Since the beginning of the 21st century, the third generation wide band gap (Eg>2.3 eV) semiconductor materials represented by gallium nitride (GaN) and zinc oxide (ZnO) are becoming the core supporting materials for development of semiconductor industry. Due to difficult growth and high cost of GaN and ZnO single crystal, epitaxial technology is always used as the substrate materials to grow GaN and ZnO films. Therefore, it is crucial to find an ideal substrate material for the development of third generation semiconductor. Compared with traditional substrate materials, such as sapphire, 6H-SiC and GaAs, scandium magnesium aluminate (ScAlMgO4) crystal, as a new self-peeling substrate material, has attracted much attention because of its small lattice mismatch rate (~1.4% and ~0.09%, respectively) and suitable thermal expansion coefficient with GaN and ZnO. In this paper, based on structure of ScAlMgO4 crystal, the unique trigonal bipyramid coordination and natural superlattice structure, the basis for its thermal and electrical properties, are introduced in detail. In addition, the layered structure of ScAlMgO4 crystal along the c-axis makes it self-peeling, which greatly reduces its preparation cost and has a good application prospect in the preparation of self-supported GaN films. However, the raw material of ScAlMgO4 is difficult to synthesize, and the crystal growth method is single, mainly through the Czochralski method (Cz), and growing techniques now in China lag far behind that in Japan. Therefore, it is urgent to develop a new growth method of growing high quality and large size ScAlMgO4 crystals to break the technical barriers.
Large-sized crystalline materials are the basic raw materials in semiconductors, lasers, and communications. Preparation of large-scale, high-quality crystalline materials has become a bottleneck restricting the development of related industries. Breaking through the preparation theory and technology of large-sized crystal materials is the key to obtaining high-quality large-sized crystals. Preparation process of crystal materials often undergoes nucleation and growth stages, including multiple processes at spatiotemporal scale: from atom/molecules, through clusters and nuclei, to bulk crystals. To further explore and accurately understand the crystal growth mechanism, we need intensively study the multiscale process,multi-scale in situ characterization techniques, and computational simulation methods. Among them, the latest in situ characterization methods for crystal growth includes optical microscopy, electron microscopy, vibration spectra, synchrotron radiation, neutron technology, and especially, machine learning method. Thus, the multi-scale computational simulation techniques for crystallization is introduced, for example, first principles calculation at atom/molecular scale, molecular dynamics simulation, Monte Carlo simulation, phase field simulation at mesoscopic scale, and finite element simulation at macroscopic scale. A single in situ characterization or simulation technique can only explore crystallization information over a specific time and space scale. To accurately and fully reflect the crystallization process, a combination of multi-scale methods is introduced. It can be speculated that the establishment of in situ characterization technology and computational simulation methods for the actual large-sized crystal growth environment will be the future development trend, which provides an important experimental and theoretical basis for developing crystallization theory and controlling crystal quality. Furthermore, it can be deduced that the combination of in situ characterization technology with machine learning and big data technology will be the trend for large-sized crystal growth.
Compared with the first and second generation semiconductor materials, the third generation semiconductor materials exhibit higher breakdown field strength, higher saturated electron drift velocity, outstanding thermal conductivity, and wider band gap, suitable for manufacturing of electronic devices with high frequency, high power, radiation resistance, corrosion resistant properties, optoelectronic devices and light emitting devices. As one of the representatives of the third generation of semiconductor materials, gallium nitride (GaN) is an ideal substrate material for preparing blue-green laser, radio frequency (RF) microwave and power electronic devices. It has broad application prospects in laser display, 5G communication, phased array radar, aerospace, etc. Hydride vapor phase epitaxy (HVPE) method is the most promising method for growth of GaN crystals due to its simple growth equipment, mild growth conditions and fast growth rate. Due to the widely used quartz reactors, unintentionally doped GaN obtained by HVPE method inevitably has donor impurities (Si and O). Therefore, the grown GaN shows n-type electrical properties, high carrier concentration and low conductivity, which limits its application in high-frequency and high-power devices. Currently, doping is the most common method to improve the electrical performance of semiconductor materials, through which different types of GaN single crystal substrates can be obtained with different dopants to improve their electrochemical characteristics and meet the different needs of market applications. In this article, the basic structure and properties of GaN semiconductor crystal material are introduced, and the recent progress of the high quality GaN crystals grown by HVPE method is reviewed; and the doping characteristics, dopant types, growth process and the influence of doped atoms on the electrical properties of GaN are introduced. Finally, the challenges and opportunities faced by the HVPE method to grow doped GaN crystals are briefly described, and the future developments in several directions are prospected.
Film capacitors are the core electronic components of modern power devices and electronic equipment. However, due to the low dielectric constant, it is difficult to obtain high energy storage density (effective energy storage density or discharged energy density) for present film capacitors, leading to a large device size and high application cost. To improve the energy storage density of film capacitors, a nanocomposite approach is an effective strategy via combining high dielectric constant of the ceramic nanoparticles with high breakdown strength of the polymer matrix. Nevertheless, for single-layer structure of 0-3 polymer/ceramic composites, the dielectric constant and breakdown strength are difficult to be effectively enhanced at the same time, which limits the further improvement of energy storage density. To solve this contradiction, researchers have combined the composite film with high dielectric constant and high breakdown strength in a superposition to prepare 2-2 type multilayer composite dielectrics, which can achieve synergistic regulation of polarization strength and breakdown strength to obtain high energy storage density. The optimization of electric field distribution and the synergistic regulation of dielectric constant and breakdown strength can be achieved through mesoscopic and microstructural modulation of multilayer composite dielectrics. In this paper, the research progress of multilayer polymer-based composite dielectrics including ceramic/polymer multilayer structure and all-organic polymer multilayer structure in recent years is reviewed. Effect of multi-layer structure control strategy on the improvement of energy storage performance is emphasized. Moreover, enhancement mechanism of energy storage performance of polymer-based multilayer structure composite dielectric is summarized. Finally, challenges and development directions of multilayer composite dielectrics are discussed.
Zintl phase Mg3X2 (X=Sb, Bi) based thermoelectric materials have attracted much attention because of their non-toxic, low cost and high performance. Compared with polycrystalline materials, the Mg3X2 crystals are of great value in revealing material’s intrinsic and anisotropic thermoelectric properties, as well as providing effective strategies for enhancing electrical and thermal transport properties. Therefore, the recent progress of single crystal growth and thermoelectric properties for Mg3X2 crystals are systematically summarizes in this paper. Due to the volatility and causticity of Mg element, several different methods such as slow cooling method, directional solidification method, flux method, and flux Bridgman method are widely used for synthesizing Mg3X2 crystals, in which the flux Bridgman method is more competitive to prepare large size bulk crystals. Researchers found that both n-type and p-type Mg3Sb2 crystals show an anisotropy thermoelectric transport property. The crystal growth rate, the concentration of self-doped Mg element, the concentration of impurity doping or alloying elements have a great impact on both electrical and thermal transport properties for Mg3Sb2 crystals. So far, the p-type and n-type Mg3Sb2 crystals with ZT value of 0.68 and 0.82 are achieved, respectively. This paper reviews the recent progress of growth and thermoelectrics properties of Zintl phase Mg3X2-based crystals, revealing that the flux Bridgman method is the most effective method to produce large-sized Mg3X2-based crystals. Tuning chemical composition of Mg3X2-based crystal by doping and forming solid solution for optimal carrier concentration and band structure engineering is expected to further improve the thermoelectric performance of Mg3X2-based crystal. The above-mentioned growth method and research strategies provide a significant guidance for the in-depth understanding of the Mg3X2-based crystal in the future.
Densification of ceramic materials by conventional sintering process usually requires a high temperature over 1000 ℃, which not only consumes a lot of energy, but also forces some ceramic materials to face challenges in phase stability, grain boundary control, and co-firing with metal electrodes. In recent years, an extremely low temperature sintering technique named cold sintering process (CSP) was proposed, which can reduce the sintering temperature to below 400 ℃, and realize the rapid densification of ceramic materials through the dissolution- precipitation process of ceramic particles by using the transient solvent in liquid phase and uniaxial pressure. The advantages of CSP, including low sintering temperature and short sintering time, have attracted extensive attention from researchers, since it was firstly reported in 2016. At present, CSP has been applied to the sintering of nearly 100 kinds of ceramics and ceramic-matrix composites, involving dielectric materials, semiconductor materials, pressure-sensitive materials, and solid-state electrolyte materials. This paper firstly introduces the low-temperature sintering techniques’ development history, process and densification mechanism. Then, application of CSP in the field of ceramic materials and ceramic-polymer composites is summarized. Based on differences of solubility, application of CSP mainly on Li2MoO4 ceramics, ZnO ceramics, BaTiO3 ceramics, and their composites preparations are introduced. Auxiliary effect of the transient solvent on cold sintering process is emphatically analyzed. Moreover, the high pressure issue in the cold sintering process and the possible solutions are discussed. At last, future development trend of cold sintering process is prospected.
The outbreak of corona virus disease 2019 (COVID-19) has aroused great attention around the world. SARS-CoV-2 possesses characteristics of faster transmission, immune escape, and occult transmission by many mutation, which caused still grim situation of prevention and control. Early detection and isolation of patients are still the most effective measures at present. So, there is an urgent need for new rapid and highly sensitive testing tools to quickly identify infected patients as soon as possible. This review briefly introduces general characteristics of SARS-CoV-2, and provides recentl overview and analysis based on different detection methods for nucleic acids, antibodies, antigens as detection target. Novel nano-biosensors for SARS-CoV-2 detection are analyzed based on optics, electricity, magnetism, and visualization. In view of the advantages of nanotechnology in improving detection sensitivity, specificity and accuracy, the research progress of new nano-biosensors is introduced in detail, including SERS-based biosensors, electrochemical biosensors, magnetic nano-biosensors and colorimetric biosensors. Functions and challenges of nano-materials in construction of new nano-biosensors are discussed, which provides ideas for the development of various coronavirus biosensing technologies for nanomaterial researchers.
The robust development of clinical medicine and biomaterials boosts diagnostic imaging, effective treatment, and precise theranostics in various diseases. The emerging interdiscipline of materials and medicine, termed as materdicine, aims to surmount the critical obstacles and challenges faced by traditional medicine, such as systemic toxicity, poor bioavailability, inferior site-targeting specificity, and unsatisfied diagnostic/therapeutic efficacy. Herein, the state-of-the-art advances regarding the applications of diverse medmaterials for disease diagnosis, therapy, and theranostics are systematically summarized in this review, especially focusing on the nanoscale medmaterials. We firstly emphasize and discuss biomedical imaging (e.g., optical imaging, magnetic resonance imaging, ultrasound imaging, computed tomography imaging) and therapeutic strategies (e.g., photothermal therapy, dynamic therapy, immunotherapy, synergistic therapy) in the field of cancer treatment. Furthermore, we highlight the important progress of medmaterials in the diagnosis and treatment of other kinds of diseases including orthopedic diseases, respiratory system, and brain diseases. Especially, the elaborated medmaterials for other representative biomedical applications, such as biosensing and antibacteria, are illustrated in detail. Finally, we discuss the current challenges and future opportunities for the practical application of these unique medmaterials in materdicine for accelerating their early realization of clinical translations, promoting the progresses of clinical medicine and benefiting the patients.
With the increase of packaging density of power electronic devices, the development of thermal interface materials with excellent thermal conductivity has received widely spread attention. Due to most traditional heat conductors showing relatively low thermal conductivity, synthesis of new high thermal conductive fillers is an important way to improve the thermal conductivity of thermal interface materials. In this study, boron phosphide (BP) particles were synthesized by a facile molten salt method, then mixed with boron nitride (h-BN) and filled into epoxy resin (EP) to prepare epoxy resin matrix composites (BP-BN/EP) by stirring and casting. With the three salts (NaCl : KCl : LiCl) method, the experimental data showed that the highest yield of BP reached 74%, 33% and 35% higher than that of the single salt method (41%) and the double salt method (39%), respectively. In the BP-BN/EP composites, BP and BN particles were uniformly dispersed in the EP matrix. When the hybrid filler loading at 30% (in volume), the thermal conductivity reached 1.81 W·m-1·K-1, 8.6 times of that of pure epoxy (0.21 W·m-1·K-1). The thermal conductivity improvement was related to the construction of thermal conductive network by BP particles linking adjacent BN sheets. In addition, to excellent thermal conductivity, the BP-BN/EP composites also showed good thermal stability and good thermodynamic properties. Therefore, the synthesized BP by molten salt method has great application prospects in the field of heat management.
Graphene has played a major role in wearable electronic textiles due to its excellent electrical conductivity, superior flexibility and environmental stability. In this work, a green-yellow reversible electrothermochromic fabric was constructed via a facial double side coating. The self-made graphene paste is coated on the surface of polyester fabric by screen printing technology. The hybrid thermochromic ink with reversible color-changing property is coated on the opposite side of the graphene layer by screen printing technology. Structural properties and discoloration principle of the fabric were analyzed. Their thermal and color-changing properties were studied by using infrared thermal imaging and colorimeter. The results show that the graphene forms a conductive layer with a thickness of 250 μm that allows Joule heating to supply the thermal resource for the electrothermochromic behavior. This fabric changes from green to yellow with a gradual heating that exceeded 45 ℃ at 12 V due to the ring closure and opening of crystal violet lactone. Its color change response time is about 15 s, while fading response time is about 27 s. The electro-thermochromic fabric is not disturbed once undergoing a bending angle range from 30° to 180° and the voltage-current curve remains stable. Performance of the fabric does not significantly degrade after 200 heating/cooling continuous cycles. In conclusion, a sensitive electro-thermochromic fabric with good cycle performance from green to yellow with the structure of graphene film‖polyester fabric‖thermochromic film is successfully prepared, which has a high application potential in the fields of military camouflage and wearable display.
BN nanofilms with hierarchical structure exhibite super-hydrophobicity, but they are not suitable for the large-scale production and application due to their complicated preparation process and expensive cost. Compared with common BN nanofilms, the application of super-hydrophobic coatings based on hydrophobic BN powders are more convenient. Herein, the hydrophobic single-phase BN powders were prepared by combustion synthesis method through magnesiothermic reduction reaction and acid washing, showing the water contact angle at (144.6±2.4)°. Their hydrophobic character lies in the micro-nano hierarchical structure of BN particles. The super-hydrophobic BN/fluorosilicone resin coatings were prepared using the combustion-synthesized hydrophobic BN powders as fillers. The water contact angle and sliding angle for 30% BN/fluorosilicone resin coatings (in mass) are (151.2±0.7)° and 8°, respectively, which are comparable to that of BN nanofilms fabricated by CVD method reported in the literature. This method is a convenient way to prepare super-hydrophobic organic-inorganic composite coatings by utilizing the hydrophobicity of ceramic powders. Therefore, hydrophobic BN powders and super-hydrophobic BN/fluorosilicone resin coatings are expected to have wide application.
Silicon carbide fiber reinforced silicon carbide (SiCf/SiC) composites have become the preferred candidate for structural applications in advanced nuclear energy systems, because of their low neutron toxicity, neutron irradiation tolerance and high-temperature oxidation resistance. In recent years, both academia and industry either domestic or abroad have carried out a lot of researches on SiCf/SiC composites for nuclear application, and numerous important achievements have been made. This paper summarized and analysed some critical directions of SiCf/SiC composites for nuclear applications, including nuclear-grade SiC fibers, fibre/matrix interfaces, composite processing, modeling and simulation, corrosion behavior and surface protection, joining technology, as well as radiation damage. The key issues and potential solutions of SiCf/SiC composites for nuclear applications have been pointed out in account to the requirements, anticipating to be beneficial to promoting further researches and final applications.
Oxygen reduction reaction (ORR) is the key reaction in cathode for fuel cells. Because of the sluggish kinetics, platinum (Pt) is widely used as the electrocatalysts for ORR. However, the high cost of Pt and poor stability of carbon black support under high voltage limit the commercialization and durability of fuel cells. Two-dimensional transition metal dichalcogenides (2D TMDs) possess large specific area, tunable electronic structure, and high chemical stability, making them a good candidate for ORR catalysts with high activity and durability. This paper reviews the recent progress of 2D TMDs-based ORR electrocatalysts. First, crystal structure, electronic properties, and ORR reaction mechanism are briefly introduced. Then some strategies for adjusting ORR performance of 2D TMDs are summarized, including heteroatom doping, phase conversion, defect engineering, and strain engineering. Meanwhile, the ORR activity enhancement arising from 2D TMDs-based heterostructures is also analyzed. Finally, perspectives are given for current issues and their possible solutions.
Spontaneous coagulation casting (SCC) is a novel in-situ ceramic forming method, not only universal for various ceramics but also working well at room temperature in air. Here presents the finding of SCC, involving an anion dispersant which acts as both dispersing and coagulating agent. Then, the difference between SCC and other in-situ coagulation methods in principle was elucidated. In SCC, particles participate in the formation of organic network which originates from hydrophobic interaction and hydrogen bonding among the dispersant molecular chains. The ceramic gel formed by SCC is a physical gel and possesses low density which is conducive to water transportation and stress relaxation during drying. In contrast, the one by conventional gelcasting is a chemical gel in which particles are fixed by a dense organic network. Based on the hydrophobic interaction, this review focuses on the design and synthesis of a series of SCC agents to meet the demand of forming dense and porous ceramics from particles with different sizes. That is, an anion dispersant is hydrophobically modified by a surfactant with a short or long chain. The obtained two agents are used for preparation of dense and porous ceramics, respectively. Progress of key technologies in this area including ceramic joining without interface, construction of grain orientation, drying, preparation of dense ceramics and porous ceramics, by SCC is summarized. Typically, alumina disc with a diameter up to 1010 nm and alumina parts with complicated shape such as dome and guide are shown. Future development of SCC is also proposed to enable SCC is a more universal forming technology for advanced ceramics with a large and/or complicated dimension.
Piezoelectric ceramic is a type of functional ceramic, which is able to convert the mechanical signal and the electronic signal mutually. Composed of piezoelectric ceramics and organic phase, piezoelectric composites have different kinds of connectivities, which not only determine the diverse applications of piezoelectric devices, but also promote the development of various shaping techniques in manufacturing piezoelectric materials and devices. In comparison with the traditional shaping methods, the most distinguishable advantage of additive manufacturing lies in its ability of quickly shaping a small batch of samples into geometrically complex designs without a mould, which makes it a highly suitable technique for investigating piezoelectric ceramics and its derivative devices in different kinds of connectivities. Meanwhile, the final additively manufactured samples require only tiny post-processing, have a high rate of utilization of the raw material and do not need cutting fluid during manufacturing. Due to the above-mentioned advantages, it attracts the widespread concerns from both academic and industrial communities. When focusing in the field of additive manufacturing ceramics, the data of scientific reports in additive manufacturing functional ceramics and devices prove that it is still in a growing period. In the perspective of different additive manufacturing techniques, this article discusses and compares additive manufacturing of both lead-free and lead-based piezoelectric ceramics in the aspects of their historical development of each technique, preparation of the raw materials, geometrical designs, measurement of functional properties, and applications of the printed samples, and forecasts the future development based on the current benefits and drawbacks of each additive manufacturing technique.
Ceramics, with its excellent thermal, physical and chemical properties, have great potential applications in various fields, such as aerospace, energy, environmental protection and bio-medicine. With the development of relevant technology in these fields, the structural design of core components is increasingly complex, and the internal microstructures gradually become customized and gradient. However, the hard and brittle features of ceramics make it difficult to realize the forming of special-shaped parts by traditional manufacturing methods, which in turn limits further application. As a rapidly developing additive manufacturing technology, laser additive manufacturing technology presents a momentous advantage in the manufacturing process of extremely precision ceramic components: free molding without mold and support, quick response feature and short developing cycle, etc. At the same time, the technology can realize the flexible deployment of ceramic parts, which is expected to solve the problems mentioned above. Three kinds of powder-based laser additive manufacturing techniques of ceramic were reviewed in this paper: selective laser sintering and selective laser melting based on powder bed fusion technology; laser engineered net shaping based on direct energy deposition technology. The forming principle and characteristics were mainly discussed; the research progress of ceramic green body densification process in selective laser sintering technology and the forming principle, propagation mechanism and control methods of ceramic green body cracks in selective laser melting, and laser engineered net shaping technology were reviewed; the technical characteristics of selective laser sintering, selective laser melting and laser engineered net shaping technologies in shaping of ceramic parts were compared and analyzed; and the future development trends of laser additive manufacturing technology of ceramic parts were prospected.
BaTiO3 has a wide range of applications in microelectromechanical systems and integrated circuits due to its excellent dielectric, ferroelectric, piezoelectric, and pyroelectric properties. For the applied research and device applications of BaTiO3 films, reducing its deposition temperature to be compatible with the CMOS-Si technology is an important Challenge. Here, with the help of a LaNiO3 buffer layer which has a closely-matched lattice with BaTiO3, (001)-textured BaTiO3 films were sputter-deposited at 450 ℃ on single crystalline Si(100) substrates, which consisting of well-cryotallized, evenly-distributed columnar nanograins with an average grain size of 27 nm. Our result showed that this deposition temperature can maintain the columnar nanograin structure with a relatively large grain size, leading to a good ferroelectric performance. In addition, a small residual strain on Si was also helpful to improve its ferroelectric and dielectric properties. The remnant polarization and saturated polarization of these BaTiO3 films reached 7 and 43 μC·cm-2, respectively, while leakage current densities were as low as 10-5 A·cm-2 at an applied electric field of 0.8 MV·cm-1. These BaTiO3 films also displayed excellent frequency stability with a low dielectric loss in which relative dielectric constant measured to be ~155 at 1 kHz, slightly being reduced to ~145 after increasing the frequency to 1 MHz. Meanwhile, the dielectric loss slightly increased from 0.01 at 1 kHz to 0.03 at 1 MHz. Lastly, through capacitance-voltage (C-V) tests, these films exhibited a large dielectric tunability of~51% and a figure of merit (FOM) of ~17 (@1 MHz). These films have a good potential for applications in tunable dielectrics.
As an important branch of nonlinear optics, second harmonic generation (SHG) is becoming one of the most important means to characterize crystal structure. Among various methods of characterization, because of nondestructive detection, high stability, tunability, ultrafast response, polarization sensitivity, versatility and simplicity, SHG is widely used to characterize the structure of two-dimensional (2D) materials. It provides important information for the physical properties and functional applications of 2D materials, as well as greatly promotes the rapid development of basic research on 2D materials. Here, the current state of the art focuses on the recent research work of SHG in 2D material structure characterization. Firstly, the principle of the second harmonic generation is briefly introduced. Then, the second harmonic generation device with femtosecond laser connected to confocal Raman spectrometer is taken as an example to present the mechanism of SHG. Afterwards, the applications of SHG are demonstrated in the thickness of interlayer stacking of 2D materials, the stacking angle between different layers of 2D materials, the grain boundary and the crystal orientation of monolayer 2D materials. The second harmonic intensity is used as a direct and sensitive means to monitor the strain amplitude, and the SHG signal changes are used to track defects in materials. Meanwhile, the importance of multi-dimensional correlation analysis of second harmonic generation, Raman spectroscopy and photoluminescence in comprehensive and in-depth characterization of materials is also explored. Finally, the potential research directions and prospects based on SHG in material characterization in the future is prospected.
Optical property, such as color, transmittance, reflectance and emissivity, of electrochromic materials can be changed reversibly under low applied voltages. Electrochromic materials have a wide range of regulatable spectrum, which can realize the broadband control from the visible to mid-far-infrared. Electrochromic materials show a wide application prospect in the fields of intelligent window, display, anti-glare rearview mirror, intelligent thermal control, and camouflage. At present, most of researches on inorganic electrochromic materials focus mainly on transmission characteristics, but less on reflection characteristics. This is mainly because most inorganic electrochromic materials have single color and are not as easy to design as organic electrochromic materials. In recent years, through special preparation and structural design, the research on reflective properties of inorganic electrochromic materials has gradually attracted researchers’ attention. Based on reflection characteristics of inorganic electrochromic materials, methods and principles of regulating the reflectance spectrum in the visible near infrared to mid-far-infrared bands are introduced, and the latest research progress is summarized. Within the visible band, reflectance spectrum control is mainly achieved by vanadium pentoxide (V2O5) and V2O5 doping, microstructure of one dimensional photonic crystal, Fabry Perot nanocavity structure and localized surface plasmon resonance (LSPR). Within the mid-to-far infrared band, electrochromic devices (ECDs) based on the molecular vibration absorption of tungsten oxide (WO3) or other electrochromic materials and related theory are designed and fabricated to regulate reflectance spectra. Finally, the practical application of inorganic electrochromic materials in future is prospected.
Vanadium dioxide (VO2), as a transition metal oxide, has thermochromic property, which undergoes metal to insulator transition (MIT) in response to external temperature changes, and is accompanied by numerous changes in physical property. It has attracted widespread attention in the field of smart windows. In recent years, research on the preparation method of VO2, the phase change mechanism, and the improvement of optical performance are quite rich. However, practical applications still face technical bottlenecks and challenges such as higher intrinsic transition temperature (Tc), lower luminous transmittance (Tlum), insufficient solar modulation ability (ΔTsol), nonideal metastability and durability, and uncomfortable color for human eyes (brownish yellow). At present, there are many researches related to the improvement of the performance of VO2 itself owing to its insufficient optical property, and general methods for improving its performance such as elements doping, multilayer film structure design, and microstructure design have been widely adopted. This review summarizes the general performance improvement strategies of VO2 film, and highlights the latest research progress of VO2-based smart window service performance, low-temperature flexible preparation and color modulation in practical applications. Future development trends are also discussed in terms of skin comfort and environmental friendliness.
Synchrotron Radiation (SR) is the electromagnetic radiation emitted along the tangent direction of the electron orbit by high-speed electrons moving in a circular accelerator when passing through a bending magnet. SR source, as a platform-type scientific and technological infrastructure, plays an important supporting role in the research and development of inorganic materials. SR techniques become an indispensable research tools of modern science and technology, and inorganic materials are one of the main application fields of SR techniques. Compared with conventional light source used for research, SR techniques in the study of inorganic materials have following obvious advantages: 1) higher obtained data qualities; 2) better spatial and temporal resolutions; 3) easier simulated in-situ and material service environment; 4) synchronously acquiring multi-scale, multi-faceted and multi-type structural information; 5) new means more likely to detect new structural characteristics. SR techniques help solve some key scientific problems in the field of inorganic materials, and greatly promote their research. Firstly, this paper briefly introduces the current status of SR sources and their three existing domestic SR facilities: Beijing Synchrotron Radiation Facility (BSRF), Shanghai Synchrotron Radiation Facility (SSRF), and National Synchrotron Radiation Laboratory (NSRL). Secondly, some application examples related to inorganic materials research are given from the four aspects of X-ray diffraction, scattering, spectroscopy and imaging. Finally, summary and prospect are given to the SR source, the structurally characterization techniques, and their application in inorganic materials.
The triboelectric nanogenerator (TENG) is a kind of green power source which can harvest and transform small mechanical energy into electricity. Triboelectric nanogenerators have various active materials, simple structures, and easy to integrate with other devices. However, its relatively low output power density hinders the further practical application of TENGs. How to improve the output performance of TENGs through the modification of the active triboelectric materials is one of the hottest spots. It is a facile and effective way to introduce functional fillers into polymer substrates to fabricate composite materials, which improve the triboelectricity of pristine material and bring new functions for the device. Thus, composite films are widely used in TENGs. For example, inorganic fillers like TiO2, SiO2, BaTiO3, ZnSnO3, MoS2, r-GO sheets, and nanofibril-phosphorene have been introduced into polymers to improve the output power density of TENGs by dozens of times. Based on domestic and international research, this review introduces the applications of the composite film in TENGs. The improvements of TENGs induced by the fillers are discussed from two aspects: the surface property and electrical property. Finally, future challenges in developing composites based TENGs are prospected.
Due to high power, high brightness, small size, energy saving, and environment friendliness, solid-state lighting has been becoming the most promising lighting technology in this century. As the key material of solid-state lighting, the luminescent properties of phosphors directly determine the crucial parameters such as the color rendering index, luminous efficacy and reliability of solid-state lighting devices. Compared with single crystals, phosphor glasses, phosphor films and quantum-well LEDs, phosphor ceramics have become the most excellent phosphor materials for high-power solid-state lighting due to its excellent thermal and optical properties and easy control of microstructure. In the future, phosphor ceramics is expected to be more widely used and developed in automotive headlights, outdoor lighting, laser TVs, laser cinema projectors, and other fields, and have a broad market prospect. In this review, design principles of high-power solid-state lighting phosphor ceramics are put forward firstly, and then their research progress of oxide phosphor ceramics (mainly refers to Y3Al5O12) and nitrogen/oxynitride phosphor ceramics are reviewed mainly. Finally, the development of phosphor ceramics for high-power solid-state lighting is prospected.
Rare earth ions doped Gd2O2S scintillators are new type of oxysulfide scintillators, which have been developed since 1980s. The Gd2O2S matrix with cross section of high density and high thermal neutron absorption has high X ray and thermal neutron stopping capacity. The doping of different rare earth ions (Pr3+, Tb3+, etc.) shows fast decay or high light yield, which plays a very important role in application of scintillation. Composition control of oxysulfide is always a key problem to be solved in the synthesis process. However, the high melting point of Gd2O2S material and the serious volatilization of sulfur restrict the preparation of Gd2O2S single crystals, with high optical quality and excellent scintillation performance. Ceramic is the main application form of Gd2O2S scintillation material. Its pure phase Gd 2O2S phosphors with small particle size, narrow particle size distribution and low agglomeration is the key to sintering high quality scintillation ceramics. These ceramics prepared by simply increasing the sintering temperature produce a large number of sulfur vacancies and oxygen vacancies, decreasing the scintillation properties. Therefore, preparation of Gd2O2S scintillation ceramics usually need pressure assistance to increase the production cost. In this paper, their scintillation mechanism and research situation are introduced firstly. Then, their fabrication process, solution of defects removal, research status and applications in neutron imaging and medical X-CT fields are overviewed. Finally, we summarized the previous and prospected the future development of Gd2O2S scintillation ceramics.
Fuel cells are highly efficient and green devices for direct chemical-to-electrical energy conversion. However, limited by slow kinetics of oxygen reduction reaction (ORR) in cathode, fuel cells require catalysts with noble metal like Pt, thus significantly increasing the cost of the fuel cells. Carbon-supported metal single atom catalysts (C-SACs) have excellent properties such as high atom utilization efficiency and selectivity. In addition, C-SACs show high ORR activity under different pH conditions, hence have been recognized as economical candidates to replace noble metal in fuel cells. This article reviewed the strategies used to improve ORR activity of C-SACs, including selecting different kinds of metal single atoms, tailoring coordination structure of metal centers, and heteroatomic doping to substrate. Performances of C-SACs in rotating disk electrode or battery device are also introduced. At last, the feasibility and potential challenges of C-SACs in practical application are prospected and summarized.
High-entropy brings high-entropy effect on thermodynamics, lattice distortion effect on structure, diffusion retardation effect on dynamics and “cocktail” effect on properties in materials. It is a hotspot to improve the properties of ceramics by high-entropy design. However, it still lacks the study of high-entropy structures and their correlation to the properties through transmission electron microscopy (TEM). In this study, high-entropy borides and carbides powders were fabricated by using metal oxides, boron carbide and graphite as raw materials. The high-entropy (TiZrHfNbTa)B2 and (TiZrHfNbTa)C ceramics were then synthesized by spark plasma sintering of the as-fabricated powders. Transmission electron microscope and energy dispersive spectrometry were used to characterize the structure of the two high-entropy ceramics at the nano-scale and atomic-scale. The integrity of crystal structure maintained after solid solution of five transition metal elements which were found to uniformly distribute in the ceramics. However, at atomic scales, concentration oscillations of solid solution elements, atomic dispersion and lattice strain were observed. The solid solution structures at atomic scales as-obtained in this work can help to understand the structure-property relationship of high-entropy ceramics and provide experimental basis for the composition and structure design of high-entropy ceramics.
Environmental barrier coatings (EBCs) have been developed to improve the durability of SiCf/SiC CMC components against harsh combustion environment. Among the most promising EBC candidates, rare-earth (RE) silicates attract attentions for their low thermal expansion coefficient, excellent high temperature water vaper and CMAS corrosion resistance, and good thermal and chemical compatibility with silicon-based ceramics and composites. Herein, we reviewed the optimizations of critical key properties of rare-earth silicates through strategic high entropy design to modify the current performance deficiencies of rare-earth silicates like thermal properties (coefficient of thermal expansion and thermal conductivity), CMAS corrosion resistance and high temperature phase stability. The present advancements demonstrate the merits of high entropy engineering for advanced EBCs for the improvement of crucial properties in engine applications.
Electrochromism is the phenomenon of reversible color/optical change of materials induced by redox reactions under an applied electric field. Since electrochromism was first introduced by Platt in 1961, electrochromic (EC) technology continues to develope due to its advantages of multiple colors energy saving and controllability, and was applied in many fields, for example, smart windows, displays, anti-dazzling rear view mirrors, etc. Recently, with the rapid development of optoelectronic and photoelectric technologies, highly integrated electronic devices attracted extensive interests, and the EC technology is developed towards functionalization and intellectualization. For example, self-powered EC devices (ECDs) were fabricated through integrating with the green energy technology, which further reduced the building energy consumption. Because of the visualization of the EC phenomena by naked eyes, the signal reading became more convenient for the sensors integrated with ECDs. In addition, because of similar device structure, electrochemical principles, active components with other functional devices, a lot of multifunctional EC technologies were explored based on single device, facilitating applications of ECDs in EC infrared control, EC energy storage, and EC actuation. In light of the recent emerging progress of EC technology, we reviewed multi-functional EC systems based on the integration of multiple devices and single device, respectively, including self-powered ECDs, EC sensors, infrared ECDs, and EC energy storage devices, etc. The integration modes, structure design and performance optimization were also summarized for different types of the multi-functional ECDs. At last, we introduced the challenges and potential pathway of multi-functional EC integration in the future.
As a new emergence material, high-entropy ceramics possess unique properties due to its high configurational entropy. Among these ceramics, high-entropy transition metal carbide ceramics (HETMCC) are expected to be the potential candidates for the thermal protection system of hypersonic aircraft. Compared with single-component ceramics, the comprehensive performance of single-phase HETMCC is greatly improved. At present, the research on HETMCC is still in the initial stage, and the composition design and theoretical analysis of HETMCC are lack of sufficient research support. In addition, it is necessary to further explore the preparation of high purity HETMCC. In terms of the properties of HETMCC, further in-depth research has been conducted. In this paper, the theoretical design and preparation methods of high-entropy ceramics are reviewed. Research progress of the mechanical properties, thermal conductivity, and oxidation resistance properties of HETMCC are introduced in detail. The concerned scientific issues of HETMCC are pointed out and their future development direction are also prospected.
As the extension of high-entropy alloy, entropy engineering has been already extensively used in thermoelectrics because it can guide the optimization of thermoelectric (TE) performance from the aspects of both electrical and thermal transports. Due to the inherent material gene-like feature, entropy can be used as a performance indicator to rapidly screen new multicomponent TE materials. In this review, we first reveal the reason why entropy can be used as the performance indicator of TE materials. The physical mechanisms of enhanced structure symmetry, improved Seebeck coefficient, and suppressed lattice thermal conductivity as a result of the increased configurational entropy are discussed. Then, the applications of entropy engineering in typical TE materials, such as liquid-like materials and IV-VI semiconductors, are outlined, and the approach to screen and identify candidate multicomponent TE materials with high configurational entropy is introduced. Finally, the future directions for entropy engineering are highlighted.
Silicon carbide is widely used because of its excellent physical and chemical properties. The chemical bonding characteristics of SiC make it difficult to be sintered. Therefore, preparation of high-quality SiC ceramics is one of the challenges in SiC research field. In this study, the ternary rare-earth carbide Dy3Si2C2 was proposed as a new sintering additive for SiC ceramics, through the phase transition of Dy-Si-C system at high temperatures to promote the densification of SiC. The Dy3Si2C2 coated SiC powders were synthesized via an in-situ reaction between metal Dy and SiC in high temperature molten salts. The Dy3Si2C2 coated SiC powder was sintered by spark plasma sintering (SPS), at 1800 ℃, 45 MPa. As the result, high-purity SiC ceramic with the density of 99% and thermal conductivity of 162.8 W·m -1·K -1was obtained to form the SiC-Dy3Si2C2 raw material with n(Dy) : n(SiC)=1 : 4. Further study shows that Dy3Si2C2 and SiC undergo a eutectic reaction at high temperatures, which generates liquid phase at the grain boundaries and promotes the densification of SiC ceramics. This study shows that the ternary rare-earth carbides Re3Si2C2 (Re=La, Ce…) has great potential to be used as the sintering additive for SiC.
Hydrolysis is a unique method for hydrogen generation at ambient condition. Widespread attentions have been paid to materials for hydrogen generation via hydrolysis due to several advantages: high theoretical hydrogen capacity, moderate storage and operation condition, safety, etc. In this paper, recent progress and development in this area were reviewed. Three types of materials including borohydride (NaBH4, NH3·BH3), metal (Mg, Al), and metal hydride (MgH2) were introduced. Several issues about them were discussed specifically: mechanism, main problems, designments of catalysts and materials, etc. Based on these discussions, we compared the different materials mentioned above, commented their current performances and practical difficulties. At last, prospects in this field were presented.
An electron irradiation induced fast phase-separation behavior was observed under convention Transmission electron microscopy (TEM) observation of spark plasma sintered AlF3 doped alumina ceramic. Spherical nanocrystalline Al precipitates separated out from original alumina grain surface within several seconds under transmission electron microscopy electron irradiation. By high resolution TEM observation combined with diffraction patterns analysis, it was found that the original alumina grain surface was in highly defected state. After electron irradiation under TEM, the defects on original alumina surface vanished accompanied by the precipitation of nanocrystalline Al particles. By thoroughly analysis of the defect reaction during doping process and the feature of cation sub-lattice of alumina, a defect assisted interstitial atom segregation mechanism was proposed to explain this behavior. According to this mechanism, doped F ions first occupied oxygen vacancy sites with corresponding Al ions at intrinsic interstitial sites. After oxygen vacancies being fully occupied, both F and Al ions tended to settle down at intrinsic octahedron interstitial sites, which resulted in a metastable doping state. Under the act of 1/3 [11ˉ00] partial dislocation of alumina matrix, distorted cation sub-lattice generated double aggregated vacant octahedron sites. When these doublets vacant octahedron sites were occupied by foreign Al ions, stacking faults composed of about three sequences were generated as that observed in high resolution TEM. Meanwhile, the segregated doping Al ions at double aggregated octahedron sites along the stacking faults worked as early stage precipitations. Under electron irradiation, with the ablation of F ions, the unstable segregated Al ions separated out as nano precipitation with the reconstruction of alumina lattice.
Chemotherapy is the main method used for cancer treatment. However, most chemotherapeutic drugs show low selectivity towards tumor cells. When killing tumor cells, chemotherapeutic drugs can also damage normal tissue cells and induce a series of side effects and toxic reactions, such as gastrointestinal reactions, calvities and so on. An effective way to reduce the adverse drug reactions is to construct targeted delivery systems based on the microenvironment properties of tumor tissue. Porous carbon nanomaterials (PCN), with excellent properties such as good structural stability, pores, and easily modified surface, are promising candidate to be used for such strategy. In this paper, the construction and application of the PCN-based targeted antitumor drugs delivery system were reviewed; the structural properties, the design philosophy of PCN suitable for drug loading were summarized; the effective strategies to improve drug loading on PCN for combined drug delivery were discussed both theoretically and experimentally. The mechanism and applications of PCN for tumor microenvironment based targeted delivery system were analyzed from the perspectives of endogenous sensitive stimulations (such as acidity, redox potential and specific enzyme), exogenous sensitive stimulations (such as light and magnetic) and multiple sensitive stimulations (such as double sensitive stimulations, including acidity/redox potential, acidity/magnetic and magnetic/light, and three sensitive stimulation, including acidity/redox potential/light). The biocompatibility and biodegradability of PCN used as anti-tumor drug delivery system was discussed, and the possible solutions were analyzed. The prospects of the application of PCN to be used in tumor drugs were discussed at the end of this review. This review provides theoretical basis and examples towards design and synthesis of porous carbon (PC) materials based anti-tumor drug delivery system, which may help the research and development of targeted and controllable tumor treatment.
The stable and reliable red phosphor with high-photon energy emission (620-650 nm) is critical for the fabrication of the phosphor-converted white light-emitting diode (WLED) with low correlated color temperature and high color rendering index. Mn 4+-activated phosphor is an emerging kind of red-emitting phosphor for WLED. Herein, the energy levels transition and photoluminescence characteristics of the Mn 4+ ion were introduced; then, the preparation, crystal structure and luminescent properties of as-far reported seven kinds of Mn 4+-doped oxyfluoride red phosphors (such as Na2WO2F4:Mn 4+) containing d 0, d 10 or s 0 cations were reviewed. Currently, only in quite rare case of oxyfluoride, Mn 4+ was found to exhibit strong R-line emission, with local coordination remaining as either [MnF6] or [MnO6]. The studies on the chemical stability and quantum efficiency of Mn 4+-doped oxyfluoride phosphors are still insufficient. Finally, we prospected the future development of Mn 4+-doped oxyfluoride phosphor.
Dynamic mechanical analysis (DMA) has the advantage of high sensitivity, excellent cooling system, flexible rotation testing part, multiple deformation mode, and continuous frequency and temperature scanning mode. DMA is able to characterize the strain response under alternating stress, creep, stress relaxation, and thermomechanical properties, which has application in the investigation of plastic, thermoset, composite, high elastomer, coating, alloy and ceramic. This paper briefly introduced the fundamental and method about DMA, the application of DMA in the investigation of ferroelectric-paraelectric phase transformation, low frequency relaxation, ferroelectric fatigue, and ferroelectric composite damping. In the measurement of relaxation behavior of PZT ceramics and single crystals, and BaTiO3 ceramics, DMA tended to be more sensitive than dielectric characterization especially in the low frequency range. DMA has been one of the critical instruments for ferroelecric investigation.
Chromogenic materials are capable of optical change reversibly in response to physical stimuli (e.g., electric field, temperature, illumination, and atmosphere). Among them, electrochromic materials are expected to be widely used in smart windows, screen displays, multi-functional energy storage devices and other fields due to their characteristics such as large adjustment range, fast response rate, high coloring efficiency and good cycle stability. However, compared with semi-solid-state electrochromic devices that are difficult to package and organic electrochromic materials that are prone to denaturation and failure, inorganic all-solid-state electrochromic materials and devices have better comprehensive application. This paper focuses on the typical inorganic all-solid-state electrochromic materials and devices, presents a brief review on the current preparation methods of each structure layer of electrochromic devices and compares its advantages and disadvantages, introduces in detail the main alternative electrochromic materials and its key performance evaluation index, and explains the principle of several representative electrochromic devices, proposes to use transparent flexible electrodes with both high light transmittance, low surface resistance and excellent bending fold to replace the traditional rigid substrate in order to realize multi-field responsible device application development. Finally, the application prospect of inorganic all-solid-state electrochromic devices is prospected from the perspective of performance bottleneck, process difficulty and industrialization opportunity, which provides reference for the industrialization process of electrochromic devices.
Solid-state cooling technology based on the electrocaloric (EC) effect is attracting increasing attention as an important alternative for traditional cooling systems because of its advantages of high efficiency, environmental friendliness, light weight, low cost, and easy miniaturization. Ferroelectric materials are suitable candidates for EC refrigeration due to their large polarization and entropy change through applying or removing an external electric field. Recently, study on the EC effect of lead-free bulk ceramics has become one of hot topics on ferroelectric community due to the requirements of sustainable development. In this review, we firstly introduce the significant history events in EC research and the basic principles of EC refrigeration. Then, design strategy for achieving a large EC temperature change near room temperature and a wide using range is summarized. Subsequently, we systematically review the research status of EC effect in BaTiO3-based, Bi0.5Na0.5TiO3-based and K0.5Na0.5NbO3-based lead-free bulk ceramics and discuss their advantages as well as challenges. Finally, we propose some prospects for the future work on EC effect in lead-free bulk ceramics.