Optimizing Thermoelectric Properties Of Lead Telluride Materials Via Various Preparation Processes

Thermoelectric materials are a family of materials able to directly convert heat to electricity.In the context of energy shortage,this research is today of crucial importance.The application of thermoelectric materials is divided into two aspects of refrigeration and power generation.Thermoelectric materials have many advantages compared to other energy materials,such as stable,noiseless,sustainable,portable and safe.PbTe-based materials are traditional middle-range temperature thermoelectric materials.They are popular with their superior electrical property and lower thermal conductivity that gives them good performances.This work studies different preparation processes of pure PbTe and doped PbTe compounds materials.The aim is to find the best preparation process to get the highest possible performance with this material.Firstly,n-type PbTe materials are far inferior to those of p-type PbTe thermoelectric materials,so we chose n-type materials as the research object.Halogen group elements and PbTe materials shows good performance,so the n-type doping elements come from halogen group.This work mainly include the research of pure PbTe,the research of iodine doped PbTe and single dope and co-dope base on the first two parts.For each technique,the electrical and thermal properties are measured experimentally and the figure of merit is calculated.Optimization of the optimum preparation process for pure lead telluride materials.By analyzing the experimental data of different groups,we find that the pure lead telluride materials grinded by hand have the best properties under water cooling.The best figure of merit is closely to 0.4.In addition,both hand milling and ball milling can improve electrical conductivity and reduce thermal conductivity.In another hand,cooling rate have no effects to the electric property,but the faster cooling rate the lower thermal conductivity.Optimization of the optimum preparation process for iodine doped PbTe materials.various iodine doping amounts are studied with the compound PbTe_1-xI_x?x=0,002,0.003,0.004,0.005,0.006?.According the research before,ingot combined with furnace cooling samples achieved a peak figure of merit of 1.35 at 723K with a doping amount x=0.004while the average figure of merit is 0.9368.The peak figure of merit achieved at x=0.005is the best with 1.39 at 773K.However,the average figure of merit is lower than at x=0.004.Furnace cooling and ingot samples show the best proformance mainly due to the higher power factor and lower lattice thermal conductivity especially at the low temperature.Carrier mobility is about 1200 cm²/VS when the doping amount is at 0.004and 0.005 in the room temperature.Through hot corrosion we observed in optical microscope that the grain size of furnace cooling and ingot samples are much larger than other samples,so their carrier mobility are higher than others.Finally,the repeatly experiments show the error is limited in fifteen percent.This work is meanful for industry.The research of halogen elements single doping and co-doping.According the study before,the preparation process is furnace cooling and ingot combination.They are PbTe_0.996Cl_0.004,PbTe_0.996Br_0.004,PbTe_0.996I_0.004,PbTe_0.996I_0.003Cl_0.001,PbTe_0.996I_0.003Br_0.001,PbTe_0.996Cl_0.002Br_0.002,PbTe_0.995Cl_0.002Br_0.003.We fund that the larger numbers of orders the better performance.Based on the whole research process,the optimum preparation process of pure lead telluride and iodine doped lead telluride materials is different.The figure of merit of furnace cooling and ingot samples can compared with the highest property reported before.In addition,co-doping cannot improve the performance of samples,but their peformance can improve by the goes up numbers of orders.Research suggestion is making larger samples to improve the performance stability.