Different mechanisms of A-site and B-site high entropy effect on radiation tolerance of pyrochlores

Abstract

The properties of high entropy pyrochlore have been studied extensively, but there is no consistent conclusion on its radiation tolerance. Besides, the mechanism of the high entropy effect on the radiation tolerance of pyrochlore is still unclear. In this work, combined with experiments and calculations of pyrochlores with similar cationic radius ratios, the A-site and B-site high entropy effects on structural evolution under irradiation are analyzed. In situ irradiation experiments were carried out on A-site high entropy pyrochlores such as (La0.2Nd0.2Sm0.2Gd0.2Er0.2)2Zr2O7, B-site Gd2(Ti1/3Sn1/3Zr1/3)2O7, and ternary pyrochlore Sm2Zr2O7 and Gd2Sn2O7 for comparison. The A-site high entropy pyrochlore can maintain a stable structure under high fluence irradiation like corresponding ternary pyrochlore, demonstrated by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), energy dispersive spectroscopy (EDS) mapping and Raman spectrum. The additional irradiation experiments on A-site high entropy pyrochlores (La1/3Nd1/3Gd1/3)2Zr2O7 and (Nd1/3Sm1/3Gd1/3)2Zr2O7 also confirm the similarity under irradiation between A-site high entropy and ternary pyrochlores. However, the B-site high entropy pyrochlore Gd2(Ti1/3Sn1/3Zr1/3)2O7 becomes amorphous at exceptionally low irradiation fluences, indicating a significantly distinct radiation tolerance compared with the A-site high entropy. The difference between the A-site and B-site high entropy effect is analyzed from cationic lattice distortion, bond strength, and inner electron binding energy by first-principles calculations. The results reveal the role and mechanism of the high entropy effect in pyrochlores and lay a foundation for material design and future applications.