Preparation And Thermoelectric Properties Of N-type Bi₂Te₃ Based Composites Incorporated With Conductive Polymer Particles

Thermoelectric materials can directly convert heat and electricity without moving parts and working media,and do not discharge any harmful substances.They can be used for thermoelectric refrigeration and power generation,and their green and environmental protection advantages make them have broad application prospects in the future.At present,the best and only commercial N-type Bi₂Te_2.7Se_0.3 alloy near room temperature has thermoelectric figure of merit ZT less than one,which cannot meet the requirements of large-scale application.Therefore,it has important research significance and application value to explore how to greatly improve its thermoelectric performance.Therefore,the thermoelectric properties of N-type Bi₂Te_2.7Se_0.3 alloy are effectively improved in this study by utilizing composite nano-polymer particles to scatter phonons and using inorganic/organic interface potential to generate energy filtering of carriers.The main results of the thesis are as follows:（1）Bi₂Te_2.7Se_0.3 based composites incorporated with conductive polyaniline（PANI）nanoparticles were prepared and their thermoelectric properties were studied.The results show that the interfacial barrier between PANI and Bi₂Te_2.7Se_0.3 will generate energy filtering effect,which will lead to the enhancement of thermopower S.In addition,lattice thermal conductivity KL of composite systems is significantly reduced.The analysis shows that PANI particles and the phase interface in the composite system enhance phonon scattering.Finally,in the Bi₂Te_2.7Se_0.3/1.5 wt.%PANI composite system,the maximum ZT=1.22（345 K）is obtained,which is about 42%higher than that of Bi₂Te_2.7Se_0.3.（2）Bi₂Te_2.7Se_0.3 based composites incorporated with conductive polypyrrole（PPy）nanoparticles were prepared and their thermoelectric properties were investigated.The results show that κL of the composites decreases significantly due to the strong phonon scattering by the polymer particles and the phase interface in the composite systems.The κL of the composite sample incorporated with 2.0 wt.%PPy is as low as 0.26 W·m-1·K-1 at 300 K,which is 57%lower than that of Bi₂Te_2.7Se_0.3 matrix.Finally,the maximum ZT is 1.19（375 K）and the average ZT value is 1.09（300-500 K）in Bi₂Te_2.7Se_0.3/0.5wt.%PPy sample,which are 34%and 30%higher than that of Bi₂Te_2.7Se_0.3 matrix,respectively.（3）Firstly,Bi₂Te_2.7Se_0.3 based composites incorporated with AgBi3S5 nanoparticles were prepared and their thermoelectric properties were studied.The results show that the incorporation of AgBi3S5 can significantly improve S of the composite systems,so as to maintain high power factor PF.On this basis,Bi₂Te_2.7Se_0.3/1.5wt.%AgBi3S5 composite sample with excellent thermoelectric performance was selected as matrix,and then PPy nanoparticles were incorporated.The results show that the double composite systems can still maintain high PF value because the significant improvement of S makes up for the increase of resistivity conductivity p.In addition,PPy and AgBi3S5 nanoparticles and the phase interface can strongly scatter phonons,thus significantly reduce the κL of Bi₂Te_2.7Se_0.3.Finally,the ZTmax value of the composite sample with 1.5 wt.%AgBi3S5 and 0.5 wt.%PPy reaches 1.30（348 K）,which is 46%larger than that of Bi₂Te_2.7Se_0.3 matrix.