Effect of Heat Treatment on the Thermoelectric Properties of Bismuth–Antimony–Telluride Prepared by Mechanical Deformation and Mechanical Alloying

In this work, p-type 20%Bi₂Te₃–80%Sb₂Te₃ bulk thermoelectric (TE) materials were prepared by mechanical deformation (MD) of pre-melted ingot and by mechanical alloying (MA) of elemental Bi, Sb, and Te granules followed by cold-pressing. The dependence on annealing time of changes of microstructure and TE properties of the prepared samples, including Seebeck coefficient, electrical resistivity, thermal conductivity, and figure-of-merit, was investigated. For both samples, saturation of the Seebeck coefficient and electrical resistivity were observed after annealing for 1 h at 380°C. It is suggested that energy stored in samples prepared by both MA and MD facilitated their recrystallization within short annealing times. The 20%Bi₂Te₃–80%Sb₂Te₃ sample prepared by MA followed by heat treatment had higher a Seebeck coefficient and electrical resistivity than specimens fabricated by MD. Maximum figures-of-merit of 3.00 × 10^?3/K and 2.85 × 10^?3/K were achieved for samples prepared by MA and MD, respectively.     

Photosensitive Elements Based on Two-Dimensional Bismuth Telluride: Obtaining and Current–Voltage Characteristics

Journal of Communications Technology and Electronics - Bismuth telluride based photosensitive elements were obtained and their properties were studied. Liquid exfoliation was used for bismuth...     

An Investigation on the Coupled Thermal–Mechanical–Electrical Response of Automobile Thermoelectric Materials and Devices

Thermoelectric (TE) materials, which can directly convert heat to electrical energy, possess wide application potential for power generation from waste heat. As TE devices in vehicle exhaust power generation systems work in the long term in a service environment with coupled thermal–mechanical–electrical conditions, the reliability of their mechanical strength and conversion efficiency is an important issue for their commercial application. Based on semiconductor TE devices wih multiple p–n couples and the working environment of a vehicle exhaust power generation system, the service conditions of the TE devices are simulated by using the finite-element method. The working temperature on the hot side is set according to experimental measurements, and two cooling methods, i.e., an independent and shared water tank, are adopted on the cold side. The conversion efficiency and thermal stresses of the TE devices are calculated and discussed. Numerical results are obtained, and the mechanism of the influence on the conversion efficiency and mechanical properties of the TE materials is revealed, aiming to provide theoretical guidance for optimization of the design and commercial application of vehicle TE devices.     

Thermoelectric Properties of Polyaniline Films with Different Doping Concentrations of (±)-10-Camphorsulfonic Acid

The temperature dependence of the thermoelectric properties was investigated for polyaniline (PANI) films doped with different concentrations of (±)-10-camphorsulfonic acid (CSA) with molar ratio x of CSA to two phenyl-nitrogen units of x = 1 to 0.2. All PANI-CSA films exhibit p-type conduction. The temperature dependence of the electrical conductivity of the films with low CSA concentrations is consistent with a transport mechanism of variable-range hopping. On the other hand, the Seebeck coefficient above room temperature shows a linear increase with temperature, attributed to the metallic nature of PANI-CSA. As the CSA concentration decreases, the absolute value of the Seebeck coefficient increases while the electrical conductivity extremely decreases, probably due to the changes not only in the carrier concentration but also in the degree of structural disorder. The power factor increases monotonically with increasing CSA concentration toward x = 1 (the maximum limit). The thermal conductivity value of CSA-PANI film with x = 1 is as low as about 0.20 W m^?1 K^?1 in the through-plane direction and about 0.67 W m^?1 K^?1 in the in-plane direction. The thermoelectric figure of merit ZT in the in-plane direction is estimated to be approximately 1 × 10^?3 for x = 1.     

Inorganic–Organic Hybrid Dielectrics for Energy Conversion: Mechanism,Strategy, and Applications

Dielectric materials with higher energy storage and electromagnetic (EM) energy conversion are in high demand to advance electronic devices, military stealth, and mitigate EM wave pollution. Existing dielectric materials for high-energy-storage electronics and dielectric loss electromagnetic wave absorbers are studied toward realizing these goals, each aligned with the current global grand challenges. Libraries of dielectric materials with desirable permittivity, dielectric loss, and/or dielectric breakdown strength potentially meeting the device requirements are reviewed here. Regardless, aimed at translating these into energy storage devices, the oft-encountered shortcomings can be caused by either of two confluences: a) low permittivity, high dielectric loss, and low breakdown strength; b) low permittivity, low dielectric loss, and process complexity. Contextualizing these aspects and the overarching objectives of enabling high-efficiency energy storage and EM energy conversion, recent advances in by-design inorganic–organic hybrid materials are reviewed here, with a focus on design approaches, preparation methods, and characterization techniques. In light of their strengths and weaknesses, potential strategies to foster their commercial adoption are critically interrogated.     

Thermoelectric Properties of Nanostructured Bismuth-Doped Lead Telluride Bi x (PbTe)1−x Prepared by Co-Ball-Milling

In this work we present a simple method to synthesize nanostructured, bismuth-doped lead telluride by co-ball-milling. The obtained nanopowders were compacted via either a cold pressing/annealing approach or by hot pressing. The two compacting methods were compared regarding sample density. Series with bismuth content up to 6 at.% were characterized by measuring the thermoelectric transport properties over a wide temperature range between 123 K and 773 K using two different techniques for the Seebeck coefficient and electrical conductivity. A decreasing thermal conductivity and increasing electrical conductivity were found with increasing doping level. The best results were obtained for samples with 5 at.% and 6 at.% bismuth, showing a maximum ZT value of 1.1 at 773 K. Transmission electron microscopy study was performed to analyze the microstructure of the nanopowders, suggesting that, in addition to n-type doping of the lead telluride matrix, segregation effects occur and the samples consist of multiple phases.     

Synthesis of 0D Manganese-Based Organic–Inorganic Hybrid Perovskite and Its Application in Lead-Free Red Light-Emitting Diode

Lead-based perovskite light-emitting diodes (PeLEDs) have exhibited excellent purity, high efficiency, and good brightness. In order to develop nontoxic, highly luminescent metal halide perovskite materials, tin, copper, germanium, zinc, bismuth, and other lead-free perovskites have been developed. Here, a novel 0D manganese-based (Mn-based) organic–inorganic hybrid perovskite with the red emission located at 629 nm, high photoluminescence quantum yield of 80%, and millisecond level triplet lifetime is reported. When applied as the emissive layer in the PeLEDs, the maximum recording brightness of devices after optimization is 4700 cd m⁻², and the peak external quantum efficiency is 9.8%. The half-life of the device reaches 5.5 h at 5 V. The performance and stability of Mn-based PeLEDs are one order of magnitude higher than those of other lead-free PeLEDs. This work clearly shows that the Mn-based perovskite will provide another route to fabricate stable and high-performance lead-free PeLEDs.     

Thermoelectric Performance of AgPb x SbTe20 (x?=?17 to 23) Bulk Materials Derived from Large-Particle Raw Materials

AgPb _x SbTe₂₀ (x?=?17 to 23) bulk materials with nanometer-sized grains were fabricated by combining mechanical alloying (MA) and spark plasma sintering (SPS) intentionally using large-sized lead and tellurium particles as raw materials to reduce oxygen impurity from surface oxides. It was found that the nominal Pb content in the starting powder mixture greatly affected the thermoelectric (TE) properties of the sintered bulk samples, with excess amount relative to the stoichiometric ratio of AgPb _m SbTe _m+2 less than previously reported. x-Ray diffraction experiments revealed that the lattice parameter increases linearly with increasing Pb content until x?=?20, which corresponds to the optimal nominal Pb content in the starting composition, showing the highest ZT value. A high ZT value of 1.2 at 675?K was achieved in the x?=?20 sample due to its lowest electrical resistivity and reduced thermal conductivity. The present study shows that using large-sized Pb particles containing less oxygen is suitable for fabrication of AgPb _m SbTe _m+2-system TE materials by MA and SPS processes.     

Discovery of III–V Semiconductors: Physical Properties and Application

Semiconductors - This overview is devoted to the discovery, development of the technology, and investigation of III–V semiconductors performed at the Ioffe Institute, where the first steps in...     

Function-Targeted Lanthanide-Anchored Polyoxometalate–Cyclodextrin Assembly: Discriminative Sensing of Inorganic Phosphate and Organophosphate

Polyoxometalate (POM) clusters containing lanthanide ion (LnPOM) possess excellent luminescence features, but the envisaged applications are hindered by the challenges in integration into functional architectures. Herein, a novel cross-linked cyclodextrin (CL-CD) and LnPOM composite is developed and applied for discriminative detection of inorganic and organic phosphate phases. For inorganic phosphates, a ratiometric fluorescence response is demonstrated with excellent selectivity, and anti-interference ability in complex analyte mixtures. The outstanding performance is attributed to the high affinity of POM and distinct interactions between La³⁺ and Eu³⁺ with the phosphate. For organophosphates, a “signal-off” fluorescence response for p-nitrophenyl-substituted organophosphates is discovered due to the encapsulation of nitrophenyl group into the hydrophobic cavity of CD that enhances the interactions between POM and p-nitrophenyl phosphate. The discriminative responses of CL-CD–LnPOM to inorganic phosphates and organophosphates bring new insights into POM-based fluorescence probes for the detection of inorganic and organic phases based on the intrinsic structural difference between the phosphate analogs.     

Novel Strategies for the Deposition of ?COOH Functionalized Conducting Copolymer Films and the Assembly of Inorganic Nanoparticles on Conducting Polymer Platforms

A method for the preparation of ? COOH functionalized conducting copolymer films; toward the ultimate goal of developing resistance‐based sensing platforms, is presented. The method involved vapor phase copolymerization of pyrrole with a monomer containing the ? COOH functionality, thiophene‐3‐acetic acid (TAA). This copolymerization strategy aided in avoiding the need to employ brittle poly(thiophene‐3‐acetic acid) (PTAA) films in sensing applications. In this strategy, variation in the gas phase feed ratio of pyrrole to TAA allowed for the variation of the composition of the copolymer film and further allowed for the variation of both the conductivity and the amount of ? COOH functionality in the films. Further, the effect of covalent attachment of silver on the conductivity of the copolymer films is performed and presented. This covalent attachment of silver served the dual purpose of verifying the presence of active ? COOH groups on the surface, and also allowed for the quantification of the change in conductivity as a result of such attachment. Use of the conjugated ring containing 4‐aminothiophenol as the linker material enhanced the conductivities of the films. In contrast, employing cysteamine to link silver nanoparticles to the copolymer films did not result in any enhancement in the conductivities. An enhancement in the conductivities, ranging from 2 to 1000 times, is observed on covalent attachment of silver nanoparticles to the copolymer films using 4‐aminothiophenol as the linker material. This increase depended on the amount of TAA in the films and increased with increasing concentrations of TAA in the films. These results clearly indicate the use of these copolymer films in resistance‐based sensing. Further, this covalent attachment could be used as a novel strategy to integrate other inorganic nanomaterials on conducting polymer platforms.     

Synthesis and Thermoelectric Properties of an Sn1 – xPbxSb4Te8 Solid Solution Doped with Bismuth

Semiconductors - The thermoelectric properties of a solid solution of Sn1 – xPbxSb4Te8 and Sn1 – xPbxSb4 – yBiyTe8...     

Deep-ultraviolet integrated photonic and optoelectronic devices: A prospect of the hybridization of group III–nitrides,III–oxides,and two-dimensional materials

Progress in the design and fabrication of ultraviolet and deep-ultraviolet group III–nitride optoelectronic devices, based on aluminum gallium nitride and boron nitride and their alloys, and the heterogeneous integration with two-dimensional and oxide-based materials is reviewed. We emphasize wide-bandgap nitride compound semiconductors (i.e., (B, Al, Ga)N) as the deep-ultraviolet materials of interest, and two-dimensional materials, namely graphene, two-dimensional boron nitride, and two-dimensional transition metal dichalcogenides, along with gallium oxide, as the hybrid integrated materials. We examine their crystallographic properties and elaborate on the challenges that hinder the realization of efficient and reliable ultraviolet and deep-ultraviolet devices. In this article we provide an overview of aluminum nitride, sapphire, and gallium oxide as platforms for deep-ultraviolet optoelectronic devices, in which we criticize the status of sapphire as a platform for efficient deep-ultraviolet devices and detail advancements in device growth and fabrication on aluminum nitride and gallium oxide substrates. A critical review of the current status of deep-ultraviolet light emission and detection materials and devices is provided.     

Covalent–Organic Framework (COF)-Core–Shell Composites: Classification,Synthesis, Properties,and Applications

Core–shell structures, where the “guest” material is encapsulated within a protective shell, integrate the advantages of different materials to enhance the overall properties of the composite. Covalent–organic frameworks (COFs) are favorable candidates for composing core–shell structures due to their inherent porosity, good activity, excellent stability, and other advantages. In particular, COFs as shells to encapsulate other functional materials are becoming increasingly popular in the fields of environmental remediation and energy conversion. However, there is a lack of reviews on COF-based core–shell materials. In this context, this review provides a systematic summary of the current research on COF-based core–shell composites. First, a simple classification is made for COF-based core–shell composites. The second part of the review describes the main synthesis methods. The changes brought about by the COF shell and core–shell structures on the properties of the composites and their applications in photocatalysis, electrocatalysis, adsorption, sensing, and supercapacitors are then emphasized. Finally, new perspectives on the future development and challenges of composites are presented. The purpose of this study is to provide future insights into the design and application of COF-based core–shell composites.     

Metal–Organic Framework Nanosheets: Programmable 2D Materials for Catalysis,Sensing, Electronics,and Separation Applications

Metal–organic framework nanosheets (MONs) have recently emerged as a distinct class of 2D materials with programmable structures that make them useful in diverse applications. In this review, the breadth of applications that have so far been investigated are surveyed, thanks to the distinct combination of properties afforded by MONs. How: 1) The high surface areas and readily accessible active sites of MONs mean they have been exploited for a variety of heterogeneous, photo-, and electro-catalytic applications; 2) their diverse surface chemistry and wide range of optical and electronic responses have been harnessed for the sensing of small molecules, biological molecules, and ions; 3) MONs tunable optoelectronic properties and nanoscopic dimensions have enabled them to be harnessed in light harvesting and emission, energy storage, and other electronic devices; 4) the anisotropic structure and porous nature of MONs mean they have shown great promise in a variety of gas separation and water purification applications; are discussed. The aim is to draw links between the uses of MONs in these different applications in order to highlight the common opportunities and challenges presented by this promising class of nanomaterials.     

Optoelectronic and photocatalytic properties of I–III–VI QDs: Bridging between traditional and emerging new QDs

Due to the quantum size effect and other unique photoelectric properties, quantum dots (QDs) have attracted tremendous interest in nanoscience, leading a lot of milestone works. Meantime, the scope and scientific connotation of QDs are constantly expanding, which demonstrated amazing development vitality. Besides the well-developed Cd-containing II–VI semiconductors, QDs of environmentally friendly I–III–VI (I = Cu, Ag; III = Ga, In; VI = S, Se) chalcogenides have been a hot spot in the QDs family, which are different from traditional II–VI QDs in terms of multi-composition, complex defect structure, synthetic chemistry and optical properties, bringing a series of new laws, new phenomena and new challenges. The composition of I–III–VI chalcogenides and their solid solutions can be adjusted within a very large range while the anion framework remains stable, giving them excellent capability of photoelectric property manipulation. The important features of I–III–VI QDs include wide-range bandgap tuning, large Stokes shift and long photoluminescence (PL) lifetime, which are crucial for biological, optoelectronic and energy applications. This is due to the coexistence of two or more metal cations leading to a large number of intrinsic defects within the crystal lattice also known as deep-donor-acceptor states, besides the commonly observed surface defects in all QDs. However, a profound understanding of their structure and optoelectronic properties remains a huge challenge with many key issues unclear. On one hand, the achievements and experience of traditional QD research are expected to provide vital value for further development of I–III–VI QDs. On the other hand, the understanding of the emerging new QDs, such as carbon and other 2D materials, are even more challenging because of the dramatically different composition and structure from II–VI semiconductors. For this, I–III–VI QDs, as a close relative to II–VI QDs but with much more complex composition and structure variation, provide a great opportunity as a gradual bridge to make up the big gap between traditional QDs and emerging new QDs, such as carbon dots. Here, we hope to compare the research progress of I–III–VI QDs and II–VI QDs, in an effort to comprehensively understand their structure, synthetic chemistry, optical electronic and photocatalytic properties. We further give insights on the key potential issues of I–III–VI QDs from the perspective of bridging between traditional QDs and emerging carbon dots, especially the profound principles behind synthetic chemistry, PL mechanism and optoelectronic applications.