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Chemical expansion of cerium oxide based thin films

Title data

Wulfmeier, Hendrik ; Kohlmann, Dhyan ; Defferriere, Thomas ; Steiner, Carsten ; Schewe, Marvin ; Rembe, Christian ; Moos, Ralf ; Tuller, Harry ; Fritze, Holger:
Chemical expansion of cerium oxide based thin films.
Event: Solid State Ionics 23 , 17.-22.07.2022 , Boston, USA.
(Conference item: Conference , Speech )

Abstract in another language

Nonstoichiometry in oxides governs many key materials properties including electronic and ionic conductivity, oxygen and cation diffusion and chemical expansion. While the atomic transport processes are well studied, the chemical expansion generally receives less attention. Materials with high chemical expansion can be utilized for the development of a new generation of high-temperature actuators. On the other hand, related induced mechanical stress in e.g. fuel cells contributes to limited lifetime and should be avoided. The focus of this work is the investigation and understanding of chemical expansion at high temperatures and its correlation with other key properties such as nonstoichiometry and electrical conductivity. In this context thin films are of particular interest as they enable miniaturization and, consequently, fast response due to short transport paths. However, their properties might differ from their bulk counterparts. In addition to the material aspects, specially tailored methods are of particular importance for the investigation of thin films at high temperatures. Here, a special Differential Laser Doppler Vibrometer (DLDV) is described and applied. As it is based on differential measurements, external disturbances are largely suppressed. As a consequence, determination of displacements on the order of picometers for periodic movements down to 1 mHz is achievable up to 1000 °C. Pr0.1Ce0.9O2-x (PCO) is taken as reference material as it shows a well-defined non-stoichiometry plateau at intermediate oxygen activities. Starting from this plateau, the chemical expansion at temperatures up to 800 °C was determined as a function of oxygen activity. At 650 °C, independently determined values match well, confirming the functionality of the DLDV. Moreover, the data correspond to calculated displacements for dense PCO films. Thin-film ceria shows a similar trend to PCO with respect to the excitation frequency dependent displacement, including the tendency to reach a constant displacement at low frequencies, suggesting the ability to reach a near equilibrium state for periodically adjusted oxygen activity at 0.1 Hz. Furthermore, Ce0.8Zr0.2O2-δ (CZO) thin films are investigated. They show cracks that partially accommodate chemical expansion. As a consequence, the calculated film thickness change for dense CZO films is larger than measured values for films with cracks. The chemical expansion of films induces sample bending. Note that the films are deposited on single crystalline yttria stabilized zirconia substrates that simultaneously serve as oxygen pumps to adjust the oxygen activity in the films. The substrate bending and the film thickness change match very well if the Stoney equation used to correlate both effects. The chemical expansion is furthermore correlated with the non-stoichiometry of the films (determined by resonant nanogravimetry) and electrical conductivity (impedance spectroscopy).

Further data

Item Type: Conference item (Speech)
Refereed: Yes
Institutions of the University: Faculties > Faculty of Engineering Science
Faculties > Faculty of Engineering Science > Chair Functional Materials > Chair Functional Materials - Univ.-Prof. Dr.-Ing. Ralf Moos
Profile Fields > Advanced Fields > Advanced Materials
Research Institutions > Research Centres > Bayreuth Center for Material Science and Engineering - BayMAT
Faculties > Faculty of Engineering Science > Chair Functional Materials
Profile Fields
Profile Fields > Advanced Fields
Research Institutions
Research Institutions > Research Centres
Result of work at the UBT: Yes
DDC Subjects: 600 Technology, medicine, applied sciences > 620 Engineering
Date Deposited: 27 Sep 2022 09:15
Last Modified: 27 Sep 2022 09:15
URI: https://eref.uni-bayreuth.de/id/eprint/71993