Project Details
Projekt
Defect chemistry and conductivity mechanisms in acceptor doped sodium-bismuth titanate (NBT)
Subject Area
Synthesis and Properties of Functional Materials
Term
from 2016 to 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 281817830
The ionic conductivity of the lead-free piezoelectric ceramic sodium-bismuth titanate (NBT) can be significantly enhanced by appropriate acceptor doping. With Mg-doping the ionic conductivity reaches values which are usually obtained for good solid electrolytes used in solid oxide fuel cells (SOFC). The defect chemical properties resulting in this high conductivity are not known so far. Knowledge about the defect chemistry would allow the evaluation whether NBT could be a new material for oxygen ion conductor applications. In this project, the defect chemistry and conductivity mechanisms of acceptor doped NBT will be investigated. Using a systematic approach combining conductivity and diffusion experiments with computer assisted modelling, the origin of the conductivity properties shall be identified. Particularly the high ionic conductivity will be the main focus of the project because it is of high scientific and technological importance.Temperature and oxygen partial pressure dependent impedance spectroscopy and permittivity measurements will allow us to identify the conductivity mechanisms and the contributing defects. 18O-tracer diffusion experiments investigated by Time-of-flight-(TOF)-SIMS will be of high importance for the investigation of the transport of oxygen and its contribution to the overall conductivity. Apart from polycrystalline material single crystals will also be examined to better distinguish between bulk and grain boundary contribution. Enthalpy of formation and migration of intrinsic defects (mainly O- and Bi-vacancies) will be determined with the help of electronic structure calculations on the basis of density functional theory. The association of these defects with dopants are calculated to predict activation energies for O-migration. Together with the experimentally obtained information a consistent picture of the defect chemistry and defect kinetics of NBT shall be revealed.
DFG Programme
Research Grants
Co-Investigators
Professor Jurij Koruza, Ph.D.; Dr. Jochen Rohrer; Professor Dr.-Ing. Jürgen Rödel
