Abstract
Effects of Ag doping and thermal annealing temperature on thermoelectric transport properties of Bi<inf>2</inf>(Se,Te)<inf>3</inf> compounds are investigated. On the basis of the comprehensive analysis of carrier concentration, Hall mobility, and lattice parameter, we identified two Ag-related interstitial (Ag<inf>i</inf>) and substitutional (Ag<inf>Bi</inf>) defects that modulate in different ways the thermoelectric properties of Ag-doped Bi<inf>2</inf>(Se,Te)<inf>3</inf> compounds. When Ag content is less than 0.5 wt %, Ag<inf>i</inf> plays an important role in stabilizing crystal structure and suppressing the formation of donor-like Te vacancy (V<inf>Te</inf>) defects, leading to the decrease in carrier concentration with increasing Ag content. For the heavily doped Bi<inf>2</inf>(Se,Te)<inf>3</inf> compounds (>0.5 wt % Ag), the increasing concentration of Ag<inf>Bi</inf> is held responsible for the increase of electron concentration because formation of Ag<inf>Bi</inf> defects is accompanied by annihilation of hole carriers. The analysis of Seebeck coefficients and temperature-dependent electrical properties suggests that electrons in Ag-doped Bi<inf>2</inf>(Se,Te)<inf>3</inf> compounds are subject to a mixed mode of impurity scattering and lattice scattering. A 10% enhancement of thermoelectric figure-of-merit at room temperature was achieved for 1 wt % Ag-doped Bi<inf>2</inf>(Se,Te)<inf>3</inf> as compared to pristine Bi<inf>2</inf>(Se,Te)<inf>3</inf>.