Dilute Cu2Te-alloying enables extraordinary performance of r-GeTe thermoelectrics

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

“…This can be qualitatively understood by the abovementioned slight variation of the interaxial angle. The critical role of Sc doping on charge carrier transport is similar to Cu doping from Bu et al [ 51 ] and Xie et al, [ 54 ] although their data look somewhat different. Indeed, the superior properties obtained by Sc doping and Cu doping represent the inherently high potential of rhombohedral GeTe.…”

“…[ 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. It can be regarded as a slightly distorted rock‐salt lattice along the [111] direction with a interaxial angle less than 90°.…”

“…As a consequence of native Ge vacancies, most of previous studies utilized the aliovalent dopant on the Ge site to reduce the hole concentration, such as Bi, [ 61,63,64,66 ] Sb, [ 62,73 ] In, [ 74,75 ] and transition metals (Ti, [ 67,68 ] Cr, [ 53 ] Cd, [ 69–71 ] and Cu [ 51,54 ] ). Among them, some dopants also obviously contributed to modifying the structure symmetry from rhombohedral to cubic, represented by means of the increased interaxial angle α.…”

“…a,c,e) Temperature dependent electrical resistivity ρ, Seebeck coefficient S , and power factor PF of Ge 1− x Sc x Te ( x = 0, 0.02, 0.04, 0.06, and 0.08), respectively. b,d,f) Room‐temperature hall carrier mobility μ H , Seebeck coefficient S , and power factor PF as a function of hall carrier concentration n H in rhombohedral GeTe‐based materials, including Sc doping, Sb doping, and Ge 1+ x Te from Li et al, [ 73 ] Cu doping from Bu et al, [ 51 ] as well as Cu doping from Xie et al [ 54 ] The solid lines in (b) and (f) are included to guide the eye whereas the solid and dashed lines in (d) represent the modified two‐band model [ 73 ] and the single parabolic band (SPB) model calculations, respectively.…”

Manipulation of Band Degeneracy and Lattice Strain for Extraordinary PbTe Thermoelectrics

“…These approaches have been frequently proven to be successful for advancing thermoelectrics, especially in p-type IV-VI compounds [16,[39][40][41][42][43][44][45][46][47]. Manipulation of the energy offset between the light valence band (L) and the heavy valence band (Σ) via alloying enables charge carriers to be transported by many band valleys (band degeneracy) for an increase in σ without explicitly reducing S [48].…”