MATERIALS SCIENTISTS at Johns Hopkins University have found a new use for solution-deposited beta-alumina, a chemical compound traditionally used as an electrical conductor. By orienting the compound in a different way, researchers have turned it into a thin-film insulator, which instead blocks the flow of electricity and can induce large electric currents elsewhere.
The material could have important applications in transistor technology and in devices such as electronic books. “This form of sodium beta-alumina has some very useful characteristics,” said Howard E. Katz, a professor of materials science and engineering who supervised the research team. “The material is produced in a liquid state, which means it can easily be deposited onto a surface in a precise pattern for the formation of printed circuits.
“But when it's heated, it forms a solid, thin transparent film. In addition, it allows us to operate at low voltages, meaning it requires less power to induce useful current. That means its applications could operate with smaller batteries or be connected to a battery instead of a wall outlet.”
The transparency and thinness of the material (the hardened film is about 100 atoms thick) suit it for e-book readers, which rely on see-through screens and portable power sources, Katz said. He added that possible transportation applications include instrument readouts that can be displayed in the windshield of an aircraft or a ground vehicle.
The emergence of sodium beta-alumina as an insulator was a surprising development, Katz said. The compound has traditionally been used to conduct electricity and has been considered as a possible battery component. The material allows charged particles to flow parallel to a two-dimensional plane formed within its atomic crystalline arrangement.
“But we found that current does not flow nearly as easily perpendicular to the planes, or in un-oriented material,” Katz said. “The material acts as an insulator instead of a conductor. Our team was the first to exploit this discovery.”
The lead author of the paper was Bhola N. Pal, a postdoctoral fellow in Katz's laboratory. In addition to Katz, the co-authors were Bal Mukund Dhar, a current doctoral student in the lab, and Kevin C. See, who recently completed his doctoral studies under Katz.