Diffusive hydrogen motion in ZrBe2H0.56: A quasielastic neutron scattering study

In ZrBe2H0.56, Be planes are separated by hexagonal Zr planes in the AlB2 structure with the H atoms occupying interstitial sites that form a honeycomb net in the Zr planes. The data from quasielastic neutron scattering above 500K using two spectrometers covering a wide range of resolutions from 1 to 64mueV can be fitted with a simple model using only two parameters for all momentum transfers at each temperature. The parameters are an elastic-like fraction and the hopping rate of a quasielastic contribution consisting of two-dimensional nearest-neighbor uncorrelated hopping among the partially occupied interstitial sites. The temperature dependence of the hopping rate follows an Arrhenius relation with an activation energy of 0.30+/-0.02eV.