Preparation, Interface Structure And Mechanic Properties Of Bi₂Te₃/CoSb₃Thermoelectric Materials For Wide Temperature

The wide-temperature range thermoelectric (TE) material is a key material that makes the TE device realizes high conversion efficiency. In this thesis, the homogeneously TE materials of low-temperature Bi2Te3(room temperature~200℃) and intermediate-temperature CoSb3(200~500℃) are used as research objects. The chemical compositions of two kinds of homogeneous materials were determined based on the matching principle of carrier concentration. A two-step spark plasma sintering method was developed to fabricate a series of n-type and p-type Bi2Te3/CoSb3wide-temperature range TE materials with different interfacial structures. The effects of different transition layers on the interfacial microstructure and mechanical property have been investigated. The main research works include:(1) The TE properties of n-type Bi2Te2.7Seo.3homogeneous material is best in the Bi2Te2.65+xSe0.35-x(x=0~0.15,△x=0.05) materials, the largest ZT value reached0.92at450K. The TE properties of p-type Bi0.48Sb1.52Te3.04homogeneous material is highest in Bio.48Sb1.52Te3+x(x=0~0.06,△x=0.02) materials, the largest ZT value reached1.31at300K. The filling fraction of Ba and In for n-type BaxInyCo4Sb12and the level of iron substitution for Co for p-type Bao.3Ino.3FexCo4.xSb12(x=1~3,△x=0.5) have been optimized based on the matching principle of carrier concentration. As a result, the carrier concentration of n-type Bao.4Ino.4Co4Sb12matches well with that of n-type Bi2Te2.7Seo.3, while that of p-type Ba0.3In0.3FeCo3Sb12was close to that of p-type Bi0.48Sb1.52Te3.04. Using the four homogeneous materials as raw materials, a series of n-type and p-type Bi2Te3/CoSb3wide-temperature range TE materials were successfully fabricated by the two-step spark plasma sintering method.(2) Interfacial microstructure and mechanical property of n-type Bi2Te3/CoSb3wide-temperature range TE materials have been studied. The results indicate that the interfacial microstructure are most compact, the crack was eliminated completely and the highest flexural strength reached12.76MPa which increased by144%compared to that of the sample without gradient layer, when the optimal FS/BT volume ratios of transition layers are composed of Ba0.4In0.4Co4Sb12(FS) and Bi2Te2.7Seo.3(BT) were3:7-5:5-7:3from FS side to BT side (namely3GLs-II gradient interface).(3) Interfacial microstructure and mechanical property of p-type Bi2Te3/CoSb3wide-temperature range TE materials have been studied. The results indicate that the interfacial microstructure are most compact, the crack was eliminated completely and the highest flexural strength reached13.68MPa which increased by116%compared to that of the sample without gradient layer, when the optimal FS/BT volume ratios of transition layers are composed of Ba0.3In0.3FeCo3Sb12(FS) and Bi0.48Sb1.52Te3.04(BT) were3:7-5:5-7:3from FS side to BT side (namely3GLs-II gradient interface).(4) The interfacial microstructures of Bi2Te3/CoSb3wide-temperature range TE materials have been investigated with SEM. The results indicate that the interfacial structure composed of transition layers may effectively relax the thermal stress induced by the large difference of thermal expansion coefficients between Bi2Te3and CoSb3. As a result, the macroscopic cracks completely disappeared, the highest flexural strength remarkably enhanced.