Rare Metals最新文献

As one of the alloy-type lithium-ion electrodes, Bi has outstanding application prospects for large volume capacity (3800 mAh·cm⁻³) and high electronic conductivity (1.4 × 10⁷ S·m⁻¹). However, the fast-charging performance is hindered by significant volume expansion (> 218%) and a low rate of phase diffusion. To overcome these two problems, an N-doped carbon nanoflower coating layer was elaborately in-situ reconstructed on a multiple-wall Bi microsphere by hydrothermal methods and subsequent calcination in this study. The carbon nanoflowers greatly increase specific surface area (40.0 m²·g⁻¹) and alleviate the volume expansion (130%). In addition, the incorporation of N-doped carbon nanoflowers leads to a gradual enhancement in the Li adsorption energy of Bi during the process of lithium insertion and improves the electrical conductivity. Therefore, the contribution rate of pseudo-capacitance reached 87.5% at the scan rate of 0.8 mV·s⁻¹, and the Li-ion diffusion coefficient ((D_{text{Li}^{+}})) was calculated in the range of 10⁻¹⁰ to 10⁻¹² cm²·s⁻¹. The Bi@CNFs anode provided a high specific volumetric capacity of 2117.0 mAh·cm⁻³ at 5C and a high capacity retention ratio of 93.2% after 800 cycles. The Bi@CNFs//LiFePO₄ full cell also displayed a stable capacity of 113.9 mAh·g⁻¹ and energy density of 296.1 Wh·kg⁻¹ after 100 cycles with a Coulombic efficiency of 97.6%. The mechanism of fast-charging lithium storage was verified by distribution of relaxation time analysis and density functional theory calculation. This paper provides a new strategy to increase the pseudo-capacitance and reduce the volume expansion for the preparation of alloy-type fast-charging electrodes.

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Lutetium aluminum garnet doped with cerium (LuAG:Ce) thin films have been identified as a promising material for high-power laser-driven lighting applications. In this study, spray pyrolysis we employed to fabricate LuAG:Ce films on sapphire substrates and the impact of film thickness on thermal management and light emission efficiency was investigated. Our results show that, regardless of thickness, LuAG:Ce films exhibit impressive internal quantum efficiencies (IQE) exceeding 83.2% and external quantum efficiencies (EQE) surpassing 56.4%, with minimal alteration of luminescent color. Notably, thinner films facilitate more efficient heat dissipation to the underlying sapphire substrate, resulting in superior thermal management and outstanding luminous performance under high-power laser excitation. Specifically, the thinnest LuAG:Ce film (15.79 μm) exhibited rapid thermal stabilization (~ 130 °C within 30 s) and maintained stability during continuous irradiation lasting 30 min, with a corresponding decrease in luminous flux to 87.9% of its initial value within the first 60 s. This film also demonstrated relatively high and stable conversion efficiency and luminous efficiency, achieving higher saturation thresholds (15 W·mm⁻²) and luminous flux (1070 lm). In contrast, thicker films exhibited a shift in the saturation point toward lower power densities. These findings provide valuable insights for the practical implementation of LuAG:Ce films in advanced lighting technologies.

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For the development of high-performance metallic glasses, enhancing their stability against viscous flow and crystallization is a primary objective. Vapor deposition or prolonged annealing is an effective method to improve glass stability, shown by increased glass transition temperature (T_g) and crystallization temperature (T_x). This contributes to the development of ultra-stable metallic glasses. Herein, we demonstrate that modulating the quenching temperature can also produce ultra-stable metallic glasses, as evidenced by an increase in T_x of 17–30 K in Cu-based metallic glasses. By modulating the quenching temperature, separated primary phases, secondary phases, and even nano-oxides can be obtained in the metallic glasses. Notably, metastable phases such as Cu-rich precipitates arising from secondary phase separation play a crucial role in enhancing glass stability. However, the enhancement of the stability of the glass has only a negligible effect on its mechanical properties. This study implies that different melt thermodynamic states generated by liquid–liquid separation and transition collectively determine the frozen-in glass structure. The results of this study will be helpful for the development of ultra-stable bulk glasses.

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Additive engineering significantly enhances the photovoltaic performance of perovskite solar cells (PSCs). The atomistic and mechanistic origins of these improvements need further investigation to fully understand the physicochemical interactions of additives with the perovskite lattice, band structure, and charge carriers. Herein, how additives of cellulose triacetate (CTA) improve the photovoltaic performance and stability of perovskite solar cells (PSCs) is shown. These improvements are found to stem from the formation of hydrogen bonds between CTA molecules and organic cations. The Kelvin probe force microscopy results show that contact potential difference variation under dark and light conditions increases from 79.68 to 141.24 mV by doping CTA, indicating enhanced separation of electron–hole pairs in perovskite. The piezoresponse force microscopy (PFM) tests indicate that CTA additives reduce the PFM amplitude by approximately 50 pm under dark and light conditions and inhibit flipping from antiferroelectric domains to ferroelectric domains. Moreover, the CTA additives regulate the charge distribution within the PbI₆ octahedron and bind organic ions through hydrogen bonding, forming a compact film structure. These findings not only improve the long-term stability of organic–inorganic hybrid perovskites (OIHPs), but also pave the way for developing novel strategies for large-scale PSCs.

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Transition metal carbonates (TMCs) hold great potential as high-performance electrodes for alkali metal-ion batteries, owing to multiple-ion storage mechanisms involving conversion process and electrocatalytic reaction. However, they still suffer from inferior electronic conductivity and volume variation during delithiation/lithiation. Heterostructure and heteroatoms doping offer immense promise in enhancing reaction kinetics and structural integrity, which unfortunately have not been achieved in TMCs. Herein, a unique TMCs heterostructure with Ni-doped MnCO₃ as “core” and Mn-doped NiCO₃ as “shell”, which is wrapped by graphene (NM@MN/RGO), is achieved by cations differentiation strategy. The formation process for core–shell NM@MN consists of epitaxial growth of NiCO₃ from MnCO₃ and synchronously mutual doping, owing to the similar crystal structures but different solubility product constant/formation energy of MnCO₃ and NiCO₃. In-situ electrochemical impedance spectroscopy, galvanostatic intermittent titration technique, differential capacity versus voltage plots, theoretical calculation and kinetic analysis reveal the superior electrochemical activity of the NM@MN/RGO to MnCO₃/RGO. The NM@MN/RGO shows excellent lithium storage properties (1013.4 mAh·g⁻¹ at 0.1 A·g⁻¹ and 760 mAh·g⁻¹ after 1000 cycles at 2 A·g⁻¹) and potassium storage properties (capacity decay rate of 0.114 mAh·g⁻¹ per cycle). This work proposes an efficient cation differentiation strategy for constructing advanced TMC electrodes.

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Although lithium-ion batteries are widely recognized as a new generation of energy storage devices, their large-scale application is severely hampered by their low energy density and restricted cyclic stability. Herein, an ingenious dual-modified interface, where the F-doping and fluorocarbon coating co-existed on Li[Ni_0.8Co_0.1Mn_0.1]O₂ surface, is rationally constructed to elevate its energy density and structural stability attributed to F⁻ grafting between the bulk material and the coating utilizing a robust super-conformal fluorocarbon coating structural framework and more stable F-doped system under high charge/discharge cut-off voltage. In comparison with a single carbon-coated modified Li[Ni_0.8Co_0.1Mn_0.1]O₂, the dual-modified sample overcomes the fatal disadvantage of carbon coating stripping during long-period cycles ascribed to the “TM-F-multifunctional coating” connector which firmly combines the bulk material with the coating with a strong interaction force, exhibiting a more stable-reversible structure and excellent comprehensive electrochemical performance under high cut-off voltage. Concomitantly, the F-transition metal bonds with stronger bond energies improve its structural reversibility during the processes of charge/discharge under high voltage. Furthermore, the fluorocarbon coating enhances its charge transfer ability and effectively restrains the interfacial side reactions. Additionally, the climbing nudged elastic band methodology is used to calculate the diffusion energy barrier of lithium-ions in the matrix material, which confirms the fundamental reason for its superior lithium-ion diffusion ability. The high pseudocapacitance contribution ratio is perfectly explained by calculating the adsorption capacity on the surface of the dual-modified sample. Consequently, experiments and theoretical calculations unequivocally confirm its distinguished electrochemical properties under high cut-off voltage.

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In this work, a novel microwave absorbing material (MAM) made of a pseudo-binary of Sr₂TiMoO₆–Al₂O₃ (STM) is proposed first. The MAMs labeled as STM X (X = 60, 70, 80 and 100, respectively), in which X is the initial weight percent of Sr₂TiMoO₆, were synthesized using the solid-state reaction method. Compared with STM100, some equilibrium phases, including SrTiO₃, Mo, Sr₈(Al₁₂O₂₄)(MoO₄)₂ and a few undefined ones, are presented in the composites as evidenced by X-ray diffraction results and scanning electron microscopy due to the chemical reaction between Sr₂TiMoO₆ and Al₂O₃ component. Besides conductance loss, heterogeneous interfaces between various equilibrium phases introduce interfacial polarization, which causes an enhancement of dissipation for the incident electromagnetic wave. Among the synthesized samples, STM80 presents the best microwave absorbing properties. It has a minimum reflection loss (RL_min) of − 26 dB and an effective absorbing bandwidth up to 2.7 GHz when the thickness is only 1 mm. This indicates that STM80 is a new type of microwave absorbing material with strong absorption and ultrathin thickness.

A novel mechanical stirring-assisted double-melt in-situ reaction casting process was developed to prepare Cu-1TiB₂ (wt%) composites. The effects of preparation parameters (melting reaction temperature, stirring rate and stirring time) on the microstructure and properties of Cu-1TiB₂ composites were investigated. The melt viscosity and particle motion during stirring process were analyzed. The strong turbulence and shear effects generated by mechanical stirring in the melt not only significantly improve the particle distribution but also contribute to adequate in-situ reactions and precise control of the chemical composition. The optimal preparation parameters were 1200 °C, a stirring rate of 100 r·min⁻¹ and a stirring time of 1 min. Combined with the cold rolling process, the tensile strength, elongation and electrical conductivity of the composite reached 475 MPa, 6.0% and 88.4% IACS, respectively, which were significantly better than the composite prepared by manual stirring. The good plasticity is attributed to the uniform distribution of TiB₂ particles, effectively retarding the crack propagation. The dispersion of particles promotes heterogeneous nucleation of Cu matrix and inhibits grain growth. On the other hand, dispersed particles contribute to grain shear fracture and dislocation multiplication during cold deformation. Therefore, the composite achieves higher dislocation strengthening and grain boundary strengthening.

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Bi-based transition metal oxide (Bi₅Nb₃O₁₅) has become a highly hopeful anode material for lithium-ion batteries (LIBs) due to its large theoretical capacity and affordable availability. Unfortunately, poor conductivity, as well as volume expansion and pulverization during repeated reactions will result in bad specific capacity and inferior cycling stability. Hence, Bi₅Nb₃O₁₅@C anode materials for LIBs were successfully synthesized using sucrose as a carbon source through a two-step high-temperature solid-phase method. Physical characterizations and electrochemical tests suggest that the highly conductive carbon shell derived from sucrose provides fast channels for Li⁺ transport and greatly reduces the charge transfer resistance. Moreover, ex situ scanning electron microscopy (SEM) indicates that the presence of carbon effectively suppresses the aggregation and pulverization of Bi₅Nb₃O₁₅ particles in the reaction process, effectively ensuring the integrity of Bi₅Nb₃O₁₅ particles. Benefiting from the above merits, the C-modified Bi₅Nb₃O₁₅, especially Bi₅Nb₃O₁₅@8%C (BNO-C3), holds charge capacity of 414.6 and 281.4 mAh·g⁻¹ at 0.1 and 0.5 A·g⁻¹, respectively. Additionally, the high specific capacity of 379.5 mAh·g⁻¹ is much greater than that of the bare Bi₅Nb₃O₁₅ (only 158.7 mAh·g⁻¹) after 200 cycles. Importantly, cyclic voltammetry (CV) combined with ex situ X-ray diffraction (XRD) confirms the conversion reaction between Bi₅Nb₃O₁₅ and Bi during cycling. This work provides a method for suppressing volume expansion and pulverization during cycling of Bi-based transition metal oxides and constructing high-performance LIBs anode materials.

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