Nanoscale phase transitions under extreme conditions within an ion track

Zhang, Jiaming; Lang, Maik; Ewing, Rodney C.; Devanathan, Ram; Weber, William J.; Toulemonde, M.

doi:10.1557/jmr.2010.0180

Cited by 96 publications

(120 citation statements)

References 42 publications

Supporting

Mentioning

101

Contrasting

Unclassified

Order By: Relevance

“…A variety of criteria have been proposed as predictors of radiation tolerance, including bond covalency 5 , susceptibility to disordering 2 , thermodynamic stability 6 and grain size 7 . However, relating trends in radiation tolerance to the dynamic process of radiation damage accumulation is difficult due to the complex nature of defect production and recovery, both of which occur at nanometric length scales, femto-and picosecond timescales, and extremely high energy densities 8 . In addition, the conditions under which a material is irradiated can drastically affect its response.…”

mentioning

confidence: 99%

“…Electronic stopping results in extensive local ionization, yielding excitation densities of up to several keV nm À 3 within a nanometric cylinder along the ion trajectory 15 . Although the atomistic modifications that occur following this electron cascade have been extensively studied 8,13 , the relaxation of these delocalized electrons is complex and difficult to relate directly to atomic behaviour 16 . It is generally assumed that electron-hole recombination leads to recovery of the pre-irradiation charge distribution 13 but, given the highly nonequilibrium conditions under which relaxation of the electron cascade occurs, electronic structure modifications are possible.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Redox response of actinide materials to highly ionizing radiation

et al. 2015

Self Cite

View full text Add to dashboard Cite

Energetic radiation can cause dramatic changes in the physical and chemical properties of actinide materials, degrading their performance in fission-based energy systems. As advanced nuclear fuels and wasteforms are developed, fundamental understanding of the processes controlling radiation damage accumulation is necessary. Here we report oxidation state reduction of actinide and analogue elements caused by high-energy, heavy ion irradiation and demonstrate coupling of this redox behaviour with structural modifications. ThO 2 , in which thorium is stable only in a tetravalent state, exhibits damage accumulation processes distinct from those of multivalent cation compounds CeO 2 (Ce 3 þ and Ce 4 þ ) and UO 3 (U 4 þ , U 5 þ and U 6 þ ). The radiation tolerance of these materials depends on the efficiency of this redox reaction, such that damage can be inhibited by altering grain size and cation valence variability. Thus, the redox behaviour of actinide materials is important for the design of nuclear fuels and the prediction of their performance.

show abstract

mentioning

confidence: 99%

mentioning

confidence: 99%

Redox response of actinide materials to highly ionizing radiation

et al. 2015

Self Cite

View full text Add to dashboard Cite

show abstract

“…Due to its radiation tolerance, pyrochlores are seen as a candidate for application such as inert matrix fuels, nuclear waste immobilization and geological age-dating. [1,2] However, radiation under such extreme conditions introduces phase transformation in the ordered pyrochlore structure, which is critical to understand for such applications. High energy ion irradiation (MeV to GeV) on pyrochlores is seen as an important experiment to understand the phase transformations which take place due to localized (nanoscale) energy transfer to the lattice in extremely short time period (~ns).…”

mentioning

confidence: 99%

Short-Range Atomic Ordering in Amorphous Ion-Tracks in Pyrochlores

et al. 2015

View full text Add to dashboard Cite

Pyrochlore structured complex oxides (A 2 B 2 O 7 ) have attracted attention due to its unique physical, chemical and electrical properties. Due to its radiation tolerance, pyrochlores are seen as a candidate for application such as inert matrix fuels, nuclear waste immobilization and geological age-dating.[1,2] However, radiation under such extreme conditions introduces phase transformation in the ordered pyrochlore structure, which is critical to understand for such applications. High energy ion irradiation (MeV to GeV) on pyrochlores is seen as an important experiment to understand the phase transformations which take place due to localized (nanoscale) energy transfer to the lattice in extremely short time period (~ns). [3] In the present work, Gd 2 Ti 2 O 7 is irradiated with high energy ions to form nanoscale amorphous tracks along the ion penetration path. It has been previously reported that a concentric shell of disordered crystalline phase of defect fluorite is formed around the amorphous ion track in Gd 2 Zr x Ti (1-x) O 7 pyrochlores.[4] In the case of Gd 2 Ti 2 O 7 , there are studies reporting similar formation of a concentric defect-fluorite phase. However, atomic scale characterization and its effect on electronic structure of material has not yet been understood which is important for performance of such materials. Here, we report the detailed study of concentric defect fluorite phase existing around amorphous ion track by using high-angle annular dark field (HAADF) imaging and electron energy-loss spectroscopy (EELS) in an aberration corrected scanning transmission electron microscope (STEM).Here, a (HAADF) image of an ion track in Gd 2 Ti 2 O 7 pyrochlore lattice oriented in [110] zone axis is shown in Fig. 1(a). The ion track was created by 2.2 GeV Au ion irradiation. The image analysis based on the atomic column contrast reveals that a distinct crystalline phase with thickness of 2-3 atomic planes (0.5-1 nm) forms at the periphery of the ion track. This phase is identified as defect fluorite phase which is a disordered crystalline derivative of the ordered pyrochlore phase. The contrast variation seen in amorphous region is due to tilting of ion track from perfect normal view. To understand the electronic structure, electron energy-loss spectroscopy (EELS) is performed. Fig. 1(b) and (c) show the Ti L-edge (456 eV) and O K-edge (532 eV) respectively from ordered crystalline and amorphous region. In an important observation, the Ti L-edge in the amorphous ion track features crystal field splitting similar to the one from crystalline region. This result indicates the presence of short-range ordering in the Ti-O octahedra in amorphous phase of Gd 2 Ti 2 O 7 . In addition to that, the shift in the e g and t 2g peaks in both L 3 and L 2 shows the evidence of Ti-O octahedral distortion in the amorphous phase. Fig. 1(c) shows that the pre-peak merges with the main peak and results in a significant

show abstract

“…Crocombette [74] has compared defect production by displacement cascades and thermal spikes and concluded that while the number of defects produced in simulations of cascades and spikes can be different, the overall characteristics of the damage are quite similar. Recently, Zhang et al [75] showed that thermal spike simulations can reproduce the microstructural features of ion tracks and the amorphization tendency observed in experimental irradiation of pyrochlore compounds. These findings suggest that thermal spike simulations can be used to quickly screen candidate waste forms based on their tendency to undergo direct-impact amorphization.…”

Section: Modeling Of Ceramic Waste Formsmentioning

confidence: 99%

Challenges in Modeling the Degradation of Ceramic Waste Forms

Devanathan¹,

Gao²,

X³

2011

View full text Add to dashboard Cite

We identify the state of the art, gaps in current understanding, and key research needs in the area of modeling the long-term degradation of ceramic waste forms for nuclear waste disposition. The directed purpose of this report is to define a roadmap for Waste IPSC needs to extend capabilities of waste degradation to ceramic waste forms, which overlaps with the needs of the subcontinuum scale of FMM (fundamental methods and method) interests. The key knowledge gaps are in the areas of i) methodology for developing reliable interatomic potentials to model the complex atomic-level interactions in waste forms; ii) characterization of water interactions at ceramic surfaces and interfaces; and iii) extension of atomic-level insights to the long time and distance scales relevant to the problem of actinide and fission product immobilization.

show abstract

Nanoscale phase transitions under extreme conditions within an ion track

Cited by 96 publications

References 42 publications

Redox response of actinide materials to highly ionizing radiation

Redox response of actinide materials to highly ionizing radiation

Short-Range Atomic Ordering in Amorphous Ion-Tracks in Pyrochlores

Challenges in Modeling the Degradation of Ceramic Waste Forms

Contact Info

Product

Resources

About