Structural and transport properties of quenched and melt-spun BixSb2−xTe3 solid solutions (x = 0.40 and 0.48)

We report on a detailed investigation of the structural and transport properties of BixSb2−xTe3 (x = 0.40 and 0.48) samples, prepared by either water quenching or melt-spinning (MS) and consolidated by spark plasma sintering, by means of X-ray diffraction, scanning and transmission electron microscopy, and transport property measurements (5–480 K). All the samples crystallize in the rhombohedral structure type of Bi2Te3. While the samples prepared by water quenching exhibit some segregations of the elements over the micron length scale, the MS samples are highly homogeneous. Unlike prior reports where an increase in the dimensionless thermoelectric figure of merit ZT has been observed in MS samples, we find that both series of samples show similar peak ZT values. Owing to slight variations in the hole concentration, the maximum ZT is shifted closer to room temperature in MS samples with a peak ZT of 1.1 achieved at 340 K for x = 0.48. Our results highlight the extreme sensitivity of the ZT values to the Bi content and, for a given chemical composition, to slight variations in the hole concentration and microstructure. We further demonstrate the good reproducibility of the MS technique indicating that this method enables controlling the defect concentration inherent to these materials.