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Engineers Study Nanodefects in Electrical Insulating Materials
June 6, 2018

Tiny defects in electrical insulating materials may lead to breakdowns, robbing the power grid and even cell phones of reliability and efficiency.

According to information provided by Iowa State University (Iowa State), a professor of materials science and engineering, Xiaoli Tan, is working to understand how those nanoscale defects, when subject to extreme electric fields, evolve into material failures. Those failures turn insulators, which do not conduct electricity, into materials that allow some current to flow.

Iowa State University's Xiaoli Tan is shown in the Ames Laboratory's Sensitive Instrument Facility with a special specimen holder, foreground, and a transmission electron microscope. He's using the tools to study how nanoscale defects in electrical materials may lead to breakdowns. Photo courtesy of Xiaoli Tan/Iowa State University.

These failures, called dielectric breakdowns, typically happen far below the insulating material’s theoretical strength and capacity, typically resulting in short circuits or blown fuses. Consequently, to protect power systems and electronic devices, insulating materials are subject to voltages well below their theoretical capacity or they’re made thicker and heavier.

“Materials that cannot function reliably with respect to extremes in electric fields are a critical roadblock to achieving higher energy efficiency,” Prof. Tan wrote in a summary of his research project.

The U.S. Department of Energy’s Basic Energy Sciences Program is supporting the nearly three-year study with a grant of $675,000. The Iowa Energy Center, Iowa State’s College of Engineering, the department of materials science and engineering, the Department of Energy’s Ames Laboratory and grant money from several Iowa State colleagues have also helped Prof. Tan purchase a $140,000 specimen holder for the experiments.

To conduct his experiments, Prof. Tan will use a technique he’s developed for in situ transmission electron microscopy that’s capable of recording images at resolutions faster than 5 millionths of a second and smaller than 1 billionth of a meter. The instrument needs to be so sensitive because the electrical breakdowns are thought to start with nanoscale defects in insulating materials, defects just billionths of a meter across. The breakdowns also happen in microseconds, just millionths of a second.

Even five or 10 years ago, scientific instruments weren’t fast or sensitive enough to catch these breakdowns. As a result, “nobody has ever directly seen these breakdowns,” Prof. Tan said.

The experiments will record how thin films, less than 100 billionths of a meter thick, of three insulating materials, titanium dioxide, lead zirconate titanate and lead zirconium oxide, break down when subjected to electric pulses up to 110 volts.

After each pulse, the test material’s nanostructure, symmetry and chemistry will be analyzed, Prof. Tan explained. That will allow the researchers to see and record the evolution of the material’s breakdown.

The experiment will also include testing and possible validation of a toughening mechanism for lead zirconium oxide.

The ultimate goal of all the tests is to find the missing links between nanoscale defects and early failure of electrical insulating materials, Prof. Tan explained. That could lead to next-generation, transformational materials capable of performing up to their theoretical limits, which in turn could help produce better power systems and smaller, lighter devices.

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