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Sökning: WFRF:(Sun Weiwei)

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1.
  • Li, Hui, et al. (författare)
  • Enabling the transition to ductile MAX phases and the exfoliation to MXenes via tuning the A element
  • 2023
  • Ingår i: Journal of The American Ceramic Society. - : Wiley-Blackwell. - 0002-7820 .- 1551-2916. ; 106:6, s. 3765-3776
  • Tidskriftsartikel (refereegranskat)abstract
    • Two-dimensional MXenes, exfoliated from their parental precursors-MAX phases, exhibit several outstanding properties and have achieved several accomplishments in a vast range of fields. Developing novel and high-performance MXenes has become a vital task in materials science, so estimating the possibilities for exfoliation is a topic positioned at the research frontier. Here, the likelihood of exfoliating 36 M(2)AC MAX phases was explored by using density functional theory. For MAX phases, the composition-dependent mechanical performances were investigated, highlighting evident trends, and, more essentially, improving MAX phases toughness, which can be achieved via modulating the A site. Two novel criteria were then introduced to assess the probability of exfoliating MXenes from MAX phases, having less complexity and lower computational cost than the prior studies. The excellent agreement provided by the new criteria with the reported results demonstrates that they are feasible, reliable as well as easily accessible. Furthermore, some key features that were previously suggested to be related to exfoliation are instead determined to be weakly correlated with it. We thus performed a detailed numerical analysis to locate representative and correlated features that are fundamental for the exfoliation. Our findings provide deep insight into the synthesis process and accelerate the discovery of new MXenes.
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2.
  • Zhang, Jing, et al. (författare)
  • Unraveling the role of the BCC-B2 transition and V occupancies in the contradictory magnetism-ductility relationship of FeCoV alloys
  • 2024
  • Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 997
  • Tidskriftsartikel (refereegranskat)abstract
    • The contradictory relationship between magnetism and ductility restricts further applications of FeCoV alloys in high-performance electrical machines. The role of the BCC-B2 transition, accompanied by vanadium (V) site occupancies, in magnetic moments and ductility has been explored using first-principles calculations. The variations in magnetism and ductility of FeCoV alloys are attributed to the coupling of the BCC-B2 transition and V occupancies. When V replaces Fe atoms in the equiatomic B2-FeCo alloy, the superior magnetism observed in B2-Fe50-cCo50Vc alloys is a consequence of the enhanced local magnetic moment of Fe and the ferrimagnetic-ferromagnetic transition in the magnetic state. Moreover, due to the preferential V occupancy in the B2 phase, the B2-Fe46Co50V4 alloy exhibits comparable ductility to the BCC-Fe50Co46V4 alloy. The results indicate that the increased brittleness in the B2 phase arises from the raised Peierls stress and the enhanced covalent component in interatomic bonding, which is caused by the strong hybridization between Fe and Co atoms. Pearson correlation analysis illustrates that valence electron concentration (VEC) and V content are significant factors in the contradictory relationship between magnetization and ductility. The theoretical results demonstrate that tuning the V content and atomic occupancies is helpful to achieve a trade-off between magnetization and ductility in B2-FeCoV alloys.
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3.
  • Lee, Chunsik, et al. (författare)
  • VEGF-B prevents excessive angiogenesis by inhibiting FGF2/FGFR1 pathway
  • 2023
  • Ingår i: SIGNAL TRANSDUCTION AND TARGETED THERAPY. - : SPRINGERNATURE. - 2095-9907 .- 2059-3635. ; 8:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Although VEGF-B was discovered as a VEGF-A homolog a long time ago, the angiogenic effect of VEGF-B remains poorly understood with limited and diverse findings from different groups. Notwithstanding, drugs that inhibit VEGF-B together with other VEGF family members are being used to treat patients with various neovascular diseases. It is therefore critical to have a better understanding of the angiogenic effect of VEGF-B and the underlying mechanisms. Using comprehensive in vitro and in vivo methods and models, we reveal here for the first time an unexpected and surprising function of VEGF-B as an endogenous inhibitor of angiogenesis by inhibiting the FGF2/FGFR1 pathway when the latter is abundantly expressed. Mechanistically, we unveil that VEGF-B binds to FGFR1, induces FGFR1/VEGFR1 complex formation, and suppresses FGF2-induced Erk activation, and inhibits FGF2-driven angiogenesis and tumor growth. Our work uncovers a previously unrecognized novel function of VEGF-B in tethering the FGF2/FGFR1 pathway. Given the anti-angiogenic nature of VEGF-B under conditions of high FGF2/FGFR1 levels, caution is warranted when modulating VEGF-B activity to treat neovascular diseases.
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4.
  • Li, Shaohan, et al. (författare)
  • Pushing the limit of thermal conductivity of MAX borides and MABs
  • 2022
  • Ingår i: Journal of Materials Science & Technology. - : Elsevier. - 1005-0302. ; 97, s. 79-88
  • Tidskriftsartikel (refereegranskat)abstract
    • The emergence of MAX borides as well as MAB phases attracted great attention because of the renewable developments of ternary ceramics and offering great opportunities in potential applications. However, the number of borides remains limited, and further fundamental descriptions and detailed investigations on various properties are still lacking. In this report, we employ an integrated computational scheme that combines density functional theory with the evolutional algorithm to search for the favorable structures of P- and S-glued ternary borides terminated by Nb metal. We discover that the structures of 212-type, as e.g. Nb2PB2 and Nb2SB2, belong to the P‾6m2 space group, while those of 211-type, as e.g. Nb2PB and Nb2SB, prefer to crystallize in the P63/mmc space group, and the corresponding carbides Nb2PC and Nb2SC are also considered for the sake of completeness and comparative analsys. The predicted Nb2PB2, Nb2PB, Nb2SB, Nb2PC and Nb2SC are energetically stable, as revealed by the negative formation energies and by the proposed reaction paths with respect to the most competing phases, as well as dynamically stable, as suggested by the non-imaginary phonon spectra. The thermal conductivities of the six materials show unusual behaviors, particularly for the acoustic and optical contributions, and are accompanied by a strong anisotropy. Most importantly, Nb2PB2 is found to be an excellent thermal conductor with a total thermal conductivity of ~65 W/(m K), while Nb2SC is found to be an ultra-low thermal conductor, with a total thermal conductivity of ~5 W/(m K). These values are clearly outside the currently reported range of thermal conductivities, which makes Nb2PB2 and Nb2SC extremely interesting for fundamental research as well as prospective applications with the aid of artificial tunings on the almost independent MB block and the A layer. The discovery of these novel materials is expected to contribute substantially to the rapid development of ternary ceramics and to accelerate attempts in the applicability of MAX phases for heat conduction.
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5.
  • Li, Yuhan, et al. (författare)
  • Understanding the electrochemical properties of A(2)MSiO(4) (A = Li and Na; M = Fe, Mn, Co and Ni) and the Na doping effect on Li2MSiO4 from first-principles calculations
  • 2016
  • Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:44, s. 17455-17463
  • Tidskriftsartikel (refereegranskat)abstract
    • To explore the feasibility of regarding silicate materials as sustainable cathode materials for rechargeable Na ion batteries, the voltage plateaus, cycling stabilities, electrical conductivities and ionic conductivities of Li2MSiO4 and Na2MSiO4 (M = Fe, Mn, Co and Ni) are investigated by first principles calculations. The calculated electrochemical performance of silicate materials gives reasonable explanations for the poor capacity retention of Li2MnSiO4 as well as the reason why Li2FeSiO4 and Li2CoSiO4 exchange only one Li ion per formula unit. In comparison with Na2MSiO4, Li2MSiO4 presents higher voltage and better cycling stability. However, Na2MSiO4 displays higher electrical and ionic conductivities. Moreover, Na2NiSiO4 also presents significant potential for application as a good cathode material for Na ion batteries, as it can deliver high voltage and reversibly exchange 1.5 Li ions per formula unit. Furthermore, to make full use of the advantages of Li2MSiO4 and Na2MSiO4, a Na doped Li1.5Na0.5MSiO4 system is explored as well. The results suggest that Na doping can improve the electronic and ionic conductivities of Li2MSiO4 materials and simultaneously maintain the voltage and cycling stability. Therefore, Na ion doping should be an effective methodology to improve the performance of Li2MSiO4 cathode materials.
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6.
  • Usman, Rabia, et al. (författare)
  • Investigation of Charge-Transfer Interaction in Mixed Stack Donor-Acceptor Cocrystals Toward Tunable Solid-State Emission Characteristics
  • 2018
  • Ingår i: Crystal Growth & Design. - : AMER CHEMICAL SOC. - 1528-7483 .- 1528-7505. ; 18:10, s. 6001-6008
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation of three mixed binary charge transfer (CT) cocrystals with tunable photoluminescence behavior featuring both CT interaction and directional hydrogen bonding is presented. Our strategy consists of the CT induced cocrystallization of three polycyclic (naphthalene, anthracene, and pyrene) carrying a-cyanostilbene (CS) derivatives, namely, 3-(naphthalene-2-yl)-2-(p-tolyl) acrylonitrile (NPA), 3-(anthracene-9-yl)-2-phenylacrylonitrile (APA), and 2-(4-methoxyphenyl)-3-(pyrene-I-yl) acrylonitrile (MPA) as donors (D) with 1,2,4,5-tetracyanobenzene (TCNB) as an acceptor (A). The as prepared cocrystals were probed in detail by various analytical techniques, namely, X-ray diffraction data, vibrational spectroscopy, diffuse reflectance absorption spectroscopy, fluorescence properties, and fluorescence quantum yields and lifetimes, affirming the formation of CT complexes. Complex IA features a mixed stack arrangement (D-A-D-A-D), while IIA and IIIA revealed (DAD-DAD) stack arrangement. The CT products showed distinct tunable emission colors and photoluminescence characteristics, which is closely associated with the CT interactions between the donor and acceptor moiety, and ionization potential or the it pi-electron rich character of the polycyclic moiety of the donor molecule. This research demonstrates the development of new hybrid CT functional materials with enhanced optical properties such as absorption, fluorescence emissions, and lifetimes compared to the pristine donors, which is important for the exploration of new solid-state luminescent materials.
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7.
  • Wei, Xiao-Ping, et al. (författare)
  • Investigations on electronic, Fermi surface, Curie temperature and optical properties of Zr2CoAl
  • 2017
  • Ingår i: Journal of Solid State Chemistry. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0022-4596 .- 1095-726X. ; 247, s. 97-104
  • Tidskriftsartikel (refereegranskat)abstract
    • Using full-potential local-orbital minimum-basis along with spin-polarized relativistic Korringa-Kohn-Rostoker methods, we study the electronic, Fermi surface, Curie temperature and optical properties of Zr2CoAl alloy. The alloy with Li2AgSb and Cu2MnAl structures are compared in terms of magnetic properties, and the electronic structures in two structures are also discussed. According to the calculated electronic states, it finds that the Zr2CoAl with Li2AgSb structure is half-metallic ferromagnet with an integral magnetic moment of 2.00 mu(beta), meanwhile we also notice the d-d and p-d hybridizations are responsible for the formation of minority-spin gap, furthermore, the fat-bands are applied to discuss the mixture between d and p electrons in the vicinity of the Fermi level. The Fermi surfaces related to the valence bands are constructed, and it is found that the spin-up valence bands 26, 27 and 28 across the Fermi energy dominate the nature of electrons. By mapping the system onto a Heisenberg Hamiltonian, we obtain the exchange coupling parameters, and observe that the Zr(A)-Co(C) and Zr(A)-Zr(B) interactions provide a major contribution for exchange interactions. Based on the calculated exchange coupling parameters, the Curie temperature is estimated to be 287.86 K at equilibrium, and also the dependence of Curie temperature on lattice constant related to the tunable Curie temperature in Zr2CoAl alloy is studied. Finally, we report the optical properties of Zr2CoAl alloy, and present the photon energy dependence of the absorption, the optical conductivity and the loss function.
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8.
  • Zhang, Jing, et al. (författare)
  • Understanding the magnetism-ductility trade-off in FeCoMn alloys: The role of the BCC-B2 transition and Mn occupancies
  • 2024
  • Ingår i: Materials & design. - : Elsevier Ltd. - 0264-1275 .- 1873-4197. ; 243
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetism-ductility contradictory relationship presents a significant challenge in the development of magnetic alloys. The impact of the BCC-B2 transition, along with Mn site occupancy, on magnetism and ductility have been investigated by using first-principles calculations. The calculations involved the evaluation of magnetic moments, density of states (DOS), phase stability and ductility of FeCoMn alloys. The results of binary alloys confirm the enhancement of magnetism due to the BCC-B2 transition. Furthermore, the ordering phase transition can strengthen the magnetic interaction between Fe and Mn atoms, which is associated with minimal variations in the density of states of Fe and Mn in the B2 structure. Regarding the ductility of FeCoMn alloys, two factors contribute to increased brittleness. Firstly, the increased covalent component in bonding, as a result of the strong hybridization between different elements, leads to an increased brittleness. Secondly, the increased Peierls stress provides a larger resistance to dislocation motion, which also contributes to the increased brittleness. Finally, the Pearson correlation coefficients and data analysis indicate that VEC, spin polarizations and Mn content provide major contributions to the contradictory relationship between magnetism and ductility.
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9.
  • Chen, Haiyang, et al. (författare)
  • Heterogeneous Nucleating Agent for High-Boiling-Point Nonhalogenated Solvent-Processed Organic Solar Cells and Modules
  • 2024
  • Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095.
  • Tidskriftsartikel (refereegranskat)abstract
    • High-boiling-point nonhalogenated solvents are superior solvents to produce large-area organic solar cells (OSCs) in industry because of their wide processing window and low toxicity; while, these solvents with slow evaporation kinetics will lead excessive aggregation of state-of-the-art small molecule acceptors (e.g. L8-BO), delivering serious efficiency losses. Here, a heterogeneous nucleating agent strategy is developed by grafting oligo (ethylene glycol) side-chains on L8-BO (BTO-BO). The formation energy of the obtained BTO-BO; while, changing from liquid in a solvent to a crystalline phase, is lower than that of L8-BO irrespective of the solvent type. When BTO-BO is added as the third component into the active layer (e.g. PM6:L8-BO), it easily assembles to form numerous seed crystals, which serve as nucleation sites to trigger heterogeneous nucleation and increase nucleation density of L8-BO through strong hydrogen bonding interactions even in high-boiling-point nonhalogenated solvents. Therefore, it can effectively suppress excessive aggregation during growth, achieving ideal phase-separation active layer with small domain sizes and high crystallinity. The resultant toluene-processed OSCs exhibit a record power conversion efficiency (PCE) of 19.42% (certificated 19.12%) with excellent operational stability. The strategy also has superior advantages in large-scale devices, showing a 15.03-cm2 module with a record PCE of 16.35% (certificated 15.97%). The heterogeneous nucleating agent (BTO-BO) is developed to suppress the excessive aggregation of L8-BO in high-boiling-point nonhalogenated solvents processing, achieving the active layer with high crystallinity and nano-scaled phase separation morphology. The resultant OSCs achieve record power conversion efficiencies of 19.42% (0.062-cm2) and 16.35% (15. 03-cm2) with excellent operational stabilities. image
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10.
  • Dai, Jingjing, et al. (författare)
  • Behavior of intrinsic defects in BaF2 under uniaxial compressions : An ab initio investigation
  • 2021
  • Ingår i: Materials Today Communications. - : Elsevier. - 2352-4928. ; 28
  • Tidskriftsartikel (refereegranskat)abstract
    • We revisit the defects and related optical properties of one of the prototypical scintillator materials, BaF2, by means of density functional theory calculations. The interstitial F atom is found to be the most favorable defect to be formed, while it is rather difficult to create a F vacancy, Ba vacancy and Ba interstitial intrinsically, unless external forces are applied to the lattice, such as shock compression. The migration barriers for the above defects are remarkably path dependent. For a Ba vacancy, the migration barrier in the (001) (loading) direction is significantly reduced compared to those in the perpendicular (100) and (010) directions, while the migration along the (101) direction has the least value, which is surprisingly smaller than that at ambient pressure. An interstitial Ba atom prefers to move along the (100) and (010) directions in a manner similar to collective diffusion. The F vacancy has the lowest energy barrier along the (001) direction, while uniaxial strain greatly hinders the diffusion of F interstitials. We also study the role of defects on the optical absorption and find that a F vacancy, and interstitial F and Ba atoms are able to introduce pronounced changes to the spectra, whereas the Ba vacancy only shows marginal effects. The favorable migration paths for the different types of defects under strain or pressure can contribute to the design of specific ionic conductor properties under extreme conditions.
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11.
  • Fu, Y. D., et al. (författare)
  • The role of group III, IV elements in Nb(4)AC(3) MAX phases (A = Al, Si, Ga, Ge) and the unusual anisotropic behavior of the electronic and optical properties
  • 2017
  • Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 19:23, s. 15471-15483
  • Tidskriftsartikel (refereegranskat)abstract
    • Niobium based Nb4AlC3, Nb4SiC3, Nb4GeC3 and Nb4GaC3 were investigated by means of density functional theory. Together with the known Nb4AlC3, the role of group III, IV elements in various properties of Nb(4)AC(3) (A = Al, Si, Ga, Ge) was systematically investigated, and particularly the bulk moduli, shear moduli, and Young's moduli helped us to approach the ductility. All the studied compounds were found to be mechanically stable, and they also exhibit the metallic nature that results from the Nb-4d states being dominant at the Fermi level. The typical 4d-2p hybridization leads to strong Nb-C covalent bonding and a relatively weaker 4d-3p (4p) hybridization between Nb and A is identified. The latter does perturb the performance of materials. By varying A elements in Nb(4)AC(3), the position and the width of the p states as well as hybridizations are altered, which determine the covalency and the ionicity of the chemical bonds. A high density of states at the Fermi level and the nesting effects in the Fermi surface are identified in Nb4SiC3 and linked to its unusual anisotropic behavior. Furthermore, Nb4GeC3 is predicted to be a very promising candidate solar heating barrier material. Overall, the present work gives insights into the role of A elements in the electronic structure and the physical properties of Nb(4)AC(3) compounds. The tendencies and rules established here will help in the designing of functional ceramic materials with desirable properties.
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12.
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13.
  • Hussain, Tanveer, et al. (författare)
  • Strain and doping effects on the energetics of hydrogen desorption from the MgH2 (001) surface
  • 2013
  • Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 101:2, s. 27006-
  • Tidskriftsartikel (refereegranskat)abstract
    • On the basis of first-principles calculations we have systematically investigated the energetics of hydrogen desorption from the MgH2 (001) surface. Based on total energy and electronic structure calculations, two modes namely strain and doping of selected dopants (Al, Si, Ti) and the combined effect of both on the dehydrogenation energies (ΔH) of MgH2 (001) systems have been analyzed. The maximum improvement in ΔH has been obtained with the combined effect of doping and strain. Among all the dopants, Al gives the lowest value of ΔH when the system Al-MgH2 is subjected to a 7.5% biaxial symmetric strain whereas the Si-MgH2 systems show the least improvement in ΔH. The doping of Ti on MgH 2 (001) is also very beneficial even without strain. The reduction in ΔH is caused by the charge localization on the metal atoms, destabilization and the weakening of metal-hydrogen bonds.
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14.
  • Kaewmaraya, Thanayut, et al. (författare)
  • Atomistic study of promising catalyst and electrode material for memory capacitors : Platinum oxides
  • 2013
  • Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 79, s. 804-810
  • Tidskriftsartikel (refereegranskat)abstract
    • Platinum oxides have the technological importance as evidenced by numerous studies concentrating on their crystal structures to attain the clear atomistic understanding but the controversy exists between the experimental and theoretical studies. In our present study, we report the electronic and optical properties of crystalline PtO and PtO2 on the basis of Heyd-Scuseria-Ernzerhof (HSE06) functional within the framework of the density functional theory (DFT). We present the structural parameters, electronic and optical properties of several proposed structures of PtO and PtO2. We find that PtS-type structure of PtO and CaCl2-type structure of PtO2 are the most stable structures of these materials on the basis of hybrid functional and they appear to be semiconductors with band gap values of 0.87 eV and 1.85 eV, respectively. The mechanical stability of these structures is also confirmed by calculating the phonon band structures. The corresponding structural parameters are found in good agreement with experimental values. Furthermore, we present the bader charge analysis and optical properties of these phases.
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15.
  • Khan, A., et al. (författare)
  • Solid emission color tuning of organic charge transfer cocrystals based on planar π-conjugated donors and TCNB
  • 2019
  • Ingår i: Journal of Solid State Chemistry. - : Academic Press. - 0022-4596 .- 1095-726X. ; 272, s. 96-101
  • Tidskriftsartikel (refereegranskat)abstract
    • Two luminescent Charge Transfer (CT) cocrystals involving planar phenanthrene derivatives namely, formyl phenanthrene (FP) and acetyl phenanthrene (AP) as donors (D) and 1,2,4,5-tetracyanobenzene (TCNB) as an acceptor (A) building block, are formed by molecular self-assembly. Detailed structural and spectroscopic measurements elucidated the mixed stack sequence DADAD in the CT cocrystals. The solid supramolecular architecture for both the cocrystals forms 2D sheet, supported by the extended network of C-H···O, and C-H···N hydrogen bonds as evidenced by the crystallographic observation. Interestingly, the two cocrystals display tunable emissions compared to the blue emissions of donor compounds, which correlate with the formation of excited CT state between the donor and acceptor motifs as a result of mixed stack orientation. The nature of the CT interactions in the two cocrystals was further explored by applying density functional theoretical (DFT) studies. Such a supramolecular cocrystal approach provides a facile platform towards the design of new luminescent two component CT complexes with desired functionalities.
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16.
  • Kvashnin, Yaroslav O., et al. (författare)
  • Electronic topological transition and noncollinear magnetism in compressed hcp Co
  • 2015
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:13
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent experiments showed that Co undergoes a phase transition from the ferromagnetic hcp phase to the nonmagnetic fcc one around 100 GPa. Since the transition is of first order, a certain region of coexistence of the two phases is present. By means of ab initio calculations, we found that the hcp phase itself undergoes a series of electronic topological transitions (ETTs), which affects both elastic and magnetic properties of the material. Most importantly, we propose that the sequence of ETTs lead to the stabilization of a noncollinear spin arrangement in highly compressed hcp Co. Details of this noncollinear magnetic state and the interatomic exchange parameters that are connected to it are presented here.
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17.
  • Li, Yunguo, et al. (författare)
  • Dynamic stability of the single-layer transition metal dichalcogenides
  • 2014
  • Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 92, s. 206-212
  • Tidskriftsartikel (refereegranskat)abstract
    • In the quest for advanced semi-conductors, we have expanded our knowledge on a series of single-layer TMDs by calculating the electronic structure and lattice dynamic stability based on the first-principles density functional theory. The single layers of Mo and W dichalcogenides are found to be stable with P-6m2 symmetry. The reduction of dimension opens up and increases the bandgap. The charge transfer is found to decrease from sulfide to selenide and to telluride due to the decrease of electronegativity of chalcogen, which also induces the reduction of bandgap. The TA mode softening is found along Gamma-K direction and becomes more significant from sulfide to selenide and to telluride in the single-layer TMDs of Mo and W, which corresponds to the vibration of transition metal cations along y-axis. The single layers of Nb dichalcogenides are found to be instable with P-6m2 symmetry but stable with P-3m1 symmetry. It is also speculated that the interactions of cations mediated by electron-phonon coupling are accountable for the dynamic instability of the single-layer TMDs of Nb with P-6m2 symmetry. The unstable P-6m2 single-layer Nb dichalcogenides can transform to the stable P-3m1 structure during the exfoliation from the bulk, via the displacement of two anion layers of the sandwich structure.
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18.
  • Panda, Swarup K., et al. (författare)
  • High photon energy spectroscopy of NiO : Experiment and theory
  • 2016
  • Ingår i: PHYSICAL REVIEW B. - 2469-9950. ; 93:23
  • Tidskriftsartikel (refereegranskat)abstract
    • We have revisited the valence band electronic structure of NiO by means of hard x-ray photoemission spectroscopy (HAXPES) together with theoretical calculations using both the GW method and the local density approximation + dynamical mean-field theory (LDA+DMFT) approaches. The effective impurity problem in DMFT is solved through the exact diagonalization (ED) method. We show that the LDA+DMFT method in conjunction with the standard fully localized limit (FLL) and around mean field (AMF) double-counting alone cannot explain all the observed structures in the HAXPES spectra. GW corrections are required for the O bands and Ni-s and p derived states to properly position their binding energies. Our results establish that a combination of the GW and DMFT methods is necessary for correctly describing the electronic structure of NiO in a proper ab initio framework. We also demonstrate that the inclusion of photoionization cross section is crucial to interpret the HAXPES spectra of NiO. We argue that our conclusions are general and that the here suggested approach is appropriate for any complex transition metal oxide.
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19.
  • Sun, Tao, et al. (författare)
  • Algorithm for Surfaces Profiles and Thickness Variation Measurement of a Transparent Plate Using a Fizeau Interferometer with Wavelength Tuning
  • 2019
  • Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 9:11
  • Tidskriftsartikel (refereegranskat)abstract
    • An interferogram obtained from a transparent plate contains information on the profiles of both surfaces and on the thickness variation. The present work is devoted to the processing of interferograms of this type. The processing technique is based on a 36-step algorithm developed by the authors for characterization of transparent plates having approximately equal reflections from both sides. The algorithm utilizes weighted multi-step phase shifting that enables one not only separately to extract the front and rear surface profiles together with the thickness variation of the tested plate but also to suppress the coupling errors between the higher harmonics and phase-shift deviation. The proposed measuring method was studied on a wavelength tunable Fizeau interferometer. The tested sample had an optical thickness and surface profile deviations equal to 0.51 µm, 1.38 µm and 0.89 µm, respectively. According to the results obtained using 10 repeated measurements, the root mean square (RMS) errors for determining both surface profiles did not exceed 1.5 nm. Experimental results show that the setup and presented 36-step algorithm are suitable for the measurement of a transparent plate of arbitrary thickness.
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20.
  • Sun, Tao, et al. (författare)
  • Determination of surface profiles of transparent plates by means of laser interferometry with wavelength tuning
  • 2019
  • Ingår i: Optics and lasers in engineering. - : ELSEVIER SCI LTD. - 0143-8166 .- 1873-0302. ; 115, s. 59-66
  • Tidskriftsartikel (refereegranskat)abstract
    • An interferogram obtained from a transparent plate contains information about the profiles of both surfaces of the plate. This information can be extracted by processing fringe patterns measured at different wavelengths. The conventional Fourier analysis applied to solve such problems for a set of a restricted number of the fringe patterns is quite sensitive to the error of detuning the wavelength shifting and suffers from fringe patterns interference noise. This study proposes a method for finding surface profiles of a transparent plate using a series of fringe patterns obtained at different phase shifts caused by wavelength changes. The data treatment is based on the analytical approach for describing spatial distributions of irradiance in interference patterns. The results show that the proposed method is feasible. The experimental setup used herein was a Fizeau interferometer with tunable wavelength laser. A glass plate approximately 1 cm thick was as the test sample. According to the obtained results, the root mean square (RMS) errors for determining both surface profiles did not exceed 2.3 nm.
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21.
  • Sun, Weiwei, et al. (författare)
  • A LDA+U and LDA+DMFT study of uranium mononitride : from nonmagnetic to paramagnetic and ferromagnetic
  • 2014
  • Ingår i: MRS Proceedings. - : Materials Research Society. - 0272-9172 .- 1946-4274.
  • Konferensbidrag (refereegranskat)abstract
    • The combination of density functional theory in local density approximation and dynamical mean field theory (LDA+DMFT) was employed in a preliminary study of the strong electron correlation effects in a promising nuclear fuel—uranium mononitride (UN). For the ferromagnetic phase, the effective impurity problem arising in the LDA+DMFT [1-3] cycle is solved with the spin-polarized T-matrix fluctuation exchange (SPTF) solver, which includes spin–orbit interactions. Concerning the paramagnetic phase, the disordered local moment (DLM) approach was used, based on both standard local density approximation (LDA) and LDA+U. Basic spectral properties and material properties, such as the spin, orbital and total magnetic moments on U atom were calculated for various values of the Hubbard parameter U with a fixed exchange parameter J. Our main focus was to compare the calculated spectral functions (density of states) for different magnetic phases and different methods to the experimental XPS data [4]. On top of that, the total moments of the paramagnetic and ferromagnetic phases are compared with the measured values by neutron spectroscopy [4, 5].
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22.
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23.
  • Sun, Weiwei, et al. (författare)
  • A new 2D monolayer BiXene, M2C (M = Mo, Tc, Os)
  • 2016
  • Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 8:34, s. 15753-15762
  • Tidskriftsartikel (refereegranskat)abstract
    • The existence of BiXenes, a new family of 2D monolayers, is hereby predicted. Theoretically, BiXenes have 1H symmetry (P (6) over bar m2) and can be formed from the 4d/5d binary carbides. As the name suggests, they are close relatives of MXenes, which instead have 1T symmetry (P (3) over bar m1). The newly found BiXenes, as well as some new MXenes, are shown to have formation energies close to that of germanene, which suggests that these materials should be possible to be synthesised. Among them, we illustrate that 1H-Tc2C and 1T-Mo2C are dynamically stable at 0 K, while 1H-Mo2C, 1T-Tc2C, 1H-Os2C, and 1T-Rh2C are likely to be stabilised via strain or temperature. In addition, the nature of the chemical bonding is analysed, emphasizing that the covalency between the transition metal ions and carbon is much stronger in BiXenes than in MXenes. The emergence of BiXenes can not only open up a new era of conducting 2D monolayers, but also provide good candidates for carrier materials aimed at energy storage and spintronic devices that have already been unveiled in MXenes.
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24.
  • Sun, Weiwei (författare)
  • Ab initio study of transition metal carbides and actinide compounds
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Two classes of materials are investigated using ab intio methods based on density functional theory. The structural properties, electronic structure and thermodynamic properties of binary and ternary transition metal carbides are discussed in details. In addition, two actinide compounds will be presented. A new actinide monoxide, ThO, is predicted to be stable under pressure, and the weakly correlated UN is investigated as regards to its magnetic properties and electronic structure.The atomic and electronic structures of various types of single defects in TiC such as vacancies, interstitial defects, and antisite defects are investigated systematically. Both the C-poor and C-rich off-stoichiometric Ti1-cCc composition (0.49≤c≤0.51) have been studied. For the electronic structure, the difference of density of states (dDOS) is introduced to characterize the changes produced by the defects. Concerning the atomic structures, both interstitial defects and antisites are shown to induce the formation of C dumbbells or Ti dumbbells. To date, the Ti self-diffusion mechanism in TiC has not been fully understood, and particularly the Ti diffusion is much less studied in comparison with the C diffusion. Therefore, the self-diffusion of Ti in sub-stoichiometric TiC is studied, and the formation energies, migration barriers for Ti interstitials, dumbbells and dumbbell-vacancy clusters are reported. Some of the calculated activation energies are close to the experimental values, and the migration of Ti dumbbell terminated by C vacancies gives the lowest activation energy, which is in good agreement with the experimental data. These studies must be continued to obtain a full description (including phonon contributions, prefactors, etc.) of all the feasible diffusion mechanisms in TiC.The focus is then shifted from the light transition metal carbides to the heavy transition metal carbides. Various structures of Ru2C under ambient conditions are explored by using an unbiased swarm structure searching algorithm. The structures with R3m (one formula unit) and R-3m symmetry (two formula units) have been found to be lower in energy than the P-3m1 structure, and also to be dynamically stable at ambient conditions. The R-3m structure is characterized by emergence of the Ru-Ru metallic bonding, which has a crucial role in diminishing the hardness of this material.The study of correlation and relativistic effects in Ta2AlC is also presented. We have shown that going from a scalar relativity to a fully relativistic description does not have a significant effect on the computed electronic and mechanical properties of Ta2AlC. In addition, the calculations show that the structural and mechanical properties of Ta2AlC are strongly dependent on other details of theoretical treatment, such as the value of the Hubbard U parameter. The comparison between our results and experimental data point to that Ta2AlC is a weakly correlated system, which originates from that the 5d band is relatively wide in comparison with that of the 3d band.The existence of a rock salt Thorium monoxide (ThO) under high pressure is theoretically predicted. A chemical reaction between Th and ThO2 can produce a novel compound thorium monoxide under sufficient external pressure. To determine the pressure range where this reaction can be observed, we have identified two extreme boundaries by means of different theoretical approaches. The first one is given by a fully relativity DFT code in local density approximation (LDA). The second one is given by a scalar relativistic DFT code in generalized gradient approximation (GGA). It is found that ThO is energetically favored between 14 and 26 GPa. The f orbitals are filled at the expense of s and d electrons states of Th metal, under the action of pressure. The d-p hybridization leads to the stability of metallic ThO. Dynamical stability is also investigated by computing the phonon dispersions for the considered structures at high pressure.The electronic structure and magnetic properties of a promising nuclear fuel material, uranium mononitride (UN), are studied by means of density functional theory (DFT) and several extensions, such as dynamical mean-field theory (DMFT), disordered local moment (DLM) approach, and the GW method. The role of the relativistic corrections is analyzed for different levels of approximation. The importance of correlation effects is assessed through a detailed comparison between calculated electronic structure and measured photoemission spectrum, which helps to clarify the dual itinerant/localized nature of the 5f states of U in UN. Important effects are also observed for the 2p states of nitrogen, which are positioned at much lower energies that are difficult to be well treated in the conventional electronic structure calculations.
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25.
  • Sun, Weiwei, et al. (författare)
  • Anisotropic distortion and Lifshitz transition in alpha-Hf under pressure
  • 2017
  • Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 95:11
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work we report a theoretical investigation on behavior of the elastic constant C-44 and the transverse optical phonon mode E(2)g of a-Hf under pressure within the density functional theory. In contrast to many other reported transition metals, the above two quantities do not show a synchronous relation as pressure increases. Below 13 GPa, an opposite shifting tendency has been observed. However, once the pressure is raised above 13 GPa, the trend is pulled back to be consistent. This anomalous behavior is figured out to be caused by the large lattice anisotropy of the c/a ratio along with the elastic anisotropy. The synchronous behavior is found to be in accordance with the behavior of c/a ratio with increased pressure. In our band-structure investigations the electronic topological transition has been discovered at 10 GPa, which relates to the change of c/a ratio suggested by recent literature. The presence of the Van Hove singularity shown in the densities of states has been identified and regarded as the origin of the variation of C-44 and E(2)g.
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26.
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27.
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28.
  • Sun, Weiwei, et al. (författare)
  • Gluing together metallic and covalent layers to form Ru2C under ambient conditions
  • 2015
  • Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 17:15, s. 9730-9736
  • Tidskriftsartikel (refereegranskat)abstract
    • Ru2C has recently been synthesised at high pressure and high temperature, and was assumed to have a structure with space group P (3) over bar m1. However, subsequent theoretical work has revealed that this structure is unstable under ambient conditions, which motivated us to look for the stable structure. In this work, we explore the structures of Ru2C by using an unbiased swarm structure searching algorithm. The structures with R3m and R (3) over barm symmetries have been found to be lower in energy than the P (3) over bar m1 structure, at the same time being dynamically stable under ambient conditions. These layered structures consist of alternating Ru bilayers and C monolayers in the R3m structure, and alternating Ru tetra-layers and C bilayers in the R (3) over barm structure. The C layers are more evenly distributed and more covalently bound to the Ru layers in the R3m structure than in the R (3) over barm structure. Instead, in the R (3) over barm structure there exists more Ru-Ru metallic bonding, which has a crucial role in diminishing the hardness of this material. Our findings should stimulate further explorations of the structures and properties of the heavy transition metal carbides and nitrides, potentially leading to industrial applications.
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29.
  • Sun, Weiwei (författare)
  • Heavy Metal Compounds and Hydrogen Storage Materials from Ab Initio Calculations
  • 2013
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In principle, most of the properties of solids can be determined by their electronic structures. So the understanding of electronic structures is essential. This thesis presents two classes of materials using ab initio method based on density functional theory. One is heavy metal compounds like Ta2AlC, ThO and the other one is hydrogen storage material namely MgH2 surfaces.The study of correlation and relativistic effects in Ta2AlC are presented. Based on our results, Ta2AlC is a weakly correlated system. Our study shows that the spin - orbital coupling does not play a very important role where as the other relativistic corrections such as mass velocity and Darwin terms have a significant effect on the electronic properties.The stability of rock salt like ThO has been proposed based on the first principle calculation. ThO can be stabilized under pressure. The driving force is the sd to f charge transfer in Th.We have investigated the energetics of hydrogen desorption from the MgH2 (110) and (001) surfaces. The doping of foreign metal elements and strain were used to reduce the dehydrogenation energy. The reduction in dehydrogenation energy is caused by the charge localization on the metal atoms which leads to destabilization and the weakening of metal - hydrogen bonds.
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30.
  • Sun, Weiwei, et al. (författare)
  • Improvement in the desorption of H-2 from the MgH2 (110) surface by means of doping and mechanical strain
  • 2014
  • Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 86, s. 165-169
  • Tidskriftsartikel (refereegranskat)abstract
    • In this letter, density functional theory has been employed to investigate the release or desorption of hydrogen from the MgH2 (1 1 0) surface. To improve upon the energetics for hydrogen desorption from this system, the effects of strain and doping by Al, Si, Ti have been explored. Both of these two effects have been found to be effective. The strain applied along the X direction induces more prominent effects than along the Y direction. Regarding the doping, the system doped with Al gives the most noticeable effect. The Si doped system shows the least improvement while the Ti doped system lies in between as compared to the other two. The combination of doping and strain effects is found to be more efficacious.
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31.
  • Sun, Weiwei, et al. (författare)
  • Monodispersed FeS 2 Electrocatalyst Anchored to Nitrogen-Doped Carbon Host for Lithium–Sulfur Batteries
  • 2022
  • Ingår i: Advanced Functional Materials. - : Wiley. - 1616-3028 .- 1616-301X. ; 32:43
  • Tidskriftsartikel (refereegranskat)abstract
    • Despite their high theoretical energy density, lithium–sulfur (Li–S) batteries are hindered by practical challenges including sluggish conversion kinetics and shuttle effect of polysulfides. Here, a nitrogen-doped continuous porous carbon (CPC) host anchoring monodispersed sub-10 nm FeS2 nanoclusters (CPC@FeS2) is reported as an efficient catalytic matrix for sulfur cathode. This host shows strong adsorption of polysulfides, promising the inhibition of polysulfide shuttle and the promoted initial stage of catalytic conversion process. Moreover, fast lithium ion (Li-ion) diffusion and accelerated solid–solid conversion kinetics of Li2S2 to Li2S on CPC@FeS2 host guarantee boosted electrochemical kinetics for conversion process of sulfur species in Li–S cell, which gives a high utilization of sulfur under practical conditions of high loading and low electrolyte/sulfur (E/S) ratio. Therefore, the surfur cathode (S/CPC@FeS2) delivers a high specific capacity of 1459 mAh g−1 at 0.1 C, a stable cycling over 900 cycles with ultralow fading rate of 0.043% per cycle, and an enhanced rate capability compared with cathode only using carbon host. Further demonstration of this cathode in Li–S pouch cell shows a practical energy density of 372 Wh kg−1 with a sulfur loading of 7.1 mg cm−2 and an E/S ratio of 4 µL mg−1.
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32.
  • Sun, Weiwei, et al. (författare)
  • Role of correlation and relativistic effects in MAX phases
  • 2012
  • Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 47:21, s. 7615-7620
  • Tidskriftsartikel (refereegranskat)abstract
    • We have performed the ab initio calculations to study the role of correlation and relativistic effects in MAX phases. As of now, there are more than 50 MAX phases reported in the literature; however, we have chosen two MAX phases, namely Cr2AlC and Ta2AlC, as representatives of MAX phases for our study as they are very poorly described from calculation point of view. Our results show that correlation effects are very important to understand the electronic and mechanical properties of Cr2AlC, but not so important for Ta2AlC. We have also studied the relativistic effects on Ta2AlC and our calculations show that going from scalar to fully relativistic effects does not have any significant effect on the electronic and mechanical properties of Ta2AlC. We conclude that Ta2AlC is a weakly correlated system, whereas Cr2AlC is a strongly correlated system. Further experiments are needed to explain the discrepancy between theory and experiments.
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33.
  • Sun, Weiwei, et al. (författare)
  • Self-diffusion of Ti interstitial based point defects and complexes in TiC
  • 2019
  • Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 165, s. 381-387
  • Tidskriftsartikel (refereegranskat)abstract
    • To date, the mechanism of Ti atom self-diffusion is unproven. Prior theoretical work mostly focused on Ti vacancy based mediators, but these do not reproduce the experimental activation energy or entropy. In this work, in density functional theory calculations, Ti interstitials and related defect complexes are systematically considered as possible mediators of Ti self-diffusion. Among these defects, the defect complex of two C vacancies tightly bound to a Ti dumbbell is found to have the lowest formation energy. A sustainable migration of the complex, in a translational or rotational fashion, is enabled in the presence of another (free) carbon vacancy nearby the complex, and thus the rate of Ti self-diffusion by this mechanism is dependent on the concentration of carbon vacancies. The calculated activation energy of the complex agrees well with the experimental value in TiC0.97. Similar analyses of the Ti self-diffusion mechanisms mediated by Ti interstitials or dumbbells yield much higher activation energies, but the corresponding migration energies are evaluated to be less than 1 eV, which suggests they can be possible mediators of the radiation-enhanced Ti self-diffusion in TiC. To fully enable the comparison with experiments that are typically conducted at temperatures as high as 2500 K, we also consider the temperature dependent vibrational contribution to the activation energy of the defect complex. The vibrational contribution imposes an additive effect on the defect formation energy, while the migration energies are lowered due to the thermal expansion of the lattice. When combined, these factors give an excellent agreement with the experiments. This work gives strong support to the concept that Ti interstitial based defect complexes are likely diffusion mediators for Ti atom self-diffusion in TiC, further establishes a solid basis for large-scale modeling, and may eventually pave the way to accurately predicting defect-controlled diffusional processes.
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34.
  • Sun, Weiwei, et al. (författare)
  • Stability of a new cubic monoxide of Thorium under pressure
  • 2015
  • Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 5
  • Tidskriftsartikel (refereegranskat)abstract
    • Density functional theory has been applied to elucidate the stability of thorium monoxide (ThO). It is found out that the pressure can stabilize the rocksalt phase of ThO, and the transition pressure is estimated between 14 and 22 GPa. The stability of ThO can be attributed due to the gradually filling 5f orbitals at the expense of 7s and 6d electrons in Th metal. For ThO, the pressure induces stronger Th-O bond reflected by the newly established 6d-2p hybridization which is the dominant cause of its stability. The phonon dispersion curves of the rocksalt phase show the positive frequencies which indicates its dynamical stability. Our successful prediction of the stabilization of the metallic ThO has proposed a route to synthesize novel actinide monoxides.
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35.
  • Sun, Weiwei, et al. (författare)
  • Stabilizing a hexagonal Ru2C via Lifshitz transition under pressure
  • 2013
  • Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:25, s. 251901-
  • Tidskriftsartikel (refereegranskat)abstract
    • A unique type of heavy transition metal carbide Ru2C was synthesized experimentally at high pressure-high temperature and consequently quenched to ambient condition. The dynamical stability study reveals the instability at ambient condition. We have found that it can be stabilized from 30 to 110 GPa. The stronger 4d-2p hybridization and the formation of a cage like Fermi surface do impact the stability. The mixed bands primarily 2p characteristic weighted crossing the Fermi level form a Fermi surface piece at Gamma point under pressure. The clear change of topology of Fermi surface verifies the Lifshitz transition from ambient condition to high pressure.
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36.
  • Sun, Weiwei, et al. (författare)
  • Structure and energy of point defects in TiC : A system ab intitio study
  • 2015
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 91:13
  • Tidskriftsartikel (refereegranskat)abstract
    • We employ first-principles calculations to study the atomic and electronic structure of various point defects such as vacancies, interstitials, and antisites in the stoichiometric as well as slightly off-stoichiometric Ti-1-C-c(c) (including both C-poor and C-rich compositions, 0.49 <= c <= 0.51). The atomic structure analysis has revealed that both interstitial and antisite defects can exist in split conformations involving dumbbells. To characterize the electronic structure changes caused by a defect, we introduce differential density of states (dDOS) defined as a local perturbation of the density of states (DOS) on the defect site and its surrounding relative to the perfect TiC. This definition allows us to identify the DOS peaks characteristic of the studied defects in several conformations. So far, characteristic defect states have been discussed only in connection with carbon vacancies. Here, in particular, we have identified dDOS peaks of carbon interstitials and dumbbells, which can be used for experimental detection of such defects in TiC. The formation energies of point defects in TiC are derived in the framework of a grand-canonical formalism. Among the considered defects, carbon vacancies and interstitials are shown to have, respectively, the lowest and the second-lowest formation energies. Their formation energetics are consistent with the thermodynamic data on the phase stability of nonstoichiometric TiC. A cluster type of point defect is found to be next in energy, a titanium [100] dumbbell terminated by two carbon vacancies.
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37.
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38.
  • Sun, Weiwei, et al. (författare)
  • The effects of strain and doping on the release of hydrogen fromthe MgH2(110) surface
  • 2013
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • In this letter, density functional theory has been employed to investigate the release ordesorption of hydrogen from the MgH2(110) surface. To improve upon the energetics for hydrogendesorption from this system, the effects of strain and doping by Al, Si, Ti have been explored.Both of these two effects have been found to be effective. The strain applied along the X directioninduces more prominent effects than along the Y direction. Regarding the doping, the systemdoped with Al gives the most noticeable effect. The Si doped system shows the least improvementwhile the Ti doped system lies in between as compared to the other two. The combination ofdoping and strain effects is found to be more efficacious.
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39.
  • Sun, Weiwei, et al. (författare)
  • The stable rock salt like ThO chemically synthesized under pressure by theory
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • The rock salt like ThO was predicted to be stable under pressure by ab initio method. The procedure is applying pressure to the following reaction: Th+ThO2=) ThO. ThO is energetically favored in a range of 14 GPa - 26 GPa by the proof of reaction enthalpy. The lattice dynamic of ThO shows its stability under high pressure. In this reaction, Thorium metal plays signicant role on the reaction by the contributing of the transformation s, d to f orbital occupation. It is found that the lled f electrons mainly are at expense of s electrons. The newly stabilized ThO is metallic. The stabilizer is the hybridization of d - p electrons. The concentration of oxygen bonded to Th induce crystal eld splitting in d and f bands. The lled f electrons do inuence the energy level of d bands. We also found that ThO2 has a indirect band gap at 20 GPa.
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40.
  • Sun, Xuan, et al. (författare)
  • Construction of Electron Transfer Network by Self-Assembly of Self-n-Doped Fullerene Ammonium Iodide
  • 2016
  • Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 28:23, s. 8726-8731
  • Tidskriftsartikel (refereegranskat)abstract
    • Construction of pi-conjugation network in ordered fullerenes by self-assembly remains challenging for improving their optoelectronic performance and developing advanced materials. Here, we present a layered stacking of self-n-doped fullerene ammonium iodide (PCBANI) through a delicate balance among iodide anion-C-60 pi, electrostatic, and C-60 pi-pi interactions to construct an unprecedented supra molecular system. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and computational modeling are carried out to clarify the structure. Remarkably, the formation of intermolecular iodide anion pi interactions between iodide and the surrounded fullerene cores yields an iodide-linked C-60 pi-pi two-dimensional (2-D) network. Consequently, the ordered and tightly packed fullerenes sandwiching iodide could facilitate electron transfer along the network system. Comparative devices incorporating the disordered films show dramatically decreased current densities and manifest the importance of the pi-extended network for electron transfer. This work provides a key strategy to control the packing of ordered electron-transport materials to suppress defect formation. Moreover, engineering self-assembly of self-n-doped fullerenes with novel architectures, such as nanowire, nanotube, and nanoparticle would yield new functionalities that are suitable for photovoltaic devices, nanoelectronics, etc.
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41.
  • Xiong, Sangqi, et al. (författare)
  • A combined machine learning and density functional theory study of binary Ti-Nb and Ti-Zr alloys: Stability and Young’s modulus
  • 2020
  • Ingår i: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 184
  • Tidskriftsartikel (refereegranskat)abstract
    • The multicomponent Ti alloys, specifically the β-phase, have experienced a strong growth over the last decades, due to their outstanding properties of ultra-high strength and low Young’s modulus. These properties play a significant role in many aerospace and biomedical applications. Selection and optimization of multicomponent alloys is challenging due to the vast chemical and compositional space. Here we investigate the use of machine learning techniques informed by density functional calculations to guide the selection of Nb- and Zr-based Ti binary alloys. From the cubic structures obtained from high throughput calculations and literature, we identify several structures with Young’s moduli below 40 GPa. The multivariant decision tree methods provide efficient surrogate models to identify structure variables have high influences on the energetic stability and Young’s modulus. We implement a workflow of incorporating DFT provided results and machine learning method to explore the chemical and composition space of other binary and multicomponent alloys, to eventually accelerate the material design via taking advantages of identified key variables.
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42.
  • Yang, Fengmei, et al. (författare)
  • Li2FePO4F and its metal-doping for Li-ion batteries : an ab initio study
  • 2014
  • Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:91, s. 50195-50201
  • Tidskriftsartikel (refereegranskat)abstract
    • The electrochemical properties of three isotopic Li2FePO4F compounds, as cathode materials under different space groups Pbcn, P (1) over bar and Pnma were investigated using first principle calculations. Their structures and average open circuit voltages for step delithiation reactions were explored, and the results are in good agreement with the reported experimental data. We estimate the substitution effect of Fe by Co in Pnma-Li2FePO4F. The substitution of Fe by Co in Li2Fe1-xCoxPO4F may enhance the discharge potential of the materials, and the rate of its volume change during the redox process is between 0.6% and 2.1%. Furthermore, from the projected density of states for Li2Fe0.5Co0.5PO4F, we found strong hybridization for Fe-3d and Co-3d bands near the Fermi level, which implies that the Co-doped Li2Fe1-xCoxPO4F may possess better electronic conductivity than the pure phase.
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43.
  • Zhang, Ben, et al. (författare)
  • Rapid solidification for green-solvent-processed large-area organic solar modules with >16% efficiency
  • 2024
  • Ingår i: Energy & Environmental Science. - : ROYAL SOC CHEMISTRY. - 1754-5692 .- 1754-5706.
  • Tidskriftsartikel (refereegranskat)abstract
    • Enabling green-solvent-processed large-area organic solar cells (OSCs) is of great significance to their industrialization. However, precisely controlling the temperature-dependent fluid mechanics and evaporation behavior of green solvents with high-boiling points is challenging. Controlling these parameters is essential to prevent the non-uniform distribution of active layer components and severe molecule aggregation, which collectively degrade the power conversion efficiency (PCE) of large-scale devices. In this study, we revealed that the temperature gradient distribution across a wet film is the root of the notorious Marangoni effect, which leads to the formation of a severely non-uniform active layer on a large scale. Thus, a rapid solidification strategy was proposed to accelerate the evaporation of toluene, a green solvent, at room temperature. This strategy simultaneously inhibits the Marangoni effect and suppresses molecular aggregation in the wet film, allowing the formation of a nano-scale phase separation active layer with uniform morphology. The resultant toluene-processed 15.64-cm2 large-area OSC module achieves an outstanding PCE of 16.03% (certified: 15.69%), which represents the highest reported PCE of green-solvent-processed OSC modules. Notably, this strategy also exhibits a weak scale dependence on the PCE, and we successfully achieved a state-of-the-art PCE of 14.45% for a 72.00-cm2 OSC module. A rapid solidification strategy was developed for simultaneously avoiding the Marangoni effect and suppressing molecular aggregation. The resultant 15.64 cm2 large-area OSC module exhibited a record power conversion efficiency of 16.03%.
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44.
  • Östlin, A., et al. (författare)
  • Electronic structure of palladium in the presence of many-body effects
  • 2016
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 93:15
  • Tidskriftsartikel (refereegranskat)abstract
    • Including on-site electronic interactions described by the multiorbital Hubbard model we study the correlation effects in the electronic structure of bulk palladium. We use a combined density functional and dynamical mean-field theory, LDA+DMFT, based on the fluctuation exchange approximation. The agreement between the experimentally determined and the theoretical lattice constant and bulk modulus is improved when correlation effects are included. It is found that correlations modify the Fermi surface around the neck at the L point while the Fermi surface tube structures show little correlation effects. At the same time we discuss the possibility of satellite formation in the high-energy binding region. Spectral functions obtained within the LDA+DMFT and GW methods are compared to discuss nonlocal correlation effects. For relatively weak local Coulomb interaction and Hund's exchange coupling the LDA+DMFT spectra show no major difference in comparison to GW.
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