Controllable fabrication of nitrogen-doped porous nanocarbons for high-performance supercapacitors via supramolecular modulation strategy

In the present work,we developed a micellar system of milk protein-surfactant(SDS)-graphene to prepare the graphene-based aerogels via hydrothermal and freeze-drying method,in which the novel surface-property of aerogels can be tuned with the decreasing of micellar size in the colloid systems resulting the improved specific surface area.The milk protein also severed as green and sustainable sources to introduce nitrogen heteroatoms into the aerogels.Subsequently,the aerogels were further graphitized and activated to fabricate N-doped porous nanocarbon at 600℃.The initial surface composition and structure of the aerogel,which was proved,has obvious impact on the final structure of the synthesized nanocarbon materials,and thus influence their electrochemical activity.The optimized nanocarbon materials(MGPC-5),with enhanced specific surface area,degree of graphitization,and nitrogen doping,exhibited excellent capacitance performance and stability in both three-electrode system(518.8 F/g at a current density of 0.1 A/g)and symmetrical electrode system(120.8 F/g at current density of 0.1 A/g and with^95%capacitance retention after 5000 cycles of charging and discharging at 3 A/g)in KOH.The assembled supercapacitor also shows ideal capacitive properties in series and parallel configurations.Tested with a stable 1.6 V windows in Li2SO4 electrolyte,the symmetric supercapacitor cell exhibits a high energy density up to 36.7 W h/kg.The present work provides a feasible fabrication method for high-performance supercapacitor based on graphene and biomass derived carbon,the proposed surfaceproperty regulation and supercapacitor performance improvement strategy may also shed light on other energy related materials or system.

Design and preliminary test of a 105/140 GHz dual-frequency MW-level gyrotron

A dual-frequency(105/140 GHz)MW-level continuous-wave gyrotron was developed for fusion application at Institute of Applied Electronics,China Academy of Engineering Physics.This gyrotron employs a cylindrical cavity working in the TE18,7 mode at 105 GHz and the TE24,9 mode at 140 GHz.A triode magnetron injection gun and a built-in quasi-optical mode converter were designed to operate at these two frequencies.For the proof-test phase,the gyrotron was equipped with a single-disk boron nitride window to achieve radio frequency output with a power of~500 k W for a short-pulse duration.In the preliminary short-pulse proof-test in the first quarter of2021,the dual-frequency gyrotron achieved output powers of 300 k W at 105 GHz and 540 k W at140 GHz,respectively,under 5 Hz 1 ms continuous pulse-burst operations.Power upgrade and pulse-width extension were hampered by the limitation of the high-voltage power supply and output window.This gyrotron design was preliminarily validated.

混合溶剂调控插层FeSe基超导体的层间距

近年来,通过湿化学方法探索合成新型插层FeSe基超导体一直是凝聚态物理的研究热点之一.本文中,我们利用溶剂热离子交换技术成功合成出两种FeSe衍生物:c轴晶胞参数为9.93Å的Li_(0.34)Se_(0.05)(EG)_(0.14)-FeSe和c轴晶胞参数为13.85Å的Li_(0.21)Se_(0.05)(EG)_(0.26)FeSe.通过调整反应溶剂可以调控以上两种FeSe衍生物的层间距.磁化率和电阻率测试表明它们的超导转变温度(Tc)均为30 K左右,似乎与FeSe层层间距的大小无关.与原始FeSe单晶相比,X射线光电子能谱结果显示FeSe层Fe的价态降低,这表明Tc的提高可能是由于电子掺杂效应引起的.我们的研究为探索合成插层铁基超导体提供了有价值的参考,并为在超导领域探索新型插层材料提供了新的可能性.

Electric-field-controlled superconductor–ferromagnetic insulator transition

Superconductivity beyond electron-phonon mechanism is always twisted with magnetism. Based on a new field-effect transistor with solid ion conductor as the gate dielectric(SIC-FET), we successfully achieve an electric-field-controlled phase transition between superconductor and ferromagnetic insulator in(Li,Fe)OHFeSe. A dome-shaped superconducting phase with optimal T_c of 43K is continuously tuned into a ferromagnetic insulating phase, which exhibits an electric-field-controlled quantum critical behavior. The origin of the ferromagnetism is ascribed to the order of the interstitial Fe ions expelled from the(Li,Fe)OH layers by gating-controlled Li injection. These surprising findings offer a unique platform to study the relationship between superconductivity and ferromagnetism in Fe-based superconductors. This work also demonstrates the superior performance of the SIC-FET in regulating physical properties of layered unconventional superconductors.

Magnetic-field enhanced high-thermoelectric performance in topological Dirac semimetal Cd3As2 crystal

Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit （ZT） in three-dimensional Dirac semimetal Cd3A 5 2 crystal. It is found that enhancement of power factor and reduction of thermal conductivity can be realized at the same time through magnetic field although magnetoresistivity is greatly increased. ZT can be highly enhanced from 0.17 to 1.1 by more than six times around 350 K under a perpendicular magnetic field of 7 T. The huge enhancement of ZT by magnetic field arises from the linear Dirac band with large Fermi velocity and the large electric thermal conductivity in CdsA 5 2. Our work paves a new way to greatly enhance the thermoelectric performance in the quantum topological materials.

Magnetic field-induced electronic phase transition in the Dirac semimetal state of black phosphorus under pressure

Different instabilities have been confirmed to exist in the three-dimensional(3D) electron gas when it is confined to the lowest Landau level in the extreme quantum limit. The recently discovered 3D topological semimetals offer a good platform to explore these phenomena due to the small sizes of their Fermi pockets, which means the quantum limit can be achieved at relatively low magnetic fields. In this work, we report the high-magnetic-field transport properties of the Dirac semimetal state in pressurized black phosphorus. Under applied hydrostatic pressure, the band structure of black phosphorus goes through an insulator-semimetal transition. In the high pressure topological semimetal phase, anomalous behaviors are observed on both magnetoresistance and Hall resistivity beyond the relatively low quantum limit field, which is demonstrated to indicate the emergence of an exotic electronic state hosting a density wave ordering. Our findings bring the first insight into the electronic interactions in black phosphorus under intense field.

Superconductivity in potassium and ammonia co-intercalated FeSe_(1-x)Te_x

The origin of the ～40 and ～30 K superconducting phases in the metal-intercalated FeSe superconductors is still unclear. We report the synthesis of K_(0.3)(NH_3)_y(FeSe_(1-x)Te_x)_2 and K_(0.6)(NH_3)_y(FeSe_(1-x)Te_x)_2 with x=0-0.6 by using the liquid ammonia method at room temperature. The superconducting transition temperature Tcof the former remains about 43 K for all the nominal Te content less than 0.3, while that of the latter is about 30 K and obviously decreases with Te doping. Superconductivity disappears for x ≥0.4 in both systems. Except for the different chemical pressure induced by substitution of Te for Se in both systems, we also observed distinct external pressure effect on superconductivity for both systems, with much more efficiency of suppressing Tcby external pressure in the former system. These dramatic differences of both chemical and external pressure effects on Tc between the ～30 and ～40 K superconducting phases revealed that the existence of the two superconducting phases can be ascribed to the moderate and negligible coupling between FeSe layers, respectively.

Structural and physical properties of the new layered transition metal material Na4Cu3TaAs4

We report the synthesis,structural and physical properties of a new layered transition metal arsenide Na4Cu3TaAs4.This material adopts the space groupⅠ√2 m,with lattice parameters of a=5.9101(3)?and c=13.8867(12)?.This structure contains two layers of Na sandwiched by antiPb O-type(Cu/Ta)As layers,similar to the"111"-type ironbased superconductor Na Fe As.The transition metal sites are occupied by 75%Cu and 25%Ta,with Ta forming a well-defined superstructure.Cu and Ta were determined to be+1 and+5 oxidation state respectively.The band structure of the Na4Cu3TaAs4 measured by angle resolved photoemission spectroscopy(ARPES)is in good agreement with the density functional theory(DFT)calculation.Both ARPES and resistivity measurement indicate that this material exhibits metallic behavior with p-type carriers.Magnetic susceptibility measurement shows that the material exhibits nearly T-independent diamagnetism.This new material extends the material system with anti-Pb O-type layers and offers a good playground to investigate this material system further.