Revealing 3D atomic packing in liquid-like solids

Abstract

Liquids and solids are two fundamental states of matter. However, due to the lack of direct experimental determination, our understanding of the 3D atomic structure of liquids and amorphous solids remained speculative. Here we advance atomic electron tomography to determine for the first time the 3D atomic positions in monatomic amorphous materials, including a Ta thin film and two Pd nanoparticles. We observe that pentagonal bipyramids are the most abundant atomic motifs in these amorphous materials. Instead of forming icosahedra, the majority of pentagonal bipyramids arrange into a novel medium-range order, named the pentagonal bipyramid network. Molecular dynamic simulations further reveal that pentagonal bipyramid networks are prevalent in monatomic amorphous liquids, which rapidly grow in size and form icosahedra during the quench from the liquid state to glass state. The experimental method and results are expected to advance the study of the amorphous-crystalline phase transition and glass transition at the single-atom level.

Quantifying the Local Structure of Nanocrystals, Glasses, and Interfaces Using TEM-Based Diffraction

“…More recently, Voronoi analysis was combined with atomic electron tomography and ePDF for the study of monatomic amorphous Ta and Pd materials. 65 The authors demonstrated that experimental PDFs of amorphous regions were consistent with a MD-generated PDF of Ta liquid, indicating that the packings of atoms in these two phases closely resemble each other. The commonality of bipyramidal motifs between phases that was observed in PDF and Voronoi analysis suggested a quenching mechanism that formed icosahedra from these motifs.…”