Electronic and thermal transport properties of Mg2Sn crystals containing finely dispersed eutectic structures

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Abstract
The electronic and thermal transport properties of Mg2Sn crystals prepared by radio‐frequency (RF) induction melting, were investigated in the temperature range 10−700 K to study the effect of adding excess silver to the melt on the microstructure and thermoelectric properties. As the Ag‐content increases the amount of silver incorporated at doping sites tends to saturate so that the carrier concentration increases asymptotically to 6.3 × 1019 cm−3. The excess amount of silver reacts with magnesium to form a fine MgAg + Mg2Sn eutectic structure. The temperature dependence of the carrier mobility varies from ∼T−1.5 for the heavily doped samples in the extrinsic range to ∼T−2.8 for the undoped sample in the intrinsic range. From electrical conductivity and Hall measurements on the undoped samples we find the energy gap to be 0.36−0.38 eV. Doped samples show broad Seebeck peaks of 150−210 µV K−1 at T = 350−550 K. The thermal conductivity decreases sharply as the addition of Ag is increased, and reaches a minimum value of κ = 3.4 W m−1 K−1 at 450 − 500 K for the doped sample containing a uniformly distributed eutectic phase, leading to a maximum figure of merit ZTmax = 0.30.

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