Homo-composition and hetero-structure nanocomposite Pnma Bi2SeS2 - Pnnm Bi2SeS2 with high thermoelectric performance

Abstract

Nanocomposite engineering decouples the transport of phonons and electrons. This usually involves the in-situ formation or ex-situ addition of nanoparticles to a material matrix with hetero-composition and hetero-structure (heC-heS) interfaces or hetero-composition and homo-structure (heC-hoS) interfaces. Herein, a quasi homo-composition and hetero-structure (hoC-heS) nanocomposite consisting of Pnma Bi2SeS2 - Pnnm Bi2SeS2 is obtained through a Br dopant-induced phase transition, providing a coherent interface between the Pnma matrix and Pnnm second phase due to the slight structural difference between the two phases. This hoC-heS nanocomposite demonstrates a significant reduction in lattice thermal conductivity (~0.40 W m−1 K−1) and an enhanced power factor (7.39 μW cm−1 K−2). Consequently, a record high figure-of-merit ZTmax = 1.12 (at 773 K) and a high average figure-of-merit ZTave = 0.72 (in the range of 323–773 K) are achieved. This work provides a general strategy for synergistically tuning electrical and thermal transport properties by designing hoC-heS nanocomposites through a dopant-induced phase transition.

Optimized Thermoelectric Properties of Sulfide Compound Bi2SeS2 by Iodine Doping

“…The XRD peaks of all samples match well with an orthorhombic Pnma phase. No phase transition can be found as the reported Br doped samples [28]. Figure 1c shows the I dopant-induced lattice parameter evolution, which was derived from the Reitveld refinement.…”

“…It shows that κ b has been reduced for the doped samples. It dropped from 0.094 Wm −1 K −1 to 0.056 Wm −1 K −1 for doped levels from x = 0 to x = 1.1% at 773 K, likely due to the trapping of minority carriers within the dense nanoscale regions [28]. Thus, although κ e increased due to n optimization, the total thermal conductivity dropped by reducing κ L and suppressing κ b .…”

“…Figure 1c shows the I dopant-induced lattice parameter evolution, which was derived from the Reitveld refinement. According to the calculated formation energy [28], I preferentially occupies the Se site when doping in Bi 2 SeS 2 . The ionic radius of I − (2.2 Å) exceeds Se 2− (1.98 Å), which should enlarge the lattice parameters.…”

“…Recent reports revealed that the ternary sulfide compound Bi 2 SeS 2 has TE potential with a high ZT (>1.0) [27,28]. Its crystalline structure was similar to Bi 2 S 3 .…”

“…By tuning the electrical conductivity via Cu doping and suppressing the lattice thermal conductivity by forming nanoprecipitates, the ZT value increased to 0.7 at 723 K, and to 1.0 at 773 K [27,30]. Recently, Br served as an effective carrier donor and induced a partial Bi 2 SeS 2 phase change from Pnma to Pnnm, which formed a quasi homo-composition and a hetero-structure (hoC-heS) nanocomposite [28]. This caused a significant lattice thermal conductivity decrease and enhanced power factor, which resulted in a large ZT value improvement.…”