Implications of Nitrogen Doping on Geometrical and Electronic Structure of the Fullerene Dimers

Because of its unsaturated bonds, C₆₀ is susceptible to polymerize into dimers. The implications of nitrogen doping on the geometrical and electronic structure of C₆₀ dimers have been ambiguous for years. A quarter‐century after the discovery of azafullerene dimer (C₅₉N)₂, we reported its single crystallographic structure in 2019. Herein, the unambiguous crystal structure information of (C₅₉N)₂ is elucidated specifically, revealing that the inter‐cage C—C single bond length of (C₅₉N)₂ is comparable with that of an ordinary C(sp³)‐C(sp³) single bond, and that the most stable conformer of (C₅₉N)₂ is gauche‐conformer with a dihedral angle of 66°. To amend the structural deviations, geometrical structure of (C₅₉N)₂ is optimized by a B3LYP‐D3BJ function, which is proved to be more consistent with its single crystal structure than those by the commonly used B3LYP function. Moreover, the calculation method is also suitable for other representative fullerene dimers, such as (C₆₀)₂ and its divalent anion. Additionally, the dissociation of (C₅₉N)₂ at 473 K under mass spectrometric conditions suggests the inter‐cage C—C bond is relatively weaker than an ordinary C—C single bond, which can be explained by the interaction energies of inter‐cages.     

Visible light induced tandem reactions: An efficient one pot strategy for constructing quinazolinones using in-situ formed aldehydes under photocatalyst-free and room-temperature conditions

A facile tandem route has been developed for constructing quinazolinones from various aminobenzamides and in-situ generated aldehydes. Visible light was found to play a dual role: first oxidizes the alcohol to the aldehyde and then facilitates its cyclization with o-substituted aniline. Furthermore, alcohols are perfect alternatives to aldehydes because they are greener, more available, more economical, more stable, and less toxic than aldehydes. The first reaction step continuously provides material for the second step, which effectively reduces loss through volatilization, oxidation, and polymerization of the aldehyde, while avoiding its toxicity. A variety of quinazolinones can be prepared in the presence of visible light without any additional photocatalyst. The developed synthesis protocol proceeds with the merits of mild conditions, broad substrate scope, operational simplicity, and high atom efficiency, with an eco-energy source under metal-free, photocatalyst-free, and ambient conditions.     

Determination of Thermal History by Photoluminescence of Core‐Shelled Quantum Dots Going Through Heating Events

A kind of novel thermal history nanosensors are theoretically designed and experimentally demonstrated to permanently record thermal events. The photoluminescence (PL) spectrum of core‐shelled quantum dots (QDs) CdSe/ZnS irreversibly shifts with heating histories (temperature and duration) of thermal events. The induced PL shift of the QDs CdSe/ZnS is employed to permanently record thermal histories. We further model a kind of thermal history nanosensor based on the thermal‐induced phenomena of core‐shelled QDs to permanently record thermal histories at microscale and demonstrate to reconstruct temperature and duration of heating events simultaneously from PL spectra of the QDs. The physical mechanism of the sensors is discussed.     

微液滴在不同能量表面上润湿状态的分子动力学模拟

微小液滴在不同能量表面上的润湿状态对于准确预测非均相核化速率和揭示界面效应影响液滴增长微观机理具有重要意义. 通过分子动力学模拟, 研究了纳米级液滴在不同能量表面上的铺展过程和润湿形态. 结果表明, 固液界面自由能随固液作用强度增加而增加, 并呈现不同液滴铺展速率和润湿特性. 固液作用强度小于1.6的低能表面呈现疏水特征, 继续增强固液作用强度时表面变为亲水, 而固液作用强度大于3.5的高能表面上液体呈完全润湿特征. 受微尺度条件下非连续、非对称作用力影响, 微液滴气液界面存在明显波动, 呈现与宏观液滴不同的界面特征. 统计意义下, 微小液滴在不同能量表面上铺展后仍可以形成特定接触角, 该接触角随固液作用强度增加而线性减小, 模拟结果与经典润湿理论计算获得的结果呈现相似变化趋势. 模拟结果从分子尺度为核化理论中的毛细假设提供了理论支持, 揭示了液滴气液界面和接触角的波动现象, 为核化速率理论预测结果和实验测定结果之间的差异提供了定性解释.     

胡克定律探究实验装置的改进

利用自制胡克定律探究实验装置对新课标中"探究弹簧弹力与形变量之间的关系"实验进行了改进,改进后的实验装置能直接在坐标纸上绘出弹簧弹力与形变量之间的对应关系点,通过拟合可得到F-x曲线,求拟合直线的斜率可求出被测弹簧的劲度系数.改进后的实验装置得出的实验结果与新课标教材中描述的现象一致.     

Extended s-wave pairing symmetry on the triangular lattice heavy fermion system

We investigate the pairing symmetry of the Kondo-Heisenberg model on triangular lattice, which is believed to capture the core competition of Kondo screening and local magnetic exchange interaction in heavy electron compounds. On the dominant background of the heavy fermion state, the introduction of the Heisenberg antiferromagnetic interaction (J _H ) leads to superconducting pairing instability. Depending on the strength of the interactions, it is found that the pairing symmetry favours an extended s-wave for small J _H and high conduction electron density but a chiral \(d_{x^2 - y^2 } + id_{xy}\)-wave for large J _H and low conduction electron density, which provides a phase diagram of pairing symmetry from the calculations of the ground-state energy. The transition between these two pairing symmetries is found to be first-order. Furthermore, we also analyze the phase diagram from the pairing strengths and find that the phase diagram obtained is qualitatively consistent with that based on the ground-state energy. In addition, we propose an effective single-band BCS Hamiltonian, which is able to describe the low-energy thermodynamic behaviors of the heavy fermion superconducting states. These results further deepen the understanding of the antiferromagnetic interaction which results in a geometric frustration for the model studied. Our work may provide a possible scenario to understand the pairing symmetry of the heavy fermion superconductivity, which is one of active issues in very recent years.     

Thermal stability of nanocrystalline ε-Fe2O3

Thermal behavior of highly crystalline ε-Fe₂O₃ nanoparticles of different apparent crystallite sizes was characterized using thermogravimetry, differential thermal analysis, and analysis of evolved gas by mass spectrometry. Phase composition of the samples was monitored ex situ by X-ray powder diffraction. The results show that the thermal stability of this metastable iron oxide polymorph decreases with increasing particle size. For the particle diameter of 19(2) nm, the transformation temperature was equal to 794(5) °C, while for 28(2) nm only 755(10) °C. Surface of the nanoparticles contained adsorbed water and carbon dioxide. Elimination of these species proceeds in two steps. Water is removed at temperatures below 200 °C and CO₂ in the temperature range between 200 and 450 °C.     

A novel ε-HNIW-based insensitive high explosive incorporated with reduced graphene oxide

A novel ε-HNIW-based explosive formula with low sensitive and high energy was developed by systematically researching the processes of recrystallization, granularity gradation, and coating of ε-HNIW and option of energetic deterrents. The grain size and morphology of HNIW crystals were modified by solvent/antisolvent recrystallization. The ε-HNIW particles were graded and coated by emulsion polymerization method with 551 glue. The binder reduced the mechanical sensitivity of ε-HNIW significantly and showed good compatibility with ε-HNIW, but also weakened the decomposition enthalpy. With the purpose of developing new energetic deterrents in insensitive high explosive formulations, novel carbon materials graphene oxide (GO) and reduced graphene oxide (rGO) were prepared and incorporated in plastic-bonded explosive (PBX) formulations. For comparison, the effects of conventional deterrent flake graphite were also involved. It turned out that the mechanical sensitivities of ε-HNIW/551 glue have all reduced to some extent with the incorporation of graphite, GO, and rGO. Flake graphite induced the PBX decompose earlier slightly and weaken the heat output. The addition of GO resulted in noticeable antedating decomposition of ε-HNIW/551 glue although remarkably increased the decomposition heat. The formula of ε-HNIW/551 glue/rGO provided a moderate growth in decomposition heat and best thermal stability. In slow cook-off tests, the formulas of ε-HNIW/551 glue and ε-HNIW/551 glue/rGO showed good thermal stability and might be qualified to apply safely under 200 °C. Comprehensively considering the mechanical sensitivity, thermals stability, energy performance, and practical application, ε-HNIW/551 glue/rGO is supposed to be an eligible insensitive high-energy PBX formula.     

Improved electrochemical performance of LiNi0.5Mn1.5O4 as cathode of lithium ion battery by Co and Cr co-doping

Three samples, LiNi_0.5Mn_1.5O₄, LiNi_0.4Mn_1.4Co_0.2O₄, and LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄, were prepared by sol–gel method and characterized by powder X-ray diffraction, Fourier transformed infrared spectroscope, scanning electron microscopy, Brunauer–Emmett–Teller surface area, four-probe resistance, cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge test. It is found that the co-doped sample LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄ exhibits an improved performance compared with the Co-doped sample LiNi_0.4Mn_1.4Co_0.2O₄ and the undoped sample LiNi_0.5Mn_1.5O₄, especially at elevated temperature. At 25 °C, the discharge capacity of LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄ is 130 mAh g^?1 at 0.1 C and 103 mAh g^?1 at 10 C. At an elevated temperature (55 °C), its 1 C discharge capacity is 136 mAh g^?1 and maintains 95.6 % of its initial capacity after 100 cycles. Compared with the reported results of LiNi_0.4Mn_1.4Co_0.2O₄ and LiNi_0.475Mn_1.475Co_0.05O₄, the co-doped sample LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄, with least content of Co, 0.05, possesses not only the high C-rate capacity but also the structural stability. The mechanism on the electrochemical performance improvement of LiNi_0.5Mn_1.5O₄ by the co-doping was discussed.     

Synthesis and characterization of PrBaCo2 − x Ni x O5 + δ cathodes for intermediate temperature SOFCs

Nickel-substituted layered perovskite PrBaCo_{2 ? x} Ni _x O_{5 + δ} (PBCN) powders with various proportions of nickel (x?=?0, 0.1, 0.2, and 0.3, abbreviated as PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively) are investigated as potential cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) based on the yttria-stabilized zirconia (YSZ) electrolyte. It is found that PBCN-1 has the highest electrical conductivity of 1,397 S cm^?1 at 400 °C. Substitution of Co by Ni decreases the thermal expansion coefficient (TEC) clearly. The average TEC at the temperature range of 35–900 °C decreases from 22.8?×?10^?6 K^?1 for PBCN-0 to 18.9?×?10^?6 K^?1 for PBCN-3. The polarization resistances of PBCN samples on YSZ electrolyte at 800 °C are 0.053, 0.048, 0.052, and 0.042 Ω cm² for PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively. The single fuel cell with the configuration of PBCN-3/YSZ/Pt delivers the highest power densities of 100, 185, 360, 495, and 660 mW cm^?2 at 600, 650, 700, 750, and 800 °C, respectively.