Phase Selection and Microstructure Refinement of Melt-Spun Zn4Sb3 –Type Compound

The Zn4Sb3 phase is considered one of the most interesting compounds for thermoelectric applications in the intermediate temperature range (400–600 K) because of its very low thermal conductivity. Typical processing routes of this material for technological applications require several steps, in order to obtain a homogeneous single phase with fine microstructure. In this work, melt spinning was used as an intermediate processing step for improving the structural homogenization and microstructure refinement of Zn4Sb3. The effect of rapid solidification on the phase stability and microstructure was investigated. Melt-spun samples show, on the one hand, other crystalline phases in addition to the expected Zn4Sb3-type phase, probably because the high cooling rate did not allow the system to reach the thermodynamic equilibrium. On the other hand, rapid solidification induced a remarkable decrease of crystallite size down to the nanoscale, as estimated by the peak broadening in the X-ray diffraction patterns and shown by scanning electron micrographs. Additionally, the presence of an irreversible exothermic peak in the differential scanning calorimetry (DSC) trace can be likely related to the crystallization of a small amount of amorphous phase, formed as a result of the high cooling rate that could not be detected by XRD. The results suggest that melt-spun flakes can be used as a starting material in the subsequent compaction steps.