Mechanisms of thermoelectric efficiency enhancement in Lu-doped Bi2Te3

The Lu x Bi2−x Te3 thermoelectrics with x = 0, 0.05, 0.1 and 0.2 have been prepared by microwave-solvothermal method and spark plasma sintering. All the compositions are semiconductors of n-type conductivity. It was found that electron concentration increases and electron mobility decreases with x increasing. The Lu doping results in remarkable increase of the thermoelectric figure-of-merit from ~0.4 for undoped Bi2Te3 up to ~0.9 for Bi1.9Lu0.1Te3. Enhancing the thermoelectric efficiency at the doping is originated from: (i) increase of the electron concentration since the Lu atoms behave as donors in the Bi2Te3 lattice that decreases the specific electrical resistance, (ii) increase of the Seebeck coefficient via increase of the density-of-states effective mass for conduction band, (iii) decrease of the total thermal conductivity via forming the point defects like antisite defects and Lu atoms substituting for the Bi sites. Formation of narrow non-parabolic impurity band lying near the Fermi energy with sharp density of states is believed to be responsible for increasing the density-of-states effective mass and decreasing the electron contribution to the total thermal conductivity.