Publications by authors named "Iurii Kogut"

2 Publications

  • Page 1 of 1

Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film CeZrO by a Resonant Nanobalance Approach.

Materials (Basel) 2021 Feb 5;14(4). Epub 2021 Feb 5.

Institute of Energy Research and Physical Technologies, Clausthal University of Technology, 38640 Goslar, Germany.

Bulk ceria-zirconia solid solutions (CeZrO, CZO) are highly suited for application as oxygen storage materials in automotive three-way catalytic converters (TWC) due to the high levels of achievable oxygen non-stoichiometry δ. In thin film CZO, the oxygen storage properties are expected to be further enhanced. The present study addresses this aspect. CZO thin films with 0 ≤ x ≤ 1 were investigated. A unique nano-thermogravimetric method for thin films that is based on the resonant nanobalance approach for high-temperature characterization of oxygen non-stoichiometry in CZO was implemented. The high-temperature electrical conductivity and the non-stoichiometry δ of CZO were measured under oxygen partial pressures O in the range of 10-0.2 bar. Markedly enhanced reducibility and electronic conductivity of CeO-ZrO as compared to CeO and ZrO were observed. A comparison of temperature- and O-dependences of the non-stoichiometry of thin films with literature data for bulk CeZrO shows enhanced reducibility in the former. The maximum conductivity was found for CeZrO, whereas CeZrO showed the highest non-stoichiometry, yielding δ = 0.16 at 900 °C and O of 10 bar. The defect interactions in CeZrO are analyzed in the framework of defect models for ceria and zirconia.
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http://dx.doi.org/10.3390/ma14040748DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7915746PMC
February 2021

Determination of the Dielectric Properties of Storage Materials for Exhaust Gas Aftertreatment Using the Microwave Cavity Perturbation Method.

Sensors (Basel) 2020 Oct 23;20(21). Epub 2020 Oct 23.

Bayreuth Engine Research Center (BERC), Department of Functional Materials, University of Bayreuth, 95440 Bayreuth, Germany.

Recently, a laboratory setup for microwave-based characterization of powder samples at elevated temperatures and different gas atmospheres was presented. The setup is particularly interesting for investigations on typical materials for exhaust gas aftertreatment. By using the microwave cavity perturbation method, where the powder is placed inside a cavity resonator, the change of the resonant properties provides information about changes in the dielectric properties of the sample. However, determining the exact complex permittivity of the powder samples is not simple. Up to now, a simplified microwave cavity perturbation theory had been applied to estimate the bulk properties of the powders. In this study, an extended approach is presented which allows to determine the dielectric properties of the powder materials more correctly. It accounts for the electric field distribution in the resonator, the depolarization of the sample and the effect of the powder filling. The individual method combines findings from simulations and recognized analytical approaches and can be used for investigations on a wide range of materials and sample geometries. This work provides a more accurate evaluation of the dielectric powder properties and has the potential to enhance the understanding of the microwave behavior of storage materials for exhaust gas aftertreatment, especially with regard to the application of microwave-based catalyst state diagnosis.
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http://dx.doi.org/10.3390/s20216024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7660336PMC
October 2020