Preparation And Thermoelectric Properties Of Single Crystalline PbSe

Thermoelectric material is a material that can directly convert thermal energy to electrical energy.It has the advantages of zero noise,no emissions,and the ability to reuse waste heat,which makes it widely used in research and application.Good thermoelectric materials need to have high Seebeck coefficients,high electrical conductivity,and low thermal conductivity.PbSe is considered to be a promising thermoelectric material in the mid-temperature region due to its lower thermal conductivity and better electrical properties.According to literature reports,the thermoelectric figure of merit of thermoelectric alloys PbTe has reached about 2.0,but the content of Te in nature is very small.Compared with this,the content of Se are much higher than Te.PbSe and PbTe are very similar in terms of lattice and electronic structure.In addition,PbSe has a higher melting point and can adapt to higher operating temperatures.Therefore,recently PbSe has been widely studied as a thermoelectric material.This article attempts to use the flux method to prepare PbSe-based single crystal thermoelectric materials.The thermoelectric properties of the material are improved by adjusting the initial amount of the flux.The effect of Bi substitution of Pb on the PbSe band structure is studied first-principles calculation.The main conclusions are as follows:PbSe single crystal thermoelectric material with better crystal quality was prepared by Pb flux method,and the carrier concentration of the material was fine-tuned by adjusting the solvent ratio of Pb.The lattice parameters of all samples increased with the increase of Pb content.The FESEM and TEM results showed that the single crystal PbSe sample prepared by Pb flux method had a complete crystal structure.Thermal analysis showed that the sample had high thermal stability in the mid-temperature range.The ZT value of the n-type PbSe system was significantly improved,and the sample with Pb content x=1.3 obtained a maximum ZT value 1.25at 300 K,which increased by 100%compared with the polycrystalline PbSe sample prepared by ball milling.the maximum electrical conductivity value of 10.53×10⁴S?m^-1 was obtained for the sample with x=1.3.A series of single crystal PbSeBix?x=2.5,3,3.5,4?samples with good thermoelectric properties were prepared by the Bi-flux method.Thermal analysis showed that the sample had high thermal stability in the medium temperature range.XRD results show that the characteristic peaks of all samples are consistent with the NaCl structure with space group Fm3?m.No grain boundaries,cracks or micropores are found in the prepared samples,and the crystal structure has good single crystal structure.The EDS line scan revealed that the elements were uniformly distribute on the single crystal PbSe,and the TEM and SAED further confirmed that the prepared sample had a typical single crystal structure.For sample with x=3,the highest conductivity at 300K reached 20.53×10⁴ S·m^-1.Combining the experimental and theoretical results,Bi replacing Pb is the reasonable result and causing both n-type conduction and resonant states.The sample with x=3.5 achieves the highest power factor of 3.6×10^-3 W·m^-1·K^-2 at 550 K and it increased by about 50%compared to the polycrystalline sample(1.8×10^-3 W·m^-1·K^-2).The PbSe?NaCl?x?x=3,3.5,4,4.5?thermoelectric materials prepared by the NaCl flux method showed excellent electrical transmission properties.The size of the prepared PbSe sample is about 13 mm.SEM images showed that there were no macro defects inside the samples prepared by the NaCl flux method.Both XPS and EPMA results indicated the presence of Na and Cl elements in the sample.The experiments show that by adjusting the initial content of NaCl flux,the carrier concentration of the PbSe sample gradually decreases,and the mobility gradually increases.The PbSe sample with x=4.5 shows the best performance,and the maximum PF value at 690 K is 2.8×10^-33 W·m^-1·K^-2,which has doubled compared with Na-doped PbSe samples prepared by hot pressing,which indicates that the carrier concentration of PbSe samples can be effectively adjusted by adjusting the content of NaCl,and the Power factor of PbSe system can be increased.