Preparation Of Cu₃SbSe₄ Based Multi-scale Microsphere And The Optimization Study On Its Thermoelectric Properties

Thermoelectric materials can make the direct conversion between waste heat and electricity without moving parts,offer a green and sustainable solution to overcome the global energy crisis.Cu₃SbSe₄ is a ternary copper-based chalcogenide semiconductor which has relatively small direct bandgap of⁰.29 eV.Its unique crystal structure leads to a low lattice thermal conductivity and it's a very promising medium-temperature thermoelectric material.However,there is still a gap between the electrical transport properties of Cu₃SbSe₄ and PbTe,which is the best medium-temperature thermoelectric material.There is still much room to improve it.In order to improve the thermoelectric properties of Cu₃SbSe₄,we do the following researchs:Cu₃SbSe₄ microspheres with self-assembled hierarchical structure have been synthesized by a microwave-assisted solvothermal method,the formation of hierarchical nanostructure might be the assembly then-assemble mechanism.We elucidate that the microwave stimulation and growth temperature are the key factor to tailor the hierarchical Cu₃SbSe₄ microspheres assembled from nanoparticles and nanosheets.Hierarchical structure contains multi-scale grains which can scatter phonons with various frequencies,makes the lattice thermal conductivity of Cu₃SbSe₄ is much lower than that reported in other literatures.The Cu₃SbSe₄ bulk was prepared by liquid phase method combined with SPS?spark plasma sintering?and the suitable sintering temperature was determined by the DSC of Cu₃SbSe₄ powder.The powder sample was annealed before sintering to completely remove the ethylenediamine which is solvent remaining in the sample,and the effect of different annealing temperatures on the microstructure and electrical properties of Cu₃SbSe₄ were explored,we find that the sample sintered after annealing at 573 K which has the highest density and best electrical properties,and finally determine the best preparation process for the Cu₃SbSe₄ bulk.Cu₃Sb_1-xTi_xSe₄ smaples were obtained after introducing Ti at the Sb site of Cu₃SbSe₄.With the point defect scattering and increased grain boundary scattering caused by Ti doping,the thermal conductivity is further reduced,leading to an ultralow thermal conductivity of 0.38 Wm^-1K^-1 at 623 K in the Ti-doped Cu₃Sb_0.93Ti_0.07Se₄sample.Meanwhile,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 of⁰.59 at 623 K,which approximately doubles that of the pristine Cu₃SbSe₄.