Grain Boundaries, Interfaces, and Surfaces in Functional Materials: Fundamental Structure-Property-Performance Relationships: Interface Anisotropy and Interfaces in Ferroelectric/Functional Oxides
Sponsored by: ACerS Basic Science Division
Program Organizers: Catherine Bishop, University of Canterbury; John Blendell, Purdue University; Shen Dillon, University of Illinois at Urbana-Champaign; Wolfgang Rheinheimer, Purdue University; Ming Tang, Rice University; Melissa Santala, Oregon State University

Wednesday 2:00 PM
November 4, 2020
Room: Virtual Meeting Room 34
Location: MS&T Virtual

Session Chair: Melissa Santala, Oregon State University

2:00 PM
Anisotropy at Interfaces in Rare-earth Pyrosilicates for High-temperature Coatings: Hadas Sternlicht¹; Nitin Padture¹; ¹Brown University
    Environmental barrier coatings (EBCs) are used to protect ceramic matrix composites (CMCs) used in the hot section of gas turbine engines against oxidation, and have to be resistant to attack of calcia-magnesia-alumino-silicate (CMAS) glass from the atmosphere, which can lead to premature failure of the coatings. In this work electron microscopy characterization of the anisotropy in the CMAS- EBCs reaction will be discussed, focusing on grain boundaries and phase boundaries. The presence of line defects, such as disconnections (which can have both a step and a dislocation component) will be discussed in light of the interaction with the glass. In addition, the chemistry of phase boundaries will be partially evaluated. The tendency of such phase boundaries to be located along different grain boundaries will be discussed, as well as how the interaction with the glass affects it.

2:20 PM  Invited
Implications of Ferroelectricity in Perovskite Solar Cells: Holger Roehm¹; Tobias Leonhard¹; Michael Hoffmann¹; Alexander Colsmann¹; ¹Karlsruhe Institute of Technology
    Methylammonium lead iodide (MAPbI3) is the archetypal semiconductor in organic metal halide solar cells. In the past four years, a controversial discussion took place about whether or not MAPbI3 is ferroelectric and if ferroelectricity can influence the solar cell performance. Yet, poling of domains in an external field could not be demonstrated in order to consolidate the discussion. In this work, we use Piezoresponse Force Microscopy to monitor ferroelectric poling of MAPbI3 thin-films across a lateral poling channel. Depending on the direction of the electric poling field relative to the domain polarization, domains can be narrowed, widened and moved within grains. Furthermore, we observe changes to the ferroelectric domain structure upon annealing of the thin-films resulting in improved solar cell performance. Our findings suggest that control of the ferroelectric domain structure in these light absorbing, semiconducting compounds may be essential in order to maximize performance of hybrid perovskite solar cells.

2:50 PM
Effect of Electrode Composition and Potential on Moisture Incorporation and Degradation in Dielectrics and Piezoelectrics: John McGarrahan¹; Elizabeth Dickey¹; ¹North Carolina State University
    The time-dependent properties of dielectric and piezoelectric materials in humid environments is an important performance metric, as humidity-related degradation can dominate device lifetime in some applications. This research aims to understand the effects of proton incorporation in such environments by measuring surface exchange and diffusion kinetics of H⁺ in commercially relevant electroceramic systems. The work focuses on in-situ impedance measurements and tracer diffusion studies using deuterated water to study incorporation pathways, mechanisms, and kinetics of H⁺ in BaTiO₃. Specifically, the effect of electrode composition on proton incorporation under high-humidity conditions will be presented, and the proton surface exchange reactions at the electrodes will be compared as a function of both electrode composition and potential. This work was funded by the Center for Dielectrics and Piezoelectric, an NSF Industry/University Cooperative Research Center, under grant IIP-1841466.

3:10 PM  Invited
Advanced TEM of Interfaces and Defects in Functional Ceramics: Joachim Mayer¹; ¹RWTH Aachen University
    Functional ceramic materials have to be developed in an integrated fashion, where design, synthesis, characterization, modelling and behaviour in applications throughout their life cycles will be considered in a concerted manner. The aim of our present high resolution TEM activities is to provide quantitative materials data on the atomistic and nanometer scale that can be used for virtual materials design and to understand structure-property-relationships. In the present lecture, several examples from our recent work will be discussed which are related to processes which are of high societal relevance in energy materials and functional materials for future information technology. Our work aims at a comprehensive understanding of diffusional properties and resistive switching mechanism in oxide materials on the basis of the local structural and chemical information at atomistic level obtained by aberration corrected (scanning) transmission electron microscopy ((S)TEM).

3:40 PM
Phase Stability of Sr_1-xBa_xMnO₃ (0 ≤ x ≤ 0.5) Films Using Combinatorial Substrate Epitaxy: Catherine Zhou¹; Paul Salvador¹; Gregory Rohrer¹; Marc De Graef¹; ¹Carnegie Mellon University
    Combinatorial substrate epitaxy is a high throughput film-growth method used herein to study the orientation relationships (ORs) and polytypic stability for (Sr,Ba)MnO₃ films grown on polycrystalline (Sr,Ba)TiO₃ substrates. (Sr,Ba)MnO₃ forms in either four-layered hexagonal (4H) or metastable three-layered cubic (3C) perovskite polytypes, depending on composition, deposition conditions, and substrate orientation. The range of substrate orientations stabilizing the 3C polytypes expands from (001) to (111) as temperature is increased or oxygen activity is decreased. 3C-SrMnO₃ polycrystalline films were stabilized over all of orientation space, while 3C-Ba_0.5Sr_0.5MnO₃ films grew on near-(001) substrate grains. Electron backscatter diffraction data was analyzed using dictionary indexing to determine the following ORs, which hold true regardless of the substrate surface orientation: (001)[100]_{4H film}||(111)[1-10]_{3C substrate} and (111)[1-10]_{3C film}||(111)[1-10]_{3C substrate}. These ORs align the eutactic planes and directions; its ubiquity indicates the interface energy is generally lower for the eutactic OR than for all other possible ORs.