Effect of Anion Mixing on Structural and Thermoelectric Properties of CoSb(S,Se)

Anionic S/Se mixing is investigated as a tool to control the structural and transport properties of the CoSb(S, Se) thermoelectrics. A series of CoSb(S 1-x Se x ) samples with the Se-for-S substitution fraction x varying from 0 to 1 were prepared through solid-state synthesis carried out in evacuated quartz ampoules. Structural characterization with powder X-ray diffraction revealed a transformation of the initial paracostibite (space group Pbca ) of CoSbS to a costibite-like (space group Pmn 2 1 ) structure for CoSbSe through a two-phase region in between 0.3 < x < 0.75. Scanning electron microscopy and energy-dispersive X-ray spectroscopy characterization provided insights into the microstructure and elemental composition of the samples. The charge carrier type/density and thermoelectric properties were evaluated by measuring the Hall effect, Seebeck coefficient, electrical conductivity, and thermal conductivity as a function of temperature. Notably, with increasing Se content, a p -type to n -type transition and a semiconductor-to-metal transition were observed. Besides the substantially increased electrical conductivity due to enhanced charge carrier density, thermal conductivity was found to decrease due to defects upon the Se-for-S substitution. These findings demonstrate that S/Se mixing is a viable strategy for tuning the thermoelectric characteristics and crystal structure of CoSb(S, Se). • Anion mixing via Se-for-S substitution in CoSbS effectively enhances thermoelectric performance by inducing structural evolution and disorder. • An optimized composition (x = 0.3) shows markedly improved electrical conductivity and suppressed thermal conductivity, yielding an enhanced ZT ≈ 0.08 at 400 K.