Exploring the thermoelectric behavior of spark plasma sintered Fe7-xCoxS8 compounds

Abstract

Sulfide-based materials are emerging as viable alternatives for the current state-of-the-art thermoelectric materials, which usually are composed of toxic, expensive and scarce elements. Here, a systematic study of one such inexpensive and environmentally friendly sulfide-based system, i.e. Fe7-xCoxS8 pyrrhotite-type compounds that were synthesized by solid-state reaction and densified by Spark Plasma Sintering are investigated for their structural and thermoelectric properties. We report that substitution of Co for Fe in pyrrhotites: (i) induces structural transition from monoclinic 4C superstructure to trigonal 3C superstructure; (ii) modifies the magnetic behavior by decreasing the magnetic ordering temperature and magnetization; (iii) alters the type of dominant charge carriers (from p-to n-type) and enhances their electrical transport properties; (iv) mitigates the phonon contribution to the thermal conductivity; and (v) amplifies the thermoelectric figure of merit when compared with that of pristine pyrrhotites.