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1. Thermal and electronic transport properties of A Cr X ₂ superionic conductors (A=Cu, Ag and X=S, Se)

   https://doi.org/10.1088/2515-7655/addf7e  

   Rahman, Md_Towhidur; Ciesielski, Kamil; Pelkey, Joseph; Shawon, A_K_M_Ashiquzzaman; Toberer, Eric; Zevalkink, Alexandra (June 2025, Journal of Physics: Energy)

   Abstract Superionic conductors, includingACrX₂(A=Ag, Cu; X = S, Se) compounds, have attracted attention due to their low lattice thermal conductivity and high ionic conductivity. These properties are driven by structural characteristics such as anharmonicity, soft bonding, and disorder, which enhance both fast ion transport and thermal resistance. In the present study, we investigate the impact of various factors (e.g.A-site disorder, microstructure, speed of sound and chemical composition) on the thermal conductivity of the compounds CuCrS₂, CuCrSe₂, AgCrS₂and AgCrSe₂. The samples were synthesized using solid state reaction, ball milling and subsequent spark plasma sintering, and thermal diffusivity, electrical resistivity, Hall coefficients and Seebeck coefficients were measured as a function of temperature. The selenides were found to behave as degenerate semiconductors, with reasonable thermoelectric figure of merit (up to 0.79 in CuCrSe₂), while the sulfides behaved as non-degenerate semiconductors with high electrical resistivity. At room temperature, all samples are in the ordered phase and show low lattice thermal conductivity ranging from 0.60 W m⁻¹-K in AgCrSe₂to 1.1 W m⁻¹-K in CuCrSe₂. Little reduction in lattice thermal conductivity was observed in the high-temperature phase, despite the increased disorder on the cation site and the onset of superionic conductivity. This suggests that the low lattice thermal conductivity inACrX₂compounds is an inherent property of the crystal structure, caused by anharmonic bonding and diffuson dominated transport. 

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2. Thermal Properties of the Very Low Thermal Conductivity Ternary Chalcogenide Cu ₄ Bi ₄ M ₉ (M = S, Se)

   https://doi.org/10.1002/pssr.202000166  

   Hobbis, Dean; Wang, Hsin; Martin, Joshua; Nolas, George S. (May 2020, physica status solidi (RRL) – Rapid Research Letters)

   Temperature‐dependent thermal properties of phase‐pure polycrystalline ternary chalcogenides Cu₄Bi₄S₉and Cu₄Bi₄Se₉are reported. The structure and bonding in these materials result in very low thermal conductivity values (<0.8 W m⁻¹ K⁻¹at room temperature) for both materials. The lattice contribution, Debye temperatures, and Sommerfeld coefficient are obtained from low‐temperature heat capacity data that also indicate very small electronic contributions to the heat capacity for these materials. This study aids in the identification of new nontoxic, earth‐abundant resistive ternary chalcogenide materials with low thermal conductivity for potential thermal barrier coating and rewriteable storage applications. 

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3. Ultralow lattice thermal conductivity of chalcogenide perovskite CaZrSe3 contributes to high thermoelectric figure of merit

   https://doi.org/10.1038/s41524-019-0253-5  

   Osei-Agyemang, Eric; Adu, Challen Enninful; Balasubramanian, Ganesh (December 2019, npj Computational Materials)

   Abstract An emerging chalcogenide perovskite, CaZrSe₃, holds promise for energy conversion applications given its notable optical and electrical properties. However, knowledge of its thermal properties is extremely important, e.g. for potential thermoelectric applications, and has not been previously reported in detail. In this work, we examine and explain the lattice thermal transport mechanisms in CaZrSe₃using density functional theory and Boltzmann transport calculations. We find the mean relaxation time to be extremely short corroborating an enhanced phonon–phonon scattering that annihilates phonon modes, and lowers thermal conductivity. In addition, strong anharmonicity in the perovskite crystal represented by the Grüneisen parameter predictions, and low phonon number density for the acoustic modes, results in the lattice thermal conductivity to be limited to 1.17 W m⁻¹ K⁻¹. The average phonon mean free path in the bulk CaZrSe₃sample (N → ∞) is 138.1 nm and nanostructuring CaZrSe₃sample to ~10 nm diminishes the thermal conductivity to 0.23 W m⁻¹ K⁻¹. We also find that p-type doping yields higher predictions of thermoelectric figure of merit than n-type doping, and values ofZT~0.95–1 are found for hole concentrations in the range 10¹⁶–10¹⁷ cm⁻³and temperature between 600 and 700 K. 

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4. Investigating the Role of Vacancies on the Thermoelectric Properties of EuCuSb‐Eu ₂ ZnSb ₂ Alloys

   https://doi.org/10.1002/anie.202301176  

   Chanakian, Sevan; Peng, Wanyue; Meschke, Vanessa; Ashiquzzaman_Shawon, A_K_M; Adamczyk, Jesse; Petkov, Valeri; Toberer, Eric; Zevalkink, Alexandra (June 2023, Angewandte Chemie International Edition)

   Abstract AMXcompounds with the ZrBeSi structure tolerate a vacancy concentration of up to 50 % on theM‐site in the planarMX‐layers. Here, we investigate the impact of vacancies on the thermal and electronic properties across the full EuCu_1−xZn_0.5xSb solid solution. The transition from a fully‐occupied honeycomb layer (EuCuSb) to one with a quarter of the atoms missing (EuZn_0.5Sb) leads to non‐linear bond expansion in the honeycomb layer, increasing atomic displacement parameters on theMand Sb‐sites, and significant lattice softening. This, combined with a rapid increase in point defect scattering, causes the lattice thermal conductivity to decrease from 3 to 0.5 W mK⁻¹at 300 K. The effect of vacancies on the electronic properties is more nuanced; we see a small increase in effective mass, large increase in band gap, and decrease in carrier concentration. Ultimately, the maximumzTincreases from 0.09 to 0.7 as we go from EuCuSb to EuZn_0.5Sb. 

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5. Ligand Crosslinking Boosts Thermal Transport in Colloidal Nanocrystal Solids

   https://doi.org/10.1002/anie.201916760  

   Wang, Zhongyong; Singaravelu, Arun Sundar S.; Dai, Rui; Nian, Qiong; Chawla, Nikhilesh; Wang, Robert Y. (April 2020, Angewandte Chemie International Edition)

   Abstract The ongoing interest in colloidal nanocrystal solids for electronic and photonic devices necessitates that their thermal‐transport properties be well understood because heat dissipation frequently limits performance in these devices. Unfortunately, colloidal nanocrystal solids generally possess very low thermal conductivities. This very low thermal conductivity primarily results from the weak van der Waals interaction between the ligands of adjacent nanocrystals. We overcome this thermal‐transport bottleneck by crosslinking the ligands to exchange a weak van der Waals interaction with a strong covalent bond. We obtain thermal conductivities of up to 1.7 Wm⁻¹ K⁻¹that exceed prior reported values by a factor of 4. This improvement is significant because the entire range of prior reported values themselves only span a factor of 4 (i.e., 0.1–0.4 Wm⁻¹ K⁻¹). We complement our thermal‐conductivity measurements with mechanical nanoindentation measurements that demonstrate ligand crosslinking increases Young's modulus and sound velocity. This increase in sound velocity is a key bridge between mechanical and thermal properties because sound velocity and thermal conductivity are linearly proportional according to kinetic theory. Control experiments with non‐crosslinkable ligands, as well as transport modeling, further confirm that ligand crosslinking boosts thermal transport. 

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