Dielectric constant characterization of large-area substrates in millimeter wave band

A possibility of the dielectric constant measurement for substrates with permittivity=+i without an essential restriction on their area has been shown experimentally. The method uses frequency measurement of quasioptical dielectric resonator (QDR) with two slots oriented along the QDR radius with a dielectric substrate in one of them. Taking QDR of teflon in 8mm waveband as an example it is found that measurable values of can ran up 15 _q , where _q is the QDR material permittivity. Absolute error of the measurements is determined by an accuracy with which the permittivity of calibrated (standard) samples is known. The relative measuring error is determined by the accuracy of the QDR frequency measurement and can be quite a small. As an example the method is demonstrated forLaAlO ₃ single crystals.     

Liberating the Electrolyte via In Situ Conversion of an Amide,Sulfonate-Containing Monomer Precursor for High-Temperature Graphite/NCM Batteries

High-temperature (HT) operation and storage performance of Li-ion batteries (LIBs) are essential for applications in electric vehicles, grid storage, or defense missions. Unfortunately, severe capacity fading is witnessed due to growing instability of the electrode/electrolyte interphase at HT. Herein, the study liberates the electrolyte from the task of film-formation. Instead, it takes advantage of the favorable solid-electrolyte interphase (SEI)-forming functional groups by priorly anchoring them on graphite surface. Specifically, via molecular design, unsaturated CC bond, together with amide and sulfonate groups, are concurrently involved, namely the lithium-2-acrylamido-2-methyl-1-propanesulfonate (Li-AMPS). Upon electrochemical cycle, the unsaturated CC bond in Li-AMPS turns into a radical that induces polymerization between CC bonds to construct a polymeric network. The presence of amide and sulfonate groups endows the SEI with nitrogen, sulfur-based reduction products OSO₂Li and Li₃N, etc. As such, the designed interphase makes the use of propylene carbonate-based electrolyte possible. By assembling full cells with the modified graphite and LiNi_0.5Co_0.2Mn_0.3O₂ (cathode loading of ≈18.5 mg cm⁻²), the capacity retention of the full cell has increased from 53.2% (with pristine graphite) to 77.8% after 300 cycles under 60 °C. A 2 Ah, 265 Wh kg⁻¹ pouch cell is also able to operate for 200 cycles at an extreme temperature of 80 °C with the modified graphite.     

Solvent-Free Electrolyte for High-Temperature Rechargeable Lithium Metal Batteries

The formation of lithiophobic inorganic solid electrolyte interphase (SEI) on Li anode and cathode electrolyte interphase (CEI) on the cathode is beneficial for high-voltage Li metal batteries. However, in most liquid electrolytes, the decomposition of organic solvents inevitably forms organic components in the SEI and CEI. In addition, organic solvents often pose substantial safety risks due to their high volatility and flammability. Herein, an organic-solvent-free eutectic electrolyte based on low-melting alkali perfluorinated-sulfonimide salts is reported. The exclusive anion reduction on Li anode surface results in an inorganic, LiF-rich SEI with high capability to suppress Li dendrite, as evidenced by the high Li plating/stripping CE of 99.4% at 0.5  mA cm⁻² and 1.0 mAh cm⁻², and 200-cycle lifespan of full LiNi_0.8Co_0.15Al_0.05O₂ (2.0 mAh cm⁻²) || Li (20 µm) cells at 80 °C. The proposed eutectic electrolyte is promising for ultrasafe and high-energy Li metal batteries.     

Ultrathin Titanium Carbide (MXene) Films for High-Temperature Thermal Camouflage

Thermal camouflage has attracted increasing attention owing to the rapid development of infrared (IR) surveillance technologies. Various materials and systems have been developed to date, but the realization of high-temperature thermal camouflage using ultrathin film/coating remains a great challenge; this is of great significance, especially for IR stealth in military equipment. This work demonstrates a series of ultrathin Ti₃C₂T_x MXene films (as low as 1 µm) with superior high-temperature indoor/outdoor thermal camouflage performance: wide camouflage temperature range (from below −10 °C to over 500 °C), large reduction in radiation temperature (exceeding 300 °C for objects with temperatures over 500 °C), long-term high-temperature or fire stability, multifunctionality including disguised Joule heating capability, and high electromagnetic interference shielding efficiency. The superior high-temperature thermal camouflage performance of the ultrathin MXene film is attributed to its low mid-IR emissivity (0.19), which is comparable to that of stainless steel but far below that of other 2D nanomaterials, such as graphene. The multifunctional ultrathin MXene films prepared through simple vacuum-assisted filtration provide a feasible method for efficient high-temperature thermal camouflage using ultrathin films, demonstrating the great promise of MXene materials for thermal camouflage, IR stealth, counter-surveillance, and security protection.     

Hydrothermal “Disproportionation” of Biomass into Oriented Carbon Microsphere Anode and 3D Porous Carbon Cathode for Potassium Ion Hybrid Capacitor

The comprehensive utilization of biomass to obtain energy-storage carbonaceous materials with special microstructures is of great significance. Herein, a universal method is proposed to fabricate oriented carbon microspheres (OCMSs) and 3D porous carbon (3DPC) block at the same time via high-temperature hydrothermal “disproportionation” of biomass including but not limited to basswood, pinus sylvestris, red walnut, beech, bamboo, and sorghum straw. Through nuclear magnetic resonance, gas chromatography mass spectrometry, as well as various morphologic and structural characterizations, it is demonstrated that OCMS with (002) orientation originates from the carbonization of organic matters produced by the successive decomposition of hemicellulose, cellulose, and lignin during the high-temperature hydrothermal process, while the 3DPC blocks exhibit abundant sp³ defects and micropores with a surface area of 855.12 m² g⁻¹ due to the constant loss of organic components from basswood blocks. As a result, the OCMS anode exhibits a high capacity of 201.1 mA h g⁻¹ at 2000 mA g⁻¹ after 2000 cycles, 3DPC cathode delivers a capacity of 95.7 mA h g⁻¹ at 1.0 A g⁻¹ after 5000 cycles. Remarkably, the as-assembled OCMS//3DPC potassium ion hybrid capacitor exhibits an energy of 140.7 Wh kg⁻¹ at 643.8 W kg⁻¹, with a long cycle life over 8500 cycles.     

SiC MOSFET栅极电参数退化机理及耦合关系

栅极一直是SiC MOSFET可靠性研究的重点,栅极老化过程中电参数之间的耦合关系对栅极可靠性研究有至关重要的作用。为此,搭建了能够同时监测阈值电压和栅极漏电流的高温栅偏(HTGB)试验平台。研究了HTGB下阈值电压和漏电流的退化趋势和影响,基于氧化层注入电荷量深入分析了两者之间的耦合关系。结果表明,热应力对载流子隧穿影响较为明显,对陷阱捕获的载流子影响相对较小,而场强则对两者均具有显著的影响。此外,提出了减小阈值电压漂移对SiC MOSFET均流特性影响的方法,指出了栅极漏电流下降现象的本质是栅极陷阱充电,并给出了栅极老化过程中漏电流失效基准值选取的方法。该研究结果为深入理解SiC MOSFET的栅极失效机理提供了理论指导。     

Static spin susceptibility in the <Emphasis Type="Italic">t</Emphasis>-<Emphasis Type="Italic">J</Emphasis> model

Based on the equation-of-motion method for the relaxation function expressed in terms of Hubbard operators, we evaluate the static spin susceptibility and correlation functions in the two-dimensional t-J model. We show that at zero temperature, a long-range antiferromagnetic order exists in the lattice for the hole concentration δ < δ_c ≃ 0.018. The calculated dependences of the spin susceptibility and correlation length on the temperature and hole concentration agree qualitatively with the experiment. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 152, No. 3, pp. 538–550, September, 2007.     

Heterogeneous flame propagation in the self-propagating high-temperature synthesis (SHS) process in multi-layer foils for three components system: Theory and experimental comparisons

A theory for the heterogeneous flame propagation in the self-propagating high-temperature synthesis (SHS) process that proceeds in multi-layer foils, consisting of alternating layers of constituents, has been extended to three-component systems, by describing a premixed mode of bulk flame propagation supported by a non-premixed reaction that proceeds at the layer surface of a constituent with higher melting-point. The formulation allows for finite rate Arrhenius reaction at the layer surface, temperature-sensitive Arrhenius mass diffusion in the liquid phase, and existence of intermixed region between constituent layers. It is confirmed that thickness ratio of the constituent layers is related to mixture ratio and that thickness ratio of the intermixed region and the constituent layer is related to degree of dilution. Results show that the burning velocity first increases, reaches the maximum, and then decreases rapidly, with decreasing alloy layer thickness, that the decrease in the burning velocity can be attributed to the increase in the substance in the intermixed region between constituent layers, playing a role of diluent, and that the increase in the activity and/or amount of the less-active component in the alloy suppresses the burning velocity. A preheating effect for the burning velocity is also predicted. In experimental comparisons, it has been demonstrated that the analytical results agree with available experimental data in the literature, indicating that the present formulation has captured the essential features of the adiabatic, heterogeneous SHS process.     

On high-temperature superconductivity

We consider electron-phonon interaction models for the case of strong coupling as well as the well-known Hubbard model. We write out the asymptotics as the number of electrons tends to infinity; this allows us to determine the temperature of the superconducting-to-normal state phase transition and the jump in the heat capacity. Translated fromMatematicheskie Zametki, Vol. 66, No. 5, pp. 706–722, November, 1999.     

高T_c超导体YBCO磁通钉扎的计算机模拟研究

临界电流密度Jc是影响高温超导体在强电领域应用的一个重要参数,在实际应用中,特别在外加磁场下,临界电流密度与超导材料的磁通钉扎性质密切相关.因此,磁通钉扎一直是高温超导体研究中的一个重要领域.由于高温超导体磁通钉扎力密度Fp的标度律存在,本文根据D.Dew-Hughes总结的钉扎力函数,主要存在两种主要作用类型(正常相和△K).我们将D.Dew-HugBes给出的钉扎力密度Fp标度函数改进为一个简化的具有物理意义的函数表达式.结合文献中已有的实验数据,我们对YBcO进行了计算机模拟,确定了它的磁通钉扎类型,模拟的研究结果与实际情况比较吻合.