Crystals

The π-hole triel bond formed by (BH)₂(NHC)₂ (NHC denotes nitrogen-heterocyclic carbene) and TrPhX₂ (Tr = B, Al, and Ga; X = F, Cl, Br, CH₃, and OH) was investigated computationally, with the B=B bond in (BH)₂(NHC)₂ being the electron donor. A large interaction energy ensures that the complex is quite stable. When the substituent X in the electron acceptor is fixed, the magnitude of the interaction energy varies with the identity of the Tr atom. When Tr is Al or Ga, the interaction energy is stronger than when it is B. With an increase in the electron-withdrawing ability of the substituents, the interaction energy shows distinct changes. When Tr is B or Al, the interaction energy varies as TrPhBr₂ > TrPhCl₂ > TrPhF₂, which is different from the order of their positive electrostatic potentials. When Tr = Ga, the interaction energy hardly changes with an increase in the electronegativity of the halogen atoms. For CH₃ and OH substitution, larger interaction energies were obtained, with the interaction energy for the OH substituent being the largest. The main interactions in these systems are a triel bond and an X· ·H hydrogen bond. When the substituents are fixed, the interaction energy of the triel bond increases in the order AlPhX₂ < GaPhX₂ < BPhX₂, which is different from the order of the positive electrostatic potentials on the Tr atom in TrPhX₂. When X is a halogen atom, the interaction energy of the triel bond decreases in the order Br > Cl > F, which is opposite to the trend for the positive electrostatic potentials on Tr in TrPhX₂. In most complexes, the interaction energy for the hydrogen bond is less than that for the triel bond; there is no hydrogen bond in the methyl-substituted complex. In general, the interaction energy of the hydrogen bonds increases with an increase in the electronegativity of the halogen atoms. Full article

The lead-free halide perovskite Cs₃Bi₂Br₉ is a promising semiconductor material for room-temperature X-ray detection due to its excellent properties. However, material purity and crystal quality still limit the use of Cs₃Bi₂Br₉ crystals as detectors. In this work, we present a highly efficient purification method using continuous vacuum extraction to sublimate BiBr₃ precursors for Cs₃Bi₂Br₉. Impurity analysis via inductively coupled plasma mass spectroscopy showed that the purification method successfully removed most of the impurities in BiBr₃ precursors and improved the purity by at least one order of magnitude. Centimeter-sized Cs₃Bi₂Br₉ single crystals were grown by the vertical Bridgman method. The improved properties after purification were confirmed by UV-Vis-NIR spectra, infrared transmittance, and current–voltage (I–V) measurements. The results showed that the average transmittance of Cs₃Bi₂Br₉ crystals significantly increased from 62% to 75% in the 0.5–20 μm spectral range. Additionally, the resistivity increased by nearly three orders of magnitude from 5.0 × 10⁹ Ω·cm to 2.2 × 10¹² Ω·cm, meaning the material will have low leakage currents and be suitable for developing applications for room temperature radiation detection. Full article

BaSi_xO_1+2x (1.61 ≤ x ≤ 1.90) and LiF-doped BaSi_1.63O_4.26 ceramics were prepared by using a traditional solid-state method at the optimal sintering temperatures. The evolution of phase compositions of BaSi_xO_1+2x (1.61 ≤ x ≤ 1.9) ceramics was revealed. The coexistence of Ba₅Si₈O₂₁ and Ba₃Si₅O₁₃ phases was obtained in BaSi_xO_1+2x (1.61 ≤ x ≤ 1.67) ceramics. The BaSi₂O₅ phase appeared inBaSi_xO_1+2x (1.68 ≤ x ≤ 1.90) ceramics. At 1.68 ≤ x ≤ 1.69, only BaSi₂O₅ and Ba₃Si₅O₁₃ phases existed. With the further increase in x, the Ba₅Si₈O₂₁ phase appeared, and BaSi₂O₅, Ba₅Si₈O₂₁ and Ba₃Si₅O₁₃ phases coexisted in BaSi_xO_1+2x (1.70 ≤ x ≤ 1.90) ceramics. The phase compositions of BaSi_xO_1+2x (1.61 ≤ x ≤ 1.90) ceramics were controlled by the ratio of Ba:Si. The BaSi_xO_1+2x (x = 1.68) ceramics with 98.15 wt% Ba₃Si₅O₁₃ and 1.85 wt% BaSi₂O₅ phases exhibited a negative τ_f value (−37.53 ppm/°C), and the good microwave dielectric properties of ε_r = 7.51, Q × f = 13,038 GHz and τ_f = +3.95 ppm/°C were obtained for BaSi_1.63O_4.26 ceramics with 70.05 wt% Ba₅Si₈O₂₁ and 29.95 wt% Ba₃Si₅O₁₃ phases. The addition of LiF sintering aids were able to reduce the sintering temperatures of BaSi_1.63O_4.26 ceramics to 800 °C. The phase composition of BaSi_1.63O_4.26 ceramics was affected by the sintering temperature, and the coexistence of Ba₅Si₈O₂₁, Ba₂Si₃O₈, BaSi₂O₅ and SiO₂ phases was achieved in BaSi_1.63O_4.26-3 wt% LiF ceramics. The BaSi_1.63O_4.26-3 wt% LiF ceramics sintered at 800 °C exhibited dense microstructures and excellent microwave dielectric properties (ε_r = 7.10, Q × f = 12,463 GHz and τ_f = +5.75 ppm/°C), and no chemical reaction occurred between BaSi_1.63O_4.26-3 wt% LiF ceramics and the Ag electrodes, which indicates their potential for low-temperature co-fired ceramic (LTCC) applications. Full article

4H-SiC wafers are more likely to sustain a lower material removal rate (MRR) and severe subsurface damage in conventional chemical mechanical polishing (CMP) methods. To overcome the material removal bottleneck imposed by aqueous chemistry, a high-efficiency polishing of 4H-SiC wafers method by applying reactive nonaqueous fluids to self-sharpening fixed abrasive pads has been proposed in our former research works. Furthermore, to improve the material removal rate and reduce the surface roughness Sa value of 4H-SiC substrates of the Si face, the effect of organic acid, H₂O₂, and Triton X-100 in nonaqueous slurry on 4H-SiC polishing was investigated. The MRR of 12.83 μm/h and the Sa of 1.45 nm can be obtained by the orthogonally optimized slurry consisting of 3 wt% H₂O₂, 0.5 wt% Triton X-100 at pH = 3. It is also found that the addition of different levels of oxidant H₂O₂ and surfactant Triton X-100 components not only increased the MRR of the 4H-SiC substrates of the Si face but also achieved a lower Sa value; in that, the polishing efficiency of the Si side of the 4H-SiC wafers and the surface quality of the 4H-SiC wafers could be effectively improved by the optimization of the polishing slurry. Full article

In this paper, we proposed a high-performance electromagnetic-wave metamaterial absorber which can be used directly for 5G technology. The absorber exhibits a high performance in a tailored frequency range of 28 ± 1 GHz. At both transverse-electric and transverse-magnetic polarization, the absorption exceeds 99% when the electromagnetic wave is incident normally, and the absorption keeps being over 97% as the incident angle increases even to 45 degrees. The absorber is flexible, and it is very suitable for mass production because the production process is simple. In addition, the minimum dimension of the meta-structure is only 0.2 mm, and the cost is relatively low. Similarly, another high-performance metamaterial absorber with a tailored bandwidth at the center frequency of 77 GHz, which is relevant to self-driving cars, was also prepared by a minimal adjustment to the original structure. Full article

This article discusses the combustion of high-energy systems based on the oxidizers ammonium nitrate, potassium nitrate, and a mixture of highly active aluminum grade PAP-1 under conditions of a deficiency or excess oxidant α, under a pressure reduction in the range of 0.1–3 MPa. The objective of this study is to develop materials for the production of high-energy compositions based on oxidizers of ammonium and potassium nitrate, fuel binder, and metallic fuel in the form of aluminum powders ASD-6 and PAP-1. The influence of the amount of excess oxidizer, the amount of metallic fuel, and the grade of aluminum on the rate and completeness of combustion of a high-energy composition have been studied. Experiments were carried out on the studied high-energy systems, depending on the grade of aluminum used and the excess of the oxidizing agent α, and the influence of pressure on the burning rate. The compositions of high-energy compositions based on highly active aluminum with the highest combustion rate of mixtures and combustion completeness were determined. Full article

The phenomenon of the strain-rate sensitivity of metallic materials has been a topic of interest since the first mechanical tests at different strain rates were performed. The problem of its theoretical description appeared simultaneously. Despite the significant number of studies covering this issue, it is necessary to rule out a few drawbacks of previously reported models, which is the goal of this work. Herein, an extension of the elastic–viscoplastic model to a generalized state of stress is proposed while aiming to describe the strain rate sensitivity of Armco-iron samples that were pulled in tension within the framework of the finite-difference method. A mathematical model was formulated using equivalent stress and strain, which alleviated the complexity of the relaxation-type constitutive equations. The critical resolved shear stress (CRSS) function describes S-type instability with a single equation. The plastic strain rate was calculated based on the well-known Orowan equation, which is related to dislocation dynamics. In addition, the model took the material’s microstructure into account based on the design of a representative volume element (RVE) using the step-by-step packing (SSP) method. The results of the modeling were compared with the available experimental data and were found to satisfactorily correlate with them. The results suggest that the misfit error between the model and experimental data did not exceed 10% in the range of strain rates under study, which is a reliable outcome. Full article

As a typical spinel ferrite, NiFe₂O₄ is suitable for use in gas sensors. Herein, we report the fabrication of porous, tremella-like NiFe₂O₄ assembled using porous, ultrathin nanosheets via the coordination of Ni²⁺ and Fe²⁺ with 1,4-phenylenediboronic acid. The optical band gap of the NiFe₂O₄ is estimated to be about 1.7 eV. Furthermore, the NiFe₂O₄ sensor annealed at 400 °C exhibits a low detection limit of 50 ppb, a fast response/recovery time (11.6 s/41.9 s to 10 ppm toluene), good reproducibility, and long-term stability at 220 °C. The suitable sensing performances can be attributed to the good catalytic activity of NiFe₂O₄ to toluene oxidation. Moreover, the ultrathin nanosheets with porous structures provide a large number of active sites to significantly favor the diffusion and adsorption/desorption of toluene molecules. This current work provides an insight into fabricating NiFe₂O₄ using 1,4-phenylenediboronic acid, which is promising for ppb-level toluene detection. Full article

Lead-free copper halide perovskite nanocrystals (NCs) are emerging materials with excellent photoelectric properties. Herein, we present a colloidal synthesis route for orthorhombic Cs₂CuCl₄ NCs with a well-defined cubic shape and an average diameter of 24 ± 2.1 nm. The Cs₂CuCl₄ NCs exhibited bright, deep blue photoluminescence, which was attributed to the Cu(II) defects. In addition, passivating the Cs₂CuCl₄ NCs by Ag⁺ could effectively improve the photoluminescence quantum yield (PLQY) and environmental stability. Full article

The control and prediction of morphological changes in annealed void microstructures is an essential and powerful tool for different semiconductor applications, for example, as part of the production of pressure sensors, resonators, or other silicon structures. In this work, with a focus on the void shape evolution of silicon, a novel simulation approach based on the level-set method is introduced to predict the continuous transformation of initial etched nano/micro-sized cylindrical structures at different annealing conditions. The developed model, which is based on a surface diffusion formulation and built in COMSOL Multiphysics^® (Stockholm, Sweden), is introduced and compared to experimental literature data as well as with other analytical approaches. Some advantages of the presented model include the capability of simulating other materials under similar phenomena, the simulation of any possible initial geometry, and the visualization of intermediate steps during the annealing processing. Full article

This work presents the results of oxidation studies on commercially available Nirosta 4016/1.4016 ferritic steel, which contains 16.3 wt.% chromium, as well as the electrical properties of steel/scale layer systems in order to determine the usefulness of this steel for constructing metallic interconnects in solid oxide fuel cell (SOFC) and solid oxide electrolyzer cell (SOEC) stacks. The E-Brite ferritic steel, consisting of up to 26 wt.% chromium, was chosen as a reference material. High-temperature isothermal oxidation kinetics studies were carried out on both steels at 1073 K for 255, 505, 760 and 1010 h in air atmosphere. These conditions are representative of those present in the cathode compartment of a SOFC and the anode compartment of a SOEC. Area specific resistance (ASR) measurements were performed on steel/scale layer systems, obtained after the previous oxidation of both steels in the above-mentioned conditions, in the air in the temperature range of 573–1073 K using the pseudo-DC four-probe method. On the basis of these studies, complemented by morphology observations, as well as chemical and phase composition analysis of the oxidation products, the usefulness of Nirosta 4016/1.4016 ferritic steel for manufacturing interconnects in energy conversion electrochemical devices operating at 1073 K was confirmed. Full article

Crystallization control of organic conjugated small molecules is in high demand for the engineering of functional materials in organic optoelectronics. Here, we report solution additive-assisted crystallization of a model non-planar aromatic hydrocarbon derivative 9,10-diphenylanthracene. Among the studied series of related aromatic hydrocarbons comprising pyrene, perylene, anthracene, tetracene, and rubrene, only tetracene revealed clear reproducible effects allowing one to perform selective crystallization of metastable 9,10-diphenylanthracene polymorphs. Additionally, crystallization of 9,10-diphenylanthracene and pyrene produced a stoichiometric co-crystal (PYR–DPA) having a segregated layered molecular packing with alternating 9,10-diphenylanthracene and pyrene layers. Remarkably, the molecular packing of pyrene within the co-crystal is unique and represented by the herringbone motif, whereas the molecular packing in known pyrene polymorphs is represented by π-stacked molecules. The co-crystal also demonstrated a bright photoluminescence with a photoluminescence quantum yield of 51%. Considering the morphology of 9,10-diphenylanthracene crystals obtained and crystal structures of PYR–DPA co-crystal and tetracene, we have proposed the mechanism of additive-assisted polymorphism based on the inhibition of (111) facet of α-DPA and promoting of the layered structure crystallization corresponding to metastable polymorphs (β- and γ-DPA). We highlight the additive-assisted crystallization approach as a powerful tool for the crystal engineering of functional materials for organic optoelectronics. Full article

Heterophases, such as precipitates, inclusions, second phases, or reinforcement particles, often drive void nucleation due to local incompatibilities in stresses/strains. This results in a significant life-limiting condition, as voids or their coalescence can lead to microcracks that reduce the ductility and fatigue life of engineering components. Continuum-mechanics-based analytical models have historically gained momentum due to their relative ease in predicting failure strain. The momentum of such treatment has far outpaced the development of theories at the atomic and micron scales, resulting in an insufficient understanding of the physical processes of void nucleation and growth. Evidence from the recent developments in void growth theories indicates that the evolution of voids is intrinsically linked to dislocation activity at the void–matrix interface. This physical growth mechanism opens up a new methodology for improving mechanical properties using hydrostatic pressurization. According to the limited literature, with a hydrostatic pressure close to 1 GPa, aluminium matrix composites can be made 70 times more ductile. This significant ductility enhancement arises from the formation of dislocation shells that encapsulate the heterophases and inhibit the void growth and coalescence. With further investigations into the underlying theories and developments of methods for industrial implementations, hydrostatic pressurization has the potential to evolve into an effective new method for improving the ductility and fatigue life of engineering components with further development. Full article

Super-hydrophobic surfaces and coatings have stimulated a great deal of research, with the aim being to achieve better wetting properties. Factors such as surface chemistry and roughness play an important role in changing the surface energy, which in turn leads to changes in the wettability. Here, we have analysed the time dependence of the oxide layer and possible surface adsorbates on the surface topography of an Al₅₉Cu₂₅Fe₁₃B₃ quasicrystalline material in relation to changes in the wettability. The quasicrystalline matrix phase was 94% of the sample volume, and it was covered by a very smooth, amorphous oxide layer. The AlB₁₂ and AlFe₂B₂ boron-rich phases were embedded in the quasicrystalline material as a result of the 3 at.% boron addition, which made atomisation of the material a simpler process. Under ambient conditions, the sample was naturally covered by an oxide layer; therefore, it is referred to as “surfenergy” to distinguish it from the conventional surface energy of a bare quasicrystal surface. The growth of the oxide layer with atmospheric ageing and annealing at 500 °C in air for various times was investigated for both cases. The phase most prone to oxidation was the boron-rich AlFe₂B₂, which influenced the topography of the surface and accordingly the wetting behaviour of the specimen. We demonstrated that the surfenergy depends on the polar component, which is the most sensitive to the operating conditions. A correlation between the surfenergy components and the surface roughness was found. In addition, theoretical models to determine the wettability were included. Full article

Based on the principles of mass conservation, chemical equilibrium, and electron charge neutrality, a thermodynamic equilibrium system was established for the nickel-cobalt-manganese sulfate leaching solution in the recovery process of spent lithium-ion batteries. By changing the ion concentration in the system, calculating the pH value, and identifying the complexes of Cu²⁺, Fe³⁺, PO₄^3-, Al³⁺, and F⁻ in the system, the results were obtained and used to draw the thermodynamic diagram. The solution thermodynamic calculation and experiment were combined to purify the nickel-cobalt-manganese-rich leachate. The results show that the main Cu²⁺, Fe³⁺, PO₄^3-, Al³⁺, and F⁻ impurity ions could all be reduced to less than 10 ppm under the optimized process parameters. Full article

The ferroelectric nematic (N_F) phase, characterised by the combination of orientational and polar order, offers unique properties that are challenging to replicate in other systems. Understanding the molecular structure requirements for generating the N_F phase is crucial for the design of new materials with enhanced properties. This study investigates UUQU-4-N, a room-temperature N_F material, using fully atomistic molecular dynamics simulations. UUQU-4-N does not spontaneously form an apolar nematic phase in silico, but exhibits a stable polar nematic configuration akin to the N_F phase. The polar order remains significant and near saturation throughout the simulations. The study also examines the cylindrical pair correlation functions, providing insights into the preferred pairing modes and intermolecular interactions which we can then attribute to specific molecular features. We then simulate structural variants of UUQU-4-N, highlighting the potential for developing further examples of near-room-temperature ferroelectric nematic materials via the manipulation of the fluorination pattern, variations in terminal chain length, and replacement of the difluoromethyleneoxy linker. Full article

Developing high-performance adsorbents for heavy metal (Cr (VI)) removal is essential for sustainable environments, but it is still challenging. Herein, a simple solvothermal method was proposed to fabricate Zr-MOFs (UiO-66), which was innovatively modified by amino groups to enhance the adsorption capacity of Cr (VI). The effects of the content of amino-functionalized ligands on the adsorption capacity and the influence of adsorbent content, solution pH, adsorption time, and adsorption temperature on the adsorption process were systematically investigated. Importantly, the pore structure and defect structure of UiO-66 can be finely regulated by adjusting the amino modification process. The adsorption process was fitted and analyzed using the kinetic model and the isotherm model. Impressively, the adsorption capacity of the amino-modified UiO-66 (UiO-66-NH₂) was greatly improved. These findings indicate that the surface functional group modification of MOFs is a promising method for adjusting their structure and improving their adsorption capacity. Full article

Pipeline leakage causes enormous safety and economic concerns; therefore, sensors which are high-performance and durable are in high demand for improving monitoring accuracy and for avoiding economic loss. In this work, mica-based flexible PZT sensors showed high sensitivity, with 140 mV N⁻¹ and 467 mV N⁻¹ for the output voltage, with regard to the tapping and bending modes, respectively. They can monitor airflow in normal conditions with high sensitivity and a linearity of 424 mV MPa⁻¹ and 0.99, respectively. In the event of a pipeline leak, the mica-based sensors exhibited a rapid response time as short as 0.578 s. Furthermore, they generated distinct voltage levels at different distances from the leakage point, thus providing valuable information for accurately locating the source of the leakage. Full article

The fracture of viscoplastic materials is a complex process due to its time-dependent and plastic responses. Numerical simulation for fractures plays a significant role in crack prediction and failure analysis. In recent years, the phase field model has become a competitive approach to predict crack growth and has been extended to inelastic materials, such as elasto-plastic, viscoelastic and viscoplastic materials, etc. However, the contribution of inelastic energy to crack growth is seldom studied. For this reason, we implement the fracture phase field model coupled with a viscoplastic constitutive in a finite element framework, in which the elastic energy and inelastic energy are used as crack driving forces. The implicit algorithm for a viscoplastic constitutive is presented; this procedure is suitable for other viscoplastic constitutive relations. The strain rate effect, creep effect, stress relaxation effect and cyclic loading responses are tested using a single-element model with different inelastic energy contributions. A titanium alloy plate specimen and a stainless-steel plate specimen under tension are studied and compared with the experimental observations in the existing literature. The results show that the above typical damage phenomenon and fracture process can be well reproduced. The inelastic energy significantly accelerates the evolution of the phase field of viscoplastic materials. For cyclic loadings, the acceleration effect for low frequency is more significant than for high frequency. The influence of the weight factor of inelastic energy $\mathsf{\beta }$ on the force-displacement curve mainly occurs after reaching the maximum force point. With the increase of $\mathsf{\beta }$, the force drops faster in the force-displacement curve. The inelastic energy has a slight effect on the crack growth paths. Full article