Neutron time-of-flight spectrometer focus at SINQ: Results from nanocrystalline matter studies

FOCUS is a time and space focusing time of flight spectrometer for cold neutrons at the Swiss Spallation Neutron Source SINQ at Paul-Scherrer institute. The instrument can be operated either in time focusing or monochromatic focusing conditions, such that it can be optimized for quasielastic and inelastic neutron scattering experiments, respectively. Because of its highly flexible concept FOCUS can be used for a broad range of applications from condensed, soft condensed and nanocrystalline matter. Due to the fact that the incoming energy can be continuously tuned between 2-30 meV a large dynamical range is covered. As an example we present data obtained from a perovskite structured barium zirconate doped with yttrium and charged with water, e.g. BaZr0.85Y0.15O2.925/0.0375H(2)O, which is a well-known proton conductor at elevated temperatures. We have studied the crystallite size influence on the proton conductivity and on diffusivity of a polycrystalline reference and of nanocrystalline samples using impedance spectroscopy (IS) and quasielastic neutron scattering (QENS) on FOCUS. While the former method yields a macroscopic diffusion coefficient, the latter one allows elucidating the microscopic proton diffusion mechanism. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.