Local atomic-scale structure of ionic conducting oxides from atom probe tomography

• Applicant: Professorin Dr. Cynthia A. Volkert
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Experimental Condensed Matter Physics ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 428906592

This proposal outlines plans for the second phase of a project focusing on Atom Probe Tomography (APT) within the research unit Energy Landscapes in Ion Conducting Solids (ELSICS). The overarching goal of ELSICS is to establish direct correlations between atom arrangements and ion mobility within the energy landscape of ion-conducting solids. APT plays a key role in this effort by providing 3D compositional mapping with near-atomic resolution. Combined with TEM (Project P4), this enables us to determine atomic positions and element-specific distributions at critical local sites, such as defects and boundaries, with state-of-the-art precision. During the first phase, we successfully developed methodologies to apply APT to ELSICS materials, which pose significant challenges due to their insulating nature, ion conductivity, and brittleness. These advancements allowed us to acquire large-scale APT datasets for SrTiO3 for the first time, including compositional mapping of a grain boundary. APT reconstructions revealed pronounced Sr depletion within a sub-nanometer region at the boundary, a finding corroborated by STEM-EELS and HAADF-STEM imaging, which also confirmed the facetted boundary structure (Project P4). DFT calculations further validated that Sr depletion is energetically favorable (Project P6). Building on this success, the second phase will continue to focus on SrTiO3 grain boundaries. Alkali and transition metal impurities will be introduced near boundaries using CAIT (Project P1) and diffusion sources (Project P4). APT will be used to measure impurity distributions and diffusion profiles in conjunction with TEM (Project P4) and will be compared with energy landscapes derived from DFT (Project P6), as well as with depth profiles from SIMS (Project P1) and XPS (Project P8). Additionally, we will extend this approach to dislocations in SrTiO3, which offer a simpler yet complementary defect for testing our methodologies with greater precision. Ultimately, this project aims to provide a rigorous and quantitative validation of the ELSICS paradigm by correlating defect-specific energy landscapes in SrTiO3 with the energetics and dynamics of mobile ions. This will deepen our fundamental understanding of ion transport mechanisms and contribute to the advancement of ion-conducting materials.

• DFG Programme: Research Units
• Subproject of: FOR 5065: Energy Landscapes and Structure in Ion Conducting Solids (ELSICS)