Structural and Electrical Properties Characterization of Sb1.52Bi0.48Te3.0 Melt-Spun Ribbons

Unraveling the Critical Role of Melt-Spinning Atmosphere in Enhancing the Thermoelectric Performance of p-Type Bi0.52Sb1.48Te3 Alloys

Melt spinning has proven effective in maintaining chemical homogeneity and introducing multiscale microstructures that can reduce the lattice thermal conductivity and consequently enhance the thermoelectric performance of consolidated bulk materials. In this work, p-type Bi_0.52Sb_1.48Te₃ bulk alloys are fabricated by melt spinning (MS) followed by subsequent plasma activated sintering (PAS). The influence of different MS atmospheres (air, Ar, N₂, and He) on the morphologies of MS ribbons and the thermoelectric properties of MS-PAS bulk materials has been investigated systematically. Because of the relatively high thermal conductivity, a He atmosphere expedites the heat dissipation in the MS process and results in severe sublimation of tellurium and thus inferior thermoelectric performance. In contrast, an Ar atmosphere can essentially prevent heat loss of the fusant and suppress the sublimation of tellurium. Consequently, the corresponding Bi_0.52Sb_1.48Te₃ sample (MS in Ar atmosphere) presents the highest peak ZT and average ZT values of 1.09 (at 340 K) and 0.81 (in 300-500 K), respectively. The average ZT of the sample prepared using an Ar atmosphere is almost three times the one prepared using a He atmosphere. This reflects the importance of using the appropriate atmosphere during the melt-spinning process. This result, which indicates that melt spinning in an Ar atmosphere is preferable to avoid heat loss, can also be extended to other materials.

Enhanced Thermoelectric Performance of Bi0.46Sb1.54Te3 Nanostructured with CdTe

Cd-containing polycrystalline Bi_0.46Sb_1.54Te₃ samples with precisely controlled phase composition were synthesized by conventional melting-quenching-annealing technique and a melt-spinning method. The pseudo ternary phase diagram for Cd-Bi/Sb-Te in the region near Bi_0.46Sb_1.54Te₃ was systematically studied. Cd serves as an acceptor dopant contributing holes, whereas for samples doped with CdTe, the combined effects of the substitution of Sb/Bi with Cd and the formation of Sb/Bi_Te antisite defects leads to the increase in hole concentration. Moreover, upon doping with Cd, the lattice thermal conductivity decreases significantly owing to the intensified point defect phonon scattering. The sample with Cd content of 0.01 attains the maximum ZT of 1.15 at 425 K. The utilization of melt-spinning method brings about the in situ nanostructured CdTe and grain size refinement, which further reduce the lattice thermal conductivity while preserving excellent electrical performance. As a result, a higher ZT of 1.30 at 425 K is realized with CdTe content x = 0.005.

Improved Thermoelectric Properties in Melt-Spun SnTe

SnTe has been the focus of numerous experimental and theoretical studies over the last years owing to its high thermoelectric performances near 800 K when appropriately doped. Here, we demonstrate that melt-spinning, an ultrafast-quenching synthesis technique, followed by spark plasma sintering results in enhanced ZT values in polycrystalline SnTe. To illustrate the impact of this technique, the results are contrasted with those obtained on two polycrystalline samples prepared by direct quenching of molten SnTe and without quenching. SnTe melt-spun ribbons are characterized by a peculiar columnar microstructure that contributes to lower the lattice thermal conductivity below 700 K in pressed samples. More importantly, this technique results in a significant decrease in the hole concentration, giving rise to enhanced thermopower values above 500 K. The variation in the hole concentration is likely due to a slight loss of elemental Te during the melt-spinning process. Thanks to the decreased hole concentration, the thermoelectric performances are significantly enhanced with a peak ZT value of 0.6 at 800 K, which represents a 40% increase over the values measured for samples prepared with and without quenching. These findings indicate that melt-spinning provides a novel strategy to improve the thermoelectric properties of SnTe that could be worthwhile extending to substituted compounds.