The optical properties and preparation methods of various kinds of plasmon nanocrystalline glasses containing precious metals and non-precious metals are briefly introduced in this paper. Due to the LSPR effect of plasmon materials, glass containing plasmon nanocrystals exhibit huge resonance absorption and strong nonlinear response in the resonance band, which makes them widely used in ultrafast photonics and nonlinear optics fields. However, the strong resonance absorption of plasmon also means huge linear absorption loss, which limits its application in, for example, the nonlinear optical switching. In addition, in the glass matrix, the growth of plasmon nanocrystals is limited. It's very difficult to control their geometric structure and composition, which makes their optical properties difficult to control. The emergence of ultrafast laser processing technology provides a new means for the spatially selective precipitation of plasmon nanocrystals, which also serves as a powerful processing tool for developing photonic devices based on this kind of glass.

Combined with the current research progress, this review looks forward to the problems and challenges that may be faced in the future development of optical functional hybrid gel glasses. The research of optical functional hybrid gel glass devices mainly focuses on exploring and developing new properties and applications of materials. By changing the composition, structure and preparation process of materials, the microstructure and distribution of functional substances of hybrid gel glass can be accurately controlled, and the performance of optical, electricity and heat can be effectively regulated. Despite the breakthrough progress, the research of optical functional hybrid gel glass devices is faced with the problems and challenges in preparation process, performance optimization and market demand. With the increasing demand for new materials and new technologies, by solving these problems, we are expected to promote the development of optical functional hybrid gel glass devices and realize their application and commercialization in various fields, optical functional hybrid gel glass devices will certainly play an important role in the fields of optics, electronics and other fields. This review will hopefully provide some insights into the design and synthesis, performance optimization, as well as device application of optical functional hybrid materials and glass devices, and further promote the development of optical functional hybrid gel glass devices.

Yttrium aluminum silicate (YAS) glass ceramics, known for their high-temperature resistance, excellent hardness, and mechanical strength, attract wide attention as coating materials for bonding or protecting silicon carbide ceramics. The precipitation of the y-Y₂Si₂O₇ crystalline phase in YAS glass, particularly in comparison with SiC, is advantageous due to the matched coefficients of thermal expansion between y-Y₂Si₂O₇ and SiC. This often leads to its use as a sintering aid or in anti-oxidation coatings for SiC. A glass composition with reported proportions of 22Y₂O₃-19Al₂O₃-59SiO₂ (in mole) has been designed to selectively precipitate only the y-Y₂Si₂O₇ crystalline phase through process engineering, achieving a softening temperature exceeding 1 400 ℃. However, this glass composition initially undergoes a droplet-type phase separation, resulting in the precipitation of y-Y₂Si₂O₇ crystals in regions enriched with Y₂O₃ and SiO₂. The large gap between these two phase-separated regions leads to non-uniform distribution of y-Y₂Si₂O₇ grain sizes. The cross-sectional morphology exhibits a fibrous structure, which may affect the mechanical properties of the glass ceramics. Compared to fibrous structures, spherical grains have a higher stress distribution, providing the glass ceramics with greater strength. Previous studies have shown that TiO₂ and CaF₂ are unsuitable as nucleating agents for achieving uniform and fine grains in YAS glass. In this study, a base glass has a composition of 22Y₂O₃·19Al₂O₃·59SiO_2., The addition of ZnO into the base glass was found to inhibit large-sized phase separation in YAS glass, resulting in a significant refinement of precipitated grain sizes. This led to a substantial improvement in the fracture toughness of the glass ceramics. By observing the crack propagation patterns in the glass ceramics, the toughening mechanism has been elucidated.

On the basis of the glass composition 22Y₂O₃·19Al₂O₃·59SiO₂, a series of glasses with varying compositions, 2xZnO·22Y₂O₃·(19-x)Al₂O₃·59SiO₂ (2x=0, 3, 6, 12, 18, in mole), were obtained by gradually replacing Al₂O₃ with ZnO at a ZnO∶Al₂O₃ ratio of 2∶1. The glasses were subjected to a nucleation temperature (T_g+30 ℃) heat treatment for 3 h, followed by ramping to the crystallization peak temperature (T_c) and holding for 2 h to obtain glass ceramics for testing. Characteristic temperatures of the glasses were determined using DSC at a heating rate of 10 K/min. The glass ceramics, after fine polishing, were etched for 60 s in a 4% HF solution (volume fraction) and then subjected to SEM testing. Vickers hardness of the samples was measured under a 2.94 N load. Fracture toughness (K_Ic) of the samples was determined under the ASTM C-1421-01b standard.

As the amount of ZnO gradually increases, the glass transition temperature (T_g) and T_c of the glass decrease progressively. The addition of ZnO reduces both T_g and T_c of the YAS glasses, which is advantageous for lowering the sealing temperature when used in conjunction with SiC ceramics. XRD patterns, SEM images, and EDS patterns confirm that the mechanism for the precipitation of y-Y₂Si₂O₇ in 22Y₂O₃·19Al₂O₃·59SiO₂ glass belongs to crystallization through phase separation. After the addition of ZnO to YAS glass, nearly spherical grains are precipitated, and the distribution of grains becomes more uniform. With increasing ZnO content, the grain size gradually decreases. The addition of ZnO has a minor impact on the hardness and density of both YAS glass and glass-ceramics. However, a significant improvement is observed in the fracture toughness of the glass ceramics, showing a 65% increase for the glass ceramic containing 18% ZnO compared to the YAS glass ceramic. In glass ceramics formed through phase separation and grain growth, both the size and distribution of grains are uneven. Cracks propagate in a straight-line manner, resulting in longer crack lengths under the same load. In contrast, when cracks propagate in glass ceramics with similar and evenly distributed grain sizes, numerous circumferential cracks around grains occur, leading to increased energy consumption during the crack propagation process and resulting in relatively shorter crack propagation distances.

As ZnO gradually replaces Al₂O₃, both the T_g and T_c of YAS glasses decrease. This leads to reduce the sealing temperature when used as sealing materials. With the addition of ZnO, the crystal phases deposited from the YAS glasses transitions from only the y-Y₂Si₂O₇ grains to two phases, i.e., ZnAl₂O₄ and y-Y₂Si₂O₇. The content of precipitated ZnAl₂O₄ phase increases with the gradual introduction of ZnO. Although no significant increase in hardness was observed following the compositional change from 0 to 18% of ZnO (in mole), a distinct enhancement of about 1 GPa in hardness after crystallization occurs for the glass with ZnO. Despite a decrease in K_Ic of YAS glass from 0.82 MPa·m^0.5 to 0.71 MPa·m^0.5 with the addition of ZnO, the prepared glass ceramics with 18% ZnO (in mole) shows a significant enhancement of K_Ic, reaching a maximum value of 1.92 MPa·m^0.5. The microscopic mechanisms of this enhancement was then revealed by further investigation using SEM.

Glass-ceramics shows excellent optical properties from crystals, and good physical and chemical properties from glass materials, facilitating its important application in infrared wavelength range. Based on the scattering theory, the factors affecting the transmittance of glass ceramics are introduced, and the conditions for realizing transparent glass ceramics are summarized. The most widely reported glass ceramics systems, including oxyfluoride silicate, tellurate and germanate glass ceramics, are introduced. The crystallization mechanism is analyzed, but remains unclear, for example, how to understand the precipitation of anti-glass phase in tellurate glass ceramics. A variety of low phonon energy fluoride or oxide crystalline phases can be precipitated in germanate glass ceramics. However, the infrared germanate glass ceramics is limited to a few systems, and there is plenty of room for exploration of infrared germanate glass ceramics luminous materials. Finally, the application of infrared glass ceramics is introduced, especially in the field of laser. Under the condition of balancing the scattering loss caused by the crystalline phases, glass ceramics shows better laser performance than the precursor glass, which indicates that glass ceramics luminous materials have great application prospects in the field of infrared laser. However, there is few reports on other applications of rare-earth ion-doped glass ceramics in the infrared range at present. It's expected that the development of relative applications based on unique properties of glass ceramics will promote rare-earth ion-doped glass ceramics to become the next generation infrared luminous materials.

As an important part of perovskite solar cells, the electron transport layer plays a role in transporting electrons and blocking holes, having an impact on the performance of perovskite cells. ZnO is a promising electron transport layer (ETL) material because of its high electron mobility, easy synthesis, low-temperature preparation and low cost. However, the chemical properties of ZnO are unstable, and the surface defects are easy to form recombination centers, leading to the decline of electron extraction and transfer efficiency, and surface residual groups destroy the perovskite structure and reduce the stability of perovskite materials, resulting in the deterioration of device performance. Therefore, selecting a suitable modification layer to improve the stability of ZnO plays an important role in improving the performance of ZnO and perovskite batteries.

ZnO/Zn₂SnO₄ NAs was prepared on ZnO NAs surface by a spin-coating method to passivate ZnO surface defects and residual groups. ZnO/Zn₂SnO₄/SnO₂ NAs was formed via in-situ growth of a layer of SnO₂ by a hydrothermal method to improve the stability of ZnO.

The phase and morphology of the heterojunction were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photoelectric performance was measured in electrochemical workstation, in which the photoelectric response ability of the nanoarray was characterized by linear sweep voltammetry. The separation performance of photogenerated electrons and holes in nanoarrays was analyzed via the change of photocurrent. The charge transfer resistance was determined by electrochemical impedance spectroscopy. The conductive type of the semiconductor was determined via the Mott-Schottky test, and the passivation effect of Zn₂SnO₄ and SnO₂ on the ZnO surface defects was reflected by the carrier concentration.

The results by XRD, SEM and TEM show that Zn₂SnO₄ and SnO₂ are coated on ZnO nanoarrays. Zn₂SnO₄ as a protective layer has a superior chemical stability in alkaline environment to prevent direct contact between ZnO and OH^- produced by urea hydrolysis, avoiding the corrosion of ZnO. This is beneficial to improving the stability and photoelectric properties of ZnO.

The linear scanning voltammetry curves of ZnO, ZnO/SnO₂, ZnO/Zn₂SnO₄ and ZnO/Zn₂SnO₄/SnO₂ NAs at 0-0.6 V vs. RHE under light conditions indicate that ZnO/Zn₂SnO₄/SnO₂ NAs have the maximum photocurrent density. These results demonstrate that the photoelectric response of nanoarrays can be improved via the modification of Zn₂SnO₄. ZnO/Zn₂SnO₄ and ZnO/Zn₂SnO₄/SnO₂ NAs modified with Zn₂SnO₄ exhibit a higher photocurrent. The ZnO/Zn₂SnO₄/SnO₂ NAs photocurrent (i.e., 140 μA·cm^-2) is 1.75 times greater than that of ZnO NAs photocurrent (i.e., 80 μA·cm^-2). This indicates that the addition of Zn₂SnO₄ and the construction of double heterojunction have a positive effect on reducing the electron-hole pair recombination phenomenon and improving the photoelectric performance of nanoarray. The charge transfer resistances of ZnO, ZnO/SnO₂, ZnO/Zn₂SnO₄, ZnO/Zn₂SnO₄/SnO₂ NAs measured by electrochemical impedance spectroscopy are 22 403 Ω, 16 854 Ω, 7 018 Ω and 3 131 Ω, respectively. The Zn₂SnO₄ modified layer reduces a charge transfer resistance via passivating the ZnO surface defects and reducing the scattering effect of the defects on the carriers. The ZnO/Zn₂SnO₄/SnO₂ co-constructed heterojunction structure promotes the separation of electron-hole pairs and electron transport at the interface, further reducing the resistance of photogenerated electrons to transfer at the interface. In the Mott-Schottky test, the carrier concentrations of ZnO, ZnO/Zn₂SnO₄, ZnO/SnO₂, ZnO/Zn₂SnO₄/SnO₂ NAs are 1.22×10¹⁹, 2.34×10¹⁸, 2.41×10¹⁸ and 1.18×10¹⁸ cm^-3, respectively. ZnO defects are passivated by Zn₂SnO₄ modification, and the carrier recombination center is reduced. The carrier concentration of ZnO/Zn₂SnO₄/SnO₂ NAs is lower than that of ZnO NAs. ZnO, Zn₂SnO₄ and SnO₂ form a double type II heterojunction with interlaced arrangement of energy level, which drives a transfer of photogenerated electrons from high energy level to low energy level, so that the photogenerated electron-hole pair can be effectively separated at the interface, thus effectively reducing the electron and hole recombination. It also reduces a charge transfer resistance and promotes a photogenerated electron transfer from SnO₂ to ZnO. The photoelectric properties of ZnO/Zn₂SnO₄/SnO₂ (i.e., current density, photocurrent and carrier concentration) are improved.

ZnO NAs surface was coated with Zn₂SnO₄ nanocrystals by a spin-coating method. Zn₂SnO₄ reduced the recombination of photo-generated charge carriers at the interface via passivating the defects and residual groups on ZnO NAs surface. Based on ZnO surface defects passivated by Zn₂SnO₄, a more stable and high-density SnO₂ nanoparticle coating layer was in-situ grown on ZnO/Zn₂SnO₄ NAs by a hydrothermal method, and the double heterojunction was formed with ZnO and Zn₂SnO₄. The alternating energy level arrangement could improve the separation efficiency of photogenerated charge carriers. The constructed ZnO/Zn₂SnO₄/SnO₂ NAs had higher current density, photocurrent, lower charge transfer resistance and carrier concentration, which could be used as an electron transport layer in perovskite solar cells.

Ge/Si avalanche photodiode (APD) has attracted much attention in optical communication, optical imaging, and security detection due to its high-speed operation, low noise, high sensitivity, and optical gain characteristics. However, a mismatch between the lattice constants of Si and Ge (i.e., a difference of 4.2%) has a challenge. This mismatch leads to a high density of threading dislocations at the Ge/Si heterojunction interface, ultimately deteriorating the performance of the device. Therefore, addressing the issue of lattice mismatch and reducing the dislocation density in Si-based Ge thin films is crucial for achieving high-performance Ge/Si APDs. To decrease the dislocation density of APDs, Si-based epitaxial Ge thin films are used as a fabrication method. However, the dislocation density continues to be relatively high. In this paper, the lattice mismatch between Ge and Si was alleviated. In addition, the theoretical underpinnings were also proposed.

In this research, a polycrystalline silicon (poly-Si) bonding layer was incorporated at the Ge/Si interface to mitigate the lattice mismatch effects. This poly-Si layer acted as a buffer, diminishing the stress and strain induced by the lattice mismatch. To assess the influence of the poly-Si bonding layer on the performance of Ge/Si APDs, a series of experiments at different doping concentrations of the poly-Si layer were carried out. The doping concentration was pivotal as it modulated the electrical and optical properties of the bonding layer, subsequently affecting the overall performance of the APD.

The charge distribution, electric field distribution, and carrier transport within the Ge/Si APD device were delineated by the Poisson equation, carrier transport equation, carrier continuity equation, and a parallel electric field dependent model. This facilitated the computation of the device's electrical characteristics. The Ge/Si APD involved electron and hole recombination, the concentration-dependent SRH model was used to characterize the spontaneous emission and Auger recombination processes of carriers. The optical radiation recombination model elucidated the photon Auger recombination process, while the trap recombination model (TRAP.AUGER) described the transition between trap states and non-trap states of carriers, along with their corresponding recombination processes. Ge/Si APD necessitated high voltage operation and substantial doping, and the band-band tunneling standard model was used to explain the carrier transport and ionization process instigated by band-band tunneling under high electric field conditions. In addition, the energy band narrowing model was used to illustrate how changes in band structure impact device performance under high doping conditions. This paper provided a theoretical analysis of Ge/Si APD device performance based on these models, and other related theories.

The results indicate that the photocurrent of APD with a bonding layer thickness of 2 nm initially increases and subsequently decreases as the doping concentration of the bonding layer escalates at 95% of the avalanche voltage. In contrast, the photocurrent of an APD with a bonding layer thickness of 5 nm diminishes as the doping concentration increases. Furthermore, the dark current of a Ge/Si APD can reach as low as 10^-10 A prior to avalanche due to the lattice mismatch buffering effect of poly-Si between Ge and Si, which is markedly lower than that of an APD based on InP. The maximum gain-bandwidth product of 63.8 GHz for the 2 nm bonding layer thickness significantly surpasses that for the 5 nm bonding layer thickness, and the bandwidth of the 2 nm bonding layer thickness also exceeds the bandwidth of the 5 nm bonding layer thickness when the bias voltage exceeds the avalanche voltage. It is recommended to select a poly-Si bonding layer with a thickness of 2 nm and a low doping concentration to achieve the optimal performance in a Ge/Si APD.

The efficacy of integrating a poly-Si bonding layer at the Ge/Si interface was under scored, thereby mitigating a threading dislocation density and augmenting the performance of Ge/Si APDs. Theoretical modeling and simulation analyses revealed that a diminished doping concentration in the poly-Si layer yielded superior outcomes. Such insights paved a way for the advancement of more dependable and efficient Ge/Si APDs, having a potential to transform domains such as optical communication, optical imaging, and security detection. The methodology delineated in this study presented a promising avenue for subsequent research within the realm of semiconductor photodiodes. For materials science and device engineering, it is anticipated that Ge/Si APDs could experience a further evolution, potentially yielding enhanced performance and expanding application potential. The incorporation of the poly-Si bonding layer signified a substantial advancement in addressing lattice mismatch challenges, which could be poised to be instrumental in the progression of next-generation photodetection technologies.

Thermal barrier coatings can be used for the stable operation of aircraft engines under high-temperature environments due to their excellent oxidation resistance, corrosion resistance and heat insulation properties. However, the high-temperature phase transition of conventional 8.0% (in mass fraction) Y₂O₃ stabilized ZrO₂ ceramic (8YSZ) materials exists when the service temperature exceeds 1 200 ℃. Developing thermal barrier coatings, such as rare-earth zirconates and rare-earth silicate, becomes popular. (Gd_0.9Yb_0.1)₂Zr₂O₇ (GYbZ)/8YSZ coatings with a low thermal conductivity and a high temperature phase stabilization are regarded as potential thermal protective materials. At present, some work focus on the preparation properties optimization of air plasma spraying, electron beam physical vapor deposition and plasma spray physical vapor deposition techniques, respectively. It is important to in-situ investigate the mechanical properties and failure mechanisms of GYbZ/8YSZ coatings at > 1 200 ℃.

GYbZ/8YSZ thermal barrier coatings were prepared with NiCrAlY, 8YSZ and GYbZ powders on an Inconel 600 nickel-based superalloy with the thickness of 2 mm via air plasma spraying. GYbZ/8YSZ thermal barrier coatings were subjected to thermal cycle treatments in a Muffle furnace at 1 100 ℃ for 1 h, and then cooled to room temperature for 1 thermal cycle. The times of thermal cycles were 10, 50 and 100, respectively. The phase and microstructure of the coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) before and after heat-treatments. The elastic modulus, hardness, fracture toughness and residual stress were measured by an indentation method at different temperatures.

The XRD patterns show that GYbZ powder and the as-sprayed coating are a defective fluorite structure, and the doping of Yb³⁺ with small ionic radius makes the material change from a pyrochrite structure to a defective fluorite structure. In addition, the samples treated for different thermal cycles all maintain a defective fluorite structure, indicating that GYbZ has an excellent high-temperature phase stability. The SEM images show that the surface of the as-sprayed GYbZ coating has a good melting state, and massive micro-cracks are distributed on the surface, which is caused due to the quenching stress generated by the molten spray particles during the preparation process and the thermal stress generated by the mismatch between the thermal expansion coefficients between the layers. The bonding between the layers of GYbZ/8YSZ coatings is good, and the bonding interface is clear without any cracks. There are tiny pores in the interior. The distribution of elements in each layer is consistent with the design. After thermal cycling, the crack width of the coating surface gradually widens and the porosity gradually decreases. The thermal growth oxide (TGO) produced between the bond layer and the 8YSZ layer gradually increases, and the TGO grows to 20 μm after 100 thermal cycles. The generation of TGO leads to a large amount of stress concentration, leading to the initiation and rapid expansion of transverse cracks in the bonding layer and 8YSZ, and damages the structural stability of the GYbZ/8YSZ coatings. Also, some vertical cracks occur in GYbZ layer and 8YSZ layer. The results of element distribution test show that the oxygen content in the bond layer increases gradually with the increase of the number of thermal cycles. The creation of vertical cracks in the coating promotes the diffusion of oxygen, thus accelerating the growth of heat-grown oxides.

The results of mechanical properties test show that the elastic modulus and hardness of GYbZ/8YSZ coatings surface firstly increase and then decrease with the increase of thermal cycle, and have the maximum values at 50 thermal cycles. After thermal cycling, the coating is sintered and its densification is improved, resulting in an increase in the elastic modulus and hardness. After 100 thermal cycles, the coating oxidation is serious, the binding force between coatings is weakened, massive vertical cracks occur in the coating, the coating structure is damaged, the deformation resistance is weakened, and the elastic modulus and hardness are reduced. The hardness of the coating decreases from 5.09 GPa to 2.20 GPa from room temperature to 700 ℃. At 700-1 100 ℃, the hardness of the coating is 2.00 GPa. The residual stress of the as-sprayed coating is -41.02 MPa. The residual stress accumulates due to thermal expansion mismatch of coating system during thermal cycling. After 10 thermal cycles, the residual stress accumulates to-147.30 MPa. After 50 thermal cycles, the stress relaxation caused by cracks gradually reduces the residual stress. After 100 thermal cycles, the residual stress decreases to -105.92 MPa. The results show that the residual stress of the coating before and after thermal cycling is a compressive stress. The fracture toughness of the as-sprayed GYbZ coating is 0.93 MPa·m^1/2. The fracture toughness of the coating firstly increases and then decreases with the increase of the number of thermal cycles, and has a maximum value of 2.02 MPa·m^1/2 after 50 thermal cycles. After heat-treatment, the pores of the coating reduce, and the dense area and the compressive stress can prevent the crack propagation. Some microcracks can increase the strain tolerance of the coating to a certain extent, and enhance the fracture toughness of the coating. After 100 thermal cycles, oxidation and massive destructive cracks lead to the instability of the coating structure, the increase of defects and the decline of performance.

The pore distribution in the as-sprayed GYbZ/8YSZ coatings was uniform, and the bonding interface of each layer was clear. Before and after thermal cycling, GYbZ coating was a defective fluorite structure and had an excellent high-temperature stability. The density of the coating increased with the increase of the number of thermal cycle, occurring some transverse and vertical cracks, and the TGO thickness grew to 20 μm. After 50 thermal cycles, the elastic modulus and hardness reached the maximum values, which were 182.01 GPa and 9.13 GPa, respectively. From room temperature to 700 ℃, the coating hardness reduced to 2.20 GPa. At 700-1 100 ℃, the coating hardness was 2.00 GPa. During the thermal cycle, the residual stress of the coating varied from -41.02 MPa to -123.67 MPa, and the fracture toughness varied from 0.93 MPa·m^1/2 to 2.02 MPa·m^1/2.

Despite the development of tunable THz metamaterials based on different principles, there are some challenges associated with the difficult etching of VO₂ as well as the limited precision of the process. In addition, VO₂ is not the most stable phase of vanadium oxide, which is greatly affected by oxygen during etching, affecting the performance of THz metamaterial devices. For future applications, power consumption and response time must be considered. It is therefore possible to achieve lower power consumption and faster thermal response time via doping vanadium dioxide or tuning the stain by the substrate to lower the phase transition temperature, although this may introduce some challenges such as a decrease in the magnitude of the conductivity change after the phase transition and a reduction in modulation depth. By contrast, it is possible to significantly improve the response time of devices by using pulsed intense laser excitation. Furthermore, machine learning and other methods can be integrated to achieve additional structural optimization. Field-programmable gate array (FPGA) controlled programmable metamaterials, which can switch different functions via changing input encoding sequences in real time, and greatly extend the application of metamaterials by dynamically manipulating electromagnetic waves. Metamaterials application and functionality will be enhanced by adding sensors to detect temperature, humidity, illumination, etc., facilitating the development of intelligent electromagnetic metamaterials with tunable properties in the future.

SiC-based ceramic matrix composites (SiC-CMCs) can meet both of these conditions for excellent high-temperature strength and oxidation resistance simultaneously, making them highly promising lightweight structural materials for future aerospace engine applications. Si dioxide generates volatile Si(OH)₄ compounds when reacting with water molecules in the high-temperature environment of an engine in which there exists water and oxygen corrosion. With the progress of the reaction, the SiC substrate is continuously lost, resulting in a sharp decline in the physical and chemical properties of CMCs. Therefore, environmental barrier coatings (EBCs) are needed to be coated on the CMCs surface to prevent the materials from being damaged by corrosive media such as water vapor and improve the service life of SiC-CMCs.

Si/Yb₂Si₂O₇ EBCs is formed by a relatively mature controllable preparation method, and its resistance to water vapor corrosion is a key to the related research. Jian et al. found thatYb₂Si₂O₇ coating had an excellent phase stability under the water vapor corrosion at 1 300 ℃. The growth of thermally grown oxides (TGO) was effectively controlled. The oxidation weight gain rate of the coated sample was lower than that of the uncoated sample, thus indicating that Yb₂Si₂O₇ topcoat could have an excellent corrosion resistance. Zhang et al. observed a "self-healing" reaction of Yb₂Si₂O₇ topcoat in the water vapor corrosion at 1 350 ℃, and the growth of the TGO layer showed a positive linear relationship with time, and the overall structure of the coating was basically intact. Ridley et al. reported that after Yb₂Si₂O₇ topcoat was subjected to water vapor corrosion at 1 400 ℃, a porous Yb₂SiO₅ layer was formed, the thickness and pore size increased with time, and a distinct layered structure appeared in the reaction layers in the high-speed area, i.e., a porous Yb₂SiO₅ layer, a dense Yb₂SiO₅ layer, and a highly porous Yb₂O₃ layer. The existence of the dense layer hindered the inward diffusion of water vapor and oxygen, reducing the total thickness of the reaction layer and effectively protecting SiC substrate. In this paper, a gradient structure yttrium silicate-based environmental barrier coating was prepared for the improvement of high-performance aero-engine thermal protection coating material. In addition, the continuous water vapor damage behavior and corrosion mechanism at 1 350-1 500 ℃ were also investigated.

SiC composite samples were cut to a cube of 10 mm × 10 mm × 10 mm. Si bond coat (~50 μm) and Yb₂Si₂O₇ topcoat (~200 μm) both were deposited by an air plasma spray technique in an air plasma spray system. These samples were annealed in vacuum at 1 300 ℃ for 2 h before the corrosion test. The equipment used for continuous water vapor exposure was a self-designed experimental platform. And the coating samples were placed in a flowing 90% (in volume) H₂O-10% O₂ under an atmospheric pressure. For the experiments, the furnace temperature was set at different temperatures (i.e., 1 350, 1 400, 1 450 ℃ and 1 450 ℃), respectively. The ten samples were prepared in a zirconia crucible. Finally, the sample was removed from the furnace tube at each temperature for different durations (i.e., 50, 100, 150 h and 200 h).

The composition phases on the surface of the samples were analyzed by a model XD-3 X-ray diffractomter (XRD, Aeris Co., the Netherlands). The microstructure of the sample cross section and the thickness of the TGO layer in secondary electron (SE) and backscattered electron (BSE) images were determined by a model MIRA 3 emission-scanning electron microscopy (SEM, Tescan Co., Czech Republic). The element distribution and proportion were characterized by an energy dispersive X-ray spectroscope (EDS).

After 200 h water vapor corrosion, the coatings at different temperatures show different results. At 1 350 ℃, the coating shows a transformation from Yb₂Si₂O₇ phase to Yb₂SiO₅ phase, as well as some holes appear due to the volatilization of Si(OH)₄. The coefficient of thermal expansion (CTE) mismatch results in a "fragmented" layer on the top of the coating. At 1 400 ℃, a "self-healing" reaction occurs in the coatings. The proportion of Yb₂Si₂O₇ phase increases slightly, and some transverse cracks heal. The "self-healing" reaction is related to Si(OH)₄ concentration. Also, Yb₂O₃ phase appears, and some cracks occur due to the CTE mismatch. At 1 450 ℃, a black phase (i.e., Yb₃Al₅O₁₂) appears on the top of the coatings. Gaseous Al(OH)₃ diffuses into the coating, and a dark mullite phase forms. The "self-healing" reaction still exists at 1 450 ℃. At 1 500 ℃, many transverse cracks appear on the top of the coatings, the "self-healing" reaction is inhibited, Yb₂O₃ phase appears at the coating interface, and many cracks and holes occur inside the coating. The coating mass gain and TGO growth are linearly related to the corrosion time at <1 500 ℃, but they are not related to the corrosion time at 1 500 ℃.

After 200 h continuous water vapor corrosion at 1 350-1 500 ℃, Yb₂Si₂O₇ topcoat exhibited an excellent phase stability, and TGO layer grew at a slow rate. This indicated that Si/Yb₂Si₂O₇ bi-layer EBCs could have a good corrosion resistance, and the preparation process of the fully covered sample could reflect the protective effect of the coating on the SiC substrate. The corrosion mechanisms were different at different starting temperatures. At 1 350 ℃, the reaction volume of Yb₂Si₂O₇ and water vapor decreased to generate cracks, and the CTE mismatch of the product Yb₂SiO₅ led to crack expansion. At 1 400 ℃ and 1 450 ℃, the "self-healing" reaction gradually played a dominant role, and the new phase generated by the penetration of Al(OH)₃ led to some holes in the coating. At 1 500 ℃, water vapor diffused to Si/Yb₂Si₂O₇ coat interface in the later stage of corrosion and reacted to produce Yb₂O₃ phase, resulting in channel cracks at the TGO layer interface.

Clay minerals with their distinct morphology, crystal structure and surface physicochemical properties have some advantages in the realm of carbon-based and silicon-based materials, having an application potential in commercialized lithium-ion battery anodes. However, the preparation of clay mineral-derived nanomaterials and their commercialization as anode materials still have several challenges.

Clay minerals from different geographic environments or mineral sources, along with differing origins and purification methods have challenges to ensure uniformity in the structure and performance of clay mineral-derived carbon-based and silicon-based materials. To address this, there is a need to strengthen mineralogical and process research of clay minerals from diverse origins, structures, and compositions. This can contribute to a comprehensive understanding of the diversity and complexity of clay minerals, and provide abundant basic data for the subsequent development of low-cost, green and efficient clay mineral purification methods and modification technologies.

The preparation of clay mineral-derived silicon nanomaterials through magnesium thermal reduction has some challenges like impurities in the products and inhomogeneous properties. The existing process is in the laboratory stage, and there is a need to improve the magnesium thermal reduction method or develop cost-effective methods for producing high-performance silicon nanomaterials to enhance commercialization possibilities. Improving reaction condition (i.e., slower ramp rates, staged ramping and the use of thermal scavengers) can mitigate some issues related to excessively high temperatures and ensure product quality. The emerging electrochemical reduction method is also in the early stages of development and requires a continuous improvement.

The development of low-cost and simple preparation methods for silicon/carbon nanocomposites is crucial for their scale-up applications. The development of more low-cost preparation techniques for silicon/carbon nanocomposites in combination with the easily tunable structure and properties of clay minerals is expected to accelerate the commercialization of silicon/carbon anode materials.

Clay mineral-derived nanomaterials are widely used in lithium-ion battery anode materials. The further developments on raw materials, preparation methods, and performance optimization are essential to meet commercialization demands. Collaborative research efforts between academia and industry are crucial to exploring key issues in the preparation process. Accelerating the transition from laboratory-scale research to industrial manufacturing via combining practical production experience with advanced technology through industry cooperation is vital for the in-depth development of clay mineral-derived nanomaterials in lithium-ion battery anode materials.