Irregularities in helium release rates from metal ditritides

Abstract

Helium release rates from erbium and zirconium ditritide films were measured with 3-s time resolution. All films exhibited some variability in 3He release rates on this time scale, but the nonuniformity of the release rate was greatest for samples undergoing the transition into accelerated release, which occurs when the occluders approach the maximum quantities of helium that they can retain. The 3He release rate variability appeared to be associated with the spontaneous release of helium in bursts of about 109 atoms. The release of bursts of helium was also stimulated by vibrating or flexing the film substrates. Although these effects are not expected based on the diffusion of isolated helium atoms of the lattice, the effects of temperature on helium release rates were consistent with the diffusion model. These observations lead to the conclusion that two distinct mechanisms are responsible for the release of helium from the metal ditritide films.

Electronic structure of hydrogen storage materials

“…Recently, a value of 0.5 was reported [28] for aged PdT x . There is also experimental evidence [29] that release occurs in bursts of 10 9 atoms, which indicates that it is not a continuous process. Concerning the location of He in the tritide, two types of models have been proposed.…”

“…The He diffusivity is also found to be very low, 10 −13 -10 −14 cm 2 /year, which indicates that a typical He atom diffuses at most a few lattice parameters per year [9]. Also, the release of He in the form of bursts of 10 9 atoms does not seem to support the model of bubble formation, because a bubble of ∼4000 Å is required to contain so many He atoms [29]. Instead, a mechanism that involves the collective movement of the He atoms is suggested.…”

“…In the latter, vacancies are created due to the implantation of He + ions that serve as traps for He and lead to bubble formation, whereas no such defects can be created by the He produced in the tritide because the recoil energy of He in the radioactive decay of tritium is too small. Thus the He produced is trapped at the interstitial sites and is immobile [9,11,29]. Experimental evidence in favor of the first model is quite indirect and comes essentially from transmission electron microscopy (TEM) observations on thin films of tritides [30] and from interpretations of the nuclear magnetic resonance (NMR) line shapes [10].…”

First-principles Study on the Properties of Point Defects in Hcp-Dy

“…-+ e  +18.582 keV,   is a beta particle and e  is an antineutrino [7]. In the present work, the point defects properties of the self-interstitial atoms (SIAs), mon-vacancy, interstitial H atoms and He atoms in hcp-Dy have been investigated by Ab initio density functional theory, which are compared with the other hcp metals.…”

First-principles study of He point-defects in HCP rare-earth metals

“…the behavior of He in metal-tritium systems is also of interest [9,10]. The experiments show that the metal tritide lattice expands as a result of He accumulation, as well as from phenomena such as surface blistering and flaking of metal ditritide films from substrates [11,12].…”