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High-quality crystals of the thermoelectric compound Mg 2 Sn doped with Ag were synthesized by radio-frequency (RF) induction melting, and their properties are compared with similar crystals prepared by the Bridgman method that uses conventional resistive furnace. The entire process of preparing an ingot of Mg 2 Sn by the RF induction melting takes about 5 hours compared to at least 100 hours by the Bridgman method. X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy shows the ingots prepared by the RF induction melting to be dense and composed of single-phase Mg 2 Sn with finely dispersed submicron secondary phases of Sn or MgAg alloy. Electrical transport properties (Hall coefficient, Seebeck coefficient, and electrical conductivity) measured between 80 and 700 K show that for the RF and Bridgman crystals these properties are quantitatively similar. The presence of the finely dispersed secondary phases in the RF crystals, however, leads to a significant decrease in the thermal conductivity and a corresponding improvement of the thermoelectric figure of merit. |
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