Study On The Preparation And Properties Of PbTe Based Thermoelectric Materials

Since industrial production generates a large amount of waste heat,it is of great significance that the industrial waste heat can be used twice.Reuse of Industrial waste heat reuse reduces waste of resources and means less pollution to the environment.Research on thermoelectric materials has a long history,but there are still two problems in the commercial application of thermoelectric materials:first,the conversion efficiency of thermoelectric materials is still very low;second,the current production cost of thermoelectric materials is high.The existence of a disadvantageous factor restricts the future development of thermoelectric materials.This thesis is mainly to study the preparation and thermoelectric properties of PbTe.The main results are as follows:The pure nano lead telluride was prepared by cyclic circulation method,and then doped with Ag and Sb elements to form Ag_0.8Pb_xSbTe_2+x?LAST alloy?.The Ag_0.8Pb_x SbTe_x+2?x=9,11,13,15?alloy enhances phonon scattering but maintains carrier mobility constant,resulting in higher Seebeck coefficients and conductivity,as well as lower heat conductivity.The experimental study shows that the conductivity of n-type Ag_0.8Pb_x SbTe_x+2?x=9,11,13,15?alloy reached 31×10³ S/m at 600 K.The Seebeck coefficient of the n-type Ag_0.8Pb_xSbTe_x+2?x=9,11,13,15?alloy reached-637?V/K at 350 K.Surfactant was added during the preparation of PbTe by hydrothermal method.When adding cetyltrimethylammonium bromide?CTAB?,the surface morphology of PbTe was still funnel-shaped.When sodium dodecyl sulfate?SDS?was added,there will be a fishbone appearance.This indicates that the surfactant SDS is more effective than CTAB when preparing PbTe by hydrothermal method.The funnel-like PbTe has a higher thermal conductivity than the fishbone PbTe,because the crystallites of funnel-like are the larger,which reduces the crystal face density of the material,and does not maximize the scattering of short-wave phonons,which is not conducive to reducing the thermal conductivity.While the fishbone-like PbTe is surrounded by smaller grains,which is more conducive to scattering phonons with different characteristic length wavelengths,thereby reducing the thermal conductivity.The alkali concentration has a great influence on the morphology and grain size of PbTe.When the alkali concentration is low,there are dense grains on the surface of PbTe.When the alkali concentration is too high,a fishbone PbTe morphology will be appearing.The experimental analysis of the alkali concentration of 4 mol/L is most suitable.An alloy of Ga_xPb_1-xTe?x=0.025,0.045,0.065?was obtained by preparing different proportions of Ga elements.Since the atomic radius of the Ga element is smaller than Pb,the Ga element will replace the position of Pb after doping.The position at which the Ga element replaces the Pb atom in PbTe changes the carrier concentration.For the Ga_xPb_1-xTe?x=0.025,0.045,0.065?alloy,the absolute value of the Seebeck coefficient increases with increasing temperature,and the Seebeck coefficient is-185?V/K at 600K.At 400 K,the power factor of the Ga_xPb_1-xTe?x=0.025,0.045,0.065?alloy reached2.95×10^-33 Wm^-1K^-2.As the temperature increases,the thermal conductivity of the alloy of Ga_xPb_1-xTe?x=0.025,0.045,0.065?gradually decreases.This is due to the doping of Ga element,which greatly improves the conductivity of the compound after doping,result in increasing of the carrier thermal conductivity.