Thermophysical property evaluation of rare-earth hafnate RE2Hf2O7 as long-life service neutron absorber component

Control rods are essential components in nuclear reactors, used to maintain the desired state of fission reactions. Among potential materials for this application, RE₂Hf₂O₇ compounds exhibit exceptional neutron absorption capacity and structural stability under prolonged radiation exposure, minimizing the risk of reduced neutron absorption efficiency. Herein, dense RE₂Hf₂O₇ ceramics (RE = Eu, Gd, Tb, Dy, Tm) were synthesized via vacuum solid-state reactive sintering. Structural analysis revealed distinct phase formations: Eu₂Hf₂O₇, Gd₂Hf₂O₇, and Tb₂Hf₂O₇ crystallized in the pyrochlore structure, while Dy₂Hf₂O₇ and Tm₂Hf₂O₇ adopted a defective fluorite configuration. The thermophysical properties of these ceramics were systematically evaluated. RE₂Hf₂O₇ demonstrated superior thermal conductivity (1.4-2.4 W·m⁻¹·K⁻¹, 298–1073 K) compared to the conventional material Dy₂TiO₅. Furthermore, their thermal expansion coefficients (6.0–10.5 × 10⁻⁶ K⁻¹, 350–1100 K) closely matched those of Dy₂TiO₅ (7.5–10.5 × 10⁻⁶ K⁻¹), ensuring compatibility in reactor environments. Mechanical testing indicated robust performance, with Vickers hardness values ranging from 12.6 to 14.9 GPa, attributed to high bulk density and enhanced atomic bond strength. This work highlights the feasibility of tailoring RE₂Hf₂O₇ ceramics through rare-earth and hafnium composition adjustments, offering a pathway to durable, high-performance neutron absorbers. The combined thermal, mechanical, and structural advantages position these materials as promising candidates for next-generation nuclear reactor control rods.