Enhanced thermoelectric performance of Bi 0.5 Sb 1.5 Te 3 via Ni-doping: A Shift of peak ZT at elevated temperature via suppressing intrinsic excitation

Bi 2 Te 3 -based thermoelectric (TE) materials have been demonstrated to be a potential candidate for mainly thermoelectric cooling/refrigeration applications. However, minority charge carriers excitation at high temperature reduces thermopower which restricts these materials for the use in power generation. In present work, substitution of Ni on Sb site in Bi 0.5 Sb 1.5-x Ni x Te 3 (x = 0, 0.01, 0.04 and 0.08) actuates the system to supress the intrinsic excitation leading to shift in highest ZT to higher temperature regime. The Density functional theory (DFT) calculations and experimental results reveal that Ni in Bi 0.5 Sb 1.5 Te 3 provides the extra holes and slightly reduces the band gap E g which enhances the σ of Ni-doped Bi 0.5 Sb 1.5-x Ni x Te 3 samples and α at elevated temperature. Moreover, Ni-doping in Bi 0.5 Sb 1.5 Te 3 also reduces κ L which is attributed to the phonon scattering due to mass fluctuations and microstructural features such as grain boundary and strain field domain observed from HRTEM investigation. These favourable condition leads to maximum ZT∼1.38 at 433K for Bi 0.5 Sb 1.46 Ni 0.04 Te 3 and ZT avg ∼1.1 between 300K and 503K. Interestingly the calculated theoretical TE conversion device efficiency η of Bi 0.5 Sb 1.46 Ni 0.04 Te 3 (η∼5.5%) was achieved to be nearly twice than the efficiency of matrix Bi 0.5 Sb 1.5 Te 3 (η∼3%). Experimental electronic transport is well corroborated with theoretically estimated DFT results.