title: Direct measurement of hydrogen dislocation pipe diffusion in deformed polycrystalline Pd using quasielastic neutron scattering.
abstract: The temperature-dependent diffusivity D(T) of hydrogen solute atoms trapped at dislocations-dislocation pipe diffusion of hydrogen-in deformed polycrystalline PdH(x) (x∼10(-3)  [H]/[Pd]) has been quantified with quasielastic neutron scattering between 150 and 400 K. We observe diffusion coefficients for trapped hydrogen elevated by one to two orders of magnitude above bulk diffusion. Arrhenius diffusion behavior has been observed for dislocation pipe diffusion and regular bulk diffusion, the latter in well-annealed polycrystalline Pd. For regular bulk diffusion of hydrogen in Pd we find D(T)=D(0)exp(-E(a)/kT)=0.005exp(-0.23  eV/kT)  cm(2)/s, in agreement with the known diffusivity of hydrogen in Pd. For hydrogen dislocation pipe diffusion we find D(T)≃10(-5)exp(-E(a)/kT)  cm(2)/s, where E(a)=0.042 and 0.083 eV for concentrations of 0.52×10(-3) and 1.13×10(-3)[H]/[Pd], respectively. Ab initio computations provide a physical basis for the pipe diffusion pathway and confirm the reduced barrier height.
authors: Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois, Urbana, Illinois 61801, USA.
authors: Brent J
authors: BJ
authors: Heuser
authors: Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801, USA.
authors: Dallas R
authors: DR
authors: Trinkle
authors: Chemical and Engineering Materials Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA and Juelich Centre for Neutron Science, Outstation at the Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors: Niina
authors: N
authors: Jalarvo
authors: Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois, Urbana, Illinois 61801, USA.
authors: Joseph
authors: J
authors: Serio
authors: Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801, USA.
authors: Emily J
authors: EJ
authors: Schiavone
authors: Chemical and Engineering Materials Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors: Eugene
authors: E
authors: Mamontov
authors: National Institute of Standards and Technology Center for Neutron Research, Gaithersburg, Maryland 20899, USA and Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA.
authors: Madhusudan
authors: M
authors: Tyagi