Rapid mechanochemical synthesis and properties in Pb–Bi–S system†‡

We prepared a ternary sulfide with a stoichiometry close to Pb₆Bi₂S₉ from PbS, Bi, and S precursors using mechanochemical synthesis. After 5 min of high-energy milling, conversion of the precursors to Pb_5.95Bi_2.02S_9.03 was confirmed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS). Further milling (up to 120 min) led to the metal-enriched and sulfur-deficient composition Pb_6.40Bi_2.24S_8.36. Values of the specific surface area of the produced powder samples were used as an indicator of the transition from the mechanical activation mode to the mechanochemical synthesis mode. The products crystallized in the galena structure, with the crystallite size ranging from 5 to 15 nm, as determined by X-ray diffractometry (XRD) with Rietveld refinement and transmission electron microscopy (TEM). The dissolution of Bi from the synthesized nanocrystals corresponds to changes in the specific surface area. Spark plasma sintering (SPS) densified ingots in the temperature range of 300–525 K exhibit semiconducting properties and a low thermal conductivity of 0.38–0.5 W m⁻¹ K⁻¹, making them promising for thermoelectric applications. The possibility of modifying the properties of a ternary Pb–Bi–S system by mechanochemistry paves the way for the synthesis of more sophisticated ternary and multinary structures suitable for energy applications.