High-entropy (Sm0.2Eu0.2Gd0.2Dy0.2Er0.2)2Hf2O7 ceramic with superb resistance to radiation-induced amorphization

Nuclear engineering materials are required to possess outstanding extreme environmental tolerance and irradiation resistance. A promising novel pyrochlore-type of (Sm 0.2 Eu 0.2 Gd 0.2 Dy 0.2 Er 0.2 ) 2 Hf 2 O 7 high-entropy ceramic (HE-RE 2 Hf 2 O 7 ) for control rod was prepared by solid-state reaction method. The ion irradiation of HE-RE 2 Hf 2 O 7 with 400 keV Kr + at 400 °C was investigated using a 400 kV ion implanter and compared with single-component pyrochlore Gd 2 Hf 2 O 7 to evaluate the irradiation resistance. For HE-RE 2 Hf 2 O 7 , the phase transition from pyrochlore to defective fluorite is revealed after irradiation at 60 dpa. After irradiation at 120 dpa, it maintained crystalline, which is comparable to Gd 2 Hf 2 O 7 but superior to the titanate pyrochlores previously studied. Moreover, the lattice expansion of HE-RE 2 Hf 2 O 7 (0.22%) is much lower than that of Gd 2 Hf 2 O 7 (0.62%), indicating excellent irradiation damage resistance. Nanoindentation tests displayed an irradiation-induced increase in hardness and a decrease in elastic modulus by about 2.6%. Irradiation-induced segregation of elements is observed on the surface of irradiated samples. In addition, HE-RE 2 Hf 2 O 7 demonstrates a more sluggish grain growth rate than Gd 2 Hf 2 O 7 at 1200 °C, suggesting better high-temperature stability. The linear thermal expansion coefficient of HE-RE 2 Hf 2 O 7 is 10.7 × 10 -6 K -1 at 298–1273 K. In general, it provides a new strategy for the design of the next advanced nuclear engineering materials.