Effects of replacing Cu with Ni and Ni-Zn on the structural, magnetic, and thermoelectric properties of the solution-processed Cu12Sb4S13 tetrahedrites

This study investigates the effects of copper substitution with transition metals , specifically nickel (Ni) and nickel-zinc (Ni-Zn), on the thermoelectric performance of Cu 12 Sb 4 S 13 tetrahedrites . The tetrahedrite nanocrystals were synthesized using a scalable, cost-effective polyol method, followed by annealing, cold pressing, and sintering. X-ray diffraction (XRD) analysis revealed that Ni and Ni-Zn substitutions result in a single-phase tetrahedrite with a cubic crystal structure. The increase in Ni content level causes a contraction of the unit cell, while the increase in Zn-Ni content level leads to an initial unit cell expansion followed by further contraction, indicating successful incorporation of transition metals at Cu sites. Raman spectroscopy showed a progressive disorder in the sublattices with Cu−S and Sb−S bonds due to Ni and Zn incorporation, with no evidence of secondary phase formation. Scanning electron microscopy (SEM) and elemental mapping confirmed that the tetrahedrites were dense and compositionally uniform. Magnetic susceptibility measurements indicated that Ni substitution increases the density of states (DOS) at the Fermi level , while Ni-Zn substitution slightly reduces it. The analysis of thermoelectric properties revealed that Ni substitution reduces both power factor ( PF ) and electronic thermal conductivity ( κ e ) in the tetrahedrites, while Ni-Zn substitution results in the exceptionally low κ e values, achieving a reduction of up to 88 % compared to pristine Cu 12 Sb 4 S 13 . This study highlights the potential of Ni and Ni-Zn substitutions at Cu sites in the tetrahedrites as promising, low-cost materials for thermoelectric applications, offering a feasible route for enhancing their thermoelectric performance through transition metal substitution.