The electromigration of hydrogen in YH3 was studied by monitoring the H-concentration dependence of the optical transmission. It was found that the effective valence of H was negative. Its value was governed by a huge wind-force like term. This value was 3 orders of magnitude larger than that which was typical for H in metals. By using an Arrhenius plot, the ratio of the H (figure 53) and electron fluxes extrapolated to unity at infinite temperature. This suggested that there was a 1-to-1 correlation between H and electron hopping. The results were explained in terms of strong electron correlation theories which predict that each proton bound 2 electrons in a form of Zhang-Rice singlet.

S.J.Van der Molen, M.S.Welling, R.Griessen: Physical Review Letters, 2000, 85[18], 3882-5

Figure 53

Diffusivity of H in YH3