Abstract
In this study, the response of Pu2Zr2O7 and La2Zr2O7 to electronic radiation is simulated, employing an ab initio molecular dynamics method. It is shown that Pu2Zr2O7 undergoes a crystalline-to-amorphous structural transition with 0.3% electronic excitation, while for La2Zr2O7, the structural amorphization occurs with 1.2% electronic excitation. During the microstructural evolution, the anion disorder further drives cation disorder and eventually results in the structural amorphization of Pu2Zr2O7 and La2Zr2O7. The difference in responses to electron radiation between Pu2Zr2O7 and La2Zr2O7 mainly results from the strong correlation effects between Pu 5f electrons and the smaller band gap of Pu2Zr2O7. These results suggest that Pu2Zr2O7 is less resistant to amorphization under local ionization rates that produce a low level of electronic excitation, since the level of the concentration of excited electrons is relatively low in Pu2Zr2O7. The presented results will advance the understanding of the radiation damage effects of zirconate pyrochlores.
Highlights
With the growing demand for nuclear power, the problem of how to treat nuclear waste safely, especially long-lived transuranic (TRU) elements such as plutonium (Pu) and minor actinides (Np, Am) that are generated through spent fuel, has become extremely important [1,2,3]
They found that when monoclinic-layered perovskite La2 Ti2 O7 is exposed to a lower degree of electronic excitation, the amorphous transition occurs, whereas a similar phenomenon does not occur in cubic pyrochlore
It is found that the mean square displacement of oxygen is considerably larger than that of La and Zr. These results indicate that the displacement of oxygen drives the pyrochlore of La2 Zr2 O7 to undergo a crystallineto-amorphous transition under 1.6% electronic excitation
Summary
With the growing demand for nuclear power, the problem of how to treat nuclear waste safely, especially long-lived transuranic (TRU) elements such as plutonium (Pu) and minor actinides (Np, Am) that are generated through spent fuel, has become extremely important [1,2,3]. Sassi et al investigated the interplay between electronic excitation, structure, and composition in lanthanumbased ceramics employing a similar method They found that when monoclinic-layered perovskite La2 Ti2 O7 is exposed to a lower degree of electronic excitation, the amorphous transition occurs, whereas a similar phenomenon does not occur in cubic pyrochlore. Their results show that La2 Zr2 O7 can be amorphized at 200 K under 1.6% electronic excitation These studies demonstrate that electronic excitation may have substantial effects on the microstructural evolution and physical properties of materials. Far, it is not clear how Pu2 Zr2 O7 pyrochlore, which is a product for immobilization of Pu in zirconate pyrochlores [26,27,28,29], responds to electronic excitation. The presented results gain fundamental insights into the radiation damage effects of Pu2 Zr2 O7 and may promote related experimental investigations
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