Phase structure of high-entropy pyrochlore oxides: From powder synthesis to ceramic sintering.

High-entropy pyrochlore ceramics have received significant attention in the field of nuclear materials due to their ability to immobilize radioactive waste. In this study, a range of medium and high-entropy Ti-based pyrochlore powders were synthesized by a two-step method. Interestingly, a monoclinic phase was observed in some powders. An innovative experiment was conducted to adjust the cation ratio at the A site, which revealed that certain cations with larger ionic radii exhibit low solid solubility in the pyrochlore lattice, resulting in the formation of the monoclinic structure. To avoid the formation of monoclinic phase, the crystal structure was adjusted by introducing Zr4+ at the B site. Based on the selection of single-phase powders, high-density pyrochlore ceramic bulks with uniform distribution of elements were prepared by spark plasma sintering. Here (Sm 1/5 Yb 1/5 Gd 1/5 Er 1/5 Dy 1/5) 2 Ti 2 O 7 bulks exhibited the smallest grain size at approximately 2.48 µm among all sintered samples and demonstrated a hardness of around 10.14 GPa. [ABSTRACT FROM AUTHOR]