Near-room-temperature rhombohedral Ge1-xPbxTe thermoelectrics

Abstract

Thermoelectric GeTe alloys have recently attracted renewed interests due to the extraordinary performance. It is particularly interesting in the low-symmetry structure, where the symmetry-breaking induced diversity in the arrangement in energy of split valence bands might enable an optimal band convergence for thermoelectric enhancements. This in principle leads to an extra degree of freedom for advancing GeTe thermoelectrics though a control of the degree of rhombohedral-distortion in the structure. Here we demonstrate this concept and realize its extraordinariness near room temperature, an extremely important temperature range for thermoelectric power generation/cooling applications in which very few options on materials other than conventional Bi2Te3 are currently available. This is enabled by a continuous manipulation of the rhombohedral-distortion in simple Ge1-xPbxTe solid solutions quenched from the high-temperature single phase region, a simultaneous optimization of carrier concentration and a reduction in lattice thermal conductivity due to PbTe-alloying. The resultant figure of merit, zT, at 200–350 K, is highly competitive to that of commercially available p-type Bi2Te3 alloys and higher than that of other known p-type thermoelectrics.