Characterization of dry milled powders of LAST (lead–antimony–silver–tellurium) thermoelectric material

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Abstract
Although thermoelectric (TE) materials are often fabricated as cast ingots, there has been recent interest in the powder processing of these materials. Cast TE materials typically have grain sizes as large as several hundred microns, but powder processing (grinding, milling and then sintering) can produce dense specimens with a reduced grain size, an improved mechanical integrity and enhanced TE properties. In the TE literature when powder processing is employed, little or no description is provided of the powder processing techniques and the powder processing parameters are either not characterized or only a mean particle size is given. In this study, powders milled from solid cast ingots of the TE compound LAST (lead–antimony–silver–tellurium) were characterized via Coulter Counter, to measure the mean powder particle size and the size distribution, scanning electron microscopy (SEM), to examine the powder particle morphology, and X-ray diffraction (XRD), to detect possible phase changes or amorphization. The impurity levels in the milled powders were examined by wear rate measurements on the milling media, as well as by energy dispersive X-ray analysis and inductively coupled plasma measurements.