Microstructure And Thermoelectric Properties Of SnTe-Zn(Te/Se/S)

Ⅳ-Ⅵ group semiconductor Sn Te has the same crystal structure（fcc）and similar two valence band structure as PbTe.Resent years,it has attracted widespread attention of scientific research workers because it is non-poisonous.But the disadvantage of Sn Te is also very obvious.The pristine Sn Te has a high concentration of Sn vacancies,resulting in a high carrier concentration.Excessive carrier concentration will adversely affect the material’s Seebeck coefficient.In addition,factors such as excessive energy difference between light and heavy valence bands,small band gap,and high thermal conductivity,also limiting the thermoelectric properties of Sn Te.In this paper,（SnTe）_2.94（In₂Te₃）_0.02 is used as the matrix material,on this basis,the chalcogenide compounds of Zn（ZnTe、ZnSe、ZnS）are introduced,high temperature melting-quenching-long time annealing combined with hot pressing sintering to prepare samples,the microstructure and thermoelectric properties is invesgated by means of scanning electron microscopy,X-ray diffraction,conductivity/Seebeck cofficient system and laser flash diffusivity,the main research results are as follows.The chalcogenide of Zn can increase the carrier concentration of the material to a certain extent without affecting the mobility.Among them,the carrier concentration of the matrix alloy at room temperature is 2.55×10²⁰ cm-3,the carrier concentration of（SnTe）_2.94（In₂Te₃）_0.02-0.12 ZnTe and（SnTe）_2.94（In₂Te₃）_0.02-0.12 ZnSe are 3.63×10²⁰ cm-3 and 3.92×10²⁰ cm-3 respectively.The carrier concentration of（SnTe）_2.94（In₂Te₃）_0.02-0.09 ZnS is about 3.06×10²⁰ cm-3,the improvement content is about 20%.Due to the large increase in conductivity,it effectively compensates for the decrease in Seebeck coefficient,the power factor of（SnTe）_2.94（In₂Te₃）_0.02-0.06 ZnTe at 300 K and（SnTe）_2.94（In₂Te₃）_0.02-0.03 ZnSe at 423 K are 27.4 μW cm^-1 K^-2 and 26.3 μW cm^-1 K^-2 respectively.Compared with the matrix alloy,the improvement content is about 30.5% and 25.2 % respectively.For Sn Te-based thermoelectric materials,the commonly used method to reduce lattice thermal conductivity is to introduce point defects or nano second phase.In this paper,the content of the second phase in the material increases as the chalcogenide content of Zn increases.However,the size of the observable second phase is about several hundred nanometers to several micrometers.The decrease in lattice thermal conductivity mainly comes from point defect scattering.Among them,the lowest lattice thermal conductivity of（SnTe）_2.94（In₂Te₃）_0.02-0.12 ZnSe at 873 K is about 0.96 Wm^-1 K^-1.The thermoelectric figure of merit of each alloy is not much different.The output power density and conversion efficiency are significantly improved.Under the condition that the the length of the material in the device is L=2 mm and the cold side temperature Tc=300 K,when the hot side temperature is 870 K,the maximum values of（SnTe）_2.94（In₂Te₃）_0.02-0.03 ZnSe are 10.4 W cm^-2 and 9.0% respectively.Compared with the matrix alloy,the improvement content are 9.1% and 9.5% respectively.