The Electrical Conduction-Type Transition in Se-Free Bi₂Te₃ Thermoelectric Materials by Decoration of Ni Nanoparticles

The composites based on Bi₂Te₃ (BT) have been extensively studied owing to their high thermoelectric performance in the range of room temperature. Herein, we introduced Ni nanoparticles (NPs) into bulk BT to examine the influence of those on the electrical conduction-type transition. As the contents of Ni NPs increased to 0.08 wt %, secondary phases, such as p-type NiTe₂ and/or n-type Ni₂Te₃, were generated in the BT matrix. As a result, the electrical conduction-type transition was observed from n-type to p-type with increase of Ni contents in Ni NPs-introduced BT. Furthermore, the highest power factor was obtained for the 0.02 wt % Ni/Bi₂T₃ sample. The corresponding thermoelectric figure of merit value was measured to be 0.52 at 303 K, the value of which was improved by approximately 19% compared with that of the pristine sample. Based on these results, introducing Ni NPs into the BT matrix is an efficient strategy to control the carrier concentration and thermoelectric properties.