Crystal dynamics of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>δ</mml:mi></mml:math>fcc Pu-Ga alloy by high-resolution inelastic x-ray scattering

Wong, Joe; Krisch, M.; Farber, Daniel L.; Occelli, F.; Xu, Ruqing; Chiang, T.‐C.; Clatterbuck, D. M.; Schwartz, Adam J.; Wall, M. A.; Boro, C.O.

doi:10.1103/physrevb.72.064115

Cited by 41 publications

(22 citation statements)

References 51 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Arguing this attribute of the structure by claiming that, for example, scattering, photoemission, microscopy, and ultrasound data contradict it ignores the fact that all experimental methods are limited to their intrinsic length and timescales. Thus, the suggestions of structural and transformational complexity that have transpired indirectly from photoemission [11,13,22,84], diffraction [23], phonon spectra [55,[85][86][87], the identification of the instabilities of some of the structures along the Bain paths that connect them [88][89][90], and even heat capacity measurements that have assigned the anomalous behavior of δ Pu alloys to the structural phenomena [49,50] can be viewed as the signatures of the individual and collective lattice distortions found in the local structure measurements. Local structure results are complementary to methods that are sensitive to the average properties of a large number of atoms or to the periodic or coherent portions of a material, so that such putative contradictions are most likely to be indicative of essential components of the structure:property relationships.…”

Section: Discussionmentioning

confidence: 99%

“…Local structure results are complementary to methods that are sensitive to the average properties of a large number of atoms or to the periodic or coherent portions of a material, so that such putative contradictions are most likely to be indicative of essential components of the structure:property relationships. Perhaps the most important example is the anomalous elastic softness that has been identified as a bulk property of the elastic moduli by resonance ultrasound [88,91,92], in particular aspects of the phonon dispersion curves [85,86,93]-some of which differ from calculations [89], and as anisotropic atomic displacements in diffraction [23].…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2014

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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

et al. 2014

View full text Add to dashboard Cite

show abstract

“…Ledbetter and Moment [58], using the ultrasonic technique, were first to show that ␦-phase Pu alloys are the most elastically anisotropic fcc materials known. The anisotropy ratio of ∼7 was confirmed with high-resolution inelastic X-ray scattering measurements of the phonon dispersion curve [59,60]. Recently, Moore et al calculated bond strengths between neighboring atoms in unalloyed and alloyed ␦-phase Pu using DFT [61].…”

Section: The Relation Between Electronic Structure and Metallurgymentioning

confidence: 73%

“…The phonon dispersion curves of ␦-phase Pu-Ga alloys, ␥-Ce, Th, La and other f-electron materials exhibit a pronounced softening in the transverse 1 1 1 branch [59,60,[63][64][65]. Stassis et al suggest that this could be a precursor of the fcc-dhcp structural phase transition in Ce.…”

Section: The Relation Between Electronic Structure and Metallurgymentioning

confidence: 96%

Plutonium metallurgy: The materials science challenges bridging condensed-matter physics and chemistry

Schwartz

2007

Journal of Alloys and Compounds

View full text Add to dashboard Cite

“…Since the measurement of the phonon dispersion curves along the high symmetry axes of small crystallites of δ-phase 239 Pu 0.98 Ga 0.2 [1,2], as well as measurements of the phonon density of states and elastic moduli on polycrystalline samples of 242 Pu 0.95 Al 0.05 [3], it has become possible to construct phenomenological phonon models which accurately reproduce the measured specific heat all the way up to 300 K [4]. Unfortunately, the vibrational frequencies or density of states were determined only at a few temperatures.…”

Section: Introductionmentioning

confidence: 99%

The Debye–Waller factor of stabilized -Pu

Graf

2007

Journal of Alloys and Compounds

View full text Add to dashboard Cite

The Debye-Waller factor has been calculated for stabilized δ-phase plutonium with 5% aluminum. A quasiharmonic Born-von Kárman force model with temperature dependent phonon frequencies was used to calculate the mean-square thermal atomic displacement from absolute zero to 800 K. Implementation of the observed anomalous softening of the long wavelength phonons with increasing temperature cannot account for the softening of the measured thermal parameter at high temperatures nor for its rather high value at low temperatures. The implications for diffraction measurements on δ-phase stabilized plutonium alloys are discussed.

show abstract

Crystal dynamics ofδfcc Pu-Ga alloy by high-resolution inelastic x-ray scattering

Cited by 41 publications

References 51 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

Plutonium metallurgy: The materials science challenges bridging condensed-matter physics and chemistry

The Debye–Waller factor of stabilized -Pu

Contact Info

Product

Resources

About