Carrier Concentration Control And Thermoelectric Performance Optimization Of Bismuth Telluride Based Materials

Bi₂Te₃-based compound,one of the benchmark room-temperature thermoelectric materials,has presented its huge potential for solid-state refrigeration.However,the early onset of intrinsic excitation caused by narrow band gap leads to that the ZT drastically decreases with temperature increasing,which limits the application on low-temperature power generation.Herein,carrier optimization is used to suppress the intrinsic excitation,thus increasing the ZT value and broadening the serving temperature range.Cu-In co-doping is employed in p-type Bi_0.4Sb_1.6Te₃ to increase the carrier concentration and delay the onset of intrinsic excitation,thereby leading to an improvement of the power factor in whole measuring temperature range.Moreover,due to the size or mass difference between dopants and the matrix elements,a large number of point defects will be introduced into the lattice to effectively enhance the phonons scattering and reduce the lattice thermal conductivity.As a result,the ZT value of Cu-In co-doped Bi_0.4Sb_1.6Te₃ is remarkably improved up to 1.19,which is 10% higher than the matrix materials.MgB₂ doping can also increase the carrier concentration of Bi_0.4Sb_1.6Te₃ materials,which suppress the intrinsic excitation and optimize the electrical properties.Then,in addition to the point defects caused by the size or mass differences between Mg and Sb/Bi,the B might be precipitate as additional phononscattering center to decrease the lattice thermal conductivity.Ultimately,a high average ZT of 1.0 between 30 ? and 300 ? is obtained for the Bi_0.4Sb_1.595Te₃/0.005?MgB₂?,which is 21% higher than the matrix.We also add excess Te to achieve the carrier optimization in n-type Bi₂Te₃ alloys.As a result,the incensement of carrier concentration leads to a large improvement for the power factor between 30 ? and 250 ?.And for the phonon transport,the lattice thermal conductivity is significantly reduced due to the formation of anion antisite defect 0)4)· and the second phase of Te.Taken together,the maximum ZT is increased up to 0.78 at 118 ? for the Bi₂Te₃+0.3wt%Te,and the average ZT reaches up to 0.67 within 30 ??250 ?.