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

We compare Bi 2 Te 3 powders prepared by conventional ball milling to powders milled in supercritical carbon dioxide (scCO 2 ). We demonstrate that scCO 2 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 scCO 2 milled case. scCO 2 milling also preserves the crystallinity and shows less oxidation than conventional milling. This is the first report of Bi 2 Te 3 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 Bi 2 Te 3 -based thermoelectric materials.