Abstract The effects of composition and cooling rate on the microstructures of alloys in the pseudo-binary PbTe–Sb 2Te 3 system were investigated as a first step towards the design of nanostructured materials with enhanced thermoelectric properties. Liquid alloys of three different compositions were cooled in three distinct ways: water quenching, air cooling and furnace cooling. The resultant structures and phases were examined by electron microscopy, electron microprobe chemical analysis and electron backscatter diffraction. The compound Pb 2Sb 6Te 11 precipitated as a metastable phase (in conjunction with PbTe and/or Sb 2Te 3) under all conditions. Furthermore, whereas PbTe exhibited dendritic morphology, Sb 2Te 3 and Pb 2Sb 6Te 11 crystallized as lamellar platelets with preferred (0 0 1) orientation. The range of cooling rates was from ∼1 to 26 K/s, while the characteristic microstructural feature size ranged from 10 to 35 μm for dendrites, and from 15 to 50 μm for lamella. The prospects for achieving nanoscale structure are discussed.