HYDROGEN-INDUCED INTERNAL-FRICTION IN NANOCRYSTALLINE PALLADIUM

The influence of H and D on the internal friction of nanocrystalline P d was studied in vibrating-reed experiments (temperatures between 5 an d 250 K; frequencies between 300 and 2000 Hz, H and D concentrations o f about 2 and about 4 at.%). The data demonstrate a strong H- or D-ind uced internal-friction peak at around 160 K. The comparison with liter ature results for H-doped ordinary coarse-grained or single-crystal Pd suggests that the peak is caused by a Snoek-Koster relaxation of H or D atoms in the grains of the nanocrystalline Pd. The data show furthe r a relaxation at around 70 K which is probably due to relaxation proc esses of H or D atoms in the grain boundaries.