Self-assembled 3D flower-like hierarchical Ti-doped Cu3SbSe4 microspheres with ultralow thermal conductivity and high zT

Highlights: • We fabricate self-assembled 3D hierarchical Ti-doped Cu₃SbSe₄ microspheres. • Unique hierarchical structures can strengthen phonon scatterings to reduce κ_tot. • Ti doping Cu₃SbSe₄ can optimize the hole concentration and improve zT. Self-assembled 3D flower-like hierarchical Ti-doped Cu₃SbSe₄ microspheres have been synthesised by a microwave-assisted solvothermal method. Through detailed structural characterization and analysis, we elucidate that the growth temperature is the key factor to tailor the hierarchical Cu₃SbSe₄ microspheres assembled from nanoparticles and nanosheets. Such unique structures can strengthen phonon scatterings, leading to an ultralow thermal conductivity of 0.38 W m⁻¹ K⁻¹ at 623 K in the Ti-doped Cu₃Sb_0.93Ti_0.07Se₄ sample. Ti doping can also increase the hole concentration to the optimal level and consequently enhance the power factor in the Cu₃Sb_0.96Ti_0.04Se₄ sample, resulting in a promising peak zT of ~ 0.59 at 623 K, which approximately doubles that of the pristine Cu₃SbSe₄. This study demonstrates a facile wet chemical method to synthesise large-scale Cu₃SbSe₄-based thermoelectric materials, which provides an alternative methodology to fabricate non-toxic thermoelectric materials.