SMU researchers develop high-entropy oxide (HEO) nanoribbons

According to Southern Methodist University (SMU), a research team has developed a more cost-effective, energy-efficient material called high-entropy oxide (HEO) nanoribbons that can resist heat, corrosion, and other harsh conditions better than current materials. These HEO nanoribbons – which were featured in the journal Science – can be especially useful in fields like aerospace, energy, and electronics, where materials need to perform well in extreme conditions.

Unlike high entropy materials that have been created in the past, the nanoribbons that SMU’s Amin Salehi-Khojin and his team developed can be 3D printed or spray-coated at room temperature for manufacturing components or coating surfaces. This makes them more energy-efficient and cost-effective than traditional high-entropy materials, which typically exist as bulk structures and require high-temperature casting.

“These nanoribbons exhibit outstanding resilience under extreme conditions and remarkable mechanical properties, said Salehi-Khojin, William T. Solomon Chair of Mechanical Engineering and ad interim Executive Director of the Hunt Institute for Engineering and Humanity at SMU’s Lyle School of Engineering.

HEO nanoribbons

Nanoribbons are extremely thin, narrow pieces of material, usually just a few nanometers (one billionth of a meter) thick and spanning from tens to hundreds of nanometers in width.

HEO nanoribbons belong to a special type of ribbon-like strips called high-entropy materials or alloys, which have a high degree of disorder within their atomic structure.

“Most materials are made primarily from one or two elements, but high-entropy materials combine five or more elements in roughly equal proportions,” said Salehi-Khojin. “This even distribution leads to a highly disordered atomic structure – what scientists call ‘high entropy’ – which can enhance the material’s strength, resistance to heat, and ability to withstand stress or corrosion.”

Materials of the future

What Salehi-Khojin, with help from researchers at the University of Illinois Chicago, Stockholm University, and the University of Washington, has done for the first time is figure out how to make these low-dimensional high-entropy materials for cost-effective and energy-efficient manufacturing.

Science study co-author Ilias Papailias, who is a Research Assistant Professor at SMU Lyle’s Mechanical Engineering Department, said a new synthesis method was developed to precisely control the morphology of high-entropy materials. “First, a sulfur element was used to etch the samples into two-dimensional (2D) structures, followed by an oxidation process to convert the 2D structures to one-dimensional (1D),” said Papailias. “This technique provides over two orders of magnitude control on the width and size of the nanoribbons produced by this approach. It has been discovered that during the oxidation process, the nucleation of 1D ribbons occurs,  eventually converting them to full 1D systems upon extended oxidation, as confirmed by a wide range of in-situ experiments.”

The study showed that the nanoribbons created by Salehi-Khojin – called 1D-HEO – maintained their structure at exceptionally high temperatures. The same was shown to be true under elevated pressure (up to 12 gigapascals) and prolonged exposure to harsh acid and base chemical environments (pH = 2.3 and 13 for 7 days).

While more testing is needed before this material can be practically utilized, Salehi-Khojin said the hardness and resilience of 1D-HEO would make it an ideal candidate for applications that require heat resistance, pressure tolerance, and durability under high mechanical loads. “This new method can revolutionize the material science field by introducing new entropy structures,” said Salehi-Khojin, who began research on these nanoribbons at the UIC.