Stabilizing n-type cubic AgBiSe2 thermoelectric materials through alloying with PbS

Phase transition generates rapid changes of transport parameters and poor mechanical property, and thus restricts the application of thermoelectric materials. AgBiSe2 exhibits cubic phase at above 580 K with high-symmetry structure and low lattice thermal conductivity, indicating the potentiality of high thermoelectric performances. In this work, the cubic structure of AgBiSe2 was achieved at ambient conditions by alloying with PbS, enhancing the configurational entropy at both cationic and anionic sites. The cubic structure was rather stable after several measurement cycles. Nb substitution at cationic sites effectively reduced band gap, and increased both carrier concentration and effective mass. All samples exhibited relatively low lattice thermal conductivity (0.68–0.34 W/(m·K)) in the temperature range of 300–773 K, due to the nanoscale inhomogeneity and the random distribution of multiple species at some atomic sites. A maximum zT of 0.65 at 773 K was obtained for (Ag0.99Nb0.01BiSe2)0.8(PbS)0.2 sample. The entropy-driven structural stabilization is a promising strategy to achieve stable structure for practical thermoelectric applications.