Article.pdf

F. Neves^a, L. Esperto^a, I. Figueira^a, J. Mascarenhas^a, J. B. Correia^a, H. Ferreira^b, E.B. Lopes^b, A.P. Gonçalves^b

^aLNEG, Laboratório Nacional de Energia e Geologia, Estrada do Paço do Lumiar, 22, 1649-038 Lisboa, Portugal

^bC2TN, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal

LocalEnergy project (http://localenergy.lneg.pt/) focuses on the valorization of endogenous resources (solar and mineral) through the development of energy-harvesting applications based on the tetrahedrite mineral, which offers a high exploitation potential. Naturally occurring tetrahedrite series consists of earth-abundant and relatively non-toxic elements and can be generically expressed as Cu₆[Cu₄(Fe,Zn)₂]Sb₄S₁₃. Besides that, tetrahedrites show p-type semiconductor material behavior with high Seebeck coefficient, a complex cubic crystal structure and extremely low thermal conductivities at moderate temperatures, reaching zT~0.7 around 700K after adequate doping. Owing to these properties they are considered as a suitable and promising thermoelectric material. However, the development of cost-effective and high yield sustainable technologies to produce synthetic tetrahedrite is still a major and relevant issue. In this work, we report a fast-solid‐state synthesis method of Cu_12-x-yZn_xFe_ySb₄S_13-z tetrahedrites, with x, y ≤ 1 and z ≤ 0.3, based on powder sintering. Key concepts in the proposed research methodology are the direct synthesis of nanocrystalline tetrahedrites with a mechanical alloying step (MA) and maintaining the nanostructure during the subsequent densification step through hot pressing (HP) in order to produce thermoelectric components consisting of nanocrystalline tetrahedrite. The influence of the chemical composition and of the doping elements will be presented in relation to the structural and thermal stability.

Figure 1 - X-ray diffractograms of the Cu₁₁Zn_1.0Sb₄S_12.7 samples after MA (2 h) and after HP (515 ºC / 1h30m). 

Acknowledgments

This work is funded by national funds through the FCT – Fundação para a Ciência e a Tecnologia, I.P., under the project PTDC/EAM-PEC/29905/2017 (LocalEnergy - Local Resources for Multifunctional Tetrahedrite-based Energy-Harvesting Applications).