Electrical and thermal transport properties of spark plasma sintered n-type Bi₂Te_3−xSe_x alloys: the combined effect of point defect and Se content

Abstract

Performance enhancement can be realized in p-type Bi 2 Te 3 but hardly in n-type Se-modified Bi 2 Te 3 alloys fabricated by powder processing as compared with conventional ingots. To reveal the reasons and investigate the optimal Se content in fine-grained n-type Bi 2 Te 3Àx Se x materials processed by mechanical alloying (MA) and spark plasma sintering (SPS), the amount of Se was varied in a wide range and electrical transport properties were investigated and discussed in association with the results of Hall measurements. Thermal transport properties were also studied with Raman spectra. It is revealed that different concentrations of point defects are induced by changing the Se content x from 0 to 1.0 in Bi 2 Te 3Àx Se x . The point defects and their interaction (including donor-like effects) not only largely change the carrier concentration and mobility, but also enhance the phonon scattering that would lead to a decrease of thermal conductivity. Consequently, the optimal composition is confirmed as Bi 2 Te 2.2 Se 0.8 with a corresponding carrier concentration of 4.5 Â 10 19 cm À3 and a maximum ZT value of 0.82 at 473 K, approximately 35% increased than that obtained at optimal Bi 2 Te 2.7 Se 0.3 conventionally used for ingots. This work indicates that the point defects as well as their interaction during MA and SPS shift the optimal Se content from traditional x = 0.3 to x = 0.8 in n-type Bi 2 Te 3Àx Se x , demonstrating the importance of comprehensive control of point defects by adjusting the Se content for different processes.

Thermoelectric performance enhancement in n-type Bi2(TeSe)3 alloys owing to nanoscale inhomogeneity combined with a spark plasma-textured microstructure

“…19,20 Our group has already confirmed that Bi 2 Te 2.2 Se 0.8 is the optimal composition for samples prepared by MA and SPS. 21 Bi 2 Te 3 is anisotropic with a layered structure composed of a quintuple atomic series in the order of Te(1)-Bi-Te(2)-Bi-Te(1) along the c-axis. Their electrical and thermal conductivities along the a-axis (in the c-plane) are approximately four and two times higher, respectively, than those along the c-axis of Bi 2 Te 3 .…”

Attaining high mid-temperature performance in (Bi,Sb)2Te3 thermoelectric materials via synergistic optimization

“…Therefore, the goal of upshifting the service temperature in this work is translated into how to conduct intrinsic point defect engineering via extrinsic Sb and In doping. 13,[32][33][34] Intrinsic point defects are primarily entropic defects. They are thermally more robust than extrinsic point defects and therefore favor robust high-temperature performance.…”

Temperature Driven Unusual Reversible p‐ to n‐Type Conduction Switching in Bi2Te2.7Se0.3

“…Hence an electronic semiconductor exhibiting conduction switching can be a good choice for application. Chalcogenide such as bismuth telluride based alloys are electronic semiconductor and they are extensively used as conventional thermoelectric material for converting waste heat into electrical energy in the temperature range of ≤300 °C . Bismuth telluride is a V–VI chalcogenide compounds with narrow band gap semiconductor of 0.16–0.3 eV .…”

“…Chalcogenide such as bismuth telluride based alloys are electronic semiconductor and they are extensively used as conventional thermoelectric material for converting waste heat into electrical energy in the temperature range of ≤300 °C . Bismuth telluride is a V–VI chalcogenide compounds with narrow band gap semiconductor of 0.16–0.3 eV . It has a hexagonal lattice type in space group , and in its structure Te and Bi atomic layers arranged in the order of –Te(1)–Bi–Te(2)–Bi–Te(1)– in the quintpule layer along the c axis direction.…”

“…As revealed by EDX and XPS composition analysis results, we propose that at low temperature ( T < 487 K) the material exhibit p‐type behavior upto 487 K due to dominance of Bi vacancies and antisite defects (Bi Te or Te Bi ) which acts like acceptor impurities. It is reported that each Bi vacancies is accompanied with formation of three holes, Te/Se vacancies leads to the formation of two electrons and antisite effects Bi Te or Te Bi donates one hole . At high temperature ( T > 487 K) the migration of Te(1)/Bi atoms (from Bi Te antiste defects) to the vacant Bi site is easily possible because of the small difference in the elctronegativity as well as in ionic radius of Bi and Te.…”