Sergei Dudarev - Academia.edu (original) (raw)
Papers by Sergei Dudarev
SSRN Electronic Journal
• Dislocation density evolution in irradiated Zr has been predicted and measured. • A transient p... more • Dislocation density evolution in irradiated Zr has been predicted and measured. • A transient peak and subsequent saturation in dislocation density has been observed. • Dislocation loop diameters in heavily irradiated Zr are power law distributed.
Fusion Engineering and Design, 2018
Future fusion reactors will operate under unprecedented environmental conditions and will rely on... more Future fusion reactors will operate under unprecedented environmental conditions and will rely on the performance of complex in-vessel components during long term operation. These new reactors have key operational differences compared to existing nuclear systems and require new materials and new design criteria for in-vessel components. Within the EUROfusion consortium, several approaches are being taken in parallel: modification of existing frameworks and development of new databases, handbooks and design criteria specific for EU-DEMO operation. These adaptations and advances need to be considered within the context of the novel materials and multi-material interfaces being considered for the unprecedented fusion in-vessel components operational environment. The materials properties required for qualification in conventional nuclear sites are reviewed along with proposed pragmatic adaptations required for DEMO reactors arising from the potentially sparse fusion irradiation spectrum materials database. The efforts ongoing within EUROfusion to assess the links between materials engineering and design for fusion reactors are highlighted focusing on developments of new DEMO specific materials databases and handbook and DEMO Design Criteria. The efforts in EUROfusion are shown to form key steps towards new fusion reactor specific design codes.
J Phys Condens Matter, 2001
Frontiers in Nuclear Engineering
We derive a simple analytical line integral expression for the relaxation volume tensor of an arb... more We derive a simple analytical line integral expression for the relaxation volume tensor of an arbitrary interconnected dislocation network. This quantity determines the magnitude of dislocation contribution to the dimensional changes and volumetric swelling of a material, and highlights the fundamental dual role of dislocations as sources of internal strain as well as carriers of plastic deformation. To illustrate applications of the method, we compute the relaxation volume of a stacking fault tetrahedron, a defect commonly occurring in fcc metals; the volume of an unusual tetrahedral configuration formed by the (a/2)〈111〉 and a〈001〉 dislocations in a bcc metal; and estimate the relative contribution of extended dislocations to the volume relaxation of heavily irradiated tungsten.
To explore the formation of noncollinear magnetic configurations in materials with strongly corre... more To explore the formation of noncollinear magnetic configurations in materials with strongly correlated electrons, we derive a noncollinear LSDA+U model involving only one parameter U, as opposed to the difference between the Hubbard and Stoner parameters U-J. Computing U in the constrained random phase approximation, we investigate noncollinear magnetism of uranium dioxide UO_2 and find that the spin-orbit coupling (SOC) stabilizes the 3k ordered magnetic ground state. The estimated SOC strength in UO_2 is as large as 0.73 eV per uranium atom, making spin and orbital degrees of freedom virtually inseparable. Using a multipolar pseudospin Hamiltonian, we show how octupolar and dipole-dipole exchange coupling help establish the 3k magnetic ground state with canted ordering of uranium f-orbitals. The cooperative Jahn-Teller effect does not appear to play a significant part in stabilizing the noncollinear 3k state, which has the lowest energy even in an undistorted lattice. The choice o...
Unraveling the complexity of non-collinear magnetism in materials with strongly correlated electr... more Unraveling the complexity of non-collinear magnetism in materials with strongly correlated electrons is a considerable task that requires developing and applying state of the art theories and computational methods. Using the Coury model Hamiltonian, which includes spin and orbital degrees of freedom and generalizes the collinear Stoner Hamiltonian, we derive an extension of the collinear LSDA+U approximation to non-collinear magnetic configurations and explore the magnetic ground state of the archetypal spin-orbit correlated oxide UO2. To find the magnetic ground state of UO2 in the non-collinear configuration space, we combine LSDA+U with a spin adiabatic occupation matrix approach. Our results show that the strong spin-orbit coupling (SOC) is the key factor stabilizing the so-called 3k spin ordered magnetic ground state of UO2. Using a relativistic atomic Hamiltonian we find that the SOC strength is colossal, 1.45 eV per uranium atom. This unusually strong SOC implies that the spi...
The Journal of Chemical Physics, Jun 14, 2019
Physical Review Materials
It has been long hypothesized that the structure of a material bombarded by energetic particles m... more It has been long hypothesized that the structure of a material bombarded by energetic particles might approach a certain asymptotic steady state in the limit of high exposure to irradiation. There is still no definitive verdict regarding the validity of this hypothesis or the conditions where it applies. To clarify this, we explore a highly simplified model for microstructural evolution that retains full atomic detail of the underlying crystal structure and involves random events of generation and relaxation of defects. We explore the dynamics of evolution of the model in the limit T = 0, where the defect and dislocation microstructure is driven purely by the spatially fluctuating stress field accumulating as a result of stochastic generation of point defects. Using body-centred cubic iron and tungsten as examples, we show that their microstructure exhibits a structural transition and then approaches a limiting asymptotic state at doses of order O(0.1) and O(1) canonical defects per atom, respectively, and analyze the microscopic and macroscopic parameters characterizing both the transition and the asymptotic microstructural state.
Physical Review Materials
To explore the formation of non-collinear magnetic configurations in materials with strongly corr... more To explore the formation of non-collinear magnetic configurations in materials with strongly correlated electrons, we derive a non-collinear LSDA+U model involving only one parameter U , as opposed to the difference between the Hubbard and Stoner parameters U − J. Computing U in the constrained random phase approximation, we investigate non-collinear magnetism of uranium dioxide UO2 and find that the spin-orbit coupling (SOC) stabilizes the 3k ordered magnetic ground state. The estimated SOC strength in UO2 is as large as 0.73 eV per uranium atom, making spin and orbital degrees of freedom virtually inseparable. Using a multipolar pseudospin Hamiltonian, we show how octupolar and dipole-dipole exchange coupling help establish the 3k magnetic ground state with canted ordering of uranium f-orbitals. The cooperative Jahn-Teller effect does not appear to play a significant part in stabilizing the non-collinear 3k state, which has the lowest energy even in an undistorted lattice. The choice of parameter U in the LSDA+U model has a notable quantitative effect on the predicted properties of UO2, in particular on the magnetic exchange interaction and, perhaps trivially, on the band gap: the value of U = 3.46 eV computed fully ab initio delivers the band gap of 2.11 eV in good agreement with experiment, and a balanced account of other pertinent energy scales.
Physical Review Materials
Body-centred cubic metals and alloys irradiated by energetic particles form highly mobile prismat... more Body-centred cubic metals and alloys irradiated by energetic particles form highly mobile prismatic dislocation loops with a/2 111-type Burgers vectors. We show how to simulate diffusion of prismatic loops using the discrete dislocation dynamics approach that treats elastic forces acting between the loops and stochastic forces associated with ambient thermal fluctuations. We find that interplay between stochastic thermal forces and internal degrees of freedom of loops, in particular the reorientation of the loop habit planes, strongly influences the observed loop dynamics. The loops exhibit three fundamental types of reactions: coalescence, repulsion, and confinement by elastic forces. The confinement reactions are highly sensitive to the internal degrees of freedom of the loops. Depending on the orientation of the loop habit planes, the barrier to enter an elastically confined bound state is lowered substantially, whereas the lifetime of the bound state increases by many orders of magnitude.
Physical Review Materials
For several decades, the striking contradiction between the Huang diffuse scattering experiments,... more For several decades, the striking contradiction between the Huang diffuse scattering experiments, resistivity recovery data, and predictions derived from density functional theory (DFT) remained one of the mysteries of defect physics in molybdenum. Since the 1970s, observations of Huang x-ray diffuse scattering appeared to indicate that a self-interstitial atom (SIA) defect in Mo adopts a 110 dumbbell configuration. However, the low temperature defect diffusion data supported the DFT prediction of a different, highly mobile 111 SIA defect structure in the same metal. Using DFT simulations, we show that an SIA adopts a symmetry-broken configuration in all the group 6 metals: chromium, molybdenum, and tungsten. The symmetry-broken defect structure, a 11ξ dumbbell, where ξ is an irrational number, agrees with nudged elastic band analyses of 110 to 111 transformations. Direct simulations of Huang diffuse scattering by symmetry-broken defect configurations predicted by DFT explain why no zero intensity lines were observed in experiment and resolve the long outstanding question about the structure of defects in Mo and similar metals. A 11ξ defect migrates on average one dimensionally through a sequence of three-dimensional nonplanar [11ξ ] to [ξ 11] or [1ξ 1] transitions. Barriers for defect migration in nonmagnetic Cr, antiferromagnetic Cr, Mo, and W derived from DFT calculations, 0.052, 0.075, 0.064, and 0.040 eV are well correlated with the onset of defect migration temperatures observed experimentally.
Physical Review Materials
Physical Review Materials
Nuclear Fusion
Predicting strains, stresses and swelling in nuclear power plant components exposed to irradiatio... more Predicting strains, stresses and swelling in nuclear power plant components exposed to irradiation directly from the observed or computed defect and dislocation microstructure is a fundamental problem of fusion power plant design that has so far eluded a practical solution. We develop a model, free from parameters not accessible to direct evaluation or observation, that is able to provide estimates for irradiation-induced stresses and strains on a macroscopic scale, using information about the distribution of radiation defects produced by high-energy neutrons in the microstructure of materials. The model exploits the fact that elasticity equations involve no characteristic spatial scale, and hence admit a mathematical treatment that is an extension to that developed for the evaluation of elastic fields of defects on the nanoscale. In the analysis given below we use, as input, the radiation defect structure data derived from ab initio density functional calculations and large-scale molecular dynamics simulations of high-energy collision cascades. We show that strains, stresses and swelling can be evaluated using either integral equations, where the source function is given by the density of relaxation volumes of defects, or they can be computed from heterogeneous partial differential equations for the components of the stress tensor, where the density of body forces is proportional to the gradient of the density of relaxation volumes of defects. We perform a case study where strains and stresses are evaluated analytically and exactly, and develop a general finite element method implementation of the method, applicable to a broad range of predictive simulations of strains and stresses induced by irradiation in materials and components of any geometry in fission or fusion nuclear power plants.
Scientific reports, Aug 23, 2016
Vacancy-mediated climb models cannot account for the fast, direct coalescence of dislocation loop... more Vacancy-mediated climb models cannot account for the fast, direct coalescence of dislocation loops seen experimentally. An alternative mechanism, self climb, allows prismatic dislocation loops to move away from their glide surface via pipe diffusion around the loop perimeter, independent of any vacancy atmosphere. Despite the known importance of self climb, theoretical models require a typically unknown activation energy, hindering implementation in materials modeling. Here, extensive molecular statics calculations of pipe diffusion processes around irregular prismatic loops are used to map the energy landscape for self climb in iron and tungsten, finding a simple, material independent energy model after normalizing by the vacancy migration barrier. Kinetic Monte Carlo simulations yield a self climb activation energy of 2 (2.5) times the vacancy migration barrier for 1/2〈111〉 (〈100〉) dislocation loops. Dislocation dynamics simulations allowing self climb and glide show quantitative ...
SSRN Electronic Journal
• Dislocation density evolution in irradiated Zr has been predicted and measured. • A transient p... more • Dislocation density evolution in irradiated Zr has been predicted and measured. • A transient peak and subsequent saturation in dislocation density has been observed. • Dislocation loop diameters in heavily irradiated Zr are power law distributed.
Fusion Engineering and Design, 2018
Future fusion reactors will operate under unprecedented environmental conditions and will rely on... more Future fusion reactors will operate under unprecedented environmental conditions and will rely on the performance of complex in-vessel components during long term operation. These new reactors have key operational differences compared to existing nuclear systems and require new materials and new design criteria for in-vessel components. Within the EUROfusion consortium, several approaches are being taken in parallel: modification of existing frameworks and development of new databases, handbooks and design criteria specific for EU-DEMO operation. These adaptations and advances need to be considered within the context of the novel materials and multi-material interfaces being considered for the unprecedented fusion in-vessel components operational environment. The materials properties required for qualification in conventional nuclear sites are reviewed along with proposed pragmatic adaptations required for DEMO reactors arising from the potentially sparse fusion irradiation spectrum materials database. The efforts ongoing within EUROfusion to assess the links between materials engineering and design for fusion reactors are highlighted focusing on developments of new DEMO specific materials databases and handbook and DEMO Design Criteria. The efforts in EUROfusion are shown to form key steps towards new fusion reactor specific design codes.
J Phys Condens Matter, 2001
Frontiers in Nuclear Engineering
We derive a simple analytical line integral expression for the relaxation volume tensor of an arb... more We derive a simple analytical line integral expression for the relaxation volume tensor of an arbitrary interconnected dislocation network. This quantity determines the magnitude of dislocation contribution to the dimensional changes and volumetric swelling of a material, and highlights the fundamental dual role of dislocations as sources of internal strain as well as carriers of plastic deformation. To illustrate applications of the method, we compute the relaxation volume of a stacking fault tetrahedron, a defect commonly occurring in fcc metals; the volume of an unusual tetrahedral configuration formed by the (a/2)〈111〉 and a〈001〉 dislocations in a bcc metal; and estimate the relative contribution of extended dislocations to the volume relaxation of heavily irradiated tungsten.
To explore the formation of noncollinear magnetic configurations in materials with strongly corre... more To explore the formation of noncollinear magnetic configurations in materials with strongly correlated electrons, we derive a noncollinear LSDA+U model involving only one parameter U, as opposed to the difference between the Hubbard and Stoner parameters U-J. Computing U in the constrained random phase approximation, we investigate noncollinear magnetism of uranium dioxide UO_2 and find that the spin-orbit coupling (SOC) stabilizes the 3k ordered magnetic ground state. The estimated SOC strength in UO_2 is as large as 0.73 eV per uranium atom, making spin and orbital degrees of freedom virtually inseparable. Using a multipolar pseudospin Hamiltonian, we show how octupolar and dipole-dipole exchange coupling help establish the 3k magnetic ground state with canted ordering of uranium f-orbitals. The cooperative Jahn-Teller effect does not appear to play a significant part in stabilizing the noncollinear 3k state, which has the lowest energy even in an undistorted lattice. The choice o...
Unraveling the complexity of non-collinear magnetism in materials with strongly correlated electr... more Unraveling the complexity of non-collinear magnetism in materials with strongly correlated electrons is a considerable task that requires developing and applying state of the art theories and computational methods. Using the Coury model Hamiltonian, which includes spin and orbital degrees of freedom and generalizes the collinear Stoner Hamiltonian, we derive an extension of the collinear LSDA+U approximation to non-collinear magnetic configurations and explore the magnetic ground state of the archetypal spin-orbit correlated oxide UO2. To find the magnetic ground state of UO2 in the non-collinear configuration space, we combine LSDA+U with a spin adiabatic occupation matrix approach. Our results show that the strong spin-orbit coupling (SOC) is the key factor stabilizing the so-called 3k spin ordered magnetic ground state of UO2. Using a relativistic atomic Hamiltonian we find that the SOC strength is colossal, 1.45 eV per uranium atom. This unusually strong SOC implies that the spi...
The Journal of Chemical Physics, Jun 14, 2019
Physical Review Materials
It has been long hypothesized that the structure of a material bombarded by energetic particles m... more It has been long hypothesized that the structure of a material bombarded by energetic particles might approach a certain asymptotic steady state in the limit of high exposure to irradiation. There is still no definitive verdict regarding the validity of this hypothesis or the conditions where it applies. To clarify this, we explore a highly simplified model for microstructural evolution that retains full atomic detail of the underlying crystal structure and involves random events of generation and relaxation of defects. We explore the dynamics of evolution of the model in the limit T = 0, where the defect and dislocation microstructure is driven purely by the spatially fluctuating stress field accumulating as a result of stochastic generation of point defects. Using body-centred cubic iron and tungsten as examples, we show that their microstructure exhibits a structural transition and then approaches a limiting asymptotic state at doses of order O(0.1) and O(1) canonical defects per atom, respectively, and analyze the microscopic and macroscopic parameters characterizing both the transition and the asymptotic microstructural state.
Physical Review Materials
To explore the formation of non-collinear magnetic configurations in materials with strongly corr... more To explore the formation of non-collinear magnetic configurations in materials with strongly correlated electrons, we derive a non-collinear LSDA+U model involving only one parameter U , as opposed to the difference between the Hubbard and Stoner parameters U − J. Computing U in the constrained random phase approximation, we investigate non-collinear magnetism of uranium dioxide UO2 and find that the spin-orbit coupling (SOC) stabilizes the 3k ordered magnetic ground state. The estimated SOC strength in UO2 is as large as 0.73 eV per uranium atom, making spin and orbital degrees of freedom virtually inseparable. Using a multipolar pseudospin Hamiltonian, we show how octupolar and dipole-dipole exchange coupling help establish the 3k magnetic ground state with canted ordering of uranium f-orbitals. The cooperative Jahn-Teller effect does not appear to play a significant part in stabilizing the non-collinear 3k state, which has the lowest energy even in an undistorted lattice. The choice of parameter U in the LSDA+U model has a notable quantitative effect on the predicted properties of UO2, in particular on the magnetic exchange interaction and, perhaps trivially, on the band gap: the value of U = 3.46 eV computed fully ab initio delivers the band gap of 2.11 eV in good agreement with experiment, and a balanced account of other pertinent energy scales.
Physical Review Materials
Body-centred cubic metals and alloys irradiated by energetic particles form highly mobile prismat... more Body-centred cubic metals and alloys irradiated by energetic particles form highly mobile prismatic dislocation loops with a/2 111-type Burgers vectors. We show how to simulate diffusion of prismatic loops using the discrete dislocation dynamics approach that treats elastic forces acting between the loops and stochastic forces associated with ambient thermal fluctuations. We find that interplay between stochastic thermal forces and internal degrees of freedom of loops, in particular the reorientation of the loop habit planes, strongly influences the observed loop dynamics. The loops exhibit three fundamental types of reactions: coalescence, repulsion, and confinement by elastic forces. The confinement reactions are highly sensitive to the internal degrees of freedom of the loops. Depending on the orientation of the loop habit planes, the barrier to enter an elastically confined bound state is lowered substantially, whereas the lifetime of the bound state increases by many orders of magnitude.
Physical Review Materials
For several decades, the striking contradiction between the Huang diffuse scattering experiments,... more For several decades, the striking contradiction between the Huang diffuse scattering experiments, resistivity recovery data, and predictions derived from density functional theory (DFT) remained one of the mysteries of defect physics in molybdenum. Since the 1970s, observations of Huang x-ray diffuse scattering appeared to indicate that a self-interstitial atom (SIA) defect in Mo adopts a 110 dumbbell configuration. However, the low temperature defect diffusion data supported the DFT prediction of a different, highly mobile 111 SIA defect structure in the same metal. Using DFT simulations, we show that an SIA adopts a symmetry-broken configuration in all the group 6 metals: chromium, molybdenum, and tungsten. The symmetry-broken defect structure, a 11ξ dumbbell, where ξ is an irrational number, agrees with nudged elastic band analyses of 110 to 111 transformations. Direct simulations of Huang diffuse scattering by symmetry-broken defect configurations predicted by DFT explain why no zero intensity lines were observed in experiment and resolve the long outstanding question about the structure of defects in Mo and similar metals. A 11ξ defect migrates on average one dimensionally through a sequence of three-dimensional nonplanar [11ξ ] to [ξ 11] or [1ξ 1] transitions. Barriers for defect migration in nonmagnetic Cr, antiferromagnetic Cr, Mo, and W derived from DFT calculations, 0.052, 0.075, 0.064, and 0.040 eV are well correlated with the onset of defect migration temperatures observed experimentally.
Physical Review Materials
Physical Review Materials
Nuclear Fusion
Predicting strains, stresses and swelling in nuclear power plant components exposed to irradiatio... more Predicting strains, stresses and swelling in nuclear power plant components exposed to irradiation directly from the observed or computed defect and dislocation microstructure is a fundamental problem of fusion power plant design that has so far eluded a practical solution. We develop a model, free from parameters not accessible to direct evaluation or observation, that is able to provide estimates for irradiation-induced stresses and strains on a macroscopic scale, using information about the distribution of radiation defects produced by high-energy neutrons in the microstructure of materials. The model exploits the fact that elasticity equations involve no characteristic spatial scale, and hence admit a mathematical treatment that is an extension to that developed for the evaluation of elastic fields of defects on the nanoscale. In the analysis given below we use, as input, the radiation defect structure data derived from ab initio density functional calculations and large-scale molecular dynamics simulations of high-energy collision cascades. We show that strains, stresses and swelling can be evaluated using either integral equations, where the source function is given by the density of relaxation volumes of defects, or they can be computed from heterogeneous partial differential equations for the components of the stress tensor, where the density of body forces is proportional to the gradient of the density of relaxation volumes of defects. We perform a case study where strains and stresses are evaluated analytically and exactly, and develop a general finite element method implementation of the method, applicable to a broad range of predictive simulations of strains and stresses induced by irradiation in materials and components of any geometry in fission or fusion nuclear power plants.
Scientific reports, Aug 23, 2016
Vacancy-mediated climb models cannot account for the fast, direct coalescence of dislocation loop... more Vacancy-mediated climb models cannot account for the fast, direct coalescence of dislocation loops seen experimentally. An alternative mechanism, self climb, allows prismatic dislocation loops to move away from their glide surface via pipe diffusion around the loop perimeter, independent of any vacancy atmosphere. Despite the known importance of self climb, theoretical models require a typically unknown activation energy, hindering implementation in materials modeling. Here, extensive molecular statics calculations of pipe diffusion processes around irregular prismatic loops are used to map the energy landscape for self climb in iron and tungsten, finding a simple, material independent energy model after normalizing by the vacancy migration barrier. Kinetic Monte Carlo simulations yield a self climb activation energy of 2 (2.5) times the vacancy migration barrier for 1/2〈111〉 (〈100〉) dislocation loops. Dislocation dynamics simulations allowing self climb and glide show quantitative ...