Formation of tetragonal gas bubble superlattice in bulk molybdenum under helium ion implantation

Sun, Cheng; Sprouster, David; Hattar, Khalid Mikhiel; Ecker, Lynne; He, Linfeng; Gao, Yipeng; Zhang, Y.; Gan, Jian

doi:10.1016/j.scriptamat.2018.01.023

Cited by 15 publications

(10 citation statements)

References 37 publications

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“…With validations by atomistic simulations and experiments, several important implications can be drawn from the discovery: i) The superlattice is a superposition of stable perturbation waves at the instability point, whose symmetry is dictated by anisotropic SIA diffusion. This is consistent with the shadowing effect (Forreman 1972;Woo and Frank 1985) and the conclusion of Walgraef et al that a small degree of SIA diffusion anisotropy is needed for vacancy loop ordering (Walgraef et al 1996). The symmetry of these waves defines the superlattice structure, which depends on the kinetics of SIA diffusion but not necessarily the host matrices; ii) A 3-stage formation process, from random voids to planar ordering and then 3D lattice, is implied.…”

Section: Resultssupporting

confidence: 86%

“…The first one states that, based on experimental observations, the superlattices are isomorphic with the hosting matrices for unknown reasons. This theory, albeit the unknown physics behind, has remained to be consistent with most experimental results except for recent observations of fcc superlattices in bcc UMo (Gan et al 2015) and bct superlattices in bcc Mo (Sun et al 2018). The second is the so-called shadowing effect.…”

Section: Introductionsupporting

confidence: 60%

“…It has been long realized that during defect accumulation under continuous irradiation, the mean defect concentration fields can lose stability to modulated waves at a certain critical point (Krishan 1980;Walgraef et al 1996). Such a dynamic instability breaks the translational symmetry, thereby giving a characteristic length which is related to the superlattice parameter.…”

Section: Introductionmentioning

confidence: 99%

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Symmetry breaking during defect self-organization under irradiation

et al. 2020

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One of the most intriguing phenomena under radiation is the self-organization of defects, such as the void superlattices, which have been observed in a list of bcc and fcc metals and alloys when the irradiation conditions fall into certain windows defined by temperature and dose rate. A superlattice features a lattice parameter and a crystal structure. Previously, it has been shown that the superlattice parameter is given by the wavelength of vacancy concentration waves that develop when the uniform concentration field becomes unstable. This instability is driven thermodynamically by vacancy concentration supersaturation and affected by the irradiation condition. However, a theory that predicts the superlattice symmetry, i.e., the selection of superlattice structure, has remained missing decades after the first report of superlattices. By analyzing the nonlinear recombination between vacancies and self-interstitial-atoms (SIAs) in the discrete lattice space, this work establishes the physical connection between symmetry breaking and anisotropic SIA diffusion, allowing for predictions of void ordering during defect self-organization. The results suggest that while the instability is driven thermodynamically by vacancy supersaturation, the symmetry development is kinetically rather than thermodynamically driven. The significance of SIA diffusion anisotropy in affecting superlattice formation under irradiation is also indicated. Various superlattice structures can be predicted based on different SIA diffusion modes, and the predictions are in good agreement with atomistic simulations and previous experimental observations.

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Section: Resultssupporting

confidence: 86%

Section: Introductionsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

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Symmetry breaking during defect self-organization under irradiation

et al. 2020

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“…Unlike the high thermal stability of the Xe GBS in irradiated U–10Mo heating to 0.78 T m ( T m is the melting point), Kr GBS is thermally unstable in Ni from 0.48–0.51 T m and in Cu from 0.42 T m . In general, the He GBS tends to form within an irradiation temperature window of 0.2–0.4 T m while Kr GBS tends to form from 0.17–0.22 T m in cubic metals , and 0.14–0.32 T m in hcp metals. , The superlattices tend to adopt the crystallographic structure of the host matrix except for fcc Xe GBS in bcc UMo fuel and the formation of tetragonal GBS in bulk Mo implanted with He ions . However, the formation mechanism of GBS especially for Kr GBS or SBS is still not well understood.…”

Section: Introductionmentioning

confidence: 95%

“…However, the self-organization of the FG bubbles or voids superlattices can be achieved under certain irradiation conditions. While He and Xe gas bubble superlattices (GBSs) have been successfully observed in metals and UMo fuel, respectively, ,− Kr GBS or solid bubble superlattices (SBSs) have been studied in limited metal systems. The difference between GBS and SBS is the physical state of the noble gas in the superlattices observed in the metallic substrates.…”

Section: Introductionmentioning

confidence: 99%

Unraveling the Early-Stage Ordering of Krypton Solid Bubbles in Molybdenum: A Multimodal Study

et al. 2021

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Self-organization of defects such as fission gas bubbles in materials can lead to high inventory capacity for fission gas storage and help mitigate swelling caused by fission gases in nuclear fuel materials under radiation in nuclear reactors. Here, we report the physical mechanism of self-organization of krypton (Kr) gas bubbles in molybdenum (Mo) under ion implantation. The ion fluence and temperature-dependent formation of Kr solid bubble superlattice (SBS) in Mo were investigated by using both synchrotron-based small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Early stage self-organization of gas bubbles is observed at a fluence of 2.5 × 10 16 ions/cm 2 at temperatures of 300−400 °C. The bubble lattice constant increases with increasing implantation temperature from 300 to 400 °C. Both experiments and atomic kinetic Monte Carlo modeling indicate that the Kr solid bubbles are weakly ordered in comparison to previously studied helium (He) gas bubble superlattice (GBS) while the lattice constant are relatively smaller for Kr SBS compared to that of He GBS. The irradiation conditions suggest that spinodal decomposition, which is a form of phase separation, probably precedes gas bubble ordering in Mo. Overall, our work sheds light on the formation mechanism of noble gas superlattice toward the development of radiation-tolerant materials which are important for the design of advanced nuclear reactors.

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