GeTe Thermoelectrics

Abstract

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 devicelevel 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.

High Power Factor and Enhanced Thermoelectric Performance in Sc and Bi Codoped GeTe: Insights into the Hidden Role of Rhombohedral Distortion Degree

“…Generally, the optimum carrier concentration range is around 2 × 10 20 cm −3 , consistent with the previous estimation. [ 39 ] The most important observation here is that the increased interaxial angle α leads to the reduced power factor, which is contradicted to the conventional understanding of the symmetry engineering in GeTe. [ 29,67,69 ] It has to be noted, however, that the previous studies do not take into account the simultaneously increased Ge‐vacancies concentration during the structural change.…”

“…[ 36,37 ] Considering the toxic problem of Pb element, GeTe, one of the analogs of PbTe, attracts renewed research attention for the replacement of PbTe. [ 38–40 ] Due to the similarly beneficial band structure and strong phonon anharmonicity with PbTe arising from the same chemical bonding mechanism, [ 41,42 ] comparable high peak ZTs ≈2 have continuously been reported in the system of GeTe. [ 29,43–56 ] One important difference between these two compounds is that GeTe undergoes the structural phase transition from the low‐temperature rhombohedral to the high‐temperature cubic phase at a critical temperature around 700 K. [ 57,58 ] The rhombohedral structure refers to a unit cell with parameters ( a = b = c and α = β = γ < 90°), belonging to the hexagonal crystal family.…”

High-Performance Mg 3 Sb 2- x Bi x Thermoelectrics: Progress and Perspective

“…With a constant endeavor of thermoelectricians in the past decades, more than ten semiconductor systems have been exploited with high zT above unity, some even higher than 2, e.g., V 2 VI 3 compounds [ 7 – 10 ], IV-VI compounds [ 11 – 18 ], transition metal chalcogenides [ 19 , 20 ], half-Heusler compounds [ 21 – 26 ], skutterudites [ 27 – 29 ], Zintl compounds [ 30 – 33 ], clathrates [ 34 , 35 ], metal silicides [ 36 – 38 ], and Si 1- x Ge x alloys [ 39 , 40 ]. Among these good TE systems, most of them exhibit peak zT in the moderate-to-high temperature range (≥600 K), of which the practical applications would be power generation.…”

Anomalous Thermopower and High ZT in GeMnTe 2 Driven by Spin’s Thermodynamic Entropy

“…The IV-VI compound GeTe is a remarkable thermoelectric material characterized by high electrical conductivity and high power factor PF = α 2 σ [ 34 , 39 – 45 ]. GeTe undergoes a phase transition from rhombohedral structure to cubic structure at 700 K [ 46 ].…”