Mechanical and structural response of radiation-damaged pyrochlore to thermal annealing

Reissner, Claudia E.; Roddatis, Vladimir; Bismayer, U.; Schreiber, Anja; Pöllmann, Herbert; Beirau, Tobias

doi:10.1016/j.mtla.2020.100950

Cited by 6 publications

(11 citation statements)

References 63 publications

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“…This work included detailed analyses of the Raman and infrared spectra of these samples. Furthermore, Reissner et al (2020) provided additional of evolution of the hardness and elastic moduli of three of the same samples as a function of the annealing temperature and time (16 h in air, per temperature step). A further assessment of the mechanical behaviour of the pyrochlores was conducted by Beirau and Huber (2021) by using finite element-voxel models the calculate the elastic moduli and hardness values as a function of alpha-decay dose and annealing temperature.…”

Section: Radiation Tolerancementioning

confidence: 99%

Perspectives on Pyrochlores, Defect Fluorites, and Related Compounds: Building Blocks for Chemical Diversity and Functionality

Lumpkin

Aughterson

2021

Front. Chem.

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In this article we provide some perspectives on a range of pyrochlore and defect fluorite type compounds with nominal A2B2O7, A2BO5, ABC2O7, and other stoichiometries. Typically, the phase transformations and stability fields in these systems are mapped as a function of the ionic radii of the A and B-site cations, e.g., the A/B cation radius ratio (rA/rB). This provides a useful guide to compatible structures and compositions for the development of advanced materials. Pyrochlore commonly transforms to a defect fluorite structure at high temperature in many systems; however, it is not uncommon to observe defect fluorite as the initial metastable phase at low temperature. The patterns of order-disorder observed in these materials are primarily due to the energetics of layer stacking, the defect formation and migration energies of cations and anions, or modulations of the parent cubic structure in 3 + n dimensional space. The first lead to predominantly non-cubic derivatives of the parent defect fluorite structure (e.g., zirconolite polytypes), the second control the order-disorder processes, and the latter lead to a variety of subtle additional scattering features within the cubic parent structure. Although the energetics of cation disorder and anion-vacancy disorder have become more accessible via atomistic approaches (e.g., MD and DFT), we continue to find interesting physical-chemical problems in these materials. For example, although there are significant differences in composition (Tb/Zr ratio and O content) between Tb2Zr2O7 and Tb2ZrO5, both of which are defect fluorites, we note that the modulations found in these two compounds by electron scattering are virtually identical with regard to the direction and magnitude of displacement from the normal Bragg diffracted beams. This suggests that neither the A/B cation ratio nor the oxygen stoichiometry have a significant effect on the modulations. The general observations on the systems of compounds noted in this paper rest primarily in the context of industrial materials for nuclear waste disposal, potential applications in inert matrix fuel designs, and other important technological applications such as ionic conductivity, electrical conductivity, and magnetism. Scientific advances in these areas have been underpinned by recent advances in ion irradiation, synchrotron X-ray, neutron scattering, and modelling and simulation capabilities. Furthermore, there has been some renewed interest in natural samples, e.g., Th-U zirconolite and pyrochlore as analogues for potential host phases in nuclear waste forms. In particular, the natural pyrochlores have provided additional details with regard to radiation damage ingrowth, percolation transitions, and the relationships between accumulated dose and physical properties including hardness, elastic modulus. Specific details of the thermal annealing of these samples have also been elucidated in considerable detail.

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Section: Radiation Tolerancementioning

confidence: 99%

Perspectives on Pyrochlores, Defect Fluorites, and Related Compounds: Building Blocks for Chemical Diversity and Functionality

Lumpkin

Aughterson

2021

Front. Chem.

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“…The radiation-damaged state is metastable, while thermal annealing leads (at least partially) to structural reorganization. [12][13][14] Nevertheless, this process has found to be not a simple reverse process of the initial damage event in, e.g., zircon and titanite. 15 During the thermally induced recrystallization of heavily damaged pyrochlore, avalanches have been detected, as phase fronts move by local singularities.…”

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confidence: 99%

“…20 In this Letter, we employ the modeling approach by Ref. 20 together with experimental nanoindentation data 14 to clarify: (i) if the radiation induced crystalline-to-amorphous transition in pyrochlore can be adequately described as a percolation problem with two percolation points and if so, (ii) do the percolation thresholds affect the thermally induced structural reorganization?…”

mentioning

confidence: 99%

“…Although the used model describes an isotropic case, reference data used for calibration were obtained from three macroscopic (111) oriented pyrochlore samples, with different degrees of structural disorder and the average main composition Ca 2 Nb 2 O 6 F. 13 As initial input parameters for the simulation an E of 235 GPa and an H of 12.5 GPa have been chosen for the crystalline phase, the E is an average value obtained from ceramics with pyrochlore structure of the composition (Ca 2 Nb 2 O 7 ) 0.25-0.5 (Gd 2 Zr 2 O 7 ) 0.5-0.75 , 23 and the H value is an initial assumption, based on the literature value for recrystallized initially less damaged Panda Hill pyrochlore [H 12.2 GPa (Ref. 14)]. While an E value of 110 GPa and an H value of 7.55 GPa have been taken for the amorphous phase in close approximation to the highly damaged Miass pyrochlore sample (100% f a after Ref.…”

mentioning

confidence: 99%

“…While an E value of 110 GPa and an H value of 7.55 GPa have been taken for the amorphous phase in close approximation to the highly damaged Miass pyrochlore sample (100% f a after Ref. 13), the elastic constants of both phases have been adjusted by fitting the predicted macroscopic response of the RVE to the measured behavior of the Young's modulus 14 as a function of the average calculated amorphous fraction 13 of reference pyrochlores before and after annealing (Fig. 1).…”

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confidence: 99%

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Percolation transitions in pyrochlore: Radiation-damage and thermally induced structural reorganization

Beirau

Huber

2021

Applied Physics Letters

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Finite element mechanical modeling is used to follow the evolution of the hardness (H), Young's modulus (E), and Poisson's ratio (ν) during the radiation-damage related crystalline-to-amorphous transition in pyrochlore (average main composition Ca2Nb2O6F). According to the model, two percolation transitions have been identified around 16% and 84% amorphous volume fraction, respectively. In this context, earlier results from thermally induced recrystallization experiments have found to indicate noticeable modifications on the short- and long-range order by passing the percolation thresholds. Both percolation points have found to act as specific kinetic barriers during stepwise annealing induced structural reorganization. As phases with pyrochlore structure have been considered as host structures for the long-term disposal of actinides, it is essential to gain better knowledge of their mechanical behavior under radiation-damage and subsequent temperature treatment. The obtained results validate the used models' robustness in predicting radiation-damage related mechanical modifications, at least for ceramics.

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Solubility of niobium(V) in cementitious systems relevant for nuclear waste disposal: Characterization of the solubility-controlling solid phases

Garbev²,

Çevirim-Papaioannou³

et al. 2022

Journal of Hazardous Materials

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Mechanical and structural response of radiation-damaged pyrochlore to thermal annealing

Cited by 6 publications

References 63 publications

Perspectives on Pyrochlores, Defect Fluorites, and Related Compounds: Building Blocks for Chemical Diversity and Functionality

Perspectives on Pyrochlores, Defect Fluorites, and Related Compounds: Building Blocks for Chemical Diversity and Functionality

Percolation transitions in pyrochlore: Radiation-damage and thermally induced structural reorganization

Solubility of niobium(V) in cementitious systems relevant for nuclear waste disposal: Characterization of the solubility-controlling solid phases

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