Behavioral nature in crystalline structures revealed at 10 million times magnitude

In a state-of-the-art materials research, a team led by Professor K. Andre Mkhoyan of the University of Minnesota has discovered that combines the two best-looking genres for touch screens and smart windows – transparency and cunning.

The researchers were the first to observe metallic lines in perovskite crystals. Perovskites are abundant in the center of the Earth, and barium stannate (BaSnO3) is one such crystal. However, metallic buildings have not been extensively studied due to the prevalence of more conductive materials on the planet such as metals or semiconductors. The discovery was made using an advanced electronic transmission microscope (TEM), a method that can produce images with magnifications of up to 10 million.

The research is published in Advances in science, a peer-reviewed scientific journal published by the American Association for the Advancement of Science (AAAS).

“The favorable behavioral and directional nature of these metallic line defects means that we can produce a material that is visibly glassy and at the same time very subtle as a metal,” said Mkhoyan, a TEM expert and Ray D. and Mary T. Johnson / Mayon Plastics Chair in the Department of Chemical and Materials Science at the University of Minnesota College of Science and Engineering. ”This will give us the two best of both worlds. We can make windows or new types of touch screens visible and at the same time directional. This is very interesting. “

Defects, or imperfections, are common in crystals – and line defects (the most common of which are separations) are a series of atoms that change from the normal order. Since dislocations have the same combination of elements as the host crystal, the changes in electronic band structure are usually not at the heart of dislocation, due to reduced symmetry and strain, but slightly different than the. the guest. The researchers had to look outside the disorders to find the metallic line defect, where the shape of a defect and the resulting atomic structure are quite different.

“We easily saw these line defects in the high-scan diffusion electric microscopy images of these BaSnO3 thin films due to their unique atomic alignment and we only saw them in the plane view,” he said. Hwanhui Yun, a graduate student in the Department of Chemical Engineering and Materials Science and lead author of the study.

For this study, BaSnO3 films were developed with molecular beam epitaxy (MBE) – a method for making high-quality crystals – in a laboratory at the University of Minnesota Twin Cities. Metallic line deficiencies observed in these BaSnO3 films are moving forward according to film growth guidelines, which means that researchers can control how or where line defects appear – and they could innovate as needed in friction screens, smart windows and other future technologies that require a combination of brightness and conductivity.

“We had to be creative to grow high-quality BaSnO3 thin films using MBE. It was inspiring when these new line defects came into the microscope,” said Bharat Jalan, associate professor affiliate and Chair of Shell in the Department of Chemical Engineering and Materials Science, which is in charge of the laboratory that grows a mixture of perovskite oxide films with MBE.

Perovskite crystals (ABX3) contain three elements in the unit cell. This gives it freedom for structural changes such as crystal composition and symmetry, and the ability to accommodate a number of defects. Due to different co-ordination and connection angles of the atoms in the core of the line fault, new electronic states are introduced and the structure of the electron band is changed locally in such a remarkable way that it turns the line fault into metal.

“It was interesting how theory and experiment agreed together here,” said Turan Birol, an assistant professor in the Department of Chemical Engineering and Materials Science and an expert in density action theory (DFT). “We were able to validate the experimental observations on the atomic structure and electron properties of this line with the main principles of DFT computation.”

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Members of the research team include the University of Minnesota Ph.D. students and postdoctoral relatives of Hwanhui Yun, Mehmet Topsakal (now associate scientist at Brookhaven national laboratory), and Abhinav Prakash (postdoc researcher of Argonne National Laboratory); and faculty members of the University of Minnesota K. Andre Mkhoyan, Bharat Jalan, Turan Birol, and Jong Seok Jeong.

This research was supported in part by SMART, one of seven centers of nCORE, the Semiconductor Research Corporation program, supported by the National Institute of Standards and Technology, and by the National Science Foundation (NSF) through the University of Minnesota University of Materials Research and Engineering. Center (MRSEC). The team also worked with the University of Minnesota Character Facility. The MBE growth work was supported in part by the NSF and the Air Force Office of Scientific Research.