The natural chalcopyrite mineral CuFeS 2 is a semi-conductor material with potential for thermoelectric applications. This study presents the thermoelectric properties -electrical resistivity ρ, Seebeck coefficient S and thermal conductivity κ -of the substituted on the Cu site and/or sulfur deficiency CuFeS 2 chalcopyrite based series Cu 1-x M x FeS 2-y (M = Mn, Co,Ni, x ≤ 0.05 and y ≤ 0.02). All samples have been densified by Spark Plasma Sintering, allowing proper measurements of S, ρ and κ at high temperature. All compounds show n-type semi-conducting properties with large absolute values of S, from -220 to -340 µV.K -1 . Maximum ZT values up to 0.20 at 623 K were obtained for Cu 0.97 Mn 0.03 FeS 2 and Cu 0.98 Co 0.02 FeS 1.98 . The veracity of Mn for Cu substitution into the structure has been confirmed by EDS analyzes, coupled to electron diffraction within a transmission electron microscope. The latter study demonstrates the existence of twinned domains. The thermal conductivity reaches values as low as κ~1.2 W.m -1 .K -1 at 623 K. Magnetic properties of a Mn substituted sample did not show any significant modification in the magnetic behavior compared to the pristine CuFeS 2 compound. The small negative magnetoresistance observed in CuFeS 2 of about -2% at 5 K in 9 T is degraded in the Mn substituted sample. Cu 0.94 Mn 0.06 FeS 2 in terms of charge, Mn would be then 4+ charged. ZT are given in Fig. 8d, the highest ZT is found for Cu 0.98 Co 0.02 FeS 1.98 with ZT = 0.20 at 623 K. This value is similar with the previously reported Cu 0.94 Co 0.06 FeS 2 . It is found at 623 K that the resistivity and the Seebeck coefficient of Cu 0.98 Co 0.02 FeS 1.98 and Cu 0.94 Co 0.06 FeS 2 were comparable, with │S│= 247 and 240 µV.K -1 and ρ = 0.95 and 1.05 mΩ.cm, respectively.Conclusion SPS process optimization and substitution/deficiency study on the Cu 1-x M x FeS 2-y series with M = Mn, Co, Ni; x ≤ 0.05 and y ≤ 0.02 have been successfully carried out. In these substitutions ranges, the chalcopyrite is formed without significant amount of impurities.Among the three transition metals: Co, Ni and Mn, the solid solution with Mn has been more
A new ternary layered compound In2Ge2Te6, belonging to the hexatellurogermanate family has been synthesized from the reaction of appropriate amounts of the pure elements at high temperature in sealed silica tubes.
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