Sodium-ion batteries (NIBs) have attracted much attention as promising alternatives to lithium-ion batteries due to the natural abundance of sodium, low cost, and enhanced safety. Among various cathode materials, layered transition metal oxides, particularly O3-type structures, are considered highly attractive due to their high specific capacity, moderate operating voltage, and facile synthesis. High-nickel ternary oxides such as NaNi_0.6Co_0.2Mn_0.2O₂ (NNCM622) exhibit superior capacity and economic viability, making them candidates for next-generation NIBs. However, the electrochemical performance of these materials is highly sensitive to synthesis conditions, especially the heat treatment process, significantly affecting the crystallinity, morphology, and structural stability. This work was to investigate the influence of calcination temperature on the structure, morphology, and electrochemical properties of O3-type NNCM622 cathode materials synthesized via a conventional solid-state reaction.

Method In the preparation of O3-type NNCM622 cathode materials, stoichiometric amounts of Ni_0.6Co_0.2Mn_0.2(OH)₂ precursor and NaOH (with a 5% excess of sodium source) were thoroughly mixed and subsequently calcined in an oxygen atmosphere at 700, 750 ℃ and 800 ℃ for 24 hours, yielding the final products denoted as NNCM622-700, NNCM622-750, and NNCM622-800, respectively.

The X-ray diffraction(XRD) patterns show that all the samples crystallize in an O3-type layered structure (space group R-3m). The clear splitting of the (006)/(012) and (018)/(110) diffraction peaks indicates a well-developed layered structure. The Rietveld refinement reveals that the sample calcined at 750 ℃(i.e., NNCM622-750) possesses the lowest refinement discrepancy factor (R_wp = 3.374%) and optimal crystallinity. In contrast, the sample NNCM622-700 has a poorer crystallinity due to incomplete reaction at a lower temperature, while the sample NNCM622-800 likely suffers from sodium volatilization and potential structural distortions at a higher temperature. The X-ray photoelectron spectra (XPS) on the sample NNCM622-750 indicate the coexistence of Ni²⁺/Ni³⁺, Co, and Mn in the material, which is consistent with the expected valence states for this composition. The inductively coupled plasma optical emission spectra (ICP-OES) show that the elemental compositions of all the samples are close to the theoretical stoichiometry.

The images of scanning electron microscopy (SEM) reveal that all the samples consist of spherical secondary particles with the sizes of 2-10 μm formed due to the agglomeration of numerous primary particles. The sample NNCM622-700 has larger primary particles due to insufficient reaction, whereas the sample NNCM622-800 exhibits over-sintering and particle cracking. The images of transmission electron microscopy (TEM) and the mapping of energy dispersive X-ray spectroscopy(EDS) of the sample NNCM622-750 further confirm its well-crystallized layered structure with an interplanar spacing of 0.263 nm, corresponding to the (102) plane, and a homogeneous distribution of elements Na, Ni, Co, and Mn.

The electrochemical performance is evaluated in half-cells versus sodium metal. The NNCM622-750 cathode has a high initial discharge capacity of 150.5 mA·h·g^-1 at 0.1 C (1 C = 150 mA·h·g^-1) within the voltage window of 1.5-4.2 V, with a high initial Coulombic efficiency of 86.5%. This cathode also demonstrates a superior rate capability, retaining discharge capacities of 106, 95 mA·h·g^-1 and 85.9 mA·h·g^-1 at 1 C, 2 C, and 5 C, respectively. After 100 cycles at 1 C, this cathode maintains 55.3% of its initial capacity, showing a better cycling stability than the other two samples. In contrast, the NNCM622-700 and NNCM622-800 cathodes deliver lower initial capacities (i.e., 119.8 mA·h·g^-1 and 97.8 mA·h·g^-1, respectively) and suffer from more rapid capacity decay. This performance degradation is attributed to incomplete sodiation (for NNCM622-700) and sodium loss/structural defects (for NNCM622-800), increasing the electrode impedance and hindering Na⁺ diffusion.

The cyclic voltammetry (CV) curves of the NNCM622-750 cathode shows a pair of well-defined redox peaks around 2.3/2.7 V, corresponding to the Ni²⁺/N⁴⁺ redox reaction. The minimum peak potential separation (ΔV = 0.4 V) for NNCM622-750 indicates the lowest polarization and optimum reaction reversibility among the three samples. The electrochemical impedance spectra (EIS) reveal that the NNCM622-750 electrode has the minimum charge-transfer resistance (i.e., R_ct = 327.1 Ω). Furthermore, based on the Warburg coefficient derived from the EIS data, the maximum Na⁺ diffusion coefficient (D_Na⁺) for NNCM622-750 (i.e., 7.53×10^-15 cm²·s^-1) can be obtained, compared to that for NNCM622-700 (i.e., 5.12×10^-15 cm²·s^-1) and NNCM622-800 (i.e., 1.92×10^-17 cm²·s^-1). These results corroborate its superior rate performance.

The nickel-rich O3-type NNCM622 cathode materials were synthesized by a high-temperature solid-state reaction method, and their microstructures and electrochemical properties were investigated. The O3-type NNCM622 cathode material prepared under calcination at 750 ℃ for 24 h exhibited a superior crystallinity, a well-defined layered structure, and the minimum Na⁺ diffusion barrier due to its excellent structural and compositional synergy. As a result, the NNCM622-750 cathode delivered the maximum initial discharge specific capacity (i.e., 150.5 mA·h·g^-1 at 0.1 C with a coulombic efficiency of 86.5%), superior rate performance (i.e., 85.9 mA·h·g^-1 at 5 C), and relatively high cycling stability (i.e., capacity retention of 55.3% after 100 cycles at 1 C). An appropriate calcination temperature could enhance the reversibility and cycling performance of the cathode material, thereby improving the structural stability and electrochemical properties of nickel-rich O3-type NNCM622 cathodes. This work could present a simple and low-cost preparation process for synthesizing nickel-rich O3-type NNCM622 cathode materials with superior electrochemical performance, offering valuable insights for addressing the challenges associated with heat treatment in the development of next-generation layered cathode materials for sodium-ion batteries.

This study was to investigate the influence of mixed alkali effect on the structure and properties of a R₂O-CaO-Al₂O₃-SiO₂ glass system, to provide theoretical support and practical guidance for optimizing the formulation of high-level radioactive liquid waste (HLW) glass vitrification technology. The safe disposal of HLW is a critical aspect for the sustainable development of the nuclear industry. The Joule-heated melter vitrification as an internationally engineered and implemented method could immobilize radioactive waste via melting HLW with base glass frit in an electric furnace to form a stable vitrified product for long-term containment.

Glass samples with varying Z-values (i.e., Z = n(Na₂O)/(n(Na₂O) + n(Li₂O)) were prepared by a high-temperature melting method. Their structure and properties were systematically analyzed by infrared spectroscopy, Raman spectroscopy, and high-temperature resistivity analysis.

The structural characterization revealed that the silicate tetrahedral units Q² and Q³ are the primary structural units influencing glass properties. The structure exhibits regular changes as Z-value increases. At Z=0.2, the proportions of Q³ and Q⁴ reach the maximum values, while Q¹ and Q² reach the minimum values. At Z=0.6, Q¹, Q³, and Q⁴ proportions reach the maximum values, while Q² reaches the minimum value, indicating the most compact glass structure and the most significant mixed-alkali effect.

The results of performance tests demonstrate that the physical and thermal properties both are governed due to the mixed-alkali effect The density and thermal expansion coefficient both increase with increasing Z-value. The density reaches the maximum value as Z=0.6, while the thermal expansion coefficient has the minimum value. The glass transition temperature (T_g) initially decreases and then increases, reaching its minimum as Z=0.2. The high-temperature viscosity has the maximum value as Z=0.4 and the minimum value as Z=0.6.

For the electrical properties in single-alkali systems, the resistivity at the melting temperature (T₂) decreases in an order of K₂O >Na₂O > Li₂O, while it at the forming temperature (T₄) decreases in an order of K₂O > Li₂O > Na₂O. In the mixed-alkali system, the resistivity reaches the maximum value at Z of 0.6-0.8, being correlated to the "blocking effect" of alkali ions. The activation energy for electrical conduction changes nonlinearly with Z-value. In single-alkali systems, it increases in the order of Na₂O < Li₂O < K₂O.

This study clarified the mixed-alkali effect on the R₂O-CaO-Al₂O₃-SiO₂ glasses, particularly highlighting the low viscosity as Z = 0.6 and the high resistivity characteristics as Z = 0.6-0.8. These findings could provide a clear guidance for glass formulation design.

Hard optical fiber imaging components as two-dimensional array imaging materials comprised of tens of millions to billions of micro- and nano-scale optical glass fibers have extensive applications in numerous optical systems, including low-light-level image intensifiers and space target detection systems. Resolution and contrast are crucial indicators affecting the performance of these components. Elemental diffusion at the core-clad interface results in a gradient distribution of material refractive index rather than the ideal abrupt distribution, thereby degrading the resolution and contrast of the components. It is necessary for the demands for refined manufacturing processes of these components to gain a comprehensive understanding of the diffusion behavior and distribution status of elements at the core-clad interface. At present, energy dispersive spectrometry (EDS) is often employed as a characterization tool for elemental distribution status, yet it suffers from a low image resolution (20 nm) and lacks corresponding quantitative calculation methods. In this study, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) was utilized to acquire high-precision images of elemental spatial distribution. Furthermore, a multi-model fusion machine learning approach was proposed to address the challenges of characterization and quantitative analysis in the study of elemental migration at the core-clad interface of hard optical fiber imaging components.

In this study, monofilaments undergoing various thermal processes were fabricated by a drawing technique. High-Angle Annular Dark-Field (HAADF) images were captured and utilized to train Tree-SVM/LDA models. These models enabled pixel-level core-clad classification and x-y two-dimensional spatial classification, thereby yielding quantitative results on elemental interface diffusion. In addition, the reliability of the models was also analyzed.

The Tree-SVM/LDA model is grounded on the following assumptions, i.e., element Si as a key component in the formation of both core and cladding glass network structures remains stable during the diffusion process. The deviation distances of other elements are benchmarked against that of Si, the average deviation (D) is defined as an arithmetic mean of the migration distances of all elements within the tested range, serving to characterize the overall diffusion behavior of elements rather than individual extreme values, elements undergo unidirectional migration, consistent with the direction of the concentration gradient, manifesting as the perpendicular direction to the interface in monofilament samples, the transition zone at the core-cladding interface is formed through the superposition of diffusion behaviors of different elements, and the algorithmic procedure of model encompasses the following steps (i.e., constructing training and prediction datasets; training the decision tree model; developing a labeled prediction dataset; and obtaining classification hyperplane parameters).

The results obtained by SVM and LDA models both indicate the thermodynamic principles at higher resolutions, with the deviation D_K∈[10, 40]nm, D_Ba∈[0, 11]nm, and D_Ti∈[0,13]nm. At lower resolutions, where the width of a single pixel in the raw data is 3 nm, the computational error of the models is amplified threefold, leading to the results that deviate from actual principles. At 810 ℃, the SVM model exhibits a poor data separability due to the low content of Ti in the cladding region, resulting in abnormal calculation results. This phenomenon underscores the superiority of the LDA model over SVM in terms of training set diversity, demonstrating a greater generalization capability. The calculation results of the SVM model and LDA model show a good consistency, while also presenting regular differences, i.e., the boundaries obtained by the LDA model tend to skew towards the cladding region relative to those of the SVM model. This regularity may be associated with differences in model characteristics and the element distribution patterns in the HAADF images of the core and cladding regions, having a further in-depth research. In general, the SVM model achieves higher accuracy than the LDA model. However, the LDA model possesses a better generalization capability.

The migration capabilities of the elements K, Ti, and Ba intensified as the wire drawing temperature increased. Specifically, the average migration distance of element K could range from 10 nm to 40 nm, while that of elements Ti and Ba could span from 0 to 13 nm. Affecting the reliability of models were since the spatial resolution of the raw data could be in atomic or sub-atomic scale, models could be sensitive to data anomalies, thus requiring repeated training, elements with great diffusion capabilities could decrease the accuracy of the model, while simultaneously enhancing its generalization capability. The SVM model demonstrated superior accuracy, compared to the LDA model, having a weaker generalization capability. The SVM model could be recommended at a high quality of the raw data, whereas the results of the LDA model could be more realistic at a low quality of the raw data.

The interfacial contact and charge conduction between the electrolyte and cathode have a direct impact on the performance and efficiency of single cells, which is a crucial area in both fundamental research and technological development of SOFCs. The following perspectives for future development are provided.

The development of novel electrolytes and electrode materials represents an effective strategy to address interfacial issues. Concurrently, the exploration of innovative interfacial structural designs can enhance the performance and stability within existing material systems. Future research endeavors should prioritize meeting the practical demands of industrial applications. Furthermore, it is essential to optimize the preparation process. The quality of the interface between the electrolyte and the cathode directly affects the overall performance of SOFCs. Therefore, optimizing the preparation process is of crucial importance. Currently, coating technologies such as pulsed laser deposition (PLD) and chemical vapor deposition (CVD) can achieve a precise preparation of specific compositions and structures. In the future, it is necessary to focus on the research and development of new high-performance, low-cost thin film preparation technologies with large-scale manufacturing capabilities to further improve interface quality. In addition, there is a focus on interdisciplinary research. Various in-situ spectroscopic characterization methods, machine learning and artificial intelligence technologies will also contribute to SOFCs research, including material performance prediction, parameter optimization design, and operating condition performance simulation. This can promote the connection between theoretical models and practical applications, driving SOFCs technology toward higher efficiency and lower costs. Finally, despite significant progress in lab-scale research, the commercialization of SOFCs still faces some challenges. In the next phase, it is necessary to further optimize the cell preparation process and operating conditions, such as electrolyte structure, composite electrode materials, and sintering processes. Reducing costs, improving cell reliability and lifespan can promote SOFCs widespread application in the energy sector.

Systematic statistical analysis reveals that distinct doping elements exert element-specific regulatory effects on the key performance metrics of layered oxide cathodes for sodium-ion batteries (i.e., capacity, rate capability, long-cycle stability, and structural integrity). Electrochemically inactive dopants enhance structural stability at the expense of reducing the number of redox-active sites due to lattice occupation, leading to capacity decay. Conversely, electrochemically active dopants improve capacity through redox reactions yet modify electron cloud distribution (i.e., exacerbating electronic disorder and altering localization/delocalization behavior), concurrently inducing lattice distortion and additional stress that compromise structural stability. Consequently, synergistic modification strategies integrating high-entropy design with doping effects emerge as a pivotal approach to transcend comprehensive performance limitations. However, this strategy confronts triple challenges, i.e., 1) synthesis requiring prolonged high-temperature annealing with precise multicomponent stoichiometric control, significantly amplifying manufacturing complexity and cost; 2) cost escalation from precious/rare-earth dopants restricting industrial scalability; and 3) insufficient mechanistic understanding of the synergistic interactions between dopant elements. A future research must prioritize developing low-cost facile synthesis techniques, advancing computational materials science-guided elemental combination optimization, and elucidating multiscale synergistic mechanisms, thereby establishing definitive composition-structure-property relationships to direct targeted fabrication of high-performance materials.

Conventional concrete suffers from its inherently low tensile strength. To address this drawback, researchers propose steel fiber reinforced concrete (SFRC) as a novel material that significantly improves tensile properties and exhibits outstanding performance in cracking resistance, toughness, and durability. However, the incorporation of steel fibers makes the mechanical behavior of SFRC more complex. To ensure its safe application in structural engineering, an accurate prediction of its mechanical properties is essential.

Artificial intelligence technologies are widely applied to accurately evaluate the mechanical properties of concrete. However, the existing machine learning models for SFRC are typically trained on a limited number of samples (i.e., fewer than 300), which restricts their generalization capability. Moreover, these models often lack interpretability, undermining their credibility and limiting their practical application in engineering projects.

This study was to establish a database for the compressive and splitting tensile strengths of SFRC, develop corresponding machine learning prediction models, and evaluate their predictive performance. Furthermore, the interpretability of the models was analyzed. The findings of this study could offer some insights into the development of high-precision machine learning models for SFRC and their interpretability analysis, thereby promoting their application in engineering practices.

In this study, a total of 636 experimental data points on SFRC were collected from 24 independent studies to establish a comprehensive database, including 419 data points for compressive strength and 217 for splitting tensile strength. Each data entry contains a mix-related information such as the water-to-binder ratio, sand ratio, aggregate-to-binder ratio, maximum size of coarse aggregate, fiber shape factor, fiber aspect ratio, fiber volume fraction, and the corresponding compressive or splitting tensile strength.

Based on this database, five machine learning models (i.e., Random Forest (RF), Gradient Boosting Regression Tree (GBRT), Extreme Gradient Boosting (XGB), Light Gradient Boosting Machine (LGBM) and Bayesian Neural Network (BNN)) were proposed. The predictive performance of these models was evaluated using the coefficient of determination (R²), mean absolute percentage error (MAPE), and root mean square error (RMSE), in order to identify the most effective prediction model.

For the selected model, the SHAP (SHapley Additive exPlanations) method was employed to analyze the trends and contribution of each input parameter on the compressive and splitting tensile strengths of SFRC. In addition, the Partial Dependence Plot (PDP) and Individual Conditional Expectation (ICE) methods were also used to quantitatively investigate the variation patterns of predicted values with respect to individual input parameters.

All the models proposed demonstrate a great predictive performance. The R² for the test set ranges from 0.84 to 0.90, while for the training set it ranges from 0.80 to 0.90. A small difference between them (i.e., both being > 0.75) indicates a good predictive accuracy and a generalization ability. For the overall performance across R², MAPE and RMSE metrics, the LGBM model shows the optimum prediction performance.

The SHAP analysis reveals that the compressive and splitting tensile strengths of SFRC decrease with increasing water-to-binder ratio and aggregate-to-binder ratio, while the strengths both increase at a higher sand ratio and a greater fiber reinforcement factor. In addition, as the maximum size of coarse aggregate increases, the compressive strength decreases, whereas the splitting tensile strength increaseds. These results are consistent with the practical observations. Based on the mean absolute SHAP values, the input parameters influencing the compressive strength in a descending order are water-to-cement ratio, sand ratio, fiber reinforcement factor, aggregate-to-cement ratio, and maximum coarse aggregate size. For splitting tensile strength, the order is fiber reinforcement factor, sand ratio, water-to-binder ratio, aggregate-to-binder ratio, and maximum coarse aggregate size.

The influence and parameter importance rankings obtained through the PDP and ICE analysis are in a reasonable agreement with those derived from SHAP, further validating the interpretability and reliability of the model.

A large-scale database containing 636 data entries was established for the compressive and splitting tensile strengths of SFRC. Based on this database, five machine learning prediction models (i.e., RF, GBRT, XGB, LGBM and BNN) were proposed. All the models exhibited good predictive performance and generalization ability, significantly outperforming the existing prediction methods. Among them, the LGBM model showed the optimum overall performance. The SHAP, PDP and ICE techniques were employed to analyze the influence and importance of each input parameter on the compressive and splitting tensile strengths. Based on the variable contribution analysis, the main factors affecting the compressive strength were the water-to-cement ratio, sand ratio, fiber reinforcement factor, aggregate-to-cement ratio, and maximum coarse aggregate size. In contrast, the key determinants of splitting tensile strength were the fiber reinforcement coefficient, sand ratio and water-to-cement ratio.

Subsea shield tunnels serve as critical passages connecting two sides of sea areas and play a vital role in supporting the development of a maritime nation and the coordinated integration of land and marine resources. In recent years, the construction of subsea shield tunnels has been rapidly developed, with representative projects including the Lion Rock Subsea Tunnel of the Guangzhou-Shenzhen-Hong Kong High-Speed Railway, the Qingdao Jiaozhou Bay Second Subsea Tunnel, and the Jintang Subsea Tunnel of the Ningbo-Zhoushan Railway, China. However, during both the construction and service phases of shield tunnels, some factors such as construction practices, aggressive environmental conditions, and uneven settlement can lead to cracking, water leakage, and even corrosion of reinforcement in segment concrete. Insufficient toughness and crack resistance of shield segment concrete can compromise the long-term operational safety of shield tunnels. During service, shield segments are subjected to high water pressure and strongly corrosive ionic environments. To enhance the durability of concrete, erosion-inhibiting materials like coatings, migrating corrosion inhibitors, and internally incorporated nanomaterials are often used during prefabrication. These materials significantly improve the durability of segment concrete, and their effect on crack resistance and toughness remains insufficiently explored.

This study was to investigate the enhancement of fracture toughness in shield segment concrete through the use of erosion-inhibiting materials, including silica nanoparticles, migrating corrosion inhibitors, and nano-sized precursors. In addition, the mechanism by which these materials could affect the microstructure of concrete was also analyzed from the perspective of interfacial transition zone optimization.

In this study, the fracture behavior of concrete was investigated by a three-point bending test method. During the loading process, the displacement of the specimens was monitored using digital image correlation (DIC). Also, the interfacial transition zone of the concrete was analyzed via backscattered electron imaging analysis. The fracture toughness of the concrete microstructure was characterized by nano-indentation scratching technique.

Based on the implementation of erosion inhibition measures, the fracture toughness of concrete is notably enhanced. In concrete specimens treated with silica nanoparticles, migrating corrosion inhibitors, and nano-precursors at various dosages, the crack initiation toughness is increased by 22.6%-48.9%, the instability toughness is improved by 18.8%-49.8%, and the fracture energy is elevated by 0.50-1.59 times. The improvement in fracture toughness is closely associated with the physical and chemical interactions of these materials within the concrete. The silica nanoparicles coating penetrates into the cement matrix, promotes a further hydration, and provides additional nucleation sites. Its reaction products effectively fill pores and reduce the number of initial defects and microcracks, resulting in a denser cement matrix with improved strength and deformation properties. The active molecules in the migrating corrosion inhibitor form coordination bonds with calcium ions in cement hydration products, anchoring themselves within the hydration phases. The main components migrate to the steel-concrete interface, forming a protective adsorbed layer that delays reinforcement corrosion. The nano-precursor material undergoes an ion-exchange reaction during cement hydration, in-situ generating calcium carboxylate compounds. These hydrophobic substances are uniformly dispersed in nanoscale within the C-S-H gel network, significantly enhancing the interfacial wetting behavior via reducing the surface energy of pore channels. Furthermore, the nanoparticles released from the precursor decomposition fill internal pores, block connected voids, optimize pore size distribution, and increase matrix density.

The application of erosion-inhibiting materials significantly enhanced the fracture toughness of the concrete. In shield segment concrete treated with nano-silica coating, migrating corrosion inhibitor, and nano-precursors at varying dosages, the peak load was increased by 16.8%-37.1%, crack initiation toughness was improved by 22.6%-48.9%, unstable fracture toughness was increased by 18.8%-49.8%, and fracture energy was enhanced by 0.50-1.59 times, compared to the reference group. Before peak load, the migrating corrosion inhibitor and nano-silica coating both contributed to a reduction in the Crack Tip Opening Displacement (CTOD), while the nano-precursor was effective in lowering CTOD values at all loading stages. During the post-peak phase (specifically at 30% beyond peak stress), the CTOD was decreased by 31.8%-47.2% with nano-precursor incorporation. The erosion-inhibiting materials also improved the properties of the Interfacial Transition Zone (ITZ). The ITZ thickness of the materials treated with silica nanoparticles coating and migrating corrosion inhibitor could be reduced by 7.1% and 6.5%, respectively.

Scintillators are functional materials that immediately emit low-energy photons after absorbing high-energy ionizing radiations. Glasses have advantages as a material form for scintillator use, such as low manufacturing costs, ease of formability, high optical transparency, and high compositional tunability. A ⁶Li-glass scintillator doped with Ce is a commercial glass scintillator, and it has been used for thermal neutron detections owing to ⁶Li(n,α)³H neutron capture reactions. In general, the ³He counter is used in practice for neutron detections; however, the depletion of the ³He supply has driven vigorous research and development of alternative materials. ¹⁰B-contained glasses have an advantage of their large thermal neutron capture cross section (3840 barn). In this study, we focused on MgO-P₂O₅-B₂O₃ glass systems. They are composed of light elements; hence, neutron detection signals can be easily distinguished from noise due to X- and γ-rays. Furthermore, alkali-earth-embedded P₂O₅-B₂O₃ glasses realize high optical transparency with good chemical durability. As luminescence centers, Eu was selected. Eu exists in two different states: Eu²⁺ in reduction states and Eu³⁺ in oxidation states. The former shows broad emission bands with fast decay times of ~μs, whereas the latter shows sharp emission bands with slow decay times of ~ms. In general, Eu³⁺ is governed in the glasses prepared in an air atmosphere; however, alkali-earth-embedded P₂O₅-B₂O₃ glasses can exhibit Eu²⁺ owing to the localized reducing atmosphere generated by NH₃ derived from the raw material (NH₄H₂PO₄). Here, Eu-doped MgO-P₂O₅-B₂O₃ glasses with various concentrations of Eu were synthesized by the conventional melt quenching technique in air, and their optical, photoluminescence (PL), and scintillation properties were examined.

Undoped and 0.1%, 0.3%, 1.0%, and 2.0% (in mole fraction) Eu-doped 25MgO-30P₂O₅-45B₂O₃ (MPB) glasses were synthesized by the melt quenching method. Raw materials were homogeneously mixed and transferred into an alumina crucible. The powders were melted at 1100 ℃ for 1 h with an electrical furnace in air. The melt was flowed onto a preheated stainless-steel plate to quench, and pressed into batches. After that, the glasses were annealed at 400 ℃ for 1 h to remove thermal and mechanical strains. The surfaces of the glasses were polished for the following optical and scintillation measurements. The glass transition temperature (T_g) of the undoped sample was measured with a TG-DTA system. The powder X-ray diffraction (XRD) patterns were measured using a diffractometer. Diffuse transmission spectra were measured using a spectrophotometer (Shimadzu, SolidSpec-3700). PL excitation and emission spectra, PL quantum yields (QYs), and PL decay curves were measured using a Quantaurus-QY and Quantaurus-τ. Scintillation spectra, scintillation decay curves, and afterglow curves under X-ray irradiations, and pulse height spectra of ²⁴¹Amα-rays and ¹³⁷Cs γ-rays were measured with our original setups.

The appearances of undoped and Eu-doped MPB glasses were transparent and included some bubbles. Under ultraviolet light at 360 nm, Eu-doped samples showed bluish-red light. Some parts of the glasses were crushed into powder and used for the XRD measurements. Precipitations of crystalline phases were not observed in the XRD patterns; hence, the prepared samples formed glass phases with no periodical structures. T_g of the undoped glass was estimated to be 535 ℃. The transmittances of all the glasses were 70%-90% at 400-700 nm. Both the undoped and Eu-doped samples showed absorption peaks at 200-250 nm; hence, this can be due to the hosts. In addition, absorption peaks emerged at 250-400 nm in Eu-doped samples. The absorption bands at 250-280 nm and 280-400 nm originated from the 4f⁷-4f⁶5d¹ (T_2g and E_g) transitions of Eu²⁺, respectively. An absorption peak due to the ⁷F₁-⁵D₃ transitions of Eu³⁺ was confirmed at 415 nm in the spectra of 2% Eu. A broad emission band due to the electronic transitions of Eu²⁺ was observed at 400-600 nm under excitation bands at 250-410 nm in the Eu-doped samples. Generally, emissions due to Eu²⁺ are difficult to observe in the glasses prepared in air because of the oxidizing atmosphere. The emissions appeared owing to the localized reduction atmosphere, which derived from NH₄H₂PO₄ and (NH₄)₂O·5B₂O₃·8H₂O. When excitation and monitored wavelengths were respectively set to 340 nm and 420 nm, the PL decay curves were fitted by a sum of two exponential functions. The PL decay time constants of both the fast (0.2-0.5 μs) and slow (0.7-1.2 μs) components were similar to those of other Eu-doped phosphors; hence, they are reasonable as 4f⁶5d¹(T_2g)-4f⁷ and 4f⁶5d¹(E_g)-4f⁷ transitions of Eu²⁺. Eu-doped samples showed emission peaks at 350-500 nm under X-ray irradiations. These emission wavelengths were consistent with those of the PL spectra. Afterglow levels (AL) of undoped and 0.1%, 0.3%, 1.0%, and 2.0% Eu-doped glasses at 20 ms passed after X-ray irradiation of 2 ms were respectively estimated to be 1700×10^-6, 4500×10^-6, 3400×10^-6, 800×10^-6, and 160×10^-6. Pulse height spectra of ²⁴¹Am α-rays (5.5 MeV) were measured using the prepared MPB glasses. Eu-doped glasses showed clear full energy absorption peaks. Light yields (LY) of 0.3%, 1.0%, and 2.0% Eu-doped MPB glasses were respectively calculated to be 70, 150 photons/5.5 MeV, and 40 photons/5.5 MeV.

Eu-doped MPB glasses were synthesized by the conventional melt quenching method. All the samples showed halo peaks with no periodic patterns in XRD measurements. The transmittances were 70%-90%, and absorptions due to electronic transitions of Eu²⁺ and Eu³⁺ were observed. All the samples showed luminescence, which originated from the 4f⁶5d¹-4f⁷ transitions of Eu²⁺. PL QYs of 0.1%, 0.3%, 1.0%, and 2.0% Eu-doped samples were respectively calculated to be 46.7%, 37.2%, 20.4%, and 9.3% when monitored at 350-560 nm under excitation at 320 nm. ALs at 20 ms passed after X-ray irradiations of 2 ms were obtained to be 1700×10^-6, 4500×10^-6, 3400×10^-6, 800×10^-6, and 160×10^-6 in undoped, 0.1%, 0. 3%, 1.0%, and 2.0% Eu-doped samples, respectively. Pulse height spectra of ²⁴¹Am α-rays were measured using the prepared samples. LYs of 0.3%, 1.0%, and 2.0% Eu-doped samples were respectively determined to be 70, 150 photons/5.5 MeV, and 40 photons/5.5 MeV.

Foamed cement paste (FCP) is a type of cementitious geotechnical material with a high porosity structure, prepared by mixing cement paste with preformed foam and sometimes incorporating soil materials such as clay, silica fume, fly ash, and sand. Due to its lightweight nature, excellent self-supporting ability, easy construction, and environmental friendliness, FCP has been widely used in embankment fills, bridge abutment backfills, slope reinforcement, and retaining wall applications. However, in saline soil regions, FCP is subjected to chemical attacks, particularly sulphate attack, in addition to environmental factors such as temperature fluctuations and water infiltration. The early stage of sulphate attack plays a critical role in determining the long-term durability of FCP. Unlike conventional concrete, which may experience initial strength gain due to ettringite and gypsum formation, FCP's unique pore structure may result in different degradation patterns. At this stage, the interaction between pore water, sulphate ions, and cement hydration products can lead to either early-stage degradation or partial densification. However, the mechanisms linking early-stage mechanical behavior and pore evolution remain unclear. This study focuses on the mechanical behavior and pore structure evolution of FCP during the early stage of sulphate attack. Specimens were exposed to Na₂SO₄ solutions (0%, 0.5%, 2.5%, 5.0%) for 28 d and 56 d, representing the early-stage exposure period. A combination of uniaxial compression testing, X-ray computed tomography (X-CT), and nuclear magnetic resonance (NMR) analysis was used to evaluate the changes in strength, aquiferous pore size distribution, and aquiferous porosity. The findings provide key insights into the initial degradation mechanisms of FCP, highlighting the competing roles of skeleton softening due to water absorption and pore densification due to sulphate reaction products, which are of great significance for further understanding of the influence of service environment on the engineering performance of FCP.

FCP specimens were prepared using P.C42.5 composite Portland cement, anionic foaming agent LG-2258, and tap water. The water-to-cement ratio (m_w/m_c) was set at 0.45, and the foam volume ratio (V_f/V_w) was controlled at 3.5 to achieve a final wet density of approximately 0.9 g/cm³. The specimens were cast in cubic molds (70.7 mm × 70.7 mm × 70.7 mm), demolded after 24 h, and cured under standard conditions [(20 ± 2) ℃, RH > 95%)] for 28 d. To eliminate the influence of initial moisture content on sulphate attack, all specimens were oven-dried at 60 ℃ to a constant weight before sulphate attacking. A multi-field coupling test device was used to control sulphate attack conditions, maintaining a constant temperature of 20 ℃ and an osmotic pressure of 10 kPa. The specimens were exposed in Na₂SO₄ solutions (0%, 0.5%, 2.5%, 5.0%) for 28 d and 56 d, simulating the early stage of sulphate attack. After attacking, NMR and X-CT analyses were conducted to assess aquiferous pore structure and aquiferous porosity, followed by uniaxial compression testing at a loading rate of 2 mm/min. Each experiment was repeated at least three times to ensure accuracy and repeatability.

Uniaxial compression test results showed that, during the early stage of sulphate attack, FCP specimens initially experienced strength reduction compared to the standard condition. However, partial strength recovery was observed after 56 d, particularly at 2.5% Na₂SO₄ concentration, where the peak strength increased by 19.28% and the residual strength increased by 55.56%. This indicates a transition from initial degradation to partial densification, likely due to the formation of sulphate reaction products. Unlike traditional concrete, which often exhibits a continuous strength increase in the early sulphate attack phase, FCP's unique pore structure resulted in a more complex response. At low sulphate concentrations (0.5%), sulphate attack increased porosity, accelerating early-stage degradation. However, at higher sulphate concentrations (2.5% and 5.0%), reaction products partially filled existing pores, leading to strength recovery. X-CT and NMR analyses revealed that sulphate attack significantly altered the aquiferous pore structure of FCP in the early stage: 1) Macropore frequency (>100 µm) decreased as sulphate concentration increased, indicating pore filling by reaction products. 2) Small pore frequency (1-10 µm) increased, particularly at 2.5% and 5.0% Na₂SO₄, due to the formation of ettringite and gypsum. 3) Total aquiferous porosity of sulphate-attacked specimens was higher than that of water-immersed specimens, suggesting that sulphate ions modified water retention behavior. A strong exponential correlation was observed between aquiferous porosity and mechanical strength. As aquiferous porosity decreased, both peak and residual strength increased, confirming that sulphate-induced microstructural changes significantly influence mechanical performance.

The main conclusion of this work are summarized as following: 1) Sulphate attack in the early stage first weakens FCP, then triggers partial strength recovery. Peak and residual strength initially declined, but after 56 d, peak strength increased by 19.28% and residual strength by 55.56%, particularly at 2.5% Na₂SO₄ concentration. 2) FCP's early-stage sulphate attack behavior differs from traditional concrete. At low sulphate concentrations (0.5%), sulphate attack increased aquiferous porosity, accelerating early-stage degradation. However, at higher concentrations (2.5% and 5.0%), sulphate reaction products partially filled pores, leading to strength recovery. 3) Sulphate attack altered FCP's aquiferous pore structure in the early stage. Macropores (>100 µm) decreased, while small pores (1-10 µm) increased, indicating that sulphate products influenced pore connectivity and densification. 4) A strong exponential relationship was identified between aquiferous porosity and strength. As aquiferous porosity decreased, both peak and residual strength increased, demonstrating that sulphate-induced pore transformations impact mechanical stability. These findings highlight the critical role of the early attack stage in determining the long-term durability of FCP, offering new insights for optimizing its application in sulphate-rich environments.

The long-term strength development of high-sulfur belite-calcium sulfoaluminate (high-sulfur BCSA) cement remains constrained by the low hydration reactivity of β-dicalcium silicate (β-C₂S) and the difficulty in obtaining its high-temperature active polymorphs. Ionic doping, which activates and stabilizes highly cementitious dicalcium silicate/calcium sulfoaluminate (C₄A₃$) crystalline phases while inducing lattice distortion, has been proven as an effective approach to enhance mineral reactivity.

With the depletion of high-grade limestone resources, the utilization of low-grade magnesian limestone and phosphorus-containing solid wastes, such as phosphogypsum and phosphorus slag, for producing high-sulfur BCSA has become an inevitable trend. This leads to the unavoidable coexistence of Mg²⁺/P⁵⁺ in the clinker mineral system. However, existing studies have primarily focused on the doping effects of individual ions, while the synergistic influence and underlying mechanisms of magnesium/phosphorus components in the quaternary clinker system (C₂S-C₄A₃$-C₄AF-CaSO₄) on sintering behavior and performance remain poorly understood.

In this study, MgCO₃ and Ca₃(PO₄)₂ were employed as the sources of MgO and P₂O₅ doping, respectively, to systematically investigate the effects of Mg/P co-doping on the phase composition, crystal structure evolution, and mechanical properties of high-sulfur BCSA clinker, along with the associated mechanisms. The findings not only provide a theoretical foundation for optimizing the strength development of high-sulfur BCSA cement but also establish a technical basis for the large-scale, high-value utilization of Mg/P-bearing industrial solid wastes.

The designed mineral composition of high-sulfur BCSA clinker was as follows (mass fraction): 50 % C₂S, 30% C₄A₃$, 7% C₄AF, and 13% f-CaSO₄. The raw meal samples were prepared using industrial raw materials and analytical-grade chemical reagents with varying Mg/P doping levels. Specifically, MgO was incorporated at 0.6%, 1.0%, 1.5%, 3.0%, and 5.0%, while P₂O₅ was added at 0.1%, 0.4%, 0.7%, 1.0%, and 1.3%. The raw mixes were fired at 1320 ℃ for 60 min to obtain clinker samples.

The effects of Mg/P co-doping on the sintering behavior and properties of high-sulfur BCSA clinker were investigated through X-ray diffraction combined with Rietveld refinement, scanning electron microscopy, and mechanical strength testing.

The Mg/P co-doping exhibits a significant synergistic effect, with an appropriate doping ratio effectively enhancing the content of highly reactive mineral phases, including cubic-calcium sulfoaluminate (c-C₄A₃$) and α'-dicalcium silicate (α'-C₂S). P₂O₅ demonstrates a favorable stabilizing effect on high-activity crystalline phases such as α'-C₂S and c-C₄A₃$, whereas MgO shows an adverse influence, particularly when the P₂O₅ content is low (P₂O₅ ≤ 0.4%). The maximum α'-C₂S formation in clinker is achieved at a doping level of 1% MgO and 1.3% P₂O₅. Moreover, Mg/P co-doping reduces the grain size of C₂S and C₄A₃$ minerals. However, excessive P₂O₅ doping 1.3% leads to noticeable melting corrosion, resulting in decreased crystallinity.

At low doping levels [w(MgO) ≤ 1.5%, w(P₂O₅) ≤ 0.7%], the 3 d compressive strength improves while the 7 d strength remains stable, with all samples showing varying degrees of enhancement in 28 d compressive strength, though excessive MgO doping leads to periclase formation and significant strength reduction. The 3 d and 28 d compressive strengths exhibit linear correlations with the total contents of C₄A₃$ and C₂S, respectively, with appropriate Mg/P doping promoting C₂S formation, particularly at 1.5% MgO and 0.4% P₂O₅, which yields the highest C₂S content and achieves a 28 d strength of 74.5 MPa.

Optimal Mg/P co-doping effectively reduces the decomposition temperature of CaCO₃ while enhancing its decomposition rate, and lowers the formation temperature of intermediate minerals C₅S₂$ and C₂S within the 900-1320 ℃ range, thereby promoting the formation of clinker minerals like C₂S. Furthermore, Mg/P doping demonstrates significant synergistic effects: P⁵⁺ selectively substitutes calcium and aluminum/silicon sites, stabilizing reactive phases such as α'-C₂S and c-C₄A₃$. As P₂O₅ content increases from 0.4% to 1.3%, the concentrations of α'-C₂S and c-C₄A₃$ markedly rise. In contrast, Mg²⁺ competes with P⁵⁺ for calcium sites, leading to reduced α'-C₂S and c-C₄A₃$ content with increasing MgO doping. The highest relative α'-C₂S content (51.5%) is achieved at 1% MgO and 1.3% P₂O₅ doping levels.

The 28 d compressive strength of doped clinker was improvd to varying degrees, initially increasing with MgO content but declining when excessive MgO forms periclase. Similarly, strength first rises then falls with increasing P₂O₅ content. Both 3 d and 28 d compressive strengths exhibit linear positive correlations with the total contents of C₄A₃$ and C₂S, respectively. Maximum C₂S formation and peak 28 d strength (74.5 MPa) occur at 1.5% MgO and 0.4% P₂O₅ doping. Comprehensive analysis of mineral formation, crystal phases, and performance reveals an optimal doping range: w(MgO)<3% and w(P₂O₅) 0.3%-1.3%, which balances clinker sintering efficiency and mechanical properties.