title: Nanocrystalline TiO2/SnO2heterostructures for gas sensing.
abstract: The aim of this research is to study the role of nanocrystalline TiO2/SnO2n-n heterojunctions for hydrogen sensing. Nanopowders of pure SnO2, 90 mol % SnO2/10 mol % TiO2, 10 mol % SnO2/90 mol % TiO2and pure TiO2have been obtained using flame spray synthesis (FSS). The samples have been characterized by BET, XRD, SEM, HR-TEM, Mössbauer effect and impedance spectroscopy. Gas-sensing experiments have been performed for H2concentrations of 1-3000 ppm at 200-400 °C. The nanomaterials are well-crystallized, anatase TiO2, rutile TiO2and cassiterite SnO2polymorphic forms are present depending on the chemical composition of the powders. The crystallite sizes from XRD peak analysis are within the range of 3-27 nm. Tin exhibits only the oxidation state 4+. The H2detection threshold for the studied TiO2/SnO2heterostructures is lower than 1 ppm especially in the case of SnO2-rich samples. The recovery time of SnO2-based heterostructures, despite their large responses over the whole measuring range, is much longer than that of TiO2-rich samples at higher H2flows. TiO2/SnO2heterostructures can be intentionally modified for the improved H2detection within both the small (1-50 ppm) and the large (50-3000 ppm) concentration range. The temperatureTmaxat which the semiconducting behavior begins to prevail upon water desorption/oxygen adsorption depends on the TiO2/SnO2composition. The electrical resistance of sensing materials exhibits a power-law dependence on the H2partial pressure. This allows us to draw a conclusion about the first step in the gas sensing mechanism related to the adsorption of oxygen ions at the surface of nanomaterials.
authors.affiliation: AGH University of Science and Technology, Faculty of Computer Science, Electronics and Telecommunications, Al. A. Mickiewicza 30, 30-059 Krakow, Poland.
authors.forename: Barbara
authors.initials: B
authors.lastname: Lyson-Sypien
authors.affiliation: AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Al. A. Mickiewicza 30, 30-059 Krakow, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Kusior
authors.affiliation: AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Al. A. Mickiewicza 30, 30-059 Krakow, Poland.
authors.forename: Mieczylaw
authors.initials: M
authors.lastname: Rekas
authors.affiliation: AGH University of Science and Technology, Academic Center for Materials and Nanotechnology, Al. A. Mickiewicza 30, 30-059 Krakow, Poland.
authors.forename: Jan
authors.initials: J
authors.lastname: Zukrowski
authors.affiliation: AGH University of Science and Technology, Academic Center for Materials and Nanotechnology, Al. A. Mickiewicza 30, 30-059 Krakow, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Gajewska
authors.affiliation: EMPA, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for High Performance Ceramics, Uberlandstrasse 129, 8600 Duebendorf, Switzerland; Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Michalow-Mauke
authors.affiliation: EMPA, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for High Performance Ceramics, Uberlandstrasse 129, 8600 Duebendorf, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Graule
authors.affiliation: AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Al. A. Mickiewicza 30, 30-059 Krakow, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Radecka
authors.affiliation: AGH University of Science and Technology, Faculty of Computer Science, Electronics and Telecommunications, Al. A. Mickiewicza 30, 30-059 Krakow, Poland.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Zakrzewska
keywords: TiO2/SnO2; gas sensors; hydrogen; nanomaterials; n–n heterojunctions