Using advanced analytical transmission electron microscopy (STEM) with a magnification of 10 million, researchers at the University of Minnesota were able to isolate and display the structure and composition of a metal defect as a line in the BaSnO3 perovskite crystal. This will help invent more innovative touch screens and smart windows with maximum transparency and conductivity. The research is published in Science Advances.
For the first time, researchers have observed metallic lines in a perovskite crystal. Perovskites are abundant in the center of the Earth, and barium stannate (BaSnO3) is one such crystal. However, its metallic properties have not been widely studied due to the prevalence 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 generate images with magnifications of up to 10 million.
“The electrically conductive nature and preferred direction of these metallic line defects means that we can make a material that is transparent, like glass, and at the same time very well directional, like metal. We can now 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, and linear defects (the most common of which is dislocation) are a series of atoms that deviate from normal order. Since the dislocations have the same elemental composition as the main crystal, changes in the electronic band structure in the core of the dislocation 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 transmission electron microscopy (STEM) with a magnification of 10 million times, researchers at the University of Minnesota were able to isolate and display the structure and composition of a metal defect as a line in the BaSnO3 perovskite crystal.
“We easily noticed these line defects in the SEM images of BaSnO3 thin films due to their unique atomic configuration, and we only saw them in the top view.”
Hwanghui Yong, PhD Student, Department of Chemical Engineering and Materials Science.
For this study, BaSnO3 films were grown 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 per unit cell. This gives it the freedom to make structural changes such as crystal composition and symmetry, as well as the ability to retain various defects. Due to the different coordination and bonding angles 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.