H-TUNNELING AND TRAPPING IN Y BY ANELASTIC RELAXATION MEASUREMENTS

We present the first evidence by acoustic measurements of H tunneling and trapping by O atoms in a rare-earth-hydride system. The YO0.0027H0.016 alloy presents three new elastic-energy-loss peaks most likely due to H trapped by O 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 O atom.