Dislocations in Ceramics: Processing, Structure, Mechanics, and Functionality: Dislocations in Ceramics: Mechanics and Functionality
Program Organizers: Xufei Fang, Technische Universität Darmstadt; Till Frömling, Technische Universität Darmstadt; Lukas Porz, Norwegian University of Science and Technology; Wolfgang Rheinheimer, University of Stuttgart; Atsutomo Nakamura, Osaka University
Wednesday 2:00 PM
October 12, 2022
Room: 409
Location: David L. Lawrence Convention Center
Session Chair: Atsutomo Nakamura, Nagoya University; Oliver Preuß, Technische Universität Darmstadt
2:00 PM Invited
In Situ Observation of Fracture Dominated by a Single Dislocation and Its Governing Mechanics: Takashi Sumigawa1; 1Kyoto University
A dislocation has a strain concentration field on the atomic scale. As material dimensions are reduced to the nano-scale, a dislocation may be the starting point of fracture, since there are no defects larger than the dislocation in the interior. In this talk, I present the results of experiments on fracture initiated from a single dislocation. Controlled edge dislocations were placed in the tiny specimens, and the fracture behavior and its criterion were obtained by loading tests in a transmission electron microscope. I explain the dominant factors of the fracture obtained from the experimental results with the aid of atomic-level simulations.
2:30 PM
Understanding and Engineering Dislocations in Oxides at Room Temperature: Xufei Fang1; Oliver Preuß1; 1Technische Universität Darmstadt
In light of the increasing interest in dislocation-tuned functionality of oxides, dislocation-based mechanical behaviour, for instance, dislocation-mediated plasticity and dislocation-based toughening have also become highly relevant. Due to the brittle nature of oxides, it remains a great challenge to introduce dislocations with controlled structures without cracking, particularly at room temperature. Here I focus on room-temperature dislocation mechanics in oxides and present a roadmap to introduce dislocations and understand the dislocation behaviour (dislocation nucleation, multiplication, and motion), and ultimately to tailor the dislocation-mediated plasticity in a model oxide, SrTiO3, by combining various testing methods across the length scales. Several useful concepts and approaches for experimental design such as cyclic indentation tests, surface dislocation engineering, and thermal treatment will be demonstrated to tailor the dislocation plasticity and, more strikingly, the hardness and fracture toughness of the crystal. The proofs-of-concept on SrTiO3 are validated on other oxides to showcase the general applicability.
2:50 PM
Effects of Light Illumination on the Dislocation-mediated Plasticity in Single-crystalline ZnO: Yan Li1; Xufei Fang2; Eita Tochigi3; Yu Oshima4; Katsuyuki Matsunaga4; Atsutomo Nakamura1; 1Osaka University; 2Technical University of Darmstadt; 3The University of Tokyo; 4Nagoya University
Dislocation-mediated plasticity in ceramics and oxides has attracted increasing research interest due to the promising mechanical and functional properties tuned by dislocations. In this work, we investigated the effects of light illumination on the dislocation-mediated plasticity in single-crystalline ZnO by using photoindentation technique. Nanoindentation tests were conducted both in darkness and in light. From the load-depth curves, evident pop-in events were observed. The maximum shear stresses at pop-in were found to be about the theoretical shear strength regardless of light conditions, indicating homogeneous dislocation nucleation without the assistance of pre-existing defect at pop-in. The average values of maximum shear stresses were slightly larger in light than in darkness, exhibiting a ‘photo-hardening’ effect in ZnO. Furthermore, the suppression of dislocation behavior by light was validated by combining with TEM observations.
3:10 PM Invited
Atomistic and Multiscale Computational Analysis of the Connection between Dislocation Slip and Ionic Transport in Plastically Deformed Oxides: Liming Xiong1; 1Iowa State University
SrTiO3, can be plastically deformable through dislocation slip without cracking. These dislocations carry high local stresses/strain, which may largely enhance the ion mobility and in turn, the material’s ionic conductivity. However, the limit of a plasticity-induced ionic transport enhancement is not achieved yet due to the lack of a commonly agreed knowledge on how ions hop nearby the complex defects, e.g., the dislocation pileup at a GB in SrTiO3, which spans from nano- to micro-meter level. To meet this challenge, here we present atomistic as well as concurrent atomistic-continuum computer simulations to probe the mechanisms underlying the interaction between the dislocation-mediated plastic flow and interstitial ion hopping along the buried GBs in SrTiO3. We will: (i) quantify the correlation between the defect-induced stresses, the local structure distortion and the ion mobility; (ii) identify the decisive factor that dictates the diffusivities of non-equilibrium GBs with long-range heterogeneities.
3:40 PM Break
4:00 PM
Charged Dislocations in Ionic Ceramics: Equilibrium and Kinetics: Edwin Garcia1; Vikrant Karra2; 1Purdue University; 2Indian Institute of Technology
The multifuncional properties of ionic ceramics have led to a great deal of applications ranging from memories, materials with runnable and switchable electrical conductivity, sensors and actuators, to technologies for energy storage and conversion applications. The possibilities seem endless, only limited by their processing, formability, and structural integrity. At its core, the presence of defects, including grain boundaries, dislocations, vacancies, and insterstitials has a central role on delivering tailored properties. In this paper, a thermodynamics-based variational formulation will be presented to rationalize the effects of electrical charge, stresses, and thermochemistry (including its couplings) and their effect on the stability and time-dependent behavior of dislocations in ionic ceramics. Applications to Yttria Stabilized Zirconia will be presented, highlighting the electro-chemo-mechanical interactions of point defects on the vicinity of the dislocation core and its impact on the observed non-elastic behavior. Comparisons against experiments will be made.
4:20 PM Cancelled
Dislocation-Modified Photoelectric Properties of Oxide Ceramics: Mehrzad Soleimany1; Maximilian Kissel1; Lukas Porz2; Till Frömling1; Marin Alexe3; Jürgen Rödel1; 1Technical University of Darmstadt; 2Norwegian University of Science and Technology; 3University of Warwick
Controlling point defects and interfaces is the usual way to tailor semiconducting ceramics' electrical and photoelectric properties. Dislocations as one-dimensional line defects have so far been mostly disregarded for modification of functional properties because of the brittle nature of ceramics. However, they are finding increasing attention recently. They provide the opportunity to modify the materials' functional properties, e.g., ferroelectric properties, thermal, electronic, and ionic conductivity. This work illustrates the impact of dislocations on the photoelectric properties of ZnS and donor doped SrTiO3. We reveal that the materials can be plastically deformed at room temperature using ball indentation and cyclic loading without the formation of cracks, which leads to the increase of the dislocation density by three orders of magnitude. Utilizing photocurrent measurements, especially local investigations by a conductive atomic force microscope under laser illumination, an increase in the current can be rationalized due to the presence of dislocations.