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1. High Thermoelectric Performance in Supersaturated Solid Solutions and Nanostructured n‐Type PbTe–GeTe

   https://doi.org/10.1002/adfm.201801617  

   Luo, Zhong‐Zhen ; Zhang, Xiaomi ; Hua, Xia ; Tan, Gangjian ; Bailey, Trevor P. ; Xu, Jianwei ; Uher, Ctirad ; Wolverton, Chris ; Dravid, Vinayak P. ; Yan, Qingyu ; et al ( June 2018 , Advanced Functional Materials)

   Sb‐doped and GeTe‐alloyed n‐type thermoelectric materials that show an excellent figure of meritZTin the intermediate temperature range (400–800 K) are reported. The synergistic effect of favorable changes to the band structure resulting in high Seebeck coefficient and enhanced phonon scattering by point defects and nanoscale precipitates resulting in reduction of thermal conductivity are demonstrated. The samples can be tuned as single‐phase solid solution (SS) or two‐phase system with nanoscale precipitates (Nano) based on the annealing processes. The GeTe alloying results in band structure modification by widening the bandgap and increasing the density‐of‐states effective mass of PbTe, resulting in significantly enhanced Seebeck coefficients. The nanoscale precipitates can improve the power factor in the low temperature range and further reduce the lattice thermal conductivity (κ_lat). Specifically, the Seebeck coefficient of Pb_0.988Sb_0.012Te–13%GeTe–Nano approaches −280 µV K⁻¹at 673 K with a low κ_latof 0.56 W m⁻¹K⁻¹at 573 K. Consequently, a peakZTvalue of 1.38 is achieved at 623 K. Moreover, a high averageZT_avgvalue of ≈1.04 is obtained in the temperature range from 300 to 773 K for n‐type Pb_0.988Sb_0.012Te–13%GeTe–Nano.

    

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2. 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)

   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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3. Distinguishing Optical and Acoustic Phonon Temperatures and Their Energy Coupling Factor under Photon Excitation in nm 2D Materials

   https://doi.org/10.1002/advs.202000097  

   Wang, Ridong ; Zobeiri, Hamidreza ; Xie, Yangsu ; Wang, Xinwei ; Zhang, Xing ; Yue, Yanan ( May 2020 , Advanced Science)

   Under photon excitation, 2D materials experience cascading energy transfer from electrons to optical phonons (OPs) and acoustic phonons (APs). Despite few modeling works, it remains a long‐history open problem to distinguish the OP and AP temperatures, not to mention characterizing their energy coupling factor (G). Here, the temperatures of longitudinal/transverse optical (LO/TO) phonons, flexural optical (ZO) phonons, and APs are distinguished by constructing steady and nanosecond (ns) interphonon branch energy transport states and simultaneously probing them using nanosecond energy transport state‐resolved Raman spectroscopy. ΔT_{OP −AP}is measured to take more than 30% of the Raman‐probed temperature rise. A breakthrough is made on measuring the intrinsic in‐plane thermal conductivity of suspended nm MoS₂and MoSe₂by completely excluding the interphonon cascading energy transfer effect, rewriting the Raman‐based thermal conductivity measurement of 2D materials.G_OP↔APfor MoS₂, MoSe₂, and graphene paper (GP) are characterized. For MoS₂and MoSe₂,G_OP↔APis in the order of 10¹⁵and 10¹⁴W m⁻³K⁻¹andG_ZO↔APis much smaller thanG_LO/TO↔AP. Under ns laser excitation,G_OP↔APis significantly increased, probably due to the reduced phonon scattering time by the significantly increased hot carrier population. For GP,G_LO/TO↔APis 0.549 × 10¹⁶W m⁻³K⁻¹, agreeing well with the value of 0.41 × 10¹⁶W m⁻³K⁻¹by first‐principles modeling.

    

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4. High Thermoelectric Performance in PbSe–NaSbSe 2 Alloys from Valence Band Convergence and Low Thermal Conductivity

   https://doi.org/10.1002/aenm.201901377  

   Slade, Tyler J. ; Bailey, Trevor P. ; Grovogui, Jann A. ; Hua, Xia ; Zhang, Xiaomi ; Kuo, Jimmy Jiahong ; Hadar, Ido ; Snyder, G. Jeffrey ; Wolverton, Chris ; Dravid, Vinayak P. ; et al ( July 2019 , Advanced Energy Materials)

   PbSe is an attractive thermoelectric material due to its favorable electronic structure, high melting point, and lower cost compared to PbTe. Herein, the hitherto unexplored alloys of PbSe with NaSbSe₂(NaPb_mSbSe_m+2) are described and the most promising p‐type PbSe‐based thermoelectrics are found among them. Surprisingly, it is observed that below 500 K, NaPb_mSbSe_m+2exhibits unorthodox semiconducting‐like electrical conductivity, despite possessing degenerate carrier densities of ≈10²⁰cm⁻³. It is shown that the peculiar behavior derives from carrier scattering by the grain boundaries. It is further demonstrated that the high solubility of NaSbSe₂in PbSe augments both the thermoelectric properties while maintaining a rock salt structure. Namely, density functional theory calculations and photoemission spectroscopy demonstrate that introduction of NaSbSe₂lowers the energy separation between the L‐ and Σ‐valence bands and enhances the power factors under 700 K. The crystallographic disorder of Na⁺, Pb²⁺, and Sb³⁺moreover provides exceptionally strong point defect phonon scattering yielding low lattice thermal conductivities of 1–0.55 W m^‐1K^‐1between 400 and 873 K without nanostructures. As a consequence, NaPb₁₀SbSe₁₂achieves maximumZT≈1.4 near 900 K when optimally doped. More importantly, NaPb₁₀SbSe₁₂maintains highZTacross a broad temperature range, giving an estimated recordZT_avgof ≈0.64 between 400 and 873 K, a significant improvement over existing p‐type PbSe thermoelectrics.

    

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5. High-throughput screening of hypothetical metal-organic frameworks for thermal conductivity

   https://doi.org/10.1038/s41524-022-00961-x  

   Islamov, Meiirbek ; Babaei, Hasan ; Anderson, Ryther ; Sezginel, Kutay B. ; Long, Jeffrey R. ; McGaughey, Alan J. H. ; Gomez-Gualdron, Diego A. ; Wilmer, Christopher E. ( January 2023 , npj Computational Materials)

   Thermal energy management in metal-organic frameworks (MOFs) is an important, yet often neglected, challenge for many adsorption-based applications such as gas storage and separations. Despite its importance, there is insufficient understanding of the structure-property relationships governing thermal transport in MOFs. To provide a data-driven perspective into these relationships, here we perform large-scale computational screening of thermal conductivitykin MOFs, leveraging classical molecular dynamics simulations and 10,194 hypothetical MOFs created using the ToBaCCo 3.0 code. We found that high thermal conductivity in MOFs is favored by high densities (> 1.0 g cm⁻³), small pores (< 10 Å), and four-connected metal nodes. We also found that 36 MOFs exhibit ultra-low thermal conductivity (< 0.02 W m⁻¹ K⁻¹), which is primarily due to having extremely large pores (~65 Å). Furthermore, we discovered six hypothetical MOFs with very high thermal conductivity (> 10 W m⁻¹ K⁻¹), the structures of which we describe in additional detail.

    

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