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Multi-mode vertical-cavity surface-emitting lasers (VCSELs) with improved bandwidth and noise performance have been developed for 100 Gb/s data communication links over multi-mode fiber. The VCSELs are designed for the peak multi-mode fiber bandwidth at 850 nm to maximize reach. The small-signal modulation 3dB bandwidth exceeds 25 GHz over temperature and relative intensity noise is below −145 dB/Hz. Transmission of 53.125 GBd PAM-4 signals over a 100m OM4 fiber is demonstrated by using equalization on both transmit and receive side. The transmitter and dispersion eye closure quaternary (TDECQ) penalty is below 4 dB for VCSEL operating up to 75°C.

A tapering vertical dimension technique (TVDT) is proposed for the quasi-periodic folded-waveguide traveling wave tube (FW-TWT) to improve the bandwidth and efficiency. The dispersion characteristics for the concentric arc FW-TWT with the TVDT are analyzed and discussed. When the power of input signal is set as 1 W and the initial beam voltage (current) is set as 4900 V (0.15 A), the peak output power of the proposed FW-TWT with the TVDT can reach 100.9 W at 88 GHz. Accordingly, the corresponding peak electron efficiency is 13.7%. Furthermore, the 3-dB bandwidth (fractional bandwidth) can reach 17 GHz (18.78%) from 82 to 99 GHz, where the output signal is steady and the corresponding frequency spectrum is quite clean. In addition, the performance of the concentric arc FW-TWT with the TVDT is also compared with that of the other quasi-periodic FW-TWTs.

A concentric arc meander line slow wave structure (CAML-SWS) for low voltage, high efficiency, and wide bandwidth ${V}$ -band traveling wave tube (TWT) with dual sheet beam (DSB) is proposed. As a nonperiodic SWS, the CAML-SWS is utilized for obtaining low operational voltage and wide bandwidth performance. The DSB is employed for efficiency enhancement. The simulated reflection loss ( $\vert ~{S} _{\mathbf {11}} \vert$ ) is smaller than −30 dB covering the whole ${V}$ -band. The 3-D particle-in-cell (PIC) simulation predicts that the output power of the proposed TWT can reach 58.6 W at 60 GHz, when the voltage is set at 940 V and the current of each sheet beam is 0.1 A. The corresponding peak gain and electron efficiency is 19.6 dB and 31.1% at 60 GHz, respectively. Furthermore, the 3-dB gain bandwidth is about 17 GHz from 51 to 68 GHz, where the output signal is steady and the frequency spectrums are quite clean.

Applied a non-radical non-oriented Slack Based Measure (SBM) model of Data Envelopment Analysis (DEA) to measure the linkage efficiency between the two sectors from 2009 to 2016. The paper analyzes the current situation of manufacturing and logistics efficiency, presents a way to improve the linkage efficiency of manufacturing and logistics industry, and using Tobit regression to analyze the environmental factors that affect the linkage efficiency. The results show that: Totality, the two industries in the three northeast provinces show a steady development trend in the period from 2009 to 2016, but the development of the two industries in northeast China is still insufficient. Unexpected pollutant output is the main reason for the decline of manufacturing efficiency in the regions. The redundancy of input factors is the main reason that affects the efficiency decline of the logistics industry. The results of Tobit regression analysis show that the investment of science and technology and opening to the outside world have a positive influence on the efficiency of the two industries, and government consumption has a negative effect on the efficiency of the two industries. This is to correctly understand and grasp the status of two industry linkage development in three northeast provinces. And it provides a certain basis for the development policy of the two-industry linkage development.

A concentric arc meander line (CAML) slow wave structure (SWS) was proposed for applications on low voltage and high efficiency Ka -band traveling wave tube (TWT). Due to the CAML formed with a series of concentric arcs, the electric field in the radial direction may be more uniform, which may make the beam–wave interaction more sufficient and the electron efficiency improved. The metal shielding structure with symmetrical ridges was employed for impedance matching to obtain a wide bandwidth. Simulated results demonstrate that the proposed CAML-SWS TWT has a good transmission performance in Ka -band. When the initial beam voltage and current is set to 720 V and 0.2 A, respectively, the output power of the TWT can reach 44.15 W at 35 GHz with the gain and the electron efficiency of 18.6 dB and 30.66%, respectively. Furthermore, the 3-dB bandwidth can cover 24–42 GHz and the electron efficiency is over 23.2% in Ka -band.

A sheet beam electron gun with high compression ratio and long transmission distance performance for $W$ -band traveling-wave tube (TWT) is presented. A beam focusing electrode (BFE) with two pairs of unequal length outstretched structures is designed to provide equal positions of beam waist in both horizontal and vertical planes, which is beneficial to obtain large compression ratio and keep the beam cross section shape over a long distance. The operational voltage is set as 30 kV. The beam current is 0.505 A, and the corresponding cathode current density is about 5.59 A/cm2. The simulation results show that the electron gun can provide a stable sheet beam under a 0.85-T magnet field. The compression ratio of the obtained sheet beam can be over 35, and the sheet beam can be transported through a 126-mm beam tunnel without interception with a 0.6 fill factor. The parameter sensitivities of the gun are analyzed and discussed as well.

Owing to the abundance of raw material reserves and low cost, Na-ion batteries (NIBs) have successfully gained widespread attention from academic and industrial communities in the past few decades. However, the insufficient cathode energy density is still one of the critical bottlenecks restricting the development of NIBs. Following a strategy of inducing Li+ into the transition-metal (TM) layer to enhance the oxygen redox reaction, a novel layered cathode material P2-Na0.6Li0.11Fe0.27Mn0.62O2 (NLFMO) was designed and successfully synthesized. This NLFMO cathode not only delivers a large initial reversible capacity of 207.3 mAh g-1, but also showing a good cyclic performance (104.2 mAh g−1 after 80 cycles) and rate capability (126.2 mAh g−1 at 1C). The ultrahigh capacity is contributed by both cationic (Fe3+/Fe4+, Mn3+/Mn4+) and partially reversible anionic redox (O2-/On-) reactions, revealed by in situ X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) techniques. Moreover, no detrimental P2-O2 phase transition was observed through ex situ X-ray diffraction (XRD) patterns, confirming the high structural stability during Na+ deintercalation/intercalation processes. These results provide valuable information about the high-energy density layered cathode materials based on anionic redox reaction for NIBs.

As nanoelectronic synapses, memristive ferroelectric tunnel junctions (FTJs) have triggered great interest due to the potential applications in neuromorphic computing for emulating biological brains. Here, we demonstrate multiferroic FTJ synapses based on the ferroelectric modulation of spin-filtering BaTiO

Studies of transition metal dichalcogenides (TMDs) can be traced back to the 1970s but they have been abandoned for a while due to the fire hazard of lithium metal batteries. Herein, a new layered material, CrSSe, is reported, whose intercalative capacity can achieve 190 mA h g−1 with charges all compensated by anionic S and Se. Fascinating performances of half-cells are also presented, with a capacity retention rate of 81.5% upon 1000 cycles at 20C and a high output of 101.7 mA h g−1 even at 200C. In addition, an ideal way to build a type of full battery without lithium anodes for CrSSe is also displayed; a Li3N film was synthesized on the electrode surface as a lithium source. Overall, the discovery of CrSSe enriches the chemistry of TMDs and the application in full batteries opens up opportunities for enabling lithium-free cathodes to be widely utilized in practical applications.

Room-temperature sodium-ion batteries (SIBs) have attracted extensive interest in large-scale energy storage applications for renewable energy and smart grid, owing to abundant sodium resources and low cost. O3-layered sodium transition metal oxides (i.e., NaMO2, M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, etc.) are considered as a promising class of cathode materials for SIBs due to their high capacity and ease of synthesis. In this work, a quaternary layered material O3–NaCr1/4Fe1/4Ni1/4Ti1/4O2 (O3-NCFNT) is successfully synthesized and investigated as a new cathode material for SIBs. Within the voltage range of 1.5–4.1 V, O3-NCFNT delivers an ultrahigh charge capacity of 213 mA h g−1 but a limited discharge capacity of 107 mA h g−1 in the initial cycle. Ex situ X-ray diffraction and X-ray absorption spectroscopy results reveal that an irreversible phase transformation as well as the irreversible redox of Cr3+/Cr6+ within the voltage range of 1.5–4.1 V should be responsible for the capacity decay in the initial cycle. While, O3-NCFNT exhibits the initial charge/discharge capacities of 135.4 and 129.2 mA h g−1 with a high coulombic efficiency of 95.4% as well as good cyclic performance within the voltage range of 1.5–3.4 V at current rate of 0.1C. Especially, O3-NCFNT shows a capacity retention of 77.1% after 300 cycles at a high rate of 1C, indicating that the structural origins of capacity decay caused by excessive sodium extraction are confirmed by XRD and XAS measurements to unlock the potential of this material for sodium-ion battery application.

Our previous work demonstrated that graphene devices with monovacancy defects possess spin filtering effect which offers potential applications in spintronics. Here, using first-principles calculations, we further study the spin-dependent electron transport properties and spin filtering efficiency of graphene devices with double vacancies that are arrayed in parallel and serial connections. It is found that devices with vacancies in parallel connection follow classical Kirchhoff circuit law. Both spin-up and spin-down currents are amplified while spin filtering efficiency remains the same as compared to the monovacancy devices. In contrast, amplification of spin filtering efficiency is realized in devices with serially connected double vacancies. In addition, it is shown that the spin current can be flipped reversibly by nanomechanical deformation as we observed in devices with monovacancy. Our findings demonstrate the possibility to engineer the spin filtering effect for vacancy based spintronic devices.

We investigate the parameter estimation problems of two-atom system driven by the phase noise lasers (PNLs) environment. And we give a general method of numeric solution to handle the problems of atom system under the PNLs environment. The calculation results of this method on Quantum Fisher Information (QFI) are consistent with our former results. Moreover, we consider the dipole–dipole (d–d) interaction between the atoms under PNLs environment with the collective decay, and the results show that larger d–d interaction and smaller collective decay rate lead to larger QFI of the two-atom system. So the collective decay will destroy the QFI while the d–d interaction will preserve the QFI, these results can be used to protect the QFI of two-atom system driven by the PNLs environment.

A band- and frequency-reconfigurable circularly polarised (CP) filtenna that exhibits good selectivity and out-of-band rejection in both its wideband and continuously tunable narrowband states is reported for cognitive radio (CR) applications. The filtenna provides two switchable operational states: a wideband state from 2.52 to 3.53 GHz for sensing and a tunable state of narrowband states from 2.44 to 3.19 GHz for communications. The corresponding 3-dB axial ratio bandwidths completely overlap these impedance bandwidths. A single PIN diode is utilised to switch between these two operational states to achieve the band-reconfigurable performance. Two varactor diodes are employed to realise the frequency-reconfigurable performance by facilitating a continuous shift of the narrowband states over the operational communication frequencies.

New cathode LiVPO4F/C with high-performance was synthesized by using polyvinylidene fluoride (PVDF) as carbon source although there is no benzene ring in it. Compared with other carbon sources, the plateau, rate and cyclic performance of LiVPO4F/C are greatly enhanced when PVDF is used. The specific capacity of LiVPO4F/C containing 8 wt% carbon at 0.1 C, 1 C and 5 C are 148.1 mAh·g−1, 144.9 mAh·g−1 and 135.8 mAh·g−1, which is nearly the best reported results. Moreover, the TG-MS analysis is used to detect the gases released by different carbon sources in the sintering process. It shows that the Li3V2(PO4)3/C impurity is greatly inhibited. This is because that HF gas released by PVDF can prevent the volatilization of fluorine and compensate the losses of fluorine. By contrast, the hydrogen free radicals released by other carbon sources can combine with fluorine and accelerate the volatilization of fluorine, resulting in the increasing of Li3V2(PO4)3/C impurity. Then, the performance of LiVPO4F/C cathode containing more Li3V2(PO4)3/C is greatly deteriorated.

A novel Na-deficient O3-type layered material Na0.83Cr1/3Fe1/3Mn1/6Ti1/6O2 has been synthesized via solid-state reaction and utilized as a cathode material for sodium-ion batteries (SIBs). It delivers initial charge/discharge capacities of 168.5 and 161.4 mAh g−1 within the voltage range of 1.5–4.1 V at current rate of 0.1C. A phase transition pathway of O3→O3+O3″→O3″ is revealed during the initial charge process by ex situ X-ray diffraction. In addition, synchrotron X-ray absorption spectroscopy suggests that the charge compensation of Na0.83Cr1/3Fe1/3Mn1/6Ti1/6O2 during the initial charge and discharge processes is contributed by Cr3+/Cr4.3+, Fe3+/Fe3+∼4+ and Mn3+∼4+/Mn4+ redox couples. The local electronic structure of layered Na1-xCr1/3Fe1/3Mn1/3-xTixO2 (x = 0, 1/6, 1/3) is proved to have a great impact on the electrochemical performance. After coating carbon layer with ∼10 nm, Na0.83Cr1/3Fe1/3Mn1/6Ti1/6O2/C exhibits the improved electrochemical performances regarding capacity retention and rate capability.

Two most widely used commercial water-based binders, polyacrylic latex (LA133) and sodium carboxymethyl cellulose/styrene butadiene rubber (CMC/SBR), are utilized for constructing sulfur cathodes t...

A mode generator consisting of an open resonant cavity and a quasi-parabolic mirror for the TE 28,8 mode excitation was presented. The excitation condition of the TE 28,8 mode was discussed and the obtained electric field distribution was analyzed and compared with the ideal TE 28,8 mode according to its scalar and vector correlativity.

Converter transformer bushing as a piece of important power equipment in HVDC transmission, need to withstand AC voltage, DC voltage, and polarity reversal voltage during operation, the complexity of the operating conditions leads to high requirements on the insulation performance of the converter transformer bushing. The dry-type SF 6 gas-insulated DC bushing meets the requirement of no oil in the valve hall, is the bushing of the current mainstream converter transformer, and it uses SF 6 gas as the upper additional insulation. Analyze the electric field distribution in SF 6 gas of converter transformer bushing under different voltages, Especially important for the design of SF 6 gas internal voltage equalization device. This paper selects ±400kV dry-type SF 6 gas insulated bushing as the research object, establishes a simulation analysis model, and uses the finite element analysis method to calculate the electric field intensity distribution of the converter transformer bushing under different voltages. Mainly analyze the distribution law of electric field intensity in SF 6 gas. The results show that under DC excitation, the distribution of equipotential lines in SF 6 gas is relatively concentrated, and the electric field intensity near the top of the capacitor core is the highest. Under the condition of polarity reversal, the electric field intensity in SF 6 gas showed a downward trend.

Sodium-ion batteries (SIBs) are attracting significant research attentions for large-scale energy storage applications. Cathode material is the vital part of SIBs to determine the capacity and cycle performance. Here, a series of F-doped Na0.66[Mn0.66Ti0.34]O2-xFx (x

In this paper, a new method was proposed to improve the sensitivity of capacitive-type pressure sensors by using the high dielectric constant materials as dielectric layer of sensors. The porous multi-wall carbon nanotubes (MWCNTs)/Ecoflex elastomer composites with high dielectric constant were prepared to serve as dielectric layers of capacitive-type pressure sensors. The MWCNTs/Ecoflex elastomer composite sensors show ultra-high sensitivity of 2.306 kPa−1, wide dynamic range and low hysteresis. The as-prepared sensors can monitor the response to pressure below 2.6 Pa. Moreover, they have exhibited excellent performances in promising practical applications as wearable devices in detecting pulses of carotid artery and heartbeats. This strategy proposed here presents a promising way to obtain high performance pressure sensors for applications in E-skin, robotics, wearable medical aids and real-time tactile sensing systems.

A Prussian blue LiFeFe(CN)6 thin-film cathode is fabricated by a nonvacuum coating technology without post-annealing process. The thin film of the solid electrolyte lithium phosphorus oxynitride (LiPON) is deposited onto the cathode by using radio-frequency magnetron sputtering. Then, the lithium metal anode is deposited on the LiPON film by the thermal evaporation method to fabricate the all-solid-state LiFeFe(CN)6/LiPON/Li battery with a thickness of 16 μm and a size of ∼10 cm2. Electrochemical properties of LiFeFe(CN)6/LiPON/Li battery are first investigated at various temperatures from −30 to 80 °C. Our results demonstrated that the all-solid-state LiFeFe(CN)6/LiPON/Li battery exhibits a discharge capacity of 82.5 mA h/g for the third cycle at 60 °C and shows stable cyclic performance within 200 cycles. These results provide the feasibility to assemble an all-solid-state lithium-ion battery by combining nonvacuum and vacuum techniques through an environmentally friendly process at low temperature.

It has been shown recently that the magnetic state of single-atom vacancy in graphene can be manipulated reversibly by mechanical deformation. Here, we investigate the possibility to flip the spin current of a model graphene device using nanomechanical distortion. Extensive first-principles calculations show that spin polarized currents can be altered by applying a shear distortion. The magnetic transitions in the central device, which is associated with the reversal of spin polarization of the π band of the vacancy state, lead to current flip with a spin filtering efficiency up to 17% (and a maximum change by 24% upon distortion). Our result opens the possibility to control spin transport properties in graphene and has potential applications in spintronics such as spin valves and spin transistors.

A conjugated aromatic compound comprising multiple fused redox centers, 5,7,12,14-tetraaza-6,13-pentacenequinone (TAPQ), is reported as an electrode of lithium-ion battery for the first time. It not only reaches a high reversible capacity but also obtains an excellent cycle ability. In addition, DFT calculations as well as FTIR, XPS and XRD analysis are performed to demonstrate the electrochemical reaction mechanism. This novel electrode can also be used in sodium and potassium batteries with a similar redox mechanism.

A new cathode LiVPO4F/C with a high working voltage of around 4.2 V was synthesized by a novel one-step method. The color of the solution turns green, which implies that V2O5 is successfully reduced to V3+. The reaction thermodynamics indicates that LiVPO4F/C is formed when the sintering temperature is higher than 650 °C, while the accompanying impurity phase Li3V2(PO4)3/C is also generated. The reaction kinetics proves that the reaction is third order and the activated energy is 208.9 kJ mol−1. X-ray photoelectron spectra imply that the components of LiVPO4F/C prepared at 800 °C (LVPF800) are in their appropriate valence. LVPF800 is composed of micron secondary particles aggregating from nano subglobose. The structural transformation shows that the V : P : F ratio in LVPF800 is close to 1 : 1 : 1. The reason behind generation of impurity Li3V2(PO4)3 at a high temperature of 850 °C is demonstrated directly, which is mainly due to the volatilization of VF3. The electrochemical performances of the cathode are related to the crystallite content of LiVPO4F/C and Li3V2(PO4)3/C. The specific capacities at 0.2 and 5C of LVPF800 are as high as 139.3 and 116.5 mA h g−1. Electrochemical analysis reveals that LVPF800 possesses an excellent reversibility in the extraction and insertion process and minimum charge transfer resistance.

Utilizing the anionic redox reaction opens new approaches for the development of new cathode materials with extra capacities. Although, it suffers from several obstacles such as voltage hysteresis and sluggish kinetics. In this paper, a new layered chalcogenide-based on dual anionic-redox reaction is reported. The newly designed layered NaCrSSe exhibits the capacity of almost all Na + intercalation/deintercalation (137 mAh g−1 at 50 mA g−1), and a unique charge/discharge feature with a small polarization of 0.15 V and high energy efficiencies of ~92% in initial cycles. Furthermore, a superior high-rate charge capacity of 115.5mAh g−1 (83.7% retention) was achieved at 27.8 C (4000 mA g−1). Systematic characterization studies on structure evolution and DFT calculation show the charge compensation of S and Se anions during cycling. These results will enrich the anion redox chemistry and provide valuable information for developing new anion-redox based cathode materials with high capacity and fast kinetics.

Neuromorphic computing is a promising candidate for next-generation information technologies. In the present work, we report the realization of long-term plasticity and synapse emulations in Ag/SrTiO3/(La,Sr)MnO3 memristors with the SrTiO3 active layers down to 3 unit cells (u.c.) in thickness. In the 3 u.c.-thick SrTiO3 device, efficient control of Ag+-ion migration gives rise to enhanced memristive properties with the conductance continuously modulated within a large memory window of ∼26 000% between an Ohmic low resistance state (LRS) and an electron-tunneling high resistance state (HRS). In addition, long-term plasticity of the Ag/SrTiO3/(La,Sr)MnO3 memristors is found to be dependent upon the resistance state. In the HRS, the devices exhibit excellent spike-timing-dependent plasticity characteristics with a large modulation of synaptic weight of ∼3500% and sensitive response to electrical stimuli of as low as ∼1.0 V and as fast as ∼0.01 ms. Adopting the spike-timing-dependent plasticity results as database, supervised learning simulations are demonstrated in the Ag/SrTiO3/(La,Sr)MnO3-based neural networks and a high accuracy rate of 95.5% is achieved for recognizing handwritten digits. These results provide more insights into the ionic migration at nanoscale for continuous resistance modulation and facilitate the design of ultrathin memristors for high-density 3D stacking artificial neural networks.

Chromium-based layered cathode materials suffer from the irreversible disproportionation reaction of Cr4+ to Cr3+ and Cr6+, which hinders the reversible multi-electron redox of Cr ions in layered cathodes, and limits their capacity and reversibility. To address this problem, a novel O3-type layer-structured transition metal oxide of NaCr1/3Fe1/3Mn1/3O2 (NCFM) was designed and studied as a cathode material. A high reversible capacity of 186 mA h g−1 was achieved at a current rate of 0.05C in a voltage range of 1.5 to 4.2 V. X-ray diffraction revealed an O3 → (O3 + P3) → (P3 + O3′′) → O3′′ phase-transition pathway for NCFM during charge. X-ray absorption, X-ray photoelectron and electron energy-loss spectroscopy measurements revealed the electronic structure changes of NCFM during Na+ deintercalation/intercalation processes. It is confirmed that the disproportionation reaction of Cr4+ to Cr3+ and Cr6+ can be effectively suppressed by Fe3+ and Mn4+ substitution. These results demonstrated that the reversible multi-electron oxidation/reduction of Cr ions can be achieved in NCFM during charge and discharge accompanied by CrO6 octahedral distortion and recovery.

The use of anion redox reactions is gaining interest for increasing rechargeable capacities in alkaline ion batteries. Although anion redox coupling of S2− and (S2)2− through dimerization of S–S in sulfides have been studied and reported, an anion redox process through electron hole formation has not been investigated to the best of our knowledge. Here, we report an O3-NaCr2/3Ti1/3S2 cathode that delivers a high reversible capacity of ~186 mAh g−1 (0.95 Na) based on the cation and anion redox process. Various charge compensation mechanisms of the sulfur anionic redox process in layered NaCr2/3Ti1/3S2, which occur through the formation of disulfide-like species, the precipitation of elemental sulfur, S–S dimerization, and especially through the formation of electron holes, are investigated. Direct structural evidence for formation of electron holes and (S2)n− species with shortened S–S distances is obtained. These results provide valuable information for the development of materials based on the anionic redox reaction., Anionic redox reactions are gaining interest as a means to optimize capacities of alkaline ion batteries. Here, the authors investigate various charge compensation mechanisms and report S–S dimerization and the formation of electron holes on sulfur in a model sulfide cathode.

Picosecond laser ultrasonics is an experimental technique for the generation and detection of ultrashort acoustic pulses using ultrafast lasers. In transparent media, it is often referred to as time-domain Brillouin scattering (TDBS). It provides the opportunity to monitor the propagation of nanometers-length acoustic pulses and to determine acoustical, optical, and acousto-optical parameters of the materials. We report on the application of TDBS for evaluating the effect of Praseodymium (Pr) substitution on the elasticity of multiferroic (Bi1&minus, xPrx)(Fe0.95Mn0.05)O3 (BPFMO) thin films. The films were deposited on Si and LaAlO3 (LAO) substrates by a sol-gel method. X-ray diffraction and Raman spectra revealed earlier that a phase transition from rhombohedral to tetragonal structure occurs at about 15% Pr substitution and is accompanied by the maxima of remnant magnetization and polarization. Combining TDBS with optical spectral reflectometry, scanning electron microscopy, and topographic measurements by atomic force microscopy, we found that the structural transition is also characterized by the maximum optical dielectric constant and the minimum longitudinal sound velocity. Our results, together with earlier ones, suggest that BiFeO3-based films and ceramics with compositions near phase boundaries might be promising materials for multifunctional applications.

Most P2-type layered oxides suffer from multiple voltage plateaus, due to Na+/vacancy-order superstructures caused by strong interplay between Na-Na electrostatic interactions and charge ordering in the transition metal layers. Here, Mg ions are successfully introduced into Na sites in addition to the conventional transition metal sites in P2-type Na0.7[Mn0.6Ni0.4]O2 as new cathode materials for sodium-ion batteries. Mg ions in the Na layer serve as "pillars" to stabilize the layered structure, especially for high-voltage charging, meanwhile Mg ions in the transition metal layer can destroy charge ordering. More importantly, Mg ion occupation in both sodium and transition metal layers will be able to create "Na-O-Mg" and "Mg-O-Mg" configurations in layered structures, resulting in ionic O 2p character, which allocates these O 2p states on top of those interacting with transition metals in the O-valence band, thus promoting reversible oxygen redox. This innovative design contributes smooth voltage profiles and high structural stability. Na0.7Mg0.05[Mn0.6Ni0.2Mg0.15]O2 exhibits superior electrochemical performance, especially good capacity retention at high current rate under a high cutoff voltage (4.2 V). A new P2 phase is formed after charge, rather than an O2 phase for the unsubstituted material. Besides, multiple intermediate phases are observed during high-rate charging. Na-ion transport kinetics are mainly affected by elemental-related redox couples and structural reorganization. These findings will open new opportunities for designing and optimizing layer-structured cathodes for sodium-ion batteries.

Oxygen-redox of layer-structured metal-oxide cathodes has drawn great attention as an effective approach to break through the bottleneck of their capacity limit. However, reversible oxygen-redox can only be obtained in the high-voltage region (usually over 3.5 V) in current metal-oxide cathodes. Here, we realize reversible oxygen-redox in a wide voltage range of 1.5-4.5 V in a P2-layered Na0.7 Mg0.2 [Fe0.2 Mn0.6 □0.2 ]O2 cathode material, where intrinsic vacancies are located in transition-metal (TM) sites and Mg-ions are located in Na sites. Mg-ions in the Na layer serve as "pillars" to stabilize the layered structure during electrochemical cycling, especially in the high-voltage region. Intrinsic vacancies in the TM layer create the local configurations of "□-O-□", "Na-O-□" and "Mg-O-□" to trigger oxygen-redox in the whole voltage range of charge-discharge. Time-resolved techniques demonstrate that the P2 phase is well maintained in a wide potential window range of 1.5-4.5 V even at 10 C. It is revealed that charge compensation from Mn- and O-ions contributes to the whole voltage range of 1.5-4.5 V, while the redox of Fe-ions only contributes to the high-voltage region of 3.0-4.5 V. The orphaned electrons in the nonbonding 2p orbitals of O that point toward TM-vacancy sites are responsible for reversible oxygen-redox, and Mg-ions in Na sites suppress oxygen release effectively.

Li3N in the form of powder as the most appealing sacrificial salt has already been investigated for prelithiation, yet not been widely acknowledged due to its incompatibility with common solvents to a great extent. Herein, we report an unexpected way by depositing metal lithium directly on cathode surface and then fixing it by nitrogen gas to synthesize pure alpha-Li3N film with (001) plane perpendicular to surface. Moreover, its decomposition pathway along the direction from the surface to the inner cathode is revealed. After being used to compensate the lithium loss in LiFePO4/graphite full cell, discharge capacity at 120th cycle has raised by 30.7% with 1% Li3N coating. Apart from that, this kind of Li3N film has successfully served as the sole lithium source to fabricate full-cell with TiS2 and graphite as electrodes, in which 142.4 mAh g−1 of capacity can remain after 50 cycles. In short, the introducing/expelling of nitrogen for Li fixation/Li+ release is a facile strategy to realize battery prelithiation with easy preparation and high efficiency.

A strategy for enabling a novel carbon fluoride (CFx) to be a high-performance cathode material for sodium batteries is proposed and realized. An amorphous and highly disordered CFx, denoted as d-CFx, is prepared through a facile synthesis route. Herein we report on a Na/d-CFx cell reversibly discharging/charging at such a low overpotential and capacity-decay rate. The polarization of the Na/d-CFx cell is about 780 mV, the lowest value reported in the state-of-the-art Na/CFx system. The initial discharge capacity is 582.5 mA h/g, with a capacity of 412.5 mA h/g after 12 cycles. The designed d-CFx improves the Na+ diffusion rate and facilitates the reaction with larger sodium ions during the discharging process. Amorphous discharge products NaF are easily decomposed, enhancing the charge reaction. The small grain size of NaF is believed to be another key factor that enables the minimal charge gap of Na/d-CFx cells and a slower capacity-decay rate, which can facilitate the decomposition of NaF and the refor...

LiVPO4F/C cathode has been successfully synthesized by a fast chemical reduction method using polyvinylidene fluoride as carbon source. NH4VO3 is reduced by oxalic acid at 60 °C in short time. The green color and binding energy peaks around 517.1 eV and 524.7 eV in dried precursors corroborate that element V in NH4VO3 is reduced to +3 valence. The crystallite of LiVPO4F/C is well developed. Nanometer granules with smooth edge aggregate and form micron size LiVPO4F/C particles. The molar ratio of V:P:F in cathode is 1:0.99:1.02, which is close to stoichiometric. The discharge capacities of LiVPO4F/C at 0.2 C, 1 C and 2 C are 140.9 mA h g−1, 127.4 mA h g−1 and 122.9 mA h g−1. It is concluded that the fast chemical reduction in this paper can be used to prepare LiVPO4F/C cathode with stable crystallite structure and excellent performances.

Nanotubes are one of the most promising functional materials in nanotechnology. Silicon nanotubes (SiNTs) have been experimentally validated; they are unique puckered nanotubular structures unlike carbon nanotubes (CNTs). Although the electronic and optical properties of SiNTs have been previously studied, their structure-related capability for electron transport has not been investigated. Here we report a comparative study of the intrinsic electronic and transport properties of four pairs of SiNTs and CNTs (one armchair nanotubes (3,3) and three zigzag nanotubes (5,0), (6,0) and (7,0)) using density functional theory (DFT) combined with the nonequilibrium Green's function (NEGF) method. All our investigated systems of SiNTs and CNTs are conductors. Both the armchair SiNTs and CNTs possess superior electron transport performance to their zigzag counterparts. Compared with CNTs, SiNTs have more advantages in the high bias voltage region. Especially, Si(3,3) possesses around double the potential charge capacity of C(3,3) under the bias voltage of 2.0 V. In particular, the CNT(6,0) exhibits distinct negative differential resistance (NDR) behavior and the peak-valley ratio (PVR) for C(6,0) is about 1.2.

Lithium metal is considered as the most promising anode material for next-generation high-energy-density lithium batteries. However, the uncontrolled Li dendrite growth results in poor electrochemical performance and severe safety hazards, hindering its practical applications. Here, we demonstrate an environmentally friendly and resource abundant electrode by using cotton-derived carbon cloth with functional groups as lithium deposition host. Contrary to the commercial carbon cloth, the carbon cloth derived from cotton (C-400) with functional groups can induce Li+ ions to form a uniform and dense Li deposition into the host structure, avoiding Li deposition on its surface, even at high current rates. Moreover, the 3D cross-linked skeletal structure of C-400 can suppress volume change of the electrode during cycling. Consequently, the C-400 electrode can afford high areal capacity over 10 mAh cm−2 without the formation of Li dendrites. Compared with the bare Li anode, the advancements of using C-400@Li anode in lithium batteries with LiNi0.8Co0.15Al0.05O2 cathode regarding capacity retention, voltage polarization and rate capability are proved, suggesting its application potential for high energy density lithium batteries.

Previous studies have shown that the impurity Li3V2(PO4)3 in LiVPO4F will adversely affect its electrochemical performance. In this work, we show that the crystalline composition of LiVPO4F/C is mainly influenced by the environmental temperature. The content of Li3V2(PO4)3 formed in LiVPO4F/C is 0, 11.84 and 18.75% at environmental temperatures of 10, 20, and 30°C, respectively. For the sample LVPF-30C, the SEM pattern shows a kind of alveolate microstructure and the result of selected area electron diffraction shows two sets of patterns. The LiVPO4F/C cathode without impurity phase Li3V2(PO4)3 was prepared at 10°C. The selected area electron diffraction result proves that the lattice pattern of LiVPO4F is a regular parallelogram. Electrochemical tests show that only one flat plateau around 4.2 V appears in the charge/discharge curve, and the reversible capacity is 140.4 mAh·g-1 at 0.1 C, and 116.3 mAh·g-1 at 5 C. From these analyses, it is reasonable to speculate that synthesizing LiVPO4F/C at a low environmental temperature is a practical strategy to obtain pure crystalline phase and good electrochemical performance.

In order to improve the electrochemical performance of Na/CFx cell, fluorinated multi-walled carbon nanotubes (F-MWCNTs) and a new composite consisting of CFx, graphene nanosheets (GNS) and FeF3 (labeled as CGF for short) were employed as cathode materials in rechargeable room-temperature sodium batteries for the first time. The polarizations of Na/F-MWCNTs and Na/CGF cell were found to be 1600 and 800 mV, respectively. These values were much lower than that of Na/CFx cell (2000 mV). MWCNTs formed after the discharge process with intrinsic high surface area, high catalytic activity and “cage” type structure enhance charge reaction activity. Analogically, the combination of GNS and FeF3 with CFx provides more active sites to facilitate the decomposition of NaF during charge process. Moreover, the CGF electrode may have specific channels to avoid the dissolution of fluorine into the electrolyte similarly as the structure function of the F-MWCNTs electrode, leading to much better cycling performance. Overall, our results have demonstrated that the electrochemical performance of Na/CFx cell can be greatly improved by using MWCNTs and FeF3–GNS as catalysts.

C6 hexenols are one of the most significant groups of volatile organic compounds with biogenic emissions. The lack of corresponding kinetic parameters and product information on their oxidation reactions will result in incomplete atmospheric chemical mechanisms and models. In this paper, experimental and theoretical studies are reported for the reactions of OH radicals with a series of C6 hexenols, (Z)-2-hexen-1-ol, (Z)-3-hexen-1-ol, (Z)-4-hexen-1-ol, (E)-2-hexen-1-ol, (E)-3-hexen-1-ol, and (E)-4-hexen-1-ol, at 298 K and 1.01 × 10(5) Pa. The corresponding rate constants were 8.53 ± 1.36, 10.1 ± 1.6, 7.86 ± 1.30, 8.08 ± 1.33, 9.10 ± 1.50, and 7.14 ± 1.20 (in units of 10(-11) cm(3) molecule(-1) s(-1)), respectively, measured by gas chromatography with a flame ionization detector (GC-FID), using a relative technique. Theoretical calculations concerning the OH-addition and H-abstraction reaction channels were also performed for these reactions to further understand the reaction mechanism and the relative importance of the H-abstraction reaction. By contrast to previously reported results, the H-abstraction channel is a non-negligible reaction channel for reactions of OH radicals with these hexenols. The rate constants of the H-abstraction channel are comparable with those for the OH-addition channel and contribute >20% for most of the studied alcohols, even >50% for (E)-3-hexen-1-ol. Thus, H-abstraction channels may have an important role in the reactions of these alcohols with OH radicals and must be considered in certain atmospheric chemical mechanisms and models.

A unified calculation of optical band positions and electron paramagnetic resonance (EPR) (or spin-Hamiltonian) parameters for the trigonal Cr3+–Li+ centre in CsMgCl3 crystal is made by using the complete diagonalisation (of energy matrix) method based on the two-spin–orbit-parameter model. In this model, the contributions from the spin–orbit parameter of central dn ion and that of ligand ion are included. From the calculation, the 11 observed optical and EPR data (eight optical band positions and three EPR parameters g//, g⊥, D) are reasonably explained with five adjustable parameters and the defect structure of the Cr3+–Li+ centre (which is consistent with the expectation based on the electrostatic interaction) in CsMgCl3 is acquired. The results are discussed.

The interest in the use of spaceborne synthetic aperture radar (SAR) for collecting earth bio/geophysical information and detecting foliage-obscured targets has been increased. However, the signals are inevitably affected by the ionosphere, particularly at very high frequency and ultrahigh frequency. Thus, it is crucial to understand the potential effects of the ionosphere on SAR systems. In this paper, three possible contributions are made to analyze these effects. First, for analyzing range resolution, in addition to linear and quadratic phase errors due to the background ionosphere, the cubic phase error is considered. The expected mean electron density inferred from the International Reference Ionosphere is used. Second, for analyzing azimuthal resolution, the effects of ionospheric irregularities are evaluated under the conditions of oblique incidence and anisotropic irregularities. The model is presented on the basis of the multiple phase screen (MPS) method. Compared with the previous model, the MPS method can give results in good agreement with both weak and strong scattering theories. Finally, based on the theory of moment equation, range resolution degradation caused by the multiple scattering is also studied in the case of anisotropic irregularities. By using the range Doppler algorithm, a number of degraded point responses due to these ionospheric effects are shown, and then, some evaluation results are listed.

The complete diagonalisation (of energy matrix) method based on the two-spin-orbit-parameter model is applied to unifiedly calculate the spin-Hamiltonian parameters (g factors g//, g⊥ and hyperfine structure constants A//, A⊥) and optical band positions for Ni+ ion in silver gallium selenide (AgGaSe2) crystal. In the model, besides the contribution due to the spin-orbit parameter of central dn ion (i.e., the one-spin-orbit-parameter model in the traditional crystal-field theory), that of ligand ions are taken into account. The calculated results are reasonably consistent with the experimental values. The local structure of Ni+ centre in AgGaSe2 is estimated through the calculation. The complete diagonalisation method based on the one-spin-orbit-parameter model is also applied to calculate these electron paramagnetic resonance and optical data. It is found that although the calculated optical band positions are close to those based on the two-spin-orbit-parameter model and hence to the experimental values,...

Metal–air batteries are important power sources for electronics and vehicles because of their remarkable high theoretical energy density and low cost. In this work, we firstly investigate the electrochemical properties of sodium air batteries (SABs) with the addition of ferrocene in the electrolyte. Combining charge–discharge measurements with field-emission transmission electron microscopy images of the discharged air cathodes, our results have demonstrated that two different pathways with ferrocene as an electrocatalyst and involved in the electrochemistry during the charge process might be governed by the morphological features of the electrode caused by the deposition of Na2O2 in SABs. The SAB with ferrocene as a catalyst exhibits a high cycling performance of up to 230 cycles with a high capacity of 1000 mA h g−1.

Heterogeneous catalysts with Co3O4 and liquid redox mediators were utilized for the morphological control of discharged products in SABs. With Co3O4 nanowires/C as air cathodes, the discharge product tended to be like nanoflakes. However, after the addition of ferrocene to the electrolyte, the discharge product tended to be like nanofilms and the cyclic performance can achieve 570 cycles.

In this article, the Dirac electron scattering problem on circular barrier of radius [Formula: see text] is studied under the generalized uncertainty principle (GUP). The expressions of scattering coefficients, scattering cross-section and scattering efficiency of massless Dirac particle are obtained by solving the massless Dirac equation under GUP and discussed by numerical methods. It shows that the scattering coefficient, the scattering cross-section, and the scattering efficiency depend explicitly on the GUP parameter [Formula: see text]. For the scattering coefficient [Formula: see text], GUP may cause slight shift in the oscillation position of [Formula: see text] and make some peaks value of [Formula: see text] smaller. For scattering cross-section and scattering efficiency, GUP may also lead to slight shift in their oscillation position and increase of amplitude when the GUP parameter increases.

We report on EISCAT ionospheric heating experiments carried out on 13 September 2010 at Tromso, Norway. This paper focuses on the long-lasting enhanced ion- and plasma-lines observed by the VHF incoherent scatter radar. In previous experiments, the enhanced ion-lines observed by VHF radar lasted ~200 ms. Observations of long-lasting enhanced ion- and plasma-lines in the VHF radar have not been reported before. The enhanced lines may be caused by Parametric Decay Instability (PDI). In addition, the VHF data show that the enhanced ion-lines are descending in altitude with time during the heater-on period. Likewise, the temporal and spatial evolution of the enhanced plasma-lines also show a similar morphology and generally occur at the same height. At last a possible mechanism for the altitude evolution is given in this paper.

The spin-Hamiltonian parameters (g factors gi and hyperfine structure constants Ai, were i=x, y and z) for Mo5+ ion occupying the Ti(1) site with approximately rhombic symmetry in KTiOPO4 crystal are calculated from the high-order perturbation formulas based on the two-mechanism model. In the model, not only the contribution due to the conventional crystal-field (CF) mechanism, but also those due to the charge-transfer (CT) mechanism are included. The six calculated spin-Hamiltonian parameters with four adjustable parameters are in reasonable agreement with the experimental values. The calculations show that for more accurate calculations of spin-Hamiltonian parameters of the high valence dn ions (e.g., Mo5+ considered here) in crystals, the contribution from CT mechanism, which is ignored in the conventional crystal field theory, should be taken into account. The reasonable crystal field energy levels of Mo5+ in KTiOPO4 are also predicted from calculations.

Seven spin-Hamiltonian parameters ( g factors g // , g ⊥ and zero-field splittings b 2 0 , b 4 0 , b 4 4 , b 6 0 , b 6 4 ) of two tetragonal Gd 3+ centers, denoted A and B, in layered perovskite fluoride Tl 2 ZnF 4 crystals doped only with Gd 3+ ion and co-doped with Gd 3+ and Li + are calculated using the diagonalization (of energy matrix) method based on the one-electron crystal-field mechanism. In the calculations, the defect models suggested in the previous paper that center A is due to Gd 3+ ion at the octahedral Zn 2+ site without any local charge compensation and center B is due to Gd 3+ ion at the nine-coordinated Tl 2+ site associated with a Li + ion at the nearest Zn 2+ site along C 4 axis for charge compensation are applied. The calculated results are in reasonable agreement with the experimental values. The suggested defect models of both Gd 3+ centers are therefore confirmed and the respective defect structural data are obtained. The results, including the validity of defect structural data, are discussed.