| Abstract |
| Because n-type Bi2Te3-based materials exhibit lower thermoelectric performance than p-type materials and because their thermoelectric properties are sensitively changed by the composition and carrier concentration, optimizing these aspects in n-type materials is necessary to improve the thermoelectric figure of merit (ZT). In this study, the thermoelectric performance of n-type Bi2Te3-based materials was improved by reducing thermal conductivity through the formation of a Bi2Te3-Bi2Se3 solid solution, Bi2Te3-ySey and optimizing the carrier concentration through doping. As the amount of Se increased in Bi2Te3-ySey, the carrier concentration decreased, resulting in decreased electrical and thermal conductivities and increased Seebeck coefficients. As a result, Bi2Te2.85Se0.15 exhibited ZT = 0.56 at 323 K, and Bi2Te2.4Se0.6 exhibited ZT = 0.60 at 423 K. Among the Bi2Te3-ySey solid solutions, the doping effect was investigated for Bi2Te2.85Se0.15 and Bi2Te2.7Se0.3, which recorded excellent thermoelectric performance at low temperatures. When halogen element (I) was doped, the power factor improved owing to the increase in carrier concentration, and the thermal conductivity decreased. As a result, the ZT values were greatly enhanced to ZT = 0.90 at 423 K for Bi2Te2.85Se0.15:I0.005 and ZT = 1.13 at 423 K for Bi2Te2.7Se0.3:I0.0075. When the transition elements (Cu and Ag) were doped, the power factor was improved by the increase in Seebeck coefficient, and thereby Bi2Te2.85Se0.15:Cu0.01 and Bi2Te2.85Se0.15:Ag0.01 exhibited ZT = 0.76 and ZT = 0.75 at 323 K, respectively, and Bi2Te2.7Se0.3:Cu0.01 exhibited ZT = 0.73 at 423 K. Conversely, doping with other transition elements (Ni and Zn), as well as group-III (Al and In) and group-IV (Ge and Sn) elements, resulted in power factors and thermal conductivities that were similar to or slightly less than those of undoped Bi2Te2.85Se0.15, leading to minimal or no improvement in ZT. Next, n-type Bi2Te2.85Se0.15:I0.005 and Bi2Te2.7Se0.3:I0.0075, which exhibited the best thermoelectric performances, were fabricated as bulky compacts, and the uniformity of their thermoelectric properties were evaluated.
(Received 2 January, 2024; Accepted 6 February, 2024) |
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| Key Words |
| thermoelectric, chalcogenide, bismuth telluride, uniformity |
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