Irradiation-induced defects frequently impede the slip of dislocations, resulting in a sharp decline in the performance of nuclear reactor structural materials, particularly core structural materials. In the present w...Irradiation-induced defects frequently impede the slip of dislocations, resulting in a sharp decline in the performance of nuclear reactor structural materials, particularly core structural materials. In the present work, molecular dynamics method is used to investigate the interactions between edge dislocations and three typical irradiation-induced defects(void,Frank loop, and stacking fault tetrahedron) with the sizes of 3 nm, 5 nm, and 7 nm at different temperatures in Fe–10Ni–20Cr alloy. The critical resolved shear stresses(CRSSs) are compared among different defect types after interacting with edge dislocations. The results show that the CRSS decreases with temperature increasing and defect size decreasing for each defect type during the interaction with edge dislocations, except for the case of 3-nm Frank loops at 900 K. According to a comparison, the CRSS in Frank loop is significantly higher than that of others of the same size, which is due to the occurrence of unfaulting and formation of superjog or stacking-fault complex during the interaction. The atomic evolution of irradiation-induced defects after interacting with dislocations can provide a novel insight into the design of new structural materials.展开更多
Nitrogen processed, cold sprayed commercially pure(CP)-Al coatings on Mg-based alloys mostly lack acceptable hardness, wear resistance and most importantly are highly susceptible to localized corrosion in chloride con...Nitrogen processed, cold sprayed commercially pure(CP)-Al coatings on Mg-based alloys mostly lack acceptable hardness, wear resistance and most importantly are highly susceptible to localized corrosion in chloride containing solutions. In this research, commercially pure α-Ti top coating having good pitting potential(~1293 mV_(SCE)), high microhardness(HV_(0.025): 263.03) and low wear rate was applied on a CP-Al coated Mg-based alloy using high pressure cold spray technology. Potentiodynamic polarization(PDP) curves indicated that the probability of transition from metastable pits to the stable pits for cold spayed(CS) Al coating is considerably higher compared to that with the CS Ti top coating(for Ti/Al/Mg system). In addition, CS Ti top coating was in the passivation region in most pH ranges even after 48 h immersion in 3.5 wt% NaCl solution. The stored energy in the CS Ti top coating(as a passive metal) was presumed to be responsible for the easy passivation. Immersion tests indicated no obvious pits formation on the intact CS Ti top coating surface and revealed effective corrosion protection performance of the CS double layered noble barrier coatings on Mg alloys in 3.5 wt% NaCl solution even after 264 h.展开更多
Ge+ ions are implanted into fused silica glass at room temperature and a fluence of 1×10 17 cm-2 . The as-implanted samples are annealed in O2, N2 and Ar atmospheres separately. Ge0 , GeO and GeO2 coexist in the ...Ge+ ions are implanted into fused silica glass at room temperature and a fluence of 1×10 17 cm-2 . The as-implanted samples are annealed in O2, N2 and Ar atmospheres separately. Ge0 , GeO and GeO2 coexist in the as-implanted and annealed samples. Annealing in different atmospheres at 600℃ leads each composite to change its content. After annealing at 1000℃, there remains some amount of Ge 0 in the substrates. However, the content of Ge decreases due to out-diffusion. After annealing in N2 , Si–N composite is formed. The absorption peak of GeO appears at 240 nm after annealing in O2 atmosphere, and a new absorption peak occurs at 418 nm after annealing in N2 atmosphere, which is attributed to the Si–N composite. There is no absorption peak appearing after annealing in Ar atmosphere. Transmission electron microscopic images confirm the formation of Ge nanoparticles in the as-implanted sample and GeO 2 nanoparticles in the annealed sample. In the present study, the GeO content and the GeO2 content depend on annealing temperature and atmosphere. Three photoluminescence emission band peaks at 290, 385 and 415 nm appear after ion implantation and they become strong with the increase of annealing temperature below 700℃, and their photoluminescences recover to the values of as-grown samples after annealing at 700℃. Optical absorption and photoluminescence depend on the annealing temperature and atmosphere.展开更多
This study presents the intercomparison of the outdoor environmental gamma dose rates measured using a Na I(Tl)based survey meter along with thermoluminescent dosimeters(TLDs)and estimation of excess lifetime cancer r...This study presents the intercomparison of the outdoor environmental gamma dose rates measured using a Na I(Tl)based survey meter along with thermoluminescent dosimeters(TLDs)and estimation of excess lifetime cancer risk(ELCR),for the inhabitants of Poonch division of the展开更多
The basic properties of defects(self-interstitial and vacancy) in BCC iron under uniaxial tensile strain are investigated with atomic simulation methods. The formation and migration energies of them show different dep...The basic properties of defects(self-interstitial and vacancy) in BCC iron under uniaxial tensile strain are investigated with atomic simulation methods. The formation and migration energies of them show different dependences on the directions of uniaxial tensile strain in two different computation boxes. In box-1, the uniaxial tensile strain along the<100>direction influences the formation and migration energies of the<110>dumbbell but slightly affects the migration energy of a single vacancy. In box-2, the uniaxial tensile strain along the <111> direction influences the formation and migration energies of both vacancy and interstitials. Especially, a <110> dumbbell has a lower migration energy when its migration direction is the same or close to the strain direction, while along these directions, a vacancy has a higher migration energy. All these results indicate that the uniaxial tensile strain can result in the anisotropic formation and migration energies of simple defects in materials.展开更多
The soft deposition of Cu clusters on a Si(001) surface was studied by molecular dynamics simulations.The embedded atom method,the Stillinger-Weber and the Lennar-Jones potentials were used to describe the interaction...The soft deposition of Cu clusters on a Si(001) surface was studied by molecular dynamics simulations.The embedded atom method,the Stillinger-Weber and the Lennar-Jones potentials were used to describe the interactions between the cluster atoms,between the substrate atoms,and between the cluster and the substrate atoms,respectively.The Cu13,Cu55,and Cu147 clusters were investigated at different substrate temperatures.We found that the substrate temperature had a significant effect on the Cu147 cluster.For smaller Cu13 and Cu55 clusters,the substrate temperature in the range of study appeared to have little effect on the mean center-of-mass height.The clusters showed better degrees of epitaxy at 800 K.With the same substrate temperature,the Cu55 cluster demonstrated the highest degree of epitaxy,followed by Cu147 and then Cu13 clusters.In addition,the Cu55 cluster showed the lowest mean center-of-mass height.These results suggested that the Cu55 cluster is a better choice for the thin-film formation among the clusters considered.Our studies may provide insight into the formation of desired Cu thin films on a Si substrate.展开更多
Ni-rich layered lithium transition metal oxides LiNi_xMn_yCo_zO_(2)(1-y-z≥0.6)are promising candidates for cathode materials,but their practical applications are hindered by high-voltage instability and fast capacity...Ni-rich layered lithium transition metal oxides LiNi_xMn_yCo_zO_(2)(1-y-z≥0.6)are promising candidates for cathode materials,but their practical applications are hindered by high-voltage instability and fast capacity fading.Using density functional theory calculations,we demonstrate that Na-,F-doping,and Na/F-co-doping can stabilize the structure and result into a higher open circuit voltage than pristine LiNi_(0.6)Mn_(0.2)Co_(0.2)O_(2)(NMC622)during the charging process,which may attain greater discharge capacity.F doping may inhibit the diffusion of Li ions at the beginning and end of charging;Na doping may improve Li ion diffusion due to the increase in Li layer spacing,consistent with prior experiments.Na/F-codoping into NMC622 promotes rate performance and reduces irreversible phase transitions for two reasons:(i)a synergistic effect between Na and F can effectively restrain the Ni/Li mixing and then enhances the mobility of Li ions and(ii)Ni/Li mixing hinders the Ni ions to migrate into Li layers and thus,stabilizes the structure.This study proposes that a layer cathode material with high electrochemical performance can be achieved via rational dopant modification,which is a promising strategy for designing efficient Li ion batteries.展开更多
We develop an isotropic empirical potential for molecular hydrogen(H_2) and deuterium(D_2) by fitting to solidstate data, which is appropriate for classical molecular dynamics(CMD) approach. Based on the prior isotrop...We develop an isotropic empirical potential for molecular hydrogen(H_2) and deuterium(D_2) by fitting to solidstate data, which is appropriate for classical molecular dynamics(CMD) approach. Based on the prior isotropic intermolecular potential used in self-consistent phonon approximation, a zero-point energy term and an embedded energy term are introduced to describe the H_2–H_2 and D_2–D_2 interactions in CMD simulations. The structure,cohesive energy and elastic properties of solid H_2(D_2) are used as the fitting database. The present method is tested by calculating the melting point of solid H_2, and the pressure and bulk elastic modulus as a function of volume. The developed potentials well reproduce many properties of solid H_2 and D_2.展开更多
We have systemically investigated the synergistic evolution of rhenium(Re)and irradiation defects in tungsten(W)-Re alloys under different temperatures and irradiation doses using object Kinetic Monte Carlo method.Our...We have systemically investigated the synergistic evolution of rhenium(Re)and irradiation defects in tungsten(W)-Re alloys under different temperatures and irradiation doses using object Kinetic Monte Carlo method.Our results revealed the underlying mechanism for the transition of Re effect on W from beneficial to harmful during the Re-defects evolution with the increase of irradiation dose,in which tem-perature always plays a critical role.On the one hand,Re will significantly promote the defect annihila-tion at low irradiation doses and high temperatures,thereby effectively reducing their sizes and number densities.This is due to the formation of stable Re-SIAs complexes that can be eliminated by the mobile vacancy-type defects,whereas the transition of the migration pattern of SIAs only plays a weak role in the defect recombination in W-Re system.On the other hand,with the increase of irradiation dose,Re will aggregate to form Re-rich clusters or even precipitates.Interestingly,the formation mechanism of Re-rich clusters is also dependent on temperature.At low temperatures,the interstitial-mediated mech-anism plays a crucial role in the Re-rich cluster formation,while at high temperatures,both SIA-type and vacancy-type defects will act as the transport carriers of Re to promote their clustering.Accordingly,the critical conditions for the transition of Re from beneficial to harmful and the formation of Re-rich clusters at different tem peratures and irradiation doses are given with the help of the phase diagram.Our work presents the temperature dependence of the synergy of Re and irradiation defects in W-Re in fusion-relevant environment,which provides a good reference for the development of radiation-resistant materials and the prediction of W performance in fusion reactors.展开更多
Spent UO2 fuel will rapidly be altered to U6+ phases in nuclear waste repositories. Be-cause most uranyl phases are based on sheet or chain structures and usually contain several mo-lecular water groups, site-mixing, ...Spent UO2 fuel will rapidly be altered to U6+ phases in nuclear waste repositories. Be-cause most uranyl phases are based on sheet or chain structures and usually contain several mo-lecular water groups, site-mixing, vacancies, as well as disorder in the orientation of hydrogen bonds may occur. A systematic survey of the published crystallographic data for uranates, uranyl oxide hydrates, phosphates, silicates, carbonates, and sulfates demonstrates that site-mixing ap-parently occurs in the structures of at least 31 uranyl phases. Calculations of the ideal site-mixing entropy indicate that the residual contribution that arises from substitution and vacancies to the third-law entropies of some uranyl phases is large. A brief examination of the crystal chemistry of water molecules in uranyl phases suggests that considerable residual entropy may be caused by the disorder of hydrogen bonds associated with interstitial H2O groups. In the geochemical envi-ronment that expected to occur in the near-field of nuclear waste repositories, the existence of structure-configurational entropy may reduce the uranium concentration of several log units in so-lutions equilibrated with some uranyl phases. Therefore, compositional analysis and structural de-terminations must be made on the samples used in calorimetric measurements, and the calorimet-ric data must be combined with solubility data to evaluate the thermodynamic stability of the inter-ested phases.展开更多
在美国Argonne国家实验室连接有IVEM-Tandem National Facility加速器的Hi-tatch3000电子显微镜上,通过400KeV Xe^+离子就位辐照研究了TiNiCu形状记忆合金的常温晶态-非晶态转变。入射的Xe离子通过级联碰撞,从0.05 dpa开始辐照诱发TiNiC...在美国Argonne国家实验室连接有IVEM-Tandem National Facility加速器的Hi-tatch3000电子显微镜上,通过400KeV Xe^+离子就位辐照研究了TiNiCu形状记忆合金的常温晶态-非晶态转变。入射的Xe离子通过级联碰撞,从0.05 dpa开始辐照诱发TiNiCu合金化学无序,非晶化过程和化学无序几乎同时进行;0.2dpa后,马氏体变体的衬度明显减小,变得非常模糊;在0.4dpa非晶化转变完成,马氏体变体的衬度完全消失。展开更多
The behavior of hydrogen(H)in metals has been a longstanding research topic in materials science.One of the most compelling subjects is the deleterious effects of H on the microstructural evolution of materials;these ...The behavior of hydrogen(H)in metals has been a longstanding research topic in materials science.One of the most compelling subjects is the deleterious effects of H on the microstructural evolution of materials;these effects include H embrittlement,superabundant vacancy formation,and blistering.Vacancies have been demonstrated through both experiments and computational simulations to have strong H trapping effects[1],resulting in increased H retention[2],展开更多
Many multicomponent concentrated solid solution alloys(CSAs),including high-entropy alloys(HEAs),exhibit improved radiation resistance and enhanced structural stability in harsh environments.To study and assess irradi...Many multicomponent concentrated solid solution alloys(CSAs),including high-entropy alloys(HEAs),exhibit improved radiation resistance and enhanced structural stability in harsh environments.To study and assess irradiation resistance of nuclear materials,energetic ion and electron beams are commonly used to create displacement damage.Moreover,charged particles of ions,electrons,and positrons are unique tools to create and characterize radiation effects.Ion beam analysis(e.g.,Rutherford backscattering spectrometry,nuclear reaction analysis,and time-of-flight elastic recoil detection analysis),electron microscopy techniques(e.g.,transmission or scanning electron microscopy,and electron diffraction),and positron annihilation spectroscopy have been applied to characterize irradiated CSAs or HEAs to understand defect formation and evolution together with chemical and microstructural information.Their distinctive analyzing power and some perspectives in these techniques are reviewed.In developing structural alloys desirable for applications in advanced reactors,neutron exposure is a critical test but the limitation in achievable high damage levels is,however,a bottleneck.Ion irradiation is often used as a surrogate for neutron irradiation,and the associated reduced transmutations and higher displacements per atom(dpa)rates are desirable for materials research.Nevertheless,cautions need to be taken when relying on ion irradiation results for reactor evaluations.Literature on differences between ions and neutrons is briefly reviewed.In addition,the links to bridge the current advances on fundamental understandings to reactor applications are discussed to lay the groundwork between neutrons and ions for radiation effects studies.展开更多
The next generation of high-power lasers enables repetition of experiments at orders of magnitude higher frequency than what was possible using the prior generation.Facilities requiring human intervention between lase...The next generation of high-power lasers enables repetition of experiments at orders of magnitude higher frequency than what was possible using the prior generation.Facilities requiring human intervention between laser repetitions need to adapt in order to keep pace with the new laser technology.A distributed networked control system can enable laboratory-wide automation and feedback control loops.These higher-repetition-rate experiments will create enormous quantities of data.A consistent approach to managing data can increase data accessibility,reduce repetitive data-software development and mitigate poorly organized metadata.An opportunity arises to share knowledge of improvements to control and data infrastructure currently being undertaken.We compare platforms and approaches to state-of-the-art control systems and data management at high-power laser facilities,and we illustrate these topics with case studies from our community.展开更多
Recently, high-entropy alloys(HEAs) or multi-principal-element alloys with unprecedented physical,chemical, and mechanical properties, have been considered as candidate materials used in advanced reactors due to their...Recently, high-entropy alloys(HEAs) or multi-principal-element alloys with unprecedented physical,chemical, and mechanical properties, have been considered as candidate materials used in advanced reactors due to their promising irradiation resistant behavior. Here, we report a new single-phase bodycentered cubic(BCC) structured Ti_2 ZrHfV_(0.5)Mo_(0.2) HEA possessing excellent irradiation resistance, i.e.,scarcely irradiation hardening and abnormal lattice constant reduction after helium-ion irradiation,which is completely different from conventional alloys. This is the first time to report the abnormal XRD phenomenon of metallic alloys and almost no hardening after irradiation. These excellent properties make it to be a potential candidate material used as core components in next-generation nuclear reactors. The particular irradiation tolerance derives from high density lattice vacancies/defects.展开更多
Motivated by a grain boundary(GB) healing mechanism that GB turns into a mobile sink through migration to eliminate the vacancies in a bulk, we have further investigated the influence of the retained hydrogen(H) on th...Motivated by a grain boundary(GB) healing mechanism that GB turns into a mobile sink through migration to eliminate the vacancies in a bulk, we have further investigated the influence of the retained hydrogen(H) on the GB migration in tungsten using a molecular dynamics simulation. We show that H hinders the GB migration at different H concentrations and temperatures, and such friction of GB migration due to the presence of H increases with the H concentration and decreases with temperature. We demonstrate that H follows the GB-migration as the temperature is higher than 300 K. Most importantly, the presence of H induces a disordering of GB, which affects the GB migration significantly.展开更多
The structure and properties of materials under neutron irradiation are an important basis in future fusion reactors.In the absence of fusion neutron sources for irradiation experiments,it is increasingly important an...The structure and properties of materials under neutron irradiation are an important basis in future fusion reactors.In the absence of fusion neutron sources for irradiation experiments,it is increasingly important and urgent to carry out neutron irradiation simulations on fusion reactor materials and then establish complete databases of defect properties and collisional cascades,where the first and foremost step is to select suitable interatomic potentials for atomistic-level simulations.In this work,six typic interatomic potentials for tungsten(W)are evaluated and reviewed systematically for radiation damage simulations.The relative lattice stability and elastic constants of bulk W are considered first with those potentials;then,the properties of point defects and defect clusters at interstitial sites and vacancies are obtained by molecular statics/dynam-ics simulations.The formation energies of interstitial/vacancy clusters,1/2<111>and<100>dislocation loops in W and the threshold displacement energies along different directions are also determined.In addition,the extended defects are further investigated,such as free surfaces and the energy profiles of 1/2<111>{110}and 1/2<111>{112}stacking faults.The current results provide a reference for selecting W potentials to simulate the radiation damage.展开更多
基金supported by the National MCF Energy Research and Development Program,China (Grant No. 2018YFE0308101)the China National Nuclear Corporation Centralized Research and Development Project (Grant No. FY18000120)。
文摘Irradiation-induced defects frequently impede the slip of dislocations, resulting in a sharp decline in the performance of nuclear reactor structural materials, particularly core structural materials. In the present work, molecular dynamics method is used to investigate the interactions between edge dislocations and three typical irradiation-induced defects(void,Frank loop, and stacking fault tetrahedron) with the sizes of 3 nm, 5 nm, and 7 nm at different temperatures in Fe–10Ni–20Cr alloy. The critical resolved shear stresses(CRSSs) are compared among different defect types after interacting with edge dislocations. The results show that the CRSS decreases with temperature increasing and defect size decreasing for each defect type during the interaction with edge dislocations, except for the case of 3-nm Frank loops at 900 K. According to a comparison, the CRSS in Frank loop is significantly higher than that of others of the same size, which is due to the occurrence of unfaulting and formation of superjog or stacking-fault complex during the interaction. The atomic evolution of irradiation-induced defects after interacting with dislocations can provide a novel insight into the design of new structural materials.
基金the financial support received from the National Science Foundation (NSF-CMMI 2131441) under the direction of Dr.Alexis Lewis。
文摘Nitrogen processed, cold sprayed commercially pure(CP)-Al coatings on Mg-based alloys mostly lack acceptable hardness, wear resistance and most importantly are highly susceptible to localized corrosion in chloride containing solutions. In this research, commercially pure α-Ti top coating having good pitting potential(~1293 mV_(SCE)), high microhardness(HV_(0.025): 263.03) and low wear rate was applied on a CP-Al coated Mg-based alloy using high pressure cold spray technology. Potentiodynamic polarization(PDP) curves indicated that the probability of transition from metastable pits to the stable pits for cold spayed(CS) Al coating is considerably higher compared to that with the CS Ti top coating(for Ti/Al/Mg system). In addition, CS Ti top coating was in the passivation region in most pH ranges even after 48 h immersion in 3.5 wt% NaCl solution. The stored energy in the CS Ti top coating(as a passive metal) was presumed to be responsible for the easy passivation. Immersion tests indicated no obvious pits formation on the intact CS Ti top coating surface and revealed effective corrosion protection performance of the CS double layered noble barrier coatings on Mg alloys in 3.5 wt% NaCl solution even after 264 h.
基金Project supported by the Foundation for Young Scholars of University of Electronic Science and Technology of China (Grant No.L08010401JX0806)
文摘Ge+ ions are implanted into fused silica glass at room temperature and a fluence of 1×10 17 cm-2 . The as-implanted samples are annealed in O2, N2 and Ar atmospheres separately. Ge0 , GeO and GeO2 coexist in the as-implanted and annealed samples. Annealing in different atmospheres at 600℃ leads each composite to change its content. After annealing at 1000℃, there remains some amount of Ge 0 in the substrates. However, the content of Ge decreases due to out-diffusion. After annealing in N2 , Si–N composite is formed. The absorption peak of GeO appears at 240 nm after annealing in O2 atmosphere, and a new absorption peak occurs at 418 nm after annealing in N2 atmosphere, which is attributed to the Si–N composite. There is no absorption peak appearing after annealing in Ar atmosphere. Transmission electron microscopic images confirm the formation of Ge nanoparticles in the as-implanted sample and GeO 2 nanoparticles in the annealed sample. In the present study, the GeO content and the GeO2 content depend on annealing temperature and atmosphere. Three photoluminescence emission band peaks at 290, 385 and 415 nm appear after ion implantation and they become strong with the increase of annealing temperature below 700℃, and their photoluminescences recover to the values of as-grown samples after annealing at 700℃. Optical absorption and photoluminescence depend on the annealing temperature and atmosphere.
文摘This study presents the intercomparison of the outdoor environmental gamma dose rates measured using a Na I(Tl)based survey meter along with thermoluminescent dosimeters(TLDs)and estimation of excess lifetime cancer risk(ELCR),for the inhabitants of Poonch division of the
基金Supported by the National Natural Science Foundation of China under Grant Nos 11375242,11675230 and 91426301
文摘The basic properties of defects(self-interstitial and vacancy) in BCC iron under uniaxial tensile strain are investigated with atomic simulation methods. The formation and migration energies of them show different dependences on the directions of uniaxial tensile strain in two different computation boxes. In box-1, the uniaxial tensile strain along the<100>direction influences the formation and migration energies of the<110>dumbbell but slightly affects the migration energy of a single vacancy. In box-2, the uniaxial tensile strain along the <111> direction influences the formation and migration energies of both vacancy and interstitials. Especially, a <110> dumbbell has a lower migration energy when its migration direction is the same or close to the strain direction, while along these directions, a vacancy has a higher migration energy. All these results indicate that the uniaxial tensile strain can result in the anisotropic formation and migration energies of simple defects in materials.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10375028)the US National Science Foundation Award (Grant No. CMMI-0700048)
文摘The soft deposition of Cu clusters on a Si(001) surface was studied by molecular dynamics simulations.The embedded atom method,the Stillinger-Weber and the Lennar-Jones potentials were used to describe the interactions between the cluster atoms,between the substrate atoms,and between the cluster and the substrate atoms,respectively.The Cu13,Cu55,and Cu147 clusters were investigated at different substrate temperatures.We found that the substrate temperature had a significant effect on the Cu147 cluster.For smaller Cu13 and Cu55 clusters,the substrate temperature in the range of study appeared to have little effect on the mean center-of-mass height.The clusters showed better degrees of epitaxy at 800 K.With the same substrate temperature,the Cu55 cluster demonstrated the highest degree of epitaxy,followed by Cu147 and then Cu13 clusters.In addition,the Cu55 cluster showed the lowest mean center-of-mass height.These results suggested that the Cu55 cluster is a better choice for the thin-film formation among the clusters considered.Our studies may provide insight into the formation of desired Cu thin films on a Si substrate.
基金the National Natural Science Foundation of China(Grant Nos.51802092 and 51771073)the Fundamental Research Funds for the Central Universities.China。
文摘Ni-rich layered lithium transition metal oxides LiNi_xMn_yCo_zO_(2)(1-y-z≥0.6)are promising candidates for cathode materials,but their practical applications are hindered by high-voltage instability and fast capacity fading.Using density functional theory calculations,we demonstrate that Na-,F-doping,and Na/F-co-doping can stabilize the structure and result into a higher open circuit voltage than pristine LiNi_(0.6)Mn_(0.2)Co_(0.2)O_(2)(NMC622)during the charging process,which may attain greater discharge capacity.F doping may inhibit the diffusion of Li ions at the beginning and end of charging;Na doping may improve Li ion diffusion due to the increase in Li layer spacing,consistent with prior experiments.Na/F-codoping into NMC622 promotes rate performance and reduces irreversible phase transitions for two reasons:(i)a synergistic effect between Na and F can effectively restrain the Ni/Li mixing and then enhances the mobility of Li ions and(ii)Ni/Li mixing hinders the Ni ions to migrate into Li layers and thus,stabilizes the structure.This study proposes that a layer cathode material with high electrochemical performance can be achieved via rational dopant modification,which is a promising strategy for designing efficient Li ion batteries.
基金Supported by the National Natural Science Foundation of China under Grant No U1430109
文摘We develop an isotropic empirical potential for molecular hydrogen(H_2) and deuterium(D_2) by fitting to solidstate data, which is appropriate for classical molecular dynamics(CMD) approach. Based on the prior isotropic intermolecular potential used in self-consistent phonon approximation, a zero-point energy term and an embedded energy term are introduced to describe the H_2–H_2 and D_2–D_2 interactions in CMD simulations. The structure,cohesive energy and elastic properties of solid H_2(D_2) are used as the fitting database. The present method is tested by calculating the melting point of solid H_2, and the pressure and bulk elastic modulus as a function of volume. The developed potentials well reproduce many properties of solid H_2 and D_2.
基金This work is financially supported by the National Natu-ral Science Foundation of China(Nos.11905135,12075022 and 12192281)the National MCF Energy R&D Program(No.2018YFE0308103).
文摘We have systemically investigated the synergistic evolution of rhenium(Re)and irradiation defects in tungsten(W)-Re alloys under different temperatures and irradiation doses using object Kinetic Monte Carlo method.Our results revealed the underlying mechanism for the transition of Re effect on W from beneficial to harmful during the Re-defects evolution with the increase of irradiation dose,in which tem-perature always plays a critical role.On the one hand,Re will significantly promote the defect annihila-tion at low irradiation doses and high temperatures,thereby effectively reducing their sizes and number densities.This is due to the formation of stable Re-SIAs complexes that can be eliminated by the mobile vacancy-type defects,whereas the transition of the migration pattern of SIAs only plays a weak role in the defect recombination in W-Re system.On the other hand,with the increase of irradiation dose,Re will aggregate to form Re-rich clusters or even precipitates.Interestingly,the formation mechanism of Re-rich clusters is also dependent on temperature.At low temperatures,the interstitial-mediated mech-anism plays a crucial role in the Re-rich cluster formation,while at high temperatures,both SIA-type and vacancy-type defects will act as the transport carriers of Re to promote their clustering.Accordingly,the critical conditions for the transition of Re from beneficial to harmful and the formation of Re-rich clusters at different tem peratures and irradiation doses are given with the help of the phase diagram.Our work presents the temperature dependence of the synergy of Re and irradiation defects in W-Re in fusion-relevant environment,which provides a good reference for the development of radiation-resistant materials and the prediction of W performance in fusion reactors.
基金This work was supported by the National Natural Science Foundation of China(Grant No.40072095)the DOE/EMSP grant of USA(DE-FG07-97ER-14816,RCE).
文摘Spent UO2 fuel will rapidly be altered to U6+ phases in nuclear waste repositories. Be-cause most uranyl phases are based on sheet or chain structures and usually contain several mo-lecular water groups, site-mixing, vacancies, as well as disorder in the orientation of hydrogen bonds may occur. A systematic survey of the published crystallographic data for uranates, uranyl oxide hydrates, phosphates, silicates, carbonates, and sulfates demonstrates that site-mixing ap-parently occurs in the structures of at least 31 uranyl phases. Calculations of the ideal site-mixing entropy indicate that the residual contribution that arises from substitution and vacancies to the third-law entropies of some uranyl phases is large. A brief examination of the crystal chemistry of water molecules in uranyl phases suggests that considerable residual entropy may be caused by the disorder of hydrogen bonds associated with interstitial H2O groups. In the geochemical envi-ronment that expected to occur in the near-field of nuclear waste repositories, the existence of structure-configurational entropy may reduce the uranium concentration of several log units in so-lutions equilibrated with some uranyl phases. Therefore, compositional analysis and structural de-terminations must be made on the samples used in calorimetric measurements, and the calorimet-ric data must be combined with solubility data to evaluate the thermodynamic stability of the inter-ested phases.
文摘在美国Argonne国家实验室连接有IVEM-Tandem National Facility加速器的Hi-tatch3000电子显微镜上,通过400KeV Xe^+离子就位辐照研究了TiNiCu形状记忆合金的常温晶态-非晶态转变。入射的Xe离子通过级联碰撞,从0.05 dpa开始辐照诱发TiNiCu合金化学无序,非晶化过程和化学无序几乎同时进行;0.2dpa后,马氏体变体的衬度明显减小,变得非常模糊;在0.4dpa非晶化转变完成,马氏体变体的衬度完全消失。
基金supported by the National Natural Science Foundation of China(Grant Nos.51720105006,and 11675009)the Science Challenge Project(Grant No.JCKY2016212A502)
文摘The behavior of hydrogen(H)in metals has been a longstanding research topic in materials science.One of the most compelling subjects is the deleterious effects of H on the microstructural evolution of materials;these effects include H embrittlement,superabundant vacancy formation,and blistering.Vacancies have been demonstrated through both experiments and computational simulations to have strong H trapping effects[1],resulting in increased H retention[2],
基金supported as part of Energy Dissipation to Defect Evolution(EDDE)an Energy Frontier Research Center funded by the U.S.Department of Energy,Office of Science,Basic Energy Sciences,under contract number DE-AC05-00OR22725.
文摘Many multicomponent concentrated solid solution alloys(CSAs),including high-entropy alloys(HEAs),exhibit improved radiation resistance and enhanced structural stability in harsh environments.To study and assess irradiation resistance of nuclear materials,energetic ion and electron beams are commonly used to create displacement damage.Moreover,charged particles of ions,electrons,and positrons are unique tools to create and characterize radiation effects.Ion beam analysis(e.g.,Rutherford backscattering spectrometry,nuclear reaction analysis,and time-of-flight elastic recoil detection analysis),electron microscopy techniques(e.g.,transmission or scanning electron microscopy,and electron diffraction),and positron annihilation spectroscopy have been applied to characterize irradiated CSAs or HEAs to understand defect formation and evolution together with chemical and microstructural information.Their distinctive analyzing power and some perspectives in these techniques are reviewed.In developing structural alloys desirable for applications in advanced reactors,neutron exposure is a critical test but the limitation in achievable high damage levels is,however,a bottleneck.Ion irradiation is often used as a surrogate for neutron irradiation,and the associated reduced transmutations and higher displacements per atom(dpa)rates are desirable for materials research.Nevertheless,cautions need to be taken when relying on ion irradiation results for reactor evaluations.Literature on differences between ions and neutrons is briefly reviewed.In addition,the links to bridge the current advances on fundamental understandings to reactor applications are discussed to lay the groundwork between neutrons and ions for radiation effects studies.
基金A.J.acknowledges the support from DOE Grant#DESC0016804.
文摘The next generation of high-power lasers enables repetition of experiments at orders of magnitude higher frequency than what was possible using the prior generation.Facilities requiring human intervention between laser repetitions need to adapt in order to keep pace with the new laser technology.A distributed networked control system can enable laboratory-wide automation and feedback control loops.These higher-repetition-rate experiments will create enormous quantities of data.A consistent approach to managing data can increase data accessibility,reduce repetitive data-software development and mitigate poorly organized metadata.An opportunity arises to share knowledge of improvements to control and data infrastructure currently being undertaken.We compare platforms and approaches to state-of-the-art control systems and data management at high-power laser facilities,and we illustrate these topics with case studies from our community.
基金supported by the National Natural Science Foundation of China (Nos. 11605271, 51471044, 51525401, 51771201 and 51401208)Support Plan for Innovation of High-level Talents (Top and Leading Talents, 2015R013)Support Plan for Innovation of High-level Talents (Youth Technology Stars, 2016RQ005)
文摘Recently, high-entropy alloys(HEAs) or multi-principal-element alloys with unprecedented physical,chemical, and mechanical properties, have been considered as candidate materials used in advanced reactors due to their promising irradiation resistant behavior. Here, we report a new single-phase bodycentered cubic(BCC) structured Ti_2 ZrHfV_(0.5)Mo_(0.2) HEA possessing excellent irradiation resistance, i.e.,scarcely irradiation hardening and abnormal lattice constant reduction after helium-ion irradiation,which is completely different from conventional alloys. This is the first time to report the abnormal XRD phenomenon of metallic alloys and almost no hardening after irradiation. These excellent properties make it to be a potential candidate material used as core components in next-generation nuclear reactors. The particular irradiation tolerance derives from high density lattice vacancies/defects.
基金supported by the National Magnetic Confinement Fusion Program(Grant No.2013GB109002)the National Natural Science Foundation of China(Grant Nos.51171008 and 51325103)
文摘Motivated by a grain boundary(GB) healing mechanism that GB turns into a mobile sink through migration to eliminate the vacancies in a bulk, we have further investigated the influence of the retained hydrogen(H) on the GB migration in tungsten using a molecular dynamics simulation. We show that H hinders the GB migration at different H concentrations and temperatures, and such friction of GB migration due to the presence of H increases with the H concentration and decreases with temperature. We demonstrate that H follows the GB-migration as the temperature is higher than 300 K. Most importantly, the presence of H induces a disordering of GB, which affects the GB migration significantly.
基金This work was financially supported by the National MCF Energy R&D Program of China(Grant No.2018YFE0308101)the National Key R&D Program of China(Grant No.2018YFB0704002)the National Natural Science Foundation of China(Grant Nos.51771073,11975260).
文摘The structure and properties of materials under neutron irradiation are an important basis in future fusion reactors.In the absence of fusion neutron sources for irradiation experiments,it is increasingly important and urgent to carry out neutron irradiation simulations on fusion reactor materials and then establish complete databases of defect properties and collisional cascades,where the first and foremost step is to select suitable interatomic potentials for atomistic-level simulations.In this work,six typic interatomic potentials for tungsten(W)are evaluated and reviewed systematically for radiation damage simulations.The relative lattice stability and elastic constants of bulk W are considered first with those potentials;then,the properties of point defects and defect clusters at interstitial sites and vacancies are obtained by molecular statics/dynam-ics simulations.The formation energies of interstitial/vacancy clusters,1/2<111>and<100>dislocation loops in W and the threshold displacement energies along different directions are also determined.In addition,the extended defects are further investigated,such as free surfaces and the energy profiles of 1/2<111>{110}and 1/2<111>{112}stacking faults.The current results provide a reference for selecting W potentials to simulate the radiation damage.