Preparation And Thermoelectric Properties Optimization Of Zone-melted N-type Bismuth Telluride-based Materials

Bismuth telluride（Bi₂Te₃）based thermoelectric materials are widely used in thermoelectric power generation and refrigeration near room temperature.At present,the thermoelectric properties（ZT）of n-type BiTeSe-based materials are still at a low level,there is an urgent need to improved.In this paper,n-type Bi₂Te_2.7Se_0.3 materials are taken as the research object,and the thermoelectric properties of n-type zone-melted Bi₂Te_2.7Se_0.3materials are comprehensively improved through doping the intrinsically low thermal conductivity Ag₉GaSe₆ materials and co-doped Bi I₃ and Sn Sb₂Te₄ at the same time.The specific research content and results are as follows:Alloyed Ag₉GaSe₆ in zone-melted Bi₂Te_2.7Se_0.3 materials,the electrical properties of the materials were optimized.The power factor of the optimized materials was improved to48.1μW cm^-1K^-2,and the lattice and bipolar thermal conductivity（κ_l+κ_b）was decreased to0.90 W m^-1 K^-1.The peak ZT(ZT_max)and average ZT(ZT_ave)from 300 to 500 K of the zone-melted Bi₂Te_2.7Se_0.3-0.14 wt.%Ag₉GaSe₆ samples were reached to 1.05 and 0.89,respectively,and its ZT_ave is 20%higher than that of the commercial BiTeSe-based materials.Then the Ag₉GaSe₆ was alloyed to Bi₂Te_2.7Se_0.3 materials after annealed at 600℃for 72 h.The power factor of composited after annealed Ag₉GaSe₆ samples was increased to 51.4μW cm^-1 K^-2,and theκ_l+κ_b was decreased to 0.92 W m^-1 K^-1.The ZT_max and ZT_avefrom 300to 500 K of Bi₂Te_2.7Se_0.3-0.14 wt.%annealed Ag₉GaSe₆ samples reached 1.0 and 0.86,respectively,and its ZT_ave is 16%higher than that of commercial BiTeSe-based materials.Co-doped Bi I₃ and Sn Sb₂Te₄ optimized the thermoelectric properties of zone-melted Bi₂Te_2.7Se_0.3 materials.The carrier concentration of doped Bi I₃ samples was optimized to2.60×10¹⁹ cm^-3,the power factor of the zone-melted materials reached the high level of 55.3μW cm^-1 K^-2,and the ZT_max is significantly increased to 1.21.Due to doped Bi I₃ inhibited the bipolar effect,the highest ZT_ave from 300 to 500 K of the materials is reached 1.04.Alloyed Sn Sb₂Te₄ further increases the carrier concentration of the materials to 5.36×10¹⁹cm^-3,the power factor of the materials improved to 58.4μW cm^-1K^-2,theκ_l+κ_b decreased to 0.73 W m^-1 K^-1.The ZT_max of Bi₂Te_2.7Se_0.3-0.15 wt.%Bi I₃-0.15 wt.%Sn Sb₂Te₄ samples is improved to 1.30,its ZT_max is about 35%higher than that of commercial BiTeSe-based materials.Based on the research results of this paper,the highest performance zone-melted materials was applied to the near room temperature thermoelectric power generation,and the thermoelectric devices with practical application value were successfully developed.The experimental results show that the materials prepared in this paper have advantages over the current commercial zone-melted BiTeSe-based materials in the application of thermal power generation near room temperature.