Stabilized cubic phase BiAgSe2−xSx with excellent thermoelectric properties via phase boundary engineering

Abstract

Quaternary compound BiAgSeS shows an excellent thermoelectric performance with ultralow thermal conductivity. However, competition between the trigonal and cubic phases, which is strongly dependent on experimental processing, results in ambiguous transport behavior. The highly stable n-type polycrystalline BiAgSe_2−xS_x (x = 1.2) sample was successfully synthesized, guided by phase boundary engineering. Whilst maintaining promising thermoelectric properties, significant enhancement of the thermodynamical stability was obtained due to the strengthened chemical bonding caused by the substitution of Se with high-electronegativity S. Cubic BiAgSe_0.8S_1.2 can be well preserved after thermoelectric measurements. Our work demonstrates that phase boundary engineering is an applicable route to stabilize some compounds with moderate thermodynamical stability.