Defect chemistry engineering and thermal treatment on dislocation mechanics in SrTiO3

• Applicant: Privatdozent Dr.-Ing. Xufei Fang
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Synthesis and Properties of Functional Materials ; Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 510801687

The properties of modern functional oxides can be tailored by selectively changing the defect chemistry, i.e. by introducing point defects. This usually involves the introduction of charges into the crystal lattice. An alternative approach to modifying functional properties is the introduction of dislocations. Dislocations are line defects, which can be strongly charged in oxides, thus interacting with point defects. In recent years, this new approach has attracted increasing research interest. Promising proofs-of-concept have shown that the functional properties of oxides, such as electrical conductivity, thermal conductivity, and superconductivity, can be selectively influenced by changing the dislocation structure. Ceramics are typically processed at high temperatures, with the point defects present being frozen far from thermodynamic equilibrium during cooling. For this reason, interactions inevitably occur between the introduced dislocations and the numerous point defects in ceramic oxides. Therefore, the following scientifically relevant questions arise:1) Are the mechanical properties, such as plasticity and cracking behavior, altered by the interaction of dislocations and point defects?2) How do point defects interact with previously introduced dislocations as a function of temperature and heating/cooling rate, the latter affecting thermodynamic equilibrium?3) What is the contribution of the electrostatic fields of line and point defects to solid solution hardening? How does a change in the defect chemistry of the sample affect dislocation mobility?In this project, we aim to answer these questions and shed new light on the thermal stability of dislocations and its influence on mechanical properties, which is crucial for dislocation-controlled functionality as well as mechanical reliability of components. For this purpose, single-crystalline SrTiO3 (with different conditions of defect chemistry) will be used as a reference material and nanong-/micromechanical tests will be performed at different temperatures to study 1) dislocation nucleation and multiplication modified by point defects. Furthermore, 2) the interaction between the generated dislocations and point defects affecting the dislocation motion will be investigated. In addition to plasticity, the cracking behavior (crack formation and propagation) of the materials will also be studied, taking into account the dislocation behavior.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Karsten Durst