Character Of Chemical Bond Research Articles

Correlation between chemical bond characteristics and microwave dielectric properties of KLa(MoO4)2 ceramics

This investigation details the synthesis process of KLa(MoO4)2 ceramic utilizing a solid-state route method, alongside an analysis of its structural characteristics and the correlation between chemical bonds and microwave dielectric properties. The KLa(MoO4)2 phase was identified to possess a Monoclinic structure (C2/c space group). Sintering the sample at 820 °C resulted in a maximum relative density of 94.6% and impressive microwave characteristics: εr = 9.63, Q×f = 50,100 GHz, and τf = -75.7 ppm/°C. Correlations between relative density and dielectric properties were observed. Further, application of the P-V-L bond theory facilitated the analysis of chemical bond parameters and their impact on microwave dielectric properties. The dielectric properties were correlated to chemical bond iconicity, packing fraction, lattice energy and bond valences.

Significant temperature tunability of the band gap in two-dimensional materials

Two-dimensional (2D) materials have great attentions due to their novel physical and chemical properties. The band gap Eg plays a significant role in influencing their applications, which can be changed by the temperature. In this work, taking the Group-IV materials (graphene, silicene, germanene, and stanene) as the examples, we first study the temperature-dependent Eg by employing the state-of-the-art electron-phonon renormalization calculations. It shows that the primary Eg at K-point is almost unchanged while that at Γ-point decreases directly with temperature increase in all the systems (e.g., Eg reduction in stanene from 100 K to 500 K is 0.006 eV at K-point and 0.148 eV at Γ-point, respectively). The differences are originated from the different chemical bond characteristics at band edges, which are π-bonding at K-point but (σ*) σ (anti-) bonding at Γ-point. The latter are more sensitive to the temperature-induced vibrations, such as the out-of-plane acoustic phonon modes in the three buckling systems. The strong sensitivity of σ-bonding to the vibrations can be further examplified by another four 2D systems (P4, InSb, MgCl2, and C2F2), screening from the database MatHub-2d. This phenomenon offers the temperature tunability for the band gaps at Γ-point of 2D materials, which may have more application significances in optoelectronics.

A novel LiMg2P3O10 microwave dielectric ceramic for ultra-wideband dielectric resonant antenna applications

In pursuit of the objective of implementing fifth-generation communication technology, a LiMg2P3O10 microwave dielectric ceramic was developed in this study, and an ultra-wideband dielectric resonant antenna was fabricated. Rietveld refinement confirmed that the monoclinic crystal structure of LiMg2P3O10 ceramics is constituted of MgO6 octahedral chains and shared angle PO4 tetrahedra. The impact of chemical bond characteristics on properties was explored through P-V-L theory. The primary contributions to the intrinsic properties were investigated through infrared spectroscopy. The LiMg2P3O10 ceramics sintered at 830 °C were found to have the best microwave dielectric properties (εr = 6.16, Q × f = 33,573 GHz (at 15.538 GHz), and τf = −35.6 ppm/°C). A novel ultra-wideband dielectric resonant antenna with 53.7 % relative bandwidth, 6.53 dBi maximum gain and 81.7 % radiation efficiency was designed and fabricated. Its wide ultra-wideband characteristics makes it suitable for signal transmission in modern wireless communication systems.

Quantum Chemical Approaches for Manipulation and Evaluation of Intracage Microelectric Field Strength of Molecular Containers in Y@C64 and Y@C64X4 (X = Cl, F, and H, Y = NH4Cl, H3O-Cl, and 2H2O).

The effect of an oriented external electric field (EEF) on materials has led to the ongoing development, which stimulates us to consider whether intracage microelectric fields (IMEFs) can be used to substitute for the EEF. Focusing on the manipulation and evaluation of the IMEF of asymmetric molecular containers, the host-guest compounds of interesting pineapple-shaped Y@C64X4 (X = vacant, Cl, F, and H; Y = NH4Cl, H3O-Cl, and 2H2O) are theoretically constructed and the strength of the IMEF was evaluated by the intrapotential energy surface analysis by using the point charge (q = +1) scanning method. Interestingly, the left and right halves of each cage are like two IMEFs connected in reverse series. Both the addition of four X atoms and the orientation of the guest can sensitively influence the IMEF's strengths and directions of both half cages and further determine the entire cage's IMEF. Subsequently, the IMEF can sensitively change the binding characteristics and properties of the guest species. Therefore, the manipulation and evaluation of the IMEF can be achievable. This work may provide support for an asymmetric molecular container with an IMEF to manipulate the novel structural and chemical bond characteristics of the guest species.

Effects of (Cd1/3Sb2/3)4+ co-substitution on the crystal structure, chemical bond characteristics, and microwave dielectric properties of CeO2-ZrO2-MoO3 ceramics

In this paper, Ce2[Zr1−x(Cd1/3Sb2/3)x]3(MoO4)9 (CZ1−x(CS)xM, x = 0.01–0.1) were prepared via the conventional solid-state method. XRD and Rietveld refinement analyses confirmed the formation of a single-phase CZ1−x(CS)xM solid solution with a space group of R-3c(167). The sintering behavior of the samples were investigated using SEM and relative density, which showed that optimal densification for CZ0.98(CS)0.02M ceramics were achieved at 675 °C with an average grain size of 1.70 μm. The P-V-L theory revealed the significant influence of the Zr(Cd/Sb)-O bond on the dielectric properties of CZ1−x(CS)xM ceramics. Furthermore, far-IR reflectance spectra indicated that the measured dielectric loss value (1.04 × 10−4) is in line with the calculated value (1.60 × 10−4), suggesting a substantial impact of phonon oscillation absorption on the dielectric properties. Notably, CZ0.98(CS)0.02M ceramics demonstrated superior performance at 675 °C, with εr = 10.44, Q × f = 93,152 GHz (at 12.96 GHz), and τf = −17.73 ppm/°C.

Relationship between chemical bond characteristics and microwave dielectric properties of low temperature sintering CoO-V2O5 ceramics

The two most fundamental compositions within the CoO-V2O5 family, namely CoV2O6 and Co2V2O7 ceramics, were synthesized using the traditional solid-state method. The microwave dielectric properties of both ceramics were investigated for the first time. The P-V-L bond theory was used to analyze the correlation between their microwave dielectric properties and chemical bond characteristics. The CoV2O6 ceramic exhibits a γ phase (εr = 11.6, Q×f = 39,177 GHz, and τf = −15 ppm/°C) when sintered at 660 °C. However, it experiences a phase transformation from the γ phase to the α phase at 690 °C, which causes the dielectric properties to degrade. The Co2V2O7 ceramic demonstrates excellent dielectric characteristics (εr = 9.4, Q×f = 88,645 GHz, and τf = −37 ppm/°C) at 720 °C. Importantly, its sintering temperature can be lowered to 660 °C while still maintaining a good combination of microwave dielectric properties (εr = 7.7, Q×f = 75,887 GHz, and τf = −58 ppm/°C). It is found that Co2V2O7 exhibits a low dielectric loss due to relatively high lattice energy resulting from the contribution of Co–O bonds. CoV2O6, on the other hand, shows a lower sintering temperature because it contains more V2O5, which acts as an effective sintering aid. These two ceramics both exhibit good chemical compatibility with aluminum and are promising candidates for applications in low-temperature and ultra-low-temperature co-fired ceramics (LTCCs and ULTCCs) that operate in the microwave frequency range or higher.

Ag decoration as a strategy to enhance the methanol and ethanol sensing on the biphenylene sheet

Efficient, miniaturized, and highly sensitive sensors to detect volatile organic compounds (VOCs) have become vital tools to minimize pulmonary diseases and other sicknesses. Therefore, the adsorption capabilities of methanol and ethanol were investigated on the recently synthesized biphenylene (BPN) monolayer using the Ag decoration. Although the pristine BPN has suitable VOCs adsorption, the lower adsorption strength and the small charge transfer affect the sensor performance. On the other hand, the Ag decoration increases the gas sensitivity, with moderate chemisorption values of –0.67eV and –0.83eV for methanol and ethanol, respectively, and transitory chemical bond character (neither ionic nor covalent) between Ag atoms and the –OH radical. In addition, significative work function changes (Δϕ > 0.23 eV), huge charge transfer, and rapid recovery times at room temperature, τ = 0.18s and τ = 87.9s for methanol and ethanol, respectively, indicate a great VOCs sensitivity. The feasibility of the Ag-BPN and Ag-BPN + VOCs systems by ab initio molecular dynamics (AIMDs) was analyzed, which confirms that both systems are stable at 500K. Therefore, the DFT calculations employed here can guide experimentalists in exploring new miniaturized sensor devices based on BPN.

EVOLUTION OF ELECTRONIC PROPERTIES ALONG THE PATH FROM COVALENT TO TETREL BOND IN THE SYNTHESIS OF TETRAPHENYL SUBSTITUTED COMPOUNDS

The evolution of the electronic characteristics of chemical bonds formed and broken along the path of the bimolecular nucleophilic substitution reaction at a tetrahedral central atom, which is the Tt = C, Si, Ge atom, is analyzed. For this purpose, the reaction paths of the step-by-step replacement of the chlorine atom with the phenyl fragment have been modeled, and the energy characteristics of the equilibrium initial, transition and nal states were obtained within the framework of DFT. For different reaction centers, which are atoms of the carbon group (Tt), changes in electron density distributions, shifts in the positions of the extremes of the total static and electrostatic potential for the forming C-Tt and breaking Tt-Cl bonds along the reaction path are compared. Quantitative criteria have been re ned that determine the region of existence of a typical noncovalent tetrel bond Tt...Cl, allowing it to be distinguished from a covalent one. Establishment of the properties of the transition state stabilizing tetrel bond may be useful for monitoring the ef cient synthesis of covalent organic framework precursors.

Effect of chemical bond characteristics on the microwave dielectric properties of olivine-type LiTmRO4 (R = Si, Ge) ceramics

Effect of chemical bond characteristics on the microwave dielectric properties of olivine-type LiTmRO4 (R = Si, Ge) ceramics

Molecular structure of coal macerals and thermal response behavior of their chemical bonds obtained by structural characterizations and molecular dynamics simulations

Clarifying the microscale reaction mechanism of macerals is crucial for achieving efficient thermal utilization of coals. Herein, we analysed the chemical structures of two coals used in coking for their macerals employing 13C NMR, FTIR, and XPS to build molecules. The pyrolysis behaviours of coals and their macerals were accessed through molecular dynamics of calculating chemical bond characteristics. Results show that inertinite with higher maturity is rich in aromatic, vitrinite with stronger thermal-reactivity is rich in aliphatic, and macerals of coking and gas coal have more advantages in hydrocarbon generation and branch-chain development, respectively. Based on the validated and optimized molecules containing C, H, O, and N elements, it is found that not only the bond lengths of the longest and shortest in macerals from gas coal are greater than those from coking coal, but the thermal response of heteroatom bonds in the former is almost twice that of the later. Moreover, vitrinite and inertinite of coking coal have N–H cleavage to produce active hydrogen in the late stage of bond dissociation, while gas coal lacks this feature. These explain why the pyrolytic properties of different coals and their macerals have variability, guiding the rational selection of coal-based feedstock for industry.

Dominant mechanisms of thermo-mechanical properties of weberite-type RE3TaO7 (RE=La, Pr, Nd, Eu, Gd, Dy) tantalates toward multifunctional thermal/environmental barrier coating applications

Weberite-type RE3TaO7 (RE=La, Pr, Nd, Eu, Gd, Dy) tantalates have been studied as multifunctional thermal/environmental barrier coating materials with working temperatures above 1500 K. This study proposes the dominant mechanisms of their thermo-mechanical properties. The relative ionicity of the RE-O bonds increased with increasing RE+3 ionic radius, which weakened the bond strength and led to decreases in Young's modulus and hardness. A model was proposed to derive the high-temperature thermal conductivity based on the relationship between the phonon thermal conductivity and temperature, and the thermal radiative conductivity was estimated. RE3TaO7 exhibited a lower thermal conductivity than other fluorite-related oxides because its weak bond strength could slow down the phonon speed and enhance the an-harmonic vibrations of the lattices. At low temperatures, the RE atomic weight was a better descriptor of the thermal conductivity than the RE+3 ionic radius, and which could aid in further regulating the thermal conductivity. The thermal expansion coefficients of the different axes were affected by both RE-O and Ta-O bonds when weak RE-O bonds dominated the linear thermal expansion. The low oxygen ion conductivity derived from the strong covalent Ta-O bonds, which increased the activation energy for oxygen hopping in lattices of RE3TaO7. This study elucidates the dominant mechanisms of properties from the characteristics of crystals and chemical bonds, which are significant for high-temperature applications of tantalates.

Bond theory, vibrational spectroscopy, and dielectric responses of trirutile ATa2O6 (A = Mg, Ni) microwave ceramics

This study established the connection between structure and dielectric responses by synergistically evaluating the chemical bond characteristics and lattice vibrational spectroscopies of trirutile ATa2O6 (A = Mg, Ni) microwave ceramics. The MgTa2O6 ceramic exhibits a uniform grain size distribution and a dense microstructure, with dielectric characteristics at microwave range of a εr value of 27.27, a high Q×f value of 109,203 GHz (8.73 GHz), and a τf of approximately 53.38 ppm/°C when sintered at 1300 °C, while the NiTa2O6 ceramic presents a smaller average grain size and minor micropores, with dielectric characteristics at microwave range of εr = 24.58, Q×f = 27,610 GHz (9.25 GHz), and τf = 33.94 ppm/°C, sintered at 1250 °C. The structural refinement and atomic arrangements confirm a trirutile structure along the [001], [100], and [3 3‾1‾] zone axes. Ta–O bonds are found to contribute the most to the ionic character of a bond, bond susceptibility, lattice stability, thermal expansion behaviors, and strength of bonding ability, indicating their significant influence on dielectric polarization, lattice stability, and temperature coefficient of resonant frequency. Raman scattering spectra analysis reveals that the A1g mode near 700 cm−1 mainly controls the Raman vibrational behaviors. The theoretical dielectric properties calculated from the infrared spectrum and dielectric properties analysis consistent with the measured dielectric performances, suggesting that the dielectric characteristics at the microwave range are mainly determined by the oscillatory absorption of structural phonons, with the first two modes at 210.48 cm−1 and 232.87 cm−1 contributing 72.02% to the εr value and 90.45% to the tanδ value, respectively.

Crystal structure and chemical bond characteristics for Li2Zn2(MoO4)3 microwave dielectric ceramics for ULTCC application

Li2Zn2(MoO4)3 (LZMO) ceramics were prepared via solid-state method. XRD analysis showed LZMO phase had an orthorhombic structure with Pnma space group, representing the only crystalline phase. Ceramic sintered at 600 °C exhibited high relative density (96.2 %) and dense microstructure, demonstrating optimal microwave dielectric properties: εr = 10.38, Q×f = 69,400 GHz, and τf = -72.81 ppm/°C. Further investigations revealed close correlation between εr and polarizability, emphasizing greater influence of relative density on Q×f than packing fraction. Increase in distortion of [Li/ZnO6] octahedra resulted in deterioration of ceramics' τf. Computation based on P-V-L theory revealed significant impact of ionicity, lattice energy, and bond energy on εr, Q×f, and τf, with Mo-O bonding dominating ceramics' microwave dielectric properties. Raman spectroscopy analysis showed majority of Raman bands attributed to vibrational modes of Mo-O bonds. LZMO ceramics have great potential in ULTCC field.

The nature of the NO bond in amine oxides

AbstractDespite the ubiquitous presence of amine oxides in chemistry, there is no consensus about the nature of the NO bond in these compounds. In this work, we have used electron density analysis to investigate the nature of this bond in substituted amine oxides, R3NO, and have compared it with the nature of the NO bond in hydroxylamines, R2NOR, and model molecules that have well‐established chemical bond character. The results showed that the NO bond length and relative stability are proportional to the inductive effect of the substituents. Quantum chemical topology, natural bond orbitals (NBO), and natural resonance theory (NRT) analyses indicated that the NO bond is polar covalent in all the studied amine oxides, but the ionic contribution is different. NBO and NRT analyses revealed that molecules with more electronegative substituents have strongly delocalized NO and NR bonds, whereas molecules with electropositive substituents have localized bonds.

Multi-objective optimization of one-part alkali-activated mortar mixes using Taguchi-Grey relational analysis

In the context of the contemporary emphasis on sustainability within the realm of construction, there is a notable surge in attention towards one-part alkali-activated (OP-AA) materials. This is primarily attributed to their enhanced performance and reduced carbon emissions as compared to conventional OPC-based concrete. In the present investigation, Taguchi and Taguchi- Grey relational analysis (GRA) methodologies were employed to execute the experimental design, involving three input parameters, each considered at three levels, to generate an L9 orthogonal array. An attempt was made to assess the impact of different parameters, such as ground granulated blast furnace slag (GGBFS) to fly ash (FA) ratio - (S/F), water-to-binder ratio - (W/B), and percentage of Na2O - (N), on the slump flow, setting time, and compressive strength characteristics and hence to optimize the proportions of the OP-AA mortar blends. The results revealed that optimum parameter levels for multi-objective optimization corresponded to S/F = 1, W/B = 0.45, and N = 5%. For these parameter levels specified, the corresponding values of slump flow, initial setting time, final setting time, and 28 days compressive strength were 208 mm, 285.4 min, 990.4 min, and 36.52 MPa, respectively. In addition, to gain insights into their mineral composition, morphology, and chemical bond characteristics, microstructural characterization such as X-ray diffraction (XRD), Field emission scanning electron microscope (FESEM), and Fourier transform infrared spectroscopy (FTIR) were also conducted on selected OP-AA mortar mixes. The microstructural examination unveiled the predominant formation of hydration products, such as C/N -A-S-H gels, in OP-AA mortar blends, resembling those found in conventional alkali-activated materials (AAMs). During the validation phase, an assessment was conducted by comparing the actual experimental results with the predicted values obtained through regression equations. The outcome of this comparison revealed that the proposed optimum mix parameter levels demonstrated the effectiveness of both the Taguchi and Taguchi-GRA approaches.

Chemical bond characteristics and microwave dielectric properties of high-Q × f Li3+xMgNbO5Fx (0 ≤ x ≤ 1.25) ceramics for LTCC applications

Chemical bond characteristics and microwave dielectric properties of high-Q × f Li3+xMgNbO5Fx (0 ≤ x ≤ 1.25) ceramics for LTCC applications

Cracking behavior of Sm2O3 ceramics and enhanced microwave dielectric properties with MgO addition: Insights from chemical bond characteristics and microstructure

Monoclinic Sm2O3 ceramics were prepared using the conventional solid-state sintering method. The influences of sintering temperature on structure, morphology, and performance of Sm2O3 ceramics were studied systematically. The excellent microwave dielectric properties (εr = 21.95, Q × f = 47,000 GHz, and τf = +30.15 ppm/°C) were achieved in Sm2O3 ceramic sintered at 1550 °C for 4 h. Interestingly, varying degrees of cracking were observed after the sintered samples were placed for a short time, with the extent depending on the sintering temperatures. The reasons for cracking were analyzed through chemical bond characteristics and microstructure. The analysis of bond valence and microstructure revealed that Sm2O3 ceramics sintered at higher temperatures exhibited larger bond strain index, global instability index, and interplanar spacings. These results suggest that the cracking of Sm2O3 ceramics originates from inner stress resulting from structural variations caused by variations in sintering temperatures. The effect of MgO addition on microwave dielectric properties and stability of Sm2O3 ceramics was also investigated. Phase identification and elemental distribution indicated that MgO existed as a secondary phase. The Sm2O3 ceramic with 20 wt% MgO addition exhibited optimal microwave dielectric properties: εr = 17.72, Q × f = 61,100 GHz, and τf = +2.4 ppm/°C. Importantly, cracking was not observed when MgO addition amounts were 5 wt% or higher. The attractive microwave dielectric properties and favorable stability confirm the possibility of the 5G applications for Sm2O3/MgO composite ceramics.

Physics infused machine learning force fields for 2D materials monolayers

Large-scale atomistic simulations of two-dimensional (2D) materials rely on highly accurate and efficient force fields. Here, we present a physics-infused machine learning framework that enables the efficient development and interpretability of interatomic interaction models for 2D materials. By considering the characteristics of chemical bonds and structural topology, we have devised a set of efficient descriptors. This enables accurate force field training using a small dataset. The machine learning force fields show great success in describing the phase transformation and domain switching behaviors of monolayer Group IV monochalcogenides, e.g., GeSe and PbTe. Notably, this type of force field can be readily extended to other non-transition 2D systems, such as hexagonal boron nitride (h BN), leveraging their structural similarity. Our work provides a straightforward but accurate extension of simulation time and length scales for 2D materials.

Microwave dielectric properties and sintering behavior of a novel low-cost lightweight,middle-εr Na2Ti6O13 ceramics

In order to develop novel lightweight low-cost microwave dielectric ceramics (MDCs), middle-εr Na2Ti6O13 ceramics were prepared by a traditional solid-state reaction method and the sintering behavior and microwave dielectric properties ((MDPs) were investigated. The detailed structural parameters of the Na2Ti6O13 ceramics were obtained by X-ray diffraction and Rietveld refinement, and the chemical bond characteristics of the structures were further studied using Raman spectroscopy. The relative density of the ceramics and scanning electron microscopy (SEM) images show that density and porosity are important factors affecting the dielectric properties of the samples. Based on the acquired Raman spectra and complex chemical bond theory (P–V–L theory), the chemical bond properties were calculated and analyzed, and the effects of intrinsic factors on the MDPs were investigated. The MDPs of Na2Ti6O13 ceramic sintered at 1025 °C were as follows: εr = 34.3, Q×f = 33660 GHz, and τf = 40.3 ppm/°C.

Molecularly imprinted polymer based on magnetic porous cellulose for specific adsorption of tetracyclines: Preparation, characterization, property evaluation, and application

A magnetic porous cellulose molecularly imprinted polymer (MPCMIP) based on tetracyclines was prepared with Fe3O4 as the magnetic core and porous cellulose as the carrier. The appearance, characteristic chemical bonds, crystal structure, thermal stability, and magnetism of MPCMIP were systematically characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and vibrating sample magnetometry. The adsorption performance of MPCMIP to tetracycline, demeclocycline, and minocycline were comprehensively investigated by static adsorption, dynamic adsorption, and adsorption experiments under different temperature and pH conditions. MPCMIP performed good adsorption performance and fast adsorption rate for tetracyclines, and adsorption quantity and efficiency of MPCMIP were four times and twice that of traditional molecularly imprinted polymer (MIP), respectively. It can be seen that the introduction of magnetic porous cellulose effectively improved the adsorption performance of the MIP. Moreover, MPCMIP showed good adsorption stability under different temperature. The adsorption properties of MPCMIP under neutral and alkaline conditions were better than those under acidic conditions. Selective experiment was conducted with the amoxicillin and levofloxacin as the coexisting interfering compounds for the three tetracyclines. The results showed that MPCMIP possessed good imprinting effect with the impact factor values for tetracycline, demeclocycline, and minocycline of 1.49, 1.66, and 3.14, respectively. Compared with interfering compounds, MPCMIP showed excellent selectivity to tetracyclines with the selectivity factor up to 36.9. Moreover, MPCMIP exhibited better selectivity towards tetracyclines than traditional MIP according to the higher imprinting and selectivity factors of MPCMIP. The simulation of hydrogen bonding interaction and electrostatic potential analysis determined that MPCMIP mainly adsorbed TCs through the hydrogen bonding and electrostatic interactions. The results of adsorption/desorption cycling experiments indicated that MPCMIP had good reusability with 95.5% of adsorption performance after four cycles. Finally, MPCMIP combined with high-performance liquid chromatography were triumphantly used to adsorb and detect the tetracycline, demeclocycline, and minocycline in river, beef, and milk samples. Furthermore, the MPCMIP method exhibited higher sensitivity, accuracy, and selectivity than the traditional method.