Synthesis and Thermoelectric Performance of (Bi_0.25Sb_0.75)₂Te₃ Polycrystals Dispersed with Ag and BN

Abstract

Mechanical alloying followed by pulse-discharge sintering (MA-PDS) is used to fabricate bulk (Bi_0.25Sb_0.75)₂Te₃ polycrystals dispersed with metal Ag, ceramic BN or both. During sintering, the dispersed second phase particles, especially BN, effectively hinder the growth of the (Bi, Sb)₂Te₃ matrix phase, giving rise to a refined microstructure in compacts. Property measurements demonstrate that the metal Ag is effective in raising electrical conductivity, while the ceramic BN is effective in decreasing thermal conductivity through reinforced phonon scattering. By adding Ag alone, we have identified a large potential for further improving the room-temperature figure of merit of the (Bi_0.25Sb_0.75)₂Te₃ mother alloy. The maximum figure of merit appears at 0.02 mass% Ag with value in the order of 3.4×10⁻³ K⁻¹, which is 18% higher than that of the mother alloy. This result is of practical significance. Because of the deterioration of Seebeck coefficient, addition of BN either alone or in combination with Ag does not produce a favorable figure of merit.