Perovskite crystal conductivity revealed at 10 million times magnification

Researchers have observed metallic lines in a perovskite crystal for the first time. Perovskites abound in

center of the Earth, and barium stannate (BaSnO3) isone of these crystals. However, its metallic properties have not been widely studied due to the dominance of more conductive materials such as metals or semiconductors on the planet. The discovery was made using advanced transmission electron microscopy (TEM), a technique that can produce images at magnifications of up to 10 million.

"Electrically conductive nature andThe preferential directionality of these metallic line defects means that we can make a material that is transparent like glass, and at the same time very highly conductive in direction, like metal. Now we can make windows or new types of touch screens transparent and conductive at the same time.”

K. Andre Mkhoyan, Department of Chemical Engineering and Materials Science, University of Minnesota.

Defects are common in crystals, andLinear defects (the most common of which is a dislocation) are a series of atoms that deviate from the normal order. Since the dislocations have the same elemental composition as the main crystal, changes in the electronic band structure in the dislocation core due to a decrease in symmetry and deformation often differ only slightly. Researchers had to look beyond dislocations to find a defect in a metal line, where the composition of the defect and the resulting atomic structure are very different.

Using advanced analytical transmissionUsing electron microscopy (STEM) at 10 million times magnification, researchers at the University of Minnesota were able to isolate and image the structure and composition of a metal line defect in a BaSnO3 perovskite crystal.

“We easily noticed these linear defects onscanning transmission electron microscopy images of BaSnO3 thin films due to their unique atomic configuration, and we only saw them in top view."

Hwanghui Yun, a graduate student in the Department of Chemical Engineering and Materials Science.

For this study, the BaSnO3 films weregrown by molecular beam epitaxy - a technique for making high-quality crystals - in a laboratory at the University of Minnesota. The metal line defects observed in these BaSnO3 films propagate in the direction of film growth, which means that researchers can potentially control how and where line defects appear and potentially design them as needed in touch screens, smart windows and other future technologies. requiring a combination of transparency and conductivity.

Perovskite crystals contain three elements inelementary cell. This gives it the freedom to make structural changes such as the composition and symmetry of the crystal, as well as the ability to retain various defects. Due to different angles of coordination and bonding of atoms in the core of the line defect, new electronic states are introduced, and the structure of the electronic band is locally modified so radically that it transforms the line defect into a metal.

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