High-temperature resonant ultrasound spectroscopy of highly radiation-damaged pyrochlore: Structural reorganization and high acoustic loss

High-temperature resonant ultrasound spectroscopy (HT-RUS) has been employed to follow in situ the thermally induced structural reorganization of highly radiation-damaged pyrochlore. The investigated sample with average composition (Na,Ca)2Nb2O6F contains ∼12 wt. % UO2 and has an amorphous fraction of ∼95%. The sample displays high acoustic loss, but an unconventional use of HT-RUS (monitoring the variation of the respective measured spectra's overall integrated intensity) nevertheless allows the thermally induced structural reorganization process to be followed in some detail. The recrystallization process is accompanied by clear changes in elastic properties, while initial heating causes elastic softening of the radiation-damaged pyrochlore. The results imply a general applicability of HT-RUS to in situ monitoring of the thermal behavior of highly attenuating materials.