Mechanism on the formation of characteristic defect clusters and dislocation multiplication in fluorite structure ceramics

具有萤石结构的氧化物，如稳定的氧化锆和氧化铈，在核工业中具有潜在的惰性基质应用。以前我们已经在稳定化的氧化锆中发现，电子辐照诱导了特征缺陷团簇，其性质和生长过程与完美位错环有很大不同。本项目的目的是深入了解这种特征缺陷簇的形成机理，并了解萤石结构陶瓷的微观结构稳定性。主要研究结果和结论如下：(1)在稳定化氧化锆、氧化铈和氟化钙中，电子辐照在{111}面上形成了小片(或位错环)。(2)对CeO_2中缺陷团簇的电子能量依赖分析表明，在CeO_2中形成了小于1250keV的氧-片和高于1500keV的完美位错环。(3)对氧Frenkel对弛豫过程的MD模拟表明，氧间隙在Ce-Ce离子面间的{111}面上聚集形成二维缺陷。(4)透射电子显微镜分析和MD模拟表明，缺陷团簇的特征是在选择性置换下形成的氧(阴离子)片对相对轻的氧元素(阴离子)的损伤。(5)低pKa在萤石结构陶瓷的辐射损伤过程中起着重要作用。其中较轻的阴离子元素聚集以形成缺陷簇和多个位错。

Oxides with fluorite structure, such as stabilized zirconia and ceria, have potential applications for inert matrix in the nuclear industry. Previously we have found in stabilized zirconia that electron irradiation induces characteristic defect clusters whose nature and growth process is quite different from perfect dislocation loops. The aim of this project is to gain insights into t he formation mechanism of such characteristic defect clusters, and to understand the microstructure stability of fluorite structure ceramics. The followings are the main results and conclusions obtained in this project.(1) Platelets (or dislocation loops) are formed under electron irradiation on {111} planes in stabilized zirconia, ceria, and calcium fluorite. They accompany strong strain contrast and convert into perfect dislocations when they grow up to a critical size.(2) Electron energy dependent analysis on the defect clusters in ceria have clarified the formation of oxygen-platelet less than 1250 keV and perfect dislocation loops above 1500 keV.(3) MD simulations for the relaxation process of oxygen Frenkel pairs have shown that oxygen interstitials aggregate to form two dimensional defects on {111} planes between two Ce-Ce ion planes.(4) TEM analysis and MD simulations in the present study conclude that the characteristic defect clusters are oxygen (anion)-platelets which are formed under selective displacement damage on relatively lighter element of oxygen (anion).(5) An important role of low PKAs are suggested on the radiation damage process in fluorite structure ceramics, in which lighter elements of anions aggregate to form defect clusters and multiple dislocations.