Thermoelectric Properties of Ag-Doped Bi2(Se,Te)3 Compounds: Dual Electronic Nature of Ag-Related Lattice Defects

Effects of Ag doping and thermal annealing temperature on thermoelectric transport properties of Bi-2(Se,Te)(3) compounds aye investigated. On the basis of the comprehensive analysis of cattier,concentration, Hall mobility, and lattice parameter, we identified two Ag-related interstitial (Ag-I) and substitutional (Ag-Bi) defects that modulate in diffetent ways the thermoelectric properties of Ag-doped Bi-2(Se,Te)(3) compounds. When Ag content is less than 0.5 wt %, Ag-i plays an important role in stabilizing crystal structure and suppressing the formation of donor-like Te vacancy (V-Te) defect, leading to the decrease in carrier concentration with increasing Ag content. For the heavily doped Bi-2(Se,Te)(3) compounds (>0.5 wt % Ag), the increasing concentration of Ag-Bi is held responsible for the increase of electron concentration because formation of Ag-Bi 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-2(Se,Te)(3) 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-2(Se,Te)(3) as Compared to pristine Bi-2(Se,Te)(3).