查看更多>>摘要：Zirconium hydride(ZrH2)is an ideal neutron moderator material.However,radiation effect significantly changes its properties,which affect its behavior and the lifespan of the reactor.The threshold energy of displacement is an important quantity of the number of radiation defects produced,which helps us to predict the evolution of radiation defects in ZrH2.Molecular dynamics(MD)and ab initio molecular dynamics(AIMD)are two main methods of calculating the threshold energy of displacement.The MD simulations with empirical potentials often cannot accurately depict the transitional states that lattice atoms must surpass to reach an interstitial state.Additionally,the AIMD method is unable to perform large-scale calculation,which poses a computational challenge beyond the simulation range of density functional theory.Machine learning potentials are renowned for their high accuracy and efficiency,making them an increasingly preferred choice for molecular dynamics simulations.In this work,we develop an accurate potential energy model for the ZrH2 system by using the deep-potential(DP)method.The DP model has a high degree of agreement with first-principles calculations for the typical defect energy and mechanical properties of the ZrH2 system,including the basic bulk properties,formation energy of point defects,as well as diffusion behavior of hydrogen and zirconium.By integrating the DP model with Ziegler-Biersack-Littmark(ZBL)potential,we can predict the threshold energy of displacement of zirconium and hydrogen inε-ZrH2.
查看更多>>摘要：Atomic simulations are executed to investigate the creep responses of nano-polycrystalline(NC)niobium established by using the Voronoi algorithm.The effects of varying temperature,applied stress,and grain size(GS)on creep properties and mechanisms are investigated.Notably,the occurrence of tertiary creep is exclusively observed under conditions where the applied stress exceeds 4.5 GPa and the temperature is higher than 1100 K.This phenomenon can be attributed to the significant acceleration of grain boundary and lattice diffusion,driven by the elevated temperature and stress levels.It is found that the strain rate increases with both temperature and stress increasing.However,an interesting trend is observed in which the strain rate decreases as the grain size increases.The stress and temperature are crucial parameters governing the creep behavior.As these factors intensify,the creep mechanism undergoes a sequential transformation:initially from lattice diffusion under low stress and temperature conditions to a mixed mode combining grain boundaries(GBs)and lattice diffusion at moderate stress and mid temperature levels,and ultimately leading to the failure of power-law controlled creep behavior,inclusive of grain boundary recrystallization under high stress and temperature conditions.This comprehensive analysis provides in more detail an understanding of the intricate creep behavior of nano-polycrystalline niobium and its dependence on various physical parameters.
查看更多>>摘要：The structural transformation from a liquid into a crystalline solid is an important subject in condensed matter physics and materials science.In the present study,first-principles molecular dynamics calculations are performed to investigate the structure and properties of aluminum during the solidification which is induced by cooling and compression.In the cooling process and compression process,it is found that the icosahedral short-range order is initially enhanced and then begin to decay,the face-centered cubic short-range order eventually becomes dominant before it transforms into a crystalline solid.
查看更多>>摘要：Glasses are known to possess low-frequency excess modes beyond the Debye prediction.For decades,it has been assumed that evolution of low-frequency density of excess modes D(ω)with frequency ω follows a power-law scaling:D(ω)～ωγ.However,it remains debated on the value of γ at low frequencies below the first phonon-like mode in finite-size glasses.Early simulation studies reported γ=4 at low frequencies in two-(2D),three-(3D),and four-dimensional(4D)glasses,whereas recent observations in 2D and 3D glasses suggested γ=3.5 in a lower-frequency regime.It is uncertain whether the low-frequency scaling of D(ω)～ω3 5 could be generalized to 4D glasses.Here,we conduct numerical simulation studies of excess modes at frequencies below the first phonon-like mode in 4D model glasses.It is found that the system size dependence of D(ω)below the first phonon-like mode varies with spatial dimensions:D(ω)increases in 2D glasses but decreases in 3D and 4D glasses as the system size increases.Furthermore,we demonstrate that the ω3.5 scaling,rather than the ω4 scaling,works in the lowest-frequency regime accessed in 4D glasses,regardless of interaction potentials and system sizes examined.Therefore,our findings in 4D glasses,combined with previous results in 2D and 3D glasses,suggest a common low-frequency scaling of D(ω)～ω3.5 below the first phonon-like mode across different spatial dimensions,which would inspire further theoretical studies.
查看更多>>摘要：A series of high-entropy alloys(HEAs)containing nanoprecipitates of varying sizes is successfully prepared by a non-consuming vacuum arc melting method.In order to study the irradiation evolution of helium bubbles in the FeCoNiCr-based HEAs with γ'precipitates,these samples are irradiated by 100-keV helium ions with a fluence of 5×1020 ions/m2 at 293 K and 673 K,respectively.And the samples irradiated at room temperature are annealed at different temperatures to examine the diffusion behavior of helium bubbles.Transmission electron microscope(TEM)is employed to charac-terize the structural morphology of precipitated nanoparticles and the evolution of helium bubbles.Experimental results reveal that nanosized,spherical,dispersed,coherent,and ordered L12-type Ni3Ti γ'precipitations are introduced into FeCoNiCr(Ni3Ti)0.1 HEAs by means of ageing treatments at temperatures between 1073 K and 1123 K.Under the ageing treatment conditions adopted in this work,γ'nanoparticles are precipitated in FeCoNiCr(Ni3Ti)0.1 HEAs,with average diameters of 15.80 nm,37.09 nm,and 62.50 nm,respectively.The average sizes of helium bubbles observed in samples after 673-K irradiation are 1.46 nm,1.65 nm,and 1.58 nm,respectively.The improvement in the irradiation resistance of FeCoNiCr(Ni3Ti)0.1 HEAs is evidenced by the diminution in bubbles size.Furthermore,the FeCoNiCr(Ni3Ti)0.1 HEAs containing γ'precipitates of 15.8 nm exhibits the minimum size and density of helium bubbles,which can be ascribed to the considerable helium trapping effects of heterogeneous coherent phase boundaries.Subsequently,annealing experiments conducted after 293-K irradiation indicate that HEAs containing precipitated phases exhibits smaller apparent activation energy(Ea)for helium bubbles,resulting in larger helium bubble size.This study provides guidance for improving the irradiation resistance of L12-strengthened high-entropy alloy.
查看更多>>摘要：Combining the deviation between thin layers'adjacent surfaces with the confining potential method applied to the quantum curved systems,we derive the effective Schrödinger equation describing the particle constrained within a curved layer,accompanied by a general geometric potential Vgq composed of a compression-corrected geometric potential Vgq*and a novel potential Vgq** brought by the deviation.Applying this analysis to the cylindrical layer emerges two types of deviation-induced geometric potential,resulting from the the cases of slant deviation and tangent deviation,respectively,which strongly renormalizes the purely geometric potential and contribute to the energy spectrum based on a very substantial deepening of bound states they offer.
查看更多>>摘要：Hafnia-based ferroelectric materials,like Hf0.5Zr0.5O2(HZO),have received tremendous attention owing to their potentials for building ultra-thin ferroelectric devices.The orthorhombic(O)-phase of HZO is ferroelectric but metastable in its bulk form under ambient conditions,which poses a considerable challenge to maintaining the operation performance of HZO-based ferroelectric devices.Here,we theoretically addressed this issue that provides parameter spaces for stabilizing the O-phase of HZO thin-films under various conditions.Three mechanisms were found to be capable of lowering the relative energy of the O-phase,namely,more significant surface-bulk portion of(111)surfaces,compressive c-axis strain,and positive electric fields.Considering these mechanisms,we plotted two ternary phase diagrams for HZO thin-films where the strain was applied along the in-plane uniaxial and biaxial,respectively.These diagrams indicate the O-phase could be stabilized by solely shrinking the film-thickness below 12.26 nm,ascribed to its lower surface energies.All these results shed considerable light on designing more robust and higher-performance ferroelectric devices.
查看更多>>摘要：With an extended Su-Schrieffer-Heeger model and Green's function method,the spin-orbit coupling(SOC)effects on spin admixture of electronic states and quantum transport in organic devices are investigated.The role of lattice distortion induced by the strong electron-lattice interaction in organics is clarified in contrast with a uniform chain.The results demonstrate an enhanced SOC effect on the spin admixture of frontier eigenstates by the lattice distortion at a larger SOC,which is explained by the perturbation theory.The quantum transport under the SOC is calculated for both nonmagnetic and ferromagnetic electrodes.A more notable SOC effect on total transmission and current is observed for ferromagnetic electrodes,where spin filtering induced by spin-flipped transmission and suppression of magnetoresistance are obtained.Unlike the spin admixture,a stronger SOC effect on transmission exists for the uniform chain rather than the organic lattices with distortion.The reason is attributed to the modified spin-polarized conducting states in the electrodes by lattice configuration,and hence the spin-flip transmission,instead of the spin admixture of eigenstates.This work is helpful to understand the SOC effect in organic spin valves in the presence of lattice distortion.
查看更多>>摘要：TiNi-based shape memory alloys have been extensively investigated due to their significant applications,but a compre-hensive understanding of the evolution of electronic structure and electrical transport in a system with martensitic transfor-mations(MT)is still lacking.In this work,we focused on the electronic transport behavior of three phases in Ni50-xFexTi50 across the MT.A phase diagram of Ni50-xFexTi50 was established based on x-ray diffraction,calorimetric,magnetic,and electrical measurements.To reveal the driving force of MT,phonon softening was revealed using first-principles calcula-tions.Notably,the transverse and longitudinal transport behavior changed significantly across the phase transition,which can be attributed to the reconstruction of electronic structures.This work promotes the understanding of phase transitions and demonstrates the sensitivity of electron transport to phase transition.
查看更多>>摘要：We study theoretically the electrical shot noise properties of tunnel junctions between a normal metal and a supercon-ductor with the mixture of singlet s-wave and chiral triplet p-wave pairing due to broken inversion symmetry.We investigate how the shot noise properties vary as the relative amplitude between the two parity components in the pairing potential is changed.It is demonstrated that some characteristics of the electrical shot noise properties of such tunnel junctions may de-pend sensitively on the relative amplitude between the two parity components in the pairing potential,and some significant changes may occur in the electrical shot noise properties when the relative amplitude between the two parity components is varied from the singlet s-wave pairing dominated regime to the chiral triplet p-wave pairing dominated regime.In the chiral triplet p-wave pairing dominated regime,the ratio of noise power to electric current is close to 2e both in the in-gap and in the out-gap region.In the singlet s-wave pairing dominated regime,the value of this ratio is close to 4e in the inner gap region but may reduce to about 2e in the outer gap region as the relative amplitude of the chiral triplet pairing component is increased.The variations of the differential shot noise with the bias voltage also exhibit some significantly different features in different regimes.Such different features can serve as useful diagnostic tools for the determination of the relative magnitude of the two parity components in the pairing potential.
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