The
growth mechanism and synthetic controls for colloidal multinary
metal chalcogenide nanocrystals (NCs) involving alkali metals and
the pnictogen metals Sb and Bi are unknown. Sb and Bi are prone to
form metallic nanocrystals that stay as impurities in the final product.
Herein, we synthesize colloidal NaBi1–xSbxSe2–ySyNCs using amine–thiol–Se
chemistry. We find that ternary NaBiSe2NCs initiate with
Bi0nuclei and an amorphous intermediate nanoparticle formation
that gradually transforms into NaBiSe2upon Se addition.
Furthermore, we extend our methods to substitute Sb in place of Bi
and S in place of Se. Our findings show the initial quasi-cubic morphology
transforms into a spherical shape upon increased Sb substitution,
and the S incorporation promotes elongation along the <111>
direction.
We further investigate the thermoelectric transport properties of
the Sb-substituted material displaying very low thermal conductivity
and n-type transport behavior. Notably, the NaBi0.75Sb0.25Se2material exhibits an ultralow thermal conductivity
of 0.25 W·m–1·K–1at
596 K with an average thermal conductivity of 0.35 W·m–1·K–1between 358 and 596 K and aZTmaxof 0.24.