Temperature Thermoelectric Performance Research Articles

Robust Room Temperature Thermoelectric Performance of Mg3(Sb, Bi)2‐Based Alloys via Multivalent Mn Doping

Abstractn‐type Mg3(Sb, Bi)2 has excellent room temperature thermoelectric performance, which is, however, severely restricted by the negatively charged Mg vacancies that significantly deteriorate the carrier mobility. Herein, by manipulating the threshold solubility and defect formation energy of Mn, multivalent Mn is selectively introduced that synergistically promotes the carrier conduction according to different Mg chemical potentials; In Mg‐rich areas, interstitial Mn dominates which effectively reduces the migration and accumulation of Mg vacancies, while in Mg poor areas, interstitial Mn switches to substitutional sites that directly compensate for the negative charge. All the Mn centers possess Jahn–Teller inactive positions, leading to an ultra‐stable room temperature thermoelectric performance with a leading ZT up to 0.97. This work reveals the critical effect of multivalent and multifunctional transition metal incorporation in Mg3(Sb, Bi)2‐based alloys toward high room‐temperature thermoelectric performance.

Excellent Room Temperature Thermoelectric Performance in Mg3Sb2-Based Alloys via Multi-Functional Doping of Nb.

Mg3Sb2-based alloys are attracting increasing attention due to the excellent room temperature thermoelectric properties. However, due to the presence and easy segregation of charged Mg vacancies, the carrier mobility in Mg3Sb2-based alloys is always severely compromised that significantly restricts the room temperature performance. General vacancy compensation strategies cannot synergistically optimize the complicated Mg3Sb2 structures involving both interior and boundary scattering. Herein, due to the multi-functional doping effect of Nb, the electron scattering inside and across grains is significantly suppressed by inhibiting the accumulation of Mg vacancies, and leading to a smooth transmission channel of electrons. The increased Mg vacancies migration barrier and optimized interface potential are also confirmed theoretically and experimentally, respectively. As a result, a leading room temperature zT of 1.02 is achieved. This work reveals the multi-functional doping effect as an efficient approach in improving room temperature thermoelectric performance in complicated defect/interface associated Mg3Sb2-based alloys.

Advancing very high temperature thermoelectric performance of Yb4Sb3 through dual-substitutions: a combined experimental and theoretical study

Yb4Sb3 and substituted derivatives were investigated through combined experimental and theoretical investigation for very high temperature thermoelectric applications.

Probing the thermoelectric properties of aluminium-doped copper iodide.

Copper iodide, an environmentally friendly material abundant in nature, holds great significance for room temperature thermoelectric (TE) applications owing to its high Seebeck coefficient and optical transparency. However, to fully unlock its thermoelectric potential and match the performance of conventional TE materials, there is a need to further enhance its electrical conductivity. In this study, we have successfully synthesized nano-crystalline powders of both undoped and aluminium-doped CuI at room temperature using the chemical precipitation method in an ethanol medium. The concentration of aluminium dopant has been optimized to maximize TE performance. At 400 K, the highest TE power factor and figure of merit achieved are 79 μW m-1 K-2 and 0.08, respectively, for CuI doped with 0.1 mol% Al. This enhancement in TE properties can be attributed to the increased carrier density resulting from aluminium doping. The impact of aluminium doping on the temperature-dependent thermal conductivity has been investigated, and the findings are explained by the decay mechanism of optical phonons, supported by the anharmonic phonon coupling theory. Our work delves into the evolution of structural, thermal, optical, and TE properties of CuI upon aluminium (Al) doping. The results provide valuable insights into the future application of CuI in transparent thermoelectric and optoelectronic fields.

Dopant dependent microstructure of hot-pressed SiGe alloys and its implications on thermoelectric properties

SiGe is a proven high temperature thermoelectric material for space application. We have investigated the role of dopants (P and B) on the densification of SiGe alloys. It was observed that on P doping there is a formation of liquidous SiP phase in the SiGe matrix during hot pressing that improves the diffusion across grain boundaries and as a result ∼98 % of theoretical density was achieved. In case of identically prepared B doped samples, the segregation of B resulted in porous microstructure and low density ∼89 %. Such a difference in microstructure resulted a figure-of-merit of ∼1.29 (at 1100K) for n-type SiGe (P doped) and ∼0.86 (at 1100K) for p-type SiGe (B doped) at a hot press temperature of 1273 K. The study suggests that in case of SiGe apart from doping the densification of materials plays a very important role in improving its thermoelectric performance.

Optimization of Thermoelectric Property of n‐Type Mg3Sb2 Near Room Temperature via Mn&Se Co‐Doping

AbstractThe Bi2Te3 family has been considered a state‐of‐the‐art thermoelectric material for room‐temperature applications for over half a century. However, scarcity of the material Te has been a persistent issue. Recently, the discovery of n‐type Mg3(Bi, Sb)2‐based materials provides new hope for replacing traditional Bi2Te3, but their thermoelectric properties near room temperature still need improvement for application to practical devices. Herein, a competitive figure of merit of ≈0.8 at 300 K and a high power factor greater than 30 µW cm−1 K−2 at 300 K in n‐type Mg3.14Mn0.06Bi1.4Sb0.59Se0.01 is reported, benefiting from the rationally tuned carrier concentration of 2.29×1019 cm−3 at room temperature. Substituting the Mg site with Mn in Mg3.2Bi1.4Sb0.59Se0.01 changes the dominant carrier scattering mechanism from a mixed scattering of acoustic phonons and ionized impurities to acoustic phonon scattering. Mn doping in Mg3.2Bi1.4Sb0.59Se0.01 also enhances the mobility to 180 cm2 V−1 s−1, reduces the thermal conductivity, and significantly increases the quality factor β of the material. The high room temperature thermoelectric performance of n‐type Mn&Se co‐doped Mg3(Bi, Sb)2‐based materials makes them a highly competitive substitute for commercialized n‐type Bi2Te3.

Ag2Se Nanorod Arrays with Ultrahigh Room Temperature Thermoelectric Performance and Superior Mechanical Properties.

Ag2Se is an intriguing material for room-temperature energy harvesting. Herein, we report the fabrication of Ag2Se nanorod arrays by glancing angle deposition technique (GLAD) followed by simple selenization in a two-zone furnace. Ag2Se planar films of different thickness were also prepared. The unique tilted Ag2Se nanorod arrays show excellent zT = 1.14 ± 0.09 and a power factor of 3229.21 ± 149.01 μW/m-K2, respectively, at 300 K. The superior thermoelectric performance of Ag2Se nanorod arrays compared to planar Ag2Se films could be ascribed to the unique nanocolumnar architecture that not only facilitates efficient electron transport but also significantly scatters phonons at the interfaces. Furthermore, the nanoindentation measurements were performed to explore mechanical properties of the as-prepared films. The Ag2Se nanorod arrays showed hardness values of 116.51 ± 4.25 MPa and elastic modulus of 10,966.01 ± 529.61 MPa, which are lowered by 51.8 and 45.6%, compared to Ag2Se films, respectively. The synergetic dependence between the tilt structure and thermoelectric properties accompanied with the simultaneous improvement in mechanical properties opens a new avenue for the practical applications of Ag2Se in next-generation flexible thermoelectric devices.

Multi-scale hierarchical microstructure modulation towards high room temperature thermoelectric performance in n-type Bi2Te3-based alloys

Bi2Te3-based thermoelectric materials are widely used in near room temperature refrigeration filed. Although Bi2Te3-based polycrystals prepared by powder metallurgy method exhibit good mechanical properties, the low room temperature dimensionless figure of merit (zT) for n-type alloys restricts their further usage. In this work, the electrical and thermal transport properties are manipulated synergistically by multi-scale hierarchical microstructure modulations in n-type Ag2Te/Bi2Te3 composites, including atomic-scale extrinsic point defects, nano-scale low-angel grain boundaries, mesoscale precipitate, and texturing. The carrier concentration is optimized by extrinsic point defects and the carrier mobility is improved due to the strengthened texture, and thus the power factor reaches a high value of 3.6 × 10−3 Wm−1/K2, which is even higher than the hot deformed counterparts. Simultaneously, the phonon scattering is enhanced by the multi-scale defects and the lattice thermal conductivity is suppressed. A high room temperature zT of ∼1.0 and an average zT of 0.96 in the 300–500 K range with good mechanical properties are obtained without hot deformation. This work puts forward a paradigm of enhancing the thermoelectric properties via multi-scale hierarchical microstructure modulations and is significant to the industrialization of manufacturing Bi2Te3-based alloys and devices.

Highly deformable Ag2Te1-xSex-based thermoelectric compounds

Thermoelectric semiconductors are crucial for many critical applications, but are also universally fragile, which greatly limits the development of room temperature flexible thermoelectric devices. Herein, an extraordinary deformability at room temperature and high thermoelectric performance are simultaneously realized in wide composition of Ag2Te1-xSex (x = 0–0.2) compounds with monoclinic structure. An average compressive strain rate of 24% at room temperature is attained for the pristine Ag2Te compound. Moreover, a tensile strain rate of 43% is measured at room temperature using the in-situ transmission electron microscopy. First Principles calculations and in-situ transmission electron microscope tensile test results indicate that the Ag2Te compound is inclined to slip along the (−102) [010] plane under external forces due to a larger ratio between the cleavage energy (Ec) and the slip energy barrier. The slipping process generates high concentrations of dislocations, deformations, and amorphous structures, which together dissipate the externally applied load energy, yielding superior deformability. Meanwhile, the maximum dimensionless figure of merit ZT of 0.61 is obtained at 380 K. This study demonstrates that Ag2Te-based compounds are promising for the fabrication of flexible thermoelectric devices in applications, such as wearable, room temperature electronic gadgets.

Promising high temperature thermoelectric performance of layered oxypnictide YZnAsO

Thermoelectric materials can convert heat into electricity directly via the Seebeck effect, providing an alternative to global energy demands. Here we present mechanical, dynamical, and thermoelectric properties of YZnAsO, a quaternary oxypnictide, in the framework of Density Functional Theory. The low value of Debye temperature (θD=308.29K) and high value of the Grüneisen parameter (∼1.77) hint for low lattice thermal conductivity (kl), and this is supported by the computed value of ∼0.4 W/mK at 800 K. The electronic transport coefficients are computed using Boltzmann transport equation beyond the constant relaxation time approximation (CRTA) including different scattering mechanisms. While the power factor for hole doping is higher along ‘a’, the kl is extremely low along ‘c’, resulting in a high figure of merit (ZT) along ‘c’. Hence, we predict YZnAsO as a promising n-type oxide thermoelectric owing to its low kl with a high ZT =1.07 at 800 K with 15% maximum thermoelectric efficiency.

Enhanced near-room temperature thermoelectric performance and mechanical strength of n-type BiTeSe materials incorporated with Ag2Se inclusions

Bi2Te3-based alloys are the best thermoelectric materials near room temperature.

Correction to: Study of high temperature electrical conductivity and thermoelectric performance in Mg2-δSi0.35-xSn0.65Gex (δ = 0–0.04 and x = 0, 0.05) intermetallic alloys

Correction to: Study of high temperature electrical conductivity and thermoelectric performance in Mg2-δSi0.35-xSn0.65Gex (δ = 0–0.04 and x = 0, 0.05) intermetallic alloys

Achieving metal-like malleability and ductility in Ag2Te1-xSx inorganic thermoelectric semiconductors with high mobility

Inorganic semiconductor Ag2Te1-x S x has been recently found to exhibit unexpected plastic deformation with compressive strain up to 30%. However, the origin of the abnormal plasticity and how to simultaneously achieve superb ductility and high mobility are still elusive. Here, we demonstrate that crystalline/amorphous Ag2Te1-x S x (x= 0.3, 0.4, and 0.5) composites can exhibit excellent compressive strain up to 70% if the monoclinic Ag2Te phase, which commonly exists in the matrix, is eliminated. Significantly, an ultra-high tensile elongation reaching 107.3% was found in Ag2Te0.7S0.3, which is the highest one yet reported in the system and even surpasses those achieved in some metals and high-entropy alloys. Moreover, high mobility of above 1000cm2 V-1 s-1 at room temperature and good thermoelectric performance are simultaneously maintained. A modified Ashby plot with ductility factor versus carrier mobility is thereby proposed to highlight the potential of solid materials for applications in flexible/wearable electronics.

125Te NMR study of the bulk of topological insulators Bi2Te3 and Sb2Te3

AbstractThe narrow band gap semiconductors Bi2Te3 and Sb2Te3 are well known for their room temperature thermoelectric performance. Recently, they were shown to serve as model systems of three‐dimensional topological insulators with a bulk band gap and very robust, spin‐resolved surface states due to a special band inversion in their periodic bulk. Evidently, it is of interest to investigate the special surface states with a local probe like nuclear magnetic resonance (NMR). However, especially the bulk NMR of these materials shows peculiar and rather unexpected phenomena, e. g., a magnetic field induced deformation of the local charge symmetry and excessive line broadening due to a special internuclear coupling. Here we report a comprehensive account of the room temperature NMR properties of the spin‐1/2 nucleus 125Te of single crystalline Bi2Te3 and Sb2Te3. This includes a very unusual spin‐lattice relaxation that seems not to be reflected in the NMR shift, as well as an exchange enhanced NMR line broadening.

A comprehensive review on Bi2Te3‐based thin films: Thermoelectrics and beyond

AbstractBi2Te3‐based materials are not only the most important and widely used room temperature thermoelectric (TE) materials but are also canonical examples of topological insulators in which the topological surface states are protected by the time‐reversal symmetry. High‐performance thin films based on Bi2Te3 have attracted worldwide attention during the past two decades due primarily to their outstanding TE performance as highly efficient TE coolers and as miniature and flexible TE power generators for a variety of electronic devices. Moreover, intriguing topological phenomena, such as the quantum anomalous Hall effect and topological superconductivity discovered in Bi2Te3‐based thin films and heterostructures, have shaped research directions in the field of condensed matter physics. In Bi2Te3‐based films and heterostructures, delicate control of the carrier transport, film composition, and microstructure are prerequisites for successful device operations as well as for experimental verification of exotic topological phenomena. This review summarizes the recent progress made in atomic defect engineering, carrier tuning, and band engineering down to a nanoscale regime and how it relates to the growth and fabrication of high‐quality Bi2Te3‐based films. The review also briefly discusses the physical insight into the exciting field of topological phenomena that were so dramatically realized in Bi2Te3‐ and Bi2Se3‐based structures. It is expected that Bi2Te3‐based thin films and heterostructures will play an ever more prominent role as flexible TE devices collecting and converting low‐level (body) heat into electricity for numerous electronic applications. It is also likely that such films will continue to be a remarkable platform for the realization of novel topological phenomena.

Enhancement of high temperature thermoelectric performance of cobaltite based materials for automotive exhaust thermoelectric generators

Thermoelectric (TE) generators can directly convert exhaust waste heat into electricity in vehicles. However, the low conversion efficiency of TE generators is the main obstacle to their commercialization in automotive. Their efficiency mainly depends on the performance of the used materials which is quantified by the figure of merit (ZT value). In the present study, single- and co-doped calcium cobaltites (CCO) with rare-earth (Tb) and transition metals (Cu, Fe, Ni, Mn, Cr) were produced using sol–gel technique in order to improve their high temperature TE properties for heat recovery in exhaust manifold applications. By the combined effect of doping approach and the production technique used in this study, a remarkable decrease in the grain size of CCO was obtained, and thus its thermal conductivity dramatically decreased. Besides, thermopower values were improved significantly. The reduction in thermal conductivity and the increase in thermopower led to an enhancement in ZT value of CCO ceramics. Among all the co-doped samples, Tb–Cu co-doped CCO displayed the maximum ZT value of 0.116 at 873 K which is 2.5 times larger than that of pure CCO. The high thermal stability and the enhanced TE performance make Tb–Cu co-doped CCO material a potential candidate for heat recovery in automotive exhaust TE generators.

Enhancing the room temperature thermoelectric performance of n-type Bismuth-telluride-based polycrystalline materials by low-angle grain boundaries

Bi2Te3-based thermoelectric materials are widely used in solid-state refrigeration near room temperature. However, the room temperature figure of merit (zT) of n-type Bi2Te3-based polycrystals produced by once sintering is always lower than 0.8. Herein, low-angle grain boundaries (LAGBs) are introduced in n-type Bi2Te2.7+xSe0.3 by a simple step-hot-pressing procedure (once sintering) and well characterized by scanning transmission electron microscopy. LAGBs consist of dislocation arrays that can effectively scatter the medium-frequency phonons and thus suppress the lattice thermal conductivity. Although LAGBs also serve as scattering centers of low-energy electrons and deteriorate the carrier mobility, they could contribute to the enhanced Seebeck coefficient owing to the increased scattering factor. Overall, the samples with LAGBs own lower electronic thermal conductivity at the same power factor level. Finally, a high room temperature zT of 0.94 is obtained in n-type Bi2Te2.7Se0.3, which is comparable to those produced by multiple-time sintering. Moreover, step-hot-pressing is also found to be effective in promoting the room temperature zT of p-type Bi2Te3-based polycrystals. This work puts forward a new and simple method to construct LAGBs in Bi2Te3-based alloys that enhances their zTs, and sheds light on the underlying mechanisms about how the LAGB affects the electrical and thermal transport properties.

Weak-ferromagnetism for room temperature thermoelectric performance enhancement in p-type (Bi,Sb)2Te3

Unceasing efforts have been devoted to performance enhancement of thermoelectric (TE) materials, and recently reports suggested a new approach by utilizing magnetism to increase power factor. This work investigated the doping effect of Fe on the TE properties of Bi2Te3-based materials. A series of Fex(Bi,Sb)2-xTe3 bulk samples were synthesized via mechanical alloying combined with spark plasma sintering. XRD results and DFT calculations indicate that Fe2+ and Fe3+ would coexist and substitute Bi3+ site firstly and shrink lattice. The co-doped Fe2+/Fe3+ in (Bi,Sb)2Te3 is helpful to reduce carrier concentration (nH), band gap (Eg) and increase effective mass (m∗). With further increase of x, ferromagnetic FeTe2 second phase was precipitated from (Bi,Sb)2Te3 matrix. A weak-ferromagnetism was observed in all Fe-doped samples via M-H curve, which could scatter low energy carriers along with little effect on high-energy carriers, whereby the mobility was enhanced effectively. Owing to the synergistic effect of weak-ferromagnetism and optimized band structure, the maximum power factor reaches up to 45 μWcm−1K−2 as x = 0.05, which is 28.5% higher than that at x = 0. The peak ZT value reaches up to 1.2 at 323 K along with a theoretical ηmax of 7.6% in the range of 303–473 K were achieved in x = 0.05 sample. The results suggest that introducing weak-ferromagnetism is an effective way to enhance room temperature TE performance of Bi–Sb–Te based materials.

High thermopower and power factors in EuFeO3 for high temperature thermoelectric applications: A first-principles approach

Thermoelectric materials that can work at operating temperatures of T ≥ 900 K are highly desirable since the key thermoelectric factors of most thermoelectric materials degrade at high temperatures. In this work, we investigate the high temperature thermoelectric performance of EuFeO3 using a combination of first-principles methods and semi-classical Boltzmann transport theory. High temperature thermoelectric performance is achieved owing to the presence of corrugated flatbands in the valence band region and extremely flatbands in the conduction band region. The lowest energetic structure of EuFeO3 lies within a G-type antiferromagnetic configuration, and the effect of compressive and tensile strains (−7% to +7%) along the (a, b) axes on thermoelectric performance is systematically analyzed. An extremely high value of the Seebeck coefficient (more than 1000 μV/K) is consistently recorded in the high temperature region between 900 K and 1400 K in this material. Furthermore, electrical conductivities and power factors are high and electronic thermal conductivities are low in the considered range of temperatures. The calculated theoretical minimum lattice conductivity is small, estimated at around 1.47–1.54 W m−1 K−1. A compressive strain of −3% is revealed to be the optimum level of strain for enhancing the key thermoelectric factors. Overall, p-type doping shows better thermoelectric performance than n-type doping in EuFeO3.

Room temperature thermoelectric performance of Methyl Ammonium Lead Iodide Perovskite and their MWCNT-PANI composites

The excellent properties of Methyl Ammonium Lead Iodide (MAPI) have already created an extensive research interest in photovoltaic applications. However, their utility in thermoelectric application is still not realized thoroughly by researchers. By continuing this interest, we have explored the formation of low dimensional CH3NH3PbI3 (MAPI) perovskite in presence of Polyaniline (PANI) and Multi-Walled Carbon Nanotubes (MWCNT) and its thermoelectric performance. For this purpose, a two stage, in-situ synthesis method was developed to prepare various composites such as MAPI-PANI, MWCNT-MAPI and MWCNT-PANI-MAPI. The as-formed MWCNT-PANI-MAPI composite revealed p-type conductivity with enhanced ZT (up to ~20,000 times) and power factor (3000 times) at room temperature as compared to pristine MAPI sample. Finally, we have demonstrated a proto-type thermoelectric power generator (TE device) fabricated using the best performing composite sample and measured its power output and efficiency at varied δT.