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Physical Chemistry

Scientists See Atomic Distortions In Crystals

Electron microscopy technique allows researchers to directly visualize crystals with unprecedented precision

by Matt Davenport
February 23, 2015 | APPEARED IN VOLUME 93, ISSUE 8

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Credit: Appl. Phys. Lett.
Black electron density clouds show “covalent cages” in crosssections of a lanthanum strontium aluminum tantalum oxide crystal. The cages are the three-dimensional translucent structures below and to the left of the crosssections.
09308-scicon-crystalstruc_19949023-690.jpg
Credit: Appl. Phys. Lett.
Black electron density clouds show “covalent cages” in crosssections of a lanthanum strontium aluminum tantalum oxide crystal. The cages are the three-dimensional translucent structures below and to the left of the crosssections.

How atoms are organized with respect to one another is critical to the performance of solids such as ceramics and alloys. Electron microscopy allows researchers to observe solid-state materials with angstrom-scale precision, but subtle, inadvertent sample motions inevitably obscure important structural details. Materials scientists led by James M. LeBeau at North Carolina State University have shown that revolving scanning transmission electron microscopy can reveal crystal lattice distortions more precisely, at the picometer scale (Appl. Phys. Lett. 2015, DOI:10.1063/1.4908124). By rotating the scan direction of their microscope’s electron beam, the researchers corrected for sample drift and directly visualized the location of individual atoms in an LSAT crystal—a metal oxide containing lanthanum, strontium, aluminum, and tantalum. The researchers found that Al and Ta atoms in their sample were effectively caged in place by covalent bonds with neighboring oxygen atoms, and La and Sr atoms had more freedom to shift their positions.

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