Glass scintillators are commonly utilized for the detection of high-energy rays in various applications such as nuclear medicine imaging, industrial non-destructive testing, high-energy nuclear physics, safety inspection, and environmental monitoring. The scintillation glass with a high density is critical for improving the absorption and interception capabilities of rays and particles, thereby favoring the enhancement of the detector efficiency. This review represented recent development on high-density scintillation glass doped with rare-earth ions like Ce³⁺, Tb³⁺, and Eu³⁺. The critical parameters such as density, decay time, light output, and radiation resistance affecting the performance of the scintillation glass were discussed.

Overall, the research delves into the scintillation mechanism of scintillation glass and presents an overview of the preparation process for high-density variants. The research progress on rare-earth ion-doped high-density scintillation glasses containing Ce³⁺, Tb³⁺, and Eu³⁺ ions was summarized, highlighting characteristics like density, light yield efficiency (LY), and decay time (τ). Some factors affecting these properties (i.e., substrate selection, energy transfer among ions, and reduction atmosphere) were also discussed.

Ce³⁺-doped glass exhibits a nanosecond-level decay time. At the present, the density of Ce³⁺ doped scintillation glass can reach up to 6 g/cm³, but the light yield of this component is significantly low. The luminescence efficiency of the glass can be improved via introducing Gd₂O₃, which enhances the energy transfer between Gd³⁺ and Ce³⁺, while increasing the glass density. Also, incorporating fluoride into the oxide glass can lower the phonon energy, decrease the chances of non-radiative transition, and enhance the light yield. Ce³⁺ is prone to oxidation to non-luminescent Ce⁴⁺ during high-temperature melting. This oxidation process can be effectively controlled by using a reducing atmosphere (CO, H₂) or adding reducing agents such as Si₃N₄, SiC, AlN, etc.

The density of Tb³⁺-doped scintillation glass can reach 7.15 g/cm³, with a decay time in the millisecond range. Enhancing the luminescence efficiency of Tb³⁺ is achievable through the energy transfer between Gd³⁺-Tb³⁺, Ce³⁺-Tb³⁺, Dy³⁺-Tb³⁺, while the introduction of fluoride and reducing agents can effectively boost the light yield. Eu³⁺-doped scintillation glass can achieve a density of 6.60 g/cm³, and the addition of Gd³⁺ and Tb³⁺ can effectively enhance the emission intensity of Eu³⁺ ions.

High density scintillating glasses doped with other rare-earth ions, such as Pr³⁺, Dy³⁺, Sm³⁺, and Er³⁺, can achieve a high density and exhibit distinct scintillation properties because of their unique energy level structures. However, the light yield of these glasses is too low to be used in practical applications.

A high-density and high-yield scintillation glass is needed. Despite the efforts of scientific research personnel, producing flashing glass with both a high density and a high yield remains a challenge. The main reason is that in high-density glass, although the introduction of heavy metal ions increases the density of the glass, it may lead to an increase in non-radiative transition channels, hindering the transfer of energy from the substrate to the luminescent center. Also, an increase in density can enhance the absorption and scattering of light, thereby reducing the effective amount of excitation light reaching the luminescent center. In addition, high density glass matrix may cause the local environment around rare-earth ions to become complex, affecting their energy level structure. To prepare scintillation glass that can meet both high-density and high light yield, several aspects can be considered. Firstly, the use of a reducing atmosphere such as H₂ or CO and the addition of reducing agents like carbon powder can effectively control the valence of luminescent ions (i.e., Ce³⁺, Tb³⁺) during the melting process, preventing the formation of high valence ions. Using fluoride instead of partial oxides can reduce the melting point of the material and improve the light output via altering the band gap structure of the glass. The smaller volume of fluoride ions simultaneously contributes to the increased density of the glass. The utilization of energy transfer between ions can significantly enhance the light yield of glass. Some impurities and defects in glass can be minimized via utilizing high-purity raw materials and optimizing process steps such as melting and annealing. This can enhance the transparency and uniformity of the matrix, leading to a reduction in non-radiative transitions and an improvement in luminescence performance. It is possible to induce the formation of microcrystalline structures in glass via controlling the cooling rate or subsequent heat treatment. This optimization can enhance the energy transfer path, minimize scattering losses, and ultimately improve the luminescence efficiency.

Zeolitic imidazolate framework (ZIF) material is a subset of metal-organic framework (MOF) materials with a structure similar to zeolite. Its basic structural unit is the [MN₄] tetrahedron formed by the coordination bond between transition metal center ions M (Co, Zn, etc.) and imidazole anions (Im, C₃H₃N₂^-) and their derivatives. Among them, ZIF-62 [Zn(C₃H₃N₂)₂-_n(C₇H₅N₂)_n] and ZIF-4 [Zn(C₃H₃N₂)₂] crystals can melt and form glasses before decomposition, which are widely used as basic research objects for MOF vitrification. For ZIF-62 and ZIF-4 glasses, changes in metal nodes can cause changes in the local coordination structure, including bond length and tetrahedral symmetry. This could further result in non-linear variations in properties such as glass transition temperature (T_g), which is known as a mixed-metal node effect. The impact of the coexistence of mixed ligands and metal nodes in ZIF structure on thermal properties and their structural origins is not elucidated. Therefore, a further exploration of the node metal mixing effect in ZIF glasses and its dependence on the ligand composition and structure can provide some insights into the relationship between the structure and performances of multi-component ZIF glasses. It is also of great significance to clarify the mixed former effect in inorganic glass and develop novel functional MOF glasses. In this study, the effect of ligand changes on the central metal node content and T_g of ZIF-4 and ZIF-62 glasses were discussed. In addition, the structural origin about the difference in mixed-metal node effect strength [(ΔT_g)_max] between ZIF-4 glass and ZIF-62 glass was also analyzed.

ZIF-4/62 crystals and ZIF-4/62 melt-quenched glass (MQG) were prepared by solvothermal and melt-quenching methods, respectively. The Zn_1-xCo_x-ZIF-4 high-density amorphous phase (HDA) was prepared by differential scanning calorimetry instruments. The cobalt contents of bimetallic ZIF-4 samples were characterized by inductively coupled plasma-optical emission spectroscopy. The cobalt contents in bimetallic ZIF-62 samples were determined by ultraviolet-visible spectroscopy. The atomic structures of Zn-ZIF-4 MQG and Zn-ZIF-62 MQG were characterized by high energy synchrotron X-ray diffraction measurements. The total scattering structure factor S(Q) and pair distribution function g(r) were calculated based on the diffraction data. The in-house written code developed was used to calculate the structural parameters of MQG, i.e., the partial pair distribution functions of atom pairs, simulated total structure factor, [ZnN₄] tetrahedral order parameter (TOP), and Zn-N bond length distortion degree.

According to the results of elemental analysis, the measured cobalt molar ratio (R) in the ZIF-4 and ZIF-62 crystals is lower than the initial one (x). Compared with the single-ligand ZIF-4 crystals, R in the mixed-ligand ZIF-62 crystals is closer to x. This is due to the different coordination reaction rates between different metal ions and ligands. Also, the T_g of the mixed-ligand ZIF-62 MQG is higher than that of the single-ligand ZIF-4 HDA. For instance, the T_g of Zn-ZIF-62 MQG is 31 ℃ higher than that of Zn-ZIF-4 HDA, and the T_g of Co-ZIF-62 MQG is 42 ℃ higher than that of Co-ZIF-4 HDA. These phenomena can be due to the presence of the bIm (C₇H₅N₂^-) ligand in ZIF-62 MQG. Based on the nonlinear variation of T_g with R, the mixed-metal node effect strength [(ΔT_g)_max] of ZIF-62 MQG is greater than that of ZIF-4 HDA. Specifically, the (ΔT_g)_max of ZIF-62 MQG is 7 ℃, which is greater than the (ΔT_g)_max of about 1 ℃ for ZIF-4 HDA.

The comparison in total scattering structure factors S(Q) shows that the intensity of the first sharp diffraction peak in Zn-ZIF-4 MQG is slightly greater than that of Zn-ZIF-62 MQG. Moreover, from the comparison in pair distribution functions g(r), the full width at half maximum of the peaks for Zn-N₁ and Zn-C atomic connections in the coordination tetrahedron of ZIF-62 MQG are broader, compared to ZIF-4 MQG. The simulations reveal that the TOP (tetrahedral order parameter) value of ZIF-62 MQG is slightly lower than that of ZIF-4 MQG. Also, the Zn—N bond length distortion degree for ZIF-62 MQG is higher than that for ZIF-4 MQG. Based on the results, the coordination tetrahedron units of Zn-ZIF-62 MQG may exhibit a higher disordered degree, compared to Zn-ZIF-4 MQG, implying greater structural flexibility and sensitivity of ZIF-62 glass when the central Zn ion is substituted by other metal ions in the structure. This indicates that the higher (ΔT_g)_max on the T_g of ZIF-62 glass is due to the presence of mixed ligand (Im and bIm).

Based on the solvothermal reaction mechanism of ZIF crystals, a faster reaction rate of Zn²⁺ with ligands to form complexes and a higher stability of the Zn²⁺-ligand coordination tetrahedra result in Zn²⁺ participating more rapidly in the formation of the ZIF network, thus leading to a lower R. Additionally, the stronger electron-donating property of the bIm ligand increases the coordination reaction rate of Co²⁺, leading to a higher R value in mixed-ligand ZIF-62, compared to that of single-ligand ZIF-4 crystals. According to the temperature-dependent topological constraint theory, the bIm increases both the number and strength of topological constraints in the ZIF-62 glass structure. As a result, the T_g of ZIF-62 glass is higher than that of ZIF-4 glass. The atomic arrangement in the [ZnN₄] tetrahedra of Zn-ZIF-62 MQG has a higher disordered degree, compared to that of Zn-ZIF-4 MQG. This can be attributed to the steric hindrance and stronger electron-donating ability of the bIm ligand in the Zn-ZIF-62 MQG. The higher disordered degree of tetrahedra indicates that the local coordination structure around the Zn metal nodes in Zn-ZIF-62 MQG is more susceptible to the influence of substituted Co nodes, thus enhancing the mixed-metal node effect on the T_g of Zn-ZIF-62 MQG.

CsPbBr₃ perovskite quantum dots are considered as excellent green light materials in the field of wide color gamut displays due to their excellent luminescence characteristics, such as high photoluminescence quantum yield (PLQY) and narrow full width at half maximum (FWHM). However, CsPbBr₃ quantum dots irreversibly deteriorate when exposed to oxygen, water, light and heat due to their low formation energy and strong ionic properties, which restricts their application. The preparation of CsPbBr₃ quantum dots via in-situ crystallization in glass is considered as one of the effective strategies to improve their stability. In this study, borosilicate glass was used as a matrix to investigate the effect of Sc₂O₃ introduction on the glass network structure and the regulatory effect on the crystallization behavior and luminescence performance of CsPbBr₃. In addition, the photostability and thermostability of the samples were analyzed. CsPbBr₃ quantum dot glass powder with the high quantum efficiency and narrow FWHM could be used to prepare white LED with a high luminous efficiency and a wide color gamut.

A series of CsPbBr₃ quantum dot glasses were prepared by a conventional melt quenching-heat treatment method. The specific molar composition ratio of the glass was 42B₂O₃-20SiO₂-4Li₂O-8ZnO-3MgO-3Cs₂O-6PbBr₂-6NaBr-xSc₂O₃ (mole fraction, x = 0, 0.1, 0.3, 0.5, and 0.7). According to the composition of each glass stoichiometric ratio, the raw materials were weighed, and fully ground in a mortar for 30 min. The mixed powder was then transferred to a corundum crucible and placed in a high-temperature muffle furnace at 1200 ℃ for 15 min. Subsequently, the melt was poured into a preheated graphite mold and annealed for 3 h to relieve thermal stress. After cooling to room temperature, a transparent precursor glass (referred to as PG) was obtained. CsPbBr₃ quantum dot glass was obtained via heat treatment of precursor glass samples at different temperatures (i.e., 460, 470, 480, 490 ℃, and 500 ℃) for 10 h. Finally, the prepared CsPbBr₃ quantum dot glass was cut, polished or ground into a powder for further characterization and use.

The results show that the average particle size of CsPbBr₃ quantum dots gradually decreases from 13.22 nm to 3.42 nm as the amount of Sc₂O₃ introduced increases. This indicates that the introduction of Sc₂O₃ can alter the glass network structure under identical external conditions, which in turn affects the particle size of the quantum dots. Note that the peak intensity of the [PbBr₆]^4- firstly increases and then decreases with increasing the amount of Sc₂O₃ introduced. The peak intensity of [BO₃]/[SiO₄] gradually decreases. This is primarily attributed to the Sc₂O₃ additive, which reduces the [BO₃] content within the network structure, strengthens the glass network, and affects the crystallization behavior of the quantum dots.

The obtained samples exhibit a typical narrow-band luminescence. Under the same amount of Sc₂O₃ introduced, PL spectra of CsPbBr₃ quantum dot glass samples heat-treated at different temperatures show that the luminescence intensity firstly increases and then decreases with the increase of the temperature, and a phenomenon is attributed to fluorescence quenching. The long lifetime is reduced by 20 ns, but the proportion of long-lived emission gradually is increased as the amount of Sc₂O₃ introduction is increased. This is due to the improvement of the surface quality of the quantum dot, indicating that carrier quenching can be effectively minimized. Also, the the internal and external photoluminescence quantum yields of the optimal CsPbBr₃ quantum dot glass samples are 62.98% and 37.92% at 460 nm excitation. Moreover, they can maintain 64.51% of the original luminescence intensity after continuous illumination upon a 455 nm blue LED chip (20 V, 20 mA) for a week, laying a foundation for developing high-brightness LED devices. After three cycles of heating and cooling (at 298-473 K), the luminescence intensity of the optimal sample can gradually return to the initial value, and the peak emission wavelength and FWHM also show obvious temperature dependence and excellent recovery ability, indicating that the CsPbBr₃ quantum dot glass has a good luminescence thermal stability.

CsPbBr₃ perovskite quantum dots with different amounts of Sc₂O₃ were precipitated in a borosilicate glass matrix by a conventional melt quenching-heat treatment method. Under the same heat treatment conditions, the structure of the glass network improved and became dense, as well as the average size of the quantum dots decreased from 13.22 nm to 3.42 nm with the increase of the amount of Sc₂O₃ introduced. After optimization, the internal and external photoluminescence quantum yields of the optimal CsPbBr₃ quantum dot glass samples were 62.98% and 37.92% at 460 nm excitation. The denser network structure effectively isolated the quantum dots from air, water, and oxygen erosion, significantly reducing phase separation and degradation caused by external environmental factors, thus having a good thermal cycle recovery. For the white LED prepared with the superior luminescent properties of the CsPbBr₃ quantum dot glass powder, the color coordinates were located at (0.3135, 0.3077), the correlated color temperature was 6647 K, and the color gamut reached 130.95% of the NTSC standard and 97.90% of the Rec. 2020 standard, indicating a potential application in the backlight display field.

Transparent ceramics are a kind of ceramic materials integrating structural and functional properties. A variety of ceramic materials such as oxides, nitrides, oxynitrides and fluorides are developed. Among them, spinel transparent ceramics are suitable for transparent armor, mid-wave infrared windows and fairings due to their low density, high hardness, high strength, high temperature stability, especially the wide transmittance range and high transmittance from near ultraviolet to mid-infrared. The development of transparent ceramics becomes a hot research spot. The design and performance optimization of new transparent ceramics are mainly realized through composition design because transparent ceramics have some strict requirements for microstructure and phase purity.

In recent years, the novel properties of the high-entropy effect in materials provide an approach for the development of materials. In this paper, a spinel-type (Li,Mg,Zn,Al,Ga)₃O₄ (LMAZGO) compound was designed with MgAl₂O₄, MgGa₂O₄, ZnAl₂O₄, ZnGa₂O₄, LiGa₅O₈ and LiAl₅O₈ as components. The sintering process of LMAZGO high-entropy transparent ceramic materials was investigated, and the microstructure of transparent ceramics was optimized. In addition, the optical transmittance and mechanical properties of LMAZGO high-entropy transparent ceramic materials were also analyzed.

Commercial powders of Li₂CO₃, MgO, α-Al₂O₃, ZnO, and Ga₂O₃ (purity of 99.99%) were used as raw materials, and the proportion of each raw material was calculated according to the elemental composition of LMAZGO. After mixing evenly, the high-entropy ceramic was synthesized in air by a high-temperature solid-state reaction method, and then ground to the target powder. LMAZGO blanks with a diameter of 20 mm were prepared via axial compression combined with cold isostatic pressing. Subsequently, the transparent ceramic pre-sintered body was prepared via pressureless pre-sintering in a muffle furnace, and the residual pores were further removed by hot isostatic post-treatment. The prepared LMAZGO transparent ceramics were ground and polished on the both sides for further characterization.

The phases of LMAZGO powders and bulk were characterized by a model X'Pert PRO X-ray diffractometer under Cu target at 40 kV and 40 mA. The density of ceramics was measured based on the Archimedes drainage principle. The thermal behavior of the blank was determined by a model DIL402SE thermodilatometer at different temperatures from room temperature to 1 500 ℃ at a heating rate of 10 ℃/min. The microstructure of powders and ceramics was characterized by a model S-3 400 scanning electron microscope, and the average grain size of the grains was determined by a linear intercept method. The linear transmission spectra of the samples were measured by a model Lambda 750S UV-NIR spectrophotometer and a model 6 700 Fourier transform infrared absorption spectrometer. The Vickers hardness was measured by a model 430SVD hardness tester. The flexural strength of high-entropy transparent ceramics was determined based on a three-point flexure test by a model MTS810 universal materials testing machine. The elastic properties of transparent ceramics were determined by a model MK7 elastic modulus meter.

The spinel LMAZGO compounds were synthesized at 1 100 ℃ for 2 h. Based on the XRD and SEM results, the synthesized powder has a spinel phase, uniform and fine grains and little agglomeration, and the average grain size is 290 nm. The configuration entropy of LMAZGO is 3.18R, calculated by the sublattice model, which has a high crystal structure stability.

The results of thermal expansion show that the shrinkage densification rate of LMAZGO ceramic blank is further accelerated from 1 200 ℃, and the maximum densification rate of LMAZGO ceramic blank occurs at 1 380 ℃ in the middle stage of sintering. According to the thermal expansion analysis of LMAZGO, 1 300, 1 350, 1 400 and 1 450 ℃ were selected as the pressureless pre-firing temperatures, and the pre-firing process of the green body was optimized. The optical transmittance of the transparent ceramic samples obtained by subsequent HIP sintering firstly increases and then decreases with the increase of pre-firing temperature. Based on the results of the sintering curve, the pressureless sintering process of LMAZGO transparent ceramics can be optimized at a sintering temperature of 1 400 ℃ for holding time of 6 h. The average grain size of the prepared LMAZGO transparent ceramic pre-burned body is 1.81 μm, and the density is 98.7%. The superior optical transparency is obtained after hot isostatic sintering (sintering conditions: argon atmosphere, incubation at 1 550 ℃ for 5 h), and there is no abnormal growth of grain size.

The optical transmittance range of the obtained high-entropy spinel LMAZGO transparent ceramics is 0.23-7.35 μm, the maximum linear transmittance is 85.2%, the Vickers hardness (H_V1) is 12.7 GPa, the Young modulus is 265 GPa, and the flexural strength is (332±30) MPa.

A spinel LMAZGO high-entropy compound with a configuration entropy of 3.18R and a high crystal structure stability was synthesized. The preparation process of LMAZGO high-entropy transparent ceramics was systematically optimized via pressureless sintering combined with hot isostatic post-treatment, and the prepared LMAZGO transparent ceramics had an excellent optical transparency, with an optical transmittance range of 0.23-7.35 μm, the maximum linear transmittance of 85.2%, the Vickers hardness (H_V1) of 12.7 GPa, the Young modulus of 265 GPa, and the flexural strength of (332±30) MPa. The results showed that the high-entropy spinel LMAZGO transparent ceramic material exhibited broad spectral transparency and excellent mechanical properties, having a promising application in the field of mid-infrared transparent window. This study provided some ideas for the development of new transparent ceramics.

Silica aerogels are highly porous materials with interconnected three-dimensional networks of silica particles, which are typically obtained via removing the liquid in gels under supercritical conditions. Silica aerogels are widely applied in the fields of thermal insulation, adsorption, catalysis, and energy storage due to their ultralow density, large surface area, and unique nanoporous structure. However, silica aerogels are fragile at relatively low stresses due to the existence of rigid skeleton consisting of weak linking of silica particles. The inherent brittleness and poor reliability restrict the application of aerogel materials to a certain extent. In this paper, the preparation and properties of SiO₂ nanotube aerogels (SiO₂-NTA) with a three-dimensional nanotubular network structure were investigated.

For the prepatation of carbon aerogels (CA) as sacrificial templates, 3.24 g of resorcinol and 4.4 mL of formaldehyde solution were dissolved in 95.5 mL of deionized water. The solution was stirred for 1 h, and 3.9 mg of sodium carbonate was added. After further stirring for 30 min, the precursor solution was poured into a container, sealed and cured in an oven at 85 ℃ for 72 h to obtain a resorcinol-formaldehyde wet gel. The gel was washed with ethanol for several times to completely remove the residual solvents. The wet gel was dried using supercritical carbon dioxide to obtain the resorcinol-formaldehyde aerogel, which was subsequently placed in a tubular furnace and carbonized in a nitrogen atmosphere to obtain the CA templates.

SiO₂-NTA were prepared via chemical vapor deposition (CVD) with argon as carrier gas, tetraethoxysilane and aqueous ammonia solution as silicon and oxygen sources, respectively. Firstly, tetraethoxysilane source tank was heated to 60 ℃. Then, CA templates were placed in CVD chamber, and was heated to different deposition temperatures (i.e., 100, 150, 200, 250 ℃ and 300 ℃), respectively. C/SiO₂ composite aerogels (CA@SiO₂) were prepared via introducing tetraethoxysilane (5 mL/min) and aqueous ammonia (15 mL/min) into the chamber, and depositing for 20 h at a target pressure. Finally, CA@SiO₂ was calcined in air at 500 ℃, and SiO₂-NTA was obtained after removing the templates.

The microstructural features and pore morphology of aerogels were determined by a model SEM4000Pro scanning electron microscope (SEM) and a model TH-F120 transmission electron microscope (TEM). The specific surface area and total pore volume were measured based on Nitrogen adsorption-desorption isotherms in a model V-Sorb X800 N₂ adsorption analyzer. The compressive strength and Young's modulus of SiO₂-NTA specimens were measured by a model UTM-4103 electronic universal testing machine at a crosshead speed of 0.5 mm/min.

SiO₂-NTA prepared by CVD method has a three-dimensional nanotubular network structure. The inner part of the skeleton is hollow, and the average thickness of tube wall ranges from 3 nm to 7 nm. The deposition temperature and pressure have a significant influence on the microstructure as well as density of SiO₂-NTA. The deposition rate and weight gain of aerogels increase gradually, and accompany the skeleton coarsening process as the deposition temperature increases from 100 ℃ to 250 ℃, which inhibits the shrinkage of the SiO₂-NTA after calcination. Silica preferentially deposits on the outside of the template as the deposition temperature further increases to 300 ℃, resulting in the blocking of SiO₂-NTA surface. The density of SiO₂-NTA firstly decreases and then increases as the temperature increases, which is strongly dependent on both weight gain and linear shrinkage. Similarly, SiO₂-NTA density ranges from 65 mg/cm³ to 51 mg/cm³ with the increase of pressure. The preparation of SiO₂-NTA based on CVD method is essentially a reaction transport process of multi-component fluids in a porous template. It is thus necessary to balance the mass transfer rate and reaction rate to obtain SiO₂-NTA with a homogeneous microstructure.

Compared with CA, the specific surface area and total pore volume of CA@SiO₂ decrease significantly because of the preferential deposition of silica at defects and junctions of framework. After calcination in air, the feature mesopore is formed via removal of the carbon skeleton, and the specific surface area and total pore volume of SiO₂-NTA can reach 592.717 m²/g and 1.047 cm³/g, respectively. The high pore volume and nanotubular skeletons lead to the low density of SiO₂-NTA. SiO₂-NTA shows relatively excellent mechanical properties. The elastic modulus and the stress at 60% strain of nanotube aerogels are 0.70 MPa and 0.83 MPa, respectively, and the specimens have no obvious fatigue damage after 100 cycles of compression, further indicating that SiO₂-NTA has an outstanding structural reliability in a certain range of strain. In addition, SiO₂-NTA also exhibits an excellent machinability while keeping a low density, compared with conventional silica aerogels, and a thin-walled aerogel specimen with a wall thickness of 200 μm can be obtained via processing.

SiO₂-NTA with a three-dimensional nanotubular network structure could be prepared via CVD of silica coating on the skeleton of CA sacrificial templates. The deposition temperature and pressure had a significant influence on the microstructure as well as density of SiO₂-NTA. Within a certain range, the density of SiO₂-NTA reduced as the deposition temperatures and pressure increased because of the decrease of linear shrinkage after calcination. However, as the temperature further increased, silica preferentially deposited on the outside of the template, resulting in the blocking of SiO₂-NTA surface. The preparation of SiO₂-NTA based on CVD method was essentially a reaction transport process of multi-component fluids in porous template. It is necessary to balance the mass transfer rate and reaction rate to obtain SiO₂-NTA with a homogeneous microstructure. The specific surface area and total pore volume of SiO₂-NTA could reach 592.717 m²/g and 1.047 cm³/g, respectively. The high pore volume and nanotubular skeletons led to the low density of SiO₂-NTA. SiO₂-NTA had relatively excellent mechanical properties. The elastic modulus and the stress at 60% strain of nanotube aerogels were 0.70 MPa and 0.83 MPa, respectively, and the specimen could be significantly compressed without obvious brittle fracture. Moreover, SiO₂-NTA had a superior machinability due to its outstanding structural reliability, which could be processed by turning, milling and laser.

Near-infrared (NIR) luminescence with emission wavelengths ranging from 700 nm to 1100 nm has attracted much attention in the fields of nondestructive testing, biometrics, and night vision. In this paper, high-temperature solid-phase method was used to synthesize Cr³⁺ single-doped and Ce³⁺, Cr³⁺ co-doped Y₂CaAl₄SiO₁₂ luminescent materials. Under 438 nm light excitation, Cr³⁺ could produce a near-infrared broadband emission at 740 nm and R-line narrowband emission at 690 nm. The quantum efficiency of mono-doped Cr³⁺ was calculated to be 24%, and the crystal field intensity was calculated to be 2.429 by excitation spectral analysis. The thermal stability and the luminescence intensity of Y₂CaAl₄SiO₁₂∶ Cr³⁺ were analyzed by variable-temperature spectroscopy. In addition, Y₂CaAl₄SiO₁₂∶ Ce³⁺, Cr³⁺ luminescent materials were also prepared, and the luminescence intensity and the quantum luminescence efficiency of Y₂CaAl₄SiO₁₂∶ 0.005Ce³⁺, 0.007Cr³⁺ were analyzed.

In accordance with the stoichiometric ratios, Y_2-xCaAl₄SiO₁₂∶ xCe³⁺ (where x = 0.001-0.011 mol) and Y₂CaAl_4-ySiO₁₂∶0.005 Ce³⁺, y Cr³⁺ (where y = 0.001-0.011 mol) were prepared via solid-state reactions with raw materials of CaCO₃, Cr₂O₃, CeO₂, Al₂O₃, SiO₂, and Y₂O₃. The mixture with anhydrous ethanol was then ground in a mortar. Subsequently, the ground material was dried in an oven at 80 ℃ before being transferred to a square crucible for sintering in a reducing atmosphere at 1550 ℃ for 4 h. Afterwards, the sample was removed and allowed to cool to room temperature for the coming analysis.

Y₂CaAl₄SiO₁₂∶ Cr³⁺ belongs to a cubic structure, the space group is $I a \overline{3} d$, the number of molecules Z=8. The optimal doping concentration of Y₂CaAl_4-ySiO₁₂∶ yCr³⁺(y = 0-0.01) is 0.007, and the quenching mechanism of concentration is dipole-dipole interaction. After co-doping of Cr³⁺ and Ce³⁺ (Cr³⁺ is 0.007), the luminescence intensity is about 3 times greater than that of single-doped Cr³⁺, and the quantum efficiency is 45%. This indicates that the co-blending improves the luminescence performance of the material. When co-doped with Y₂CaAl₄SiO₁₂∶Ce³⁺ and Cr³⁺, the luminescence properties of the sample can reach 77.6% of the room temperature at 423 K (150 ℃), and the thermal stability is good.

Near-infrared luminescent materials of Y_2-xCaAl₄SiO₁₂∶ Cr³⁺ and Y₂CaAl₄SiO₁₂∶ Ce³⁺, Cr³⁺ were synthesized via soild-state reactions. The luminescence properties and thermal stability of the samples were thoroughly analyzed, and Ce³⁺ was incorporated as a sensitizer to investigate the energy transfer mechanism between Ce³⁺ and Cr³⁺ within the matrix. The results indicated that Y₂CaAl₄SiO₁₂ exhibits a garnet structure, Cr³⁺ generated a broad near-infrared emission spectrum peaking at 740 nm alongside a sharp peak at 690 nm, achieving a quantum efficiency of 24% when doped alone. Y₂CaAl₄SiO₁₂∶ Ce³⁺, Cr³⁺ prepared had an energy transfer from Ce³⁺ to Cr³⁺. The energy transfer mechanism of this system was elucidated through IS0 and c fitting analyses. The luminous intensity of Y_1.995CaAl_3.993SiO₁₂∶ 0.005Ce³⁺ and 0.007Cr³⁺ was threefold greater than that of Y₂CaAl_3.993SiO₁₂∶0.007Cr³⁺. At this juncture, the quantum efficiency for co-doping reached 45%. When y was 0.011, the energy transfer efficiency measured was 30.01%. The thermal stability of Y₂CaAl₄SiO₁₂∶ 0.007Cr³⁺ revealed that its luminous intensity at 150 ℃ retained 77.6% of its value at room temperature, with a thermal activation energy calculated of 0.207 eV. This work could provide essential data for future applications of this material.

The chemical stability of phosphate glass is vital for its applications in various fields, i.e., biomedicine, laser gain media, sealing, and high-level nuclear waste solidification. Alkali metals affect the chemical stability of phosphate glass. Some studies indicate that alkali metals with a higher ionic field strength can enhance the chemical stability of glass via reinforcing the ionic crosslinking between alkali ions and non-bridging oxygen atoms. However, a few studies indicate that certain phosphate glasses containing low-field strength alkali metals exhibit a better chemical stability, compared to the glasses containing high-field strength alkali metals. These results cannot be explained based on the simple field strength. It is thus necessary to further investigate the influence of alkali metals on the chemical stability of phosphate glass. In this study, we utilized various advanced solid-state nuclear magnetic resonance (SSNMR) techniques to analyze the network structure of the aluminum phosphate glasses containing different alkali metals in an atomic scale. The intrinsic correlation among alkali metals, glass structure, and chemical stability was discussed.

The glasses with molar compositions of [xNa₂O-yK₂O-(41.6-x-y)Cs₂O]-16.7Al₂O₃-41.7P₂O₅ were synthesized by melt quenching methods. The values of (x, y) used were (41.6, 0), (0, 41.6), (20.8, 0), and (0, 20.8), respectively. The raw materials required for glass preparation were Al(OH)₃ (purity>99%), Al(PO₃)₃ (purity>99%), NaPO₃ (purity>95.0%), KPO₃ (purity>99%,), Cs₂CO₃ (purity>99%), and NH₄H₂PO₄ (purity>99%). Each batch, consisting of 20 g of mixed raw materials, was loaded into a platinum crucible and subjected to a high-temperature furnace at 1250-1300 ℃ for 30 min to melt raw materials. Thereafter, the melt was poured onto a steel plate and quickly pressed to obtain a bulk glass.

The chemical stability of these glasses was assessed by the Product Consistency Test B (PCT-B) method. 1 g of dried glass powder with particle sizes of 75-150 μm was mixed with 10 mL of neutral deionized water in a sealed polytetrafluoroethylene (PTFE) container. The container was then placed in a constant temperature environment at 90 ℃ for 7 d. After the corrosion experiments, the concentrations of leached elements in the leachates were measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), thus calculating the normalized mass loss (NL) of each element within the different glasses.

All the SSNMR measurements were performed on a model Bruker Avance III HD 500 MHz spectrometer in a magnetic field of 11.7 T at room temperature. The measurements included ²⁷Al magic-angel spinning (MAS), ³¹P MAS, ²⁷Al{³¹P} rotational echo double resonance (REDOR), ³¹P{²⁷Al} rotational echo adiabatic passage double resonance (REAPDOR), and ³¹P 1D refocused INADEQUATE.

The Raman spectra were determined by a model Renishaw inVia spectrometer, with a laser wavelength of 488 nm.

The NL of phosphorus (P) in the glasses containing alkali metals Na, K, and Na/Cs are 0.7, 15.2, and 21.1 g/m², respectively. The glass containing K/Cs exhibits a complete corrosion without detectable leachate obtained. These findings indicate that the chemical stability of the aluminum phosphate glasses with varying alkali metal compositions follows a decreased order of Na, K, Na/Cs, K/Cs. The P units within the different glasses are predominantly Q¹ units (Qⁿ, "n" represents the number of P-O-P bonds per P unit), indicating a consistent proportion of P—O—P bonds in these glasses. The variation in alkali metals does not affect the P—O—P bonds within the glasses. However, the variation in alkali metals significantly affects the Al species within the glasses. Specifically, the glasses containing alkali metals with a high ionic field strength exhibit a higher proportion of high-coordinated Al. In these glasses, the Al species with different coordinations are exclusively surrounded by phosphorus oxygen tetrahedra (PO₄), indicating that all Al species exist solely in the form of Al—O—P bonds. The compactness of the glass network increases with the proportion of Al—O—P bonds. The compact glass network can impede the dissolution and leaching of glass elements, as well as the diffusion of hydrogen species from solution into glass, thereby enhancing the chemical stability of the glass. The compactness of the glass network can be characterized by the reciprocal of the molar volume (1/V_mol). A higher value of 1/V_mol indicates a greater number of atoms per unit volume, corresponding to a higher compactness of the glass network. The values of 1/V_mol (×10⁴ mol/L) in these glasses containing alkali metals Na, K, Na/Cs, and K/Cs are 2.6, 2.2, 2.1, and 2.0, respectively. Correspondingly, the proportions of Al—O—P bonds are 54.5%, 52.6%, 50.7%, and 50.5%, respectively. A decreasing order of Na, K, Na/Cs, K/Cs is consistent with a decreasing order of the chemical stability. These results provide an evidence that the proportion of Al—O—P bonds increases as the ionic field strength of alkali metal increased, resulting in an enhanced compactness of the glass network and improved chemical stability. Furthermore, it is noteworthy that the proportion of Al-O-P bonds in the glass containing Na/Cs is comparable to that in the glass containing K/Cs. The former demonstrates a denser glass network. This can be attributed to the smaller ionic radius and higher ionic field strength of Na, compared to K. The smaller ionic radius results in narrower structural gaps within the glass network, while the higher ionic field strength enhances its electric field attraction to non-bridging oxygen.

The chemical stability of the aluminum phosphate glasses containing different alkali metals decreased in an order of Na, K, Na/Cs, K/Cs. The chemical stability increased as the ionic field strength of alkali metals increased. The change in alkali metals affected the compactness of the glass network via modulating the electric field attraction to non-bridging oxygen, and substantially modified the network structure of the glass. In these glasses, the Al species with varying coordination numbers were exclusively surrounded by phosphorus oxygen tetrahedra (PO₄). The proportion of high-coordinated Al increased with increasing the ionic field strength of alkali metals, resulting in an augmentation of the chemical bond connections between Al and PO₄. This structural adjustment further enhanced the compactness of the glass network, ultimately improving its chemical stability.

In alpine saline soil environments, concrete has a multi-factor coupling degradation due to the freeze-thaw cycles, as well as sulfate and chloride corrosion. This degradation results in a significant decline in structural lifespan primarily due to reduced material durability. The maintenance process is complex and incurs substantial economic losses, attracting considerable attentions. Under the influence of these coupled factors, the presence of salt facilitates the migration of water toward the salt. Upon reaching the critical freezing point, ice jams occur, leading to concrete damage from ice pressure. Also, the formation of numerous expansion products generates an expansion pressure during dry-wet cycles, further contributing to concrete deterioration. Although the use of fiber-reinforced concrete has a potential to mitigate these issues, tight construction timelines can result in an initial damage, such as cracks during winter construction, which are often unavoidable. The existing research on the durability and mechanisms of fiber-reinforced concrete in real crack states within this environment remains insufficient, indicating a need for a further research.

This study examined the fiber-reinforced concrete used in a project located in the alpine saline soil region of Tibet, China. Three distinct types of fiber concrete specimens were designed and manufactured with polypropylene fiber (PPF), polyacrylonitrile fiber (PANF), and modified polyester fiber (PEF). After 150 d outdoor curing, the actual cracks were analyzed by a microscope. Two accelerated degradation tests were conducted, i.e., composite salt-freeze-thaw and composite salt-dry-wet cycles. The durability damage mechanisms and patterns were investigated in detail through measurements of ultrasonic wave velocity and splitting tensile strength, as well as by scanning electron microscopy.

According to the crack information statistics of the specimens after outdoor exposure and curing, the cracks in plain concrete are straight and singular, whereas the cracks in fiber-reinforced concrete are interconnected, forming a ring network structure. The presence of these cracks accelerates the connection rate between surface and internal cracks during composite salt-freeze-thaw and dry-wet cycles, leading to a reduction in wave velocity and splitting tensile strength. The mechanistic analysis indicates that under the influence of salt-freeze-thaw, the saturation of the concrete pore solution increases, and the combined effects of crystallization pressure, stress, and chemical expansion products contribute to the initiation and propagation of internal cracks within the concrete. Damage can be categorized into surface damage and internal damage. During the composite salt-dry-wet cycle, the water pressure in the wet state gradually diffuses the salt solution from the concrete surface to its interior, resulting in the formation of expansive products. In the dry state, the solution is heated and evaporated, causing soluble salts to crystallize due to temperature effects. The alternating dry-wet conditions produce a compounded damage. The fibers exhibit a bridging-cracking-toughening effect, which enhances crack propagation resistance. Furthermore, an analysis model correlating the relative values of ultrasonic wave velocity damage with splitting tensile strength, which is proposed based on material decay theory, demonstrates a correlation coefficient of exceeding 0.95. This model effectively reflects the attenuation behavior of the splitting tensile strength of fiber concrete under conditions of composite salt-freeze-thaw and dry-wet cycles, highlighting its significance in predicting the tensile properties of concrete structures.

The initial crack width of plain concrete ranged from 6 μm to 15 μm with a maximum length of 20 mm. In comparison, the early crack resistance of polyester fiber reinforced concrete was superior, exhibiting a width of less than 10 μm and a maximum length of approximately 10 mm, alongside the maximum anti-deterioration capability. Upon reaching the designated number of cycles in the durability test, the wave velocity was decreasesd by 29.36% and 16.05%, respectively, while the splitting tensile strength was diminished by 43.80% and 37.19%, respectively. This deterioration in durability resulted in the expansion of cracks within the interfacial transition zone of the concrete. However, the fibers could form a network that bridged these cracks, thereby reducing tensile stress, enhancing crack propagation resistance in the interfacial transition zone, ultimately delaying the overall damage.

Lead halide perovskites have attracted much attention in optoelectronic research due to their exceptional properties, such as long carrier diffusion lengths, low exciton binding energies, and cost-effective production. However, their inherent lead toxicity and poor environmental stability have challenges, restricting their wider adoption. It is thus important to search for safer, lead-free alternatives. Cesium copper halides emerge as promising candidates, offering the similar photoluminescent properties and potential for full-spectrum emission. Nevertheless, these materials still suffer from degradation under harsh conditions, which limits their practical use. Embedding cesium copper halides in glass matrices can enhance the stability via protecting the quantum dots from environmental factors like moisture and oxygen. However, challenges such as low transparency and limited tunability remain. To overcome these issues, the introduction of rare-earth ions like europium (Eu²⁺/Eu³⁺) into the glass matrix is proposed. In this work, transparent Eu²⁺/Eu³⁺ doped Cs₃Cu₂I₅/CsCu₂I₃ dual-phase quantum dot glass was synthesized by an one-step melt-quenching method. The resulting glass exhibits a full-spectrum cold white light emission with a correlated color temperature (C) of 7 421 K, a general color rendering index (R) of 82, and a photoluminescence quantum yield of 75.1%.

In this study, a transparent Eu²⁺/Eu³⁺ doped Cs₃Cu₂I₅/CsCu₂I₃ biphasic quantum dot glass was synthesized by an one-step melt-quenching method. The glass composition designed was 20% SiO₂, 50% B₂O₃, 5% ZnO, 3% Al₂O₃, 10% Cs₂CO₃, and 12% NaI, all in molar percentages. To induce the precipitation of biphasic quantum dots within the glass matrix, additional components were introduced, i.e., 1% CuI to promote the formation of cesium copper iodide, 0.04% SnO to prevent the oxidation of Cu⁺, 1% CaO to facilitate the precipitation process, and 1% MnO to reduce the viscosity of the glass. Various concentrations of Eu₂O₃ (i.e., 0%, 0.02%, 0.05%, and 0.10%) were added to enhance the glass emission properties.

The crystalline phases in the glass were determined by X-ray diffraction (XRD). The glass transition temperature and crystallization temperature were determined by differential scanning calorimetry (DSC) as indicatives of the thermal stability of the glass. The photoluminescence (PL) spectra were employed to evaluate the optical properties of the glass (i.e., the emission spectrum, quantum yield, and R). The oxidation states of the elements within the glass were analyzed by X-ray photoelectron spectroscopy, providing an insight into the distribution of Eu²⁺/Eu³⁺. The absorption spectra of the glass were characterized by UV-visible spectrophotometry.

The results demonstrate that the Eu²⁺/Eu³⁺ doped Cs₃Cu₂I₅/CsCu₂I₃ biphasic quantum dot glass exhibits enhanced photoluminescent properties, compared to the undoped samples. The introduction of Eu₂O₃ can increase the overall emission intensity and broaden the emission spectrum, resulting in a full-spectrum cold white light emission. Specifically, the glass doped with 0.05% Eu₂O₃ achieves a photoluminescence quantum yield of 75.1%, with a C of 7421 K and a general R of 82. These results indicate that the Eu²⁺/Eu³⁺ co-doping effectively improves the glass emission characteristics via providing additional emission centers in the blue and red regions of the spectrum, attributed to Eu²⁺ and Eu³⁺, respectively. The structural analysis shows the effective incorporation of Eu²⁺/Eu³⁺ ions into the Cs₃Cu₂I₅/CsCu₂I₃ matrix without disrupting the existing crystal structures. The XRD patterns indicate that the doped glass maintains the characteristic diffraction peaks of Cs₃Cu₂I₅ and CsCu₂I₃, indicating that the addition of Eu₂O₃ does not alter the fundamental crystal structure of the biphasic quantum dots. Moreover, the DSC analysis reveal a high glass transition temperature of 652 K and a crystallization temperature of 717 K, indicating that the doped glass has an excellent thermal stability. The glass samples are also subjected to long-term stability tests, showing a minimal degradation in their optical properties after three months of storage. The photoluminescence spectra of the stored samples exhibit only minor shifts in emission peak positions and intensity, indicating that the glass retains its luminescent properties. In addition, the Eu²⁺/Eu³⁺ doping also improves the glass transparency and color rendering capabilities. The doped glass samples have a higher degree of transparency, compared to the undoped samples, which is attributed to the clarifying effect of Eu₂O₃. The Eu²⁺/Eu³⁺ ions provide complementary blue and red emission, thus enhancing the overall color rendering and allowing for the production of cold white light with a high color quality. The improved transparency and color rendering make the doped glass suitable for use in lighting and display applications in which high brightness and accurate color representation are required.

Eu²⁺/Eu³⁺ doped Cs₃Cu₂I₅/CsCu₂I₃ biphasic quantum dot glass was synthesized as a stable, lead-free photoluminescent material. The synthesized glass demonstrated an excellent full-spectrum cold white light emission, making it a promising candidate for various optoelectronic applications (i.e., lighting, displays, and sensors). The one-step melt-quenching method was effective in producing a material with a high thermal stability, a robust structural integrity and an enhanced optical performance. The introduction of Eu₂O₃ provided additional emission centers, improved transparency, and enhanced color rendering, addressing the limitations of previous cesium copper halide quantum dot glasses. This study could provide a viable strategy for the design and fabrication of advanced quantum dot glasses that meet the stringent demands of modern optoelectronic devices, offering a safer and more stable alternative to lead-based perovskites.

Solid oxide fuel cell (SOFC) is one of the strong competitors of energy technology. SOFC has the characteristics of wide fuel selection, less pollution emission, high safety, and low noise as an excellent energy conversion and utilization device. However, the existing commercial SOFC still has some problems like high working temperature and large attenuation rate due to the limitation of material performance, restricting the application. Among the components of SOFC, the performance of air pole material is a key factor affecting SOFC. LSC material is one of the main research directions of solid oxide fuel cells (SOFC) air polar materials with the superior electrochemical properties, but its major disadvantage is a great thermal expansion coefficient (TEC). The negative thermal expansion (NTE) material provides an effective way to reduce the TEC of the SOFC air pole material. NTE material is named because of the characteristics of thermal contraction in the specific temperature interval. Theoretically, it can reduce the TEC of composite material and facilitate the thermal match between SOFC air electrode material and electrolyte material. Some NTE materials are a perovskite structure with a higher conductivity than Gd_0.2Ce_0.8O_2-δ (GDC) of fluorite structure. These advantages make the theoretical cell power density of NTE composite air electrode material above the GDC composite cathode In this paper, La_0.6Sr_0.4CoO_3-δ (LSC) material was used as a matrix, Sm_0.85Zn_0.15MnO₃ (SZM) material with the superior negative thermal expansion characteristics was selected as a composite phase, and a series of LS-xSZM (x = 0-40%) materials were designed to achieve the thermal matching of composite materials.

LSC and SZM powders were synthesized by a solid-liquid composite method. First, the corresponding quality of acetate raw materials was accurately weighed according to the stoichiometric ratio, and then the appropriate citric acid (CA) was weighed as a complexing agent according to the total metal particle weight and citric acid (CA) amount of 5∶1. All the raw materials were mixed with an appropriate amount of deionized water and ground in a ball mill at a speed of 300 r/min for more than 12 h. The turbid liquid in the ball mill was taken out and placed in a beaker, and the precursor powder was obtained after drying in the oven at 250 ℃ for 6 h, and then the LSC powder was obtained via calcination in a muffle furnace at 950 ℃ for 2 h, and the SZM powder was obtained via calcination at 1 300 ℃ for 2 h. The two powders were mixed with ethanol and ground in the ball mill for 6 h. The cathode slurry was prepared by mixing powders, and then full cells and symmetrical cells were made by screen printing for subsequent tests.

The X-ray diffraction patterns show that the SZM is chemically compatible with LSC. The thermal expansion test indicates that SZM has an excellent thermal offset ability, and the average thermal expansion coefficient of the composite material from room temperature to 800 ℃ at x of 30% is 13×10^-6 K^-1, which is similar to that of the barrier material. The area specific resistance of the LSC-30% SZM composite material at 800-500 ℃ decreases from 0.012-1.240 Ω·cm² in the case of LSC to 0.008-0.620 Ω·cm², indicating a good interfacial contact. The power density of the button cell at 750 ℃ is 1 702 mW·cm^-2, while the pure phase LSC at the same temperature is 1 209 mW·cm^-2, which is increased by 41%. The polarization resistance Rp reduces from 0.65 Ω·cm² to 0.50 Ω·cm². The voltage drop of thermal cycling and constant current discharge is below 1%. In the 200 h constant current discharge test at 300 mA·cm^-2, the voltage of the battery remains stable after the initial increase, and the whole process only reduces to 10 mV, which is decreased by 1.2%, showing a good long-term stability. No delamination occurs in the SEM images of the battery cross-section after the test. The comprehensive analysis of a better interfacial contact due to a good thermal matching of the composites ultimately achieves a simultaneous increase in the power density and stability of the cell.

A perovskite structural oxide material of Sm_0.85Zn_0.15MnO₃ (SZM) with negative thermal expansion characteristics was synthesized by a solid-liquid recombination method. The XRD analysis indicated that SZM was chemical compatible with LSC. The pure phase SZM had special thermal shrinkage characteristics, while the thermal expansion characteristics of the composite materials decreased. The TEC of the pure phase LSC was 20 ×10^-6 K^-1, while the TEC of the 30% SZM composite LSC was only 13×10^-6 K^-1. The ASR of the composite material at 750 ℃ decreased from 0.02 Ω·cm² to 0.013 Ω·cm², while that at 550 ℃ decreased from 1.2 Ω·cm² to 0.6 Ω·cm², having an excellent performance. The battery of LSC-30% SZM material was improved at 750 ℃ from 1 209 mW·cm^-2 of pure phase LSC to 1 702 mW·cm^-2 of LSC-30% SZM, which was increased by 41%. In the thermal cycle test, the variation of battery OCV was within 1%, and the voltage decay rate of long-term constant current discharge at 200 h was 1.2%. The microscopic section analysis indicated that there was little interface stratification phenomenon. LSC-30% SZM composite material had good long-term thermal stability and structural stability.