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Phonon scattering effects from point and extended defects on thermal conductivity studied via ion irradiation of crystals with self-impurities

Physical Review Materials

Scott, Ethan A.; Hattar, Khalid M.; Rost, Christina M.; Gaskins, John T.; Fazli, Mehrdad; Ganski, Claire; Li, Chao; Bai, Tingyu; Wang, Yekan; Esfarjani, Keivan; Goorsky, Mark; Hopkins, Patrick E.

Fundamental theories predict that reductions in thermal conductivity from point and extended defects can arise due to phonon scattering with localized strain fields. To experimentally determine how these strain fields impact phonon scattering mechanisms, we employ ion irradiation as a controlled means of introducing strain and assorted defects into the lattice. In particular, we observe the reduction in thermal conductivity of intrinsic natural silicon after self-irradiation with two different silicon isotopes, Si+28 and Si+29. Irradiating with an isotope with a nearly identical atomic mass as the majority of the host lattice produces a damage profile lacking mass impurities and allows us to assess the role of phonon scattering with local strain fields on the thermal conductivity. Our results demonstrate that point defects will decrease the thermal conductivity more so than spatially extended defect structures assuming the same volumetric defect concentrations due to the larger strain per defect that arises in spatially separated point defects. With thermal conductivity models using density functional theory, we show that for a given defect concentration, the type of defect (i.e., point vs extended) plays a negligible role in reducing the thermal conductivity compared to the strain per defect in a given volume.

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TYPE Journal Article YEAR 2018
DOIOSTIScopus

Fundamentals of Pellet-Clad Debonding

Dingreville, Remi; Hattar, Khalid M.; Boyle, Timothy; Monterrosa, Anthony; Barr, Christopher M.; Weck, Philippe F.; Juan, Pierre-Alexandre

This project focused on providing a fundamental mechanistic understanding of the complex degradation mechanisms associated with Pellet/Clad Debonding (PCD) through the use of a unique suite of novel synthesis of surrogate spent nuclear fuel, in-situ nanoscale experiments on surrogate interfaces, multi-modeling, and characterization of decommissioned commercial spent fuel. The understanding of a broad class of metal/ceramic interfaces degradation studied within this project provided the technical basis related to the safety of high burn-up fuel, a problem of interest to the DOE.

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TYPE SAND Report YEAR 2018
DOIOSTI

Radiation damage in nanostructured materials

Progress in Materials Science

Zhang, Xinghang; Hattar, Khalid M.; Chen, Youxing; Shao, Lin; Li, Jin; Sun, Cheng; Yu, Kaiyuan; Li, Nan; Taheri, Mitra L.; Wang, Haiyan; Wang, Jian; Nastasi, Michael

Materials subjected to high dose irradiation by energetic particles often experience severe damage in the form of drastic increase of defect density, and significant degradation of their mechanical and physical properties. Extensive studies on radiation effects in materials in the past few decades show that, although nearly no materials are immune to radiation damage, the approaches of deliberate introduction of certain types of defects in materials before radiation are effective in mitigating radiation damage. Nanostructured materials with abundant internal defects have been extensively investigated for various applications. The field of radiation damage in nanostructured materials is an exciting and rapidly evolving arena, enriched with challenges and opportunities. In this review article, we summarize and analyze the current understandings on the influence of various types of internal defect sinks on reduction of radiation damage in primarily nanostructured metallic materials, and partially on nanoceramic materials. We also point out open questions and future directions that may significantly improve our fundamental understandings on radiation damage in nanomaterials. The integration of extensive research effort, resources and expertise in various fields may eventually lead to the design of advanced nanomaterials with unprecedented radiation tolerance.

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TYPE Journal Article YEAR 2018
DOIOSTIScopus

Examining the influence of grain size on radiation tolerance in the nanocrystalline regime

Applied Physics Letters

Barr, Christopher M.; Li, Nan; Boyce, Brad L.; Hattar, Khalid M.

Nanocrystalline materials have been proposed as superior radiation tolerant materials in comparison to coarse grain counterparts. However, there is still a limited understanding whether a particular nanocrystalline grain size is required to obtain significant improvements in key deleterious effects resulting from energetic irradiation. This work employs the use of in-situ heavy ion irradiation transmission electron microscopy experiments coupled with quantitative defect characterization and precession electron diffraction to explore the sensitivity of defect size and density within the nanocrystalline regime in platinum. Under the explored experimental conditions, no significant change in either the defect size or density between grain sizes of 20 and 100 nm was observed. Furthermore, the in-situ transmission electron microscopy irradiations illustrate stable sessile defect clusters of 1-3 nm adjacent to most grain boundaries, which are traditionally treated as strong defect sinks. The stability of these sessile defects observed in-situ in small, 20-40 nm, grains is the proposed primary mechanism for a lack of defect density trends. This scaling breakdown in radiation improvement with decreasing grain size has practical importance on nanoscale grain boundary engineering approaches for proposed radiation tolerant alloys.

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TYPE Journal Article YEAR 2018
DOIOSTIScopus

Characterizing single isolated radiation-damage events from molecular dynamics via virtual diffraction methods

Journal of Applied Physics

Dingreville, Remi; Stewart, James A.; Price, Patrick M.; Ji, W.; Franco, M.; Hattar, Khalid M.

The evolution and characterization of single-isolated-ion-strikes are investigated by combining atomistic simulations with selected-area electron diffraction (SAED) patterns generated from these simulations. Five molecular dynamics simulations are performed for a single 20 keV primary knock-on atom in bulk crystalline Si. The resulting cascade damage is characterized in two complementary ways. First, the individual cascade events are conventionally quantified through the evolution of the number of defects and the atomic (volumetric) strain associated with these defect structures. These results show that (i) the radiation damage produced is consistent with the Norgett, Robinson, and Torrens model of damage production and (ii) there is a net positive volumetric strain associated with the cascade structures. Second, virtual SAED patterns are generated for the resulting cascade-damaged structures along several zone axes. The analysis of the corresponding diffraction patterns shows the SAED spots approximately doubling in size, on average, due to broadening induced by the defect structures. Furthermore, the SAED spots are observed to exhibit an average radial outward shift between 0.33% and 0.87% depending on the zone axis. This characterization approach, as utilized here, is a preliminary investigation in developing methodologies and opportunities to link experimental observations with atomistic simulations to elucidate microstructural damage states.

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TYPE Journal Article YEAR 2018
DOIOSTIScopus

High temperature irradiation induced creep in Ag nanopillars measured via in situ transmission electron microscopy

Scripta Materialia

Jawaharram, Gowtham S.; Price, Patrick M.; Barr, Christopher M.; Hattar, Khalid M.; Averback, Robert S.; Dillon, Shen J.

Irradiation induced creep (IIC) rates are measured in compression on Ag nanopillar (square) beams in the sink-limited regime. The IIC rate increases linearly with stress at lower stresses, i.e. below ≈2/3 the high temperature yield stress and parabolically with pillar width, L, for L less than ≈300 nm. The data are obtained by combining in situ transmission electron imaging with simultaneous ion irradiation, laser heating, and nanopillar compression. Results in the larger width regime are consistent with prior literature.

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TYPE Journal Article YEAR 2018
DOIOSTIScopus
Results 201–250 of 613
Results 201–250 of 613