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

Abstract

Nuclear engineering materials are required to possess outstanding extreme environmental tolerance and irradiation resistance. A promising novel pyrochlore-type of (Sm0.2Eu0.2Gd0.2Dy0.2Er0.2)2Hf2O7 high-entropy ceramic (HE-RE2Hf2O7) for control rod was prepared by solid-state reaction method. The ion irradiation of HE-RE2Hf2O7 with 400 keV Kr+ at 400 °C was investigated using a 400 kV ion implanter and compared with single-component pyrochlore Gd2Hf2O7 to evaluate the irradiation resistance. For HE-RE2Hf2O7, 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 Gd2Hf2O7 but superior to the titanate pyrochlores previously studied. Moreover, the lattice expansion of HE-RE2Hf2O7 (0.22%) is much lower than that of Gd2Hf2O7 (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-RE2Hf2O7 demonstrates a more sluggish grain growth rate than Gd2Hf2O7 at 1200 °C, suggesting better high-temperature stability. The linear thermal expansion coefficient of HE-RE2Hf2O7 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.