Analysis of defect chemistry and microstructural effects of non-stoichiometric ceria by the high-temperature microwave cavity perturbation method. Issue 2 (February 2022)

• Record Type: Journal Article
• Authors: Steiner, Carsten; Hagen, Gunter; Kogut, Iurii; Fritze, Holger; Moos, Ralf
• Is Part Of: Journal of the European Ceramic Society. Volume 42:Issue 2(2022)
• Page Start: 499
• Page End: 511
• Publication Date: 2022-02
• Subjects: Ceria -- Defect chemistry -- Oxygen vacancy -- Small polaron hopping mechanism -- Microstructure -- Microwave cavity perturbation -- Resonant frequency -- Quality factor -- Dielectric properties -- Exhaust gas aftertreatment; Ceramic materials -- Periodicals; Composite materials -- Periodicals; Matériaux céramiques -- Périodiques; Composites -- Périodiques; Ceramic materials; Composite materials; Periodicals; Electronic journals; 666.05
• DOI: 10.1016/j.jeurceramsoc.2021.08.053
• Languages: English
• ISSNs: 0955-2219

Abstract

Highlights: Comprehensive study about non-stoichiometric ceria using the high temperature microwave cavity perturbation method. The microstructure is observed to have and huge impact on the dielectric and defect properties of nano-structured ceria. Inverse correlation of microwave frequency and dielectric losses confirms small-polaron hopping mechanism in ceria. For a nanocrystalline powder a higher conductivity and an activation of the small polaron hopping is observed. For sintered samples the lower conductivities are probably related to acceptor impurities and synthesis route. Abstract: The defect chemistry of ceria has been studied using a microwave resonator. The dielectric properties of powder samples were investigated up to 600 °C and at different oxygen partial pressures p O2 (10 −26 – 0.2 bar) and evaluated using the microwave cavity perturbation theory. For the ceria powder, an activation of the oxygen incorporation and release kinetics was observed from 480 °C onwards. The data suggest that the increased losses in non-stoichiometric ceria originate from the small polaron hopping mechanism, as known from literature. In addition, an increase in material polarization due to the formation of oxygen vacancies was experimentally observed. A comparison with sintered, coarse-grained samples of the same material and with literature data also demonstrated the importance of the microstructure for the defect chemistry of ceria. For the powder (ca. 80 nm grain size), significantly higher electronic conductivities (assumedly due to the higher concentration of small polarons) and lower activation energies were detected at 600 °C. On the other hand, lower conductivities, controlled by the concentration of acceptor cations in the material were reported for the sintered samples (1.1 μm) at this temperature. The findings are well in-line with existing defect chemical models of ceria. This study presents an analysis of the microwave behavior of ceria and provides insights into intrinsic and extrinsic mechanisms of oxygen exchange in ceria. The findings also contribute to a better understanding of microwave-based state diagnosis of three-way catalysts in automotive applications.