Chalcopyrite ZnSnSb_2: A Promising Thermoelectric Material

Ternary compounds with a tetragonal chalcopyrite structure, such as CuGaTe2, are promising thermoelectric (TE) materials. It has been demonstrated in various chalcopyrite systems, including compounds with quaternary chalcopyrite-like structures, that the lattice parameter ratio, c/a, being exactly 2.00 to have a pseudo-cubic structure is key to increase the degeneracy at the valence band edge and ultimately achieve high TE performance. Considering the fact that ZnSnSb_2 with a chalcopyrite structure is reported to have c/a close to 2.00, it is expected to have multiple valence bands leading to a high p-type zT. However, there are no complete investigations on the high temperature TE properties of ZnSnSb_2 mainly because of the difficulty of obtaining a single-phase ZnSnSb_2. In the present study, pure ZnSnSb_2 samples with no impurities are synthesized successfully using a Sn flux-based method and TE properties are characterized up to 585 K. Transport properties and thermal analysis indicate that the structure of ZnSnSb_2 remains chalcopyrite with no order–disorder transition and clearly show that ZnSnSb_2 can be made to exhibit a high zT in the low-to-mid temperature range through further optimization

Microscale Seebeck Scanning of Polycrystalline Samples of N-Type AgPb₁₈SbTe₂₀ and P-Type AgPb₉Sn₉SbTe₂₀

We prepared polycrystalline-sintered samples of n-type AgPb18SbTe20 and p-type AgPb9Sn9SbTe20 and performed the microscale Seebeck scanning examination under room temperature conditions. Despite both samples appeared to be homogeneous by Energy Dispersive X-ray (EDX) and X-ray Diffraction (XRD) analyses, both samples contained apparently a microscale distribution of the Seebeck coefficient as observed by Seebeck microprobe analysis. The degree of the Seebeck coefficient distribution became larger in the order of PbTe, AgPb18SbTe20, and AgPb9Sn9SbTe20, indicating that an increase in the number of compositional elements of the materials led to a broader distribution of the Seebeck coefficient values. The statistical analysis of the Seebeck coefficient distribution of p-type AgPb9Sn9SbTe20 indicated a homogeneous phase seemed to appear only at the lowest Seebeck coefficient values (slightly above 50 μV/K)