Enhanced grain growth in barium zirconate membranes by heat assisted sputter deposition and laser annealing

• Applicants: Professorin Dr. Christiane A. Helm; Dr. Angela Kruth
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 556920556

Acceptor-doped barium zirconate perovskites are characterized by high chemical stability and the highest ionic bulk conductivity of all known material systems in the temperature range from 450°C to 600 °C. These materials are therefore attractive electrolytes in fuel cells, electrolysers and hydrogen sensors. However, due to the fracturing nature of these ceramics and the space charge zones that form in the grain boundaries, the real protonic conductivity in the application is often 3 orders of magnitude lower. Conventionally, high temperatures above 1500 °C are required to improve grain growth, but this leads to vaporization of the barium in the crystal system. Therefore, 1 wt% of sintering aids (e.g. NiO) are added to lower the temperature of the resulting eutectic. Thin layers are preferred for the application to reduce the ohmic resistance, which poses additional challenges to the annealing process. In the proposed Memgrain project, barium zirconate layers are deposited via a magnetron co-sputtering process on a substrate heated to 800 °C in order to synthesize the perovskite phase using sintering aids during layer growth. A subsequent laser annealing step is used to improve the crystallinity to enhance the specific conductivity of the thin films. Optical emission spectroscopy on subsystems will help to better understand the deposition conditions of complex oxides and to optimize layer growth. In addition to phase purity and conductivity, a particular emphasis on the layer stress of the deposited layers is added, which is determined by X-ray diffraction and helps to make predictions about the layer stability. For the first time in the project, the proton dynamics for thin-film systems will be measured on the nanosecond scale using neutron spin echo experiments, thus establishing a correlation between local proton diffusion and macroscopic conductivity.

• DFG Programme: Research Grants
• International Connection: Czech Republic
• Partner Organisation: Czech Science Foundation
• Cooperation Partner: Professor Dr. Jiri Olejnicek, Ph.D.
• Co-Investigator: Dr. Jan Wallis