Chemical trends in high thermoelectric pe

image: Figure 1. (a) Crystal structures and bonds between atoms in pyrite-like dichalcogenides IIB-VIA2 [Pa3(_)-MX2, M=transition metal (Zn and Cd), X=S and Se]. (b) The first corresponding Brillouin zone and its points of high symmetry.
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Credit: JIA Tiantian

Recently, Professor ZHANG Yongsheng’s research group at the Institute of Solid State Physics, Hefei Institutes of Physical Science, systematically investigated the thermoelectric (TE) properties of three kinds of pyrite IIB-VIA2 dichalcogenides (ZnS2CDS2and CdSe2), and successfully explored the physical mechanisms and several chemical trends.

Their findings were published in Physics Review B.

Through high-throughput (HT) calculations, the three types of pyrite IIB-VIA2 dichalcogenides (ZnS2CDS2and CdSe2) with a simple cubic structure and the cheap elements had been predicted to possess promising TE properties by the same team. However, the detailed behaviors of TEs and the fundamental underlying physical mechanisms that underlie them still remain ambiguous.

In this research, the team studied the thermal and electrical transport properties of the three types of pyrite IIB-VIA2 dichalcogenides, and evaluated their thermoelectric performances by taking advantage of more precise methods.

After calculating and analyzing the phonon properties, they concluded that the three pyrite-like dichalcogenides had localized high-frequency optical phonons contributed by their strongly covalently bound nonmetallic dimers and soft phonon modes contributed by their click-like metallic atoms, which resulted in their strong anharmonicities. and low thermal conductivities.

Additionally, certain chemical trends in these heavier atom masses, larger atomic shift parameters, and longer bond lengths between metallic and nonmetallic atoms could result in softer phonon frequencies.

In addition, the three compounds showed promising electrical transport properties for both p-type and n-type doping, due to their high-density-of-states effective masses and low-conductivity effective masses, which could s explain in terms of a non-spherical complex. iso energy Fermi surfaces in the valence and conduction bands.

In addition to this, they found that the lattice’s low thermal conductivity and promising electrical transport properties contributed to their excellent thermoelectric performance.

“This research illustrated the effects of localized non-metallic dimers and rattle-like metal atoms on thermal transport properties, and the importance of different effective masses of carriers for electrical transport properties in these pyrite-like dichalcogenides, which could be used to predict and optimize the TE properties of other TE compounds in the future,” said JIA Tiantian, first author of the paper.

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