Strong correlation between the crystal structure and the thermoelectric properties of pavonite homologue Cu_x+yBi_5−yCh₈(Ch = S or Se) compounds

Abstract

Complex structured semiconducting compounds are promising thermoelectric materials due to their inherently low thermal conductivities. It has been demonstrated that the limited phonon mean free path with structural complexities such as a large unit cell, disorders, or a variety of atom types resulted in low lattice thermal conductivity. However, there is still a missing piece to elucidate which structural component manipulates the transport properties effectively. Herein we review our recent progress on the thermoelectric properties of the intrinsically disordered system, pavonite homologue Cu x+y Bi 5Ày Ch 8 (Ch = S or Se). Through the controlled tuning of composition and occupancy for each atomic site based on the comprehensive structural analysis, we found that the structural factor (occupancy of interstitial Cu) could be a critical basis for determining both electronic and thermal transport properties. Also, we present a short overview of common structural traits inhibiting phonon propagation in complex structured thermoelectric materials. This consideration outlines a strategy to search for new high performance complex structured thermoelectric materials in relation with the possibilities of their chemical and structural modifications.

Ultralow Thermal Conductivity in Earth-Abundant Cu1.6Bi4.8S8: Anharmonic Rattling of Interstitial Cu

“…A high-quality polycrystalline ingot of Cu 1.6 Bi 4.8 S 8 , an earth- abundant metal sulfide, − was synthesized via melting reaction in a sealed quartz tube at 1323 K and then densified into pellets using spark plasma sintering (SPS). It is a low band gap compound ∼0.37 eV (Figure S2, SI) which crystallizes in a monoclinic structure (Figure a) having C 2 /m space group.…”

“…In this case, nontoxic metal sulfides are therefore viewed as an alternative and promising substitute to overcome such obstacles. Here, S, also being earth abundant and low cost as compared to Te and Se (Figure S1, Supporting Information, SI), provides long-term availability and price stability, and thus, significant attention has been diverted toward producing the next generation of intrinsically low κ lat materials, which are primarily S based. ,,,,,− …”

Raman Spectroscopy Study of Phonon Liquid Electron Crystal in Copper Deficient Superionic Thermoelectric Cu2–xTe

“…To achieve high power factor ( S 2 σ ), various materials with high crystal symmetry, multiple valleys near the Fermi level through insertion of resonant levels, convergence of multiple valence bands, − and doping of heavy elements with small electronegativity differences of constituent elements have been explored. On the other hand, strategies such as exploring complex crystal structure, , alloying, ,, solid solutions, ,, rattling atoms, , nanostructuring, , and acoustic phonon scattering through optical phonons − are utilized to reduce κ.…”

Phase‐Controlled Synthesis of High‐Bi‐Ratio Ternary Sulfide Nanocrystals of Cu1.57Bi4.57S8 and Cu2.93Bi4.89S9

“…Compounds composed of Cu−Bi−S have been reported with various phases according to their compositions, such as Cu 9 BiS 6 , Cu 3 BiS 3 ,22 CuBiS 2 , Cu 4 Bi 4 S 9 ,, and a theoretical phase of Cu 4 Bi 5 S 10 . Although some of phases of high Bi ratio Cu−Bi−S have been reported previously, such as CuBi 5 S 8 and its derivatives,, however the synthetic method for these compounds needs a tedious vacuum‐sealed high temperature melted flux process. Generally, ternary Cu−Bi−S sulfides could be synthesized with reactive sintering method, solvothermal method, polyol route, chemical bath deposition method,, vacuum‐sealed solid state reaction, and colloidal hot‐injection method ,.…”