Synergistically Optimized Carrier and Phonon Transport Properties in Bi–Cu₂S Coalloyed GeTe

Abstract

GeTe is an emerging lead-free thermoelectric material, but its excessive carrier concentration and high thermal conductivity severely restrict the enhancement of thermoelectric properties. In this study, the synergistically optimized thermoelectric properties of p-type GeTe through Bi−Cu 2 S coalloying are reported. It can be found that the donor behavior of Bi and the substitution−interstitial defect pairs of Cu + ions effectively reduce the hole concentration to an optimal level with carrier mobility less affected. At the same time, Bi−Cu 2 S coalloying induces many phonon scattering centers involving stacking faults, nanoprecipitations, grain boundaries and tetrahedral dislocations and suppresses the lattice thermal conductivity to 0.64 W m −1 K −1 . Consequently, all effects synergistically yield a peak ZT of 1.9 at 770 K with a theoretical conversion efficiency of 14.5% (300−770 K) in the (Ge 0.94 Bi 0.06 Te) 0.988 (Cu 2 S) 0.012 sample, which is very promising for mid-low temperature range waste heat harvest.

Structural modulation and resonant level enable high thermoelectric performance of GeTe in the mid-to-low temperature range

“…An ideal TE material requires a large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. [4][5][6] Since the three parameters are intrinsically coupled with one another, it is difficult to signicantly optimize the TE performance by adjusting a single variable. Previous strategies have been proved to achieve higher zTs, such as tuning the carrier concentration to an optimal level, [7][8][9][10] band structure engineering to enhance the power factor S 2 s by promoting band convergence [11][12][13][14][15] or inducing a resonant level, [16][17][18][19] and phonon engineering to suppress the lattice thermal conductivity.…”

Achieving High Carrier Mobility And Thermal Stability in Plainified Rhombohedral GeTe Thermoelectric Materials with zT > 2

“…The remarkably high peak zT values of above 2.0 have been achieved in GeTe-based materials. [44][45][46][47][48][49][50][51][52][53][54] For instance, by band convergence induced by Pb, Bi, and Mn co-doping, an enhanced zT of 2.3 is achieved in the cubic Ge 0.82 Pb 0.1 Bi 0.04 Mn 0.04 Te at 573 K. [50] Tailoring grain boundary via Ga 2 Te 3 precipitates combined with Sb and Pb co-alloying enables a peak zT of 2.1 at 773 K in the cubic Ge 0.78 Ga 0.01 Pb 0.1 Sb 0.07 Te. [54] The excellent TE performance makes GeTe a potential system for power generation applications in the medium temperature range.…”

“…The n opt of GeTe at its operating temperature range is theoretically estimated to be 1-3 × 10 20 cm −3 (Figure 1a), using the single parabolic band (SPB) model. [59] In light of the over-high n H in the as-fabricated binary GeTe, the counter doping, using aliovalent elements, such as Bi [33,42,46,47,50,[60][61][62][63] and Sb, [27][28][29][30][31]34,[39][40][41]43,[51][52][53] is a common method for reducing the over-high n H to n opt . In addition, previous studies also found that n H can be reduced by increasing the formation energy of Ge vacancies (V Ge ) through hetero-alloying.…”