Tungsten is a primary candidate materials for the high neutron flux, high temperature components ... more Tungsten is a primary candidate materials for the high neutron flux, high temperature components of a future demonstrate fusion reactor. Despite this, there is a lack of data on W under fusion relevant neutron doses and irradiation temperatures. Transmutation reactions result in the production of Re and Os solute atoms. In this study, single crystal and polycrystalline W samples irradiated at the High Flux Reactor (HFR) at 900 • C were characterised using Atom Probe Tomography (APT). Bulk chemical and isotopic concentration predictions were validated by analysing the mass spectrum from APT experiments. A post irradiation composition of W-1.263±0.149at.%Re-0.083±0.017at.%Os-0.009±0.004at.%Ta was measured in the single crystal sample, whereas W-1.090±0.067at.%Re-0.080±0.016at.%Os-0.009±0.004at.%Ta was measured for the polycrystalline. APT showed that a high number density of Re and Os rich precipitates had formed due to neutron irradiation. These typically presented with a core rich in Re and Os, surrounded by a less dense Re rich cloud. Multiple analysis methods were applied to investigate the composition of these clusters. APT showed that in the centres of some of the precipitates, a dense rod-shaped Re and Os rich region was correlated with these higher compositional measurements obtained using line profile analysis. Line profile analysis suggests that in the centre of the precipitates, the threshold composition for phase formation may have been reached, as has been observed on a larger scale in higher transmutation rate experiments. Line dislocations and dislocation loops were observed to be decorated with both Re and Os, in agreement with predictions from DFT.
A viable fusion power station is reliant on the development of plasma facing materials that can w... more A viable fusion power station is reliant on the development of plasma facing materials that can withstand the combined effects of high temperature operation and high neutron doses. In this study we focus on W, the most promising candidate material. Re is the primary transmutation product and has been shown to induce embrittlement through cluster formation and precipitation below its predicted solubility limit in W. We investigate the mechanism behind this using a kinetic Monte Carlo model, implemented into Stochastic Parallel PARticle Kinetic Simulator (SPPARKS) code and parameterised with a pairwise energy model for both interstitial and vacancy type defects. By introducing point defect sinks into our simulation cell, we observe the formation of Re rich clusters which have a concentration similar to that observed in ion irradiation experiments. We also compliment our computational work with atom probe tomography (APT) of ion implanted, model W-Re alloys. The segregation of Re to gr...
Graphic health warnings (GHW) on tobacco packages have proven to be effective in increasing quit ... more Graphic health warnings (GHW) on tobacco packages have proven to be effective in increasing quit attempts among smokers and reducing initial smoking among adolescents. This research aimed to examine the relative importance of different attributes of graphic health warnings on tobacco packages in Viet Nam. A discrete choice experimental (DCE) design was applied with a conditional logit model. In addition, a ranking method was used to list from the least to the most dreadful GHW labels. With the results from DCE model, graphic type was shown to be the most important attribute, followed by cost and coverage area of GHW. The least important attribute was position of the GHW. Among 5 graphic types (internal lung cancer image, external damaged teeth, abstract image, human suffering image and text), the image of lung cancer was found to have the strongest influence on both smokers and non-smokers. With ranking method, the image of throat cancer and heart diseases were considered the most dreadful images. GHWs should be designed with these attributes in mind, to maximise influence on purchase among both smokers and non-smokers.
Two years after implementation of the graphic health warning intervention in Vietnam, it is very ... more Two years after implementation of the graphic health warning intervention in Vietnam, it is very important to evaluate the intervention's potential impact. The objective of this paper was to predict effects of graphic health warnings on cigarette packages, particularly in reducing cigarette demand and smoking-associated deaths in Vietnam. In this study, a discrete choice experiment (DCE) method was used to evaluate the potential impact of graphic tobacco health warnings on smoking demand. To predict the impact of GHWs on reducing premature deaths associated with smoking, we constructed different static models. We adapted the method developed by University of Toronto, Canada and found that GHWs had statistically significant impact on reducing cigarette demand (up to 10.1% through images of lung damage), resulting in an overall decrease of smoking prevalence in Vietnam. We also found that between 428,417-646,098 premature deaths would be prevented as a result of the GHW intervention. The potential impact of the GHW labels on reducing premature smoking-associated deaths in Vietnam were shown to be stronger among lower socioeconomic groups.
The discovery of quasicrystals phases and approximants in Al(rich)-Mn system has revived the inte... more The discovery of quasicrystals phases and approximants in Al(rich)-Mn system has revived the interest for complex aluminides containing transition-metal atoms. On one hand, it is now accepted that the Hume-Rothery stabilization plays a crucial role. On the other hand, transition-metal atoms have also a very important effect on their stability and their physical properties. In this paper, we review studies
ABSTRACTThe intermetallic compound MoSi2, which adopts the C11b crystal structure, and related al... more ABSTRACTThe intermetallic compound MoSi2, which adopts the C11b crystal structure, and related alloys exhibit an excellent corrosion resistance at high temperatures but tend to be brittle at room and even relatively high temperatures. The limited ductility of MoSi2 in ambient conditions along with the anomalous temperature dependence of the critical resolved shear stress (CRSS) of the {110)<111], {011)<100] and…
Magnetic Cluster Expansion method is applied to the investigation of magnetic properties of Fe-Cr... more Magnetic Cluster Expansion method is applied to the investigation of magnetic properties of Fe-Cr alloys treated as a function of Cr content, the spatial distribution of Cr atoms, and temperature. Random Fe-Cr alloys and Cr clusters formed in concentrated alloys are analyzed. We find significant differences between the types of magnetic order characterizing those systems, which are reflected in the characteristic variation of the temperature-dependent magnetic specific heat. Simulations show that in random Fe-Cr alloys and in alloys containing Cr clusters, the interplay between antiferromagnetic interactions characterizing Fe-Cr and Cr-Cr atom pairs gives rise to unusual patterns of finite temperature magnetic ordering.
Aluminum based alloys which contain transition metal elements with concentrations up to 25% and a... more Aluminum based alloys which contain transition metal elements with concentrations up to 25% and additional small quantities of silicon, have a wide variety of atomic structures with unusual physical properties. Among these materials are the famous quasiperiodic alloys which were discovered in 1984 in Al-Mn by Shechtman et al. One find also numerous complex phases which atomic structures bear resemblance with medium-range structure of quasicrystalline phases. Some of these complex phases, but not all of them, are crystalline approximants of quasicrystals. This review focuses on the effect of the transition metal elements on the electronic structure of these alloys. The case of Al(Si)-Mn alloys is considered as a benchmarking one for the present study. But many of the results and concepts developed here can still be applied to other Al-rich alloys containing TM atom from the 3d, 4d, and 5d series. On the one hand, it is now well accepted that the Hume-Rothery stabilization of the valence electrons plays a crucial role in these materials. On the other hand, it has been shown that the TM atoms are also very important for their stability and their physical properties. But, until
The structural changes during the phase change between the amorphous and crystalline phase in Ge ... more The structural changes during the phase change between the amorphous and crystalline phase in Ge 2 Sb 2 Te 5 have been the subject of intense study due to the importance of Ge 2 Sb 2 Te 5 in phase change memory devices. In our study, the energetics of the transition between the crystalline and the amorphous phase of Ge 2 Sb 2 Te 5 is explored using density functional theory ͑DFT͒ calculations, electron diffraction, and reverse Monte Carlo model refinement. No energy barrier was found between the crystalline and the previously suggested amorphous structure of Ge 2 Sb 2 Te 5. Further DFT calculations have led to a different building block of the amorphous structure, which is shown to agree with the experimental reduced density function determined from electron diffraction experiments and previously reported extended x-ray absorption fine structure measurements.
We present a first-principles modeling study of a new class of nanomaterials in which buckminster... more We present a first-principles modeling study of a new class of nanomaterials in which buckminsterfullerene (C60) and graphene (G) are bridged by Cr via coordination bonds. Two nanostructures denoted as G(C54)-Cr-C60 and G(C150)-Cr-C60 are investigated, which share many similarities in the configuration geometries but differ in the distribution densities of Cr-C60 on the graphene surface. The binding energies between C60 and the rest of the system in these complexes are calculated to be 2.59 and 2.10 eV, respectively, indicative of their good structural stability. Additional spin-polarized calculations indicate that G(C54)-Cr-C60 is weakly ferromagnetic, which is chiefly due to the contribution from the 3d shell of Cr. We then investigate three model complexes of C60-Cr-G(C54) and a metal cluster (Ni4, Pd4, or Pt4). The binding energies of these three nanostructures are significantly large (3.57, 2.38, and 4.35 eV, respectively). Electron density analysis along the Ni-C, Pd-C, and Pt-C bonds consistently affirms that the Pt-C bond is the strongest while the Pd-C bond is the weakest. The strong Pt-C bond is attributed to the effective overlap of 5d(z(2)) (Pt) and 2p(z) (C) orbitals. Partial density of states analysis indicates that Ni4 and Pd4 substantially contribute to the strong ferromagnetism of the complexes, whereas Pt4 is observed to be non-magnetic even when the spin-orbit coupling is taken into account. H2 dissociation on the Ni4 complex is also examined, and the estimated reaction barrier is relatively low (0.76 eV).
The arrangement of rare-earth atoms at {100} prism planes of La-and Lu-containing polycrystalline... more The arrangement of rare-earth atoms at {100} prism planes of La-and Lu-containing polycrystalline Si 3 N 4 specimens is studied using high-angle annular dark-field scanning transmission electron microscopy. For both systems, the attachment sites of rare-earth atoms are well-defined and largely conform to the periodicity of the terminating plane of the Si 3 N 4 grain. We observe significant differences between the structural arrangement of La and Lu atoms at the interface.
Internal interfaces are of intrinsic importance to the properties of all materials, and the link ... more Internal interfaces are of intrinsic importance to the properties of all materials, and the link between their structure and properties continues to be an active field of research in materials science. Electron microscopy offers several techniques that provide an unparalleled degree of detail in the characterisation of these interfaces. In the present work, the structural arrangements of interfaces in doped silicon nitride ceramics are studied at the atomic scale using the electron-based techniques of high resolution transmission electron microscopy, high-angle annular dark field scanning transmission electron microscopy and reduced density function analysis using electrons. The investigation shows that these interfaces have a structure distinct from that of the bounding phases that abut them. Furthermore, this study provides a template for the future investigation of internal interfaces at the atomic scale.
The long-term objective of the European Fusion Development Agreement (EFDA) fusion materials prog... more The long-term objective of the European Fusion Development Agreement (EFDA) fusion materials programme is to develop structural and armor materials in combination with the necessary production and fabrication technologies for reactor concepts beyond the International Thermonuclear Experimental Reactor. The programmatic roadmap is structured into four engineering research lines which comprise fabrication process development, structural material development, armor material optimization, and irradiation performance testing, which are complemented by a fundamental research programme on ''Materials Science and Modelling.'' This paper presents the current research status of the EFDA experimental and testing investigations, and gives a detailed overview of the latest results on materials research, fabrication, joining, high heat flux testing, plasticity studies, modelling, and validation experiments.
Tungsten is a primary candidate materials for the high neutron flux, high temperature components ... more Tungsten is a primary candidate materials for the high neutron flux, high temperature components of a future demonstrate fusion reactor. Despite this, there is a lack of data on W under fusion relevant neutron doses and irradiation temperatures. Transmutation reactions result in the production of Re and Os solute atoms. In this study, single crystal and polycrystalline W samples irradiated at the High Flux Reactor (HFR) at 900 • C were characterised using Atom Probe Tomography (APT). Bulk chemical and isotopic concentration predictions were validated by analysing the mass spectrum from APT experiments. A post irradiation composition of W-1.263±0.149at.%Re-0.083±0.017at.%Os-0.009±0.004at.%Ta was measured in the single crystal sample, whereas W-1.090±0.067at.%Re-0.080±0.016at.%Os-0.009±0.004at.%Ta was measured for the polycrystalline. APT showed that a high number density of Re and Os rich precipitates had formed due to neutron irradiation. These typically presented with a core rich in Re and Os, surrounded by a less dense Re rich cloud. Multiple analysis methods were applied to investigate the composition of these clusters. APT showed that in the centres of some of the precipitates, a dense rod-shaped Re and Os rich region was correlated with these higher compositional measurements obtained using line profile analysis. Line profile analysis suggests that in the centre of the precipitates, the threshold composition for phase formation may have been reached, as has been observed on a larger scale in higher transmutation rate experiments. Line dislocations and dislocation loops were observed to be decorated with both Re and Os, in agreement with predictions from DFT.
A viable fusion power station is reliant on the development of plasma facing materials that can w... more A viable fusion power station is reliant on the development of plasma facing materials that can withstand the combined effects of high temperature operation and high neutron doses. In this study we focus on W, the most promising candidate material. Re is the primary transmutation product and has been shown to induce embrittlement through cluster formation and precipitation below its predicted solubility limit in W. We investigate the mechanism behind this using a kinetic Monte Carlo model, implemented into Stochastic Parallel PARticle Kinetic Simulator (SPPARKS) code and parameterised with a pairwise energy model for both interstitial and vacancy type defects. By introducing point defect sinks into our simulation cell, we observe the formation of Re rich clusters which have a concentration similar to that observed in ion irradiation experiments. We also compliment our computational work with atom probe tomography (APT) of ion implanted, model W-Re alloys. The segregation of Re to gr...
Graphic health warnings (GHW) on tobacco packages have proven to be effective in increasing quit ... more Graphic health warnings (GHW) on tobacco packages have proven to be effective in increasing quit attempts among smokers and reducing initial smoking among adolescents. This research aimed to examine the relative importance of different attributes of graphic health warnings on tobacco packages in Viet Nam. A discrete choice experimental (DCE) design was applied with a conditional logit model. In addition, a ranking method was used to list from the least to the most dreadful GHW labels. With the results from DCE model, graphic type was shown to be the most important attribute, followed by cost and coverage area of GHW. The least important attribute was position of the GHW. Among 5 graphic types (internal lung cancer image, external damaged teeth, abstract image, human suffering image and text), the image of lung cancer was found to have the strongest influence on both smokers and non-smokers. With ranking method, the image of throat cancer and heart diseases were considered the most dreadful images. GHWs should be designed with these attributes in mind, to maximise influence on purchase among both smokers and non-smokers.
Two years after implementation of the graphic health warning intervention in Vietnam, it is very ... more Two years after implementation of the graphic health warning intervention in Vietnam, it is very important to evaluate the intervention's potential impact. The objective of this paper was to predict effects of graphic health warnings on cigarette packages, particularly in reducing cigarette demand and smoking-associated deaths in Vietnam. In this study, a discrete choice experiment (DCE) method was used to evaluate the potential impact of graphic tobacco health warnings on smoking demand. To predict the impact of GHWs on reducing premature deaths associated with smoking, we constructed different static models. We adapted the method developed by University of Toronto, Canada and found that GHWs had statistically significant impact on reducing cigarette demand (up to 10.1% through images of lung damage), resulting in an overall decrease of smoking prevalence in Vietnam. We also found that between 428,417-646,098 premature deaths would be prevented as a result of the GHW intervention. The potential impact of the GHW labels on reducing premature smoking-associated deaths in Vietnam were shown to be stronger among lower socioeconomic groups.
The discovery of quasicrystals phases and approximants in Al(rich)-Mn system has revived the inte... more The discovery of quasicrystals phases and approximants in Al(rich)-Mn system has revived the interest for complex aluminides containing transition-metal atoms. On one hand, it is now accepted that the Hume-Rothery stabilization plays a crucial role. On the other hand, transition-metal atoms have also a very important effect on their stability and their physical properties. In this paper, we review studies
ABSTRACTThe intermetallic compound MoSi2, which adopts the C11b crystal structure, and related al... more ABSTRACTThe intermetallic compound MoSi2, which adopts the C11b crystal structure, and related alloys exhibit an excellent corrosion resistance at high temperatures but tend to be brittle at room and even relatively high temperatures. The limited ductility of MoSi2 in ambient conditions along with the anomalous temperature dependence of the critical resolved shear stress (CRSS) of the {110)<111], {011)<100] and…
Magnetic Cluster Expansion method is applied to the investigation of magnetic properties of Fe-Cr... more Magnetic Cluster Expansion method is applied to the investigation of magnetic properties of Fe-Cr alloys treated as a function of Cr content, the spatial distribution of Cr atoms, and temperature. Random Fe-Cr alloys and Cr clusters formed in concentrated alloys are analyzed. We find significant differences between the types of magnetic order characterizing those systems, which are reflected in the characteristic variation of the temperature-dependent magnetic specific heat. Simulations show that in random Fe-Cr alloys and in alloys containing Cr clusters, the interplay between antiferromagnetic interactions characterizing Fe-Cr and Cr-Cr atom pairs gives rise to unusual patterns of finite temperature magnetic ordering.
Aluminum based alloys which contain transition metal elements with concentrations up to 25% and a... more Aluminum based alloys which contain transition metal elements with concentrations up to 25% and additional small quantities of silicon, have a wide variety of atomic structures with unusual physical properties. Among these materials are the famous quasiperiodic alloys which were discovered in 1984 in Al-Mn by Shechtman et al. One find also numerous complex phases which atomic structures bear resemblance with medium-range structure of quasicrystalline phases. Some of these complex phases, but not all of them, are crystalline approximants of quasicrystals. This review focuses on the effect of the transition metal elements on the electronic structure of these alloys. The case of Al(Si)-Mn alloys is considered as a benchmarking one for the present study. But many of the results and concepts developed here can still be applied to other Al-rich alloys containing TM atom from the 3d, 4d, and 5d series. On the one hand, it is now well accepted that the Hume-Rothery stabilization of the valence electrons plays a crucial role in these materials. On the other hand, it has been shown that the TM atoms are also very important for their stability and their physical properties. But, until
The structural changes during the phase change between the amorphous and crystalline phase in Ge ... more The structural changes during the phase change between the amorphous and crystalline phase in Ge 2 Sb 2 Te 5 have been the subject of intense study due to the importance of Ge 2 Sb 2 Te 5 in phase change memory devices. In our study, the energetics of the transition between the crystalline and the amorphous phase of Ge 2 Sb 2 Te 5 is explored using density functional theory ͑DFT͒ calculations, electron diffraction, and reverse Monte Carlo model refinement. No energy barrier was found between the crystalline and the previously suggested amorphous structure of Ge 2 Sb 2 Te 5. Further DFT calculations have led to a different building block of the amorphous structure, which is shown to agree with the experimental reduced density function determined from electron diffraction experiments and previously reported extended x-ray absorption fine structure measurements.
We present a first-principles modeling study of a new class of nanomaterials in which buckminster... more We present a first-principles modeling study of a new class of nanomaterials in which buckminsterfullerene (C60) and graphene (G) are bridged by Cr via coordination bonds. Two nanostructures denoted as G(C54)-Cr-C60 and G(C150)-Cr-C60 are investigated, which share many similarities in the configuration geometries but differ in the distribution densities of Cr-C60 on the graphene surface. The binding energies between C60 and the rest of the system in these complexes are calculated to be 2.59 and 2.10 eV, respectively, indicative of their good structural stability. Additional spin-polarized calculations indicate that G(C54)-Cr-C60 is weakly ferromagnetic, which is chiefly due to the contribution from the 3d shell of Cr. We then investigate three model complexes of C60-Cr-G(C54) and a metal cluster (Ni4, Pd4, or Pt4). The binding energies of these three nanostructures are significantly large (3.57, 2.38, and 4.35 eV, respectively). Electron density analysis along the Ni-C, Pd-C, and Pt-C bonds consistently affirms that the Pt-C bond is the strongest while the Pd-C bond is the weakest. The strong Pt-C bond is attributed to the effective overlap of 5d(z(2)) (Pt) and 2p(z) (C) orbitals. Partial density of states analysis indicates that Ni4 and Pd4 substantially contribute to the strong ferromagnetism of the complexes, whereas Pt4 is observed to be non-magnetic even when the spin-orbit coupling is taken into account. H2 dissociation on the Ni4 complex is also examined, and the estimated reaction barrier is relatively low (0.76 eV).
The arrangement of rare-earth atoms at {100} prism planes of La-and Lu-containing polycrystalline... more The arrangement of rare-earth atoms at {100} prism planes of La-and Lu-containing polycrystalline Si 3 N 4 specimens is studied using high-angle annular dark-field scanning transmission electron microscopy. For both systems, the attachment sites of rare-earth atoms are well-defined and largely conform to the periodicity of the terminating plane of the Si 3 N 4 grain. We observe significant differences between the structural arrangement of La and Lu atoms at the interface.
Internal interfaces are of intrinsic importance to the properties of all materials, and the link ... more Internal interfaces are of intrinsic importance to the properties of all materials, and the link between their structure and properties continues to be an active field of research in materials science. Electron microscopy offers several techniques that provide an unparalleled degree of detail in the characterisation of these interfaces. In the present work, the structural arrangements of interfaces in doped silicon nitride ceramics are studied at the atomic scale using the electron-based techniques of high resolution transmission electron microscopy, high-angle annular dark field scanning transmission electron microscopy and reduced density function analysis using electrons. The investigation shows that these interfaces have a structure distinct from that of the bounding phases that abut them. Furthermore, this study provides a template for the future investigation of internal interfaces at the atomic scale.
The long-term objective of the European Fusion Development Agreement (EFDA) fusion materials prog... more The long-term objective of the European Fusion Development Agreement (EFDA) fusion materials programme is to develop structural and armor materials in combination with the necessary production and fabrication technologies for reactor concepts beyond the International Thermonuclear Experimental Reactor. The programmatic roadmap is structured into four engineering research lines which comprise fabrication process development, structural material development, armor material optimization, and irradiation performance testing, which are complemented by a fundamental research programme on ''Materials Science and Modelling.'' This paper presents the current research status of the EFDA experimental and testing investigations, and gives a detailed overview of the latest results on materials research, fabrication, joining, high heat flux testing, plasticity studies, modelling, and validation experiments.
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Papers by Duc Bui Manh