Boosting the Thermoelectric Performance of Pseudo‐Layered Sb₂Te₃(GeTe)_n via Vacancy Engineering

Abstract

An ultrahigh figure of merit ZT value ≈2.4 at 773 K for p‐type pseudo‐layered Sb2Te3(GeTe)17 along the parallel direction is reported by synergistically optimizing its electrical and thermal properties via vacancy engineering. The microstructural origin of thermoelectric property enhancement is studied by spherical aberration corrected transmission electron microscopy and its in situ mode. The results reveal that upon annealing, Ge vacancy gaps in quenched samples tend to migrate and recombine into long‐range gaps in order to minimize the elastic and electrostatic energies. The recombination of Ge gaps would lead to an overall reduction of carrier concentration and electrical thermal conductivity. The detailed study of Ge vacancies migration via heat treatment and its effects on thermoelectric performance in pseudo‐layered Sb2Te3(GeTe)17 materials can provide enlightening clues for future research in a number of thermoelectric materials of similar structures.

Positive Effect of Ge Vacancies on Facilitating Band Convergence and Suppressing Bipolar Transport in GeTe‐Based Alloys for High Thermoelectric Performance

“…The evidence of Ge vacancies clusters and planar Ge vacancies in the GeTe‐based alloys have been widely revealed by previous reported transmission electron microscopy (TEM), [ 29,37,46,48,50,57,58 ] which is also presented by our TEM test ( Figure ). As shown in Figure 7a, we have examined a () plane that is perpendicular to the (111) plane, revealing the separated Ge and Te atomic layers.…”

“…The Bi and Sb have been widely used to reduce the hole concentration of GeTe due to their donor dopant nature. [ 29–33 ] Other doping or alloying with Pb, [ 25,34–36 ] Se, [ 30,37–39 ] Bi‐Sb, [ 40 ] Bi‐Cu, [ 41 ] Mn‐Bi, [ 42 ] Mn‐Sb, [ 43 ] Pb‐Sb, [ 28,44 ] Pb‐Bi, [ 45 ] Cd‐Bi, [ 46,47 ] Sb‐Zn, [ 48 ] Sb‐In, [ 49 ] Bi 2 Te 3 , [ 23,26 ] Sb 2 Te 3 , [ 50 ] and AgSbTe 2 [ 51,52 ] have also been widely applied to optimize the carrier density and to reduce κ lat for enhancing the ZT of GeTe‐based alloys. Combined with the synergic effects of carrier‐density optimization, band engineering and phonon engineering strategies, many GeTe‐based alloys with peak ZT of around 2 have been reported recently.…”

“…Bayikadi et al have shown that Ge‐vacancy level can also be decreased by proper heat treatment, resulting in a peak ZT of ≈1.37 in pristine GeTe. [ 55 ] On the other hand, high density of planar Ge‐vacancy arrays have been frequently observed in GeTe‐based materials by alloying with Cd‐Bi, [ 46 ] Bi 2 Te 3 , [ 57,58 ] and Sb 2 Te 3 , [ 37,50,59 ] which have been demonstrated as an efficient way for reducing κ lat . Other effects of Ge vacancies such as phase transition [ 60 ] and lattice hardening [ 61 ] have also been reported in the GeTe‐based materials.…”

Realizing Excellent Thermoelectric Performance of Sb2Te3 Based Segmented Leg with a Wide Temperature Range Using One‐Step Sintering

“…[3b] Meanwhile, with Mg doping, the electrical conductivity is significantly increased due to the increased carrier concentration far outperforms the reduced carrier mobility as shown in Figure 1b. The positive value indicates a p-type semiconductor behavior with the hole as the dominant charge carrier [24] and displays an inverse trend with electrical conductivity. Figure 1c shows the temperature dependent Seebeck coefficient (S).…”

High‐Performance GeTe‐Based Thermoelectrics: from Materials to Devices

“…As an additional scattering source, stacking defect (planar vacancies) under the nanometer scale can effectively scatter the intermediate frequency phonons. [ 140 ] Within the Callaway model, [ 69,132 ] τ associated with planar vacancies can be expressed as [ 83 ] among them, where, σ s is the characteristic area size of vacancies, l is the characteristic length of the visible “linear” vacancies, t is the characteristic length of the “invisible” vacancies (perpendicular to the visible “linear” vacancies direction), V 0 is the number density of the planar vacancies, where, d is the characteristic distance between two nearest planar vacancies. The τ Sd can be reduced into which is directly proportional to v and inversely proportional to d .…”