Evolution of the Intrinsic Point Defects in Bismuth Telluride-Based Thermoelectric Materials

Abstract

In polycrystalline bismuth telluride-based thermoelectric materials, mechanical-deformation-induced donor-like effects can introduce a high concentration of electrons to change the thermoelectric properties through the evolution of intrinsic point defects. However, the evolution law of these point defects during sample preparation remains elusive. Herein, we systematically investigate the evolution of intrinsic point defects in n-type Bi 2 Te 3 -based materials from the perspective of thermodynamics and kinetics, in combination with positron annihilation measurement. It is found that not only the mechanical deformation but also the sintering temperature is vital to the donor-like effect. The mechanical deformation can promote the formation of cation vacancies and facilitate the donor-like effect, and the sintering process can provide excess energy for Bi antisite atoms to surmount the diffusion potential barrier. This work provides us a better understanding of the evolution law of intrinsic point defects in Bi 2 Te 3 -based alloys and guides us to control the carrier concentration by manipulating intrinsic point defects.

Tuning Optimum Temperature Range of Bi2Te3‐Based Thermoelectric Materials by Defect Engineering

“…Therefore the higher N D + can suppress the generation of the minority carriers . The lower carrier concentration is advantageous for the higher S , and the higher carrier concentration can suppress the κ b and the deterioration of S caused by the minority carriers.…”

“…As mentioned above, improving the room temperature zT of n ‐type Bi 2 Te 3 ‐based polycrystals is also important. The extremely high carrier concentration, caused by the donor‐like effect, is one reason for the degraded room temperature zT . Recently, Chen et al.…”

“…The equivalent dopants, such as Se, Sb and S, are neutral, but they may affect the formation of intrinsic point defects thus the carrier concentration. The intrinsic point defects play an important roles in Bi 2 Te 3 ‐based alloys and more attentions have been paid to it recently . The Bi 2 Te 3 and Bi 2 Se 3 ZM ingots are p ‐type and n ‐type semiconductors resulted from the antisite defects and anion vacancies , respectively .…”

“…Similarly, increasing the Se content in Bi 2 (Te,Se) 3 alloys will result in the increasing anion vacancy concentration and hence electron concentration . For the polycrystals, the cation and anion vacancy pairs would be generated during the mechanical deformation and the original would react with as follow during the sintering process, …”

“…With rising temperature, the intrinsic excitation becomes severe and the minority carrier concentration increases, then the bipolar effect gradually dominates, which deteriorates the zT rapidly and restricts their usage in medium temperature. The room temperature zT for n ‐type polycrystals are relatively low comparing to the p ‐type counterparts, so optimizing the room temperature zT for n ‐type Bi 2 Te 3 ‐based polycrystals is also important and meaningful …”