Search

The doping effects of transition metals with various numbers of d electrons on Li2MnO3 are different. The summary of variation of the charge compensation mechanism facilitates the design of Li-rich cathodes.

Curious X chromosome-shaped Cs3Cu2I5 microcrystals synthesized for the first time and used for high-performance self-powered UV photodetectors under ultralow light intensity at the μW cm−2 level.

Diffusion coefficients in the hexagonal close-packed (hcp) Mg–Sn and Mg–Sc solid solutions and the body-centered cubic (bcc) Mg–Sc solid solution were re-evaluated via a method combing diffusion couple experiments, error function expansion fitting, and Sauer–Freise/Hall numerical calculation. The interdiffusion coefficients in hcp Mg–Sn alloys were found to gently rise as the content of Sn increases. The new experimental data amended the compositional dependency of Mg–Sn interdiffusion coefficients and gave rise to a new set of mobility parameters. The interdiffusion coefficients in Mg–Sc alloys were determined at 773 K, 803 K, and 848 K. They showed a slightly parabolic composition dependence in the hcp phase but a monotonic decreasing trend with the increase in Sc content in the bcc phase. The experimental results in this work enriched the determined diffusion coefficients in Mg alloys and effectively justified the assessed mobility parameters in assessments.

China's economy has entered the ‘New Normal’ era, transferring from the fast growth to the medium-high growth with ambitious targets on climate change mitigation and pollution alleviation. As the largest CO2 source among all industrial sectors, the electricity sector plays an important role in China's recent stagnating CO2 emissions and achieving mitigation targets. Here we estimate CO2 emissions from electricity production by using up-to-date emission factors and calculate the CO2 emissions embodied in purchased electricity using the Quasi-Input-Output (QIO) model. In addition, we quantify the drivers of CO2 emissions from electricity production and consumption using the index and structural decomposition analysis. Our results show that China's economic transition and increasing electricity intensity largely contributed to the growth of CO2 emissions in the electricity sector, while the improvement of energy efficiency, non-fossil fuel substitution, and shrinking share of industrial output reduced CO2 emissions. The consumption-based CO2 emissions in developed regions in China are higher than their production-based CO2 emissions in 12 provinces. The recent slowing down of economic growth, energy transition, improved efficiency, non-fossil fuel substitution, and electricity trade have altered the CO2 trajectory in the electricity sector since 2008 global financial crisis. This study could help policymakers better understand CO2 emissions in the electricity sector and formulate effective policies to decarbonize the electricity sector in the future.

The first-principles method of density functional theory (DFT) is used to study the structural stability and electrochemical properties of B doped graphene with concentrations of 3.125%, 6.25% and 18.75% respectively, and their lithium storage mechanism and characteristics are further studied. The results show that the doped systems all have negative adsorption energy, indicating that the structures can exist stably, and the adsorption energy of lithium ions on graphene decreases with the increase of B doping concentration. Among them, the B

Single-phase white-emission phosphors possess a judicious usage potential in phosphor-converted white-light-emitting diodes (WLEDs). Recently, numerous efforts have been made toward the development of new patterns of white-emitting phosphors that achieve excellent quantum yield, superior thermal stability, and applaudable cost effectiveness of WLEDs. Finding suitable single-component white phosphor hosts to provide an ideal local environment for activators remains urgent. Inspired by the original discovery of the promising host MgIn2(P2O7)2 (MIP) and its structural dependence on alkali-metal cations, we synthesized a brand-new phosphor host, SrIn2(P2O7)2 (SIP), via the traditional solid-state reaction. Its crystal structure was determined using an ab initio analysis and the Rietveld method. It belongs to a monoclinic unit cell with the space group C2/c. Besides, SIP exhibits a special layered three-dimensional framework in which the monolayer [SrO10]∞ was surrounded by a bilayer [In2P4O14]∞ made of the InO6 octahedra and P2O7 groups. A series of pure SIP:Tm3+,Dy3+ phosphors with tunable blue-white-yellow emission were prepared by adjusting the dopant concentration and utilizing the Tm3+-Dy3+ energy transfer. The daylight-white-emitting phosphor SIP:0.01Tm3+,0.04Dy3+ (the correlated color temperature is 4448 K) exhibits an abnormal thermal antiquenching property, and the emission intensity of 423 K reaches 103.7% of the initial value at 300 K. On the basis of the temperature-dependent lattice evolution and microenvironment analysis, the reduction of β and lattice distortion can lead to lower asymmetry of the activators and benefit the compensation of trapped-electron thermal activation. In this work, an integration study was carried out on the crystal structure of the new matrix, the occupation of the luminescent center, the interaction of different activators in the host, and the distortion degree of the local structure for the activators, which is of great practical sense for producing a novel single-matrix white phosphor possessing superior thermal endurance for UV-light-stimulated WLEDs.

The friction between a molybdenum disulphide (MoS2) nanoflake and a MoS2 substrate was analyzed using a modified Tomlinson model based on atomistic force fields. The calculations performed in the study suggest that large deformations in the substrate can induce a dramatic decrease in the friction between the nanoflake and the substrate to produce the so-called superlubricity. The coefficient of friction decreases by 1–4 orders of magnitude when a high strain exceeding 0.1 is applied. This friction reduction is strongly anisotropic. For example, the reduction is most pronounced in the compressive regime when the nanoflake slides along the zigzag crystalline direction of the substrate. In other sliding directions, the coefficient of friction will reduce to its lowest value either when a high tensile strain is applied along the zigzag direction or when a high compressive strain is applied along the armchair direction. This anisotropy is correlated with the atomic configurations of MoS2.

The construction of van der Waals heterostructures based on 2D polarized materials is a unique technique to achieve enhanced photocatalytic performance. We have investigated the intrinsic electric field and photocatalytic properties of the MoTe2/GeS heterostructure via first-principles calculations. The results showed that a dipole-induced electric field induced by the GeS monolayer and an interface-induced electric field induced by the interface between the GeS monolayer and the MoTe2 monolayer emerge in the 2D polarized MoTe2/GeS heterostructure. The dipole-induced electric field contributes mainly to the total intrinsic electric field. Moreover, the 2D polarized MoTe2/GeS heterostructure possesses many excellent and distinguished photocatalytic performance parameters, such as a direct semiconductor bandgap of 1.524 eV, a wide light spectrum ranging from the ultraviolet to near-infrared region with a high absorption coefficient (about 106 cm−1), a total intrinsic electric field, which reduces the probability of the recombination of photo-generated electron–hole pairs effectively, and a suitable band alignment for the water-splitting reaction. These indicate that the 2D polarized MoTe2/GeS van der Waals heterostructure is a potential novel high-efficient photocatalyst for water-splitting.

Decarbonization of the power sector is one of the most important efforts to meet the climate mitigation targets under the Paris Agreement. China's power sector is of global importance, accounting for similar to 25% of global electricity production in 2015. The carbon intensity of China's electricity is still much higher than the global average, but the country has made important strides toward a low-carbon transition based on two main pillars: improvement of energy efficiency and decreasing the share of fossil fuels. By applying a decoupling indicator, our study shows that 21 provinces achieved a "relative decoupling" of carbon emissions and electricity production and the remaining nine provinces achieved "absolute decoupling" between 2005 and 2015. We updated China's emission factors based on the most recent data by also considering the quality of imported coal and compared our results with the widely used Intergovernmental Panel on Climate Change coefficients to show the sensitivity of results and the potential error. Our decomposition analysis shows that improvement of energy efficiency was the dominant driver for decarbonization of 16 provincial power sectors, while the access to low-carbon electricity and substitution of natural gas for coal and oil further accelerated their decarbonization.

Herein, the feasibility of Fe substitution by Ga, Ge and As in Li2FeSiO4 in modulating its structural, mechanical, electrochemical, capacity and electronic properties was systematically studied via first-principles calculations based on density functional theory within the generalized gradient approximation with Hubbard corrections (GGA+U). The calculated results show that Ga, Ge and As doping can effectively reduce the range of the cell volume change during Li+ removal, improving the Li+ detachment ability and cycle stability of the system. Meanwhile, the calculated mechanical properties including modulus ratio, B/G, and Poisson ratio, ν, indicate that the doped systems of Ga, Ge and As exhibit excellent mechanical properties. In addition, besides the increase in theoretical average deintercalation voltage induced by the Ga dopant when more than one Li+ ion is removed in the formula unit, the doping of Ga, Ge and As all reduce the theoretical average deintercalation voltage in the process of Li+ extraction. Especially in the case of doping of Ge, when 0.5 Li+ is removed from LiFe0.5Ge0.5SiO4, the theoretical average deintercalation voltage only increases by 0.19 V compared with the case of the removal of one Li+ in Li2Fe0.5Ge0.5SiO4, which causes the cathode material to have a longer and more stable discharge platform. Moreover, in the process of Li+ removal, the doping of Ga, Ge and As can effectively participate in the charge compensation of the system, and Ge and As can provide further charge, increasing the capacity of the Li2FeSiO4 cathode material considerably.

HfC and HfTaC2 coatings with gradient composition manufactured by double-cathode glow discharge plasma surface metallurgy technology were designed to improve the wear resistance of TA15 titanium alloy. The deposition mechanism of plasma and diffusion mechanism of atoms were investigated, and the growth process of coatings was revealed. The mechanical properties comprising microhardness and elastic modulus were investigated via first-principles calculations and experimental verification. The results reveal that the wear resistance of HfC and HfTaC2 coatings with abrasive wear mechanism is always better than that of the substrate with abrasive wear, adhesive wear and oxidation wear mechanism. The volume wear rates of the coatings are reduced by 90%–97% compared with the substrate, and that of HfTaC2 coatings are reduced by 29.9%–45.5% compared with HfC coatings. Furthermore, V-shaped cross section profiles of wear scars formed on HfC coatings, and U-shaped on HfTaC2 coatings, which is attributed to the addition of tantalum which causes HfC to form a sufficient solid solution, a 0.187–0.030 Å elongation of Ta-C bond length and 0.039–0.051 Å shortening of Hf-C bond length led to the unit cell shrinkage and the Bragg lattice changes from face-centered cubic to face-centered square lattice; accordingly, hardness and wear behavior were further improved.

Funding Information: This work is part of the POSITION-II project funded by the ECSEL Joint Undertaking under grant number Ecsel-783132-Position-II-2017-IA. www.position-2.eu . The authors would like to acknowledge the Innovation Funding Agency Business Finland for their financial support. Dr. Jari Paloheimo and Dr. Heikki Holmberg from Okmetic Oy, Finland, are acknowledged for useful discussions. One of the authors, Dr. Xiaoma Tao, acknowledges the support from National Natural Science Foundation of China [Grants Nos. 51661003 and 51961007], and the Guangxi Natural Science Foundation [Grant No. 2018GXNSFAA281254]. Publisher Copyright: © 2021, The Author(s). Copyright: Copyright 2021 Elsevier B.V., All rights reserved. | openaire: EC/H2020/783132/EU//POSITION-II Phosphorus (P) is one of the most widely used donor dopants for fabricating a low-resistivity silicon (Si) substrate. However, its volatile nature and the relatively small equilibrium segregation coefficient in Si at the melting temperature of Si impede the efficient and effective growth of low-resistivity Czochralski (CZ) Si single crystal. The primary objective of this work is to theoretically perceive the influence of germanium co-doping on the heavily P-doped Si crystal by means of CALculation of PHase Diagrams (CALPHAD) approaches and density functional theory (DFT) calculations. Phase equilibria at the Si-rich corner of the Si-Ge-P system has been thermodynamically extrapolated based on robust thermodynamic descriptions of involved binary systems, where Si-P and Ge-P have been re-assessed in this work. Phase diagram calculation results indicate that at a given P concentration (e.g. 0.33 at.% P) Ge co-doping lowers the solidification temperature of the Si(Ge, P) alloys, as well as the relevant equilibrium segregation coefficients of P in the doped Si. DFT calculations simulated the formation of (i) monovacancy in Si as well as (ii) solutions of Si(P) and Si(Ge) with one dopant substitutionally inserted in 64- and 216-atom Si cubic supercells. Binding energies were calculated and compared for Ge-Ge, Ge-P and P-P bonds positioning at the first nearest-neighbors (1NN) to the third nearest-neighbors (3NN). P-P bonds have the largest bonding energy from 1NN to 3NN configurations. The climbing image nudged elastic band method (CL-NEB) was utilized to calculate the energy barriers of P 1NN jump in the 64-atom Si cubic supercell with/without a neighboring Ge atom. With Ge present, a higher energy barrier for P 1NN jump was obtained than that without involving Ge. This indicates that Ge can impede the P diffusion in Si matrix.

The construction of van der Waals heterostructures based on 2D polarized materials is a unique technique to achieve enhanced photocatalytic performance. We have investigated the intrinsic electric field and photocatalytic properties of the MoTe

Regulating green electroluminescence (EL) of ZnO is an important but difficult task to produce white-light sources due to its strong background green emission. We have demonstrated that the green EL from solution-processed ZnO nanocrystals (NCs) can be improved and manipulated by erbium (Er) doping. Er3+ ions can be doped and activated without any high-temperature post-annealing treatment. Incorporation of the Er3+ ions in the ZnO host induces lattice expansion primarily along the (002) direction. Er3+-related characteristic green emissions are observed at 535 and 556 nm and manipulated with increasing Er concentration under forward bias. The EL mechanism is investigated and found to be driven by the energy transfer from the deep-level defects of the ZnO NCs to the nearby Er3+ ions. Our findings have demonstrated the feasibility of producing green light-emitting diodes by solution-processable Er-doped ZnO NCs and inspired a promising way to develop white-light sources based on printable ZnO NCs simply by incorporating different rare earth ions into the ZnO NCs simultaneously.

The growth and release processes of helium bubbles near tungsten surface have been investigated by molecular dynamics (MD) simulations. The results indicate that the surface morphologies are dependent on orientation of surfaces. Before bubble rupture occurs, stepped, thin schistose and pyramidal structures are observed on the (1 1 0), (1 0 0) and (1 1 1) surfaces, respectively. When the angle between the normal direction of surface and the sliding direction (〈1 1 1〉 direction) is larger, flatter surface would be formed and the subsequent release process would be more violent. In the bursting process, the release rate of helium and the degree of surface damage are correlated with the surface stacking height before bubble bursts. Unrepaired crack structures have been observed on the (1 1 0) and (1 0 0) surfaces, while a smaller hole on the (1 1 1) surface. The stacking atoms have a tendency to make the surface restore to the bcc structure. At high temperature, the surface pore with radius ∼1 nm can be self-healed from outer to inner by the diffusion of surface atoms, while no recovery is observed in MD time scale when the ratio of He/V in the bubble is high.