Hydrogen absorption and diffusivity in ZnO single crystals

ZnO single crystals electrochemically charged with hydrogen were characterized. The concentration of hydrogen introduced into the crystals was determined by nuclear reaction analysis and was found to be in a reasonable agreement with the value estimated from the Faraday's law. Moreover, a sub-surface layer with very high concentration of hydrogen and very high density of open-volume defects was formed by plastic deformation caused by hydrogen-induced stress. Specific surface modification caused by hydrogen-induced slip in the c-direction was observed on hydrogen loaded crystals. Hydrogen diffusion coefficient in ZnO was estimated by in situ electrical resistivity measurement. It was found that hydrogen diffusion in the c-direction is faster than in the a-direction most probably due to open channels existing in the wurtzite structure along the c-axis. (C) 2013 Elsevier B.V. All rights reserved.