Thermoelectric Performance Of GeTe Research Articles

Exceptional figure of merit achieved in boron-dispersed GeTe-based thermoelectric composites

GeTe is a promising p-type material with increasingly enhanced thermoelectric properties reported in recent years, demonstrating its superiority for mid-temperature applications. In this work, the thermoelectric performance of GeTe is improved by a facile composite approach. We find that incorporating a small amount of boron particles into the Bi-doped GeTe leads to significant enhancement in power factor and simultaneous reduction in thermal conductivity, through which the synergistic modulation of electrical and thermal transport properties is realized. The thermal mismatch between the boron particles and the matrix induces high-density dislocations that effectively scatter the mid-frequency phonons, accounting for a minimum lattice thermal conductivity of 0.43 Wm−1K−1 at 613 K. Furthermore, the presence of boron/GeTe interfaces modifies the interfacial potential barriers, resulting in increased Seebeck coefficient and hence enhanced power factor (25.4 μWcm−1K−2 at 300 K). Consequently, we obtain a maximum figure of merit Zmax of 4.0 × 10−3 K−1 at 613 K in the GeTe-based composites, which is the record-high value in GeTe-based thermoelectric materials and also superior to most of thermoelectric systems for mid-temperature applications. This work provides an effective way to further enhance the performance of GeTe-based thermoelectrics.

High wide-temperature-range thermoelectric performance in GeTe through hetero-nanostructuring

GeTe is emerging as promising medium-temperature thermoelectric material due to its highly competitive performance and good mechanical properties. Strong Rashba spin splitting was harnessed to markedly improve the Seebeck coefficient and power factor of Bi and Sn codoped GeTe at low-medium temperature. Moreover, it is found that Bi-Sn-Cu doping reduces the phase-transition temperature to extend better electrical transport behavior of cubic phase to low temperature. As a result, the electrical transport properties in low-medium temperature were overall enhanced. In the meanwhile, endotaxial hetero-nanostructures efficiently scatter phonons and play a dominant role on affecting phonon propagation. The lattice thermal conductivity was reduced to 0.2 W m−1K−1 at 673 K. Drive by strengthening Rashba effect and endotaxial hetero-nanostructures, a record-high average ZT (300–823 K) of 1.6 and a high ZT of 2.1 were obtained in lead-free GeTe-based compounds. The vast increase of ZT promotes GeTe as a promising candidate for a wide range of applications in waste heat recovery and power generation.

Modifying Roles of CuSbSe2 in Realizing High Thermoelectric Performance of GeTe

AbstractThermoelectric materials are widely researched for their energy conversion capabilities in the fields of power generation and refrigeration. And a superior thermoelectric conversion efficiency requires an excellent power factor and low thermal conductivity. Herein, a remarkable thermoelectric figure of merit（ZT） ∼ 2.6 at 673 K is realized in GeTe with 20% addition of CuSbSe2. Multiple synergistic effects of CuSbSe2 alloying collectively contribute to the excellent thermoelectric performance in GeTe. CuSbSe2 alloying effectively tunes ultrahigh carrier density of GeTe to the optimum. The introduction of Cu, Sb, and Se atoms create numerous point defects that scatter high‐frequency phonons. Additionally, surplus CuSbSe2 facilitates the formation of copper‐selenium phases, which embed at grain boundaries and generate interfaces after sintering. Combining the planar defects evolved from Ge vacancies, multi‐dimension defects effectively scatter multiple frequency phonons. An extraordinarily low lattice thermal conductivity of 0.3 Wm−1 K−1 at 673 K is obtained, approaching the theoretical estimation predicted by Cahill model. Eventually, the peak conversion efficiency of 7.4% is obtained in segmented device with ΔT of 419 K. The commingled effects of CuSbSe2 in GeTe further open up an elitist route to designing high‐performance materials.

Enhancing thermoelectric performance in GeTe through Ge enrichment regulation and AgCuTe alloying

Germanium telluride (GeTe) exhibits substantial potential as a thermoelectric material well-suited for mid-temperature applications. The presence of a significant amount of off-stoichiometric Ge leads to the formation of Ge precipitates and vacancies, which exert a pronounced influence on the electrical and thermal transport properties of GeTe. In this study, a heat treatment process is initially applied to alleviate Ge enrichment within pristine GeTe, resulting in the achievement of a uniform distribution of Ge precipitates throughout the matrix. Subsequently, we coarsely optimize the carrier concentration through Bi counter-doping, thereby attaining the desired range for optimal performance. Notably, we finely adjust the Ge/Te ratio through AgCuTe alloying, effectively modulating Ge precipitation, reducing lattice thermal conductivity, and enhancing the thermoelectric performance of GeTe. Consequently, the synthesized sample (Ge0.94Bi0.06Te)0.98(AgCuTe)0.02 exhibits a peak ZT value of approximately 2.27 at 773 K, with an average ZT value of approximately 1.38 within the temperature range of 323 to 773 K, making this material as a prominent candidate for medium-temperature thermoelectric applications.

Functionally separated electronic band engineering via multi-element doping plus high-density defects advances board-temperature-range thermoelectric performance in GeTe

GeTe has attracted widespread attention as an ideal mid-temperature thermoelectric (TE) material, but its peak performance within a narrow mid-temperature range limits the conversion efficiency improvement of future TE devices. Here, to achieve the overall enhancement of GeTe over a broad temperature range, especially near room temperature, we demonstrate the functionally separated electronic band engineering strategy (resonance energy levels and band convergence) coupling the construction of high-density defects by designing multi-element SnSe-In-Sb co-doping. Fundamentally, to distinguish the functions of selected elements, it was found that SnSe alloying mainly promotes the band convergence of GeTe in elevated temperatures, In doping can create the resonance energy level for enhancing the TE performance near room temperature, and Sb can optimize symmetry and the overall carrier concentration, thereby jointly improving the effective mass and Seebeck coefficient. Moreover, the construction of various phonon scattering centers including high-density Ge micro/nano-precipitates, van der Waals gaps, dislocations, and strong stress fields, strongly inhibits phonon transport. Benefiting from these synergistic effects, a peak ZT of ∼ 2.0 at 653 K, ZTave of ∼ 1.2 in the range from 303 to 803 K, and Vickers microhardness of ∼ 234 Hv are obtained in (Ge0.91In0.01Sb0.08Te)0.98(SnSe)0.02 sample. This study demonstrates a promising strategy to optimize thermoelectric performance by selectively co-doping functionally separated elements for developing high-performance TE materials.

Tailoring band structure and Ge precipitates through Er and Sb/Bi co-doping to realize high thermoelectric performance in GeTe

Tailoring band structure and Ge precipitates through Er and Sb/Bi co-doping to realize high thermoelectric performance in GeTe

Interstitial Cu: An Effective Strategy for High Carrier Mobility and High Thermoelectric Performance in GeTe

AbstractDense point defects can strengthen phonon scattering to reduce the lattice thermal conductivity and induce outstanding thermoelectric performance in GeTe‐based materials. However, extra point defects inevitably enlarge carrier scattering and deteriorate carrier mobility. Herein, it is found that the interstitial Cu in GeTe can result in synergistic effects, which include: 1) strengthened phonon scattering, leading to ultralow lattice thermal conductivity of 0.48 W m−1 K−1 at 623 K; 2) weakened carrier scattering, contributing to high carrier mobility of 80 cm2 V−1 s−1 at 300 K; 3) optimized carrier concentration of 1.22 × 1020 cm−3. Correspondingly, a high figure‐of‐merit of ≈2.3 at 623 K can be obtained in the Ge0.93Ti0.01Bi0.06Te‐0.01Cu, which corresponds to a maximum energy conversion efficiency of ≈10% at a temperature difference of 423 K. This study systematically investigates the doping behavior of the interstitial Cu in GeTe‐based thermoelectric materials for the first time and demonstrates that the localized interstitial Cu is a new strategy to enhance the thermoelectric performance of GeTe‐based thermoelectric materials.

Condensed point defects enhance thermoelectric performance of rare-earth Lu-doped GeTe

Heavy rare-earth element doping can effectively strengthen phonon scattering, suppress the lattice thermal conductivity, and enhance the overall thermoelectric performance of GeTe. However, the large electronegativity difference between rare-earth elements (such as La, Eu, and Gd) and Ge refrains the doping limit of rare-earth elements below 1 mol.% in GeTe. Here, compared with other rare earth elements, Lu was found to have a relatively small radius and electronegativity difference with Ge, which can induce a high doping level in GeTe. The result shows that Lu doping effectively reduces the lattice thermal conductivity from 0.77 W m−1 K−1 of GeTe to 0.35 W m−1 K−1 of Ge0.98Lu0.02Te at 673 K, and further induces a high zT value of 1.5 in Ge0.98Lu0.02Te at 673 K. Extra Sb alloying optimizes the carrier concentration from 1.02 × 1021 cm−3 of Ge0.98Lu0.02Te to 1.77 × 1020 cm−3 of Ge0.90Lu0.02Sb0.08Te, which results in a reasonable power factor of 33.82 µW cm−1 K−2 and a low electrical thermal conductivity of 0.75 W m−1 K−1 at 673 K in Ge0.90Lu0.02Sb0.08Te. Correspondingly, a peak zT of 1.75 at 673 K and an average zT of 0.92 within the temperature range of 303–723 K are obtained in Ge0.9Lu0.02Sb0.08Te. This study indicates that Lu and Sb co-doping can effectively boost the thermoelectric performance of GeTe-based thermoelectric materials.

Enhanced Thermoelectric Performance in GeTe by Synergy of Midgap state and Band Convergence

AbstractThe good co‐existence of midgap state and valence band degeneracy is realized in Bi‐alloyed GeTe through the In‐Cd codoping to play different but complementary roles in the valence band structure modification. In doping induces midgap state and results in a considerably improved Seebeck coefficient near room temperature, while Cd doping significantly increases the Seebeck coefficient in the mid‐high temperature region by promoting the valence band convergence. The synergistic effects obviously increase the density of state effective mass from 1.39 to 2.65 m0, and the corresponding carrier mobility still reaches 34.3 cm2 V−1 s−1 at room temperature. Moreover, the Bi‐In‐Cd co‐alloying introduces various phonon scattering centers including nanoprecipitates and strain field fluctuations and suppresses the lattice thermal conductivity to a rather low value of 0.56 W m−1 K−1 at 600 K. As a result, the Ge0.89Bi0.06In0.01Cd0.04Te sample obtains excellent thermoelectric properties of zTmax ≈2.12 at 650 K and zTavg ≈1.43 between 300 and 773 K. This study illustrates that the thermoelectric performance of GeTe can be optimized in a wide temperature range through the synergy of midgap state and valence band convergence.

High thermoelectric performance in GeTe with compositional insensitivity

Thermoelectric materials have obtained worldwide attention as they are attractive for waste heat recovery and solid-state cooling. However, their performance is usually sensitive to material compositions, which is less favorable for industrial applications. In this work, we developed composition-insensitive GeTe-based compounds ((100-x-y)%GeTe-x%CuBiSe2-y%PbTe, CBSx-Pby) with high ZTmax as well as ZTave values. The compositional insensitivity can be associated with the persistently high quality factors across the range of compositions. This is largely due to the interplay between electrical and thermal transport caused by the synergy of CuBiSe2 and PbTe alloying. CuBiSe2 alloying can effectively tune the carrier concentrations, while PbTe alloying can significantly decrease the thermal conductivity at a minor sacrifice of electrical properties. The combined effects of CuBiSe2 and PbTe alloying lead to high carrier mobility of 60 cm2V−1s−1 and low thermal conductivities for CBSx-Pby samples simultaneously. Consequently, high ZTave values of 1.4–1.5 in the temperature range of 400 K and 773 K for broad compositions (CBS3-Pby, y = 2 – 8 and CBSx-Pb6, x = 2 – 5) are achieved. A single-leg module is also fabricated, which shows a high power density of 1.46 W/cm2 and an excellent efficiency of 13.4%. The high ZTave with compositional insensitivity and the outstanding module performance demonstrate the promising large-scale application of the developed GeTe-based compositions.

Anomalous enhancement of thermoelectric performance in GeTe with specific interaxial angle and atomic displacement synergy

Discovery and engineering of novel phase structures pave new avenues in the study of phonon-electron decoupling in thermoelectric materials, with the final aim of enhancing their figure of merit ZT . Here, we report a metastable GeTe phase that shows coexisting cubic and rhombohedral phases and enhances the ZT of GeTe-based alloys to ∼0.8 at 300 K and ∼1.3 at 373 K. This is comparable with the state-of-the-art Bi 2 Te 3 -based alloys in the low-temperature range. The ZT enhancement shows a positive correlation with an increased contribution of a special rhombohedral GeTe phase with synergetic specific interaxial angle and atomic displacement, which triggers a multiple-band convergence for enhancing carrier mobility. Moreover, quenching-induced extra phase boundaries and enhanced anharmonicity may cause extra phonon scattering that reduces the lattice thermal conductivity. This work highlights the importance of precision designing phase structures for solving the phonon-electron coupling problem in thermoelectric materials. • A metastable GeTe with coexisting cubic and rhombohedral phases is revealed • An r-GeTe with a specific interaxial angle and atomic displacement is extracted • Weight carrier mobility can be dramatically increased by engineering this phase • The obtained thermoelectric performance is comparable with Bi 2 Te 3 Phase engineering provides an avenue to realize phonon-electron decoupling in thermoelectric materials. Wang et al. reveal a metastable GeTe with coexisting cubic and rhombohedral phases where the rhombohedral GeTe with synergetic specific interaxial angle and atomic displacement triggers multiple-band convergence for sharply increasing the carrier mobility.

Enhanced near-room-temperature thermoelectric performance in GeTe

Enhanced near-room-temperature thermoelectric performance in GeTe

Se-alloying reducing lattice thermal conductivity of Ge0.95Bi0.05Te

l Se-alloying induces dense point defects scatter high-frequency phonons. l Se-alloying induce resonant states strengthen Umklapp phonon scattering. l Approaching low lattice thermal conductivity of ∼0.65 W m −1 K −1 at 723 K. l Approaching a peak figure of merit value of ∼1.6 at 723 K. High lattice thermal conductivity of intrinsic GeTe limits the wide application of GeTe-based thermoelectrics. Recently, the optimization of GeTe-based thermoelectric materials has been focusing on reducing lattice thermal conductivity via strengthening phonon scattering. In this study, we systematically studied thermoelectric properties of Se-alloyed Ge 0.95 Bi 0.05 Te via theoretical calculations, structural characterizations, and performance evaluations. Our results indicate that Se-alloying can induce dense point defects with mass/strain-field fluctuations and correspondingly enhance point defect phonon scattering of the Ge 0.95 Bi 0.05 Te matrix. Se-alloying might also change chemical bonding strength to introduce resonant states in the base frequency of Ge 0.95 Bi 0.05 Te matrix, which can strengthen Umklapp phonon scattering. Finally, a decreased lattice thermal conductivity from ∼1.02 W m −1 K −1 to ∼0.65 W m −1 K −1 at 723 K is obtained in Ge 0.95 Bi 0.05 Te 1- x Se x pellets with increasing the Se content from 0 to 0.3. A peak figure of merit of ∼1.6 at 723 K is achieved in Ge 0.95 Bi 0.05 Te 0.7 Se 0.3 pellet, which is ∼77% higher than that of pristine GeTe. This study extends the understanding on the thermoelectric performance of GeTe.

Thermoelectric performance of Ge1-xSnxTe (0 ≤ x ≤ 0.2) prepared by facile method

Ge1-xSnxTe (0 ​≤ ​x ​≤ ​0.20) alloys have been fabricated through a novel hydrogen decrepitation method followed by a spark plasma sintering process. The impact of Sn substitution on the Structural, morphological and thermoelectric performance of GeTe have been systematically studied. The Seebeck coefficient of all Ge1-xSnxTe (0 ​≤ ​x ​≤ ​0.20) alloys showed the positive sign value at an entire temperature range, while Ge0.95Sn0.05Te showed high in Seebeck coefficient value compared to other samples. The electrical resistivity of Ge1-xSnxTe (0 ​≤ ​x ​≤ ​0.20) alloys were increases with increasing Sn2+(x) content, due to its lowering the carrier density and higher charge carrier mobility. Concomitantly, the isoelectronic substitution of Sn2+ ions at the Ge site effectively to suppress the thermal conductivity of GeTe. Sn substitution drastically reduced the thermal conductivity of Ge1-xSnxTe alloys from 4.0 Wm−1K−1 to 2.6 Wm−1K−1 ​at 723 ​K, which was mainly due to anharmonicity in phonon vibration caused by lattice distortion. As a result, Ge0.95Sn0.05Te alloy exhibited a high dimensionless figure of merit (ZT) of ∼0.63 ​at 723 ​K, which is ∼17.4% higher than pristine GeTe.

Realizing high thermoelectric performance in GeTe by defect engineering on cation sites

A large ZT of 1.89 is obtained in GeTe with Ti/Bi co-doping and Ge self-doping on cation sites. Doping of 1.5 mol% Ti can enhance the effective mass and quality factor B. The Ge-excess method has a better modulation effect than the Ge-deficient method.

High Thermoelectric Performance in Gete with Compositional Insensitivity

High Thermoelectric Performance in Gete with Compositional Insensitivity

Regulation of Ge vacancies through Sm doping resulting in superior thermoelectric performance in GeTe

A high thermoelectric figure of merit ZT of 2.5 at 730 K is achieved in Ge1−xSmxTe through synergetic optimization of electrical and thermal transport properties, leading to superior thermoelectric performance of the materials.

Low-Pressure CVD of GeE (E = Te, Se, S) Thin Films from Alkylgermanium Chalcogenolate Precursors and Effect of Deposition Temperature on the Thermoelectric Performance of GeTe.

The homologous series [GenBu3(EnBu)] (E = Te, Se, S; (1), (3) and (4)) and [GenBu2(TenBu)2] (2) have been synthesized as mobile oils in excellent yield (72-93%) and evaluated as single-source precursors for the low-pressure chemical vapor deposition (LPCVD) of GeE thin films on silica. Compositional and structural characterizations of the deposits have been performed by grazing-incidence X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, and Raman spectroscopy, confirming the phase purity and stoichiometry. Electrical characterization via variable-temperature Hall effect measurements is also reported. Given the strong interest in GeTe and its alloys for thermoelectric applications, variable-temperature Seebeck data were also investigated for a series of p-type GeTe films. The data show that it is possible to tune the thermoelectric response through intrinsic Ge vacancy regulation by varying the deposition temperature, with the highest power factor (40 μW/K2cm@629 K) and effective ZT values observed for the films deposited at higher temperatures.

(GeTe)1-x(AgSnSe2)x: Strong Atomic Disorder-Induced High Thermoelectric Performance near the Ioffe-Regel Limit.

In thermoelectrics, the material's performance stems from a delicate tradeoff between atomic order and disorder. Generally, dopants and thus atomic disorder are indispensable for optimizing the carrier concentration and scatter short-wavelength heat-carrying phonons. However, the strong disorder has been perceived as detrimental to the semiconductor's electrical conductivity owing to the deteriorated carrier mobility. Here, we report the sustainable role of strong atomic disorder in suppressing the detrimental phase transition and enhancing the thermoelectric performance in GeTe. We found that AgSnSe2 and Sb co-alloying eliminates the unfavorable phase transition due to the high configurational entropy and achieve the cubic Ge1-x-ySbyTe1-x(AgSnSe2)x solid solutions with cationic and anionic site disorder. Though AgSnSe2 substitution drives the carrier mean free path toward the Ioffe-Regel limit and minimizes the carrier mobility, the increased carrier concentration could render a decent electrical conductivity, affording enough phase room for further performance optimization. Given the lowermost carrier mean free path, further Sb alloying on Ge sites was implemented to progressively optimize the carrier concentration and enhance the density-of-state effective mass, thereby substantially enhancing the Seebeck coefficient. In addition, the high density of nanoscale strain clusters induced by strong atomic disorders significantly restrains the lattice thermal conductivity. As a result, a state-of-the-art zT ≈ 1.54 at 773 K was attained in cubic Ge0.58Sb0.22Te0.8(AgSnSe2)0.2. These results demonstrate that the strong atomic disorder at the high entropy scale is a previously underheeded but promising approach in thermoelectric material research, especially for the numerous low carrier mobility materials.

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

AbstractOwing 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 Ge1−xVxTe samples are demonstrated to have an enhanced Seebeck coefficient from ≈163 to ≈191 µV K−1. Extra alloying with Bi in Ge1−x−yVxBiyTe 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 grain boundaries, stacking faults, nanoprecipitates, and point defects, reinforcing the wide‐frequency phonon scattering and in turn, securing an ultralow thermal conductivity of ≈0.59 W m−1 K−1. As a result, the Ge0.9V0.02Bi0.08Te sample shows a peak ZT of >2.1 at 773 K, with an average plateaued average ZT of >2.0 from 623 and 773 K, which extends better thermoelectric behavior for GeTe over a wider temperature range. This study clarifies the multiple benefits of V‐doping in GeTe‐based derivatives and provides a framework for a new‐type of high‐performance middle‐temperature thermoelectric material.