Theoretical study on the improvement of the doping efficiency of Al in 4H-SiC by co-doping group-IVB elements

The p-type doping efficiency of 4H silicon carbide (4H-SiC) is rather low due to the large ionization energies of p-type dopants. Such an issue impedes the exploration of the full advantage of 4H-SiC for semiconductor devices. In this study, we show that co-doping group-IVB elements effectively decreases the ionization energy of the most widely used p-type dopant, i.e., aluminum (Al), through the defect-level repulsion between the energy levels of group-IVB elements and that of Al in 4H-SiC. Among group-IVB elements Ti has the most prominent effectiveness. Ti decreases the ionization energy of Al by nearly 50%, leading to a value as low as ~0.13 eV. As a result, the ionization rate of Al with Ti co-doping is up to ~5 times larger than that without co-doping at room temperature when the doping concentration is up to 10¹⁸ cm^-3. This work may encourage the experimental co-doping of group-IVB elements such as Ti and Al to significantly improve the p-type doping efficiency of 4H-SiC.     

钒的冲击熔化原位X射线衍射测量研究

高压结构与相变研究对理解物质在极端压缩条件下的性质变化和动力学响应行为具有重要的科学价值,然而部分过渡金属的动/静高压熔化线差异一直是多年来悬而未解的科学难题.其中动、静高压固-液相界幅值差异最大的是第五副族金属,以钒最为反常,至今仍缺乏自洽的物理认识和理解.本文采用高能脉冲激光驱动的瞬态X射线衍射诊断技术,对冲击压缩下钒的熔化特性进行了研究,首次获取了冲击压缩下钒在200 GPa范围内的晶体结构响应随压力变化的衍射图谱.研究发现,冲击压力为155 GPa时,钒仍保持固态bcc相;至约190 GPa时转变为液态.这一结果否定了早期确定的静压熔化线,与最新的冲击熔化线及高温高压相图符合,为钒高压熔化线的统一认识提供了新的微观实验证据.本工作亦可推广至其他材料熔化特性的研究工作中.     

Low-temperature Li-S batteries enabled by all amorphous con version process of organosulfur cathode

The high degree of crystallinity of discharging in termediates of Li-S batteries(Li₂S₂/Li₂S)causes a severe capacity attenuation at low temperatures.Herein,a sulfur-rich polymer is fabricated,which enables all the discharging in termediates to exist in an amorphous state without long-range order,promoti ng the substantial conversion of discharging intermediates and enhancing Li-S batteries'performance at low temperatures greatly.This cathode material exhibits excellent performance both at room and low temperatures.Even under an extremely low temperature(-40℃),the discharge capacity can remain 67% of that at room temperature.Besides,in-situ UV/Vis spectroscopy and density functional theory calculations reveal that this organosulfur cathode undergoes a new mechanism during discharge.Li₂S₆ and Li₂S₃ are the primary discharging intermediates that are quite different from conventional Li-S batteries.These results provide a new directi on for a broader range of applications of Li-S batteries.     

Electrostatic self-assembly of MXene and edge-rich CoAl layered double hydroxide on molecular-scale with superhigh volumetric performances

It is highly desirable to design and synthesize two-dimensional nanostructured electrode materials with high electrical conductivity,large electrolyte-accessible surface area and more exposed active sites for energy storage applications.Herein,MXene/Co Al-LDH heterostructure has been prepared through electrostatic ordered hetero-assembly of monolayer MXene and edge-rich Co Al-LDH nanosheets in a faceto-face manner on molecular-scale for supercapacitor applications.Benefiting from the unique structure,strong interfacial interaction and synergistic effects between MXene and Co Al-LDH nanosheets,the electrical conductivity and exposed electrolyte-accessible active sites are significantly enhanced.The asprepared MXene/Co Al-LDH-80%(ML-80)film exhibits high volumetric capacity of 2472 C cm-3 in 3 M KOH electrolyte with high rate capability of 70.6%at 20 A g-1.Notably,to the best of our knowledge,the high volumetric capacity is the highest among other previously reported values for supercapacitors in aqueous electrolytes.Furthermore,our asymmetric supercapacitor device fabricated with ML-80 and MXene/graphene composite as cathode and anode,respectively,exhibits impressive volumetric energy density of 85.4 Wh L-1 with impressive cycling stability of 94.4%retention ratio after 30,000 continuous charge/discharge cycles.     

A new class of ion-ion interaction: Z-bond

The hydrogen-bond interactions in ionic liquids have been simply described by the conventional hydrogen-bond model of A–H···B. Coupling with the strong electrostatic force, however, hydrogen bond between the cation and anion shows particular features in the geometric, energetic, electronic, and dynamic aspects, which is inherently different from that of the conventional hydrogen bond. A general model could be expressed as +[A–H···B]-, in which A and B represent heavy atoms and "+" and "–" represent the charges of the cation containing A atom and anion containing B atom, respectively. Because the structure shows a "zig-zag" motif, this coupling interaction is defined here as the Z-bond. The new model could be generally used to describe the interactions in ionic liquids, as well as bio-systems involved in ions, ionic reaction, and ionic materials.     

Thieno[3,4-c]pyrrole-4,6-dione based copolymers for high performance organic solar cells and organic field effect transistors

Donor-acceptor type copolymers have wide applications in organic field-effect transistors and organic photovoltaic devices. Thieno[3,4-c]pyrrole-4,6-dione (TPD), as an electron-withdrawing unit, has been widely used in D-A type copolymers recently. Till now, the highest power conversion efficiency and mobility of TPD-based copolymers are over 8% and 1.0 cm² V^-1 s^-1 respectively. In this review, the recent progress of TPD-based copolymers in organic solar cells and organic transistors is summarized.     

LiF and LiNO3 as synergistic additives for PEO-PVDF/LLZTO-based composite electrolyte towards high-voltage lithium batteries with dualinterfaces stability

Solid electrolytes with desirable properties such as high ionic conductivity,wide electrochemical stable window,and suitable mechanical strength,and stable electrode-electrolyte interfaces on both cathode and anode side are essential for high-voltage all-solid-state lithium batteries(ASSLBs)to achieve excellent cycle stability.In this work,a novel strategy of using LiF and LiNO₃ as synergistic additives to boost the performance of PEO-PVDF/LLZTO-based composite solid electrolytes(CSEs)is developed,which also promotes the assembled high-voltage ASSLBs with dual-interfaces stability characteristic.Specifically,LiF as an inactive additive can increase the electrochemical stability of the CSE under high cut-off voltage,and improve the high-voltage compatibility between cathode and CSE,thus leading to a stable cathode/CSE interface.LiNO₃ as an active additive can lead to an enhanced ionic conductivity of CSE due to the increased free-mobile Li+and ensure a stable CSE/Li interface by forming stable solid electrolyte interphase(SEI)on Li anode surface.Benefiting from the improved performance of CSE and stable dualinterfaces,the assembled NCM622/9[PEO₁₅-LiTFSI]-PVDF-15 LLZTO-2 LiF-3 LiNO₃/Li cell delivers a high rate capacity of 102.1 mAh g^-1 at 1.0 C and a high capacity retention of 77.4%after 200 cycles at 0.5 C,which are much higher than those of the ASSLB assembled with additive-free CSE,with only 60.0 mAh g^-1 and 52.0%,respectively.Furthermore,novel cycle test modes of resting for 5 h at different charge states after every 5 cycles are designed to investigate the high-voltage compatibility between cathode and CSE,and the results suggest that LiF additive can actually improve the high-voltage compatibility of cathode and CSE.All the obtained results confirm that the strategy of using synergistic additives in CSE is an effective way to achieve high-voltage ASSLBs with dual-interfaces stability.     

Melt Crystallization of Poly(butylene 2,6-naphthalate)

Poly(butylene 2,6-naphthalate)(PBN)is a crystallizable linear polyester containing a rigid naphthalene unit and flexible methylene spacer in the chemical repeat unit.Polymeric materials made of PBN exhibit excellent anti-abrasion and low friction properties,superior chemical resista nee,and outstanding gas barrier characteristics.Many of the properties rely on the presence of crystals and the formatio n of a semicrystalline morphology.To develop specific crystal structures and morphologies during cooling the melt,precise information about the melt-crystallization process is required.This review article summarizes the current knowledge about the temperature-controlled crystal polymorphism of PBN.At rather low supercooling of the melt,with decreasi ng crystal I izatio n temperature,0'-and a-crystals grow directly from the melt and organize in largely different spherulitic superstructures.Formation of a-crystals at high supercooling may also proceed via intermediate formation of a transient monotropic liquid crystalline structure,then yielding a non-spherulitic semicrystalline morphology.Crystallization of PBN is rather fast since its suppression requires cooling the melt at a rate higher than 6000 K-s_1.For this reason,investigation of the two-step crystallization process at low temperatu res requires application of sophisticated experimental tools.These in elude temperatureresolved X-ray scattering techniques using fast detectors and synchrotron-based X-rays and fast scanning chip calorimetry.Fast scanning chip calorimetry allows freezi ng the transie nt liquid-crystalline structure before its con version into a-crystals,by fast cooling to below its glass transition temperature.Subsequent an alysis using polarized-light optical microscopy reveals its texture and X-ray scatteri ng con firms the smectic arrangement of the mesogens.The combination of a large variety of experimental techniques allows obtaining a complete picture about crystallization of PBN in the entire range of melt-supercoolings down to the glass transition,including quantitative data about the crystallization kinetics,semicrystalline morphologies at the micrometer length scale,as well as nanoscale X-ray structure information.     

Boron-doping induced lithophilic transition of graphene for dendrite-free lithium growth

Li metal,possessing advantages of high theoretical specific capacity and low electrochemical potential,is regarded as the most promising anode material for next-generation batteries.However,despite decades of intensive research,its practical application is still hindered by safety hazard and low Coulombic efficiency,which is primarily caused by dendritic Li deposition.To address this issue,restraining dendrite growth at the nucleation stage is deemed as the most effective method.By utilizing the difference of electronegativity between boron atoms and carbon atoms,carbon atoms around boron atoms in boron-doped graphene(BG)turn into lithiophilic sites,which can enhance the adsorption capacity to Li⁺at the nucleation stage.Consequently,an ultralow overpotential of 10 mV at a current density of 0.5 mA/cm² and a high average Coulombic efficiency of 98.54%over more than 140 cycles with an areal capacity of 2 mAh/cm² at a current density of 1 m A/cm² were achieved.BG-Li|LiFePO₄ full cells delivered a long lifespan of480 cycles at 0.5 C and excellent rate capability.This work provides a novel method for rational design of dendrite-free Li metal batteries by regulating nucleation process.     

Synthesis and luminescent properties of a silylated-terpyridine derivative and its metalated complexes in solutions and self-assembled monolayers

A silylated-terpyridine(Si TPy) derivative was newly synthesized and reacted with various transition metal ions in the solutions and self-assembled monolayers(SAMs).Composition and morphology of the SAMs were characterized by using absorption spectra,X-ray photoelectron spectra and atomic force microscope.The silylated-TPy compound gave off a luminescent emission at about 456 nm,which slightly shifted to 452 nm in the Zn2+-Si TPy and Fe2+-Si TPy metalated complexes.The absorbed energy can be further transferred to lanthanide ions(Tb3+and Eu3+) to give off the typical emissions of the lanthanide complexes together with an emission of the silylated-TPy at about 363 nm.