Dynamic annealing of defects in irradiated zirconia-based ceramics
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Dynamic annealing of defects in irradiated zirconia-based ceramics Ram Devanathana) and William J. Weberb) Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (Received 16 July 2007; accepted 12 December 2007)
We have observed efficient damage recovery in large-scale molecular dynamics simulations of 30 keV Zr recoils in pure zirconia and yttria-stabilized zirconia, which is in stark contrast to radiation damage accumulation in zircon. Dynamic annealing is highly effective in zirconia during the first 5 ps of damage evolution, especially in the presence of oxygen structural vacancies. This results in near-complete recovery of damage. Damage recovery on the cation sublattice is assisted by the anion sublattice recovery, which explains the remarkable radiation tolerance of stabilized zirconia. Ceramics engineered to heal themselves in this fashion hold great promise for use in high-radiation environments or for safely encapsulating high-level radioactive waste over geological time scales.
Radiation-tolerant materials are needed to expand the use of nuclear energy in a manner consistent with the proliferation resistance, energy security, and waste reduction goals of the Global Nuclear Energy Partnership.1 Fluorite-structured ceramics, such as uranium dioxide and yttria-stabilized zirconia (YSZ), are well known for their remarkable radiation tolerance.2 The fundamental physics that underlies radiation tolerance of ceramics is, however, not well understood despite extensive experimental examination, because experiments are limited in their ability to probe dynamic radiation damage processes occurring at picosecond and nanometer scales. Atomistic computer simulations of energetic recoils in ceramics are needed to fill the knowledge gaps, interpret experimental data, and gain insights into the radiation response of materials. One of the features of stabilizing the cubic phase of zirconia (ZrO2) with aliovalent doping (e.g., Y2O3) is that oxygen structural vacancies (V¨O) are introduced as follows: x + OOx → 2Y⬘Zr + V¨O + 2ZrO2 Y2O3 + 2ZrZr a)
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Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http:// www.mrs.org/publications/JMR/policy.html DOI: 10.1557/JMR.2008.0104
It is of basic scientific interest to examine the primary damage state produced by energetic recoils in YSZ and the effect of pre-existing structural vacancies on damage evolution. Such work also has broad relevance to materials selection for nuclear reactors and nuclear waste disposal and in applications of YSZ, such as fuel cell electrolyte, oxygen sensor, thermal barrier coating, and gate dielectric. We have performed molecular dynamics simulation of radiation damage in a YSZ crystal that contains preexisting defects (V¨O) and substitutional impurities (Y⬘Zr) and contrasted it with rad
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