Unconventional Electronic Properties of Mg₂Si Thermoelectrics Revealed by Fast-Neutron-Irradiation Doping

Abstract

In this work, we systematically investigated the electrical resistivity, Hall, and magnetoresistance effects of Aldoped Mg 2 Si thermoelectrics, irradiated with a fluence of fast neutrons and consequently isochronally annealed at moderate high temperatures up to 500 °C. We found that the fastneutron bombardment itself only slightly modified the electronic properties. Meanwhile, a series of the postirradiation high-temperature anneals affected the properties dramatically. Thus, after annealing at temperatures of 275−325 °C, Mg 2 Si:Al showed pronounced jumps in both the electrical resistivity and the Hall constant values by several orders of magnitude. This unexpected electronic transition corresponded to a significant variation in the carrier concentration. We proposed that this unusual electronic transition may be related to temperature-assisted chemical bonding of the radiation defects that can involve free charge carriers in the sample, thereby tuning dramatically its transport properties. We proposed a simple model for Mg 2 Si:Al thermoelectrics, which links the chemical bonding of the interstitial Mg ions with the electronic properties of this material. This finding suggests a new avenue to tuning of electronic properties and unconventional electronic transitions in materials with a high concentration of defects.

Strategies and challenges of high-pressure methods applied to thermoelectric materials

“…The application of pressure or stress to members of another thermoelectric family based on the Group IV elements, namely, Mg 2 X (where X = Si, Ge, Sn), which crystallize in a cubic anti-CaF 2 -type structure (Fig. 1), 164,165 demonstrated that this method is capable of enhancing their thermoelectric properties. An experimental room-temperature study showed that both the electrical resistivity and Seebeck coefficient of n-type Mg 2 Si:Al decrease dramatically with pressure [ Fig.…”

Stress-controlled thermoelectric module for energy harvesting and its application for the significant enhancement of the power factor of Bi2Te3-based thermoelectrics

“…This approach has been used in both experimental and theoretical explorations for various thermoelectrics, e.g. Bi 2 Te 3 -Sb 2 Te 3 alloys , BiTeI [31], Bi [32][33][34], PbTe [34][35][36][37], Mg 2 Si alloys [38][39][40][41][42][43][44], SnSe [45], MgAgSb [46], ZnGeSb 2 [47] and some others. The results gathered in these works testified that this method is indeed very promising.…”