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Evolution of intrinsic point defects in fluorite-based materials: Insights from atomic-level simulation.

机译：萤石基材料中本征点缺陷的演变：原子级模拟的见解。

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摘要

Point defects play a significant role in materials properties. On the one hand, point defects are exploited in applications such as fuel cells; on the other hand, they are deleterious to performance of in such applications as nuclear fuels. To tailor materials with desired properties, it is thus important to understand point defect behavior in materials under specific environments/applications. This thesis is focused on understanding the evolution of point defects in materials, primarily fluorite-related, used in solid oxide fuel cell (SOFC) and nuclear applications. Molecular-dynamics simulation (MD) and density functional theory (DFT) are used as materials modeling tools.;Cubic bismuth oxide (delta-Bi2O3) is a promising SOFC electrolyte and a fluorite-based model material, in which, it is found that while intrinsic oxygen vacancies contribute in high oxygen diffusion, under certain circumstances, they themselves act as limiting factors by forming a 110>-111> vacancy-ordered system. It is found that high cationic polarizability plays a significant role in achieving high oxygen diffusivity. It is also found that the oxygen diffusivity may be limited due to the formation of covalent character bonds by some Bi ions.;Fluorite-structured UO2 is the fuel in almost all operating nuclear reactors. Due to irradiation, UO2 undergoes damage resulting in the formation of Frenkel pairs (FPs) on both uranium and oxygen sub-lattices. It is found that, while damage on oxygen sub-lattice alone is not deleterious, in that oxygen FPs annihilate by mutual recombination, presence of FPs on uranium sub-lattice cause long-lasting damage and make UO2 less radiation tolerant. Regardless of FPs on oxygen sub-lattice, FPs on uranium sub-lattice nucleate new O FPs, which form clusters. The oxygen vacancies' sequestration by uranium vacancies is found to be the mechanism of cluster formation.;The point-defect evolution is rocksalt MgO is also elucidated. MgO is an important engineering material and has nuclear applications. As in UO 2, it is found that when defects are present on both Mg and O sub-lattice, new FPs, in this case, both on Mg and O are formed. Defects present only on either Mg or O sub-lattice annihilate by mutual recombination.;While UO2 and MgO studies are done on single crystals to elucidate FPs elimination by mutual recombination only, to understand their evolution in the presence of GBs, similar studies are done on nanocrystalline Mo. This allows elucidation of dominant mechanism of point-defect elimination. It is found that for the grain size and temperature under study, mutual recombination of FPs dominates and GBs have little effect on the point-defect elimination.
机译：点缺陷在材料特性中起着重要作用。一方面，在燃料电池等应用中利用了点缺陷。另一方面，它们对诸如核燃料的应用的性能有害。为了使材料具有所需的特性，因此重要的是要了解特定环境/应用下材料中的点缺陷行为。本文的重点是了解固体氧化物燃料电池（SOFC）和核应用中主要与萤石有关的材料中点缺陷的演变。分子动力学模拟（MD）和密度泛函理论（DFT）用作材料建模工具。立方氧化铋（δ-Bi2O3）是一种很有前途的SOFC电解质和萤石基模型材料，其中发现尽管固有​​的氧空位有助于高氧扩散，但在某些情况下，它们本身通过形成<110>-<111>空位有序系统而成为限制因素。发现高的阳离子极化率在实现高的氧扩散率中起重要作用。还发现由于某些Bi离子形成共价特征键，氧的扩散率可能受到限制。氟结构的UO2是几乎所有运行中的核反应堆的燃料。由于辐照，UO2受到破坏，导致铀和氧亚晶格上形成弗伦克尔对（FPs）。已发现，虽然仅对氧亚晶格的损害不是有害的，但氧FPs通过相互复合而消失，铀亚晶格上FPs的存在会造成长期破坏，并使UO2的耐辐射性降低。不论氧亚晶格上的FP为何，铀亚晶格上的FP都会使新的O FP成核。发现铀空位对氧空位的螯合是形成团簇的机制。点缺陷演化为岩盐MgO。氧化镁是一种重要的工程材料，具有核应用。与UO 2一样，发现在Mg和O子晶格上都存在缺陷时，在这种情况下，在Mg和O上都会形成新的FP。仅在Mg或O亚晶格通过相互重组而消失时才存在缺陷;虽然在单晶上进行了UO2和MgO研究以仅通过相互重组来阐明FP消除，以了解在存在GB的情况下它们的演化，但也进行了类似的研究可以阐明点缺陷消除的主要机理。发现对于所研究的晶粒尺寸和温度，FPs的相互复合起主导作用，而GBs对消除点缺陷的影响很小。

著录项

  • 作者

    Aidhy, Dilpuneet Singh.;

  • 作者单位

    University of Florida.;

  • 授予单位 University of Florida.;
  • 学科 Engineering Civil.;Operations Research.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 197 p.
  • 总页数 197
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 建筑科学;运筹学;
  • 关键词

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