Irradiation-induced grain growth and defect evolution in nanocrystalline zirconia with doped grain boundaries

Abstract

Grain boundaries are effective sinks for radiation-induced defects, ultimately impacting the radiation tolerance of nanocrystalline materials (dense materials with nanosized grains) against net defect accumulation. However, irradiation-induced grain growth leads to grain boundary area decrease, shortening potential benefits of nanostructures. A possible approach to mitigate this is the introduction of dopants to target a decrease in grain boundary mobility or a reduction in grain boundary energy to eliminate driving forces for grain growth (using similar strategies as to control thermal growth). Here we tested this concept in nanocrystalline zirconia doped with lanthanum. Although the dopant is observed to segregate to the grain boundaries, causing grain boundary energy decrease and promoting dragging forces for thermally activated boundary movement, irradiation induced grain growth could not be avoided under heavy ion irradiation, suggesting a different growth mechanism as compared to thermal growth. Furthermore, it is apparent that reducing the grain boundary energy reduced the effectiveness of the grain boundary as sinks, and the number of defects in the doped material is higher than in undoped (La-free) YSZ.

Defect‐fluorite Gd2Zr2O7 ceramics under helium irradiation: Amorphization, cell volume expansion, and multi‐stage bubble formation

“…Moreover, the increasing local concentration (number) and size of vacancy clusters can be distinguished as grain size increases. According to an earlier study, the vacancy‐type defects dominate the major radiation defect forms inside grains is because of the much weaker mobility compared with that of interstitials, which are eventually absorbed by the GBs or are migrated into the material surface . Furthermore, the total defect concentration increases as the grain size increases, in which the GBs act as neutralizer for both vacancies and interstitials …”

He irradiation‐induced lattice distortion and surface blistering of Gd2Zr2O7 defect‐fluorite ceramics

“…Interestingly, compared with the unirradiated region, the irradiated region of nanograin ceramic is found to have a lower degree of porosity after irradiation at 5 × 10 16 ions/cm 2 . Since irradiation-induced interstitial defects normally have a higher migration rate than that of vacancy defects, the porosity within the irradiated region may serve as favorable sites to accommodate and regulate the interstitial defects and implanted He ions, 33,34 leading to pore volume reduction. Figure 10 shows the AFM images of the Gd 2 Zr 2 O 7 ceramics surfaces before and after He ions irradiation.…”

In-situ TEM study of irradiation-induced damage mechanisms in monoclinic-ZrO2

“…Similar modelling results suggest that a system with completely separated vacancies has very high energy and is not stable [6], and as a result the formation of Schottky defects is favoured [10] by the diffusion of mobile anion vacancies to the less-mobile cation vacancies. There have been extensive modelling studies on the evolution of point defects in zirconia [9][10][11][12][13][14][15], but much less experimental work has been done, probably because the point defects in zirconia exist preferentially in very small clusters [16] that are very challenging to detect by conventional microscopy techniques.…”