Compressing binary crystals into glasses*

A polycrystal transforms into a glass when its grain size is small enough. However, the boundary between polycrystal and glass is unclear partly because ultrafine-grained nanocrystals are unstable and undergo grain coarsening constantly. Here we propose a simple approach to induce the polycrystal-glass transition by compressing binary single crystals composed of hard and soft disks into polycrystals and further into glasses. At low pressure, both types of disks have the same effective diameter and form a crystal. At high pressures, soft disks are compressed into a smaller size, resulting in a glass. The full spectrum of grain sizes enables the study of the polycrystal-glass crossover. We observed rich structural, mechanical, dynamical and thermodynamic features at the polycrystal-glass boundary, which could serve as criteria for the polycrystal-glass transition. These analyses reveal the Hall-Petch and inverse-Hall-Petch behaviors in polycrystals and identify three different glass regimes. Such a crystal-to-glass transition is expected to occur widely in alloys when the pressure is high enough. These results cast new light on the fabrication and theories of both polycrystals and glasses.