High thermoelectric potential of Bi_2Te_3 alloyed GeTe-rich phases

摘要

In an attempt to reduce our reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of p-type (GeTe)_(1-X)(Bi_2Te_3)_x alloys, with x values of up to 20%. Higher solubility limit of Bi_2Te_3 in GeTe, than previously reported, was identified around ～9%, extending the doping potential of GeTe by the Bi_2Te_3 donor dopant, for an effective compensation of the high inherent hole concentration of GeTe toward thermoelectrically optimal values. Around the solubility limit of 9%, an electronic optimization resulted in an impressive maximal thermoelectric figure of merit, ZT, of ～1.55 at ～410 ℃, which is one of the highest ever reported for any p-type GeTe-rich alloys. Beyond the solubility limit, a Fermi Level Pinning effect of stabilizing the Seebeck coefficient was observed in the x= 12%-17% range, leading to stabilization of the maximal ZTs over an extended temperature range; an effect that was associated with the potential of the governed highly symmetric Ge_8Bi_2Te_(11) and Ge_4Bi_2Te_7 phases to create high valence band degeneracy with several bands and multiple hole pockets on the Fermi surface. At this compositional range, co-doping with additional dopants, creating shallow impurity levels (in contrast to the deep lying level created by Bi_2Te_3), was suggested for further electronic optimization of the thermoelectric properties.