Origin of Intrinsically Low Thermal Conductivity in Talnakhite Cu_17.6Fe_17.6S₃₂ Thermoelectric Material: Correlations between Lattice Dynamics and Thermal Transport

Abstract

Understanding the nature of phonon transport in solids and the underlying mechanism linking lattice dynamics and thermal conductivity is important in many fields, including the development of efficient thermoelectric materials where a low lattice thermal conductivity is required. Herein, we choose the pair of synthetic chalcopyrite CuFeS2 and talnakhite Cu17.6Fe17.6S32 compounds, which possess the same elements and very similar crystal structures but very different phonon transport, as contrasting examples to study the influence of lattice dynamics and chemical bonding on the thermal transport properties. Chemically, talnakhite derives from chalcopyrite by inserting extra Cu and Fe atoms in the chalcopyrite lattice. The CuFeS2 compound has a lattice thermal conductivity of 2.37 W m–1 K–1 at 625 K, while Cu17.6Fe17.6S32 features Cu/Fe disorder and possesses an extremely low lattice thermal conductivity of merely 0.6 W m–1 K–1 at 625 K, approaching the amorphous limit κmin. Low-temperature heat capacity measurements and phonon calculations point to a large anharmonicity and low Debye temperature in Cu17.6Fe17.6S32, originating from weaker chemical bonds. Moreover, Mössbauer spectroscopy suggests that the state of Fe atoms in Cu17.6Fe17.6S32 is partially disordered, which induces the enhanced alloy scattering. All of the above peculiar features, absent in CuFeS2, contribute to the extremely low lattice thermal conductivity of the Cu17.6Fe17.6S32 compound.

Origin of the Distinct Thermoelectric Transport Properties of Chalcopyrite ABTe2 (A = Cu, Ag; B = Ga, In)

“…Others [9,[73][74][75]78] attribute the boson peak to the strong coupling between acoustic phonons and low-frequency optic phonons, which has been observed in BaAg 2 SnSe 4 , [9] Cd 2 ReO 7 , [78] and CuFeS 2 . [81] For instance, in BaAg 2 SnSe 4 , [9] the vibrations of the AgSe cluster act as two Einstein oscillators in the Debye host. This leads to an ultralow thermal conductivity in BaAg 2 SnSe 4 .…”

“…In this study, Umklapp scattering, grain boundary scattering, point defect scattering, and phonon resonance scattering are included. Taking these processes as substantially independent, the relaxation rate is [81,86,87]…”

α-Bi2Sn2O7: a potential room temperature n-type oxide thermoelectric

“…Building upon this, several ternary and quaternary compounds with complex structures and incorporating heavy elements have been identied that have lower k l values compared to the industry standard Bi 2 Te 3 . [6][7][8][9][10] Such complex structures oen also have higher effective masses and thus high Seebeck coefficients.…”

Thermoelectric Properties of Nano‐grained Mooihoekite Cu9Fe9S16

“…Figure 6 plots the κ L values for typical Cu-based sulfides. [15,21,29,[39][40][41][42][43] It can be seen that Cu 9 Fe 9 S 16 has relatively low κ L even comparing with those compounds including heavy Sb and Sn elements. Most recently, Xie et al found that Cu 17.6 Fe 17.6 S 32 also has intrinsically low κ L as compared with CuFeS 2 , which has the same component elements.…”

“…Cu-Fe-S-based compounds, including CuFeS 2 , [18] Cu 5 FeS 4 , [20] CuFe 2 S 3 , [19] Cu 17.6 Fe 17.6 S 32 , [21] and Cu 9 Fe 9 S 16 , [22,27,28] gain the interest from TE community because all the consisting elements, Cu, Fe, and S, are non-toxic and earth-abundant. These Cu-Fe-S-based TE compounds are also natural minerals that cated Cu 9 Fe 9 S 16 has a natural nanostructure.…”