Servicenavigation

Detailseite

Zurück

Projekt Druckansicht

The Influence of Mechanical Loads on the Functional Properties of Perovskite Oxides

Fachliche Zuordnung Herstellung und Eigenschaften von Funktionsmaterialien
Förderung Förderung von 2013 bis 2022
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 230321406
 
Erstellungsjahr 2022

Zusammenfassung der Projektergebnisse

The focus of this project was understanding the role of stress on the electromechanical and ionic conductivity of lead-free perovskites. These phenomena were specifically selected as they are found in many other material systems and are critical to influencing as well as in many cases enabling the functional properties, allowing a transfer of information and knowledge to new research areas. In that regard, the originally proposed material systems were primarily used as model systems with the express goal to expand into other material groups based on the knowledge gained, which was successfully accomplished within this project. Both of these functionalities are strongly influenced by mechanical fields and lattice defects as well as structural and chemical disorder, which were experimentally characterized in this project using a number of novel measurement techniques, some of which were custom developed within the framework of these investigations. Here, the in situ measurement of the stress-dependent crystal structure using transmission geometry synchrotron diffraction was especially important, revealing new insights into the role of stress on the crystal structure, disorder, and field induced phase transitions, in addition to more recently stress-dependent Raman and Brillouin spectroscopy. Studies on electromechanical properties of perovskites concentrated to two primary areas: (i) characterizing the influence of stress on the local disorder in lead-free relaxor ferroelectrics and (ii) developing ceramic/ceramic composites for enhancement of the unipolar strain response. Firstly, numerous small- and large-signal properties of NBT-based ceramics were characterized, such as the stress-dependent dielectric and piezoelectric properties as well as the temperature-dependent mechanical constitutive behavior. These data were combined with in situ diffraction techniques to reveal the stress-induced formation of long-range ferroelectric order in a relaxor ferroelectric, analogous to the well-known electrical case. This allowed for the development of a stress-temperature phase diagram that showed the shifting phase boundaries and relaxor-ferroelectric transition temperatures. Further work focused on developing multilayered ceramic/ceramic composites in order to directly investigate the role of interfacial effects, such as chemical diffusion, porosity, and internal stresses. Here, local techniques, such as TEM, PFM, microXRD, nanoindentation, and EDX, in collaboration with various national and international groups were required, but revealed interesting and novel data. Together with DIC and FEM simulations, performed together with research groups at KIT and TUD, respectively, the effect of strain- and polarization-coupling on the response was determined. More recent research has also begun to address the role of Na on relaxor state, as (Bi 1/2K1/2)TiO3 displays a significantly different dielectric response. This section of the project also opened up numerous other avenues of research on the stress-dependent electromechanical properties of lead-free ferroelectrics, such as mechanical stability of phase boundaries, blocking force measurements, frequency dependent mechanical constitutive behavior. These studies were performed with numerous international collaborators. The second part of this project was originally focused on BSCF, due to the excellent electrical and ionic conductivity values. Fuel cells, which consist of various components, can experience large internal stresses due to the differences in thermal and chemical expansion at elevated temperatures, leading to creep and eventual failure. As such, the focus here was on experimentally characterizing the mechanical properties of lead-free perovskite ionic conductors, with a focus on the influence of stress, defect concentration, and atmosphere on the conductivity. Here, experimental limitations restricted in situ characterization of mechanical properties in varying atmospheres, although this was compensated for by designing and constructing a custom annealing oven system that allowed for in situ small-signal electrical characterization in various atmospheres and ex situ mechanical measurements of annealed samples. In conjunction with this, a stress-dependent dilatometer method was also developed in order to directly observe the stress-dependent oxygen exchange at elevated temperatures. In addition to the investigations of BSCF, this project also extended into LSCF and NBT, where in situ structural investigations revealed significant differences with the cubic BSCF. Here, ferroelastic domains and relaxor properties were of particular importance, and in the case of NBT, the role of A-site nonstoichiometry was also found to be critical. These results show that stress, although it does influence of the ionic conductivity, plays a more minor role when compared with other effects, such as temperature and stoichiometry. Despite this, understanding the mechanical properties, especially other with the local phenomena at the lattice length scale, is critical for implementation into devices, where large stresses can be found. In summary, although this Emmy Noether Programme project followed the original plan relatively closely, successfully completing the proposed work packages, the research did evolve over the past seven years into new research directions, which has both improved the impact as well as enriched the learning experience for all involved. This project was the true starting point for my career and opened numerous doors, allowing me to progress to the point where I am today. In that regard, this project was successful.

Projektbezogene Publikationen (Auswahl)

 
 

Zusatzinformationen

© 2026 DFG Kontakt / Impressum / Datenschutz

Textvergrößerung und Kontrastanpassung