Applying the two-state invar model to delta-phase plutonium

Lawson, A. C.; Roberts, J. A.; Martinez, B.; Ledbetter, Hassel; Migliori, A.; Richardson, James W.

doi:10.1007/s11837-003-0026-x

Cited by 5 publications

(9 citation statements)

References 15 publications

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“…The different temperatures at which the two sets of measurements were made cannot be the source of the discrepancy between this analysis and previous reports anyway. The Invar effect [30,82,83] in δ PuGa, whereby the thermal contraction increases with increasing Ga concentration, could enhance the shortening of the bond lengths with higher amounts of Ga. The issue of deviations from Vegard's law in δ Pu-Ga that are >0.02Å for materials with more than 6 at.…”

Section: H Direct Approach To Changes In Local Structure: Phase Subtmentioning

confidence: 99%

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: H Direct Approach To Changes In Local Structure: Phase Subtmentioning

confidence: 99%

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

et al. 2014

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“…These stable twins can be formed only at the special points in the triangle shown in Figure 2, and the locus of these points is the three directions, as indicated by dashed lines in this figure. The value of each point on these three directions is designated as [17] where is a parameter characterizing the vector along . The twin elements of these three stable transformation twins and their corresponding vectors are listed in Table I …”

Section: A Stable Transformation Twinmentioning

confidence: 99%

“…Given the fact that the lattice parameters of Pu-Ga alloys significantly depend on the gallium concentration, temperature, and heat-treatment procedure, [1,12,[15][16][17][18] any theoretical predictions based on the IPS theory require very accurate measurements of the crystal-lattice parameters at the states where the microstructure is formed. The existing data on the plutonium MT do not provide this accuracy.…”

Section: ϳϳmentioning

confidence: 99%

“…(These heterogeneities will cause variations in the lattice parameters of both the ␣Ј and ␦ phases. [17]) The other factors are the ordering of gallium in the ␣Ј phase, [16,25] which relaxes the lattice expansion, and the formation of vacancies or vacancy clusters due to self-irradiation damage. To take into account this uncertainty in volume change, we have used the dilatation parameter ␦, characterizing the relative deviation of the transformation-induced volume change with respect to that of the "standard reference state" characterized by the most recent crystal-lattice parameters (Eq.…”

Section: ϳϳ ϳϳmentioning

confidence: 99%

“…Several possible lattice correspondences relating the fcc ␦ phase to the monoclinic ␣ phase were first proposed by Olson and Adler, [3] and the possible twin modes and slip-accommodation modes have been studied by various researchers. [3,5,[7][8][9]11] However, given the facts that previous studies investigated a limited number of possible crystal-lattice rearrangements and that the existing theoretical models are insufficient to explain existing experimental observations, [1,[9][10][11][12][13][14][15][16][17][18] the crystallographic mechanism of this transformation is still open for further investigation.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Crystallography of the δ→α martensitic transformation in plutonium alloys

Jin

Khachaturyan

Wang

et al. 2005

Metall Mater Trans A

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A new stress-accommodating crystallographic mechanism of the martensitic transformation in plutonium alloys is proposed. According to this mechanism, an orientation variant of the ␣ phase is produced by a combination of a homogeneous strain and shuffling of the alternating close-packed (111) ␦ planes. It is shown that the formation of stable transformation-induced twins whose twin-plane orientations and twinshear directions do not depend on the small variations of the crystal-lattice parameters is the preferred stressaccommodating mode. Only these stable twins have dislocation-free twin boundaries, while the twin boundaries of all others are decorated by an ultradense distribution of partial dislocations. The theory predicts a crystal-lattice rearrangement mechanism involving the (205) ␣ stable twins. The corresponding invariant plane-strain (IPS) solutions, with special emphasis on the two simplest shuffling modes (the single and double elementary modes), are presented and compared with the existing experimental observations. It is shown that the habit-plane orientation is highly sensitive to the input values of the crystal-lattice parameters and, especially, to the accuracy of the measured volume change in the transformation. An analysis of these effects on the habit-plane orientation and orientation relations is also presented.

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Intrinsic Nanoscience of δ Pu–Ga Alloys: Local Structure and Speciation, Collective Behavior, Nanoscale Heterogeneity, and Aging Mechanisms

Conradson¹,

Bock²,

Castro³

et al. 2014

J. Phys. Chem. C

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δ Pu−Ga alloys and their response to self-irradiation are important scientifically because of the unique complexity of Pu and technologically because of their importance in Science Based Stockpile Stewardship. The local order and structure and the role of the Ga are crucial to understanding the phase stability and the aging effects. X-ray diffraction that gives the long-range average structure of the periodic component of the materials and pair distribution functions analysis and X-ray absorption fine structure that give the overall and the element specific local structure have been used to examine a variety of new and aged materials, including a set of high purity δ Pu 1−x Ga x alloys with 1.7 ≤ x ≤ 6.4 atom % Ga that span the low [Ga] portion of the δ region of the phase diagram across the ∼3.3 atom % Ga metastability boundary, a ∼1.7 atom % Ga alloy that was enriched with Pu 238 to accelerate the aging process, and others. We find that metastable alloys contain tens of percents of a novel, "σ", Pu structure that we attribute to rearrangement of the Ga-depleted regions after the self-organization of the Ga to form quasi-intermetallic Pu 25−35 Ga. This collective and cooperative behavior involving the Ga and other defects in terms of a tendency to aggregate into domains with structures that differ from the δ host and the resulting nanoscale heterogeneity also appears to play an important role in the observation of analogous locally ordered structures in aged materials. This description of these materials and their aging is radically different from current conceptual basis derived from other experiments that are insensitive to ordering on the angstrom−nanometer length scale.

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Applying the two-state invar model to delta-phase plutonium

Cited by 5 publications

References 15 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

Crystallography of the δ→α martensitic transformation in plutonium alloys

Intrinsic Nanoscience of δ Pu–Ga Alloys: Local Structure and Speciation, Collective Behavior, Nanoscale Heterogeneity, and Aging Mechanisms

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