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Dual-Cation CuAgSe-Based Material: Rapid Mass Transfer in Synthesis and High Thermoelectric Performance Realization. ACS APPLIED MATERIALS & INTERFACES 2024; 16:22189-22196. [PMID: 38651521 DOI: 10.1021/acsami.4c02217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/25/2024]
Abstract
Understanding mass transfer mechanisms is vital for developing new material synthesis and densification technologies. Ion transport, serving both mass and charge transfer, is essential for the rapid preparation of high-performance fast ionic conductor thermoelectric materials like Zn4Sb3 and Cu2Q (Q = S, Se). In the case of dual-cation fast ion conductor materials like CuAgSe, exploring the relationship between cation transport becomes pertinent. In this study, copper (Cu) and selenium (Se) undergo a reaction in the presence of an electric field (∼15 A), resulting in the formation of the CuSe compound. Subsequent to this initial reaction, a subsequent thermal environment facilitates the interaction among Cu, CuSe, and Ag2Se, culminating in the rapid formation and densification of CuAgSe (with a relative density exceeding 99%) in just 30 s. Evidently, the diffusion of copper ions substantiates a pivotal role in facilitating mass transfer. As a result, CuAg1+xSe samples with different silver contents (x = 0.01, 0.02, 0.03, 0.04 and 0.05) can effectively inhibit cation vacancy, and introduce highly ordered Ag nanotwins to enhance the electrical transport performance. For CuAg1.04Se, a peak ZT value of 1.0 can be achieved at 673 K, which is comparable to the literatures. This work will guide the future electric field-assisted rapid mass transfer of materials.
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Silver Copper Chalcogenide Thermoelectrics: Advance, Controversy, and Perspective. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024:e2313146. [PMID: 38608290 DOI: 10.1002/adma.202313146] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Revised: 04/09/2024] [Indexed: 04/14/2024]
Abstract
Thermoelectric technology, which enables a direct and pollution-free conversion of heat into electricity, provides a promising path to address the current global energy crisis. Among the broad range of thermoelectric materials, silver copper chalcogenides (AgCuQ, Q = S, Se, Te) have garnered significant attention in thermoelectric community in light of inherently ultralow lattice thermal conductivity, controllable electronic transport properties, excellent thermoelectric performance across various temperature ranges, and a degree of ductility. This review epitomizes the recent progress in AgCuQ-based thermoelectric materials, from the optimization of thermoelectric performance to the rational design of devices, encompassing the fundamental understanding of crystal structures, electronic band structures, mechanical properties, and quasi-liquid behaviors. The correlation between chemical composition, mechanical properties, and thermoelectric performance in this material system is also highlighted. Finally, several key issues and prospects are proposed for further optimizing AgCuQ-based thermoelectric materials.
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High-Mobility Topological Semimetals as Novel Materials for Huge Magnetoresistance Effect and New Type of Quantum Hall Effect. MATERIALS (BASEL, SWITZERLAND) 2023; 16:7579. [PMID: 38138720 PMCID: PMC10744697 DOI: 10.3390/ma16247579] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2023] [Revised: 12/04/2023] [Accepted: 12/06/2023] [Indexed: 12/24/2023]
Abstract
The quantitative description of electrical and magnetotransport properties of solid-state materials has been a remarkable challenge in materials science over recent decades. Recently, the discovery of a novel class of materials-the topological semimetals-has led to a growing interest in the full understanding of their magnetotransport properties. In this review, the strong interplay among topology, band structure, and carrier mobility in recently discovered high carrier mobility topological semimetals is discussed and their effect on their magnetotransport properties is outlined. Their large magnetoresistance effect, especially in the Hall transverse configuration, and a new version of a three-dimensional quantum Hall effect observed in high-mobility Weyl and Dirac semimetals are reviewed. The possibility of designing novel quantum sensors and devices based on solid-state semimetals is also examined.
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A novel bifunctional thioarsenate based on unprecedented molecular [Cd 4As 8Se 16(Se 2) 2] 8- cluster anions. Chem Commun (Camb) 2023; 59:12124-12127. [PMID: 37740276 DOI: 10.1039/d3cc03538g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/24/2023]
Abstract
Exploring and developing new functional inorganic chalcogenides with unique structures is always one of the most important missions in solid-state chemistry, especially those with molecular structures. Herein, a novel quaternary thioarsenate, Cs2CdAsSe5, is found to be based on an unprecedented molecular (poly)chalcogenide cluster architecture, which has never been discovered in inorganic chalcogenide systems. This rare windmill-like [Cd4As8Se16(Se2)2]8- cluster is made of four [CdSe4] and [As(V)Se4] tetrahedra via corner-sharing Se atoms and Se-Se bonds. Specifically, Cs2CdAsSe5 exhibits a remarkable photocurrent response and a large computationally predicted birefringence, and the origin of the optoelectronic performance and optical anisotropy is confirmed by detailed theoretical investigation.
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Balanced High Thermoelectric Performance in n-Type and p-Type CuAgSe Realized through Vacancy Manipulation. ACS APPLIED MATERIALS & INTERFACES 2023; 15:40781-40791. [PMID: 37589126 DOI: 10.1021/acsami.3c08897] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/18/2023]
Abstract
As a liquid-like material, CuAgSe has high carrier mobility and ultralow lattice thermal conductivity. It undergoes an n-p conduction-type transition during β- to α-phase transition with increasing temperature. Moreover, optimization of the thermoelectric performance of CuAgSe is rather difficult, owing to the two-carrier conduction in this material. In this work, we reported the free tuning of the conduction type and thermoelectric performance of CuAgSe by manipulating the cation vacancies. Positron annihilation measurements reveal that the increase in CuAg content can effectively suppress the cation vacancies and reduce the hole carrier concentration, resulting in n-type conduction at high temperatures. Doping with Zn at the Cu sublattice in the CuAg-excessive CuAgSe can further decrease the number of vacancies, leading to a significant decrease in hole carrier concentration. Furthermore, the reduction of vacancies leads to weakening of carrier scattering. As a result, carrier mobility is also enhanced, thus improving the thermoelectric performance of n-type CuAgSe. On the other hand, high-performance p-type CuAgSe can be achieved by decreasing the CuAg content to introduce more cation vacancies. Ultimately, both n-type and p-type CuAgSe with superb thermoelectric performance are obtained, with a zTmax of 0.84 in Cu1.01Ag1.02Zn0.01Se (n-type) and 1.05 in (CuAg)0.96Se (p-type) at 600 K and average zT of 0.77 and 0.94 between 470 and 630 K for n-type and p-type, respectively.
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Incommensurately Modulated Structure in AgCuSe-Based Thermoelectric Materials for Intriguing Electrical, Thermal, and Mechanical Properties. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2023; 19:e2300699. [PMID: 36843312 DOI: 10.1002/smll.202300699] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2023] [Revised: 02/09/2023] [Indexed: 06/02/2023]
Abstract
AgCuSe-based materials have attracted great attentions recently in thermoelectric (TE) field due to their extremely high electron mobility, ultralow lattice thermal conductivity, and abnormal "brittle-ductile" transition at room temperature. However, although the investigation on the crystal structure of AgCuSe low-temperature phase (named as β-AgCuSe) was started more than half a century before, it is still in controversy yet, which greatly limits the understanding of its intriguing electrical, thermal, and mechanical performance. In this work, via adopting the advanced three-dimensional electron diffraction technique, this study finds that the AgCuSe-based materials crystalize in an incommensurately modulated structure with an orthorhombic Pmmn(0β1/2)s00 superspace group. The local lattice distortion in the incommensurately modulated structure has weak effects on the conduction band minimum due to the delocalized and isotropic feature of Ag 5s states, leading to high carrier mobility. Likewise, the inhomogeneous, weak, and anisotropic Ag-Se bonds result in the high degree of anharmonicity and ultralow lattice thermal conductivity. Furthermore, alloying S in AgCuSe reinforces the interaction between the adjacent Ag-Se layers, yielding the "brittle-ductile" transition at room temperature. This work well interprets the structure-performance relationship of AgCuSe-based materials and sheds light on the future investigation of this class of promising TE materials.
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Magnetism Modulation for Cryogenic Thermoelectric Enhancements in Fe 3O 4 Nanoparticle-Incorporated Bi 0.85Sb 0.15 Nanocomposites. ACS APPLIED MATERIALS & INTERFACES 2023; 15:8105-8119. [PMID: 36732879 DOI: 10.1021/acsami.2c20778] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
The internal magnetism introduced by the magnetic nanoparticles combined with the external magnetic field can provide an effective way to modulate the thermoelectric (TE) properties of materials. Herein, we comparably investigate the effect of magnetism of Fe3O4 nanoparticles (Fe3O4-NPs) and the external magnetic field on the cryogenic thermoelectric properties of Fe3O4-NP/Bi0.85Sb0.15 nanocomposites. With the ferromagnetism-superparamagnetism transition, the Fe3O4-NPs in the superparamagnetic state exhibit a stronger magneto-trapped carrier effect, where the electron concentration at high temperature is evidently reduced. With the simultaneous increase of S and reduction of electronic thermal conductivity, a high ZT value of 0.33 at 180 K is obtained for 0.05 wt % Fe3O4/Bi0.85Sb0.15. Meanwhile, under the external magnetic field, the magnetoresistance of the composites is suppressed by Fe3O4-NPs, which results in a remarkable enhancement of the electronic transport performance. Consequently, the highest ZT value of 0.48 at 220 K under 1 T is achieved for 0.1 wt % Fe3O4-NPs/Bi0.85Sb0.15, increased by 55% compared with that of the matrix. A single-leg device is prepared using 0.1 wt % Fe3O4-NP/Bi0.85Sb0.15 nanocomposites. Its cooling temperature difference at 180 K reaches 1.3 and 3.2 K under 0 and 1 T when applying 300 mA current, increased by 20 and 46% compared with that of the matrix, respectively. This work suggests that magnetism modulation with introducing magnetic nanoparticles will enhance the TE and magneto-TE performance of composite materials.
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Ag 2 Q-Based (Q = S, Se, Te) Silver Chalcogenide Thermoelectric Materials. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2110236. [PMID: 36036433 DOI: 10.1002/adma.202110236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 05/18/2022] [Indexed: 06/15/2023]
Abstract
Thermoelectric technology provides a promising solution to sustainable energy utilization and scalable power supply. Recently, Ag2 Q-based (Q = S, Se, Te) silver chalcogenides have come forth as potential thermoelectric materials that are endowed with complex crystal structures, high carrier mobility coupled with low lattice thermal conductivity, and even exceptional plasticity. This review presents the latest advances in this material family, from binary compounds to ternary and quaternary alloys, covering the understanding of multi-scale structures and peculiar properties, the optimization of thermoelectric performance, and the rational design of new materials. The "composition-phase structure-thermoelectric/mechanical properties" correlation is emphasized. Flexible and hetero-shaped thermoelectric prototypes based on Ag2 Q materials are also demonstrated. Several key problems and challenges are put forward concerning further understanding and optimization of Ag2 Q-based thermoelectric chalcogenides.
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Energy-Saving Pathways for Thermoelectric Nanomaterial Synthesis: Hydrothermal/Solvothermal, Microwave-Assisted, Solution-Based, and Powder Processing. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2022; 9:e2106052. [PMID: 35843868 PMCID: PMC9443476 DOI: 10.1002/advs.202106052] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Revised: 05/06/2022] [Indexed: 05/16/2023]
Abstract
The pillars of Green Chemistry necessitate the development of new chemical methodologies and processes that can benefit chemical synthesis in terms of energy efficiency, conservation of resources, product selectivity, operational simplicity and, crucially, health, safety, and environmental impact. Implementation of green principles whenever possible can spur the growth of benign scientific technologies by considering environmental, economical, and societal sustainability in parallel. These principles seem especially important in the context of the manufacture of materials for sustainable energy and environmental applications. In this review, the production of energy conversion materials is taken as an exemplar, by examining the recent growth in the energy-efficient synthesis of thermoelectric nanomaterials for use in devices for thermal energy harvesting. Specifically, "soft chemistry" techniques such as solution-based, solvothermal, microwave-assisted, and mechanochemical (ball-milling) methods as viable and sustainable alternatives to processes performed at high temperature and/or pressure are focused. How some of these new approaches are also considered to thermoelectric materials fabrication can influence the properties and performance of the nanomaterials so-produced and the prospects of developing such techniques further.
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Abstract
Energy storage and conversion in a clean, efficient, and safe way is the core appeal of a modern sustainable society, which is built on the development of multifunctional materials. Superlattice structures can integrate the advantage of their sublayers while new phenomena may arise from the interface, which play key roles in modern semiconductor technology; however, additional concerns such as stability and yield challenge their large-scale applications in industrial products. In this Perspective we focus our interest on a distinctive category of easily available multilayered inorganic materials that have well-defined subunit structures and can be regarded as bulk superlattice analogues. We illustrate several specific combining forms of subunits in bulk superlattice analogues, including soft/rigid sublayers, electron/phonon transport sublayers, quasi-two-dimensional layers, and intercalated metal layers. We hope to provide insights into material design and broaden the application scope in the field of energy conversion by integrating the versatility of subunits into these bulk superlattice analogues.
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Phase Transition Behaviors and Thermoelectric Properties of CuAgTe 1-xSe x near 400 K. ACS APPLIED MATERIALS & INTERFACES 2022; 14:1015-1023. [PMID: 34951308 DOI: 10.1021/acsami.1c20333] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Phase transition is an effective strategy to engineer thermal conductivity and electrical transports. Recently, p-type CuAgTe1-xSex materials were reported to show excellent thermoelectric performance at 300-450 K, but the data are controversial due to the cooccurrence of phase transition in this temperature range. Accurately measuring and analyzing the electrical and thermal transport properties in the narrow phase transition temperature range is a quite challenging task. In this work, we systemically investigate the phase transition behavior, and electrical and thermal transport properties of p-type CuAgTe1-xSex (x = 0.3, 0.4, and 0.5) near 400 K. CuAgTe1-xSex (x = 0.3, 0.4, and 0.5) materials show similar phase transition temperatures but quite different phase transition speeds. The phase transition has a weak influence on the electrical transport properties of CuAgTe0.7Se0.3 and CuAgTe0.6Se0.4, but a strong influence on those of CuAgTe0.5Se0.5. Likewise, an obvious underestimation of thermal diffusivity, with a maximum deviation about 20% off the real value, is observed during the phase transition temperature range for CuAgTe1-xSex. Finally, CuAgTe0.7Se0.3 shows a peak zT around 0.9 at 390 K. The present study proves that CuAgTe1-xSex solid solutions are one kind of promising near-room-temperature thermoelectric material.
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12
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Some Thermoelectric Phenomena in Copper Chalcogenides Replaced by Lithium and Sodium Alkaline Metals. NANOMATERIALS 2021; 11:nano11092238. [PMID: 34578562 PMCID: PMC8466618 DOI: 10.3390/nano11092238] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/11/2021] [Revised: 07/31/2021] [Accepted: 08/05/2021] [Indexed: 11/16/2022]
Abstract
This review presents thermoelectric phenomena in copper chalcogenides substituted with sodium and lithium alkali metals. The results for other modern thermoelectric materials are presented for comparison. The results of the study of the crystal structure and phase transitions in the ternary systems Na-Cu-S and Li-Cu-S are presented. The main synthesis methods of nanocrystalline copper chalcogenides and its alloys are presented, as well as electrical, thermodynamic, thermal, and thermoelectric properties and practical application. The features of mixed electron–ionic conductors are discussed. In particular, in semiconductor superionic copper chalcogenides, the presence of a “liquid-like phase” inside a “solid” lattice interferes with the normal propagation of phonons; therefore, superionic copper chalcogenides have low lattice thermal conductivity, and this is a favorable factor for the formation of high thermoelectric efficiency in them.
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Decoupling of the Electrical and Thermal Transports in Strongly Coupled Interlayer Materials. J Phys Chem Lett 2021; 12:7832-7839. [PMID: 34379422 DOI: 10.1021/acs.jpclett.1c01783] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Thermoelectric materials which enable heat-to-electricity conversion are fundamentally important for heat management in semiconductor devices. Achieving high thermoelectric performance requires blocking the thermal transport and maintaining the high electronic transport, but it is a challenge to satisfy both criteria simultaneously. We propose that tuning the interlayer distance can effectively modulate the electrical and thermal conductivities. We find group IV-VI and V semiconductors with a moderate interlayer distance can exhibit high thermoelectric performance. Taking SnSe as an example, we reveal that in the out-of-plane direction the delocalized pz orbitals combined with the relatively small interlayer distance lead to overlapping of the antibonding state wave functions, which is beneficial for high electronic transport. However, because of the breakdown of the chemical bond, the out-of-plane thermal conductivity is small. This study provides a strategy to enhance electrical conductivity without increasing thermal conductivity and thus sheds light on the design of thermoelectric devices.
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Macroscopic weavable fibers of carbon nanotubes with giant thermoelectric power factor. Nat Commun 2021; 12:4931. [PMID: 34389723 PMCID: PMC8363648 DOI: 10.1038/s41467-021-25208-z] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 07/26/2021] [Indexed: 11/29/2022] Open
Abstract
Low-dimensional materials have recently attracted much interest as thermoelectric materials because of their charge carrier confinement leading to thermoelectric performance enhancement. Carbon nanotubes are promising candidates because of their one-dimensionality in addition to their unique advantages such as flexibility and light weight. However, preserving the large power factor of individual carbon nanotubes in macroscopic assemblies has been challenging, primarily due to poor sample morphology and a lack of proper Fermi energy tuning. Here, we report an ultrahigh value of power factor (14 ± 5 mW m−1 K−2) for macroscopic weavable fibers of aligned carbon nanotubes with ultrahigh electrical and thermal conductivity. The observed giant power factor originates from the ultrahigh electrical conductivity achieved through excellent sample morphology, combined with an enhanced Seebeck coefficient through Fermi energy tuning. We fabricate a textile thermoelectric generator based on these carbon nanotube fibers, which demonstrates high thermoelectric performance, weavability, and scalability. The giant power factor we observe make these fibers strong candidates for the emerging field of thermoelectric active cooling, which requires a large thermoelectric power factor and a large thermal conductivity at the same time. Preserving the large power factor of carbon nanotubes is challenging, due to poor sample morphology and a lack of proper Fermi energy tuning. Here, the authors achieve a value of power factor of 14 ± 5 mW m−1 K−2 originating from the preserved conductivity and the ability to tune Fermi energy.
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Intrinsically ultralow thermal conductive inorganic solids for high thermoelectric performance. Chem Commun (Camb) 2021; 57:4751-4767. [PMID: 33884387 DOI: 10.1039/d1cc00830g] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Thermoelectric materials which can convert heat energy to electricity rely on crystalline inorganic solid state compounds exhibiting low phonon transport (i.e. low thermal conductivity) without much inhibiting the electrical transport. Suppression of phonons traditionally has been carried out via extrinsic pathways, involving formation of point defects, foreign nanostructures, and meso-scale grains, but the incorporation of extrinsic substituents also influences the electrical properties. Crystalline materials with intrinsically low lattice thermal conductivity (κlat) provide an attractive paradigm as it helps in simplifying the complex interrelated thermoelectric parameters and allows us to focus largely on improving the electronic properties. In this feature article, we have discussed the chemical bonding and structural aspects in determining phonon transport through a crystalline material. We have outlined how the inherent material properties like lone pair, bonding anharmonicity, presence of intrinsic rattlers, ferroelectric instability, weak and rigid substructures, etc. influence in effectively suppressing the heat transport. The strategies summarized in this feature article should serve as a general guide to rationally design and predict materials with low κlat for potential thermoelectric applications.
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Ultralow Lattice Thermal Conductivity at Room Temperature in Cu
4
TiSe
4. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202014222] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Ultralow Lattice Thermal Conductivity at Room Temperature in Cu 4 TiSe 4. Angew Chem Int Ed Engl 2021; 60:9106-9113. [PMID: 33146447 DOI: 10.1002/anie.202014222] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Indexed: 11/09/2022]
Abstract
Ultralow thermal conductivity draws great attention in a variety of fields of applications such as thermoelectrics and thermal barrier coatings. Herein, the crystal structure and transport properties of Cu4 TiSe4 are reported. Cu4 TiSe4 is a unique example of a non-toxic and low-cost material that exhibits a lattice ultra-low thermal conductivity of 0.19 Wm-1 K-1 at room temperature. The main contribution to the unusually low thermal conductivity is connected with the atomic lattice and its dynamics. This ultralow value of lattice thermal conductivity (kL ) can be attributed to the presence of the localized modes of Cu, which partially hybridize with the Se atoms, which in turn leads to avoidance of crossing of acoustic phonon modes that reach the zone boundary with a reduced frequency. Like a phonon glass electron crystal, Cu4 TiSe4 could also open a route to efficient thermoelectric materials, even, with chalcogenides of relatively high electrical resistivity and a large band gap, provided that their structures offer a sublattice with lightly bound cations.
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Thermoelectric cooling materials. NATURE MATERIALS 2021; 20:454-461. [PMID: 33288897 DOI: 10.1038/s41563-020-00852-w] [Citation(s) in RCA: 85] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2020] [Accepted: 09/30/2020] [Indexed: 06/12/2023]
Abstract
Solid-state thermoelectric devices can directly convert electricity into cooling or enable heat pumping through the Peltier effect. The commercialization of thermoelectric cooling technology has been built on the Bi2Te3 alloys, which have had no rival for the past six decades around room temperature. With the discovery and development of more promising materials, it is possible to reshape thermoelectric cooling technology. Here we review the current status of, and future outlook for, thermoelectric cooling materials.
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Evidence of Highly Anharmonic Soft Lattice Vibrations in a Zintl Rattler. Angew Chem Int Ed Engl 2020; 60:4259-4265. [DOI: 10.1002/anie.202013923] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Indexed: 11/06/2022]
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Ecofriendly Highly Robust Ag 8SiSe 6-Based Thermoelectric Composites with Excellent Performance Near Room Temperature. ACS APPLIED MATERIALS & INTERFACES 2020; 12:54653-54661. [PMID: 33215926 DOI: 10.1021/acsami.0c15877] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Bi2(TeSe)3 is a dominant n-type thermoelectric material used in commercial applications. However, its toxicity and rarity hamper further large-scale industrial applications. Herein, we develop a Ag8SiSe6-based composite as a promising n-type semiconductor with the advantages of nontoxicity and elemental abundance. Ag8SiSe6 composites with Ag2Se and Si nanoprecipitation are fabricated by a unique precipitation reaction sensitive to the hot pressing process. The energy-filtering effect between these phases optimizes electrical resistivity (∼14.59 μΩ·m) and the Seebeck coefficient (above -150 μV·K-1) of the composites, resulting in a maximum power factor of ∼1772 μW·m-1·K-2(@125 °C), which is the highest value in an argyrodite system near room temperature. Nanoprecipitation of Ag2Se and Si can also scatter more phonons and further reduce the lattice thermal conductivity to 0.20 W·m-1·K-1. As a result, a maximum ZT value of ∼0.9 (@125 °C) and an average ZT value of ∼0.7 (25-200 °C) are obtained in the composite with 12 vol % Ag2Se and 0.23 vol % Si, which is sintered at 525 °C. These thermoelectric properties are comparable to those of a commercial n-type Bi2Te3 compound. In addition, the Ag8SiSe6 composite has robust mechanical properties (Vickers hardness of >110 HV and bending strength of 70.6 MPa), much better than those of other thermoelectric compounds, because of which Ag8SiSe6 has great commercial application as an alternative to Bi2Te3-based compounds.
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Enhanced Mobility and Large Linear Nonsaturating Magnetoresistance in the Magnetically Ordered States of TmNiC_{2}. PHYSICAL REVIEW LETTERS 2020; 125:176601. [PMID: 33156671 DOI: 10.1103/physrevlett.125.176601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2020] [Revised: 09/02/2020] [Accepted: 09/11/2020] [Indexed: 06/11/2023]
Abstract
We have studied the magnetic, magnetotransport, and galvanomagnetic properties of TmNiC_{2}. We find that the antiferromagnetic and field induced metamagnetic and ferromagnetic orderings do not suppress the charge density wave. The persistence of Fermi surface pockets, open as a result of imperfect nesting accompanying the Peierls transition, results in an electronic carriers mobility of the order of 4×10^{3} cm^{2} V^{-1} s^{-1} in ferromagnetic state, without any signatures for a significant deterioration of nesting properties. This is independently evidenced by high, nonsaturating linear magnetoresistance reaching 440% at T=2 K and an analysis of the Hall conductivity. We thus demonstrate that, the coexistence of charge density wave and magnetism provides an alternative route to maintain high electronic mobility in the magnetically ordered state.
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Functional Energy Accumulation, Photo- and Magnetosensitive Hybridity in the GaSe-Based Hierarchical Structures. ENERGIES 2020. [DOI: 10.3390/en13174321] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
We report on the complex GaSe-based hierarchical structures GaSe(CS(NH2)2), GaSe(SmCl3) and GaSe(CS(NH2)2(SmCl3)) synthesized by an intercalation method. The conductive properties of synthesized clathrates and their relation to hierarchical structural complexity were explored by an impedance spectroscopy technique. The impedance response, thermostimulated discharge spectra, and photo- and magnetoresistive effects are reported. Based on the obtained results, the impurity energy spectra were calculated. A strong low-frequency inductive response, observable in the GaSe(SmCl3) clathrate, makes this material promising for the development of gyrator-free nanodelay lines potentially applicable in nanoelectronics. Hierarchical GaSe(CS(NH2)2(SmCl3)) clathrate, on the other hand, reveals hysteresis of the current–voltage characteristics, apparently confirming an accumulation of electric energy at interphase boundaries. A relevant spin battery effect, observable experimentally in stationary magnetic fields, demonstrates a principal possibility of the electric energy accumulation at a quantum level.
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Large linear magnetoresistance caused by disorder in WTe 2-δthin film. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:355703. [PMID: 32489186 DOI: 10.1088/1361-648x/ab8d74] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2019] [Accepted: 04/27/2020] [Indexed: 06/11/2023]
Abstract
Weyl semimetal WTe2has attracted considerable attention owing to its extremely large, unsaturated and quadratic magnetoresistance. Here, we study the magnetotransport properties of WTe2-δthin film, which shows an unsaturated and linear magnetoresistance of up to ∼1650%. A more complex and accurate method, known as the maximum entropy mobility spectrum, is used to analyze the mobility and density of carriers. The results show that linear magnetoresistance can be explained by the classical disorder model because the slope of linear magnetoresistance and the crossover field are proportional to the mobility and inverse mobility, respectively. Furthermore, the validity of the maximum entropy mobility spectrum is validated by the Shubnikov-de Haas oscillations. Moreover, at low temperature, we determined that the unsaturated and near-quadratic magnetoresistance in the WTe1.93thin film can be explained by charge compensation. Note that the electron-hole compensation is broken in the WTe1.42thin film, which indicates that the carrier scattering induced by the disorder may suppress the charge compensation in the WTe2sample with defects/dopants. To summarize, the discovery of disorder-induced linear magnetoresistance allows us to explain different magnetoresistance behaviors of WTe2.
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Temperature-driven n-p conduction type switching without structural transition in a Cu-rich chalcogenide, NaCu 5S 3. Chem Commun (Camb) 2020; 56:4882-4885. [PMID: 32285903 DOI: 10.1039/d0cc01429j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report for the first time the discovery of reversible n-p conduction type switching in a chalcogenide, NaCu5S3, without structural transition. AC impedance and first-principles simulations of the ionic migration confirmed the local melting trends of the hexagonal copper lattice at high temperatures, which could result in superionic conductivity within NaCu5S3.
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Decoupling Thermoelectric Performance and Stability in Liquid-Like Thermoelectric Materials. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2020; 7:1901598. [PMID: 31921552 PMCID: PMC6947709 DOI: 10.1002/advs.201901598] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Revised: 09/07/2019] [Indexed: 06/10/2023]
Abstract
Liquid-like materials are one family of promising thermoelectric materials discovered in the past years due to their advantanges of ultrahigh thermoelectric figure of merit (zT), low cost, and environmental friendliness. However, their practial applications are greatly limited by the low service stability from the Cu/Ag metal deposition under large current and/or temperature gradient. Both high zT for high efficiency and large critical voltage for good stability are required for liquid-like materials, but they are usually strongly correlated and hard to be tuned individually. Herein, based on the thermodynamic analysis, it is shown that such a correlation can be decoupled through doping immobile ions into the liquid-like sublattice. Taking Cu2- δ S as an example, doping immobile Fe ions in Cu1.90S scarcely degrades the initial large critical voltage, but significantly enhances the zT to 1.5 at 1000 K by tuning the carrier concentration to the optimal range. Combining the low-cost and environmentally friendly features, these Fe-doped Cu2- δ S-based compounds show great potential in civil applications. This study sheds light on the realization of both good stability and high performance for many other liquid-like thermoelectric materials that have not been considered for real applications before.
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Room-temperature conversion of Cu2−xSe to CuAgSe nanoparticles to enhance the photocatalytic performance of their composites with TiO2. Dalton Trans 2020; 49:3580-3591. [DOI: 10.1039/c9dt04726c] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Surfactant-free CuAgSe–TiO2 composites show an improved photocatalysis as compared to Cu2−xSe–TiO2 composites or TiO2 alone.
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Ultralow Thermal Conductivity in Chain-like TlSe Due to Inherent Tl + Rattling. J Am Chem Soc 2019; 141:20293-20299. [PMID: 31804809 DOI: 10.1021/jacs.9b10551] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Understanding the mechanism that correlates phonon transport with chemical bonding and solid-state structure is the key to envisage and develop materials with ultralow thermal conductivity, which are essential for efficient thermoelectrics and thermal barrier coatings. We synthesized thallium selenide (TlSe), which is comprised of intertwined stiff and weakly bonded substructures and exhibits intrinsically ultralow lattice thermal conductivity (κL) of 0.62-0.4 W/mK in the range 295-525 K. Ultralow κL of TlSe is a result of its low energy optical phonon modes which strongly interact with the heat carrying acoustic phonons. Low energy optical phonons of TlSe are associated with the intrinsic rattler-like vibration of Tl+ cations in the cage constructed by the chains of (TlSe2)nn-, as evident in low temperature heat capacity, terahertz time-domain spectroscopy, and temperature dependent Raman spectroscopy. Density functional theoretical analysis reveals the bonding hierarchy in TlSe which involves ionic interaction in Tl+-Se while Tl3+-Se bonds are covalent, which causes significant lattice anharmonicity and intrinsic rattler-like low energy vibrations of Tl+, resulting in ultralow κL.
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Facile synthesis of Ag2Te nanowires and thermoelectric properties of Ag2Te polycrystals sintered by spark plasma sintering. CrystEngComm 2019. [DOI: 10.1039/c8ce01863d] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ag2Te nanowires with a diameter of approximately 200 nm and a length of several micrometers were prepared using a simple one-step solvothermal method without templates and surfactants.
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Suppression of atom motion and metal deposition in mixed ionic electronic conductors. Nat Commun 2018; 9:2910. [PMID: 30046101 PMCID: PMC6060128 DOI: 10.1038/s41467-018-05248-8] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 06/19/2018] [Indexed: 11/08/2022] Open
Abstract
Many superionic mixed ionic-electronic conductors with a liquid-like sublattice have been identified as high efficiency thermoelectric materials, but their applications are limited due to the possibility of decomposition when subjected to high electronic currents and large temperature gradients. Here, through systematically investigating electromigration in copper sulfide/selenide thermoelectric materials, we reveal the mechanism for atom migration and deposition based on a critical chemical potential difference. Then, a strategy for stable use is proposed: constructing a series of electronically conducting, but ion-blocking barriers to reset the chemical potential of such conductors to keep it below the threshold for decomposition, even if it is used with high electric currents and/or large temperature differences. This strategy not only opens the possibility of using such conductors in thermoelectric applications, but may also provide approaches to engineer perovskite photovoltaic materials and the experimental methods may be applicable to understanding dendrite growth in lithium ion batteries.
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Tuning of p-n-p-Type Conduction in AgCuS through Cation Vacancy: Thermopower and Positron Annihilation Spectroscopy Investigations. Inorg Chem 2018; 57:7481-7489. [PMID: 29847926 DOI: 10.1021/acs.inorgchem.8b01246] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Understanding the complex phenomenon behind the structural transformations is a key requisite to developing important solid-state materials with better efficacy such as transistors, resistive switches, thermoelectrics, etc. AgCuS, a superionic semiconductor, exhibits temperature-dependent p-n-p-type conduction switching and a colossal jump in thermopower during an orthorhombic to hexagonal superionic transition. Tuning of p-n-p-type conduction switching in superionic compounds is fundamentally important to realize the correlation between electronic/phonon dispersion modulation with changes in the crystal structure and bonding, which might contribute to the design of better thermoelectric materials. Herein, we have created extrinsic Ag/Cu nonstoichiometry in AgCuS, which resulted in the vanishing of p-n-p-type conduction switching and improved its thermoelectric properties. We have performed the selective removal of cations and measured their temperature-dependent thermopower and Hall coefficient, which demonstrates only p-type conduction in the Ag1- xCuS and AgCu1- xS samples. The removal of Cu is much more efficient in arresting conduction switching, whereas in the case of Ag vacancy, p-n-p-type conduction switching vanishes at higher vacant concentrations. Positron annihilation spectroscopy measurements have been done to shed further light on the mechanisms behind this structural transition-dependent conduction switching. Cation (Ag+/Cu+) nonstoichiometry in AgCuS significantly increases the vacancy concentration, hence, the p-type carriers, which is confirmed by positron annihilation spectroscopy and Hall measurement. The Ag1- xCuS and AgCu1- xS samples exhibit ultralow thermal conductivity (∼0.3-0.5 W/m·K) in the 290-623 K temperature range because of the low-energy cationic sublattice vibration that arises as a result of the movement of loosely bound Ag/Cu within the stiff S sublattice.
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Soft Phonon Modes Leading to Ultralow Thermal Conductivity and High Thermoelectric Performance in AgCuTe. Angew Chem Int Ed Engl 2018; 57:4043-4047. [PMID: 29488301 DOI: 10.1002/anie.201801491] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Indexed: 11/10/2022]
Abstract
Crystalline solids with intrinsically low lattice thermal conductivity (κL ) are crucial to realizing high-performance thermoelectric (TE) materials. Herein, we show an ultralow κL of 0.35 Wm-1 K-1 in AgCuTe, which has a remarkable TE figure-of-merit, zT of 1.6 at 670 K when alloyed with 10 mol % Se. First-principles DFT calculation reveals several soft phonon modes in its room-temperature hexagonal phase, which are also evident from low-temperature heat-capacity measurement. These phonon modes, dominated by Ag vibrations, soften further with temperature giving a dynamic cation disorder and driving the superionic transition. Intrinsic factors cause an ultralow κL in the room-temperature hexagonal phase, while the dynamic disorder of Ag/Cu cations leads to reduced phonon frequencies and mean free paths in the high-temperature rocksalt phase. Despite the cation disorder at elevated temperatures, the crystalline conduits of the rigid anion sublattice give a high power factor.
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Soft Phonon Modes Leading to Ultralow Thermal Conductivity and High Thermoelectric Performance in AgCuTe. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201801491] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Realizing zT of 2.3 in Ge 1-x-y Sb x In y Te via Reducing the Phase-Transition Temperature and Introducing Resonant Energy Doping. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018. [PMID: 29349887 DOI: 10.1002/aenm.201701797] [Citation(s) in RCA: 153] [Impact Index Per Article: 25.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
GeTe with rhombohedral-to-cubic phase transition is a promising lead-free thermoelectric candidate. Herein, theoretical studies reveal that cubic GeTe has superior thermoelectric behavior, which is linked to (1) the two valence bands to enhance the electronic transport coefficients and (2) stronger enharmonic phonon-phonon interactions to ensure a lower intrinsic thermal conductivity. Experimentally, based on Ge1-x Sbx Te with optimized carrier concentration, a record-high figure-of-merit of 2.3 is achieved via further doping with In, which induces the distortion of the density of states near the Fermi level. Moreover, Sb and In codoping reduces the phase-transition temperature to extend the better thermoelectric behavior of cubic GeTe to low temperature. Additionally, electronic microscopy characterization demonstrates grain boundaries, a high-density of stacking faults, and nanoscale precipitates, which together with the inevitable point defects result in a dramatically decreased thermal conductivity. The fundamental investigation and experimental demonstration provide an important direction for the development of high-performance Pb-free thermoelectric materials.
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An argyrodite-type Ag9GaSe6 liquid-like material with ultralow thermal conductivity and high thermoelectric performance. Chem Commun (Camb) 2017; 53:11658-11661. [DOI: 10.1039/c7cc05935c] [Citation(s) in RCA: 64] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ag9GaSe6 argyrodite-type compound is a promising thermoelectric material which exhibits ultralow lattice thermal conductivity and high thermoelectric performance.
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Ba5Cu8In2S12: a quaternary semiconductor with a unique 3D copper-rich framework and ultralow thermal conductivity. Chem Commun (Camb) 2017; 53:2590-2593. [DOI: 10.1039/c6cc09904a] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A novel quaternary semiconductor, Ba5Cu8In2S12, with a unique 3D copper-rich framework and unusual Cu coordination exhibits ultralow thermal conductivity.
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Quantum Oscillations at Integer and Fractional Landau Level Indices in Single-Crystalline ZrTe 5. Sci Rep 2016; 6:35357. [PMID: 27739474 PMCID: PMC5064405 DOI: 10.1038/srep35357] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Accepted: 09/28/2016] [Indexed: 11/08/2022] Open
Abstract
A three-dimensional (3D) Dirac semimetal (DS) is an analogue of graphene, but with linear energy dispersion in all (three) momentum directions. 3D DSs have been a fertile playground in discovering novel quantum particles, for example Weyl fermions, in solid state systems. Many 3D DSs were theoretically predicted and experimentally confirmed. We report here the results in exfoliated ZrTe5 thin flakes from the studies of aberration-corrected scanning transmission electron microscopy and low temperature magneto-transport measurements. Several unique results were observed. First, a π Berry phase was obtained from the Landau fan diagram of the Shubnikov-de Haas oscillations in the longitudinal conductivity σxx. Second, the longitudinal resistivity ρxx shows a linear magnetic field dependence in the quantum limit regime. Most surprisingly, quantum oscillations were also observed at fractional Landau level indices N = 5/3 and 7/5, demonstrating strong electron-electron interaction effects in ZrTe5.
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Two-Carrier Transport Induced Hall Anomaly and Large Tunable Magnetoresistance in Dirac Semimetal Cd3As2 Nanoplates. ACS NANO 2016; 10:6020-6028. [PMID: 27166504 DOI: 10.1021/acsnano.6b01568] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Cd3As2 is a model material of Dirac semimetal with a linear dispersion relation along all three directions in the momentum space. The unique band structure of Cd3As2 is made with both Dirac and topological properties. It can be driven into a Weyl semimetal by symmetry breaking or a topological insulator by enhancing the spin-orbit coupling. Here we report the temperature and gate voltage-dependent magnetotransport properties of Cd3As2 nanoplates with Fermi level near the Dirac point. The Hall anomaly demonstrates the two-carrier transport accompanied by a transition from n-type to p-type conduction with decreasing temperature. The carrier-type transition is explained by considering the temperature-dependent spin-orbit coupling. The magnetoresistance exhibits a large nonsaturating value up to 2000% at high temperatures, which is ascribed to the electron-hole compensation in the system. Our results are valuable for understanding the experimental observations related to the two-carrier transport in Dirac/Weyl semimetals, such as Na3Bi, ZrTe5, TaAs, NbAs, and HfTe5.
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Origin of the Order–Disorder Transition and the Associated Anomalous Change of Thermopower in AgBiS2 Nanocrystals: A Combined Experimental and Theoretical Study. Inorg Chem 2016; 55:6323-31. [DOI: 10.1021/acs.inorgchem.6b00997] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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40
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The effect of order-disorder phase transitions and band gap evolution on the thermoelectric properties of AgCuS nanocrystals. Chem Sci 2016; 7:534-543. [PMID: 29896345 PMCID: PMC5952868 DOI: 10.1039/c5sc02966j] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 10/07/2015] [Indexed: 11/21/2022] Open
Abstract
Copper and silver based chalcogenides, chalco-halides, and halides form a unique class of semiconductors, as they display mixed ionic and electronic conduction in their superionic phase. These compounds are composed of softly coupled cationic and anionic substructures, and undergo a transition to a superionic phase displaying changes in the substructure of their mobile ions with varying temperature. Here, we demonstrate a facile, ambient and capping agent free solution based synthesis of AgCuS nanocrystals and their temperature dependent (300-550 K) thermoelectric properties. AgCuS is known to show fascinating p-n-p type conduction switching in its bulk polycrystalline form. Temperature dependent synchrotron powder X-ray diffraction, heat capacity and Raman spectroscopy measurements indicate the observation of two superionic phase transitions, from a room temperature ordered orthorhombic (β) to a partially disordered hexagonal (α) phase at ∼365 K and from the hexagonal (α) to a fully disordered cubic (δ) phase at ∼439 K, in nanocrystalline AgCuS. The size reduction to the nanoscale resulted in a large variation in the thermoelectric properties compared to its bulk counterpart. Temperature dependent Seebeck coefficient measurements indicate that the nanocrystalline AgCuS does not display the p-n-p type conduction switching property like its bulk form, but remains p-type throughout the measured temperature range due to the presence of excess localized Ag vacancies. Nanocrystalline AgCuS exhibits a wider electronic band gap (∼1.2 eV) compared to that of the bulk AgCuS (∼0.9 eV), which is not sufficient to close the band gap to form a semimetallic intermediate state during the orthorhombic to hexagonal superionic phase transition, thus AgCuS nanocrystals do not show conduction type switching properties like their bulk counterpart. The present study demonstrates that ambient solution phase synthesis and size reduction to the nanoscale can tailor the order-disorder phase transition, the band gap and the electronic conduction properties in superionic compounds, which will not only enrich solid-state inorganic chemistry but also open a new avenue to design multifunctional materials.
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Ambient Synthesis of One‐/Two‐Dimensional CuAgSe Ternary Nanotubes as Counter Electrodes of Quantum‐Dot‐Sensitized Solar Cells. Chempluschem 2015; 81:414-420. [DOI: 10.1002/cplu.201500466] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Revised: 11/23/2015] [Indexed: 11/11/2022]
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Tuning magnetotransport in a compensated semimetal at the atomic scale. Nat Commun 2015; 6:8892. [PMID: 26600289 PMCID: PMC4673487 DOI: 10.1038/ncomms9892] [Citation(s) in RCA: 116] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Accepted: 10/14/2015] [Indexed: 01/21/2023] Open
Abstract
Either in bulk form, or in atomically thin crystals, layered transition metal dichalcogenides continuously reveal new phenomena. The latest example is 1T'-WTe2, a semimetal found to exhibit the largest known magnetoresistance in the bulk, and predicted to become a topological insulator in strained monolayers. Here we show that reducing the thickness through exfoliation enables the electronic properties of WTe2 to be tuned, which allows us to identify the mechanisms responsible for the observed magnetotransport down to the atomic scale. The longitudinal resistance and the unconventional magnetic field dependence of the Hall resistance are reproduced quantitatively by a classical two-band model for crystals as thin as six monolayers, whereas a crossover to an Anderson insulator occurs for thinner crystals. Besides establishing the origin of the magnetoresistance of WTe2, our results represent a complete validation of the classical theory for two-band electron-hole transport, and indicate that atomically thin WTe2 layers remain gapless semimetals.
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Dielectric Mismatch Mediates Carrier Mobility in Organic-Intercalated Layered TiS2. NANO LETTERS 2015; 15:6302-8. [PMID: 26308495 DOI: 10.1021/acs.nanolett.5b01013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The dielectric constant is a key parameter that determines both optical and electronic properties of materials. It is desirable to tune electronic properties though dielectric engineering approach. Here, we present a systematic approach to tune carrier mobilities of hybrid inorganic/organic materials where layered two-dimensional transition-metal dichalcogenide TiS2 is electrochemically intercalated with polar organic molecules. By manipulating the dielectric mismatch using polar organic molecules with different dielectric constants, ranging from 10 to 41, the electron mobility of the TiS2 layers was changed three times due to the dielectric screening of the Coulomb-impurity scattering processes. Both the overall thermal conductivity and the lattice thermal conductivity were also found to decrease with an increasing dielectric mismatch. The enhanced electrical mobility along with the decreased thermal conductivity together gave rise to a significantly improved thermoelectric figure of merit of the hybrid inorganic/organic materials at room temperature, which might find applications in wearable electronics.
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Enhanced Thermoelectric Performance in Cu-Intercalated BiTeI by Compensation Weakening Induced Mobility Improvement. Sci Rep 2015; 5:14319. [PMID: 26394841 PMCID: PMC4585808 DOI: 10.1038/srep14319] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Accepted: 08/26/2015] [Indexed: 11/08/2022] Open
Abstract
The low weighted carrier mobility has long been considered to be the key challenge for improvement of thermoelectric (TE) performance in BiTeI. The Rashba-effect-induced two-dimensional density of states in this bulk semiconductor is beneficial for thermopower enhancement, which makes it a prospective compound for TE applications. In this report, we show that intercalation of minor Cu-dopants can substantially alter the equilibria of defect reactions, selectively mediate the donor-acceptor compensation, and tune the defect concentration in the carrier conductive network. Consequently, the potential fluctuations responsible for electron scattering are reduced and the carrier mobility in BiTeI can be enhanced by a factor of two to three between 10 K and 300 K. The carrier concentration can also be optimized by tuning the Te/I composition ratio, leading to higher thermopower in this Rashba system. Cu-intercalation in BiTeI gives rise to higher power factor, slightly lower lattice thermal conductivity, and consequently improved figure of merit. Compared with pristine BiTe0.98I1.02, the TE performance in Cu0.05BiTeI reveals a 150% and 20% enhancement at 300 and 520 K, respectively. These results demonstrate that defect equilibria mediated by selective doping in complex TE and energy materials could be an effective approach to carrier mobility and performance optimization.
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A combined experimental and theoretical study of the structural, electronic and vibrational properties of bulk and few-layer Td-WTe2. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:285401. [PMID: 26102263 DOI: 10.1088/0953-8984/27/28/285401] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The recent discovery of non-saturating giant positive magnetoresistance has aroused much interest in Td-WTe(2). We have investigated structural, electronic and vibrational properties of bulk and few-layer Td-WTe(2) experimentally and theoretically. Spin-orbit coupling is found to govern the semi-metallic character of Td-WTe(2) and its structural link with the metallic 1 T form provides an understanding of its structural stability. There is a metal-to-insulator switch-over in the electrical conductivity and a change in the sign of the Seebeck coefficient around 373 K. Lattice vibrations of Td-WTe(2) have been analyzed using first-principles calculations. Out of the 33 possible zone-center Raman active modes, five distinct Raman bands are observed around 112, 118, 134, 165 and 212 cm(-1) in bulk Td-WTe(2). Based on symmetry analysis and calculated Raman tensors, we assign the intense bands at 165 cm(-1) and 212 cm(-1) to the A'(1)and A''(1) modes, respectively. Most of the Raman bands stiffen with decreasing thickness, and the ratio of the integrated intensities of the A''(1) to A'(1) bands decreases in the few-layer sample, while all the bands soften in both the bulk and few-layer samples with increasing temperature.
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Rapid direct conversion of Cu(2-x)Se to CuAgSe nanoplatelets via ion exchange reactions at room temperature. NANOSCALE 2015; 7:9452-6. [PMID: 25965176 DOI: 10.1039/c5nr01451d] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The use of template nanostructures for the creation of photovoltaic and thermoelectric semiconductors is becoming a quickly expanding synthesis strategy. In this work we report a simple two-step process enabling the formation of ternary CuAgSe nanoplatelets with a great degree of control over the composition and shape. Starting with hexagonal nanoplatelets of cubic Cu2-xSe, ternary CuAgSe nanoplatelets were generated through a rapid ion exchange reaction at 300 K using AgNO3 solution. The Cu2-xSe nanoplatelet template and the final CuAgSe nanoplatelets were analyzed by electron microscopy and X-ray diffraction (XRD). It was found that both the low temperature pseudotetragonal and the high temperature cubic forms of CuAgSe phase were created while maintaining the morphology of the Cu2-xSe nanoplatelet template. Thermal and electronic transport measurements of hot-pressed pellets of the synthesized CuAgSe nanoplatelets showed a drastic reduction in the thermal conductivity and a sharp transition from n-type (S = -45 μV K(-1)) to p-type (S = +200 μV K(-1)) semiconducting behavior upon heating above the structural transition from the low temperature orthorhombic to the high temperature super-ionic cubic phase. This simple reaction process utilizing a template nanostructure matrix represents an energy efficient, cost-efficient, and versatile strategy to create interesting materials with lower defect density and superior thermoelectric performance.
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Superionic adjustment leading to weakly temperature-dependent ZT values in bulk thermoelectrics. Inorg Chem 2015; 54:867-71. [PMID: 25418200 DOI: 10.1021/ic502102e] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Thermoelectric (TE) materials are of worldwide interest for energy sustainability through direct waste-heat-to-electricity conversion. Practically, a TE power generator requires a large working temperature gradient; to achieve high efficiency, key TE materials with high ZT values are necessary and, furthermore, their ZT values should decline as little as possible over the imposed temperature range. Unfortunately, sharp ZT declines in all of the known materials are inevitable. Here we found the bulk superionic α-Ag(1-x)CuSe material exhibits unusual weakly temperature-dependent ZT values in the range of 480-693 K with the smallest ZT-T slope known to date. These result from the Seebeck coefficient balance of the countercontributions of holes and electrons and the weakly temperature-dependent thermal conductivity.
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Thermal conductivity of ordered-disordered material: a case study of superionic Ag2Te. NANOTECHNOLOGY 2015; 26:025702. [PMID: 25525816 DOI: 10.1088/0957-4484/26/2/025702] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Thermoelectric devices, which can generate electricity from waste heat, offer an attractive pathway for addressing an important niche in the globally growing landscape of energy demand. In the past few decades, the search for high-efficiency thermoelectrics has been guided by the concept of 'phonon-glass electron-crystal' (PGEC), i.e. an ideal thermoelectric material should have high carrier mobility and low thermal conductivity. Although remarkable progress has already been made along this line, the efficiency of thermoelectrics is still too poor to compete with other electricity producing methods. Ordered-disordered material, an emerging trend of high performance thermoelectrics under the concept of PGEC, is a new hot topic in the current thermoelectric research community. Taking superionic phase silver telluride (α-Ag2Te) as an example, we performed a comprehensive study of the thermal transport properties and of its physical mechanism by means of equilibrium molecular dynamic simulations. The results show that the thermal conductivity of α-Ag2Te is intrinsically very low. By analyzing the different contributions to the overall thermal conductivity, we revealed for the first time from atomistic simulations that the vibration of the Te(2-) sublattice dominates the thermal transport of α-Ag2Te, while the collision between the randomly diffusing Ag(+) ions and the Te(2-) sublattice yields a significant negative contribution to the thermal transport. We also studied the effect of isotropic compressive stain and carrier concentration on the thermal conductivity of α-Ag2Te. It has been found that the thermal conductivity can be largely reduced by applying compressive strain or with stoichiometric quantity modulation. Our studies shed light on the governing mechanism of thermal transport in ordered-disordered materials and could offer useful guidance for engineering the thermal transport properties of superionic conductors in terms of enhancing their thermoelectric performance.
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Temperature driven p–n–p type conduction switching materials: current trends and future directions. Phys Chem Chem Phys 2015; 17:10316-25. [DOI: 10.1039/c4cp06088a] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
In the present perspective, we highlight the key concepts, present the current fundamental understanding and show the latest developments in the field of p–n–p type conduction switching materials. Near room temperature p–n–p type conduction switching can have potential applications in diodes or transistor devices that operate reversibly upon temperature or voltage change.
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