Superlattice structures resulting from vacancy ordering have been observed in many materials.Here we report vacancy ordering behavior inⅢ_(2)Ⅵ_(3)nanowires.The formation of layer-like structural vacancies has been a...Superlattice structures resulting from vacancy ordering have been observed in many materials.Here we report vacancy ordering behavior inⅢ_(2)Ⅵ_(3)nanowires.The formation of layer-like structural vacancies has been achieved during the synthesis of In_(2)Se_(3)nanowires through a vapor-transport route.Doping In_(2)Se_(3)nanowires with small amounts of Ga during synthesis can completely change the structural vacancy ordering from a layer-like to a screw-like pattern for(In_(x)Ga_(1-x))_(2)Se_(3)nanowires.Lithium atoms can fill in the layer-like structural vacancies of In_(2)Se_(3)nanowires and generate new types of vacancy and lithium atom ordering superlattices.The screw-patterned vacancies of(In_(x)Ga_(1-x))_(2)Se_(3)nanowires show reversible lithium insertion.Our results contribute to the understanding of structure property correlations ofⅢ_(2)Ⅵ_(3)materials used in lithium ion storage,photovoltaics,and phase change memory.展开更多
Tailoring the degree of structural disorder in Ge-Sb-Te alloys is important for the development of non-volatile phase-change memory and neuro-inspired computing.Upon crystallization from the amorphous phase,these allo...Tailoring the degree of structural disorder in Ge-Sb-Te alloys is important for the development of non-volatile phase-change memory and neuro-inspired computing.Upon crystallization from the amorphous phase,these alloys form a cubic rocksalt-like structure with a high content of intrinsic vacancies.Further thermal annealing results in a gradual structural transition towards a layered structure and an insulator-to-metal transition.In this work,we elucidate the atomic-level details of the structural transition in crystalline GeSb_(2)Te_(4) by in situ high-resolution transmission electron microscopy experiments and ab initio density functional theory calculations,providing a comprehensive real-time and real-space view of the vacancy ordering process.We also discuss the impact of vacancy ordering on altering the electronic and optical properties of GeSb_(2)Te_(4),which is relevant to multilevel storage applications.The phase evolution paths in Ge-Sb-Te alloys and Sb_(2)Te_(3)are illustrated using a summary diagram,which serves as a guide for designing phase-change memory devices.展开更多
The modification of the electron diffraction pattern(EDP) of B2 in an as rapidly quenched then short time aged Ti Ni shape memory alloy(SMA) has been studied systematically using TEM. It was found that the diffusio...The modification of the electron diffraction pattern(EDP) of B2 in an as rapidly quenched then short time aged Ti Ni shape memory alloy(SMA) has been studied systematically using TEM. It was found that the diffusion scattering rings in EDP of an as rapidly quenched Ti-Ni SMA is associated with short range order (SRO) of vancancies in parent B2. After aging at 450℃ for 5 min the diffusion scattering rings are replaced by 1/2 {001} and 1 / 4 {012} extra reflections. It indicates that the SRO of vacancies has transformed into long range order (LRO) of vacancies,moreover,the LRO of vacancies exists in microdomains.展开更多
2D MBenes have been theoretically predicted to possess unique electronic structures and physicochemical properties,and thus shown great promise in various applications.However,the synthesis of individual single-layer ...2D MBenes have been theoretically predicted to possess unique electronic structures and physicochemical properties,and thus shown great promise in various applications.However,the synthesis of individual single-layer MBene remains a grand challenge due to its orthorhombic structure of MAB phases.Recently,scientists from Link?ping University have fabricated 2D monolayer Mo4/3B2-xTzwith ordered metal vacancies.Their results demonstrated the feasibility of top-down approach by chemical exfoliation of laminated compounds and provided the principle for further preparation of a wealth of MBenes.展开更多
Vacancy-ordered double perovskites(VODPs)are promising alternatives to three-dimensional lead halide perovskites for optoelectronic applications.Mixing these materials creates a vast compositional space for tunable pr...Vacancy-ordered double perovskites(VODPs)are promising alternatives to three-dimensional lead halide perovskites for optoelectronic applications.Mixing these materials creates a vast compositional space for tunable properties but complicates efficient screening of target candidates.Here,we illustrate the diverse electronic and optical characteristics as well as the nonlinear mixing effects within mixed VODPs.Furthermore,inspired by the observation that all physical properties of mixed systems with limited local environment options can be uniquely determined by the information regarding atomic-site occupation,we developed a method combining data augmentation and a transformer-inspired graph neural network to effectively encodes atomic-site information in mixed systems.This approach accurately predicts band gaps and formation energies for mixed VODPs,achieving RootMean Square Errors of 21 meV and 3.9 meV/atom,respectively.Trained with samples with up-to three mixed elements and small supercells(<72 atoms),the model not only can be generalized to medium-and high-entropy systems and larger supercells(>200 atoms),but also well reproduces the bandgap bowing effect in Sn-based mixed VODPs.展开更多
P2-Na_(0.67)N_(i0.33)Mn_(0.67)O_(2)is considered as a promising cathode material for sodium-ion battery (SIBs)because of its high capacity and discharge potential.However,its practical use is limited by Na^(+)/vacancy...P2-Na_(0.67)N_(i0.33)Mn_(0.67)O_(2)is considered as a promising cathode material for sodium-ion battery (SIBs)because of its high capacity and discharge potential.However,its practical use is limited by Na^(+)/vacancy ordering and P2-O2 phase transition.Herein,a Ti^(4+)/F^(-) co-doping strategy is developed to address these issues.The optimal P2-Na_(0.67)Ni_(0.33)Mn_(0.37)Ti_(0.3)O_(1.9)F_(0.1) exhibits much enhanced sodium storage performance in the high voltage range of 2.0–4.4 V,including a cycling stability of 77.2%over 300cycles at a rate of 2 C and a high-rate capability of 87.7 m Ah g^(-1) at 6 C.Moreover,the P2-Na_(0.67)Ni_(0.33)Mn_(0.37)Ti_(0.3)O_(1.9)F_(0.1) delivers reversible capacities of 82.7 and 128.1 m Ah g^(-1) at-10 and 50℃ at a rate of 2 C,respectively.The capacity retentions over 200 cycles at-10℃ is 94.2%,implying more opportunity for practical application.In-situ X-ray diffraction analysis reveals that both P2-O2 phase transitions and Na^(+)/vacancy ordering is suppressed by Ti^(4+)/F^(-) co-doping,which resulting in fast Na^(+) diffusion and stable phase structure.The hard carbon//P2-Na_(0.67)Ni_(0.33)Mn_(0.37)Ti_(0.3)O_(1.9)F_(0.1) full cell exhibits a high energy density of 310.2 Wh kg^(-1) and remarkable cyclability with 82.1%retention after 300 cycles at 1 C in the voltage range of 1.5–4.2 V.These results demonstrate that the co-doping Ti^(4+)/F^(-) is a promising strategy to improve the electrochemical properties of P2-Na_(0.67)Ni_(0.33)Mn_(0.67)O_(2),providing a facile tactic to develop high performance cathode materials for SIBs.展开更多
The Na-deficient P3-type layered oxide cathode material usually experience complex in-plane Na^(+)/vacancy ordering rearrangement and undesirable P3-O3 phase transitions in the high-voltage region,leading to inferior ...The Na-deficient P3-type layered oxide cathode material usually experience complex in-plane Na^(+)/vacancy ordering rearrangement and undesirable P3-O3 phase transitions in the high-voltage region,leading to inferior cycling performance.Additionally,they exhibit unsatisfactory stability when exposed to water for extended periods.To address these challenges,we propose a Cu/Ti co-doped P3-type cathode material(Na_(0.67)Ni_(0.3)Cu_(0.03)Mn_(0.6)Ti_(0.07)O_(2)),which effectively mitigates Na^(+)/vacancy ordering and suppresses P3-O3 phase transitions at high voltages.As a result,the as-prepared sample exhibited outstanding cyclic performance,with 81.9%retention after 500 cycles within 2.5–4.15 V,and 75.7%retention after300 cycles within 2.5–4.25 V.Meanwhile,it demonstrates enhanced Na^(+)transport kinetics during desodiation/sodiation and reduced growth of charge transfer impedance(R_(ct))after various cycles.Furthermore,the sample showed superb stability against water,exhibiting no discernible degradation in structure,morphology,or electrochemical performance.This co-doping strategy provides new insights for innovative and prospective cathode materials.展开更多
A<sub>2</sub>FeCoO<sub>6-δ</sub> (A = Ca or Sr) is synthesized by the solid-state synthesis method and their specific heat capacities are evaluated at 40˚C using a heat flow meter. The effect ...A<sub>2</sub>FeCoO<sub>6-δ</sub> (A = Ca or Sr) is synthesized by the solid-state synthesis method and their specific heat capacities are evaluated at 40˚C using a heat flow meter. The effect of the A-cation size on the specific heat capacity of these compounds is observed. The specific heat capacity of Sr<sub>2</sub>FeCoO<sub>6-δ</sub> is found to be the highest, and that of Ca<sub>2</sub>FeCoO<sub>6-δ</sub> is the lowest while CaSrFeCoO<sub>6-δ</sub> shows the intermediate value. The specific heat capacity decreases with the decrease of the average A-site ionic radius, demonstrating the relationship between heat capacity and A-site ionic radius. The relationship between specific heat capacity and molar mass is also confirmed as the δ value decreases or molar mass increases from Ca<sub>2</sub>FeCoO<sub>6-δ</sub> to CaSrFeCoO<sub>6-δ</sub> to Sr<sub>2</sub>FeCoO<sub>6-δ</sub>.展开更多
Iron-based oxides are promising bifunctional electrocatalysts. The energy conversion efficiency of water splitting is limited by the scarcity of active sites and sluggish surface reactions in Fe_(2)O_(3). Therefore, w...Iron-based oxides are promising bifunctional electrocatalysts. The energy conversion efficiency of water splitting is limited by the scarcity of active sites and sluggish surface reactions in Fe_(2)O_(3). Therefore, we prepared one-dimensional Fe_(2)O_(3) nanobelt arrays (HNBs-V_(O)(LRO)-S) with ordered oxygen vacancy (V_(O)) structures via Pd-catalyzed oxygen reduction and sulfide thermal treatment. While preserving the ordered oxygen vacancy structure, sulfur (S) atoms selectively fill the trap-state oxygen vacancies to improve the bifunctional electrocatalytic activity and stability of Fe_(2)O_(3). Fe_(2)O_(3) nanobelt arrays with synergistic interactions between S atoms and ordered oxygen vacancies have low overpotentials for the anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER). Under 1 M potassium hydroxide (KOH), HNBs-V_(O)(LRO)-S exhibited excellent electrocatalytic performance for both the HER (226 mV@100 mA·cm^(-2)) and the OER (262 and 306 mV@100 mA·cm^(-2)). In addition, the HNBs-V_(O)(LRO)-S bifunctional catalyst only requires a low cell voltage of 1.92 V to deliver a current density of 100 mA·cm^(-2) and exhibits excellent long-term durability for over 100 h. The long-range ordered oxygen vacancies serve as fast channels for electron transfer and as active sites for the catalytic reaction. The S atoms only fill the trap-state oxygen vacancies (TS-V_(O)) in the Fe_(2)O_(3) nanobelts, which eliminates the negative effect of TS-V_(O) in the reaction. Moreover, the formed Fe-S coordination structure both stabilizes the ordered oxygen vacancy structure of HNBs-V_(O)(LRO)-S and provides more reactive active sites for the electrocatalytic reaction. Theoretical calculations show that the filling of S atoms lowers the free energy barrier such that the formation of OOH^(*) from O^(*) optimizes the free energy of uptake of the hydrogen intermediate H^(*) (∆G_(H^(*))) of the Fe_(2)O_(3) surface. This ingenious synergistic mechanism of vacancy filling provides new insights into the defective design of catalysts.展开更多
The two-orbital Hubbard model is studied numerically by using the Hartree-Fock approximation in both real space and momentum space, and the ground-state properties of the alkali metal iron selenide semiconducting KFel...The two-orbital Hubbard model is studied numerically by using the Hartree-Fock approximation in both real space and momentum space, and the ground-state properties of the alkali metal iron selenide semiconducting KFel.5Se2 are investigated. A rhombus-type Fe vacancy order with stripe- type antiferromagnetic （AFM） order is found, as was observed in neutron scattering experiments [J. Zhao, et al., Phys. Rev. Lett. 109, 267003 （2012）]. Hopping parameters are obtained by fitting the experimentally observed stripe AFM phase in real space. These hopping parameters are then used to study the ground-state properties of the semiconductor in momentum space. It is found to be a strongly correlated system with a large on-site Coulomb repulsion U, similar to the AFM Mort insulator -- the parent compound of copper oxide superconductors. We also find that the electronic occupation numbers and magnetizations in the dxz and dyz orbitals become different simultaneously when U 〉 Uc （～3.4 eV）, indicating orbital ordering. These results imply that the rotational symmetry between the two orbitals is broken by orbital ordering and thus drives the strong anisotropy of the magnetic coupling that has been observed by experiments and that the stripe-type AFM order in this compound may be caused by orbital ordering together with the observed large anisotropy.展开更多
Two-dimensional(2D)transition metal chalcogenides(TMCs)are promising for nanoelectronics and energy applications.Among them,the emerging non-layered TMCs are unique due to their unsaturated dangling bonds on the surfa...Two-dimensional(2D)transition metal chalcogenides(TMCs)are promising for nanoelectronics and energy applications.Among them,the emerging non-layered TMCs are unique due to their unsaturated dangling bonds on the surface and strong intralayer and interlayer bonding.However,the synthesis of non-layered 2D TMCs is challenging and this has made it difficult to study their structures and properties at thin thickness limit.Here,we develop a universal dual-metal precursors method to grow non-layered TMCs in which a mixture of a metal and its chloride serves as the metal source.Taking hexagonal Fe_(1-x)S as an example,the thickness of the Fe_(1-x)S flakes is down to 3 nm with a lateral size of over 100 μm.Importantly,we find ordered cation Fe vacancies in Fe_(1-x)S,which is distinct from layered TMCs like MoS_(2) where anion vacancies are commonly observed.Low-temperature transport measurements and theoretical calculations show that 2D Fe_(1-x)S is a stable semiconductor with a narrow bandgap of60 meV.In addition to Fe_(1-x)S,the method is universal in growing various non-layered 2D TMCs containing ordered cation vacancies,including Fe_(1-x)Se,Co_(1-x)S,Cr_(1-x)S,and V_(1-x)S.This work paves the way to grow and exploit properties of non-layered materials at 2D thickness limit.展开更多
“Intrinsic”strategies for manipulating the local electronic structure and coordination environment of defect-regulated materials can optimize electrochemical storage performance.Nevertheless,the structure–activity ...“Intrinsic”strategies for manipulating the local electronic structure and coordination environment of defect-regulated materials can optimize electrochemical storage performance.Nevertheless,the structure–activity relationship between defects and charge storage is ambiguous,which may be revealed by constructing highly ordered vacancy structures.Herein,we demonstrate molybdenum carbide MXene nanosheets with customized in-plane chemical ordered vacancies(Mo_(1.33)CT_(x)),by utilizing selective etching strategies.Synchrotron-based X-ray characterizations reveal that Mo atoms in Mo1.33CTx show increased average valence of+4.44 compared with the control Mo_(2)CT_(x).Benefited from the introduced atomic active sites and high valence of Mo,Mo_(1.33)CT_(x)achieves an outstanding capacity of 603 mAh·g^(−1)at 0.2 A·g^(−1),superior to most original MXenes.Li+storage kinetics analysis and density functional theory(DFT)simulations show that this optimized performance ensues from the more charge compensation during charge–discharge process,which enhances Faraday reaction compared with pure Mo_(2)CT_(x).This vacancy manipulation provides an efficient way to realize MXene’s potential as promising electrodes.展开更多
Wurtzite-type ferroelectrics are highly promising for next-generation microelectronic devices due to their ferroelectric properties and integration with exiting semiconductors.However,their high coercive fields,which ...Wurtzite-type ferroelectrics are highly promising for next-generation microelectronic devices due to their ferroelectric properties and integration with exiting semiconductors.However,their high coercive fields,which are close to breakdown electric fields,need to be lowered.To deal with this issue and secure device reliability,much effort has been devoted to exploring novel wurtzite compounds with lower polarization switching barriers and implementing doping strategies.Here,we report first-principles calculations on polarization switching in cation-vacancy ordered wurtziteα-Al2S3,unveiling its uniaxial quadruple-well ferroelectricity and moderate switching barrier,51 meV/cation,which is much lower than that of conventional wurtzite ferroelectrics.There are three important features relevant to the Al vacancies leading to the uncommon quadruple-well ferroelectricity and the moderate switching barrier:mitigation of cation-cation repulsion,structural flexibility that alleviates an in-plane lattice expansion,and formation ofσ-like bonding states consisting of Al 3pz and S 3pz orbitals.Biaxial compressive strain and Ga doping lower the switching barriers by up to 40%.This study encourages experimental investigation of the ferroelectric properties for defective wurtziteα-Al2S3 as a new promising material with unconventional and intriguing ferroelectricity and suggests a potential strategy for reducing switching barriers in wurtzite ferroelectrics:introducing cation vacancies.展开更多
基金Y.C.acknowledges support from U.S.Department of Energy under the Award Number DE-FG36-08GOI8004.
文摘Superlattice structures resulting from vacancy ordering have been observed in many materials.Here we report vacancy ordering behavior inⅢ_(2)Ⅵ_(3)nanowires.The formation of layer-like structural vacancies has been achieved during the synthesis of In_(2)Se_(3)nanowires through a vapor-transport route.Doping In_(2)Se_(3)nanowires with small amounts of Ga during synthesis can completely change the structural vacancy ordering from a layer-like to a screw-like pattern for(In_(x)Ga_(1-x))_(2)Se_(3)nanowires.Lithium atoms can fill in the layer-like structural vacancies of In_(2)Se_(3)nanowires and generate new types of vacancy and lithium atom ordering superlattices.The screw-patterned vacancies of(In_(x)Ga_(1-x))_(2)Se_(3)nanowires show reversible lithium insertion.Our results contribute to the understanding of structure property correlations ofⅢ_(2)Ⅵ_(3)materials used in lithium ion storage,photovoltaics,and phase change memory.
基金support of National Natural Science Foundation of China(61774123)support of National Natural Science Foundation of China(52150710545)+4 种基金support of their work at CAID.J.-J.W.and M.W.acknowledges financial support from Alexander von Humboldt Foundationfunding from Deutsche Forschungsgemeinschaft within SFB 917“Nanoswitches”support of 111 Project 2.0(BP2018008)the International Joint Laboratory for Micro/Nano Manufacturing and Measurement Technologies of Xi'an Jiaotong Universityprovided by the HPC platform of Xi'an Jiaotong University and the Hefei Advanced Computing Center,and the National Supercomputing Center in Xi'an.
文摘Tailoring the degree of structural disorder in Ge-Sb-Te alloys is important for the development of non-volatile phase-change memory and neuro-inspired computing.Upon crystallization from the amorphous phase,these alloys form a cubic rocksalt-like structure with a high content of intrinsic vacancies.Further thermal annealing results in a gradual structural transition towards a layered structure and an insulator-to-metal transition.In this work,we elucidate the atomic-level details of the structural transition in crystalline GeSb_(2)Te_(4) by in situ high-resolution transmission electron microscopy experiments and ab initio density functional theory calculations,providing a comprehensive real-time and real-space view of the vacancy ordering process.We also discuss the impact of vacancy ordering on altering the electronic and optical properties of GeSb_(2)Te_(4),which is relevant to multilevel storage applications.The phase evolution paths in Ge-Sb-Te alloys and Sb_(2)Te_(3)are illustrated using a summary diagram,which serves as a guide for designing phase-change memory devices.
文摘The modification of the electron diffraction pattern(EDP) of B2 in an as rapidly quenched then short time aged Ti Ni shape memory alloy(SMA) has been studied systematically using TEM. It was found that the diffusion scattering rings in EDP of an as rapidly quenched Ti-Ni SMA is associated with short range order (SRO) of vancancies in parent B2. After aging at 450℃ for 5 min the diffusion scattering rings are replaced by 1/2 {001} and 1 / 4 {012} extra reflections. It indicates that the SRO of vacancies has transformed into long range order (LRO) of vacancies,moreover,the LRO of vacancies exists in microdomains.
基金supported by the National Natural Science Foundation of China(Nos.52172205,11804166)the China Postdoctoral Science Foundation(No.2018M630587)Tianjin Natural Science Foundation(No.18JCQNJC77100)。
文摘2D MBenes have been theoretically predicted to possess unique electronic structures and physicochemical properties,and thus shown great promise in various applications.However,the synthesis of individual single-layer MBene remains a grand challenge due to its orthorhombic structure of MAB phases.Recently,scientists from Link?ping University have fabricated 2D monolayer Mo4/3B2-xTzwith ordered metal vacancies.Their results demonstrated the feasibility of top-down approach by chemical exfoliation of laminated compounds and provided the principle for further preparation of a wealth of MBenes.
基金support by the National Natural Science Foundation of China(12474221 and 12104080)the Guangdong Provincial Quantum Science Strategic Initiative(Grant No.GDZX2401002),and GHfund A(202407011848),Computational resources are provided by the National Supercomputer Center at Wuzhen.
文摘Vacancy-ordered double perovskites(VODPs)are promising alternatives to three-dimensional lead halide perovskites for optoelectronic applications.Mixing these materials creates a vast compositional space for tunable properties but complicates efficient screening of target candidates.Here,we illustrate the diverse electronic and optical characteristics as well as the nonlinear mixing effects within mixed VODPs.Furthermore,inspired by the observation that all physical properties of mixed systems with limited local environment options can be uniquely determined by the information regarding atomic-site occupation,we developed a method combining data augmentation and a transformer-inspired graph neural network to effectively encodes atomic-site information in mixed systems.This approach accurately predicts band gaps and formation energies for mixed VODPs,achieving RootMean Square Errors of 21 meV and 3.9 meV/atom,respectively.Trained with samples with up-to three mixed elements and small supercells(<72 atoms),the model not only can be generalized to medium-and high-entropy systems and larger supercells(>200 atoms),but also well reproduces the bandgap bowing effect in Sn-based mixed VODPs.
基金supported by the National Natural Science Foundation of China(21901146,51907110,22078179)the Key Research and Development Program of Shandong Province(2019GGX103027)+2 种基金the Natural Science Foundation of Shandong Province(ZR2019MB034)the Taishan Scholar Foundation(tsqn201812063)the 111 Project(B12015)。
文摘P2-Na_(0.67)N_(i0.33)Mn_(0.67)O_(2)is considered as a promising cathode material for sodium-ion battery (SIBs)because of its high capacity and discharge potential.However,its practical use is limited by Na^(+)/vacancy ordering and P2-O2 phase transition.Herein,a Ti^(4+)/F^(-) co-doping strategy is developed to address these issues.The optimal P2-Na_(0.67)Ni_(0.33)Mn_(0.37)Ti_(0.3)O_(1.9)F_(0.1) exhibits much enhanced sodium storage performance in the high voltage range of 2.0–4.4 V,including a cycling stability of 77.2%over 300cycles at a rate of 2 C and a high-rate capability of 87.7 m Ah g^(-1) at 6 C.Moreover,the P2-Na_(0.67)Ni_(0.33)Mn_(0.37)Ti_(0.3)O_(1.9)F_(0.1) delivers reversible capacities of 82.7 and 128.1 m Ah g^(-1) at-10 and 50℃ at a rate of 2 C,respectively.The capacity retentions over 200 cycles at-10℃ is 94.2%,implying more opportunity for practical application.In-situ X-ray diffraction analysis reveals that both P2-O2 phase transitions and Na^(+)/vacancy ordering is suppressed by Ti^(4+)/F^(-) co-doping,which resulting in fast Na^(+) diffusion and stable phase structure.The hard carbon//P2-Na_(0.67)Ni_(0.33)Mn_(0.37)Ti_(0.3)O_(1.9)F_(0.1) full cell exhibits a high energy density of 310.2 Wh kg^(-1) and remarkable cyclability with 82.1%retention after 300 cycles at 1 C in the voltage range of 1.5–4.2 V.These results demonstrate that the co-doping Ti^(4+)/F^(-) is a promising strategy to improve the electrochemical properties of P2-Na_(0.67)Ni_(0.33)Mn_(0.67)O_(2),providing a facile tactic to develop high performance cathode materials for SIBs.
基金supported by the National Natural Science Foundation of China(Nos.22179077,51774251,21908142)Shanghai Science and Technology Commission’s“2020 Science and Technology In-novation Action Plan”(No.20511104003)Natural Science Foundation in Shanghai(No.21ZR1424200)。
文摘The Na-deficient P3-type layered oxide cathode material usually experience complex in-plane Na^(+)/vacancy ordering rearrangement and undesirable P3-O3 phase transitions in the high-voltage region,leading to inferior cycling performance.Additionally,they exhibit unsatisfactory stability when exposed to water for extended periods.To address these challenges,we propose a Cu/Ti co-doped P3-type cathode material(Na_(0.67)Ni_(0.3)Cu_(0.03)Mn_(0.6)Ti_(0.07)O_(2)),which effectively mitigates Na^(+)/vacancy ordering and suppresses P3-O3 phase transitions at high voltages.As a result,the as-prepared sample exhibited outstanding cyclic performance,with 81.9%retention after 500 cycles within 2.5–4.15 V,and 75.7%retention after300 cycles within 2.5–4.25 V.Meanwhile,it demonstrates enhanced Na^(+)transport kinetics during desodiation/sodiation and reduced growth of charge transfer impedance(R_(ct))after various cycles.Furthermore,the sample showed superb stability against water,exhibiting no discernible degradation in structure,morphology,or electrochemical performance.This co-doping strategy provides new insights for innovative and prospective cathode materials.
文摘A<sub>2</sub>FeCoO<sub>6-δ</sub> (A = Ca or Sr) is synthesized by the solid-state synthesis method and their specific heat capacities are evaluated at 40˚C using a heat flow meter. The effect of the A-cation size on the specific heat capacity of these compounds is observed. The specific heat capacity of Sr<sub>2</sub>FeCoO<sub>6-δ</sub> is found to be the highest, and that of Ca<sub>2</sub>FeCoO<sub>6-δ</sub> is the lowest while CaSrFeCoO<sub>6-δ</sub> shows the intermediate value. The specific heat capacity decreases with the decrease of the average A-site ionic radius, demonstrating the relationship between heat capacity and A-site ionic radius. The relationship between specific heat capacity and molar mass is also confirmed as the δ value decreases or molar mass increases from Ca<sub>2</sub>FeCoO<sub>6-δ</sub> to CaSrFeCoO<sub>6-δ</sub> to Sr<sub>2</sub>FeCoO<sub>6-δ</sub>.
基金financial support from the National Natural Science Foundation of China(NSFC)(Nos.52472300 and 62004137)the Central Leading Science and Technology Development Foundation of Shanxi Province(No.YDZJSX20231A020)+3 种基金the Special Project for Science and Technology Cooperation and Exchange in Shanxi Province(No.202404041101025)the Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering(No.2022SX-TD002)the Shanxi Scholarship Council of China(No.2020-050)the Science and Technology Program of Yuncheng City(No.YCKJ-2023056)。
文摘Iron-based oxides are promising bifunctional electrocatalysts. The energy conversion efficiency of water splitting is limited by the scarcity of active sites and sluggish surface reactions in Fe_(2)O_(3). Therefore, we prepared one-dimensional Fe_(2)O_(3) nanobelt arrays (HNBs-V_(O)(LRO)-S) with ordered oxygen vacancy (V_(O)) structures via Pd-catalyzed oxygen reduction and sulfide thermal treatment. While preserving the ordered oxygen vacancy structure, sulfur (S) atoms selectively fill the trap-state oxygen vacancies to improve the bifunctional electrocatalytic activity and stability of Fe_(2)O_(3). Fe_(2)O_(3) nanobelt arrays with synergistic interactions between S atoms and ordered oxygen vacancies have low overpotentials for the anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER). Under 1 M potassium hydroxide (KOH), HNBs-V_(O)(LRO)-S exhibited excellent electrocatalytic performance for both the HER (226 mV@100 mA·cm^(-2)) and the OER (262 and 306 mV@100 mA·cm^(-2)). In addition, the HNBs-V_(O)(LRO)-S bifunctional catalyst only requires a low cell voltage of 1.92 V to deliver a current density of 100 mA·cm^(-2) and exhibits excellent long-term durability for over 100 h. The long-range ordered oxygen vacancies serve as fast channels for electron transfer and as active sites for the catalytic reaction. The S atoms only fill the trap-state oxygen vacancies (TS-V_(O)) in the Fe_(2)O_(3) nanobelts, which eliminates the negative effect of TS-V_(O) in the reaction. Moreover, the formed Fe-S coordination structure both stabilizes the ordered oxygen vacancy structure of HNBs-V_(O)(LRO)-S and provides more reactive active sites for the electrocatalytic reaction. Theoretical calculations show that the filling of S atoms lowers the free energy barrier such that the formation of OOH^(*) from O^(*) optimizes the free energy of uptake of the hydrogen intermediate H^(*) (∆G_(H^(*))) of the Fe_(2)O_(3) surface. This ingenious synergistic mechanism of vacancy filling provides new insights into the defective design of catalysts.
文摘The two-orbital Hubbard model is studied numerically by using the Hartree-Fock approximation in both real space and momentum space, and the ground-state properties of the alkali metal iron selenide semiconducting KFel.5Se2 are investigated. A rhombus-type Fe vacancy order with stripe- type antiferromagnetic （AFM） order is found, as was observed in neutron scattering experiments [J. Zhao, et al., Phys. Rev. Lett. 109, 267003 （2012）]. Hopping parameters are obtained by fitting the experimentally observed stripe AFM phase in real space. These hopping parameters are then used to study the ground-state properties of the semiconductor in momentum space. It is found to be a strongly correlated system with a large on-site Coulomb repulsion U, similar to the AFM Mort insulator -- the parent compound of copper oxide superconductors. We also find that the electronic occupation numbers and magnetizations in the dxz and dyz orbitals become different simultaneously when U 〉 Uc （～3.4 eV）, indicating orbital ordering. These results imply that the rotational symmetry between the two orbitals is broken by orbital ordering and thus drives the strong anisotropy of the magnetic coupling that has been observed by experiments and that the stripe-type AFM order in this compound may be caused by orbital ordering together with the observed large anisotropy.
基金supported by the National Science Fund for Distinguished Young Scholars(52125309)the National Natural Science Foundation of China(51991343,51920105002,51991340,52188101,and 11974156)+3 种基金Guangdong Innovative and Entrepreneurial Research Team Program(2017ZT07C341 and 2019ZT08C044)the Bureau of Industry and Information Technology of Shenzhen for the “2017 Graphene Manufacturing Innovation Center Project”(201901171523)Shenzhen Basic Research Project(JCYJ20200109144616617 and JCYJ20190809180605522)Shenzhen Science and Technology Program(KQTD20190929173815000 and 20200925161102001)。
文摘Two-dimensional(2D)transition metal chalcogenides(TMCs)are promising for nanoelectronics and energy applications.Among them,the emerging non-layered TMCs are unique due to their unsaturated dangling bonds on the surface and strong intralayer and interlayer bonding.However,the synthesis of non-layered 2D TMCs is challenging and this has made it difficult to study their structures and properties at thin thickness limit.Here,we develop a universal dual-metal precursors method to grow non-layered TMCs in which a mixture of a metal and its chloride serves as the metal source.Taking hexagonal Fe_(1-x)S as an example,the thickness of the Fe_(1-x)S flakes is down to 3 nm with a lateral size of over 100 μm.Importantly,we find ordered cation Fe vacancies in Fe_(1-x)S,which is distinct from layered TMCs like MoS_(2) where anion vacancies are commonly observed.Low-temperature transport measurements and theoretical calculations show that 2D Fe_(1-x)S is a stable semiconductor with a narrow bandgap of60 meV.In addition to Fe_(1-x)S,the method is universal in growing various non-layered 2D TMCs containing ordered cation vacancies,including Fe_(1-x)Se,Co_(1-x)S,Cr_(1-x)S,and V_(1-x)S.This work paves the way to grow and exploit properties of non-layered materials at 2D thickness limit.
基金support from the National Key Research and Development Program of China(Nos.2020YFA0405800,2019YFA0405601)the National Natural Science Foundation of China(NSFC)(Nos.U1932201,U2032113)+4 种基金the Youth Innovation Promotion Association of CAS(No.2022457)USTC Research Funds of the Double First-Class Initiative(No.YD2310002003)the Fundamental Research Funds for the Central Universities(Nos.WK2060000039,WK2310000088),Institute of Energy,Hefei Comprehensive National Science Center,University Synergy Innovation Program of Anhui Province(No.GXXT-2020-002)Collaborative Innovation Program of Hefei Science Center,CAS(No.2021HSC-CIP016)C.D.W.(No.202006340190)acknowledge financial support from the China Scholarship Council(CSC).L.S.acknowledges support from the Key Laboratory of Advanced Energy Materials Chemistry(Ministry of Education).
文摘“Intrinsic”strategies for manipulating the local electronic structure and coordination environment of defect-regulated materials can optimize electrochemical storage performance.Nevertheless,the structure–activity relationship between defects and charge storage is ambiguous,which may be revealed by constructing highly ordered vacancy structures.Herein,we demonstrate molybdenum carbide MXene nanosheets with customized in-plane chemical ordered vacancies(Mo_(1.33)CT_(x)),by utilizing selective etching strategies.Synchrotron-based X-ray characterizations reveal that Mo atoms in Mo1.33CTx show increased average valence of+4.44 compared with the control Mo_(2)CT_(x).Benefited from the introduced atomic active sites and high valence of Mo,Mo_(1.33)CT_(x)achieves an outstanding capacity of 603 mAh·g^(−1)at 0.2 A·g^(−1),superior to most original MXenes.Li+storage kinetics analysis and density functional theory(DFT)simulations show that this optimized performance ensues from the more charge compensation during charge–discharge process,which enhances Faraday reaction compared with pure Mo_(2)CT_(x).This vacancy manipulation provides an efficient way to realize MXene’s potential as promising electrodes.
基金supported by Japan Society of the Promotion of Science(JSPS)KAKENHI Grants Nos.JP17K19172,JP18H01892,JP19H00883,JP21K19027,JP21H05568,JP21H04619,JP23H02069,and JP23H01869H.A.appreciates Murata Science Foundation and Collaborative Research Project of Laboratory for Materials and Structures,Institute of Innovative Research,Tokyo Institute of Technology.S.O.gratefully acknowledges the Toyota Riken for financial support through a Rising Fellow Program.The computation was carried out using the computer resource offered under the category of General Projects by Research Institute for Information Technology,Kyushu University.
文摘Wurtzite-type ferroelectrics are highly promising for next-generation microelectronic devices due to their ferroelectric properties and integration with exiting semiconductors.However,their high coercive fields,which are close to breakdown electric fields,need to be lowered.To deal with this issue and secure device reliability,much effort has been devoted to exploring novel wurtzite compounds with lower polarization switching barriers and implementing doping strategies.Here,we report first-principles calculations on polarization switching in cation-vacancy ordered wurtziteα-Al2S3,unveiling its uniaxial quadruple-well ferroelectricity and moderate switching barrier,51 meV/cation,which is much lower than that of conventional wurtzite ferroelectrics.There are three important features relevant to the Al vacancies leading to the uncommon quadruple-well ferroelectricity and the moderate switching barrier:mitigation of cation-cation repulsion,structural flexibility that alleviates an in-plane lattice expansion,and formation ofσ-like bonding states consisting of Al 3pz and S 3pz orbitals.Biaxial compressive strain and Ga doping lower the switching barriers by up to 40%.This study encourages experimental investigation of the ferroelectric properties for defective wurtziteα-Al2S3 as a new promising material with unconventional and intriguing ferroelectricity and suggests a potential strategy for reducing switching barriers in wurtzite ferroelectrics:introducing cation vacancies.
