High-Temperature Mechanical Characterization of CeO₂ as a Ceramic Surrogate Fuel Based on FIB and Nanoindentation

CeO₂ is widely used as a non-radioactive surrogate for UO₂ because of its fluorite crystal structure and similar thermophysical characteristics. In this study, an FIB-assisted specimen preparation route combined with high-temperature nanoindentation was used to evaluate the micromechanical behavior of CeO₂ from room temperature to 400 °C. Hardness and Young's modulus were experimentally measured at room temperature, 100 °C, 200 °C, 300 °C, and 400 °C. The load-displacement curves were smooth, and no obvious pop-in events were observed within the tested load range. From 100 °C to 400 °C, both Young's modulus and hardness decreased approximately linearly with increasing temperature, and linear fitting was used to describe their temperature dependence. The measured Young's modulus decreased from 191.3 ± 14.0 GPa at 100 °C to 136.7 ± 9.5 GPa at 400 °C, while the hardness decreased from 6.79 ± 0.58 GPa to 5.08 ± 0.48 GPa. The obtained temperature-dependent trend is consistent with previously reported high-temperature nanoindentation data for fluorite-structured oxides. These results provide useful micromechanical data and methodological support for elevated-temperature small-scale mechanical characterization of ceramic nuclear fuel surrogate materials.