Journal of Rare Earths最新文献

This work reports the synthesis, characterization, and energy focused applications of the novel lanthanides co-doped tantalum pentoxide hetero-system (Sm³⁺-Eu³⁺-Tm³⁺:Ta₂O₅). Ln³⁺-doped Ta₂O₅ express excellent opto-electronic features reflected by the narrow band gap energy of 3.87 eV. Different vibrations confirm the presence of Ta–O–Ta and Ta–O bonds. The synthesized system possesses orthorhombic geometry with 59.46 nm particle size. With the smoother and compact morphology, the synthesized material succeeds in augmenting the performance of different systems aimed at energy applications. Fully ambient perovskite solar cell device fabricated with the Ln³⁺-doped Ta₂O₅ as an electron transport layer excels in achieving an efficiency and fill factor of 14.17% and 76% under artificial sun. This device was marked by the negligible hysteresis behavior showing profound photovoltaic performance. The electrochemical activity of the Ln³⁺-doped Ta₂O₅ decorated electrode was evaluated for electrical charge storage potential with pseudocapacitive behavior. With the highest specific capacitance of 355.39 F/g and quicker ionic diffusion rate, the designed electrode excels conventionally used materials. Electro-catalysis of water with Ln³⁺-doped Ta₂O₅ material indicates its capacity for H₂ production with the lowest overpotential and Tafel slope values of 148 and 121.2 mV/dec, while the O₂ generation is comparatively lower. With the stable electrochemical output, this rare earth modified material has the potential to replace conventionally used environmentally perilous and costly materials.

The magnetic properties, magnetic phase transition and magnetocaloric effects (MCE) of Er₃Si₂C₂ compound were investigated based on theoretical calculations and experimental analysis. Based on the first principles calculations, the antiferromagnetic (AFM) ground state type in Er₃Si₂C₂ compound was predicted and its electronic structure was investigated. The experimental results show that Er₃Si₂C₂ compound is an AFM compound with the Néel temperature (T_N) of 7 K and undergoes a field-induced first-order magnetic phase transition from AFM to ferromagnetic (FM) under magnetic fields exceeding 0.6 T at 2 K. The magnetic transition process of Er₃Si₂C₂ compound was investigated and discussed. The values of the maximum magnetic entropy change (${-\Delta S}_M^{\max })$ and the refrigeration capacity (RC) are 17 J/(kg·K) and 193 J/kg under changing magnetic fields of 0–5 T, respectively. As a potential cryogenic magnetic refrigerant, the Er₃Si₂C₂ compound also provides an interesting research medium to study the magnetic phase transition process.

In perovskite EuTiO₃, the magnetic characteristics and magnetocaloric effect (MCE) can be flexibly regulated by converting the magnetism from antiferromagnetic to ferromagnetic. In the present work, a series of Eu(Ti,Nb,Mn)O₃ compounds, abbreviated as ETNMO for convenience of description, was fabricated and their crystallography, magnetism together with cryogenic magnetocaloric effects were systematically investigated. The crystallographic results demonstrate the cubic perovskite structure for all the compounds, with the space group of Pm3m. Two magnetic phase transitions are observed in these second-order phase transition (SOPT) materials. The joint substitution of elements Mn and Nb can considerably manipulate the magnetic phase transition process and magnetocaloric performance of the ETNMO compounds. As the Mn content increases, gradually widened –ΔS_M-T curves are obtained, and two peaks with a broad shoulder are observed in the –ΔS_M-T curves for Δμ₀H≤0–1 T. Under a field change of 0–5 T, the values of maximum magnetic entropy change (−Δ$S_M^{\text{max}}$) and refrigeration capacity (RC) are evaluated to be 34.7 J/(kg·K) and 364.9 J/kg for EuTi_0.8625Nb_0.0625Mn_0.075O₃, 27.8 J/(kg·K) and 367.6 J/kg for EuTi_0.8375Nb_0.0625Mn_0.1O₃, 23.2 J/(kg·K) and 369.2 J/kg for EuTi_0.8125Nb_0.0625Mn_0.125O₃, 17.1 J/(kg·K) and 357.6 J/kg for EuTi_0.7875Nb_0.0625Mn_0.15O₃, respectively. The considerable MCE parameters make the ETNMO compounds potential candidates for cryogenic magnetic refrigeration.

Phosphor-converted near-infrared light-emitting diodes (NIR pc-LEDs) are finding applications in various fields including food quality analysis, biomedical imaging, night vision, and biomedicine. The crucial factor in the development of NIR pc-LEDs devices lies in the advancement of high-performance broadband NIR phosphors. In this work, novel Cr³⁺-activated silicate phosphors NaRESi₃O₉ (RE = Y, Lu, Sc) are reported. This silicate has a special 3D network structure in which RE has four different sites, forming four octahedrons and providing suitable occupation sites for Cr³⁺. The phosphors demonstrate a wide emission spectrum ranging from 750 to 1450 nm when excited by light at 468 nm. The full width at half maximum (FWHM), which benefits from the presence of Cr³⁺ ions occupying multiple sites, is measured to be 203 nm. Notably, the strongest emission peak is observed at a longer wavelength of 984 nm compared to most other systems activated by Cr³⁺. The Na₃ScSi₃O₉ lattice provides a weak crystal field (Dq/B = 1.97) and weak phonon-photon coupling for Cr³⁺, and the integrated emission intensity of Na₃ScSi₃O₉:0.03Cr³⁺ is 4.66 times stronger than that of Na₃YSi₃O₉:0.03Cr³⁺.

Thermal barrier coatings (TBCs) materials with lowered thermal and oxygen ion conductivity can provide thermal and oxidative protection for high temperature hot-end components in aeronautical engines and gas turbines. The rare-earth tantalate RETaO₄ (RE = Dy, Gd and Sm) ceramics with monoclinic (m) phase were successfully synthesized via spark plasma sintering. Oxygen vacancies responsible for the thermal and oxygen ion conductivities of RETaO₄ were demonstrated by atomic-resolution energy dispersive X-ray and X-ray photoelectron spectroscopy. Among the three samples, DyTaO₄ has excellent oxygen/thermal barrier performance. Compared to the current service thermal barrier coating material ZrO₂-8 wt% Y₂O₃ (8 YSZ), DyTaO₄ has an ultra-low oxygen ion conductivity benefiting from low oxygen vacancy concentration and strong stretching force constants. The intrinsic thermal conductivity of DyTaO₄ is 68.2% less than that of 8 YSZ. Additionally, the thermal expansion rate curves indicate that the phase transformation does not happen from room temperature to 1200 °C. The above results demonstrate that high-growth rate thermally grown oxide can be retarded by creating dense DyTaO₄ coating with lowered thermal and oxygen ion conductivity.

Lanthanum doped nickel–cobalt nano ferrites with chemical formula Ni_0.5Co_0.5La_xFe_2–xO₄ (x = 0.05, 0.10, 0.15 and 0.20) were prepared using a simple sol–gel auto combustion method. The basic structural properties were determined by X-ray diffraction method and the formation of single phased spinel ferrite was confirmed. The crystalline size decreased from 25 to 11 nm and lattice parameter a increases with increase of La doping. The surface morphology of these ferrites was observed by field-emission scanning electron microscopy (FESEM) and agglomerated irregular grains are observed with increase of the rare earth element La doping. Energy-dispersive X-ray spectroscopy (EDX) result confirms the presence of the required elements. The Fourier transform infrared spectroscopy (FTIR) spectrum indicates the formation of the spinel ferrite structure with M−O bonds. Optical direct band measurements from ultraviolet–visible spectroscopy (UV-Vis) spectroscopy indicate that the direct band gap decreases from 1.39 to 1.19 eV for x = 0.05 to x = 0.15, then increases to 1.28 eV for x = 0.20. The room temperature magnetic properties of these ferrites were studied by a vibrating sample magnetometer (VSM). The enhanced saturation magnetization of 49.73 emu/g is observed for x = 0.10 and then saturation magnetizations are gradually decreased for x = 0.15 and x = 0.20. Interestingly the remanent magnetization and coercivity also follow the same trend.

Light emitting diode (LED) is the fourth generation lighting source, but it has some shortcomings such as complex chip packaging process and the unbalanced light color of phosphor in long-time application. In this study, a kind of Eu-terephthalic acid/Tb-sulfosalicylate/ZrO₂/ZnZrO₃ (Eu-PTA/Tb-SSA/ZrO₂/ZnZrO₃) phosphor with warm white light emission properties was prepared, and the warm white light LED (w-WLEDs) was successfully prepared by encapsulating Eu-PTA/Tb-SSA/ZrO₂/ZnZrO₃ phosphors together with 270 nm UV-chip. The ZrO₂/ZnZrO₃, Tb-SSA/ZrO₂/ZnZrO₃ and Eu-PTA/ZrO₂/ZnZrO₃ samples show blue emission, green emission and red emission under deep ultraviolet (UV, 270 nm) excitation, respectively. The Tb-SSA and Eu-PTA are co-doped into ZrO₂/ZnZrO₃ matrix with blue emission to achieve the warm white light emission, and the light color can be adjusted by controlling the doping amount of Eu³⁺ and Tb³⁺. Through the excitation method of single-component phosphor by the single chip, the complex chip packaging process of w-LED can be solved. By doping rare earth organic complexes into porous ZrO₂/ZnZrO₃ matrix, the problems of the light color unbalanced of phosphor and the low luminescence intensity of rare earth doped metal oxides composites can be solved.

With the increasing demand for non-contact fluorescence intensity ratio-based optical thermometry, novel phosphor materials with high-efficiency, dual-emitting centers, and differentiable temperature sensitivity are highly desired. In this work, rare earth Eu²⁺ ions were incorporated into CsCu₂I₃ microcrystals by solid-state reaction. Under a single UV excitation, the as-synthesized samples exhibit two emissions: 452 nm blue emission from the 5d→4f transition of Eu²⁺ and 582 nm yellow emission from self-trapped exciton emission of CsCu₂I₃. The photoluminescence quantum yield reaches to 50%. The dual-band emission of Eu²⁺-doped CsCu₂I₃ shows different temperature responses in the range of 260–360 K. Based on fluorescence intensity ratio technology, the maximum absolute sensitivity and relative sensitivity are 0.091 K^–1 (at 360 K) and 2.60%/K (at 260 K), respectively. These results suggest that Eu²⁺-doped CsCu₂I₃ could be a good candidate for highly sensitive optical thermometer.

At present, in-situ leaching of weathered crust elution-deposited rare earth ores (WCE-DREOs) encounter with problems such as long leaching cycles, slow infiltration rate and low product purity. In order to solve the above problems, the conventional leaching agent ammonium sulfate ((NH₄)₂SO₄) was compounded with polymeric surfactant polyethyleneimine (PEI) to form a composite leaching agent. The effects of leaching temperature, PEI concentration, flow rate and pH on leaching kinetics and permeability of rare earths (RE) and aluminum (Al) in orebody were studied. It is found that with temperature increasing, the time required to reach leaching equilibrium for both RE and Al is shortened, the apparent activation energies of RE and Al are 14.79 and 13.45 kJ/mol, respectively, and the leaching processes are in accordance with the outer diffusion control. When the concentrations of (NH₄)₂SO₄ and PEI in the composite leaching agent are 2.0 wt% and 0.4 wt%, the time required to reach leaching equilibrium for RE and Al is about 50% shorter than that using (NH₄)₂SO₄ alone, and the leaching efficiencies of RE are slightly higher than that of Al. Properly increasing the temperature and flow rate of the composite leaching agent can improve the leaching efficiencies of RE and Al, but pH has neglected effects on the leaching efficiencies of RE. At PEI concentrations below 0.4 wt%, the addition of PEI promotes the leaching of RE and Al. In column leaching studies of the WCE-DREO, the addition of 0.4 wt% PEI to the traditional leaching agent (NH₄)₂SO₄ has no impact on the leaching efficiencies of RE. However, it can significantly increase the infiltration rate of WCE-DREO, shortening the leaching time per 10 mL effluent from about 30 min for (NH₄)₂SO₄ leaching system to 20 min for the composite leaching system. The leaching time is shortened by one-third, and the leaching cost is reduced, which can provide theoretical guidance for the development and commercial implementation of novel composite leaching agent for WCE-DREO.

The use of high-permittivity (high-k) thin films as gate dielectrics is essential in the development of low-power electronics. In this work, rare-earth thulium oxide (Tm₂O₃) thin films were prepared by a facile solution process and annealed at various temperatures from 400 to 700 °C. The evolution of the physical and dielectric properties of Tm₂O₃ thin film with annealing temperature was investigated. It is demonstrated that the Tm₂O₃ thin film annealed at 600 °C exhibits the optimal performance, including a low leakage current of 3 × 10⁻¹⁰ A/cm², a large areal capacitance of 250 nF/cm² at 100 Hz, and a high permittivity value of 14.2. The Tm₂O₃ thin film as a gate insulator was integrated into the thin film transistor (TFT) employing In₂O₃-based semiconducting channels. The In₂O₃ TFT with 600 °C-annealed Tm₂O₃ dielectric exhibits the superior performance, with a high I_on/I_off of 1.65 × 10⁷, a small subthreshold swing (SS) value of 0.2 V/dec, a V_TH of +1.8 V, and a mobility of 1.68 cm²/(V·s). Furthermore, an inverter constructed by connecting the TFT with a resistor exhibits full-swing characteristics. This work provides a facile and appealing method for preparing the high-k Tm₂O₃ thin films as alternative gate dielectrics with the potential for use in low-power electronics and logic circuit applications.