INTERNAL-FRICTION STUDY OF HYDROGEN AND DEUTERIUM RELAXATION IN YTTRIUM

The anelastic relaxation caused by H and D in polycrystalline hexagona l (alpha-phase) YH(x) and Y D(x) was studied with the help of the vibr ating reed technique (x less-than-or-equal-to 0.17, 5 K less-than-or-e qual-to T less-than-or-equal-to 330 K, frequencies f between 100 and 1 100 Hz). The measurements yielded a single relaxation peak located, e. g. for f = 500 Hz, at 272 and 279 K in the case of H and D, respective ly. The peak position is independent of x, and the relaxation strength rises roughly linearly with x. The widths of the relaxation peaks exc eed those expected for an ideal Debye relaxation by about 40%. The rel axation rates tau-1 can be described by an Arrhenius relation tau0(-1) exp(E/k(B)T) with an identical activation energy E = (0.60 +/- 0.05) eV for both H and D. The microscopic H or D jump processes, which may lead to the relaxation, are discussed.