Oxide ceramics are the candidate materials for encapsulating minor actinides. Since the decay of radioactive elements generates a large amount of heat and radiation, knowledge on structural changes and stability under radiation environments is required. Oxygen-deficient fluorite structural derivatives have attracted attention for their radiation effects, because oxide ceramics with a fluorite type structure are known to exhibit excellent radiation resistance. We have recently performed swift heavy ion irradiation into δ-Sc4Hf3O12 and found the formation of a metastable phase with a bixbyite (C-rare-earth) structure [1]. However, the stability of this structure is not well understood. In the present study, we examined the effects of heat treatment and electron beam irradiation on the bixbyite phase. [1] M. Iwasaki, Y. Kanazawa, D. Manago, M. K. Patel, G. Baldinozzi, K. E. Sickafus, and M. Ishimaru, J. Appl. Phys. 132, 075901 (2022).