Preparation And Transport Properties Of Highly Textured Nanocrystalline N-type Bi₂Te₃

Thermoelectric material is a kind of semiconductor functional material that uses the movement of carriers in a solid to realize thermoelectric conversion.It can be used for thermoelectric power generation and thermoelectric refrigeration.Bismuth telluride-based thermoelectric materials are relatively mature commercial thermoelectric materials with a wide range of applications.Commercial single crystal bismuth telluride has excellent thermoelectric properties,but poor mechanical properties and low yield.The laboratory nanostructured bismuth telluride has better mechanical properties,but its thermoelectric performance is lower than that of commercial bismuth telluride,especially n-type bismuth telluride.Therefore,this thesis selects n-type bismuth telluride-based thermoelectric materials as the main research object,and conducts research from two aspects of preparation process and composition optimization to improve the thermoelectric and mechanical properties of the material.The n-type bismuth telluride system thermoelectric material is prepared by smelting+melting spin quenching+hot pressing sintering.The microstructure analysis and composition analysis of the samples obtained at each stage of the preparation process found that the composition was uniform,the structure was uniform,and there was no second phase.It is proved that the best melting spin quenching copper roll speed is 4000r/min.Under this parameter,the peak ZT value of the n-type Bi₂Te_2.7Se_0.3 sample prepared by melting spin quenching is 0.61,which appears at 200?.Further optimize the doping of the n-type Bi₂Te_2.7Se_0.3 composition.The composition of Cu_0.01Bi_1.995In_0.005Te_2.7Se_0.3was discovered,and the maximum value of ZT was 0.81 at 100?,and the maximum temperature was moved to the low temperature range.In the process of composition optimization,a sample with Cu_0.01Bi_1.995In_0.005Te_2.7Se_0.3+(Bi I₃)_0.15(wt%)composition was prepared,and the maximum ZT value was 0.75,which appeared at 150?.And in the range of 200?-250?,the ZT value of the doped Bi I3 sample is higher than that of the undoped sample,which provides important theoretical support for the segmented bismuth telluride-based thermoelectric device.We further designed the micro-nano texture sintering method,the best Cu_0.01Bi_1.995In_0.005Te_2.7Se_0.3 composition was micro-nano texture sintered,and the maximum value of ZT was 0.85,which appeared at 100?.Compared with the commercial ZM zone melting sample,it has increased by 7%,and compared with the nano-polycrystalline Cu_0.01Bi_1.995In_0.005Te_2.7Se_0.3 bulk sample,it has increased by 5%.Finally,the mechanical strength of samples prepared by different processes was characterized,that is,compressive strength and micro Vickers hardness.The results show that the compressive strength of the samples prepared by the micro-nano texture method will increase by 270%compared with the commercial samples,and the micro Vickers hardness will increase by 110%.