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Md Mofasser Mallick1 Satish Vitta1

1, Indian Institute of Technology Bombay, Mumbai, , India

Layered cuprous chalcogenides such as Cu2S, Cu2Se and Cu2Te have attracted significant attention recently due to their ‘Phonon-Liquid-Electron-Crystal’ like thermoelectric behavior. Among these three compounds Cu2Se has been reported to exhibit a high figure-of-merit but it lacks stability. Hence in the present work Cu2Te which has a relatively better thermal stability compared to Cu2Se has been explored and its figure-of-merit enhanced by doping both the cation and anion simultaneously. Li- and Se-doped Cu2Te, Cu2-xLixTe1-ySey alloys have been synthesized by a simple, conventional arc melting process. The resulting alloy ingots were characterized without subjecting to any intermediate annealing process. The alloys have two polymorphic phases-a orthorhombic super structure and a hexagonal phase corresponding to P3m1 space group. The hexagonal form however is found to be predominant in all the alloys. Morphologically, the phases have a platelet like layered nanostructure with the plate-like grains oriented in random directions. The alloys exhibit a degenerate semiconducting behavior in the range 300 K to 1000 K. The high temperature electrical resistivity varies from 0.3 mΩcm to 1.4 mΩcm depending on the type and extent of doping. The Seebeck coefficient of all the alloys increases with increasing temperature with the high temperature value in the range 30 µVK-1 to 135 µVK-1. All the alloys have a positive Seebeck coefficient indicating that holes are predominant charge carriers. The highest power factor achieved is 16 µW-1cm-1K-2 for the alloy with Li-0.1 and Se-0.03 substitution. The thermal conductivity of this alloy decreases to 1.6 W-1m-1K-1 at highest temperature resulting in a figure-of-merit of 1.0. An interesting aspect of these alloys is that even at these temperatures they do not exhibit onset of bipolar conduction indicating the robustness of charge carriers.

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