Massachusetts Institute of Technology
Kathleen Alexander thought little about science or mathematics while growing up in rural northern Idaho. But for an economics project, she proposed incorporating a composting company into city government. It would collect organic waste, compost it and sell it to farmers, then reinvest the profits to improve recycling technology.
The project sparked an interest in materials, the first step on Alexander’s path to a Department of Energy Computational Science Graduate Fellowship (DOE CSGF) and a doctorate from the Massachusetts Institute of Technology.
At MIT, Alexander developed computational methods to help researchers understand minuscule defects in metals with the goal of improving their properties, a key to developing higher-efficiency engines and energy storage cells. She hasn’t strayed far from her high school project’s aims: using science and technology “to really push the limits on what it would mean to be a sustainable society.”
Those goals led Alexander to revamp her career path. To find new recycling technologies, “I would need to pursue engineering, and I didn't, clearly, have the background.” So Alexander shored up her math and science knowledge with two years at American River Community College in Sacramento, California, before going to MIT.
When Alexander learned it would take three more years of school, not two, to complete her undergraduate degree, she opted for a yearlong exchange with Great Britain’s University of Cambridge.
At MIT, Alexander delved into both experimental and computational research. With supervision from a postdoctoral researcher in Vladimir Bulović’s group, she helped double the efficiency of a device that splits water into hydrogen and oxygen gases.
Alexander also did a summer 2010 Sandia National Laboratory internship in New Mexico, using computational modeling to study erbium tritide, a material involved in neutron generation.
For her Ph.D., Alexander chose to work with Christopher Schuh, a metallurgy professor who studies material defects far smaller than the eye can see. At Sandia, Schuh says, Alexander “had become interested in this idea of understanding and controlling defects in materials, and she had fallen in love with the idea of using computers to do it.”
But a different love led Alexander on another detour before graduate school. At Sandia, she met William Lane, an engineering student from Canada. They married in 2011 and Alexander moved to New Brunswick while Lane finished his undergraduate degree. It proved to be a valuable experience: Alexander took additional mathematics classes and did computational research with Ghislain Deslongchamps, a University of New Brunswick chemistry professor.
At MIT, Alexander examined the atomic structure and organization of materials and their defects. In metals, such inquiries require an understanding of grain boundaries – defect features that shape materials’ fundamental properties. There are few reliable ways for researchers to study grain boundaries and how they relate to material behavior, so Alexander focused on developing a new computational method.
The angles between grains – the individual crystals that comprise compounds – make a big difference in how materials perform. Grain boundaries determine properties related to failure, like cracking and corrosion, as well as qualities that dictate a material’s manufacturability. Schuh says Alexander addressed a major issue in computational materials science: the timescale challenge of matching simulations with laboratory results. It often takes weeks for computers to calculate chemical behavior that occurs in a few nanoseconds, but experimentalists typically can’t measure phenomena happening over such a short period.
Alexander’s method modeled chemical behavior for many thousands of times longer, providing data that are easier to match with experiments, Schuh says. She then validated the method in chemical systems such as chromium and tungsten mixtures.
Alexander’s DOE CSGF practicum focused on a different grain-boundary problem: how defects influence a promising material for rechargeable lithium batteries. Working with Bobby Sumpter and his Oak Ridge National Laboratory team, Alexander used electronic structure calculations based on fundamental physics to examine composition, organization and transport in lithium lanthanum titanate, a promising solid electrolyte. Such substances are important for batteries because they would be safer and could last longer than liquid electrolytes used today.
In her few weeks at ORNL, Alexander worked with electron microscopists and computational researchers to connect experiments and simulations, finding ways to identify lithium lanthanum titanate defects that improve or inhibit performance.
Alexander finished her doctorate in July 2016 and took a research position at Nucleus Scientific, an MIT spinoff.
Read the entire article in DEIXIS, the DOE CSGF annual. [PDF, pages 10-12]
Image caption: In this potential energy landscape, atomic arrangements of a grain boundary modeled in copper are shown as examples of configurations for the indicated points of interest: saddle point (the energy barrier to an atomic rearrangement) and minima (low-energy, stable configurations). The atoms are colored according to centrosymmetry (blue atoms are in a perfectly symmetric environment and red atoms are in a highly asymmetric environment), and only those on the boundary are shown. The potential energy surface is plotted as energy versus a two-dimensional projection of configuration space. Credit: Kathleen Alexander; images generated with the AtomEye visualization program.