Enhanced thermoelectric performance in polymorphic heavily Co-doped CuSnS through carrier compensation by Sb substitution.

Heavily acceptor-doped CuSnS (CTS) shows promisingly large power factor () due to its rather high electrical conductivity () which causes a modest with a high electronic thermal conductivity ( ). In the present work, a strategy of carrier compensation through Sb-doping at the Sn site in CuSnCoS was investigated, aiming at tailoring electrical and phonon transport properties simultaneously. Rietveld analysis suggested a complex polymorphic microstructure in which the cation-(semi)ordered tetragonal phase becomes dominant over the coherently bonded cation-disordered cubic phase, as is preliminarily revealed using TEM observation, upon Sb-doping and Sb would substitute Sn preferentially in the tetragonal structure. With increasing content of Sb, the was lowered and the Seebeck coefficient () was enhanced effectively, which gave rise to high s maintained at ~10.4 μWcmK at 773 K together with an optimal reduction in by 60-70% in the whole temperature range. The lattice thermal conductivity was effectively suppressed from 1.75 WmK to ~1.2 WmK at 323 K while maintained very low at 0.3-0.4 WmK at 773 K. As a result, a peak of ~0.88 at 773 K has been achieved for CuSnSbCoS, which stands among the tops so far of the CTS-based diamond-like ternary sulfides. These findings demonstrate that polymorphic microstructures with cation-disordered interfaces as an approach to achieve effective phonon-blocking and low lattice thermal conductivity, of which further crystal chemistry, microstructural and electrical tailoring are possible by appropriate doping.