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 neu trons at the Swiss Spallation Neutron Source SINQ at Paul-Scherrer institut e. The instrument can be operated either in time focusing or monochromatic focusing conditions, such that it can be optimized for quasielastic and ine lastic neutron scattering experiments, respectively. Because of its highly flexible concept FOCUS can be used for a broad range of applications from c ondensed, soft condensed and nanocrystalline matter. Due to the fact that t he incoming energy can be continuously tuned between 2-30 meV a large dynam ical 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. BaZr0.85Y0.15O2.9 25/0.0375H(2)O, which is a well-known proton conductor at elevated temperat ures. We have studied the crystallite size influence on the proton conducti vity and on diffusivity of a polycrystalline reference and of nanocrystalli ne samples using impedance spectroscopy (IS) and quasielastic neutron scatt ering (QENS) on FOCUS. While the former method yields a macroscopic diffusi on coefficient, the latter one allows elucidating the microscopic proton di ffusion mechanism. (C) 2001 Acta Materialia Inc. Published by Elsevier Scie nce Ltd. All rights reserved.