CAREER: Dynamic Point Defect Architectonics - Uncovering Crystal Chemical Design Rules for Tailored Chemical Expansion

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: A number of ceramic materials “breathe” – they can exchange, e.g., oxygen or water, with the gas around them, causing a change in their size. This stretching of the brittle ceramics can cause problems for their durability when they are constrained in devices, such as sensors, reactors, batteries, and fuel cells: it can cause cracks and fracture. On the other hand, this “breathing” behavior raises the possibility to develop a new application: actuators for use in extreme environments. Additionally, over the past 5-10 years, advanced materials characterization techniques that leverage this behavior have emerged. Therefore, it is an excellent time to measure and understand the breathing more completely and to investigate how to design materials with controlled size changes. This project focuses on a technologically important class of ceramics, called perovskites, and seeks to understand how their structure at the level of local charge, atom, and bond arrangements impacts how they change size during breathing. Experiments are testing three specific ideas about how the local structure of these materials can be tailored to control the amount of expansion. Students are being trained to observe the stretching across many length scales, using precise expansion measurements, advanced microscopy techniques, and the intense light sources available at national laboratories. The expected outcome is knowledge of how to design ceramics with better durability for energy conversion and storage applications and tailored responses for novel actuators and optimized measurements. These research efforts are integrated with educational approaches including international exchange visits to Japan, which train students to be clear communicators, cross-culturally sensitive, both computationally and experimentally literate, and motivated toward deep learning. A new summer camp module links to the research applications in sustainable energy. It aims to encourage participation of under-represented groups in materials science at the undergraduate level by intervening at the high school level to increase students’ confidence, motivation, and self-efficacy. TECHNICAL DETAILS: The project seeks to establish quantitative relationships between bond architecture, local point defect-induced distortions, and macroscopic chemically-induced strain in mixed- and proton-conducting perovskite oxides. Point defects govern the behavior of technical ceramics, and this work’s insight into the structure of defects and their role in chemo-mechanical coupling will add to the development of the “defect genome.” Methods including dilatometry, in situ diffraction, thermogravimetric analysis, advanced electron microscopy, and X-ray absorption and scattering, are being used to quantify stoichiometry changes, defect-induced local distortions, and macroscopic strain. The outcome will be the establishment of crystal chemical design rules for tailored coefficients of chemical expansion. These rules can be applied to improve durability and optimize responses of ceramics in energy conversion, storage, sensing, and actuation applications. Additionally, students will be trained in not only technical skills in university and national laboratory settings, but also in a variety of broader professional skills in a global context. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.