Studies on oxygen chemical surface exchange and electrical conduction in thin film nanostructured titania at high temperatures and varying oxygen pressure.
J Chem Phys
; 134(1): 014704, 2011 Jan 07.
Article
em En
| MEDLINE
| ID: mdl-21219017
ABSTRACT
We report on oxygen surface exchange studies in â¼450-nm-thick nanocrystalline titania films with an average grain size of â¼13 nm by electrical conductivity relaxation along with the conductivity measurements at varying temperatures and oxygen partial pressures (pO(2)s). By electrochemical impedance spectroscopy technique, the high temperature conductivity was measured in the pO(2) range from â¼10(-16) to â¼10(-6) Pa at temperatures from 973 to 1223 K and activation energy, ΔE(a), for conduction was estimated as â¼3.23 eV at pO(2) â¼10(-11) Pa. Under reducing atmosphere (pO(2) < 10(-6) Pa), two distinct n-type conduction regimes were observed and corresponding predominant defects are discussed while, at high pO(2) regime (pO(2) >10(-6) Pa), ionic conduction appears dominant leading to a conductivity plateau. The surface relaxation was observed to have two independent time constants likely originating from microstructural effects. The surface exchange coefficients are measured as â¼10(-8)-10(-7) m∕s and â¼10(-9)-10(-8) m∕s for each contribution with ΔE(a)s of 2.79 and 1.82 eV, respectively, without much pO(2) dependence across several orders of pO(2) range of â¼10(-16)-10(-6) Pa in the temperature range between 973 and 1223 K. The results are of potential relevance to understanding the near-surface chemical phenomena in nanocrystalline titania which is of great interest for energy and environmental studies.
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Base de dados:
MEDLINE
Assunto principal:
Oxigênio
/
Temperatura
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Titânio
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Nanoestruturas
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Membranas Artificiais
Idioma:
En
Ano de publicação:
2011
Tipo de documento:
Article