Extending the Momentum Transfer Range in QENS Measurements on Sc-Doped Barium Zirconates
Publicerad
Författare
Typ
Examensarbete för masterexamen
Program
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
In this work, a range of scandium-doped, proton-conducting barium zirconates have
been subject to two complementary quasi-elastic neutron scattering (QENS) experiments;
one featuring a traditional range of momentum transfer (Q) values (0.5 – 2
Å−1) and one featuring an extended Q-range (1 – 4 Å−1). Recent data suggests that
the extended Q-range may allow differentiation between jump and rotational motions
of protons within a Grotthuss-type diffusion model. However, so far measurements
have been conducted only on the traditional and extended dynamical ranges
separately, using different samples. By collecting QENS spectra in both momentum
transfer regimes for the same sample, this work aims to achieve a comparison of
QENS results over these regimes and their corresponding time-scales. Furthermore,
theoretical models for jump and rotational localized motions are compared to experimental
data over both Q regimes. It was found that the atomic-scale proton
dynamics probed using an extended Q-range are somewhat more rapid (processes
with characteristic time-scales of 0.8 – 2.0 picoseconds) than those probed using a
traditional Q-range (3.0 – 12.3 picoseconds), as expected from the inherently lower
energy-transfer resolution of extended Q-range experiments. QENS measurements
further suggested that the more rapid dynamics targeted by the extended Q-range
measurement require higher temperatures to initiate. Models for jump-type and
rotation-type proton motions both display good fits with the experimental data,
preventing discrimination between the models. Nonetheless, it is shown why the extended
Q range is useful for ensuring reliability in fitting these models. Activation
energies and correlation times are largely consistent with previous measurements on
traditional Q-range experiments.
Beskrivning
Ämne/nyckelord
proton conductor, Grotthuss mechanism, neutron scattering, QENS, hydrogen bond, barium zirconate, scandium, local proton dynamics