Rare Earth Oxides Research Articles

Influence of Zr-doping on the structure and transport properties of rare earth high-entropy oxides

Fluorite-type ceria-based ceramics are well established as oxygen ion conductors due to their high conductivity, superseding state-of-the-art electrolytes such as yttria-stabilized zirconia. However, at a specific temperature and oxygen partial pressure they occasionally exhibit electronic conduction attributed to polaron hopping via multivalent cations (e.g. Pr and Ce). (Ce, La, Pr, Sm, Y)O2−δ is a high-entropy oxide with a fluorite-type structure, featuring low concentrations of multivalent cations that could potentially mitigate polaron hopping. However, (Ce, La, Pr, Sm, Y)O2−δ undergoes a structural transition to the bixbyite-type structure above 1000 °C. In this study, we introduce Zr doping into (Ce, La, Pr, Sm, Y)O2−δ to hinder the structural transition at elevated temperatures. Indeed, the fluorite structure at elevated temperatures is stabilized at approximately 10 at.% Zr doping. The total conductivity initially increases with doping, peaking at 5 at.% Zr doping, and subsequently decreases with further doping. Interestingly, electronic conductivity in (Ce, La, Pr, Sm, Y)1−x Zr x O2−δ under oxidizing atmospheres is not significant and is lowest at 8 at.% Zr. These results suggest that ceria-based high-entropy oxides can serve as oxygen ion conductors with a significantly reduced electronic contribution. This work paves the way for new compositionally complex electrolytes as well as protective coatings for solid oxide fuel cells.

Achieving excellent mechanical and electrical properties in transition metal oxides and rare earth oxide‐doped KNN‐based piezoceramics

AbstractPotassium sodium niobate (KNN)‐based piezoelectric ceramics have emerged as a promising alternative to lead‐based systems due to their exceptional properties. While extensive research has focused on improving the electrical properties of KNN‐based ceramics through doping and processing optimization, the concurrent investigation of their mechanical properties has been lacking. This study presents a comprehensive analysis of the mechanical and electrical properties of KNN‐based lead‐free piezoceramics doped with various transition metal oxides and rare earth oxides, based on substantial experimental data. Our findings reveal that the as‐sintered KNN‐based ceramics exhibit not only outstanding electrical properties but also remarkable mechanical robustness compared to conventional toughened lead zirconate titanate (PZT)‐based ceramics. These exceptional electrical and mechanical properties are attributed to the micro‐scale and atomic‐scale structure of the modified KNN‐based ceramics, characterized by a highly condensed structure, an inhomogeneous distribution of nano‐domain structure, and the presence of amorphous intergranular films at grain boundaries.

MOFs-derived 3D flower-like Y2O3/C microspheres with efficient electromagnetic wave absorption properties

Y2O3 has emerged as a promising material for electromagnetic wave (EMW) absorption due to its excellent dielectric properties. However, the inherent insulating nature and single loss mechanism limit its absorption performance. Research on the microstructure modulation and component regulation of Y2O3-based absorbers remains relatively unexplored. In this work, Y2O3/C composites with flower-like architectures were synthesized for the first time via a metal-organic framework (MOFs) templating method. The effects of pyrolysis temperature on the microstructure, phase composition, and EMW absorption performance of the Y2O3/C composites were systematically investigated. At a pyrolysis temperature of 800 °C, the flower-like Y2O3/C microsphere exhibited optimal EMW absorption performance. The minimum reflection loss (RL) of pristine Y2O3 was only −4.75 dB, while the Y2O3/C composite achieved a minimum RL of −51.77 dB and a maximum effective absorption bandwidth of 4.32 GHz. Moreover, by simply adjusting the matching thickness, the optimal sample exhibited strong absorption (RL < −30 dB) over a wide frequency range of 4–18 GHz. The incorporation of carbon effectively neutralized the insulating nature of Y2O3, thereby optimizing the impedance matching. The synergistic effects of multiple loss mechanisms, including polarization loss, resistance loss, and interfacial polarization, facilitated substantial EMW attenuation. This study provides a promising strategy for the design and fabrication of high-performance rare-earth oxide EMW absorbers with tunable morphologies and properties.

Incorporation of neodymium, holmium, erbium, and samarium (oxides) in zinc-borotellurite glass: Physical and optical comparative analysis

Investigating the effect of different types of rare-earth oxides on zinc borotellurite glass is important to determine the potential application in optical devices. The addition of rare-earth oxides in zinc borotellurite glass is well-known to enhance the optical properties due to the effects of 4f-4f transitions. In this work, we aim to compare the effect of different rare-earth oxides on zinc borotellurite glass denoted as ZBTNd, ZBTHo, ZBTEr and ZBTSm. The glass samples were successfully fabricated via the melt-quenched technique. The physical investigation of the glasses has been done by measuring the density and molar volume. It was found that ZBTNd glass has the lowest density than the other glasses due to the small atomic radius in neodymium oxide. High-density value for ZBTHo glass shows potential to be used as radiation shielding properties. The high value of molar volume for ZBTNd glass is advantageous for fiber optics as ZBTNd glass has good performance in elasticity. It was found that ZBTEr has a lower refractive index than the other glasses due to low dispersion characteristics. However, ZBTEr glass has good performance to be used in optical communication applications. It was found that the optical absorption shifts to a longer wavelength beginning from ZBTEr &gt; ZBTHo &gt; ZBTNd &gt; ZBTSm. The optical band gap energy for ZBTEr glass is higher than the other glasses due to the Coulomb repulsion energy for erbium which is greater than neodymium and samarium and slightly higher than holmium. The pattern of electronic polarizability for all glasses was found as follows ZBTSm&gt;ZBTNd&gt;ZBTEr&gt;ZBTHo. The optical basicity for ZBTEr was found highest which indicates a higher acidity, meanwhile, the ZBTNd glass has the lowest value which corresponds to a higher basicity.

Autothermal Oxidative Coupling of Methane over Pt/Al2O3 Catalysts Doped with Rare Earth Oxides

AbstractThe effect of rare earth oxides as dopants on the Pt‐governed oxidative coupling of methane (Pt‐OCM) is investigated. The addition of 20 wt.‐% of La‐, Nd‐, Sm‐, and Pr‐oxides to the support benefits the C2 product selectivity and offers the potential to enhance the catalyst stability. Compared to the reference catalyst Pt/Al2O3, the addition of Sm2O3 increased the total selectivity by up to 23 %. Furthermore, La2O3 addition was found beneficial with respect to the (thermal) stability of the catalyst. Dopant content variations uncovered that the catalyst formulation with 20 wt.‐% La2O3 represents an optimum regarding performance and stability.

Isothermal and non-isothermal decomposition mechanisms of bastnaesite during the hydrogen-based mineral phase transformation

The hydrogen-based mineral phase transformation-flotation process can realize the efficient development of iron-bearing rare earth ores. The isothermal and non-isothermal decomposition mechanisms of bastnasite in the hydrogen atmosphere were studied to optimize the hydrogen-based mineral phase transformation process. The thermal decomposition of bastnasite first produced REOF, which would react with oxygen to produce rare earth oxides and fluorides during the analysis process. The thermal decomposition was an endothermic reaction, and the generated gas were mainly CO2 and trace CO, with a mass loss of about 20%. Increasing the temperature can greatly promote the thermal decomposition. After thermal decomposition, the particles showed a layered structure, and many parallel slits run through the particles. The porosity and specific surface area of the particles were significantly improved. The apparent activation energy of isothermal decomposition was 71.80 ± 5.40 kJ/mol, and the kinetic mechanism was random nucleation and growth model (n = 2). The apparent activation energy of non-isothermal decomposition was 201.96 kJ/mol, and the kinetic mechanism was phase-boundary controlled reaction mechanism (n ≈ 2).

Effects of dissolved organic matter on soil aggregate dynamics using rare earth oxides as tracers in A Japanese Andisol

Effects of dissolved organic matter on soil aggregate dynamics using rare earth oxides as tracers in A Japanese Andisol

Optimized Field Emission from Graphene Sheets with Rare Earth Oxides

This paper demonstrates a simple method to improve the field emission of graphene sheets (GSs) by coating them with thin films of rare earth oxides. The rare earth oxide films are coated on GS using drop coating, without changing the surface morphology, resulting in a remarkable improvement in the field emission properties of GSs. The field emission property of GSs is tunable and can be optimized by applying various rare earth oxide films at the appropriate level. It is found that the turn-on field of GSs is reduced from 4.2 V/mm to 1.7 V/mm by Gd2O3 and to 2.2 V/mm by La2O3. The threshold field of GS is also reduced from 7.8 V/mm to 3.4 V/mm and 4.8 V/mm, respectively. Field emission results indicate that the improvement is due to the low work function surface and more effective emission sites generated around the GS surface after coating. The field emission test and the emission pattern suggest that the field emission performance of GS can be significantly enhanced through the application of La2O3 and Gd2O3 coating, as well as by optimizing the concentration of rare earth oxides in the coating. Hence, the rare earth-coated GS can serve as a potential field emitter.

Sm2O3-doped all-inorganic perovskite nanocrystalline glass induces self-crystallization of CsPbBr3 nanocrystals and is used in WLEDs

All-inorganic perovskite quantum dots (QDs) in glass materials, specifically CsPbX3 (X = Cl, Br, I), are being considered as the next-generation fluorescent materials due to their impressive luminous performance and stability. However, the crystallization process of quantum dots within the glass presents uncontrollable challenge, leading to uneven crystallinity and subsequent reductions in light efficiency, thereby affecting practical applications. In glass ceramics doped with rare-earth oxides, the introduction of rare-earth ions as nucleating agents can promote the self-precipitation of nanocrystalline crystals within the glass. Building upon this principle, we have doped rare-earth ions into borosilicate glass for the first time to induce the self-crystallization of CsPbBr3 QDs. This approach effectively enhances the equilibrium distribution of quantum dots within the glass, resulting in a significant improvement in luminosity. Furthermore, the luminescence spectrum range of quantum dot-shaped luminescent glass materials can be finely tuned through rare-earth ion doping. This finding holds both theoretical and practical significance for their application in the field of lighting.

Effects of rare earth oxides on wear resistance and corrosion resistance of 316L/TiC composite coating by laser cladding

In this paper, 316L/TiC composite coatings with different kinds of REOs (Y2O3, La2O3, CeO2, PrO2, Nd2O3) at identical contents (2%) were prepared on S355 marine steel using the laser cladding technology. The surface morphology, phase composition, microhardness, coefficient of friction curve (COF), Tafel curve and electrochemical impedance spectroscopy (EIS) impedance of the test specimens were studied with such instruments as scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer, Vickers microhardness tester, friction and wear tester, and multi-channel electrochemical workstation. The results show that the coating with REO added owns increased thickness and is uniform and dense without such defects as crack, and hole. The microstructure evolution mechanism of the coating from the bottom up is as follows: Cellular crystal, planar crystal → columnar crystal → equiaxed crystal. The phase composition of the coating with REO added remains unchanged, and is still Ni–Cr–Fe austenite phase and TiC phase. Further comparison shows that the coating with Nd2O3 added owns improved hardness, with a mean hardness of 3 times that of the substrate, and has a COF decreasing to 0.69, with wear loss becoming small. The coating with Nd2O3 added has the largest Ecorr, the smallest Icorr, large Z value and phase angle, the greatest Rct, and an nct value of 1, indicating that the coating has dense passivation film and small corrosion tendency, with low corrosion rate. Therefore, this study provides reference experimental and theoretical bases for application of 316L/TiC composite coating with Nd2O3 added at 2% in surface strengthening and repair of steel for marine engineering equipment.

Simultaneous Interface Engineering and Phase Tuning of CeO2-Decorated Catalysts for Boosted Oxygen Evolution Reaction.

Heterogeneous catalysts have attracted extensive attention among various emerging catalysts for their exceptional oxygen evolution reaction (OER) capabilities, outperforming their single-component counterparts. Nonetheless, the synthesis of heterogeneous materials with predictable, precise, and facile control remains a formidable challenge. Herein, a novel strategy involving the decoration of catalysts with CeO2 is introduced to concurrently engineer heterogeneous interfaces and adjust phase composition, thereby enhancing OER performance. Theoretical calculations suggest that the presence of ceria reduces the free energy barrier for the conversion of nitrides into metals. Supporting this, the experimental findings reveal that the incorporation of rare earth oxides enables the controlled phase transition from nitride into metal, with the proportion adjustable by varying the amount of added rare earth. Thanks to the role of CeO2 decoration in promoting the reaction kinetics and fostering the formation of the genuine active phase, the optimized Ni3FeN/Ni3Fe/CeO2-5% nanoparticles heterostructure catalyst exhibits outstanding OER activity, achieving an overpotential of just 249mV at 10mAcm-2. This approach offers fresh perspectives for the conception of highly efficient heterogeneous OER catalysts, contributing a strategic avenue for advanced catalytic design in the field of energy conversion.

Multifunctional rare earth oxide/MBG composite microspheres as a carrier for bone tumor treatment

With the development of advanced composites, biomaterials have brought the field of tissue engineering and regeneration into a new era. Among them, composites of inorganic nonmetallic materials and rare earth oxides have unique structures and biochemical properties and have attracted widespread interest. In this work, rare earth oxides (CeO2)/inorganic nonmetallic materials (mesoporous bioactive glass, MBG) composite microspheres (CeO2/MBGs) were synthesized by a sol-gel method, and the in vitro biological effect of CeO2/MBGs was systematically studied. The filling of CeO2/MBGs in irregular bone tumor defects not only promoted osteogenic mineralization in MG63 cells but also had significant antibacterial effects on E. coli and S. aureus. CeO2 enters the MBG network as a network modifier, while doxorubicin (DOX) is adsorbed into the mesoporous structure through electrostatic interactions, which endows CeO2/MBGs with excellent bioactivity and controlled DOX release behavior. Moreover, the results of in vitro experiments showed that the proper addition of rare earth oxides had no toxic effect on normal cells, and the combination of rare earth oxides with antitumor drugs could slow the release of DOX through the use of an intelligent response design system, thus inducing the apoptosis of MG63 cells. This work suggested that combination chemotherapy and the design of a rare earth oxide/MBG composite microspheres may be potential therapeutic approaches for the postoperative repair of bone tumor defects. The construction of this multifunctional rare earth oxide/inorganic biocomposite provides a way to apply the material to bone tissue.

Effect of La2O3 on hardness, wear resistance and corrosion resistance of WC/Fe90 iron-based composite coatings

In this paper, WC/Fe90 iron-based composite coatings were prepared using plasma spraying technology. The influence of rare earth oxide La2O3 on the microstructure and properties of the composite coatings was studied through microstructural characterization, phase identification, microhardness, wear resistance, and corrosion resistance. The results showed that the composite coatings were mainly composed of α-Fe, M7C3, Fe-Cr, FexCy, and other reinforcing phases. The addition of La2O3 promoted the decomposition of WC particles and improved the uniformity of the coatings. When the La2O3 content reached 1.0 wt%, the hardness was the highest, reaching 885.481 HV, which was 10% higher than that of the untreated coatings. The addition of La2O3 increased the friction coefficient but still improved the wear resistance. Compared to the coatings without La2O3, the mass loss due to wear was reduced by approximately 40%. Moreover, the addition of La2O3 formed a passive film on the surface of the coatings, effectively preventing the penetration of Cl- ions and refining the grain structure of the coatings, significantly enhancing the corrosion resistance. When the La2O3 content was 1.0 wt%, the corrosion resistance of the coatings was the best.

Unlocking the performance evolution of GdBCO coated conductors irradiated by deuterium plasma

REBa2Cu3O7-δ (REBCO, RE: rare earth) coated conductors (CCs) can generate a powerful magnetic field and are optimal for sustaining the reaction in fusion devices. However, the REBCO CCs will inevitably be exposed to neutron radiation during device operation. Transmutation produces gas atoms such as hydrogen will affect their properties. In this paper, GdBCO CCs were irradiated by 20 eV deuterium plasma. It was found that the irradiation introduced smaller (2–4 nm) pinning sites that formed a mixed pinning landscape with rare earth oxides (tens of nanometres) in the pristine samples, leading to an improved vortex pinning. At an irradiation fluence of 5.0 × 1018 D cm−2, the J c values of the samples irradiated by deuterium can maintain the best enhancement of in-field performance at 4.2 K. Excess irradiation results in a decrease in J c, a broadening of the superconducting transition width, and an enhanced disorder in GdBCO. This study provides some valuable insights for potential changes in the properties of REBCO CCs irradiated in fusion devices.

Design and Implementation of Large-Scale Hard Rock AMD Dewatering and REE Production

To develop a domestic Rare Earth Elements (REE) supply chain the Hydraulic Preconcentrate (HPC) produced at the Horseshoe bend treatment plant (HSB) was evaluated as a potential source for feedstock. After the clarifiers were flipped to the desired pH set points, a total of 24 Geobags were repeatedly filled and allowed to passively dewater. The Geobags evaluated were comprised of a mix of Woven, Non-woven, and Capillary Channel Fiber (CCF). The bags were constructed with either a composite of woven and nonwoven or only woven geotextile. Half of the bags of both types also included “fins” made of CCF to evaluate their impact on dewatering. Column Filtration Tests (CFTs) were performed onsite to provide laboratory value for hydraulic conductivity. Throughout their dewatering, the geobags were sampled to determine their rate of dewatering. Influent samples from HSB were also tested to produce a Specific Gravity (Gs), via pycnometer testing and Grain Size Distribution (GSD), via sieve and hydrometer analysis. The dewatering ability of the geobags was high regardless of bag material with a mean total solids percentage of approximately 40% across all samples after only one month of dewatering. The GSD performed on the HPC is gap graded with most particles having a diameter of approximately 0.5-0.05mm. Hydraulic conductivity values for the filter cakes during Column Filtration Testing ranged from 0.5 to 2.5 meters/day. This data will help to guide development of future large-scale HPC dewatering and the parametric design of an REE oxide production plant at the HSB site.

Trace detection of SF6 gas decomposition component H2S based on Pr6O11-In2O3

Sulfur hexafluoride (SF6) from Gas Insulated Switchgear (GIS) will decompose and produce hydrogen sulfide (H2S) in the event of equipment failure. Therefore, the detection of H2S can determine whether the equipment has malfunctioned. Due to the low concentration of the SF6 decomposition product H2S and its application in industrial environments, sensors must have a low detection limit and rapid response time. Considering that the oxides of rare earth elements can improve the sensing characteristics, praseodymium oxide (Pr6O11)-indium oxide (In2O3) was prepared. The impact of Pr6O11 doping on In2O3 was investigated through characterization methods. To validate its feasibility for use in GIS, the best sensor (F3) exhibits good sensing characteristics for H2S in the SF6 and air ambient. The responses to 10 parts per million (ppm) H2S at 190°C were 146.6 in SF6 and 190.8 in air. In SF6 ambient, the F3 sensor demonstrated a low detection limit (50 parts per billion (ppb)). The good sensing characteristics are attributed to the doping of rare earth elements, which induces an increase in the proportion of defect oxygen and accelerate the chemical reaction. The sensing characteristics of the material can be attributed to the doping of Pr6O11 and the electronic effect. This study provides a novel approach for detecting H2S generated from SF6 decomposition.

Static and dynamic strain-driven photoluminescence tuning in rare-earth doped perovskite oxide thin films

Recently, there have been significant interest in the wide potential of photoluminescence (PL) response of rare-earth doped perovskite oxide thin films in the field of optoelectronics. This work reports an effective method to modulate the PL properties of 0.8 mol%Sm3+-doped BaTiO3 (BTO:Sm) thin films through static and dynamic strain. BTO:Sm films were epitaxially grown on LaAlO3 (LAO), 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT), MgO, and Mica single-crystal substrates by pulsed laser deposition technique. Compared with the BTO:Sm/PMN-PT heterostructure which experiences minimal lattice mismatch effect, the PL intensity of BTO:Sm/LAO and BTO:Sm/MgO is enhanced by 818.1% and 1014.7%, respectively, due to static tensile/compressive strain (-0.429% and 0.461%) during the epitaxial growth process. In the flexible BTO:Sm/Mica heterostructure, dynamic strain is introduced through mechanical bending. Compared with the unbent state, the u-type and n-type bending modes increase the relative changes in PL intensity (ΔI/I) by 599.0% and 768.5%, respectively. Particularly, BTO:Sm/Mica also exhibits a remarkable optical transmittance exceeding 75% (500–2500 nm). The enhancement of PL intensity is closely related to the adjustment of lattice strain, which changes the crystal field strength of the BTO:Sm and the radiative transition probability. This work provides valuable insights for designing future optoelectronic devices and environmental monitoring equipment. It has the potential to advance photonics and sensor technologies, paving the way for innovation and exploration in these fields.

Investigation on improving the comprehensive performance of environmental barrier coating materials by high-entropy multiphase design

It is difficult to obtain a single-phase environmental barrier coating material that simultaneously offers the advantages of low thermal conductivity, a suitable coefficient of thermal expansion, and excellent corrosion resistance. Herein, to synthesize the advantages of single-phase materials, we have developed an effective approach for the design of high-entropy multiphase ceramics of rare earth oxides and silicates. Such a specific design approach is capable of making high-entropy RE2SiO5/RE2O3 and RE2SiO5/RE2Si2O7 (RE = Lu, Yb, Tm, Er, Ho, and Y) multiphase ceramics as two types of potential environmental barrier coating materials for Al2O3f/Al2O3 and SiCf/SiC ceramic matrix composites.

Humidity-resistant hydrogen sensors based on rare-earth-doped tin dioxide nanofibers with hydrophobic mesoporous silica sieve encapsulation

Air humidity is a major factor that degrades the performance and long-term stability of metal-oxide-semiconductor (MOS) based gas sensors. In this work, we propose an encapsulation strategy by coating a mesoporous silica molecular sieve (SBA-15) on rare earth doped tin oxide (RE-SnO2) nanofibers for humidity-resistant hydrogen detection. In this design, the hydrophobic SBA-15 sieve layer effectively blocks the water molecules without affecting hydrogen diffusion, while the RE dopant greatly improves the responsivity and lowers down the operating temperature of the sensors, As a result, the Er-SnO2/SBA-15 and Tb-SnO2/SBA-15 sensors respectively show the maximum response values of 27.71 and 33.68 (to 10 ppm hydrogen at 280 °C, 4.67 and 5.67 times that of the bare SnO2 ones, respectively), short response/recovery time (< 1.0 s / < 1.0 s), as well as a low limit of detection for hydrogen (200 ppb) and a good gas selectivity. Under the protection of the SBA-15 sieve layer, the response retention of the sensors is significantly improved when the humidity increases from 25% to 85% RH (Er-doping, from 38.8% to 60.0%; Tb-doping, form 25.6–57.8%). Besides, further analysis on enhancement mechanism of response indicates that the SBA-15 coating contribute about 1/3 of the response enhancements via its own hydrogen physical adsorption capacity and the induced oxygen vacancies during the calcination processes.

Performance degradation due to thermal cycling in soldered Faraday and SuperPower HTS tape stacks

Soldering stacks of high temperature superconducting (HTS) tapes results in a current carrying matrix with high electrical, thermal, and mechanical stability. In some applications, these tape stacks may be exposed to elevated temperatures during thermal heat cycles. Previous research on thermal degradation of high temperature superconductors has been performed with isolated crystals or individual HTS tapes, showing that oxygen-out diffusion from the rare-earth barium copper oxide (REBCO) results in a reduction of the superconducting performance. In this work, the performance of Pb37Sn63 soldered HTS tape stacks with thermal cycling to 170∘ C is quantified through determination of the critical current Ic , the n-value, the linear resistance R in the pre-transition region of the tape stack current–voltage (I–V) traces, and the diffusion coefficient D associated with oxygen-out diffusion. The effect of tape manufacturer and nickel electroplating were considered; three soldered stacks each of unplated Faraday, nickel electroplated Faraday, unplated SuperPower, and nickel electroplated SuperPower tapes were fabricated. Across 20–30 one hour thermal cycles, there are no significant differences in degradation profiles observed between the unplated and nickel electroplated tape stacks for a given manufacturer. There is however a marked difference in degradation profiles observed between the SuperPower and Faraday tape stacks. For the unplated and plated SuperPower tape stacks, the degradation in Ic generally follows the model to describe oxygen-out diffusion from the superconducting REBCO layer. Significantly less degradation is observed in the unplated and plated Faraday tape stacks, and in some sections Ic even increases slightly across cycles. Further, cases of increasing Ic accompanied with decreasing n are observed, a decoupling between the two parameters. Across all samples, the linear resistance was highest in current-redistribution regions near the leads. Consistent with the model of oxygen-out diffusion and the formation of an increasingly wide oxygen deficient layer in the REBCO, the linear resistance increased with cycle number.