Geometric stabilization of polar NdNiO3 via octahedral tilt engineering.
Engineers and Physicists have created an entirely new material in which completely contradictory properties can coexist.”Polar metals should not be possible,” says Chang-Beom Eom, the professor of materials science and engineering. Undeterred by the laws of the universe, Eom et al created a compound that is a scientific oxymoron. Through a new synthesis approach supported by computational modeling, the group made a crystal with multiple personalities: part polar, part metallic.
Metals conduct electricity because electrons flow freely throughout them. Polar materials, by contrast, impede the free flow of electrons and work as electrical insulators. First, they separated the polar and metallic parts of the crystal. Some electrons gave rise to the metallic nature, moving within the material to conduct electricity. Other electrons contributed to the polar properties.
However, because the natural molecular structure of the material is symmetrical, even after separating the 2 components, the material as a whole would not act polar. Equal and opposite arrangements of electrons canceled each other out. To overcome this obstacle, the researchers synthesized the substance with slightly off-kilter atoms, which threw off the internal symmetry enough to make the material polar.
Ultimately, Eom and colleagues made the polar metal by painstakingly growing thin films of material one atom at a time. Crucially, they grew the substance on top of a supporting lattice with a slightly offset molecular organization. Tightly clamping the growing film to this support skewed the internal arrangement of their material, stabilizing its internal geometry in the asymmetrical orientation necessary to maintain polarity.
The researchers counted every atom deposited on the surface, as the substance slowly grew one layer at a time. They then used multiple complex optical and electronic and structural measurements to determine its properties. Their approach is an attempt to accelerate the discovery of multifunctional materials with unusual coexisting properties, paving the way to devices with the ability to perform simultaneous electrical, magnetic and optical functions.
http://dx.doi.org/10.1038/nature17628Â
http://news.wisc.edu/new-material-combines-useful-typically-incompatible-properties/
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