Preparation And Performance Of Cobalt?Nickel-doped Bismuth Sulfide-Based Thermoelectric Materials

Thermoelectric materials can realize the mutual transformation between thermal and electric energy through thermoelectric effect,promote the multi-level effective use of energy,and discard no pollutant in the process,which provides a new way to solve the problem of energy shortage and environmental pollution.Among them,Bismuth sulfide compound is considered as a promising thermoelectric material due to their high element abundance,non-toxicity and low thermal conductivity.But its electrical conductivity is not high,resulting in a low z T value,which retards its practical application.Researchers optimize the thermoelectric properties of bismuth sulfide by band engineering and nanostructuring.At present,the preparation of metal sulfides mostly adopts smelting method,which requires a high temperature and a long time.However,the solution method has a much lower reaction temperature and the preparation process consumes less energy and time.Against this background,bismuth sulfide thermoelectric materials were studied.Bismuth sulfide thermoelectric materials were successfully prepared by solution method and spark plasma sintering.The thermoelectric properties of bismuth sulfide were improved by Co doping and Ni doping.Bismuth sulfide thermoelectric materials with low thermal conductivity is obtained.The main research content of this paper is as follows:(1)Bi₂S₃-based powder materials with nominal stoichiometric ratios of Bi_2-xCo_xS₃(x=0,0.04,0.10,0.13,0.16 and 0.20)and Bi_2-xNi_xS₃(x=0,0.03,0.04,0.10 and 0.16)were prepared by the solution method.The results show that the Bi₂S₃ prepared by the solution method belongs to the monoclinic crystal system and exhibits anisotropic structure.The sample is a one-dimensional nanorod oriented along the[001]direction,and its length is 200?500 nm.The densified Bi_2-xCo_xS₃ and Bi_2-xNi_xS₃ blocks with structural anisotropy were successfully prepared by spark plasma sintering,and the crystal grains grew from 200?500 nm before sintering to 1?2?m after sintering.(2)In the vertical sintering pressure direction,at 773 K,the lattice thermal conductivity of Bi1.₈₄Co_0.16S₃ is extremely low,only 0.23 W/m·K,and the electronic conductivity is 169 S/cm,which is 2.56 times of Bi₂S₃.And the z T value of Bi_1.90Co_0.10S₃ is 0.54,which is 12.5%higher than that of undoped Bi₂S₃.(3)In the vertical sintering pressure direction,at 773 K,the lattice thermal conductivity of Bi_1.84Ni_0.16S₃ is 0.31 W/m·K,which is 38.0%lower than that of the pure Bi₂S₃,and the electronic conductivity is 157 S/cm,which is 2.37 times that of undoped Bi₂S₃.In addition,in parallel to the sintering pressure direction,the z T value of Bi_1.96Ni_0.04S₃ at 773 K is 0.47,which is 12.1%higher than that of Bi₂S₃.(4)The thermoelectric property of the sample in the direction of perpendicular to sintering pressure is better than that in the direction of parallel to sintering pressure.