Preparation And Property Modulation Of SnSe Bulk Thermoelectric Materials

Thermoelectric material is a kind of functional material which converts thermal energy into electricity directly and has a prospective application in the energy conversion field.Single-crystal SnSe has become a new promising thermoelectric material since 2014 due to its ultralow thermal conductivity and high ZT values,which has been attracted extensive attentions and become a focus research in thermoelectric materials.However,compare to the single crystal SnSe,the polycrystalline SnSe shows the lower power factors and the enhancement of thermoelectric performance is limited by its poor electrical conductivity.Therefore,there seems to be an urgent issue to improve the electrical transport properties in polycrystalline SnSe.In this dissertation,an efficient method has been employed to quickly synthesize SnSe-based polycrystalline materials by rapid induction melting and rapid induction hot pressing(RIM+RHP).In order to enhance the thermoelectric performance of polycrystalline SnSe,the low dimensional layered MoS2/grapheme was introduced to modify the SnSe structure.The effective doping of SnSe is achieved by using the alkali halide of NaCl,KBr and so on.The main content and conclusions are as follows:1.We investigated the effect on the thermoelectric properties of SnSe by the composite of the layered MoS2/graphene(MoS2/G).The SnSe-x wt%MoS2/G(x=0,0.2,0.4,0.8,1.6,3.2)series of composite samples have been prepared by the RIM+RHP.After introducing the low dimensional layered MoS2/G,we found that an obvious amorphous phase interface,a spinodal decomposition and the layer of MoS2 nanoparticles in the matrix of sample.An electrical conductivity of 70.9 Scm-1 for the sample of SnSe-3.2wt%MoS2/G was obtained at 423K and a ZT value of 0.98 was achieved at 81 0K,which indicates that the incorporation of the low dimensional layered MoS2/G into the SnSe matrix can effectively control the electrical and thermal transport of SnSe and enhance the thermoelectric properties of SnSe materials.2.The influence of Na+ and Cl-co-doped on the thermoelectric properties of SnSe materials was studied.A series of NaxSni-xSeClx(x=0,0.005,0.01,0.02,0.03,0.04)samples have been synthesized by the RIM+RHP.The results show that Na+ and Cl-co-doping not only increases the conductivity of polycrystalline SnSe,but the defects of co-doping further reduces the thermal conductivity of SnSe materials,creating a ZT value of 0.84 in the Nao.005Sno.995SeCl0.005 sample at 81OK.3.We studied the effect of KBr doping on the thermoelectric properties of SnSe materials.KxSn1-xSeBrx(x=0,0.01,0.02,0.03,0.04,0.05,0.06)series of samples have been synthesized by the RIM+RHP.We found that the KBr can improve the carrier concentration of polycrystalline SnSe materials.The electrical conductivity rapidly increased to 39.1 Scm-1 for the K0.05Sno0.95SeBr0.05 sample at 373K and the lattice thermal conductivity reduced to 0.26 W/(m · K),which contributes to a ZT value of 0.85.4.We investigated the effects of alkali-halide of NaM(M=Cl,Br,I)and KX(M=Cl,Br,I)on the thermoelectric properties of polycrystalline SnSe.Results showed that the Br is the most effective in improving the thermoelectric properties of polycrystalline SnSe materials in the doping of 2mol%NaM(M=Cl,Br,I),and fhe ZT value reached 1.15 at 810 K;Meanwhile,the Cl is the best to increase the thermoelectric properties of polycrystalline SnSe materials in the doping of 5mol%KM(M=Cl,Br,I),and the sample’s ZT value reached 1.32 at 810 K.