Abstract
The present study aims to see the enhancement in thermoelectric properties of bismuth telluride (Bi(2)Te(3)) annealed at different temperatures (573 and 773 K) through silver (Ag) nano-inclusions (0, 2, 5, 10, 15 and 20 wt %). Transmission electron microscopy (TEM) images of Ag incorporated in Bi(2)Te(3) annealed at 573 K shows tubular, pentagonal, trigonal, circular and hexagonal nanoparticles with sizes of 6-25 nm (for 5 wt % Ag ) and 7-30 nm (for 20 wt % Ag). Ag incorporated in Bi(2)Te(3) annealed at 773 K shows mainly hexagonally shaped structures with particle sizes of 2-20 nm and 40-80 nm (for 5 wt % Ag) and 10-60 nm (for 20 wt % Ag). Interestingly, the samples annealed at 573 K show the highest Seebeck coefficient (S, also called thermopower) at room temperature (p-type behavior) for 5% Ag which is increased ca. five-fold in comparison to Ag-free Bi(2)Te(3), whereas for samples with the same content (5% Ag) annealed at 773 K the increment in thermopower is only about three-fold with a 6.9-fold enhancement of the power factor (S (2)σ). The effect of size and shape of the nanoparticles on thermoelectric properties can be understood on the basis of a carrier-filtering effect that results in an increase in thermopower along with a control over the reduction in electrical conductivity to maintain a high power factor yielding a high figure of merit.