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1. Measured and simulated thermoelectric properties of FeAs _2−x Se _x ( x = 0.30–1.0): from marcasite to arsenopyrite structure

   https://doi.org/10.1039/d0ma00371a  

   Perez, Christopher J.; Devlin, Kasey P.; Skaggs, Callista M.; Tan, Xiaoyan; Frank, Corey E.; Badger, Jackson R.; Kang, Chang-Jong; Emge, Thomas J.; Kauzlarich, Susan M.; Taufour, Valentin; et al (August 2020, Materials Advances)

   null (Ed.)

   FeAs 2−x Se x ( x = 0.30–1.0) samples were synthesized as phase pure powders by conventional solid-state techniques and as single crystals ( x = 0.50) from chemical vapor transport. The composition of the crystals was determined to be Fe 1.025(3) As 1.55(3) Se 0.42(3) , crystallizing in the marcasite structure type, Pnnm space group. FeAs 2−x Se x (0 < x < 1) was found to undergo a marcasite-to-arsenopyrite ( P 2 1 / c space group) structural phase transition at x ∼ 0.65. The structures are similar, with the marcasite structure best described as a solid solution of As/Se, whereas the arsenopyrite has ordered anion sites. Magnetic susceptibility and thermoelectric property measurements from 300–2 K were performed on single crystals, FeAs 1.50 Se 0.50 . Paramagnetic behavior is observed from 300 to 17 K and a Seebeck coefficient of −33 μV K −1 , an electrical resistivity of 4.07 mΩ cm, and a very low κ l of 0.22 W m −1 K −1 at 300 K are observed. In order to determine the impact of the structural transition on the high-temperature thermoelectric properties, polycrystalline FeAs 2−x Se x ( x = 0.30, 0.75, 0.85, 1.0) samples were consolidated into dense pellets for measurements of thermoelectric properties. The x = 0.85 sample shows the best thermoelectric performance. The electronic structure of FeAsSe was calculated with DFT and transport properties were approximately modeled above 500 K. 

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2. 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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3. Ethanol exposure can inhibit red spruce ( Picea rubens ) seed germination

   https://doi.org/10.15258/sst.2018.46.2.07  

   Butnor, John R.; Verrico, Brittany M.; Vankus, Victor; Keller, Stephen R. (June 2018, Seed Science and Technology)

   Flotation of seeds in solvents is a common means of separating unfilled and filled seeds. While a few protocols for processing red spruce (Picea rubens) seeds recommend ethanol flotation, delayed and reduced germination have been reported. We conducted an ethanol bioassay on seeds previously stored at -20°C to quantify the concentration required to separate red spruce seeds and the effects on germination. We used seeds from Canada (CAN) that had been exposed to ethanol during processing, and seeds from the United States (USA) that had not been exposed to ethanol during processing. Seeds were exposed to 10 ethanol concentrations (10-100%) and deionised water was used as a control. The effective concentration of ethanol for 50% (EC50) of the seeds to sink ranged by source from 70.9 to 90.7%, with all seeds sinking in 100% ethanol. The use of less than 100% ethanol is not adequate for seed separation, as some filled seeds could float and be mistakenly categorised as unfilled. The mean EC50 of ethanol that inhibits germination was significantly higher for USA sources (52.7%), than for CAN sources (40.8%; P < 0.05). Ethanol concentrations that inhibited germination coincided with delays in germination. The mechanism of phytotoxity was not determined; however, damage during extraction, desiccation and storage at -20°C are potential sources. We recommend separating red spruce seeds by physical means rather than ethanol flotation to avoid potential negative impacts on germination. 

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4. Thermoelectric properties of copper chalcogenide alloys deposited via the solution-phase using a thiol–amine solvent mixture

   https://doi.org/10.1039/c6ra15929j  

   Ma, Yuanyu; Vartak, Prathamesh B.; Nagaraj, Prajwal; Wang, Robert Y. (January 2016, RSC Advances)

   There has been a growing interest in solution-phase routes to thermoelectric materials due to the decreased costs and novel device architectures that these methods enable. Many excellent thermoelectric materials are metal chalcogenide semiconductors and the ability to create soluble metal chalcogenide semiconductor precursors using thiol–amine solvent mixtures was recently demonstrated by others. In this paper, we report the first thermoelectric property measurements on metal chalcogenide thin films made in this manner. We create Cu 2−x Se y S 1−y and Ag-doped Cu 2−x Se y S 1−y thin films and study the interrelationship between their composition and room temperature thermoelectric properties. We find that the precursor annealing temperature affects the metal : chalcogen ratio, and leads to charge carrier concentration changes that affect the Seebeck coefficient and electrical conductivity. Increasing the Se : S ratio increases electrical conductivity and decreases the Seebeck coefficient. We also find that incorporating Ag into the Cu 2−x Se y S 1−y film leads to appreciable improvements in thermoelectric performance by increasing the Seebeck coefficient and decreasing thermal conductivity. Overall, we find that the room temperature thermoelectric properties of these solution-processed materials are comparable to measurements on Cu 2−x Se alloys made via conventional thermoelectric material processing methods. Achieving parity between solution-phase processing and conventional processing is an important milestone and demonstrates the promise of this binary solvent approach as a solution-phase route to thermoelectric materials. 

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5. Thermoelectric transport contribution from topological surface states vs 2D-electron gas in 10 nm Bi ₂ Se ₃

   https://doi.org/10.1063/5.0100991  

   Nimmagadda, Lakshmi Amulya; Bai, Yang; Rajagopal, Manjunath C.; Suresh Babu, Soorya; Eckstein, James N.; Sinha, Sanjiv (October 2022, Journal of Applied Physics)

   Topological surface states (TSSs) coexist with a rapidly formed two-dimensional electron gas (2DEG) at the surface of Bi 2 Se 3 . While this complex band structure has been widely studied for its interactions between the two states in terms of electrical conductivity and carrier density, the resulting thermopower has not been investigated as thoroughly. Here, we report measurements of the temperature dependent Seebeck coefficient ( S) and electrical conductivity ( σ) on an undoped 10 nm thin Bi 2 Se 3 film over the temperature range of 100–300 K to find an overall metal-like behavior. The measured S is consistent with the theory when assuming that both the TSS and the 2DEG contribute to thermoelectric transport. Our analysis further shows that the coefficient corresponds to a Fermi level situated well above the conduction band minima of the 2DEG, resulting in comparable contributions from the TSS and the 2DEG. The thermoelectric power factor ( S 2 σ) at 300 K increases by 10%–30% over the bulk. This work provides insights into understanding and enhancing thermoelectric phenomena in topological insulators. 

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