Electrical Properties of Mg[sub 2]Sn Crystals Grown from Nonstoichiometric Melts

Abstract

Resistivity and Hall measurements were carried out on Mg2normalSn crystals in the temperature range 300°–60°K. Single crystals were grown by a modified Bridgman technique from stoichiometric melts and from melts containing 1, 2, 10, and 18 at. % excess Sn and 3 at. % excess Mg. In the mixed conduction and extrinsic ranges, it was found possible to describe the calculated temperature dependence of the conduction mobility on the basis of a combination of lattice vibration (acoustic mode) and ionized impurity scattering. A stoichiometry effect is observed. The Mg2normalSn crystals appear to dissolve the excess constituent producing n‐type crystals (excess Sn) and p‐type crystals (excess Mg). The observed effect corresponds to a solubility of 10−5‐10−6 action excess constituent. This result is briefly discussed in terms of bonding in Mg2normalSn .

Solid State Synthesis of Ternary Thermoelectric Magnesium Alloy, Mg<SUB>2</SUB>Si<SUB>1&minus;<I>x</I></SUB>Sn<I><SUB>x</SUB></I>

“…In fact, the thermal conductivities in Refs. 16,17,19) were much lower than the present data for Mg 2 Si 1Àx Sn x in 0:2 < x < 0:8. This might be because phonon scattering is enhanced by fine microstructure with two phases of Mg 2 Si þ Mg 2 Sn.…”

“…As first reported in Ref. 16), M 2 Sn has a stoichiometric effect. Mg 2 Sn becomes p-type by enrichment of magnesium while it is n-type when including excess amount of tin.…”

“…16,17,19), the band-gap for Mg 2 Si 1Àx Sn x decreases with the tin content, x, and it has a kink-point at the vicinity of x ¼ 0:7 as shown as a broken line with solid circles in Fig. 8.…”

“…In Refs. 16,17), the samples were prepared at the temperature, 50 K higher than the liquidus temperature using direct melting and mixing in the crucibles and placed in the argon-filled ampoules. After homogenizing annealing for 100-500 h at temperature, 200 K lower than solidus temperature, the solidified ingots were obtained not to have second-phase impurities or inclusions in the microscopic level.…”

“…A few reports of liquid-phase synthesis of Mg 2 Sn were found in literature. [16][17][18] Mg 2 Sn crystals grown from melts by the modified Bridgeman procedure have unique characteristics: it becomes n-type for excess tin content and p-type for excess magnesium content. Mechanical alloying by ball milling was also used for solid-state synthesis to evaluate the thermoelectric properties of Mg 2 Sn.…”