Calculated lattice relaxation in Pu-Ga

Becker, J.D.; Wills, J. M.; Cox, L.E.; Cooper, Bernard R.

doi:10.1103/physrevb.58.5143

Cited by 15 publications

(10 citation statements)

References 14 publications

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“…5, containing twelve representative) spectra from these same samples all show three prominent features through R = 6Å that are independent of composition [20,21,25,35,36,59,60]. Curve-fits demonstrate that these features correspond to the first three shells of a contracted, quasi-fcc cluster that is nevertheless highly ordered with respect to the widths of these shells and that (Fig.…”

Section: The Composition Of σ Pu and The Homogeneous/heterogeneousmentioning

confidence: 87%

Nanoscale heterogeneity, premartensitic nucleation, and a new plutonium structure in metastableδfcc Pu-Ga alloys

et al. 2014

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The scientifically fascinating question of the spatial extent and bonding of the 5f orbitals of Pu and its six different phases extends to its δ-retained alloys and the mechanism by which Ga and a number of other unrelated elements stabilize its low density face-centered-cubic (fcc) structure. This issue of phase stability is also important technologically because of its significance to Science-Based Stockpile Stewardship. Answering these questions requires information on the local order and structure around the Ga and its effects on the Pu. We have addressed this by characterizing the structures of a large number of Pu-Ga and two Pu-In and one Pu-Ce δ alloys, including a set of high purity δ Pu 1−x Ga x materials with 1.7 ࣘ x ࣘ 6.4 at. % Ga that span the low [Ga] portion of the δ region of the phase diagram across the ß3.3 at. % Ga metastability boundary, with extended x-ray absorption fine structure (EXAFS) spectroscopy that probes the element specific local structure, supplemented by x-ray pair distribution function analysis that gives the total local structure to longer distances, and x-ray diffraction that gives the long-range average structure of the periodic component of the materials. Detailed analyses indicate that the alloys at and below a nominal composition of ß3.3 at. % Ga are heterogeneous and in addition to the δ phase also contain up to ß20% of a novel, coexisting "σ " structure for Pu that forms in nanometer scale domains that are locally depleted in Ga. The invariance of the Ga EXAFS with composition indicates that this σ structure forms in Ga-depleted domains that result from the Ga atoms in the δ phase self-organizing into a quasi-intermetallic with a stoichiometry of Pu 25−35 Ga so that δ Pu-Ga is neither a random solid solution nor the more stable Pu 3 Ga + α. Above this 3.3 at. % Ga nominal composition, the δ Pu-Ga alloy is homogeneous, and no σ phase is present. These results that demonstrate that collective and cooperative behavior in the interactions between the alloy elements as well as local elastic forces are crucial in determining the properties of complex materials and contradict the conventional mechanism for martensitic transformations, in this case indicating that nucleation is not the rate limiting step.

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Section: The Composition Of σ Pu and The Homogeneous/heterogeneousmentioning

confidence: 87%

Nanoscale heterogeneity, premartensitic nucleation, and a new plutonium structure in metastableδfcc Pu-Ga alloys

et al. 2014

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“…Faure et al [4] have studied such a behavior as function of Ga composition. While non-spin-polarized LDA calculations do not reproduce the experimental interatomic distance [25], in a very recent study, Sadigh and Wolfer [11] have shown that spin-polarized DFT is able to predict the observed departure from fcc symmetry for an alloy composition of 3.2 at.% Ga. Here, we propose to study plutonium-plutonium and plutonium-gallium distances as a function of composition using a supercell of 108 atoms.…”

Section: Local Relaxation Around Gallium Impuritymentioning

confidence: 94%

Thermodynamic, alloying and defect properties of plutonium: Density-functional calculations

Robert

Pasturel

Siberchicot

2007

Journal of Alloys and Compounds

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“…In spite of these attempts, a fundamental understanding of the electronic structure properties of Pu, and the mechanisms responsible for the to volume collapse is still lacking. As a direct consequence of this lack of understanding, the phase stability properties of Pu alloys are still poorly described from a fundamental standpoint [9][10][11][12][13]. For example [14,15], the solubility limits of Ga in and Pu (respectively 12.5 and 20 at.%), and the definite tendency toward ordering and phase formation (with the existence of six intermediate phases stable at room temperature) still need to be explained.…”

Section: T T T H H H E E E R R R M M M O O O D D D Y Y Y N N N a A A mentioning

confidence: 99%

Thermodynamics and Kinetics of Phase Transformations in Plutonium Alloys - Part I

Turchi¹,

Kaufman²,

Liu³

et al. 2004

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In this report we investigate order, stability, and phase transformations for a series of actinidebased alloys. The statics and kinetics of precipitation and ordering in this class of alloys are modeled with a scheme that couples fundamental information on the alloy energetics obtained from experimental and assessed thermo-chemical data to the CALPHAD approach commonly used in industry for designing alloys with engineering specificity with the help of the Thermo-Calc software application. The CALPHAD approach is applied to the study of the equilibrium thermodynamic properties of Pu-based alloys, Pu-X, where X=Al, Fe, Ga. The assessment of the equilibrium phase diagrams in the whole range of alloy composition has been performed with the PARROT module of the Thermo-Calc application software. Predictions are made on the low temperature and Pu-rich side of the phase diagrams of Pu-Ga and Pu-Al for which controversy has been noted in the past. The validity of the assessed thermo-chemical database will be discussed by comparing predicted heats of transformation for pure Pu with measured values from differential scanning calorimetry analysis. An overall picture for the stability properties of Pu-Ga and Pu-Al that reconciles the results of past studies carried out on these alloys is proposed. Results on phase stability in the ternary Fe-Ga-Pu and Al-Fe-Pu alloys are discussed. The information collected in this study is then used to model metastability, long-term stability and aging for this class of alloys by coupling Thermo-Calc with DICTRA, a series of modules that allow the analysis of DIffusion Controlled TRAnsformations. Kinetics information is then summarized in so-called TTT (temperature-time-transformations) diagrams for the most relevant phases of actinide alloys. Specifically, results are presented on kinetics of phase transformations associated with the eutectoid-phase decomposition reaction occurring at low temperature, and with the martensitic transformation that takes place at low Ga content in Pu-Ga alloys. Finally, after a summary of the most salient results, suggestions are made for further studies at the micro-and mesoscales.

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Calculated lattice relaxation in Pu-Ga

Cited by 15 publications

References 14 publications

Nanoscale heterogeneity, premartensitic nucleation, and a new plutonium structure in metastableδfcc Pu-Ga alloys

Nanoscale heterogeneity, premartensitic nucleation, and a new plutonium structure in metastableδfcc Pu-Ga alloys

Thermodynamic, alloying and defect properties of plutonium: Density-functional calculations

Thermodynamics and Kinetics of Phase Transformations in Plutonium Alloys - Part I

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