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Abstract
Bulk samples of hafnium (Hf) hydride and deuteride were prepared and the thermal properties, heat capacity (CP) and thermal conductivity (κ) were measured. In the CP–temperature curves for both samples, typical lambda-type peaks were observed at around 350 K, which was due to the second-order phase transition from the δ′-phase to the δ-phase. In Hf hydride, it is considered that the δ′-phase and the δ-phase consist of regularly arranged and randomly arranged hydrogen atoms, respectively. Therefore, it can be said that the δ′/δ phase transition observed in both Hf hydride and deuteride is an order–disorder phase transition. The values of κ as well as CP changed significantly at around the phase transition temperature.
Acknowledgements
The present study includes results from “Development Study of Fast Reactor Core with Hydride Neutron Absorber” entrusted to Tohoku University by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT).