Synergistic Influence of Cu Intercalation on Electronic and Thermal Properties of n-Type CuxBi2Te2.7Se0.3 Polycrystalline Alloys

Cu intercalation is known to be an effective strategy for improving the reproducibility of thermoelectric properties in n-type Bi2Te2.7Se0.3 alloys. In this study, the effect of Cu intercalation on the electronic and thermal properties of n-type Bi2Te2.7Se0.3 polycrystalline alloys was investigated systematically with respect to bipolar conduction and point defect phonon scattering by using the two-band model and Debye–Callaway model. The mobility and concentration of majority carriers (electrons) increased simultaneously while those of minority carriers (holes) decreased with increase in the amount of Cu. Thus, bipolar conduction, which has a detrimental effect on both electronic and thermal properties, was gradually reduced in the Cu-intercalated Bi2Te2.7Se0.3 samples. The reduction of the lattice thermal conductivity was analyzed quantitatively to show that Cu intercalation was also effective for enhancing point defect phonon scattering as interstitials. Thus, Cu intercalation in n-type Bi2Te2.7Se0.3 alloys enhanced the thermoelectric properties by controlling bipolar conduction and phonon scattering synergistically.