Cu/Sb Codoping for Tuning Carrier Concentration and Thermoelectric Performance of GeTe-Based Alloys with Ultralow Lattice Thermal Conductivity

Luo, Yi; Fang, Teng; Zheng, Shuqi; Cui, Wenlin; Wu, Yue; Chang, Siyi; Wang, Lijun; Bai, Pengpeng; Zhao, Huaizhou

doi:10.1021/acsaem.8b02213

Cited by 48 publications

(27 citation statements)

References 65 publications

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“…In order to address the inherently high hole concentration in GeTe, aliovalent elements (e.g., Bi or Sb) have been frequently alloyed into GeTe with reproducible peak ZT values exceeding 1.5 or even 2.0. [ 26,33–38 ] Recently, doping of transition metals with partially filled d orbitals (e.g., Ti, Mn, and Cr) have been reported to have a significant impact on the structures and subsequently the ZT of GeTe‐based materials, [ 11,29,39–42 ] providing new insights when screening cutting‐edge thermoelectric candidates. For instance, Ti and Mn doping can reduce the c / a ratio to obtain cubic GeTe at room temperature, which promotes the band degeneracy and band convergence for a higher effective mass and ZT ; [ 11,29,42 ] Cd and Cu can form various lattice defects acting as extrinsic phonon scattering sources, for example, planar vacancies, point defects, and nanoprecipitates (NP), to push κ l toward the amorphous limit.…”

Section: Introductionmentioning

confidence: 99%

Versatile Vanadium Doping Induces High Thermoelectric Performance in GeTe via Band Alignment and Structural Modulation

Sun

Shi

et al. 2021

Advanced Energy Materials

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Thermoelectric materials, which enable the direct conversion between heat and electricity, have attracted worldwide attention for applications in waste heat recovery, wearable devices, space exploration, and refrigeration. [1][2][3][4][5][6][7] The processes for conversion of heat-to-electricity are in favor of high output voltage (large Seebeck coefficient, S), low heat loss (large electrical conductivity, σ), and stable temperature gradients (small thermal conductivity, κ). Accordingly, the characteristics of thermoelectric materials can be evaluated by the dimensionless figure-of-merit ZT = S 2 σT/κ, where T presents the absolute temperature, S 2 σ is known as the power factor, κ is comprised of the electronic κ e and lattice κ l fractions. [4,8] The foremost task of thermoelectric research is to enhance the ZT value, which generally requires enhanced S 2 σ and reduced κ by modulating the transport of carriers and phonons, respectively. For instance, great effort has been devoted to decoupling the trade-off between S and σ through band engineering, including band convergence, [9] resonant state doping, [10] phase transition manipulation, [11] and quantum confinement. [12] While κ (mainly κ l ) can be more independently modulated through reinforcing intrinsic phonon scattering and introducing extrinsic phonon scattering sources via introducing nanostructuring, [13,14] hierarchical architecture, [3,15] and defect engineering. [16,17] GeTe-based thermoelectrics have attracted increasing attention owing to their state-of-the-art mid-temperature performance. [18][19][20][21] Pristine GeTe undergoes a reversible transition from the low-temperature rhombohedral phase (space group R3m, a = 4.172 Å, c = 10.71 Å) to the high-temperature cubic phase (space group Fm3m, a = 5.98 Å) at around 700 K. As shown in Figure 1a,b, the phase transition is accompanied by elongated diagonal and displacement of the central site within the GeTe unit cell. This arrangement favors strengthened optical-acoustic phonon interaction [22] and enhanced band degeneracy. However, due to the low formation energy of Ge vacancies, excessive Owing to the moderate energy offset between light and heavy band edges of the rock-salt structured GeTe, its figure-of-merit (ZT) can be enhanced by the rational manipulation of electronic band structures. In this study, density functional theory calculations are implemented to predict that V is an effective dopant for GeTe to enlarge the bandgap and converge the energy offset, which suppresses the bipolar conduction and increases the effective mass. Experimentally, V-doped Ge 1−x V x Te samples are demonstrated to have an enhanced Seebeck coefficient from ≈163 to ≈191 µV K −1 . Extra alloying with Bi in Ge 1−x−y V x Bi y Te can optimize the carrier concentration to further enhance the Seebeck coefficient up to ≈252 µV K −1 , plus an outstanding power factor of ≈43 µW cm −1 K −2 . Comprehensive structural characterization results also verify the refinement of grain size by V-doping, associated with highly dense ...

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Section: Introductionmentioning

confidence: 99%

Versatile Vanadium Doping Induces High Thermoelectric Performance in GeTe via Band Alignment and Structural Modulation

Sun

Shi

et al. 2021

Advanced Energy Materials

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“…Many studies have considered Ge vacancies as negative effects for enhancing ZT of GeTe‐based alloys, [ 24,42,44,53–56 ] and have also proposed various approaches for suppressing Ge vacancies. Dong et al have reported that excess Ge can be effective in eliminating the Ge vacancies in pristine GeTe for reducing carrier density and increasing carrier mobility, [ 24 ] resulting in a peak ZT of ≈1.6 around 650 K. As reported by Li et al, [ 53 ] alloying with PbSe can elevate the formation energy of Ge vacancies by increasing the mean size of cations and decreasing the average size of anions, resulting in suppressed Ge vacancies.…”

Section: Introductionmentioning

confidence: 99%

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

Ding

et al. 2020

Adv Funct Materials

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Because the intrinsic Ge vacancies in GeTe usually lead to high hole concentration beyond the optimal range, many previous studies tend to consider Ge vacancies as negative effects on increasing the figure of merit ZT of GeTe-based alloys, and consequently have proposed various approaches to suppress Ge vacancies. However, in this work, it is demonstrated that the Ge vacancies can have great positive effects on enhancing the ZT of GeTe-based alloys when the hole concentration falls into the optimal range. First, hole concentration of GeTe is reduced close to the optimal range by co-alloying of Pb and Bi, and then the Ge vacancies are increased by adding excess Te into the Ge 0.8 Pb 0.1 Bi 0.1 Te 1+x . The Ge vacancies can cause lattice shrinkage and promote rhombohedral-to-cubic phase transition. As revealed by firstprinciple calculations, theoretical simulations, and experimental tests, Ge vacancies can facilitate the band convergence, suppress the bipolar transport at higher temperature range, and reduce the lattice thermal conductivity. Combining these effects, a peak ZT of 1.92 at 637 K and an average ZT of 1.34 within 300-773 K in Ge 0.8 Pb 0.1 Bi 0.1 Te 1.06 can be obtained, demonstrating the great significance of utilizing vacancy-type defects for enhancing ZT.

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“…[ 118 ] As a result, the average ZT ( ZT avg ) from 300 to 773 K approaches to ≈1.1 in cubic Ge 0.81 Mn 0.15 Bi 0.04 Te, which is superior to most thermoelectric materials (Figure 8d). [ 118,127 ]…”

Section: Electrical Transport Properties Optimizationmentioning

confidence: 99%

“…Table 4 compares different GeTe‐based thermoelectric materials synthesized by different method, including high‐vacuum and high‐temperature melting [ 80,127,128,140,144–147 ] or solid‐state reaction [ 148,149 ] method. The high temperature can secure sufficient reaction of precursors to form high‐purity and composition‐homogeneous solid solutions.…”

Section: Materials Preparationmentioning

confidence: 99%

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

Liu

Wang

et al. 2020

Advanced Energy Materials

182

128

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m ), [52] enlarging band degeneracy (N V ), [43] and introducing resonant energy levels, [26] can also tune n p effectively. Taking Ge 1−x−y Sb x Zn y Te as an example, Zn doping can reduce the energy offset (ΔE) between L and Σ point. [52] The minimization of thermal transport properties is mainly achieved through suppressing the electrical property-independent κ l . [53][54][55][56][57] Thermoelectric materials with High-performance GeTe-based thermoelectrics have been recently attracting growing research interest. Here, an overview is presented of the structural and electronic band characteristics of GeTe. Intrinsically, compared to lowtemperature rhombohedral GeTe, the high-symmetry and high-temperature cubic GeTe has a low energy offset between L and Σ points of the valence band, the reduced direct bandgap and phonon group velocity, and as a result, high thermoelectric performance. Moreover, their thermoelectric performance can be effectively enhanced through either carrier concentration optimization, band structure engineering (bandgap reduction, band degeneracy, and resonant state engineering), or restrained lattice thermal conductivity (phonon velocity reduction or phonon scattering). Consequently, the dimensionless figure of merit, ZT values, of GeTe-based thermoelectric materials can be higher than 2. The mechanical and thermal stabilities of GeTe-based thermoelectrics are highlighted, and it is found that they are suitable for practical thermoelectric applications except for their high cost. Finally, it is recognized that the performance of GeTe-based materials can be further enhanced through synergistic effects. Additionally, proper material selection and module design can further boost the energy conversion efficiency of GeTe-based thermoelectrics.

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Cu/Sb Codoping for Tuning Carrier Concentration and Thermoelectric Performance of GeTe-Based Alloys with Ultralow Lattice Thermal Conductivity

Cited by 48 publications

References 65 publications

Versatile Vanadium Doping Induces High Thermoelectric Performance in GeTe via Band Alignment and Structural Modulation

Versatile Vanadium Doping Induces High Thermoelectric Performance in GeTe via Band Alignment and Structural Modulation

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

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

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