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Some transition-metal dichalcogenides have been actively studied recently owing to their potential for use as thermoelectric materials due to their superior electronic transport properties. Iron-based chalcogenides, FeTe2, FeSe2 and FeS2, are narrow bandgap (~1 eV) semiconductors that could be considered as cost-effective thermoelectric materials. Herein, the thermoelectric and electrical transport properties FeSe2–FeS2 system are investigated. A series of polycrystalline samples of the nominal composition of FeSe2−xSx (x = 0, 0.2, 0.4, 0.6, and 0.8) samples are synthesized by a conventional solid-state reaction. A single orthorhombic phase of FeSe2 is successfully synthesized for x = 0, 0.2, and 0.4, while secondary phases (Fe7S8 or FeS2) are identified as well for x = 0.6 and 0.8. The lattice parameters gradually decrease gradually with S content increase to x = 0.6, suggesting that S atoms are successfully substituted at the Se sites in the FeSe2 orthorhombic crystal structure. The electrical conductivity increases gradually with the S content, whereas the positive Seebeck coefficient decreases gradually with the S content at 300 K. The maximum power factor of 0.55 mW/mK2 at 600 K was seen for x = 0.2, which is a 10% increase compared to the pristine FeSe2 sample. Interestingly, the total thermal conductivity at 300 K of 7.96 W/mK (x = 0) decreases gradually and significantly to 2.58 W/mK for x = 0.6 owing to the point-defect phonon scattering by the partial substitution of S atoms at the Se site. As a result, a maximum thermoelectric figure of merit of 0.079 is obtained for the FeSe1.8S0.2 (x = 0.2) sample at 600 K, which is 18% higher than that of the pristine FeSe2 sample.

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Transition metal dichalcogenides have being actively studied on the account of their large density-of-state effective mass and low lattice thermal conductivity. Herein, thermoelectric and electrical transport properties of MoSe 2 -MoTe 2 system are investigated. A series of Mo(Se 1−x Te x ) 2 (x = 0, .25, .5, .75, and 1) polycrystalline samples was synthesized by conventional solid-state reaction. Single hexagonal phase was identified for each sample without secondary phase, confirming the formation of complete solid solutions between MoSe 2 and MoTe 2 .The electrical conductivity and magnitude of the Seebeck coefficient increased simultaneously with increasing Te content x at high temperatures, with the power factor following the same trend. As results, the MoTe 2 sample exhibited the maximum power factor of .014 mW/(m K 2 ) at 823 K. The lattice thermal conductivities of the alloyed samples (x = .25, .5, and .75) significantly decreased compared to MoSe 2 and MoTe 2 owing to point defect phonon scattering via anion substitution, which is verified by the Debye-Callaway model. A maximum zT of .0044 was obtained for MoTe 2 sample at 773 K; however, the calculated quality factor B values of the samples with x = .75 and 1 at 773 K were almost identical, suggesting that a further enhancement of zT can be achieved by optimizing an n H of the Mo(Se 0.25 Te 0.75 ) 2 sample. K E Y W O R D Schalcogenides, thermal conductivity, thermoelectric properties 1 where S, σ, κ tot , and T are the Seebeck coefficient, electrical conductivity, total thermal conductivity, and absolute temperature, respectively, and generally, the κ tot is divided 3170

Bi₂Te₃-based alloys have been extensively studied as thermoelectric materials near room temperature. In this study, the electrical, thermal, and thermoelectric transport properties of a series of Co-doped <i>n</i>-type Cu_0.008Bi₂Te_2.6Se_0.4 polycrystalline alloys (Cu_0.008Bi_2−xCo_xTe_2.6Se_0.4, <i>x</i> = 0, 0.03, 0.06, 0.09 and 0.12) are investigated. The electrical conductivity of the Cu_0.008Bi_1.97Co_0.03Te_2.6Se_0.4 (<i>x</i> = 0.03) sample was significantly enhanced, by 34%, to 1199 S/cm compared to 793 S/cm of the pristine Cu_0.008Bi₂Te_2.6Se_0.4 (<i>x</i> = 0) sample at 300 K, and gradually decreased to 906 S/cm for <i>x</i> = 0.12 upon further doping. Power factors of the Co-doped samples decreased compared to the 3.26 mW/mK² of the pristine Cu_0.008Bi₂Te_2.6Se_0.4 sample at 300 K. Meanwhile, the power factor of the Cu_0.008Bi_1.97Co_0.03Te_2.6Se_0.4 (<i>x</i> = 0.03) sample became higher at 520 K. The lattice thermal conductivities of the Co-doped samples decreased due to additional point defect phonon scattering by the Co dopant. Consequently, the <i>zT</i> for the Cu_0.008Bi_1.97Co_0.03Te_2.6Se_0.4 alloy at 520 K was 0.83, which is approximately 15% larger than that of pristine Cu_0.008Bi₂Te_2.6Se_0.4, while the <i>zT</i> of the Cu doped samples at 300 K was smaller than that of the pristine Cu_0.008Bi₂Te_2.6Se_0.4 sample. Electrical transport properties of the Co-doped Cu_0.008Bi_2−xCo_xTe_2.6Se_0.4 samples were analyzed by experimental phenomenological parameters, including the density-of-state, effective mass, weighted mobility, and quality factor.