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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. Experimental validation of high thermoelectric performance in RECuZnP ₂ predicted by high-throughput DFT calculations

   https://doi.org/10.1039/D0MH01112F  

   Pöhls, Jan-Hendrik; Chanakian, Sevan; Park, Junsoo; Ganose, Alex M.; Dunn, Alexander; Friesen, Nick; Bhattacharya, Amit; Hogan, Brea; Bux, Sabah; Jain, Anubhav; et al (January 2021, Materials Horizons)

   null (Ed.)

   Accurate density functional theory calculations of the interrelated properties of thermoelectric materials entail high computational cost, especially as crystal structures increase in complexity and size. New methods involving ab initio scattering and transport (AMSET) and compressive sensing lattice dynamics are used to compute the transport properties of quaternary CaAl 2 Si 2 -type rare-earth phosphides RECuZnP 2 (RE = Pr, Nd, Er), which were identified to be promising thermoelectrics from high-throughput screening of 20 000 disordered compounds. Experimental measurements of the transport properties agree well with the computed values. Compounds with stiff bulk moduli (>80 GPa) and high speeds of sound (>3500 m s −1 ) such as RECuZnP 2 are typically dismissed as thermoelectric materials because they are expected to exhibit high lattice thermal conductivity. However, RECuZnP 2 exhibits not only low electrical resistivity, but also low lattice thermal conductivity (∼1 W m −1 K −1 ). Contrary to prior assumptions, polar-optical phonon scattering was revealed by AMSET to be the primary mechanism limiting the electronic mobility of these compounds, raising questions about existing assumptions of scattering mechanisms in this class of thermoelectric materials. The resulting thermoelectric performance ( zT of 0.5 for ErCuZnP 2 at 800 K) is among the best observed in phosphides and can likely be improved with further optimization. 

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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. Potential for high thermoelectric performance in n-type Zintl compounds: a case study of Ba doped KAlSb ₄

   https://doi.org/10.1039/c6ta09532a  

   Ortiz, Brenden R.; Gorai, Prashun; Krishna, Lakshmi; Mow, Rachel; Lopez, Armando; McKinney, Robert; Stevanović, Vladan; Toberer, Eric S. (January 2017, Journal of Materials Chemistry A)

   High-throughput calculations (first-principles density functional theory and semi-empirical transport models) have the potential to guide the discovery of new thermoelectric materials. Herein we have computationally assessed the potential for thermoelectric performance of 145 complex Zintl pnictides. Of the 145 Zintl compounds assessed, 17% show promising n-type transport properties, compared with only 6% showing promising p-type transport. We predict that n-type Zintl compounds should exhibit high mobility μ n while maintaining the low thermal conductivity κ L typical of Zintl phases. Thus, not only do candidate n-type Zintls outnumber their p-type counterparts, but they may also exhibit improved thermoelectric performance. From the computational search, we have selected n-type KAlSb 4 as a promising thermoelectric material. Synthesis and characterization of polycrystalline KAlSb 4 reveals non-degenerate n-type transport. With Ba substitution, the carrier concentration is tuned between 10 18 and 10 19 e − cm −3 with a maximum Ba solubility of 0.7% on the K site. High temperature transport measurements confirm a high μ n (50 cm 2 V −1 s −1 ) coupled with a near minimum κ L (0.5 W m −1 K −1 ) at 370 °C. Together, these properties yield a zT of 0.7 at 370 °C for the composition K 0.99 Ba 0.01 AlSb 4 . Based on the theoretical predictions and subsequent experimental validation, we find significant motivation for the exploration of n-type thermoelectric performance in other Zintl pnictides. 

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5. Zintl Phase Compounds Mg3Sb2−xBix (x = 0, 1, and 2) Monolayers: Electronic, Phonon and Thermoelectric Properties From ab Initio Calculations

   https://doi.org/10.3389/fmech.2022.876655  

   Chang, Zheng; Ma, Jing; Yuan, Kunpeng; Zheng, Jiongzhi; Wei, Bin; Al-Fahdi, Mohammed; Gao, Yufei; Zhang, Xiaoliang; Shao, Hezhu; Hu, Ming; et al (April 2022, Frontiers in Mechanical Engineering)

   The Mg 3 Sb 2− x Bi x family has emerged as the potential candidates for thermoelectric applications due to their ultra-low lattice thermal conductivity ( κ L ) at room temperature (RT) and structural complexity. Here, using ab initio calculations of the electron-phonon averaged (EPA) approximation coupled with Boltzmann transport equation (BTE), we have studied electronic, phonon and thermoelectric properties of Mg 3 Sb 2− x Bi x (x = 0, 1, and 2) monolayers. In violation of common mass-trend expectations, increasing Bi element content with heavier Zintl phase compounds yields an abnormal change in κ L in two-dimensional Mg 3 Sb 2− x Bi x crystals at RT (∼0.51, 1.86, and 0.25 W/mK for Mg 3 Sb 2 , Mg 3 SbBi, and Mg 3 Bi 2 ). The κ L trend was detailedly analyzed via the phonon heat capacity, group velocity and lifetime parameters. Based on quantitative electronic band structures, the electronic bonding through the crystal orbital Hamilton population (COHP) and electron local function analysis we reveal the underlying mechanism for the semiconductor-semimetallic transition of Mg 3 Sb 2-− x Bi x compounds, and these electronic transport properties (Seebeck coefficient, electrical conductivity, and electronic thermal conductivity) were calculated. We demonstrate that the highest dimensionless figure of merit ZT of Mg 3 Sb 2− x Bi x compounds with increasing Bi content can reach ∼1.6, 0.2, and 0.6 at 700 K, respectively. Our results can indicate that replacing heavier anion element in Zintl phase Mg 3 Sb 2− x Bi x materials go beyond common expectations (a heavier atom always lead to a lower κ L from Slack’s theory), which provide a novel insight for regulating thermoelectric performance without restricting conventional heavy atomic mass approach. 

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