Neutron Irradiation-Induced Structural Evolution and Defect-Related Phase Stability in ZrO ₂ –Fe Ceramics

In this study, neutron-irradiation-induced structural changes in ZrO 2 -Fe samples containing 4 wt% Fe were investigated by neutron diffraction. Rietveld refinement showed that the initial sample consisted mainly of monoclinic ZrO 2 with space group P 1 21/c 1 (No. 14), together with a minor η-Zr 4 Fe 2 O phase with space group F d -3 m (No. 227). After neutron irradiation in the fluence range from 8.98 × 10 12 to 3.59 × 10 13 n/cm 2 , the reflections of the secondary phase became strongly weakened, while the monoclinic ZrO 2 matrix remained structurally stable. The irradiation-induced structural evolution was reflected in the non-monotonic changes of the lattice parameters and unit-cell volume of monoclinic ZrO 2 . In addition, the ZrO 7 polyhedral distortion increased from 3.8 % in the initial sample to 6.7 % at the highest fluence, indicating an average long-range oxygen-sublattice response to neutron irradiation. The initial lattice expansion and subsequent contraction at higher fluences are consistent with irradiation-induced defect redistribution.