Modulation Doping Leads to Optimized Thermoelectric Properties in <i>n</i>‐Type Bi<sub>6</sub>Cu<sub>2</sub>Se<sub>4</sub>O<sub>6</sub> due to Interface Effects
Junqing Zheng, Siqi Wang, Zhe Zhao, Xiang Gao, Tao Hong, Li‐Dong Zhao
Abstract
Abstract Heterogeneous composites consisting of Bi 6 Cu 2 Se 3.6 Cl 0.4 O 6 and Bi 2 O 2 Se are prepared according to the concept of modulation doping. With prominently increased carrier mobility and almost unchanged effective mass, the electrical transport properties are considerably optimized resulting in a peak power factor ≈1.8 µW cm −1 K −2 at 873 K, although the carrier concentration is slightly deteriorated. Meanwhile, the lattice thermal conductivity is lowered to ≈0.62 W m −1 K −1 due to the introduction of the second phase. The modified Self‐consistent Effective Medium Theory is utilized to explain the deeper mechanism of modulation doping. The enhancement of apparent carrier mobility is derived from the highly active phase interfaces as fast carrier transport channels, while the reduced apparent thermal conductivity is ascribed to the existence of thermal resistance at the phase interfaces. Ultimately, an optimized ZT ≈0.23 is obtained at 873 K in Bi 6 Cu 2 Se 3.6 Cl 0.4 O 6 + 13% Bi 2 O 2 Se. This research demonstrates the effectiveness of modulation doping for optimizing thermoelectric properties once again, and provides the direct microstructure observation and consistent theoretical model calculation to emphasize the role of interface effects in modulation doping, which should be probably applicable to other thermoelectrics.