Hydrogen mobility parameters and dislocation pinning rates at very low temperatures in tantalum

Abstract

Pinning rates of dislocations by hydrogen and deuterium have been analysed in monocrystalline tantalum samples of ultrahigh purity. For this purpose, measurements of internal friction and elastic modulus were performed down to 2 K, using a vibrating strip system. A marked pinning stage located between 8 K and 11 K was revealed for hydrogen. The authors show that it reflects the arrival of the hydrogen atoms at dislocation sites, resulting in the pinning of the dislocation kinks. The inferred jump rate of hydrogen atoms is 3*102+or-1 s-1 at 8.3 K. The temperature dependence of diffusion was found to obey a power law, with a large exponent, 15+or-3. Deuterium migration was also detected, at around 14 K. The results obtained are compared with previous data at higher or similar temperatures and discussed in relation to the existing theories for quantum diffusion.