Dynamic hysteresis relation for guiding poling condition of high-performance KNN-based ceramics

Currently, the poling condition selection for KNN-based ceramics still requires an inefficient and time-consuming empirical attempt process owing to the lack of relevant theoretical guidance. Herein, the dynamic hysteresis relations and polarization reversal behavior of KNNS-BNZ-Ba ceramics were explored to guide the poling condition selection. The scaling relations of the loop area <A> on electric field amplitude E₀ and frequency f were determined. The three-stages E₀-dependent scaling relation and two-stages f-dependent scaling relation (at the high electric field) were clarified. The relevance between hysteresis dynamics and poling process was analyzed. It suggested that the optimal poling field amplitude corresponds to the terminal electric field of non-180° domain switching. Meanwhile, excellent electromechanical properties (d₃₃ = 408 pC/N, k_p = 51%, and k₃₃ = 69%) were achieved in KNNS-BNZ-Ba ceramics. Our work provides a scientific theory to guide the poling technology in KNN-based ceramics by exploring the polarization reversal kinetics.     

Effects of Al2O3 and LiAlO2 Co-coating on electrochemical properties of LiNi0.8Co0.1Mn0.1O2 cathode materials

Lithium-ion batteries are widely used in aerospace, power vehicles, portable electronic devices and other fields because of their environmental friendliness, rechargeable cycle and high energy density. The nickel-cobalt-manganese ternary materials with high nickel has high specific discharge capacity and is regarded as one of the most promising cathode materials. However, with the increase of the number of cycles, the cycle performance becomes worse and the specific capacity decays sharply. In this work, Al₂O₃ and LiAlO₂ were coated on the surface of NCM811 by combining ball milling mixing and solid-phase synthesis to prepare the AL-NCM811 cathode material. The coating thickness formed by Al₂O₃ and LiAlO₂ was 10–70 nm, which effectively improves the cycle stability and rate performance of NCM811 material. When charged and discharged at 0.1C, the first discharge specific capacity and capacity retention rate after 100 cycles of 0.5AL-NCM811 were 196.26 mAh/g and 96.47%, respectively, while those of NCM811 were only 193.78 mAh/g and 72.18%, respectively. When the current density was 5.0C, the discharge specific capacity of 0.5AL-NCM811(139.16 mAh/g) was 55.368 mAh/g higher than that of NCM811(83.80 mAh/g).     

One-pot synthesis of hexagonal NaLuF4:Yb,Er microcrystals with enhanced upconversion emission and high production yield

In this work,monodisperse β-NaLuF₄:Yb,Er microcrystals with intense upconversion emission were synthesized via a modified hydrothermal method.With the increase of reactant concentration,their production yield is increased obviously,and the upconversion emission intensity in β-NaLuF₄:Yb,Er microcrystals is also enhanced significantly.The luminescence enhancement should be attributed to minimal internal OH defects,validated by a combination of analytical X-ray diffraction(XRD...     

Giant Energy Storage Density with Antiferroelectric-Like Properties in BNT-Based Ceramics via Phase Structure Engineering

Driven by the information industry, advanced electronic devices require dielectric materials which combine both excellent energy storage properties and high temperature stability. These requirements hold the most promise for ceramic capacitors. Among these, the modulated Bi_0.5Na_0.5TiO₃ (BNT)-based ceramics can demonstrate favorable energy storage properties with antiferroelectric-like properties, simultaneously, attaching superior temperature stability resulted from the high Curie temperature. Inspired by the above properties, a strategy is proposed to modulate antiferroelectric-like properties via introducing Ca_0.7La_0.2TiO₃ (CLT) into Bi_0.395Na_0.325Sr_0.245TiO₃ (BNST) ((1−x)BNST-xCLT, x = 0.10, 0.15, 0.20, 0.25). Combining both orthorhombic phase and defect dipole designs successfully achieve antiferroelectric-like properties in BNST-CLT ceramics. The results illustrate that 0.8BNST-0.2CLT presents superior recoverable energy storage density ≈8.3 J cm⁻³ with the ideal η ≈ 80% at 660 kV cm⁻¹. Structural characterizations demonstrate that there is the intermediate modulated phase with the coexistence of the antiferroelectric and ferroelectric phases. In addition, in situ temperature measurements prove that BNST-CLT ceramics exhibit favorable temperature stability over a wide temperature range. The present work illustrates that BNT-based ceramics with antiferroelectric-like properties can effectively enhance the energy storage performance, which provides novel perspectives for the subsequent development of advanced pulsed capacitors.     

Near room temperature tunability of thermochromic VO2 thin films prepared via thermal oxidation method,influence of CO2:N2 gas flux ratios

In this study, we have investigated the thermochromic characterizations of VO₂ thin films synthesized by the thermal oxidation method. The oxidation process of a DC sputtered metallic vanadium layer on glass substrates, at 450 °C for 1 h, was carried out in the presence of CO₂:N₂ gases with different flux ratios of 30:70, 40:60, 50:50, 60:40, and 70:30, respectively. Using CO₂, as the oxidizing gas, provides an easy control route for obtaining the VO₂ phase among various vanadium oxide phases. The layers were characterized by FESEM, XRD & Raman spectra, sheet resistance vs. temperature (20–120 °C), and UV–Vis–NIR spectra at 25 and 90 °C. The XRD and Raman spectra confirmed all prepared layers have a VO₂ polycrystalline structure in monoclinic phase. We found among the studied samples CN30-70 and CN50-50 having desirable optical characteristics of peak visible transmittance of about 55%, with low transition temperatures (T_cr) of ∼42 and 31 °C, and also relatively high amounts of ΔT_1700nm, ΔT_sol and T_lum,av are good candidates for thermochromic smart windows, both from optical properties and economical fabrication method points of view.     

Preparation,mechanical properties and long-term ablation resistance of Cf/SiBCN–ZrB2 composites

The C_f/SiBCN–ZrB₂ composites were prepared by dipping and winding combined with reactive hot pressing. The flexural strength and fracture toughness reached 261 MPa and 11.96 MPa • m^1/2, respectively, through continuous carbon fibers debonding, pulling and bridging mechanisms. Excellent mechanical properties ensured that the C_f/SiBCN–ZrB₂ composites remained intact after exposure to a plasma flame with a heat flux of 9.37 MW/m² for 300 s, with the mass and linear ablation rates of 1.78 mg/s, 1.01 μm/s, respectively. The excellent ablation resistance was due to the formation of dense oxide layers separating the matrix from the plasma flame. The SiO₂ formed in the low-temperature areas away from the center was the main ablation-resistant barrier, while the ZrO₂/SiO₂ double oxide layer formed in the high-temperature region at the center was the major ablation-resistant barrier.     

Comparative analysis of associated cost of nuclear hydrogen production using IAEA hydrogen cost estimation program

The interest in non-electric applications of nuclear energy is rising ranging from hydrogen production, district heating, seawater desalination, and various industrial applications to provide long-term answers for a variety of energy issues that both present and future generations will confront. Hydrogen is a dynamic fuel that can be used across all industrial sectors to lower carbon intensity. This study, therefore, aims at estimating the cost of nuclear hydrogen production from some light water reactors using International Atomic Energy Agency (IAEA) Hydrogen Calculator (HydCalc) program and comparing the result with similar existing studies conducted by other scholars using the Hydrogen Economic Evaluation Program (HEEP) program. The study employs six existing Light Water Reactors (LWRs) comprised of Korea Advanced Power Reactor 1400 MW electricity (APR1400), Russian VVER-1200, Davis-Besse Nuclear Power Plant in Ohio, Prairie Island NPP in Minnesota, Nine Mile Point NPP in New York, and Arizona Public Service's Palo Verde NPP to evaluate the Levelized cost of nuclear hydrogen production. Estimation of hydrogen demand was performed without carbon dioxide (CO₂) tax since nuclear power has zero CO₂ emission. The Levelized costs obtained using IAEA HydCalc and HEEP Programme were compared as follows; APR1400 cost are 2.6$/kg and 3.18$/kg, VVER1200 cost are 3.8$/kg and 3.44$/kg; Exelon cost are 1.7$/kg and 4.85$/kg; Davis Besse cost are 3.9$/kg and 3.09$/kg; Parlo Verde cost are 3.5$/kg and 4.77$/kg; Xcel Energy cost are 3.63$/kg and 0.69$/kg. The cost of hydrogen production using HEEP for Xcel Energy's Prairie Island NPP is 0.69 $/kg. This is because the reactor utilizes High Temperature Steam Electrolysis, method of hydrogen production, while the other methods employs Low Temperature Electrolysis. The results shows that the final price of the hydrogen for each reactor technology depends not only on the production method but also on the cost of the nuclear power plant and the production rate of the hydrogen plant.     

Continuous preparation of composition-controllable Y–Ni alloy in LiF–YF3–Y2O3 molten salt

The Y–Ni alloy is a primary precursor for the preparation of high-performance La–Y–Ni-based hydrogen storage materials. However, it cannot be produced continuously at low cost, which limits the wide popularization and application of La–Y–Ni-based materials. In this paper, this problem was solved perfectly using electrochemical reduction of Y₂O₃ in the LiF-YF₃ system. It is found that the reversible reduction from Y³⁺ to Y on the W electrode takes only one step, namely a significant soluble–soluble reaction controlled by Y³⁺ diffusion throughout the melt. Four typical signals of square wave voltammetry (SWV) corresponding to different kinds of Y–Ni intermetallic compounds are observed in LiF−YF₃ and LiF–YF₃–Y₂O₃ melts, and reduction potential can become positive with the addition of Y₂O₃, probably because of the formation of more complexes in the melts. Homogeneous Y–Ni alloy samples were produced continuously and prepared via galvanostatic electrolysis by using bargain-price raw material (Y₂O₃) and setting the current density at 10 A/cm² on the nickel electrode, before they were collected into a bottom receiver. A series of analyses including scanning electron microscopy-energy idspersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS), demonstrate that concentration of yttrium in Y–Ni alloy is adjustable within the wide range of 44 wt% to 72 wt% by fine-tuning the electrolysis temperature (875–1060 °C) in the LiF-YF₃ system to ensure the optimal hydrogen storage performance and economic efficiency of La–Y–Ni-based hydrogen-storage materials.     

Investigating the effect of pH on the growth of coprecipitated Ni0.8Co0.1Mn0.1(OH)2 agglomerates as precursors of cathode materials for Li-ion batteries

Understanding how the morphology and microstructure of secondary particles are affected by pH is essential to design spherical and dense hydroxide aggregates as precursors of high-performance cathode materials for lithium-ion batteries. To investigate the interplay between thermodynamic reaction conditions and the physicochemical properties of precursors, a chemical equilibrium model is used to describe the evolution of metal ammonia complexes. Furthermore, the formation and growth of aggregates are studied by monitoring the changes in surface morphologies and crystal structures of precursors at different reaction times. As the pH value varied, two notable phenomena occurred during crystal growth: the fast growth of grains in the early stage as the pH decreased and the layered growth of grains in the later stage with increased pH values. Such findings could be explained from the following two perspectives. First, the decrease in pH causes a significant increase in the complex ion concentration, thereby facilitating the growth of crystals along the [010] direction. Second, an increase in pH generally accelerates deprotonation of the crystal surface, thus strengthening the adsorption of complex ions on the crystal surface and promoting layer-by-layer growth of primary grains along the [001] direction.