Top-down approach using supercritical carbon dioxide ball milling for producing sub-10 nm Bi2Te3 grains

Abstract

We compare Bi2Te3 powders prepared by conventional ball milling to powders milled in supercritical carbon dioxide (scCO2). We demonstrate that scCO2 milling overcomes size-reduction limitations reported for conventional milling. XRD and TEM reveal nanograins with smaller average sizes (< 10 nm) and narrower grain size distributions in the scCO2 milled case. scCO2 milling also preserves the crystallinity and shows less oxidation than conventional milling. This is the first report of Bi2Te3 with a sub-10 nm grain size whilst conserving high quality crystallinity, made using a top-down approach. Our study offers a route for developing unprecedentedly fine bulk nanostructured Bi2Te3-based thermoelectric materials.