Regulating The Thermoelectric Transport Behavior Of SnSe By Doping/Composite Microstructure

The energy lost about 60%in the form of waste heat in the energy conversion process,and there is a huge market demand for the full utilization of waste heat.SnSe thermoelectric materials meet the strategic requirement of the environment and resource development of waste heat with reusing.Its elemental crust is abundant,the cost is low,and it does not pollute the environment which has huge engineering application prospects and economic value.In this paper,vacuum smelting method was used to prepare polycrystalline SnSei+x(x=-0.05,-0.03,-0.01,0,0.01,0.03)powder samples,and vacancy defects were controlled by composition design;the series of SnSe1+x blocks were prepared by spark plasma sintering.Through XRD structure characterization in different directions,the results show that there is a clear preferred orientation on the plane perpendicular to the pressure axis,the(400)diffraction peak becomes the main diffraction peak,and both ion vacancies can promote the preferred orientation.The results of the hall coefficient testing show that Vsn significantly increases the carrier concentration along the direction perpendicular to the pressure axis,which mainly due to the adjustment of the Fermi level by Vsn.The σ of SnSe1.01 reaches 3570S/m and the Power factor(PF)reaches 528μW/m/K2 at 773K.Both Vsn and Vse significantly decrease thermal conductivity in the direction parallel to the pressure axis and have a slight increase in the direction vertical to the pressure axis.Through coordinated regulation of vacant microstructures,the ZT value of SnSei.oi sample is 0.87 at 773K.In order to improve the thermoelectric properties of the vacant samples,SnSe1.03 samples were doped with Co/Pb/Cu elements to explore the effect of double doping on the material properties.According to the XRD results,Co2+/Pb2+/Cu+ hydronium enters the crystal lattice of the SnSe1.03 sample respectively,and SnSe2 phase is detected in both directions.Doping these elements is not effective to improve the thermoelectric performance.As the effect of Pb,SnSe/SnSe1.03 samples were compounded with Pb sheets to form solid-state diffusion,then powders were prepared into solid blocks and the two samples were annealed as comparison finally.The interplanar spacing of SnSe is reduced duing to texture after compositing Pb,and the interplanar spacing becomes larger after annealing as more Pb2+come into the lattice of SnSe.The elemental Pb accelerates the transport of carriers between grains before annealing for Pb/SnSe in the direction vertical to the pressure axis;Pb and Se combine to form a Pb-Se bondings at the same time,and the difference in electronegativity is reducing,then decrease the localization of electrons and promote the movement of electrons to the conduction band.The combined effect of Pb2+ and Pb-Se bonding increase the carrier concentration to 10-11*1018/cm3,so the σ is greatly improved.XPS results show that part of simple substance Pb is transformed into Pb-Se bonding after annealing,and the content of elemental Pb decrease.Although the inter-grain resistance increases after annealing and the elemental Pb scatter carriers which reduce the carrier mobility,however the low-energy carriers are dispersed by the lattice distortion.That increases the Seebeck coefficient to 471 μV/K at 773K,the PF is 623 uW/m/K2。And the ZT value reaches 1.12 with the point defect scattering phonon which reduce the thermal conductivity.The thermoelectric performance also has improved along the parallel direction.In the Pb/SnSe1.03 sample,SnSe2 phase appears which hinders carrier transport with reducing Vsn.The loss of electrical performance is larger although the thermal conductivity decreases after annealing in the vertical direction,and the ZT value of SnSe is less improved.