Structural, substructural, magnetic, and electrical properties of Ti-substituted tetrahedrites with enhanced thermoelectric performance

Abstract

This study demonstrates the effect of substituting titanium (Ti) in place of copper (Cu) in Cu_12−xTi_xSb₄S₁₃ tetrahedrite solid solutions on their structural, substructural, magnetic, and thermoelectric (TE) properties. Tetrahedrite materials with a nominal Ti substitution content of x = 0.0, 0.3, 0.5, 1.0, and 1.5 are synthesized via a low-cost and scalable polyol method using posterior annealing, pressing, and sintering treatments. X-ray diffraction analysis and Raman spectroscopy confirm that the solid solutions contain nanocrystallites with sizes ranging from ∼60 to ∼65 nm, which possess a single tetrahedrite phase. The replacement of Ti at Cu sites induces convoluted changes in the lattice parameter, unit cell volume, coherent scattering domains, and levels of macrodeformations, macrostresses, and dislocations. Moreover, the crystalline quality of the tetrahedrites is observed to depend on Ti substitution content. Scanning electron microscopy and energy-dispersive X-ray analysis indicate that the tetrahedrites comprise grains with sizes ranging from ∼70 to ∼200 nm with homogeneous distribution of constituent elements and closeness to stoichiometric composition. Ti substitution decreases the electrical conductivity and increases Seebeck coefficient because of hole concentration reduction caused by Ti⁴⁺ substitution at Cu¹⁺/Cu²⁺ sites. The power factor slightly decreases with increased Ti content; however, electronic thermal conductivity notably reduces by two times in comparison to pure tetrahedrite. Furthermore, magnetic parameters of the tetrahedrites are identified to assess the change in the electronic density of states. This study provides a practical approach for the fabrication of low-cost and efficient TE materials based on environmentally benign and earth-abundant Ti-substituted tetrahedrites.