Synergistic Influence of Cu Intercalation on Electronic and Thermal Properties of n-Type Cu _x Bi ₂ Te _2.7 Se _0.3 Polycrystalline Alloys

Cu intercalation is known to be an effective strategy for improving the reproducibility of thermoelectric properties in n-type Bi ₂ Te _2.7 Se _0.3 alloys. In this study, the effect of Cu intercalation on the electronic and thermal properties of n-type Bi ₂ Te _2.7 Se _0.3 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 Bi ₂ Te _2.7 Se _0.3 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 Bi ₂ Te _2.7 Se _0.3 alloys enhanced the thermoelectric properties by controlling bipolar conduction and phonon scattering synergistically.