Competing Effects of Enhanced Density-of-States Effective Mass and Reduced Mobility on the Thermoelectric Properties of Ni-Doped Sb2Te3

Abstract

Sb2Te3 alloys are well-known p-type thermoelectric material exhibiting strong thermoelectric performance in the mid-tem-perature range, and Sb2Te3 composition serves as the parent compound for many of the highest-performing thermoelectric materials in the low-to-mid temperature range, including (Bi, Sb)(2)Te-3 and In-doped Sb2Te3. This study systematically investigates the thermoelectric transport properties of Ni-doped Sb2Te3 alloys with nominal compositions of (Sb1 - xNix)(2)Te-3(x = 0, 0.015, 0.03, 0.045, and 0.06). Ni substitution at Sb sites effectively increased the Hall carrier concentration from 5.41 x 10(19) cm(-3) (x = 0) to 8.41 x 10(19) cm(-3) (x = 0.06). Although the density-of-states effective mass (md*) increased with Ni content, a substantial reduction in non-degenerate mobility led to an overall 20% decrease in the power factor. Regarding thermal transport, the reduction in lattice thermal conductivity was offset by a significant increase in electronic thermal conductivity, resulting in a net increase in total thermal conductivity. Consequently, the maximum thermoelectric figure of merit (zT) decreased from that of the pristine sample, with the lowest zT of 0.31 observed for the x = 0.06 sample at 300 K, a similar to 17% reduction. However, analysis based on the single parabolic band (SPB) model revealed that the enhanced m(d)* at higher doping levels holds significant potential. By optimizing the carrier concentration to similar to 1.13 x 10(19) cm(- 3), a peak zT of 0.67 was predicted for the x = 0.06 composition, suggesting a clear pathway for future performance enhancemen