By simulating substances inside the silicon brains of powerful computers, University of Wisconsin-Madison engineers are finding ways to accelerate the arduous process of making new materials.
And using this approach, they identified a promising candidate compound that could be used in next-generation vacuum electronic devices for long-distance communications and thermionic energy converters. Led by Dane Morgan, the Harvey D. Spangler Professor in materials science and engineering at UW-Madison, the researchers published details of their advance in the 24 May, 2016, online edition of the journal Advanced Functional Materials.
Synthesizing high-performance compounds is no trivial task—each attempt to mix molecules in the lab and measure the resulting properties costs money and takes time. So rather than spending unnecessary resources creating a cornucopia of candidates that ultimately won’t work out, the researchers characterized virtual versions of materials to guide their experimental efforts. They zeroed in on an electrical property called the work function, which refers to the energy required to remove an electron from a material—a critical property of electron emission materials.
“We can take a material for which measuring the work function in the lab is very difficult, and calculate that critical property on the computer,” says Morgan.
This computational approach enabled the researchers to determine work functions for 25 different materials hailing from a general class of compounds called perovskite oxides. Not only did they identify chemical trends within the calculated values, one perovskite in particular stood out for its potential usefulness in practical applications.
Materials with low work functions easily emit electrons to generate electron beams in vacuum electronic devices or potentially to help send currents flowing through photovoltaic panels. But finding a compound that readily gives off electrons without falling apart in the process has long been a challenge for materials engineers, complicated by difficulties in obtaining accurate experimental work function measurements.
“One reason that computational modeling is so powerful is that it enables accurate predictions of physical quantities that are very hard to measure experimentally. The work function is one such quantity,” says Ryan Jacobs, a postdoctoral scholar in Morgan’s group and the lead author on the paper.
The researchers relied on a computational modeling method called density functional theory, which solves the fundamental equations of quantum mechanics to describe how electrons behave in materials. Performing these calculations many hundreds of times over for bulk materials would be impossible without powerful high-throughput computing regimes.
Morgan was an early pioneer in implementing computationally guided materials design, but lately, more and more researchers are realizing the advantages of the approach.
“A large part of the future of materials design will probably come from this kind of activity,” says Morgan. “Calculations aren’t equivalent to doing an experiment, but for certain quantities you can get close to experimental accuracy with orders of magnitude increases in speed and reduction in costs. It’s completely game changing in terms of our ability to explore and design materials properties.”
This work is also an example of the power of cross-disciplinary study and interdepartmental collaboration, as it combined the materials computation tools in Morgan’s group with the expertise in electron emitting materials from electrical and computer engineering Professor John Booske, the Duane H. and Dorothy M. Bluemke and a Vilas Distinguished Achievement Professor at UW-Madison, an author on the paper.
Now that the researchers have a material in mind, their next steps are to synthesize it in the laboratory to determine if it truly lives up to its predicted properties. Sufficient quantities of pure compound could give rise to new cathode elements for high-powered microwave sources, which is an arena of research they intend to pursue in collaboration with Booske.
“If the measured material’s properties confirm what the models predict, this would be a very, very big advance. The resulting cathodes would enable high power microwave amplifiers that cost less, have better efficiency, provide higher power at high frequencies, and can handle higher data rates. As a result, satellite wireless communications and tv services could be significantly improved while better radar and electronic countermeasure systems could better protect the lives of men and women serving in the armed forces during military conflicts,” says Booske.
The researchers filed a patent on the perovskite material through the Wisconsin Alumni Research Foundation. The U.S. Air Force Office of Scientific Research and the National Science Foundation funded the research. The paper is accessible online.
Author: Sam Million-Weaver