Verlag des Forschungszentrums Jülich
JUEL-3442
Using impedance spectroscopy the contributions from the bulk and the grain boundary
regions to the conductivity have been separated. In the wet state the main charge carriers in
the bulk are protons and the conductivity decreases with increasing sintering temperature.
In the dry state hole conduction dominates both in the bulk and at grain boundaries which
form effective barriers for charge transport. For samples prepared after the wet chemical
route the conductivity at grain boundaries in the wet state is considerably higher than in the
dry state. In contrast, the grain boundary conductivity in conventionally prepared samples
remains unaffected after charging with protons.
Maxima in the loss tangent have been observed as a function of temperature or frequency
which can be explained by conductivity contributions to the dielectric loss. No further loss
contributions -e. g. due to local defect reorientations -could have been identified. This has
been shown for the system BaCa0.393NbO.607O3-[gamma], also.
By means of anelastic relaxation measurements the internal friction of the samples has
been found to be related to the proton content of the samples. The stoichiometric
compound BaCa0.33NbO.66O3 did not show any water uptake and no relaxation maxima at all.
For dry, nonstoichiometric samples contributions to the damping with Ea~1.0eV and
Ea~ 1.2 eV have been found. After proton incorporation, contributions to the damping with
Ea~O.6 eV and Ea~O.7 eV have been identified. An atomistic model is presented with
attributes these contributions to local reorientations of Vo-CaNb-pairs and
(OH)o-CaNb-pairs, respectively.
Bausch, Stefan
Impedanzanalyse und mechanische Relaxation von keramischen Protonenleitern
107 S., 1997
High temperature proton conductors are candidate materials for solid electrolytes in
different applications like sensors or fuel cells. Non-stoichiometric compounds like
BaCa0.393NbO.607O3-[gamma] or BaCe0.9 YO.1O3-[gamma] show considerable water uptake and subsequent
proton conductivity after exposure to wet atmospheres. In order to study the microscopic
details of the diffusion process of the protons )impedance measurements and anelastic
relaxation spectroscopy have been combined. The conductivity of the complex perovskite
BaCa0.393NbO.607O3-[gamma] has been determined for different samples prepared with the
conventional rnixed oxide or a wet chemical route after various sintering temperatures. The
main results are:
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