)O3 and Gd(5TM0.2)O3 high-entropy oxides

We herein fabricated two gadolinium-transition metal-based high entropy (HE) oxides of Gd(Mn0.25Fe0.25Al0.25Cr0.25)O3 [denoted as Gd(4TM0.25)O3] and Gd(Mn0.2Fe0.2Al0.2Co0.2Ni0.2)O3 [denoted as Gd(5TM0.2)O3] and determined their structural, magnetic, and magnetocaloric properties. Both of present HE oxides are found to crystallize in the single-phase perovskite-type orthorhombic structure with a homogeneous microstructure and exhibit prominent cryogenic magnetocaloric performances. The values of magnetic entropy change, refrigerant capacity, and temperature-averaged entropy change (6K-lift) under the magnetic field change of 0–7 T are estimated to be 20.34 J/kgK, 295.4 J/kg, and 19.56 J/kgK for Gd(4TM0.25)O3, and to be 22.45 J/kgK, 258.2 J/kg, and 20.79 J/kgK for Gd(5TM0.2)O3, respectively, which are comparable with recently reported candidate materials for practical magnetic cooling. These findings not only indicate potential applications of present perovskite-type Gd(4TM0.25)O3 and Gd(5TM0.2)O3 HE oxides, but also provide meaningful clues for exploring HE oxides with prominent cryogenic magnetocaloric performances.

High-temperature tribological performance of stir-cast and heat-treated EV31A magnesium alloy: Experiments and predictions

The temperature effect on the wear behaviour of EV31A Mg alloy during dry sliding wear was investigated. Wear tests were carried out at 50, 100, 150, 200, and 250 °C using a standard load of 10 N and a sliding distance of 1000 m. Weight loss method was used to calculate the wear rate. Optical microscopy was used to examine the microstructure of the EV31A alloy. FE-SEM with EDS analysis was used to investigate the wear morphology, and XRD analysis was performed both before and after the wear test. A high wear coefficient (K) value (more than 10−4) indicates extreme wear for EV31A in all the scenarios. T4 EV31A had a maximum wear rate of 20.2 mg at 150 °C. The as-cast EV31A alloy exhibits an excellent wear rate at the price of mechanical properties under all test scenarios. Wear resistance is improved by Nd and Zr oxides, although Mg and Gd oxides have little effect. Zn has no effect on the wear behaviour of the EV31A. In as-cast, T4, and T6 heat-treated conditions, the EV31A alloy exhibits delamination (abrasive wear), oxide development (corrosive wear), and delamination mixed with plastic deformation (adhesive wear). A Three-layered ANN and adapted Fine Gaussian SVM predicted tribological characteristics. In ANN prediction, the maximum R2 was 0.99 for CoF and 0.89 for wear rate, respectively. Despite the fact that the study's normal load is constant, machine learning models allow to deduce that temperature and normal load are the main influential parameters in CoF and wear rate, respectively.

Study of microstructure and corrosion resistance of FeCrAl-Gd alloys

The corrosion resistance of Fe–21Cr–4Al alloys with different gadolinium (Gd) contents was investigated by means of microstructure, salt spray corrosion and electrochemical tests. The microstructural analysis shows that Gd and Gd2O3 formed at grain boundaries will pinch the grain boundaries and slow down the grain growth, thus reducing the grain size. The corrosion results showed that as with the increase of the Gd component, there are two competing corrosion mechanisms: 1) the grain size becomes smaller, which makes the corrosion pit difficult to expand; more Gd oxides are formed, which hinders the penetration of Cl−; 2) the number of grain boundaries and dislocations increases, which expedite the corrosion rate; and the increasing Gd-rich phase serve as cathodes for the micro-galvanic corrosion. A minimum corrosion rate of 1.94 mm/year was achieved for the Gd-containing alloy, a reduction of 46.4% compared to the original alloy.

A tetrad effect in the glass transition of lanthanide‐doped sodium disilicate glasses

AbstractScanning calorimetric determination of the glass transition temperatures (Tg) of sodium disilicate doped individually with 25 wt.% of the oxides of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu reveals the presence of the so‐called “lanthanide tetrad effect” in their glass transition temperatures. This is to the best of our knowledge the first observation of a tetrad effect in the macroscopic properties of a high‐temperature silicate phase.

Determination of rare earth elements in gadolinium-based contrast agents by ICP-MS

A simple ICP-MS procedure for the determination of trace element concentrations in GBCAs is described here. Abundances of most of the REEs, Y, Ba and Pb concentrations were determined. We confirm that GBCAs contain traces of non-Gd REEs, Y, Ba and Pb. REE patterns of the five GBCAs actually administered in France have been obtained. They display specific shapes that make it possible to identify the different Gd oxides oxides used by pharmaceutical laboratories to produce them. Our method enables us to quickly evaluate the quantities of impurities in these products and, if necessary, to follow the evolution of their quality in the future. The presence of small but not negligible quantities of Y and REEs other than Gd cannot be ignored in these products, and their behaviour in the human body must be considered. The concentrations measured for Pb and Ba, on the other hand, are much lower and do not pose any particular problems.

Decoupling of Gd–Cr magnetism and giant magnetocaloric effect in layered honeycomb tellurate GdCrTeO6

We report the decoupling of Gd–Cr magnetism and the resulting giant magnetocaloric effect in honeycomb-lattice tellurate GdCrTeO6. This compound adopts the hexagonal structure with the space group P-3. The susceptibility curve presents a paramagnetic behavior from room temperature to 2 K. Very intriguingly, however, the heat capacity measurement probes a λ-like peak at TN = 10 K, characterizing the long-range antiferromagnetic order. This suggests that the Gd and Cr sublattices are magnetically independent, i.e., the Gd ions are paramagnetic and the strong paramagnetism nearly masks the antiferromagnetic order of Cr ions, which is further evidenced by our ESR data. The maximum magnetic entropy change at 2 K is 41.8 J kg−1 K−1 in a field range of 0–7 T and 30.3 J kg−1 K−1 for 0–3 T, larger than those of most of the Gd oxides reported. The observed giant magnetocaloric effect is due to strong paramagnetism of Gd ions.

Thermophysical properties of Ca3Ln3Ce7Ta2O26.5 (Ln=Gd and Yb) oxides for thermal barrier coating applications

Ca3Ln3Ce7Ta2O26.5 (Ln = Gd or Yb) oxides were synthesised using a high-temperature sintering technology at 1873 K for 10 h in air. The crystal lattice structures and thermophysical properties of these two oxides were estimated. The fabricated ceramics present an onefold pyrochlore-kind lattice. Because of the relatively higher atomic weight of Ca3Yb3Ce7Ta2O26.5 than that of Ca3Gd3Ce7Ta2O26.5, the heat-insulation ability of Ca3Yb3Ce7Ta2O26.5 is less than that of Ca3Gd3Ce7Ta2O26.5. Due to the minor electro-negativity of Yb than that of Gd, Ca3Yb3Ce7Ta2O26.5 exhibits greater thermal expansion coefficient than Ca3Gd3Ce7Ta2O26.5.

Structural and thermophysical performances of Sm2LaTaO7 and Gd2LaTaO7 oxides

In this present paper, two kinds of Ln2BTaO7 (Ln=Sm, Gd) oxides were prepared by solid state reaction at 1873 K for ten hours. The phase-composition, microstructure and thermophysical performances of sintered samples were studied. Results show that the synthesized Ln2BTaO7 oxides present onefold orthorhombic weberite lattice. Due to the phonon scattering resulted by complex crystal-lattice and numerous oxygen vacancies, the heat conductivities of obtained products are less than that of YSZ. Because of the low ionic radius of Sm3+ ions，the heat expansion quotiety of Sm2LaTaO7 is greater than that of Gd2LaTaO7.

Structure and transport properties of proton-conducting BaSn0.5In0.5O2.75 and A-site substituted Ba0.9Ln0.1Sn0.5In0.5O2.8 (Ln = La, Gd) oxides

In this work, characterization of BaSn0.5In0.5O2.75, Ba0.9La0.1Sn0.5In0.5O2.8 and Ba0.9Gd0.1Sn0.5In0.5O2.8 perovskite-type oxides is reported concerning crystal structure, presence of protons in hydrated samples and transport properties of dense pellets in dry and wet atmospheres at elevated temperatures. Compounds possess cubic structure at room temperature, which is in accordance with Goldschmidt's tolerance factor t being close to 1. Introduction of smaller Ln partially substituting Ba results in a decreased unit cell volume. Upon hydration in wet air unit cell of the materials enlarge, with magnitude of the effect correlated with chemical composition. High temperature X-ray measurements in synthetic air revealed release of water from hydrated materials occurring above 200°C, and associated non-monotonous dependence of the respective unit cell parameter. No significant influence of dopants is found concerning thermal expansion of the studied oxides. Performed thermogravimetric measurements on hydrated and dried samples with supplementary mass spectroscopy analysis are in agreement with structural results, confirming presence of water in the hydrated compounds, but also show CO2 release during heating. Electrochemical impedance measurements, conducted for densified pellets in dry, H2O- and D2O-containing synthetic air, indicate an appearance of proton conductivity, with different dependence of bulk and grain boundary components on chemical composition. Supplementary electrical conductivity relaxation experiments, which allowed calculating diffusion and surface coefficients are also provided.

Effects of Lewis acidity of metal oxide promoters on the activity and selectivity of Co-based Fischer–Tropsch synthesis catalysts

Metal oxides of Ce, Gd, La, Mn, and Zr were investigated as promoters for improving the activity and selectivity of Co-based FTS catalysts. The extent to which these promoters decrease the selectivity toward CH4 and increase the selectivity toward C5+ hydrocarbons was found to depend on both the loading and the composition of the oxide promoter. Elemental mapping by STEM–EDS revealed that the propensity for a given metal oxide to associate with Co affects the sensitivity of the product distribution to changes in promoter loading. For all promoters, a sufficiently high loading resulted in the product distributions becoming insensitive to further increases in promoter loading, very likely due to the formation of a half monolayer of promoter oxide over the Co surface. Simulations suggest that the fraction of Co active sites that are adjacent to the promoter moieties approaches unity at this degree of coverage. The oxidation state of the promoter metal cation under reaction conditions, determined by in situ XANES measurements, was used to calculate relative Lewis acidity of the promoter metal cation. A strong positive correlation was found between the C5+ product selectivity and the Lewis acidity of the promoter metal cations, suggesting that the promotional effects are a consequence of Lewis acid–base interactions between the reaction intermediates and the promoter metal cations. Rate data obtained at different pressures were used to estimate the apparent rate coefficient and the CO adsorption constant appearing in the Langmuir–Hinshelwood expression that describes the CO consumption kinetics for both unpromoted and the metal oxide-promoted catalysts. Both parameters exhibited positive correlations with the promoter Lewis acidity. These results are consistent with the hypothesis that the metal cations of the promoter act as Lewis acids that interact with the O atom of adsorbed CO to facilitate CO adsorption and dissociation.

Influence of Ce, Nd, Sm and Gd oxides on the properties of alkaline-earth borosilicate glass sealant

In this study, the influence of CeO2, Nd2O3, Sm2O3 and Gd2O3 on various properties of the melt-quench route derived SrO–CaO–ZnO–B2O3–SiO2 glass have been investigated. Both the precursor glasses and heat treated glasses are characterized by dilatometry, differential scanning calorimetry (DSC), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The density and coefficient of thermal expansion of the glasses varies in the range 3.557–3.804 g cm−3 and 10.5–11.2 × 10−6 K−1 (50–800 °C) respectively. Decrease in crystallization tendency with increase in cationic field strength of the ions is well supported by the increasing crystallization activation energy of the glasses calculated by Kissinger, Augis–Bennett and Ozawa models. XPS study revealed the presence of both Ce3+ and Ce4+ ions and an increase in characteristic binding energy of the respective rare earth elements from their core level studies. The Knoop hardness of the glasses varies in the range 6.03–6.28 GPa. The glass transition, glass softening and crystallization temperature; density and hardness of the glasses increased with increase in cationic field strength of the incorporated ions. The thermomechanical properties of the Gd2O3 containing glass advocate its applicability as the most promising sealant in solid oxide fuel cell.

Ericsson-like giant magnetocaloric effect in GdCrO4–ErCrO4 composite oxides near liquid hydrogen temperature

In this paper, magnetic and magnetocaloric properties of RCrO4 (R=Gd and Er) oxides have been investigated. It is found that GdCrO4 and ErCrO4 exhibit a second-order magnetic transition from ferromagnetic to paramagnetic states at their Curie temperatures of 22.0K and 14.9K, respectively. The maximal magnetic entropy change (ΔSM) for a field variation of 0–5T have reached 22.8Jkg−1K−1 for GdCrO4 and 20.5Jkg−1K−1 for ErCrO4. The collective magnetic contributions from R3+ and Cr5+ ions lead to the large ΔSM. For the same field variation, table-like ΔSM of ~19.5Jkg−1K−1 and a large refrigerant capacity (RC) of 117Jkg−1 have been achieved for the composite material formed by GdCrO4 and ErCrO4 with the mass ratio of 1:1 from 16.0K to 22.0K. Since the liquid hydrogen temperature (20.3K) locates within this range, large reversible magnetocaloric effect, high RC as well as the low cost make GdCrO4–ErCrO4 composite material a potential candidate for magnetic refrigerant for the storage of liquid hydrogen.

Potential use of rare earth oxides as tracers of organic matter in grassland

AbstractTracing organic matter (OM) in soil is challenging, because runoff and leaching processes are interrelated and have multiple sources. Therefore, multiple tracers with low background concentrations such as rare earth element oxides (REOs) are necessary to delineate the origin of sources of the organic materials in groundwater, rivers or in catchments. The main objective of this study was to examine the potential use of REOs as a tracer in various forms of OM (1) whole slurry, (2) solid, and (3) liquid phase of cattle slurry after mechanical separation. A laboratory experiment was carried out using five REOs (La, Gd, Sm, Pr, and Nd oxides) mixed directly into soil or mixed with various fractions of cattle slurry and then applied to the soil surface. In the additional grassland experiment, Gd oxide was spiked with soil and cattle slurry and then applied to the soil surface. The mineral N in the liquid phase (urine) of the slurry in the grassland experiment was labelled with 15N urea (16 atom%). In the laboratory experiment, results showed that the five REOs concentration of soil in 0–1 cm soil section after the rainfall simulation was still up to 20 times more than the background values. In 1–2 cm soil section, the concentration of only Gd (two fold higher) and La oxides (50% higher) were significantly higher than the soil background values. Therefore, we hypothesized that Gd and La oxides were associated also with relatively finer organic particles in slurry, thus 1–2 cm soil section were enriched with these oxides. The five REOs concentration below 2 cm soil depth were similar to the background values in all treatments. In line with the laboratory experiment, Gd concentrations in the deeper soil layers (2–4 and 4–8 cm) in the grassland experiment were not significantly affected by any treatment. Both in grassland and laboratory experiment, solid phase of the slurry (dung) was collected from the soil surface after rainfall simulation. Here, about 56% of REOs were measured on the solid phase of the slurry which indicates the strong binding potential of REOs on slurry OM. The present novel study, where REO tagged slurry was uniquely tested to study geochemical cycle of organic fertilizers, clearly highlighted the potential for their use as multiple‐tracers of (animal derived‐) OM in agricultural soils.

Phase and fracture toughness evolution during isothermal annealing of spark plasma sintered zirconia co-doped with Yb, Gd and Nd oxides

Dense pellet of rare-earth oxide (5YbO1.5+1.5GdO1.5+1.5NdO1.5) stabilized zirconia, a candidate thermal barrier composition, was prepared by spark plasma sintering. Isothermal annealing was carried out at 1250°C up to 192h. X-ray diffraction and Raman spectroscopy were used to characterize the phases. Cubic precipitates formed in the initial tetragonal phase from 6h, with volume fraction of 22.31% after 192h. 15.35vol.% of monoclinic phase was observed in XRD at 192h along with cubic and two tetragonal phases. Indentation toughness increased by 49% from 155±24Jm−2 at 0h to 231±71Jm−2 at 6h of annealing and it decreased towards the initial value upon further annealing to 192h. Ferroelastic toughening dominates until transformation toughening ensues at 192h. The toughness is consistently higher than for singly doped, sintered t′ zirconia pellets that are reported in the literature.

Development of Ternary Cathodes Using MyCe1–x–yMnxO2–δ (M = La, Gd) as Catalysts for Oxygen Reduction Reactions

AbstractMyCe1–x–yMnxO2–δ (M = La, Gd) oxides have been investigated as oxygen reduction catalysts for LSM–YSZ based ternary cathodes. MyCe1–x–yMnxO2–δ samples are characterized by X‐ray diffraction (XRD), temperature programmed reduction of H2 (H2‐TPR), and temperature programmed desorption of O2 (O2‐TPD). The results show that the incorporation of M (M = La, Gd) ions increases the solution limit of Mn in the solid solutions, which increases the amount of oxygen vacancies and promotes oxygen adsorption and dissociation processes. The ternary cathodes show much higher electrochemical performance than LSM–YSZ binary cathode, and greatly accelerate oxygen dissociative adsorption and diffusion of oxygen species. The MyCe1–x–yMnxO2–δ catalysts exhibit greatly high activity for oxygen reduction at intermediate temperature. The ternary cathodes have high stability and high resistance to CO2 at 600 °C.

Anion Disorder in Lanthanoid Zirconates Gd2–xTbxZr2O7

The pyrochlore-defect fluorite order-disorder transition has been studied for a series of oxides of the type Gd(2-x)Tb(x)Zr2O7 by a combination of diffraction and spectroscopy techniques. Synchrotron X-ray diffraction data suggest an abrupt transition from the coexistence of pyrochlore and defect fluorite phases to a single defect fluorite phase with increasing Tb content. However neutron diffraction data, obtained at λ ≈ 0.497 Å for all Gd-containing samples to minimize absorption, not only provide evidence for independent ordering of the anion and cation sublattices but also suggest that the disorder transition across the pyrochlore-defect fluorite boundary of Ln2Zr2O7 is rather gradual. Such disorder was also evident in X-ray absorption measurements at the Zr L3-edge, which showed a gradual increase in the effective coordination number of the Zr from near 6-coordinate in the pyrochlore rich samples to near 7-coordinate in the Tb rich defect fluorites. These results indicate the presence of ordered domains throughout the defect fluorite region, and demonstrate the gradual nature of the order-disorder transition across the Gd(2-x)Tb(x)Zr2O7 series.