Surface chemistry of pure tetragonal ZrO2and gas-phase dependence of the tetragonal-to-monoclinic ZrO2transformation.
The surface chemical properties of undoped tetragonal ZrO2and the gas-phase dependence of the tetragonal-to-monoclinic transformation are studied using a tetragonal ZrO2polymorph synthesized via a sol-gel method from an alkoxide precursor. The obtained phase-pure tetragonal ZrO2is defective and strongly hydroxylated with pronounced Lewis acidic and Brønsted basic surface sites. Combined in situ FT-infrared and electrochemical impedance measurements reveal effective blocking of coordinatively unsaturated sites by both CO and CO2, as well as low conductivity. The transformation into monoclinic ZrO2is suppressed up to temperatures of ∼723 K independent of the gas phase composition, in contrast to at higher temperatures. In inert atmospheres, the persisting structural defectivity leads to a high stability of tetragonal ZrO2, even after a heating-cooling cycle up to 1273 K. Treatments in CO2and H2increase the amount of monoclinic ZrO2upon cooling (>85 wt%) and the associated formation of either Zr-surface-(oxy-)carbide or dissolved hydrogen. The transformation is strongly affected by the sintering/pressing history of the sample, due to significant agglomeration of small crystals on the surface of sintered pellets. Two factors dominate the properties of tetragonal ZrO2: defect chemistry and hydroxylation degree. In particular, moist conditions promote the phase transformation, although at significantly higher temperatures as previously reported for doped tetragonal ZrO2.
Institute of Physical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria. simon.penner@uibk.ac.at.
Eva-Maria
EM
Köck
Institute of Physical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria. simon.penner@uibk.ac.at.
Michaela
M
Kogler
Institute of Physical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria. simon.penner@uibk.ac.at.
Thomas
http://orcid.org/0000-0003-3673-317X
T
Götsch
Fachgebiet Keramische Werkstoffe/Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften- und technologien, Technische Universität Berlin, Hardenbergstr. 40, D-10623 Berlin, Germany.
Lukas
http://orcid.org/0000-0001-7054-7587
L
Schlicker
Fachgebiet Keramische Werkstoffe/Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften- und technologien, Technische Universität Berlin, Hardenbergstr. 40, D-10623 Berlin, Germany.
Maged F
http://orcid.org/0000-0003-1778-0288
MF
Bekheet
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Andrew
A
Doran
Fachgebiet Keramische Werkstoffe/Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften- und technologien, Technische Universität Berlin, Hardenbergstr. 40, D-10623 Berlin, Germany.
Aleksander
A
Gurlo
Institute of Physical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria. simon.penner@uibk.ac.at.
Bernhard
B
Klötzer
Institute of Inorganic and Theoretical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria.
Benedikt
B
Petermüller
Institute of Inorganic and Theoretical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria.
Daniel
D
Schildhammer
Institute of Materials Chemistry, Vienna University of Technology, Getreidemarkt 9/BC, A-1060 Wien, Austria.
Nevzat
N
Yigit
Institute of Physical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria. simon.penner@uibk.ac.at.
Simon
http://orcid.org/0000-0002-2561-5816
S
Penner