Copper Chalcogenide-Copper Tetrahedrite Composites-A New Concept for Stable Thermoelectric Materials Based on the Chalcogenide System.

Andrzej Mikuła,Paweł Nieroda,Krzysztof Mars,Paweł Rutkowski

doi:10.3390/ma14102635

Abstract

For the first time, an alternative way of improving the stability of Cu-based thermoelectric materials is proposed, with the investigation of two different copper chalcogenide–copper tetrahedrite composites, rich in sulfur and selenium anions, respectively. Based on the preliminary DFT results, which indicate the instability of Sb-doped copper chalcogenide, the Cu1.97S–Cu12Sb4S13 and Cu2−xSe–Cu3SbSe3 composites are obtained using melt-solidification techniques, with the tetrahedrite phase concentration varying from 1 to 10 wt.%. Room temperature structural analysis (XRD, SEM) indicates the two-phase structure of the materials, with ternary phase precipitates embed within the copper chalcogenide matrix. The proposed solution allows for successful blocking of excessive Cu migration, with stable electrical conductivity and Seebeck coefficient values over subsequent thermal cycles. The materials exhibit a p-type, semimetallic character with high stability, represented by a near-constant power factor (PF)—temperature dependences between individual cycles. Finally, the thermoelectric figure-of-merit ZT parameter reaches about 0.26 (623 K) for the Cu1.97S–Cu12Sb4S13 system, in which case increasing content of tetrahedrite is a beneficial effect, and about 0.44 (623 K) for the Cu2−xSe–Cu3SbSe3 system, where increasing the content of Cu3SbSe3 negatively influences the thermoelectric performance.

Highlights

In the era of global energy and the climate crisis, the development of low-pollution energy-conversion technologies constitutes one of the top priorities among the scientific community
Copper chalcogenides with a general formula of Cu2−x Ch are often classified as so-called superionic conductors, the unique transport properties of which can be described on the basis of the phonon-liquid electron-crystal (PLEC) theory [5,8]
Based on the combined theoretical and and experimental studies, it is shown that the reduction of excessive Cu ion migration can experimental studies, it is shown that the reduction of excessive Cu ion migration can be be achieved by obtaining a mixture of stable binary and ternary Cu-Sb-Ch phases

Summary

Introduction

In the era of global energy and the climate crisis, the development of low-pollution energy-conversion technologies constitutes one of the top priorities among the scientific community. While a vast number of different structural and compositional substructures can be distinguished in Cu2−x Ch systems, high-temperature, highly symmetrical cubic structures (Figure 1a,b, phase transition at about 600 K for both Cu2−x S and Cu2−x Se, respectively) are by far the most interesting with regard to energy-conversion technologies. They are characterized by the high diffusivity values of copper ions resulting from multiple structural positions, between which the copper ions can jump in short time periods, while low-mobility chalcogenide ions create a crystalline pathway for charge carriers.

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