GeTe Thermoelectrics

Although GeTe has been known as thermoelectrics since 1960s, it has attracted intensive renewed attention recently. GeTe undergoes a phase transition from a high-T cubic (c-GeTe) to a low-T rhombohedral structure (r-GeTe) through slightly distorting along the [111] direction at ∼720 K. Previous thermoelectric studies have mostly focused on high-symmetry c-GeTe. To date, low-symmetry r-GeTe has been revealed to show a thermoelectric figure of merit zT as high as that of c-GeTe, because the symmetry breaking electronically enables a diversified rearrangement of split bands for a high band degeneracy and thermally allows hierarchical bonds and microstructures for a low lattice thermal conductivity. This work summarizes the advancements in both r- and c-GeTe and the corresponding device-level progress, clearly demonstrating GeTe as one of the most efficient thermoelectrics for both mid-temperature (500–800 K) and near-room-temperature applications. In addition, topics that might be of interest and lead to further advancements are outlined. Although GeTe has been known as thermoelectrics since 1960s, it has attracted intensive renewed attention recently. GeTe undergoes a phase transition from a high-T cubic (c-GeTe) to a low-T rhombohedral structure (r-GeTe) through slightly distorting along the [111] direction at ∼720 K. Previous thermoelectric studies have mostly focused on high-symmetry c-GeTe. To date, low-symmetry r-GeTe has been revealed to show a thermoelectric figure of merit zT as high as that of c-GeTe, because the symmetry breaking electronically enables a diversified rearrangement of split bands for a high band degeneracy and thermally allows hierarchical bonds and microstructures for a low lattice thermal conductivity. This work summarizes the advancements in both r- and c-GeTe and the corresponding device-level progress, clearly demonstrating GeTe as one of the most efficient thermoelectrics for both mid-temperature (500–800 K) and near-room-temperature applications. In addition, topics that might be of interest and lead to further advancements are outlined.