Grain size and phonon thermal conductivity of sintered bulk undoped lead telluride compacts processed via mechanical grinding and alloying

This study focused on investigating the influence of processing undoped, dense lead telluride (PbTe) either via mechanical grinding (MG) or mechanical alloying (MA), based on the milling rotation speed (1.5–3.0 Hz), followed by hot pressing (HP) on the grain size and phonon thermal conductivity (κphonon). The samples prepared via MG-HP were single-phased, had high relative densities (> 99%), and exhibited uniform morphologies. For a milling rate of 2.5 Hz, the minimum κphonon of MG-HP was 0.90 W m−1 K−1 and the average grain size was 0.47 µm. Furthermore, the grains produced by MG-HP and milled at 2.5 Hz comprised subgrains with a size of approximately 50 nm. The samples prepared using MA-HP showed higher theoretical relative densities. For a milling rate of 2.0 Hz, the minimum κphonon of MA-HP was 1.36 W m−1 K−1 and the average grain size was 0.52 µm. The electrical conductivity and Seebeck coefficient of MG-HP and MA-HP were similar to those of the p-type doped materials. Thus, the MG-HP process is an appropriate method for producing undoped PbTe with a high Seebeck coefficient and a low κphonon