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strontium titanate; proton conductivity; hydride ion conductivity; transport number; quantum molecular dynamics simulations; chemical compound; SrTiO3
Abstract:
Hydrogen ion conductivity in 2% and 10% Al-substituted SrTiO3
has been investigated by transport number measurements using
the concentration cell/emf method in wet atmospheres as a
function of pO(2) (10 (- 20) -1 atm) and temperature (350 -
1000 degreesC). Earlier indications of apparent negative charge
transport by hydrogen under reducing conditions and high
temperatures have been confirmed. By the present measurements,
possible artefacts from the type of acceptor-dopant, gas
buffer, electrode material, and porosity of the sample appear
to have been ruled out. Electrochemical pumping experiments
with gas chromatography were inconclusive with respect to
hydride ion transport. Thermogravimetry as a function of
hydrogen activity did not show evidence of hydride ion
incorporation, but indicated uptake of neutral hydrogen under
reducing conditions and high temperatures. Quantum molecular
dynamics simulations indicate the existence of defect species
or clusters that may be reminiscent of interstitial hydrogen
with a tendency to associate with effective negative charge,
e.g., on neighbouring titanium ions, under simulated reducing
conditions. (C) 2002 Elsevier Science B.V. All rights reserved.
