H tunneling and trapping in Y by anelastic relaxation measurements

We present the first evidence by acoustic measurements of H tunneling and trapping by 0 atoms in a rare-earth-hydride system. The YO00027HOO]6 alloy presents three new elastic-energy-loss peaks most likely due to H trapped by 0 between 1.4 and 330 K. The peak at the lowest temperature is due to tunneling of the trapped H; its relaxation rate strongly depends on temperature, indicating a dominant contribution of multiphonon processes already at a few kelvin. The other two peaks, with activation energies of 0.14 and 0.22 eV, can be attributed to jumps of H in the distorted environment of the 0 atom.