Regulation Of Thermoelectric Properties Of Polycrystalline SnSe By Double Doping At Sn Site

SnSe single crystals have emerged in the thermoelectric materials system for their excellent thermoelectric properties,and attracted many researchers to study them in depth.Although SnSe single crystal has good thermoelectric properties,polycrystalline SnSe is more conducive to large-scale application in terms of production conditions.Therefore,the thermoelectric properties of polycrystalline SnSe have become the research focus of researchers.Compared with reported SnSe single crystal,pure polycrystalline SnSe has lower conductivity and higher thermal conductivity.Researchers optimize the thermoelectric properties of polycrystalline SnSe by band engineering,nanostructuring and all-scale hierarchical structure and so on.At present,most of the dimensionless figure of merit of polycrystalline SnSe are about 1.1.Against this background,polycrystalline SnSe thermoelectric materials were studied.Polycrystalline SnSe thermoelectric materials were successfully prepared by low temperature hydrothermal synthesis and spark plasma sintering.The electrical and thermal properties of polycrystalline SnSe were improved by Pb doping and introducing Sn vacancies,?Pb,Zn?co-doping and?Mn,Zn?co-doping.Polycrystalline SnSe thermoelectric materials with high thermoelectric value were obtained.The main contents of this paper are as follows:1.Pb-doped and Sn vacancies containing polycrystalline SnSe were prepared by hydrothermal synthesis method.The study found that enhanced carrier concentration induced by Pb doping and introducing Sn vacancies contributes to enhancements of electrical conductivity and power factor of polycrystalline SnSe.Pb substitution and Sn vacancy enhance the lattice anharmonicity by forming weakening bonds,while suddenly changing the local bond environment to enhance phonon scattering.Pb substitution can also introduce a huge stress field in SnSe grains.The thermal conductivity can be greatly reduced by lattice anharmonicity strengthening and applying huge strain field.?_L is reduced to as low as 0.18 Wm^-1K^-11 in Sn_0.92Pb_0.03Se sample at 773 K.As a result,a remarkable high ZT of?1.4 was achieved at 773K in Sn_0.93Pb_0.02Se sample through lattice anharmonicity strengthening and strain engineering.2.?Pb,Zn?codoped polycrystalline SnSe were prepared by hydrothermal synthesis method.The study found that Pb doping and Zn and introduction of PbSe secondary phase contribute to remarkable enhancement of electrical conductivity and power factor.The peak power factor reaches to 5.43?W cm^-1 K^-22 in Sn_0.98Pb_0.01Zn_0.01Se.Phase-separation and nanostructuring strategies construct all-hierarchical architectures to scattering phonons.The lattice thermal conductivity is significantly reduced to 0.13 W m^-1 K^-1 in Sn_0.96Pb_0.01Zn_0.03Se through constructing all-hierarchical architectures and dual-atom point-defect scattering.A record high ZT=2.2 was achieved in polycrystalline Sn_0.98Pb_0.01Zn_0.01Se through enhancing electrical transport properties while keeping ultralow thermal conductivity.This work offers new strategies to realize high value of ZT in polycrystalline SnSe.3.?Mn,Zn?codoped polycrystalline SnSe were prepared by hydrothermal synthesis method.The study found that Zn doping can effectively increase the hole carrier concentration of polycrystalline SnSe,and then improve the electrical conductivity and power factor of polycrystalline SnSe.The power factor of polycrystalline Sn_0.96Mn_0.01Zn_0.03Se sample reaches5.08?W cm^-1 K^-2.The lattice thermal conductivity of polycrystalline SnSe can be effectively reduced by diatomic point defect scattering.The lowest lattice thermal conductivity of all doped Sn_0.96Mn_0.01Zn_0.03Se samples is 0.236 W m^-1 K^-1 at 873 K.By maintaining low thermal conductivity while enhancing electrical transport performance,polycrystalline SnSe obtained a good high ZT of 1.4.