Grain Boundaries, Interfaces, and Surfaces in Ceramics: Fundamental Structure—Property—Performance Relationships: On-Demand Oral Presentations
Sponsored by: ACerS Basic Science Division, ACerS Electronics Division
Program Organizers: Rheinheimer Wolfgang, Forschungszentrum Jülich; Catherine Bishop, University of Canterbury; Shen Dillon, University of California, Irvine; Ming Tang, Rice University; John Blendell, Purdue University; Wayne Kaplan, Technion - Israel Institute of Technology; Melissa Santala, Oregon State University
Friday 8:00 AM
October 22, 2021
Room: On-Demand Room 7
Location: MS&T On Demand
Invited
Interface Migration: From Grain Boundary Structure to Microstructure Evolution: David Srolovitz1; Jian Han1; Marco Salvalaglio2; 1City University of Hong Kong; 2TU Dresden
Most models of grain growth/microstructure evolution start from an ansatz about the underlying interface/grain boundary (GB) equations of motion. In most cases, these are deduced from thermodynamic models and the assumption that GB motion is overdamped; the GB parameters may be fit to experimental observations. Here, we present a derivation of the GB equation of motion that, unlike most models, respects the bicrystallography, the underlying mechanisms of how GBs move, and the intrinsic anisotropy. The GB migration mechanism is disconnection motion (disconnections are line defects with dislocation and step character). Our new equation of motion is directly applicable to arbitrary grain shapes, microstructure topology and anisotropy. We apply this equation of motion in a sharp interface formalism for simple geometries and in a diffuse interface simulation. We apply the diffuse interface method to nucleation of precipitates, followed by growth and impingement, and finally followed by grain growth.
Invited
Triggering the Catalytic Activity of SrTiO3-based Ceramics by Electric-field-assisted Treatments: Simone Mascotto1; 1University of Hamburg
The exposure of ceramic materials to electric fields during high temperature treatments has revealed to be an interesting approach to tune their densification and manipulate their grain boundary structure. Recently, this method was also used to modify the surface states of ceramics and influence their wetting properties. In the present work, we show how chemically inert SrTiO3 and donor-doped SrTiO3 ceramics can be turned into catalytically active materials by improving the concentration and reactivity of surface oxygen defects using electric-field-assisted treatments. The consolidation of perovskite oxides in presence of an electric field arrested the grain growth, retained the specific surface area and enhanced the concentration of Sr vacancies and O─ species. The dramatic change of the materials’ defect structure significantly improved their surface reactivity. Field-treated ceramics exhibited more than 95% of methane conversion at 800 °C, with performance over 3 times higher than conventionally treated systems and other donor-doped perovskites.
Invited
Abnormal Grain Growth in Nanocrystalline PdAu: The Case of the Fractal Fingerprint: Raphael Zeller1; Markus Fischer1; Christian Braun2; Mingyan Wang1; Rainer Birringer2; Carl Krill1; 1Ulm University; 2Saarland University
In most polycrystalline materials, coarsening tends to be a civilized affair, with adjacent grains taking pains to exchange atoms so as to maintain a smooth boundary. The grains that grow in nanocrystalline PdAu, however, behave like uncouth neighbors crashing a fancy dinner party: once they get revved up, all hell breaks loose! Before you know it, a few nanometer-sized grains have grown four orders of magnitude in diameter, and the resulting interfaces are so convoluted that they resemble fractal objects. Our usual notion of curvature-driven grain boundary migration fails to explain the persistence of these interfacial fluctuations, but recent experiments find the onset of fractality to depend on the Au concentration as well as on a characteristic length scale. We consider this evidence to be a kind of “fractal fingerprint” that, ultimately, incriminates a specific mechanism as the responsible party for the system’s abnormal grain growth.
Invited
Fast Grain-boundary Diffusion in Oxides: Roger De Souza1; 1RWTH Aachen University
In contrast with the bulk phase, an extended defect (dislocation, grain boundary, surface, domain wall) in an ionic solid is not constrained in equilibrium to remain locally electroneutral. Because of interactions between the extended defect and point defects, the extended defect will in general become electrostatically charged, with the adjacent bulk phase concomitantly developing diffuse, enveloping space-charge zones.The altered concentrations of point defects in these space-charge zones have long been understood to affect, for instance, the transport of charge across grain boundaries in polycrystalline systems. In this presentation, I will draw attention to two aspects that have received far less attention: that space-charge zones can affect the excess Gibbs free energy of a grain boundary; and that space-charge zones can provide an unusual contribution to accelerated diffusion along grain boundaries. Throughout the presentation, I will emphasise the need to consider space-charge zones from a thermodynamic perspective.
Invited
Influence of Planar Defects on the Electrochemical Cycling and Diffusion of Li in LixMn2O4: Torben Erichsen1; Cynthia Volkert1; 1University of Goettingen
Planar defects are present in the pristine and cycled transition metal oxide nanoparticles used in battery cathodes, and are expected to impact charging kinetics and capacity of Li-ion batteries. In this study on LixMn2O4, we use in-situ transmission electron microscopy (TEM) and atom probe tomography (APT) to investigate the effect of planar defects on redistribution of Li during charging and discharging. Both APT and in-situ TEM show that (111) stacking faults can either accelerate or block Li diffusion, while APT of partially delithiated LixMn2O4 tips reveal a strong dependence of Li mobility on Li concentration. We explain these results with a simple model for vacancy mediated diffusion of Li on tetrahedral sites. The planar defects generated during charging into the x>1 region impose additional obstacles to Li diffusion and may account for the capacity fade observed in Li-ion batteries.
On the Role of Plasticity in High Heating Rate Sintering: Does Flash Sintering Involve Plastic Flow?: Rheinheimer Wolfgang1; Xin Phuah2; Lukas Porz3; Michael Scherer3; Jaehun Cho2; Haiyan Wang2; 1Forschungszentrum Jülich; 2Purdue University; 3TU Darmstadt
During flash sintering, very rapid densification of a ceramic powder compact occurs during a thermal runaway induced by electrical power dissipation from an applied voltage and current. After flash sintering of SrTiO3, a high dislocation density was observed by transmission electron microscopy. Uniaxial compression revealed a much higher deformation rates after flash sintering compared to conventional sintering, likely caused by the high dislocation density. Based on these findings, it is argued that the dislocations are generated and migrate during sintering resulting in plastic flow. This becomes possible by the high heating rates, which conserve high driving forces for sintering up to high temperatures by minimizing neck growth at lower temperatures. In this light, the most important parameter of flash sintering is the extremely high heating rate. Beyond extending our understating of flash sintering, the presented framework offers new perspectives for materials engineering by introducing dislocations for enhanced functional properties.
3-D Quantification of Grain Boundary Defect Chemistry Using TEM + APT: Brian Gorman1; 1Colorado School of Mines
Recent work has shown that Atom Probe Tomography (APT) has the requisite counting statistics, 3-dimensionality, detectability limits, and spatial resolution to quantify point defect accumulations at grain boundaries in many ceramic systems. Combined with TEM and EELS, full quantification of the defect chemistry reactions is possible in 1 nm^3 volumes. APT has also enabled the conversion of defect accumulations directly to space charge voltages and band alignments. A direct relationship between characterization and grain boundary dominated properties can thus be achieved. Counting vacancies is heavily dependent upon the detection efficiency of the APT experiment that can vary between 15 and 80% and upon the volume being sampled. Detecting substitutional cations and defect pairs can be completed as long as the elements are distinguishable in the mass spectrum. Detecting Frenkel defects will have to wait for Atomic Scale Tomography, which has recently been proposed to be possible using TEM + APT.
Geometrical Asymmetry Enabled Low Field Nucleation and Manipulation of Skyrmion at Magnetic Domain Boundaries in a Centro-symmetric Magnet: Binbin Wang1; Po-kuan Wu1; Nuria Bagues1; Qiang Zheng2; Jiaqiang Yan2; Mohit Randeria1; David McComb1; 1The Ohio State University; 2Oak Ridge National Laboratory
Understanding the dynamics of skyrmion nucleation and manipulation is important for applications in spintronic devices. Here, we have investigated the magnetic texture transformation using Lorentz transmission electron microscopy (LTEM) in a centrosymmetric magnet Fe3Sn2 with an engineered geometrical asymmetry in thickness gradient. Sample tilting and tunable magnetic field strength in LTEM enabled a new strategy for skyrmion nucleation at magnetic domain boundaries. This allows us to nucleate isolated skyrmions in Fe3Sn2 using in-plane fields (< 5 mT) that are two orders of magnitude lower than the previously reported critical magnetic field (~800 mT). Micromagnetic simulations combined with LTEM experiments reveal that the rotatable anisotropy and thickness dependence of the response to the external in-plane field are the critical factors for the skyrmion formation. The results suggest that magnetic materials with rotatable anisotropy are potential skyrmionic systems and provides a novel approach for manipulation of skyrmions in spintronic devices.
Dislocation and Grain Boundary Interaction in Oxides: Slip Transmission or Cracking?: Kuan Ding1; Wolfgang Rheinheimer2; Wenzhen Xia3; Christian Dietz1; Enrico Bruder1; Karsten Durst1; Atsutomo Nakamura4; Xufei Fang1; 1TU Darmstadt; 2Forschungszentrum Jülich; 3Max-Planck-Institut für Eisenforschung; 4Nagoya University
Grain boundaries (GBs) play a key role on the mechanical properties for polycrystalline materials. GBs could act as effective barriers for dislocation glide. For brittle ceramic materials, the interaction between dislocation and GB has a crucial influence on the deformation behavior. Here, we studied room temperature GB-dislocation interaction in SrTiO3 with sandwich-type structure having single crystal in the middle and polycrystals on both sides fabricated. The GB structures were characterized using EBSD. Nanoindentation next to GBs and nanoscratch across GBs were carried out to generate dislocations and evaluate the incipient plasticity. Etch pits study, SEM and AFM characterization were conducted to reveal the dislocation structure. We found both slip transmission across GB and GB cracking occurred. For low angle GB, dislocation could propagate through the GB into the adjacent grain. Our findings provide insights for potential improvement of deformation of polycrystalline oxides at room temperature via grain boundary engineering.