Electronic and thermal transport properties of complex structured cu-bi-se thermoelectric compound with low lattice thermal conductivity

Monoclinic Cu_x+yBi_5-ySe₈ structure has multiple disorders, such as randomly distributed substitutional and interstitial disorders by Cu as well as asymmetrical disorders by Se. Herein, we report the correlation of electronic and thermal properties with the structural complexities of Cu_x+yBi_5-ySe₈. It is found that the interstitial Cu site plays an important role not only to increase the electrical conductivity due to the generation of electron carriers but also to reduce the thermal conductivity mainly due to the phonon scattering by mass fluctuation. With impurity doping at the interstitial Cu site, an extremely low lattice thermal conductivity of 0.32 W·m^-1·K ^-1 was achieved at 560 K. These synergetic effects result in the enhanced dimensionless figure of merit (ZT).