Homologous compounds with complex
crystal structures are considered
as a new class of potential thermoelectric materials due to the possible
low thermal conductivity. The thermoelectric properties of Pb
m
Bi2S3+m
(m = 0, 1, and 3) homologous series are investigated
in the temperature range of 300–800 K. The samples are prepared
by a solution-based method assisted with EDTA-2Na in aqueous media,
followed by sintering at 973 K. All obtained Pb
m
Bi2S3+m
show an N-type
degenerate semiconducting behavior, providing thermoelectric power
factors, PF, of 3.7 μW·cm–1·K–2 for PbBi2S4 and 2.5 μW·cm–1·K–2 for Pb3Bi2S6 at 800 K. Meanwhile, very low thermal conductivities,
κtotal, ranging from 0.55 to 0.65 and 0.93 to 1.17
W·m–1·K–1 are achieved
at 300–800 K for PbBi2S4 and Pb3Bi2S6, respectively. Significantly, both PbBi2S4 and Pb3Bi2S6 reveal extremely low lattice thermal conductivities, κLat, of less than 0.46 and 0.79 W·m–1·K–1 over the entire temperature range, respectively.
As a result, the highest thermoelectric figure of merit zT of 0.46
at 800 K is observed in PbBi2S4 due to a higher
power factor and lower thermal conductivity compared with Pb3Bi2S6.