CaTiO₃-based compounds emerge as a promising thermoelectric material due to their environmentally benign, thermally stable, and cost-efficient merits. Nonetheless, pristine CaTiO₃ manifests inherently inferior electronic transport properties. In this paper, Ca_1-xDy_xTi_0.95Nb_0.05O₃ (x=0-0.15) bulk ceramics were prepared via solid-phase sintering combined with hot-pressing sintering, and the composition, microstructure, and thermoelectric properties were analyzed. The results show that Dy and Nb doping can significantly increase the carrier concentration and effectively improve the electronic transport properties. Also, the lattice thermal conductivity is drastically reduced due to the introduction of large mass-field strain and stress-field strain, thus scattering high-frequency phonons. Ca_0.85Dy_0.15Ti_0.95Nb_0.05O₃ bulk ceramic has a zT maximum of 0.29 at 1073 K, showing that the CaTiO₃-based materials have a promising prospect for thermoelectric applications.

Ca_1-xDy_xTi_0.95Nb_0.05O₃ (x=0-0.15) bulk ceramics were synthesized by solid-phase sintering and hot pressing. First, powders of CaCO₃, Nb₂O₅, Dy₂O₃, and TiO₂ were mixed and ground in a planetary ball mill for 12 h, then dried and cold-pressed. The pre-burned samples were ground for 6 h and the dried powders were cold-pressed again. The pressed samples were then placed in a graphite mold with a diameter of 13 mm for hot pressing at 1573 K for 1.5 h to obtain dense disks with a thickness of 2 mm.

The phase composition of the bulk samples was performed by a model EMPYREAN X-ray diffractometer (XRD, PANalytical Co., the Netherlands). The elemental distribution of the samples was measured by a model JXA-8530F electron probe X-ray micro-analyzer (EPMA, JEOL Co., Japan). The Seebeck coefficient and resistivity of the samples were measured simultaneously by a model LSR-3 device (Linseis Co., Germany). The samples used for the test were long strips with the sizes of approximately 11.0 mm ×2.0 mm × 2.5 mm. The carrier concentration and Hall mobility of the system were measured by a model 8400 Hall measurement system (Lake Shore Co., Ltd., USA). The thermal conductivity of the system was measured by a model LFA-457 laser flash thermal conductivity meter (Netzsch Co., Germany), and the specific heat capacity of the bulk samples was calculated according to the Debye-Dulong law.

The polycrystalline Ca_1-xDy_xTi_0.95Nb_0.05O₃ (x=0-0.15) samples with a single phase were prepared. The main phase of the synthesized samples is an orthorhombic structure, with a space group of Pnma. Dy³⁺ and Nb⁵⁺ occupy Ca²⁺ and Ti⁴⁺ sites in the matrix, respectively, causing the lattice expansion and introducing the donor impurity levels, transforming CaTiO₃ from an insulating wide-bandgap semiconductor to a good electrical conductivity thermoelectric material. The actual amounts of elements Dy and Nb in the bulk samples are basically consistent with the nominal doping concentrations, indicating that elements Dy and Nb are incorporated into the CaTiO₃ matrix effectively. The electrical conductivity decreases with increasing temperature, while the absolute value of the Seebeck coefficient increases with increasing temperature, showing typical characteristics of degenerate semiconductor electron transport. At high temperatures, the lattice vibrations are violent, and the acoustic wave scattering dominates the carrier transport, with other scattering mechanisms having little effect on the electronic transport properties. As Dy concentration increases, the effective mass of the density of states decreases. When x=0.15, the maximum zT value can reach 0.29 at 1073 K, which is comparable to the others reported CaTiO₃ based thermoelectric performances in the literature.

Polycrystalline Ca_1-xDy_xTi_0.95Nb_0.05O₃ (x=0-0.15) samples with a single phase were prepared by solid-phase reaction combined with HP sintering. Dy and Nb doping could significantly increase the carrier concentration and effectively improve the electronic transport performance. Meanwhile, the high-frequency phonons were scattered due to the large mass difference and covalent radius difference between Dy³⁺ and Ca²⁺, resulting in a substantial reduction in the lattice thermal conductivity of the system. Ca_0.85Dy_0.15Ti_0.95Nb_0.05O₃ achieved the maximum zT value of 0.29 at 1073 K due to the simultaneous optimization of electrical and thermal properties, indicating that CaTiO₃ oxide thermoelectric materials could have a promising prospect for thermoelectric applications.

Thermal barrier coatings (TBCs), primarily composed of yttria-stabilized zirconia (YSZ), are critical materials for protecting the hot section components of gas turbine engines due to their high fracture toughness, melting point, and thermal stability. However, increasing operational temperatures has some challenges, particularly from molten CMAS (CaO-MgO-Al₂O₃-SiO₂) deposits that can penetrate TBCs, reduce their strain tolerance, and accelerate failure. The performance of YSZ deteriorates upon interaction with CMAS, leading to phase transformation and coating detachment. Research efforts focus on modifying YSZ with TiO₂, Cr₂O₃, or Al₂O₃ based on sacrificial protection strategies, enhancing resistance to CMAS via promoting the crystallization of compounds such as gehlenite (CaAl₂Si₂O₈). This study was to investigate the effect of Ti on the reactivity of sacrificial protective Al₂O₃ coatings with CMAS. Al and Ti layers were deposited on YSZ by magnetron sputtering and heat treatment to form mixed oxide layers to improve the protective efficacy against CMAS attack.

In this study, graphite was utilized as a substrate for YSZ coatings. After degreasing and cleaning, graphite substrates were roughened with alumina sand (WA22). A YSZ powder (KF231) was sprayed onto the substrates in Ar-H₂ as a plasma gasby a model Multicoat APS system (Oerlikon Metco Co., Switzerland) to deposit a YSZ coating with the thickness of 1500 μm. The graphite substrate was removed by heat treatment at 750 ℃ for 3 h. Subsequently, Al and Ti films were deposited on the YSZ surface via magnetron sputtering, and followed via annealing at 1000 ℃ for 2 h to form TiO₂-Al₂O₃ modified YSZ (TA-YSZ) coatings. An additional control group of Al₂O₃-modified YSZ (A-YSZ) without Ti deposition was also prepared.

CMAS powders with a composition of 33%CaO-9%MgO-13%AlO_1.5-45%SiO₂ (in mole fraction) were synthesized via melt quenching. The melting and crystallization temperatures of CMAS and its mixtures with Al₂O₃ and TiO₂ were characterized by differential scanning calorimetry (DSC). The thermal corrosion test was performed by painting the coated surface with a CMAS slurry and exposing it to 1300 ℃ for 5 min or 1250 ℃ for 2 h and 10 h (after 2 h heat treatment, the temperature was lowered in a furnace and then raised to 1250 ℃ for 2 h, and this was repeated for 5 times). The phase structure was determined by X-ray diffraction (XRD, Rigaku Smart Lab., Japan). The surface and cross-sectional microstructures of the corroded samples were analyzed by a model Phenom ProX field emission scanning electron microscope (SEM, Thermo Scientific, Netherlands) equipped with an energy-dispersive X-ray spectroscopy (EDS) system. The corroded samples were embedded in epoxy resin, cut and diamond-polished before performing the SEM analysis of the coating cross-section. The phase structure of YSZ was determined by a model InVia-Reflex Fourier-transform Raman spectroscopy (Renishaw Co., UK).

Al and Ti films are sequentially deposited on the surface of YSZ coatings via magnetron sputtering. Al film exhibits a typical physical deposition structure. After heat treatment, the Ti element shows a dotted band above Al layer and forms an oxide layer. The results of DSC analysis reveal that the crystallization and melting characteristic temperatures of the three powder samples (i.e., CMAS, CMAS+Al₂O₃, and CMAS+Al₂O₃+TiO₂) shift towards lower temperatures in such an order. This indicates that the addition of Al₂O₃ and TiO₂ effectively reduces the crystallization temperature of CMAS and affects its melting characteristics.

TA-YSZ and A-YSZ coatings coated with CMAS and subjected to treatments at 1300 ℃ for 5 min or 1250 ℃ for up to 2 h and 10 h show that Ti promotes reactions between CMAS and Al₂O₃ to form high-melting-point crystalline phases such as gehlenite (CaAl₂Si₂O₈) and spinel (MgAl₂O₄). The introduction of Ti significantly enhances the interfacial reaction kinetics between the coating and the CMAS melt. Ti facilitates the formation of high-melting-point crystalline phases. Also Ti accelerates the crystallization process of corrosion products, forming a dense reaction barrier layer that effectively consumes molten CMAS and inhibits its penetration into the YSZ substrate. Moreover, the time and spatial distribution characteristics of the reaction products can occur during corrosion testing due to the different reaction kinetics characteristics of high-melting-point crystalline phases. Under the sacrificial protection mechanism of the surface coating, no phase transformation appears in the YSZ substrate.

YSZ coatings prepared by the atmospheric plasma spraying method were subjected to magnetron sputtering to deposit Al and TiAl films on their surface, which were then in-situ oxidized to form Al₂O₃ and TiO₂-Al₂O₃ (TA-YSZ) layers. The synergistic effect of Ti and Al on the enhancement of the CMAS corrosion resistance of YSZ coatings was investigated. The results showed that Ti significantly accelerated the reaction between CMAS and Al₂O₃, leading to the formation of high-melting-point products such as gehlenite and spinel, and promoted the crystallization of corrosion products. These actions effectively hindered the penetration of molten CMAS into the YSZ coating interior.

The gelation of lignin often requires considerable time, which hampers production efficiency. Also, the carbonization process is complex and difficult to control with precision, leading to inconsistencies in product quality. A future research should focus on modifying lignin to enhance its reactivity, thereby reducing gelation time. The development of more advanced composite templates for carbonization should facilitate a better control for pore structure. In addition, investigating novel methods to introduce functional groups into lignin-based carbon aerogels can broaden their applications in emerging fields like flexible electronics and biosensors.

This review represents the research progress on Si-based anodes from material structure to electrolyte design, and highlights the need to clarify the degradation mechanisms of Si-based anodes, develop novel characterization methods, and design new molecular structures to improve interfacial stability. Some efforts in future research should be directed towards the following aspects, i.e., 1) further elucidating the degradation mechanisms of Si-based anodes from the chemomechanical viewpoint. The Si-based anodes work under cyclic stress and chemical corrosion, which are highly intertwined. This coupling effect is highly analogous to the "stress corrosion cracking" well known in metals. Clarifying and decoupling these two failure mechanisms can guide the design of both electrodes and electrolytes, 2) developing novel interdisciplinary characterization and research methods. These methods should employ both in-situ and ex-situ techniques in microscale to investigate crack propagation and structural evolution of electrodes and interfaces under various chemical environments, 3) evaluating novel electrolytes under realistic conditions. It is essential to assess the performance of batteries, including cycling and gas generation, under realistic conditions such as high-loading electrodes, lean electrolytes, large-format cells and extreme temperatures to analyze the battery degradation mechanisms, 4) electrolyte design for Si-C anodes must consider the compatibility of both Si and Graphite. Since the requirements for electrolytes differ between graphite and silicon, a design needs to balance the compatibility of different solvents and additives with the both materials, and 5) developing novel additives and solvent molecules. Designing new molecules to replace FEC and address the gassing issue at high temperatures is quite meaningful for practical applications. The design of these molecules should ensure superior oxidation resistance, compatibility with high-voltage cathodes, stability with trace amounts of water in the electrolyte, and good chemical stability at high temperatures.

Porous silicon-based anode materials with their high theoretical specific capacity (i.e., approximately 4200 mA·h·g^-1) and unique porous structure have a promising application potential in the field of lithium-ion batteries. Their porous structure provides effective buffering space for the significant volume change (i.e., 300%) of silicon during charging and discharging, effectively mitigating material pulverization and maintaining the integrity of the electrode structure, thereby enhancing battery cycle stability and Coulombic efficiency, and greatly increases the utilization rate and conductivity of active materials, thus enhancing the energy density of lithium-ion batteries. However, despite the enormous application prospects of porous silicon-based anode materials, their high preparation costs, low initial Coulombic efficiency, and capacity fade after long-term cycling remain some critical factors restricting their commercialization.

To address these issues, recent studies mainly focus on nanostructure design, composite material development, electrolyte optimization, and large-scale preparation techniques. The emergence of silicon-carbon composite materials, which embed silicon nanoparticles into a porous carbon matrix, can construct a good conductive network, effectively improving material conductivity, and further enhance the buffering capacity for silicon volume changes, significantly improving battery cycle stability and rate performance. In this paper, a porous silicon-carbon layered silicon-based composite was prepared as an anode material. In addition, the electrochemical performance of this material was also investigated.

In the preparation process, silicon nanopowder was first uniformly dispersed with a mixed solvent of deionized water and anhydrous ethanol, and then sonicated under ultrasound to ensure uniform dispersion of silicon nanopowder. Subsequently, PVP (polyvinylpyrrolidone) and glucose/sucrose were added to the dispersed suspension as a pore-forming agent and two carbon sources, and stirred at room temperature to form a uniform precursor sol. The two precursor sols, i.e., Si/PVP/glucose and Si/PVP/sucrose, were placed into the ink cartridges of a microelectronic printer, and the gels were uniformly printed onto copper foil by a 3D printing technology. Finally, the carbon-containing substances in the electrode were completely reduced to amorphous carbon after vacuum drying and carbonization treatment. Note that different carbon sources (i.e., glucose and sucrose) released different amounts of gas during the carbonization process, leading to subtle changes in the electrode structure and subsequently affecting its electrochemical performance.

The prepared electrode materials were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and other characterization techniques.

The results show that larger pores with a uniform pore distribution exist in Si@PVP/glucose structure, and the electrode exhibits minimal cracking after charging and discharging cycles, demonstrating the superior mechanical stability and resistance to expansive internal stresses. In contrast, the pore distribution of Si@PVP/sucrose is relatively uneven, and the electrode exhibits greater cracking after cycling, leading to a decrease in cycle stability and electrochemical performance. These results demonstrate that the Si@PVP/glucose structure electrode exhibits a greater ability to withstand expansive internal stresses and has a higher cycle retention rate. The electrochemical performance tests further validate the superiority of the Si@PVP/glucose composite material. After 100 cycles of charging and discharging, the specific capacity of the Si@PVP/glucose electrode reaches 1095 mA·h·g^-1, with a reversible capacity retention rate of 97.4%, while the specific capacity of the Si@PVP/sucrose electrode is only 970 mA·h·g^-1, with a reversible capacity retention rate of 91.0%. It is indicated that the Si@PVP/glucose composite material has significant advantages in optimizing the performance of porous silicon-based anode materials, particularly in improving cycle stability and rate performance.

This study prepared a porous silicon-carbon layered silicon-based composite (i.e., Si@PVP/glucose) as an anode material, and the performance was optimized. The results showed that the Si@PVP/glucose electrode material exhibited a greater ability to withstand expansive internal stresses and had a higher cycle retention rate. The electrochemical performance tests further validated the superiority of the Si@PVP/glucose material. It is indicated that this porous silicon-based anode material could have a promising application potential in the field of energy storage and conversion for high-energy-density and long-life batteries.

The treatment of dye wastewater remains a formidable challenge within the realm of industrial wastewater management. The existing methods for treating dye wastewater include adsorption, electrochemical oxidation, photocatalysis, biodegradation, and membrane separation. Among these, membrane separation is particularly advantageous due to its energy efficiency, high efficacy, and ease of process control. Separation membranes can be categorized into two primary types, i.e., organic and inorganic membranes. Inorganic membranes have attracted significant attention due to their high mechanical strength, controllable size distribution, resistance to high temperature and pressure, and chemical stablility. Despite these benefits, the advancement of conventional inorganic ceramic membranes is hindered by their complex preparation processes and high energy demands. This limitation underscores a urgent need for the development of simple and cost-effective inorganic membranes. A promising innovation in this field is a geopolymer-zeolite composite membrane, which is synthesized through in-situ hydrothermal conversion following the formation of reactive silica-aluminum materials under alkali or acid excitation. Coal gangue (CG), as a solid waste from coal mining primarily composed of SiO₂ and Al₂O₃, can be used as a raw material for the production of geopolymer-zeolite composite membrane. In this paper, A cost-effective geopolymer-zeolite composite membrane was prepared by a polymerization-hydrothermal method with CG as the main raw material for the separation of RhB in water. The objective was to propose a novel utilization strategy for CG and to lay a foundation for the development of membrane separation technology.

Coal gangue (CG) (Zhunger, Inner Mongolia, China) was calcinated at 800 ℃ for 2 h, resulting in the formation of calcined coal gangue (CCG). The CCG was then uniformly mixed with other additives in a mass ratio of CCG:NaOH:Na₂SiO₃: H₂O (100∶10∶40∶45). This mixture was poured into polytetrafluoroethylene moulds with the diameters of 50 mm and thicknesses of 5 mm. The samples were cured at 70 ℃ for 24 h to produce coal gangue-geopolymer membrane (CCG-GM). Afterwards, the CCG-GM was hydrothermally treated in a 100 mL 1 mol/L NaOH solution at 140 ℃ for 12 h, resulting in a coal gangue-geopolymer-zeolite composite membrane (CCG-GZCM).

The prepared CCG-GZCM was incorporated into a custom-built terminal filtration system, and its performance was evaluated via measuring the pure water flux, membrane flux, and RhB removal rate under varying conditions (i.e., system pressure, initial RhB solution concentrations, and pH values of the RhB solution). In addition, the circular utilization of CCG-GZCM was also examined to assess its reusability. The selectivity of CCG-GZCM for the removal contaminants (i.e., RhB, methylene blue (MLB), methyl violet (MV), methyl blue (MB), methyl orange (MO), and eosin Y (EY)) was determined.

The XRD patterns reveals that CG primarily consists of quartz and kaolinite. Upon calcination at 800 ℃ for 2 h, kaolinite in CG transforms into metakaolinite, thus froming CCG. For alkali activation, a broad diffraction peak of CCG initially appears at 15°-25°, and then shifts to 20°-40°, indicating the conversion of CCG into a geopolymer, thus forming CCG-GM. Subsequently, CCG-GZCM, with a main phase composition of NaP1 zeolite, is obtained via in-situ hydrothermal transformation of CCG-GM. The FTIR spectra of CCG-GZCM confirm the presence of NaP1 zeolite absorption bands. The XPS spectra further identify Na, Si, O, and Al as the predominant elements on the surfaces of both CCG-GM and CCG-GZCM. Note that CCG-GZCM exhibits a larger specific surface area and pore volume, compared to CCG-GM, albeit with a smaller average pore size. The TG-DSC spectra indicate that the weight loss of CCG-GZCM primarily occurs at 30-253 ℃, indicating its good thermal stability. In addition, the compressive strength of CCG-GM also increases from 18.84 MPa to 47.01 MPa (CCG-GZCM) after hydrothermal transformation.

CCG-GZCM exhibits varying removal efficiencies for different dye types. At an initial concentration of 10 mg/L and a pH value of 7, the pure water flux and membrane flux to RhB solution of CCG-GM and CCG-GZCM increase linearly with the increase of system pressure, while the RhB removal rate decreaseslinearly. At a system pressure of -0.08 MPa and a pH value of 7, the RhB removal rate by CCG-GZCM gradually decreases with the increase of initial concentration within 60 min. Conversely, at the same system pressure and an initial RhB concentration of 10 mg/L, the RhB removal rate by CCG-GZCM gradually increases with increasing pH value of the RhB solution within 60 min, and the maximum is 99.11%. However, when the system pressure maintains at -0.08 MPa, at an initial RhB concentration of 10 mg/L and an initial pH value of 11, the RhB removal rate by CCG-GZCM decreases with an increasing number of cycles, reducing to 94.25% after 6 cycles. In addition, CCG-GZCM demonstrates different removal rates within 30 min for different dye types. It achieves a high removal rate of exceeding 99% for cationic dyes including RhB, MLB, and MV. In contrast, the removal rates for anionic dyes, including MB, MO, and EY, are 70.00%, 25.82%, and 42.69%, respectively.

The pore structure of geopolymer membrane was modified and converted it into CCG-GZCM with larger specific surface area, higher pore volume and smaller average pore size by a hydrothermal method. The CCG-GZCM was characterized by an amorphous geopolymer matrix with NaP1 zeolite and a minor presence of NaA zeolite on the surface. At a system pressure of-0.08 MPa, an initial RhB concentration of 10 mg/L, and a pH value of 11, the CCG-GZCM achieved a remarkable RhB removal rate of 99.11% for 60 min. In addition, the CCG-GZCM also demonstrated a high circular utilization efficiency for RhB removal, maintaining a removal rate of exceeding 99% for cationic dyes for 30 min. The CCG-GZCM could be used as a promising approach for the effective utilization of coal gangue, having a significant potential for application in water pollutant treatment.

With the development of aero-engine towards large thrust, high thrust-to-weight ratio, high thermal efficiency, low fuel consumption and long life, the turbine inlet temperature is bound to continuously increase. Thermal barrier coating (TBC) with high thermal insulation and long life becomes popular. Multi-rare-earth doped zirconia (especially Gd₂O₃-Yb₂O₃-Y₂O₃ co-doped ZrO₂, GdYb-YSZ) as one of the most potential candidate materials for ultra-high temperature TBCs has a better high-temperature phase stability and a lower thermal conductivity rather than YSZ. It is easy to generate thermal stress during thermal cycling due to GdYb-YSZ with a low fracture toughness, resulting in a poor thermal cycling performance of GdYb-YSZ/NiCrAlY TBC. The design of double ceramic layer (DCL) TBC can alleviate the thermal stress mismatch and effectively solve this problem. In the DLC TBCs system, the thickness ratio between ceramic layers can seriously affect the thermal insulation effect and thermal cycle life of the coating. However, little work on the effect of thickness ratio of GdYb-YSZ/8YSZ ceramic layers on the mechanical properties and thermal cycle life of GdYb-YSZ/8YSZ DLC TBCs system has been reported yet.

In this paper, four kinds of GdYb-YSZ/8YSZ DLC TBCs systems with different ceramic layer thickness ratios were prepared. The microstructure, mechanical properties and water quenching-thermal shock cycle properties of GdYb-YSZ/8YSZ DLC TBCs systems with different ceramic layers thickness ratios were investigated. The failure behavior and failure mechanism of GdYb-YSZ/8YSZ DLC TBCs at 1150 ℃ were also discussed.

GdYb-YSZ/8YSZ DLC TBCs systems with different ceramic layer thickness ratios (i.e., GdYb-YSZ∶8YSZ=5∶1, 2∶1, 1∶1, and 1∶2) were prepared with GH4169 nickel-based superalloy as a matrix, NiCoCrAlY as a bond coating, 8YSZ as the first ceramic layer, and GdYb-YSZ as the second ceramic layer., and then four TBC systems on the surface of GH4169 nickel-based superalloy were prepared by a model UniCoatPro^TM atmospheric plasma spraying system (Oerlikon Metco Inc., USA). Subsequently, the microstructure and phase composition of four kinds of GdYb-YSZ/8YSZ DLC TBCs systems were characterized. The bonding strength and water quenching-thermal shock cycle behavior at 1150 ℃ were tested, and the failure mechanism was analyzed. To analyze the water quenching-thermal shock cycle behavior at 1150 ℃, the coated sample was kept in a high-temperature furnace at 1150 ℃ for 5 min and then quickly cooled in distilled water to room temperature. After drying, the sample surface was recorded as a cycle experiment. Repeating the steps above until the cracking or peeling area of the coating surface of greater than 5% was considered as the TBC failure.

Most of the GdYb-YSZ and 8YSZ spraying powders were melted in a high-temperature plasma flame flow, and interacted with the matrix to form the smooth structures via high speed jetting. A small number of unmelted and partially melted particles can form a rough microstructure during deposition, accompanied by micro-cracks and pores. The interfaces of each layer are closely bonded and clearly demarcated in GdYb-YSZ/8YSZ/NiCoCrAlY/substrate TBC system. The average bonding strength of the four GdYb-YSZ/8YSZ thermal barrier coating systems all is greater than 40 MPa. The macro-image of fracture after tensile test shows that most of the fracture occurs at the interface between 8YSZ and NiCoCrAlY. The average porosity of GdYb-YSZ/8YSZ TBC systems with different ceramic layer thickness ratios (i.e., 5∶1, 2∶1, 1∶1, and 1∶2) calculated by a software named Image J is 3.39%, 2.65%, 4.0%, and 2.64%, respectively. The GdYb-YSZ ceramic layer is composed of 98% (mole fraction) c-ZrO₂ phase and 2% m-ZrO₂ phase, which is basically the same as the phase composition in the spraying powder.

Four kinds of TBCs with different thickness ratios are intact after 80 quenching-thermal shock cycles at 1150 ℃. GdYb-YSZ/8YSZ TBC systems with four ceramic layer thickness ratios (5∶1, 2∶1, 1∶1, and 1∶2) begin to peel off at the edge of the coating after 85, 165, 120, and 195 water quenching-thermal shock cycles, respectively. The water quench-thermal shock cycle resistance of the GdYb-YSZ/8YSZ TBC system becomes better as the thickness of the GdYb-YSZ ceramic layer decreases and the thickness of the 8YSZ ceramic layer increases at a constant total thickness of the ceramic layer. The GdYb-YSZ/8YSZ TBC systems with different ceramic layer thickness ratios (i.e., 5∶1, 2∶1, 1∶1, and 1∶2) have a quenching-thermal shock cycle life of 125, 195, 200, and 205 times at 1150 ℃, respectively. The GdYb-YSZ/8YSZ TBC systems with different ceramic layer thickness ratios are mainly characterized via the peeling of ceramic layer during the water-quenching-thermal shock cycle at 1150 ℃. The thermal stress is one of the main factors leading to the failure of TBCs. The residual stress of 8YSZ ceramic layer with different layer thickness ratios of 5∶1, 2∶1, 1∶1 and 1∶2 is 0.01, 0.08, 0.12 GPa and 0.15 GPa, respectively, after the water quenching-thermal shock cycle failure at 1150 ℃. The stress increases gradually with the increase of the thickness of the ceramic interlayer 8YSZ. The residual stress (i.e., compressive stress) in the TGO layer in the coating system with different layer thickness ratios is 0.51, 0.29, 0.72 GPa and 0.62 GPa, respectively. The compressive stress of the TGO layer will cause the 8YSZ/TGO interface to buckle, and the tensile stress will be generated at the crest of the wave, thus promoting the generation of cracks. In the process of water quenching-thermal shock cycle of GdYb-YSZ/8YSZ TBCs, some micro-cracks are easy to form on one side of the 8YSZ ceramic layer near the 8YSZ/TGO interface under the combined action of residual stress in the ceramic layer and TGO layer. The microcracks can further spread into TGO layer as the TGO layer increases, seriously weakening the interface bonding force between ceramic layer and adhesive layer, and finally leading to the failure of coating spalling.

GdYb-YSZ/8YSZ double ceramic layer thermal barrier coatings (i.e., DCL TBC) with different layer thickness ratios (i.e., GdYb-YSZ/8YSZ = 5∶1, 2∶1, 1∶1, and 1∶2) were prepared by an atmospheric plasma spraying technology. GdYb-YSZ ceramic top coated with four coatings were composed of c-ZrO₂ phase and a small amount of m-ZrO₂. The bonding strength of the four coatings was greater than 40 MPa, and the average bonding strength of the coatings was the maximum when the thickness of GdYb-YSZ/8YSZ was 5∶1. The thermal shock cycle resistance of GdYb-YSZ/8YSZ TBC system became better as the thickness of the GdYb-YSZ ceramic coat decreased and the thickness of the 8YSZ ceramic coat increased. At the thickness ratio of GdYb-YSZ/8YSZ of 1∶2, the water quenching-thermal shock of the TBC was up to 205 cycles at 1150 ℃, having the optimum thermal shock resistance. In addition, GdYb-YSZ/8YSZ TBCs with different ceramic layer thickness ratios did not undergo a phase transformation under the water-quenching-thermal shock cycle at 1150 ℃. The failure mechanism of GdYb-YSZ/8YSZ TBCs with different ceramic layer thickness ratios under the quench-thermal shock cycle at 1150 ℃ was as follows, i.e., in the process of water quenching-thermal shock cycle at 1150 ℃, the residual stress in 8YSZ coating increased with the increase of the thickness of 8YSZ ceramic layer, and micro-cracks were easy to form on one side of 8YSZ ceramic layer at near 8YSZ/TGO interface. In addition, the formation of TGO in the process of thermal cycling was accompanied by the generation of compressive stress. TGO further increased, and the micro-cracks in the coating expanded into TGO with the increase of the number of thermal cycles, reducing the binding force of the coating, and eventually causing the coating to flake and fail.

In the macro-scale modification, constructing an environmentally friendly coating system to reduce the use of organic solvents is a future development direction. However, inorganic modifiers have some limitations in enhancing the coating performance. The use of organic modifiers can lead to the emission of volatile organic compounds (VOCs), which negatively impacts the environment. It is thus important for the dual goals of optimizing coating performance and environmental protection to develop eco-friendly inorganic silicate coatings that balance the use of inorganic and organic modifiers. The performance of the prepared inorganic silicate anti-corrosion coatings is relatively singular. A future research can explore multifunctional composite anti-corrosion coatings that can be used under various environmental conditions, such as super-hydrophobicity, self-cleaning, self-healing, oxidation resistance, and wear resistance. In the micro-scale, the modification of inorganic silicate coatings with nanoparticles may reduce economic viability due to the high cost of nano-materials. A future research should focus on the development of more cost-effective methods for synthesizing nanoparticles, such as microwave-assisted synthesis, solvothermal methods, and sol-gel techniques. In addition, introducing specific functional groups on the surface of nanoparticles or combining them with other materials to impart the coatings with multifunctional properties like self-healing, super-hydrophobicity, antibacterial activity, and flame retardancy can be an important development direction. In the molecular/atomic scale, studies on the modification of inorganic silicate coatings primarily focus on experimental approaches, failing to delve into the molecular or atomic mechanisms. This results in an incomplete understanding of the coatings performance. A future research should focus on molecular design and optimization, as well as molecular dynamics simulations, to clarify the modification mechanisms for inorganic silicate coatings.

The Aldol condensation reaction, as a pivotal organic reaction in forming C-C bonds, plays a crucial role in various fields such as pharmaceutical synthesis, total synthesis of natural products, and the industrial production of perfumes and dyes. Conventional Aldol condensation reactions often rely on liquid alkaline catalysts, which suffer from some issues such as difficulty in recovery, complex waste liquid treatment, strong corrosion to equipment, and severe environmental pollution, thereby restricting their application in industrial production. Therefore, the development of efficient, recyclable, and environmentally friendly solid alkaline catalysts becomes a key to promoting the greening and efficiency of the Aldol condensation reactions. Layered double hydroxides (LDHs), with their unique layered structure and adjustable composition have a great potential in catalysis. Recent research indicates that functional modifications, such as ion exchange, intercalation, and doping, can further enhance their catalytic performance. Among them, sulfate-intercalated magnesium aluminum LDH (MgAl-SO₄^2--LDH) as a special LDH material, through the introduction of sulfate ions, can enhance the structural stability of LDH and introduce additional acidic sites. This makes MgAl-SO₄^2--LDH effectively activate aldehyde or ketone molecules during the catalysis of Aldol condensation reactions, thereby promoting the progress of the condensation reaction. In addition, the morphology of the catalyst has a significant impact on its catalytic performance. The flower-like spherical structure, as a special nanostructure, has attracted much attention in the field of catalysis due to its high specific surface area, abundant pore structure, and superior mass transfer performance. Combining the flower-like spherical structure with MgAl- SO₄^2--LDH can be expected to further improve the catalytic efficiency of the catalyst.

The flower-like MgAl-SO₄^2--LDH catalyst was prepared in the molar ratios of n(Mg)∶n(Al)=2∶1 and n(urea)∶n(NO₃^-)=1∶1. In the preparation, magnesium nitrate hexahydrate (Mg(NO₃)₂·6H₂O), aluminum nitrate nonahydrate (Al(NO₃)₃·9H₂O) and urea were mixed and dissolved in deionized water under stirring. The mixed solution was then transferred to a hydrothermal reaction vessel and reacted at 120 ℃ for 6 h. The resulting product was washed with deionized water for several times and then dried thoroughly in an oven. The dried material was calcined in a muffle furnace at 500 ℃ for 8 h to obtain the magnesium-aluminum composite oxide (LDO). Subsequently, a series of ammonium persulfate solutions ((NH₄)₂S₂O₈) with different concentrations (i.e., 0, 0.05, 0.10, 0.15 mol/L, and 0.20 mol/L) were prepared. The reaction was proceeded in a nitrogen atmosphere at room temperature for a certain period, and the solvent was removed through filtration and drying, yielding the S₂O₈^2- intercalated magnesium-aluminum hydrotalcite compounds (i.e., S₂O₈^2-/LDH). Finally, the prepared S₂O₈^2-/LDH was calcined in a muffle furnace at 550 ℃ for 8 h to obtain the modified magnesium-aluminum composite oxide. The modified magnesium-aluminum composite oxide was uniformly dispersed in deionized water, and the hydration-reduction process was repeated when sulfate ions were introduced to replace persulfate ions. A final catalyst MgAl-SO₄^2--LDH was obtained after completing the hydration-reduction and subsequent treatment.

MgAl- SO₄^2--LDH catalyst prepared has a flower-like spherical structure assembled from two-dimensional MgAl-SO₄^2--LDH sheets with a uniform morphology and a diameter of 2 μm. The SEM images reveal that, in contrast to the irregular shape of traditional MgAl-LDH catalysts, the MgAl-SO₄^2--LDH sample after sulfate ion intercalation modification exhibits a flower-like spherical structure. This interconnected sheet structure divides the catalyst surface into numerous small chambers, which provides abundant reaction sites for the catalytic reaction and promotes the mass transfer process between reactants and products, thereby contributing to an enhanced catalytic performance. The results of EDS analysis confirm that sulfate ions are introduced into the catalyst structure and distributed uniformly.

The XRD patterns indicate that the crystallinity of MgAl-SO₄^2--LDH catalyst is inferior to that of the MgAl-LDH, exposing more active sites due to the intercalation of sulfate ions. The FTIR spectra reveal that MgAl-SO₄^2--LDH catalyst contains a rich number of Brönsted acid sites, enhancing the activation of acetone and p-nitrobenzaldehyde, thus effectively improving catalytic performance. The optimized MgAl-SO₄^2--LDH catalyst has a p-nitrobenzaldehyde conversion rate of 70.5%, and after one regeneration the catalytic conversion rate remains 64.03%, demonstrating a good reusability. The FTIR spectra of the reaction products indicate a mixture of 4-(4-nitrophenyl)-3-hydroxy-2-butanone and 4-(4-nitrophenyl)-3-penten-2-one.

The study prepared a flower-like sulfate-intercalated MgAl-SO₄^2--LDH catalyst with a uniform microstructure and a diameter of 2 μm, assembled from two-dimensional MgAl-SO₄^2--LDH sheet structures. The catalyst showed an improved surface activity due to the intercalation of sulfate ions, thus increasing the number of active sites. The FTIR spectra confirmed the abundance of the Brönsted acid sites in MgAl-SO₄^2--LDH catalyst, which significantly enhanced the activation of acetone and p-nitrobenzaldehyde, effectively improving catalytic performance. The optimized catalyst showed a high conversion rate of 70.5% for the aldol condensation of acetone with p-nitrobenzaldehyde, and after regeneration it maintained a conversion rate of 64.03%, indicating a good reusability. The reaction products consisted of a mixture of 4-(4-nitrophenyl)-3-hydroxy-2-butanone and 4-(4-nitrophenyl)-3-penten-2-one, indicating a possible mechanism involving the Brönsted acid sites on MgAl-SO₄^2--LDH catalyst facilitating the nucleophilic addition reaction between the activated enol of acetone and the protonated aldehyde group of p-nitrobenzaldehyde.

Frequency-dependent dielectric response is one of the important properties of ferroelectrics, reflecting the polarization response to high-frequency electric fields. Polarizations are closely related to ferroelectric domain structures, such as single domain, which represents the region with homogeneous polarizations direction. Ferroelectrics usually possess complex domain structures with domain walls (DWs) separating adjacent homogeneously polarized domains. DWs have attracted much attention during the past two decades due to their properties and potential for device designing. The related issues include DW motion, nonvolatile memory, topological defects, enhanced susceptibility, enhanced quality factor, low dielectric loss, and others. (Ba_0.8, Sr_0.2)TiO₃ (BST_0.8) is a ferroelectric usually with multi-domain structures. Previous work identified two typical types of domain walls (DWs), i.e., 90° DWs and 180° DWs. The enhancement of dielectric response in systems with 90° DWs is now well understood, and the behavior of dielectric response in multi-domain systems with 180° DWs remains unclear. Therefore, gaining insights into how 180° DWs affect the dielectric response can clarify the effects in multidomain systems.

We performed molecular dynamics simulations using the ALFE-H code with the first-principles-based effective Hamiltonian method to study the BST_0.8 system. All the calculations were performed in the NPT ensemble using the Evans-Hoover thermostat, and periodic boundary condition (PBC) along all three directions. To simulate the substrate, a uniform biaxial strain was fixed to the 1.55% in-plane strain. To analyze the multi-domain with different DWs, the simulations started with a self-constructed initial multi-domain polarization configuration. Subsequent 50 ps MD simulation was performed under chosen strains for structural relaxation. In the initial configuration, the magnitude of non-zero components of soft mode on each site was set to 0.1 Å, atomic occupations (alloying) were randomized, and unless otherwise specified, all other mode variables were set to zero. The trajectory of local mode averaged over the supercell during MD simulations was extracted to calculate the dielectric response. The 8 ns MD simulations were performed to obtain an autocorrelation function for any time t ranging from 0 to 1 ns by one step of 10 fs. The fast Fourier transformation (FFT) was performed to calculate the dielectric response. Then two uncoupled damped harmonic oscillators (DHOs) were used to fit the data of dielectric response.

The dielectric response of single domain at 300 K with the different electric fields along [110] from 0 to 2 MV/cm was computed. The computational results can be well fitted with the model of two uncoupled DHOs. The real and imaginary parts of the predicted dielectric response at each chosen electric field both exhibit two peaks. As the electric field increases, the low-frequency mode with 300 GHz at zero field in the system gradually disappears, and a high-frequency mode of larger than 8 THz appears when electric field is larger than 1 MV/cm. The high frequencies modes of 3 THz at zero filed and 8 THz under 1 MV/cm shift towards higher frequencies as the electric field increases. In other words, the present simulations reveal that it is possible to manipulate the frequency of peaks in dielectric response via changing the magnitude of the external electric field.

The dielectric responses of multi-domain with 90° DWs and 180° DWs are further analyzed. According to the experimental PFM results, the multi-domain structures are simulated and the dielectric response through MD simulations is calculated. The analysis of the dielectric response of single domain structure and multi-domain structures shows that the single domain structures exhibit high-frequency peaks at > 300 GHz, whereas the multi-domain structures exhibit low-frequency peaks at 8 GHz and 120 GHz for 180° DWs system and at 10 GHz for 90° DWs system, revealing that there exists a low-frequency mode related to collective oscillation of DWs in multi-domain structures. In addition, the frequencies of peaks in multi-domain with DWs are in a gigahertz range, whereas the single domain structure exhibits peaks in a terahertz range. The contribution of DWs to the dielectric response primarily arises from the timescale of DWs motion, such as sliding or breathing, which differs significantly from the high-frequency vibrations of optical phonon modes. The vibrational frequency of DWs is much lower, with relaxation times in the order of nanoseconds, resulting in a response frequency in GHz range, which is far below the terahertz range of optical phonon modes. Therefore, DWs oscillations dominate the dielectric response at a low frequency. Moreover, multi-domain structure with 180° DWs exhibits a unique low frequency mode at 120 GHz, which is significantly different from single domain and 90° DWs system. In other words, multi-domain structures with 180° DWs and 90° DWs exhibit different dielectric responses. There exists a common low-frequency mode related to the oscillations of DWs in BST_0.8.

It was possible to manipulate the frequency of peaks in dielectric response of single domain through changing the magnitude of the external electric field. Domain walls oscillations dominated the dielectric response in a low frequency gigahertz range, whereas the single domain structures exhibited resonant peaks in a terahertz range. Moreover, multi-domain structures with different domain walls in BST_0.8 had different dielectric responses, but the both have a same low-frequency mode at 10 GHz related to the domain walls oscillations. The results of this study indicated the dielectric response behaviors of ferroelectrics induced in an external electric field and internal multi-domain configurations and provided the potential mechanisms and guidance for optimizing application performance.