Changes In Bond Lengths Research Articles

Investigation of Structural and Thermal Properties of Mg(ClO4)2 Based PVC + ZnO Nanocomposite Polymer Electrolytes

PVC+ZnO+Mg(ClO4)2 nanocompistie polymer electrolyte of differnet concentrations of Mg(ClO4)2 electrolytes were prepared using solution casting technique and further characterized using XRD, FTIR and TGA & DTA. The results of XRD suggests that the high amorphous of the PVC/ZnO nanocomposite with x=50 wt.% Mg(ClO4)2. As it due to high amorphous nature it can show a good ionic conductivity. The FTIR peaks shifting may also representing change of bond length and attaining good amorphous nature. The high heat resistance for all the sample can notice for DGA-DTA. Key word: polymer electrolyte, XRD, FTIR, TGA & DTA, Nanofiller

‘Rhythmite’, Ca29(SiO4)8Cl26, an Anthropogenic Phase from the Chelyabinsk Coal Basin (Ural, Russia) with a Complex Modular Structure Related to α-Ca3SiO4Cl2 (‘Albovite’): Crystal Structure, Raman Spectra, and Thermal Expansion

‘Rhythmite’, Ca29(SiO4)8Cl26, an anthropogenic calcium chloride silicate from the Chelyabinsk coal basin (South Ural, Russia), was investigated using chemical microprobe analysis, in situ single-crystal X-ray diffraction analysis (27–727 °C), and Raman spectroscopy. ‘Rhythmite’ is orthorhombic, Pnma: a = 17.0749(6), b = 15.1029(5), c = 13.2907(4) Å, and V = 3427.42(18) Å3 (R1 = 0.045). The crystal structure of ‘rhythmite’ consists of a porous framework formed by Ca-O bonds and SiO4 tetrahedra with additional Ca2+ cations and Cl− anions in the structure interstices. The framework is built up from multinuclear [Ca15(SiO4)4]14+ fundamental building blocks (FBBs) cut from the crystal structure of α-Ca3SiO4Cl2 (‘albovite’). The FBBs are linked by sharing common Ca atoms to form a network with an overall pcu topology. The empirical chemical formula was calculated as Ca29.02(Si7.89Al0.05P0.05)Ʃ7.99O32Cl26 (on the basis of Cl + O = 58). ‘Rhythmite’ is stable up to 627 °C and expands slightly anisotropically (αmax/αmin = 1.40) in the ab and bc planes and almost isotropically in the ac plane (α33/α11 = 1.02) with the following thermal expansion coefficients (×106 °C−1): α11 = 14.6(1), α22 = 20.5(4), α33 = 15.0(3), and αV = 50.1(6) (room temperature). During expansion, the silicate tetrahedra remain relatively rigid with average bond length changes of less than 0.5%. A structural complexity analysis indicates that ‘rhythmite’ is complex, with IG,total = 920.313 (bits/u.c.), which significantly exceeds the average value of structural complexity for silicates and is caused by the modular framework construction and the presence of a large number of independent positions in the crystal structure.

On the Interplay Between Force, Temperature, and Electric Fields in the Rupture Process of Mechanophores.

The use of oriented external electric fields (OEEFs) shows promise as an alternative approach to chemical catalysis. The ability to target a specific bond by aligning it with a bond-weakening electric field may be beneficial in mechanochemical reactions, which use mechanical force to selectively rupture bonds. Previous computational studies have focused on a static description of molecules in OEEFs, neglecting to test the influence of thermal oscillations on molecular stability. Here, we performed ab initio molecular dynamics (AIMD) simulations based on density functional theory (DFT) to investigate the behaviour of a model mechanophore under the simultaneous influence of thermal and electric field effects. We show that the change in bond length caused by a strong electric field is largely independent of the temperature, both without and with mechanical stretching forces applied to the molecule. The amplitude of thermal oscillations increases with increasing field strength and temperature, but at low temperatures, the application of mechanical force leads to an additional increase in amplitude. Our research shows that methods for applying mechanical force and OEEFs can be safely combined and included in an AIMD simulation at both low and high temperatures, allowing researchers to computationally investigate mechanochemical reactions in realistic application scenarios.

Structural, optical and magnetic characteristics of Mg2+- doped (Ba0.94Sr0.06)(Fe0.80Al0.20-xMgx)O3-ẟ (x = 0–0.20) oxides

Perovskite-type ABO3 oxides have attracted immense attention in recent technologies e.g., gas sensors, solar cells, fuel cells, oxygen-permeable membranes, etc. An attempt has been made here to synthesize (Ba0.94Sr0.06)(Fe0.80Al0.20-xMgx)O3-ẟ (x = 0–0.20) oxides using sol-gel method and characterized with regards to phase, Raman and magnetic properties. X-ray diffraction-cum-Rietveld refinement shows the structural transformation from cubic (Pm3m) to hexagonal (P63/mmc) via cubic (Pm3m) + rhombohedral (R3c) and increase of cubic lattice parameter ac = 4.0369–4.1296 Å with magnesium. FT-IR spectra exhibit different vibrational bands at 548, 555, 638, 667, and 692 cm−1, representing the metal-oxygen (M-O-M) bond vibrations (M - Fe, Mg, Al), deformation of MO6 octahedral, and internal changes in bond lengths. No Raman band was appeared for cubic phase with x=0–0.10. Bands between ∼ 250–450 cm−1 assign the tilting, rotation, and asymmetric bending vibrations of Fe – O, Mg – O and Al – O bonds and asymmetric bending mode of (Fe/Mg/Al)O6 octahedra. Oxygen bending vibration, anti-stretching mode and presence of oxygen vacancies lie in the bands of range ∼498–656 cm−1. Maximum coercivity (Hc ∼ 1081 Oe) and remanent magnetization (Mr ∼ 0.033 emu/g) have been observed for x = 0 and found similar variation with ‘x’. The saturation magnetization (Ms) and anisotropic constant (K1) values lie as Ms = ∼ 0.678 – 0.754 emu/g and K1 = ∼ 1.38× 104 – 1.53× 104 erg/cm3, respectively with magnesium (x). Presence of anion vacancies and high coercivity make the materials suitable for industrial applications.

Implications for electronic structures of S-doped graphene nanoribbons from a DFTB algorithm at atomic scale

Self-consistent charge density functional tight binding simulations were used to provide implications for the effect of S atoms’ doping on geometrical structures and electronic states in armchair graphene nanoribbons with different widths. The geometric configurations, energy, charge density differences, Mulliken charges, and molecular orbitals at HOMO and LUMO energy levels are characterized. Besides the changes of bond length and bond angles, the calculation results indicate that the band structures and bandgaps of the graphene nanoribbons is affected by the nanoribbon width as well as S doping positions, where the ribbons exhibit metallic or semiconductor properties. Doping S atoms result significant changes in the charge density differences and Mulliken charges on the atoms near the doped atom. At the same time, the HOMOs and LUMOs also present differences.

Determination of the discreteness correction in dislocation equations for sphalerite crystals

Abstract The discreteness correction for simple lattices has been determined, however, there is still no detailed and rigorous derivation of the discreteness correction for compound lattices due to the relatively complex structure (simple lattices have only one set per slip system, while complex lattices have at least two sets). A lattice dynamics model which takes into account the energy increments caused by changes in bond length and bond angle is constructed for sphalerite crystals and the relationships between discreteness parameters and elastic constants are determined for the slip system. Compared to glide set, the discreteness correction for shuffle set is much larger due to it is mainly contributed by the interactions between nearest neighbor atoms. Based on the results obtained from the model, the dislocations in ZnS crystal are investigated. The theoretical prediction result of Peierls stress for shuffle dislocation closely matches the experimental critical shear stress. It is inferred that the initial plastic deformation of ZnS is closely related to the movement of shuffle dislocations.

Uniaxial Strain Engineering of Anisotropic Phonon in Few‐Layer Violet Phosphorus with High Stretchability for Polarized Sensitive Flexible Photodetector

AbstractThe manifestation of mechanical phenomena in quantum materials at the macroscopic level is intricately linked to pronounced electron‐electron interactions within their lattices, a relationship that becomes especially evident in low‐dimensional materials. Violet phosphorous (VP), a nascent 2D material distinguished by its unique vertically aligned tubular structures, has garnered considerable attention owing to its layer‐dependent electronic bandgap, exceptional carrier mobility, and robust air stability. Herein, a comprehensive exploration of the phonon modes exhibited by few‐layer VP through an integrated experimental‐theoretical approach, focusing on the modulation of their Raman response under the uniaxial strain along a‐axis, b‐axis, and tube direction, respectively, is undertaken. Density functional theory calculations highlight when strain is applied along the a‐ or b‐axis direction, the strain is predominantly mitigated through tube rotational adaptations instead of the change of bond length and bond angle, culminating in a pronounced anisotropic Raman response. Moreover, the strain engineering can effectively optimize the photoelectric response performance of VP, including increase the responsivity ≈2500% and elevate the anisotropic ratio from 2.26 to 3.38. This investigation not only confirms the superior stretchability and impact resistance properties of cross‐structured VP but also establishes the groundwork for exploring the strain‐induced anisotropic optoelectric properties to VP.

Combined non-destructive evaluation of the damage precursors in fused silica optics

Combined non-destructive evaluation methods for fused silica’s damage precursors including UV photothermal weak absorption, ultrafast fluorescence, steady-state fluorescence, Raman spectroscopy, and stress distribution, are proposed to explain the damage mechanism from multiple perspectives. The correlation between each non-destructive characterization method and damage behaviors is simultaneously verified, in general, the damage threshold test of R on 1. The results have shown that regions with high photothermal absorption are accompanied by low damage thresholds, because the photothermal conversion process is associated with laser-induced damage. The damage threshold is also lower at locations of bright ultrafast fluorescence signals with a lifetime ranging from 1.2∼3 ns, as ultrafast fluorescence is associated with high densities of defects. A complementary relationship between the distribution of ultrafast fluorescence and the distribution of photothermal absorption signals is constructed. This indicates that the steady-state fluorescence cannot accurately evaluate the precursor’s damage performance. Furthermore, Raman spectroscopy is utilized to identify the structural changes in bond lengths and angles, as well as locations of damages coinciding with stress distribution.

A Strategy to Mitigate Jahn Teller Effect of Mn-Rich NASICON Framework for Sodium-Ion Batteries.

Mn-based sodium superionic conductors have driven attention to the low-cost advanced cathode materials for sodium-ion batteries (SIBs). However, low-rate capability and unsatisfactory cyclic performance due to the Jahn teller effect of Mn3+ redox couple which occurs from the change in Mn-O bond length at the octahedral site of crystal structure during charge-discharge, eventually limiting their application. Herein, a disordered and sodium deficient NASICON Na4-xMn(FeVCrTi)0.25(PO4)3 (termed as Na4-xMn(HE)) is synthesized to mitigate this Jahn teller effect to achieve high rate and ultrastable cathode material. Interestingly, the as-prepared Na3.5Mn(HE) shows five reversible electron reactions (i.e., Ti3+/Ti4+, Fe2+/Fe3+, V3+/V4+, Mn2+/Mn3+, and Mn3+/Mn4+) and demonstrates 141mA h g-1 at 0.2 C with 80% capacity retention at 1 C after 500 cycles which is far superior to its counterparts binary Mn-based materials. The excellent cyclic performance is due to the remediation of the Jahn teller effect in sodium-deficient entropy-stabilized material. The structural reversibility, enhanced kinetics, and electronic properties are further studied in detail by in situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), and first principal calculations. Na3.5Mn(HE)//HC full cell delivered 89.7 mAh g-1 capacity at 0.2 C. This work sheds light on designing Mn-based cathodes with superior electrochemical performance for wide energy storage applications.

Theoretical investigation of the excited-state intramolecular double proton transfer process of 2,2'-(benzo[1,2-d:4,5-d']bis(thiazole)-2,6-diyl)diphenol.

In this work, the excited state intramolecular double proton transfer (ESIDPT) mechanism of 2,2'-(benzo[1,2-d:4,5-d']bis(thiazole)-2,6-diyl)diphenol (BTAP) is proposed using density functional theory (DFT) and time-dependent DFT (TDDFT). The changes in bond lengths, bond angles and IR vibrational spectra associated with two intramolecular hydrogen bonds of BTAP upon photoexcitation indicate that the hydrogen bonds are strengthened in the excited state, facilitating the ESIDPT process. Investigation of the constructed S1-state potential energy surface proposes that BTAP prefers a stepwise ESIDPT mechanism. Electronic spectra and frontier molecular orbitals (FMOs) are also presented to illustrate the luminescent properties of BTAP.

Structural Evolution of Photoexcited Methylcobalamin toward a CarH-like Metastable State: Evidence from Time-Resolved X-ray Absorption and X-ray Emission.

CarH is a protein photoreceptor that uses a form of B12, adenosylcobalamin (AdoCbl), to sense light via formation of a metastable excited state. Aside from AdoCbl bound to CarH, methylcobalamin (MeCbl) is the only other example─to date─of photoexcited cobalamins forming metastable excited states with lifetimes of nanoseconds or longer. The UV-visible spectra of the excited states of MeCbl and AdoCbl bound to CarH are similar. We have used transient Co K-edge X-ray absorption and X-ray emission spectroscopies in conjunction with transient absorption spectroscopy in the UV-visible region to characterize the excited states of MeCbl. These data show that the metastable excited state of MeCbl has a slightly expanded corrin ring and increased electron density on the cobalt, but only small changes in the axial bond lengths.

Adsorption and Potential CO Gas-Sensing Performance of the Fe-Doped Ti2CO2-MXenes: A First-Principles Study.

The adsorption behaviors and electronic properties of five gas molecules (CO, H2O, NH3, NO, and C2H6O) on the intrinsic Ti2CO2 and Fe-doped Ti2CO2 were calculated and studied based on first principles. The adsorption height, bond length change, adsorption energy, charge transfer, band structure, differential charge, work function, and recovery time of the two gas adsorption systems were discussed, and their sensing performance was evaluated. The results show that the CO gas molecules have the best adsorption energy and charge transfer on Ti2CO2 modified by the Fe atom (Ti2CO2-Fe). The electrical conductivity obviously increases with the decrease of the band gap, which changes from semiconductor to conductor behavior. The reduction of the work function in the Ti2CO2-Fe system weakens the binding of the electron, which improves the electron flow between the substrate and the gas molecules. In addition, the Ti2CO2-Fe system with H2O molecule participation remained the best adsorption effect on CO gas, and the fast recovery time was 625 s at 398 K. Therefore, Ti2CO2-Fe is a prospective material for the advancement of CO gas-sensitive sensors.

Unusual negative thermal expansion of inter-cluster –C–BC–C– bond in carbon rich boron carbide observed using in situ x-ray diffraction technique

Temperature dependent bonding behavior plays a significant role in deciding properties of high temperature ceramics like boron carbide. However, few studies to date have addressed the physical properties of this class of materials with respect to their temperature dependent bonding nature. In addition, materials with the flexibility to accommodate variations in interatomic bonding and lattice vibrations over a wide range of temperatures are less known. In this work, temperature dependent structural analyses of carbon-rich boron carbide microflakes using in situ powder x-ray diffraction techniques (up to 1000 °C) supported by transmission electron microscopy measurements reveal that while most bonds in the rhombohedral structure increase in length with temperature; there is no change in certain bond lengths. However, there is an unusual decrease in length (∼1.03%) of the inter-cluster –C–(central boron)BC–C– without any polyhedral redistribution. This is accompanied by an increase in lattice vibrations without significant alteration to the crystal structure over the wide temperature range studied. Temperature dependent micro-Raman experiments further confirmed the above observations. The above bonding behavior could be directly correlated to the trends in reported results of high temperature conductivity via the model of hole hopping through specific atomic positions of the rhombohedral framework, thus opening the scope to investigate structure–property relationships in high temperature functional materials.

Topological constraints-induced radiation shielding efficiency of SiO2 α-cristobalite polymorphism: Signatures from Hirshfeld pseudo-surfaces

The paper presents a synergetic and comprehensive investigation into γ-radiation shields properties on SiO2 α-cristobalite subject varying external pressures (0<p < 9.1 GPa). Utilizing crystallographic methods involving γ-rays and Hirshfeld pseudo-surface (HPSs) analyses, we explore the structural responses of SiO2 α-cristobalite to external pressure and its consequent impact on MAC and LAC. The study encompasses a broad energy range (0.015<E < 15.0 MeV), employing online tool for analysis. Our findings reveal that the fundamental shielding characteristics of SiO2 α-cristobalite, including (5.809<MAC<0.021 cm2/g), (3.10 × 1023<Neff< 3.74 × 1023 e/g), (10.32<Zeff<12.43), and (10.79<Zeq<11.56), remain reliable across different polymorphic forms within the energy domain and varying pressures. The LAC values exhibit a clear dependency on both incident photon energies where it's LAC ∈ [0.042 to 11.776] cm−1 as pressure elevated on the crystal. This relationship underscores the influence of pressure-induced changes in crystal density on LAC values. Additionally, changes in lattice parameters (4.975<a<4.599 Å) and bond lengths under pressure contribute to this observed variation in the LAC values. Further analysis of the topological constraints (TCs) (i.e., 1.603<Si⋯O < 1.610 Å, 111.42°<O⋯Si⋯O < 112.00°, and 146.49°<Si⋯O⋯Si < 127.80° bending and twisting angles respectively) reveals defined correlations with LAC values.HPS topological analyses were also employed shed light on valuable insights into the mutual forces of interaction between atoms in the crystal unit cell. Changes in external stress lead to transformations in the HPSs, reflecting the impact of pressure on topological constraints. The evolution of HPS volume (i.e., 179.59-35.24 Å3) and area (i.e., 205.73-161.51 Å2) as well as void's volume (i.e., 10.20-0.17 Å3) and surface area (i.e., 46.10-3.12 Å2) within the crystal lattice is also observed, indicating a direct relationship between HPSs, crystal compactness, electron density and radiation effectiveness. These signatures have been correlated with TCs and thus on the γ-rays shield effectiveness.

Catalytic Water Electrolysis by Co-Cu-W Mixed Metal Oxides: Insights from X-ray Absorption Spectroelectrochemistry.

Mixed metal oxides (MMOs) are a promising class of electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Despite their importance for sustainable energy schemes, our understanding of relevant reaction pathways, catalytically active sites, and synergistic effects is rather limited. Here, we applied synchrotron-based X-ray absorption spectroscopy (XAS) to explore the evolution of the amorphous Co-Cu-W MMO electrocatalyst, shown previously to be an efficient bifunctional OER and HER catalyst for water splitting. Ex situ XAS measurements provided structural environments and the oxidation state of the metals involved, revealing Co2+ (octahedral), Cu+/2+ (tetrahedral/square-planar), and W6+ (octahedral) centers. Operando XAS investigations, including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), elucidated the dynamic structural transformations of Co, Cu, and W metal centers during the OER and HER. The experimental results indicate that Co3+ and Cu0 are the active catalytic sites involved in the OER and HER, respectively, while Cu2+ and W6+ play crucial roles as structure stabilizers, suggesting strong synergistic interactions within the Co-Cu-W MMO system. These results, combined with the Tafel slope analysis, revealed that the bottleneck intermediate during the OER is Co3+ hydroperoxide, whose formation is accompanied by changes in the Cu-O bond lengths, pointing to a possible synergistic effect between Co and Cu ions. Our study reveals important structural effects taking place during MMO-driven OER/HER electrocatalysis and provides essential experimental insights into the complex catalytic mechanism of emerging noble-metal-free MMO electrocatalysts for full water splitting.

Investigating adsorption characteristics and electronic properties of Clar’s Goblet and beyond

Our study explores the structural diversity and stability of Clar’s Goblets (CG) derivatives, nCG-mC, analyzing dihedral angles and bond lengths to reveal various planar and non-planar conformations. We highlight the exceptional stability of 3CG-7C through binding energy assessments. Examining electronic, magnetic, and optical properties, we show how CG unit variations impact energy gaps and molecular orbitals. Functionalizing 3CG-7C enhances stability and electronic properties, suggesting diverse applications. Adsorption studies of chlorinated methane on 3CG-7C-NO demonstrate stable interactions, confirmed by changes in bond lengths and Mulliken charges, underscoring the potential of CG derivatives in various fields.

Ti3C2Tx (T = F, O, OH) as a sensor for dissolved gas in transformer oil: A theoretical study

Power transformer is the hub of power grid energy transmission, and its safe and reliable operation is very important to power grid. In this paper, based on density functional theory, Ti3C2Tx (T = F, O, OH) material was used as sensing material. The adsorption models of Ti3C2Tx and dissolved characteristic gases (H2, CH4, C2H4, C2H6, C2H2, CO, and CO2) in transformer oil are constructed. The adsorption distance, bond length change, adsorption energy, charge transfer and density of states (DOS) of the adsorption system were analyzed. The results showed that the gases can adsorb on the surface of Ti3C2Tx spontaneously. Specifically, CO2, CO, C2H2 and C2H4 exhibit a strong adsorption effect on Ti3C2(OH)2, forming hydrogen bonds or chemical bonds, accompanied by large charge transfer and adsorption energy, indicating Ti3C2(OH)2 shows a good sensing performance for these gases.

Adsorption of Gadolinium Bisphthalocyanine on Atomically Flat Surfaces: Comparison of Graphene and Hexagonal Boron Nitride from DFT Calculations

We studied the noncovalent interactions of gadolinium bisphthalocyanine (GdPc2) with cluster models for graphene and hexagonal boron nitride (hBN) of variable size by using the PBE functional of the generalized gradient approximation in conjunction with Grimme’s dispersion correction and a DND double numerical basis set (that is, PBE-D2/DND). We found that in terms of the bonding strength, changes in the Gd-N bond lengths, the charge and spin of the Gd central ion, and the spin of the GdPc2 molecule, the behaviors of the graphene- and hBN-based model systems are rather similar. As expected, when increasing the size of the graphene and hBN cluster models, the strength of the interaction with GdPc2 increases, in which the bonding with the hBN models is usually stronger by a few kcal/mol. One of the main questions addressed in the present work was whether a change in the antiferromagnetic spin alignment to a ferromagnetic one, which is typical for GdPc2, is (at least theoretically) possible, as it has been observed previously for a number of graphene models when a smaller basis set DN was employed. We found that the use of a larger DND basis set dramatically reduces the occurrence of ferromagnetic adsorption complexes but does not exclude this possibility completely.

Terahertz spectroscopic study of the dehydration process and hydrogen bonding network of DL-glutamic acid and its monohydrate

The dehydration process involves the dissociation and reorganization of hydrogen bonds, and for the characterization of the dehydration process of amino acid-based hydrates, the analysis of their molecular vibrational modes and hydrogen bonds is still challenging nowadays. In this paper, the dynamic process of the dehydration of DL-glutamic acid monohydrate was monitored using terahertz spectroscopy. Quantitative simulations were performed on DL-glutamic acid and its monohydrate, with vibrational mode assignments and hydrogen bonding network analysis based on Density Functional Theory (DFT) for terahertz absorption peaks. The results show that the hydrogen bond stretching vibration is intermixed with atomic vibration. Specifically, the intermolecular hydrogen bond O4-H9···O2 of DL-glutamic acid exhibits a stronger vibration at 2.43 THz. Furthermore, the intramolecular hydrogen bond O5-H11···O4 in DL-glutamic acid monohydrate shows significant changes in bond length and bond angle at 1.85 THz. These findings validate the effectiveness of terahertz spectroscopy in monitoring the transformation process of the hydrate and the analysis of the hydrogen bond.

Tracking nuclear motion in single-molecule magnets using femtosecond X-ray absorption spectroscopy

The development of new data storage solutions is crucial for emerging digital technologies. Recently, all-optical magnetic switching has been achieved in dielectrics, proving to be faster than traditional methods. Despite this, single-molecule magnets (SMMs), which are an important class of magnetic materials due to their nanometre size, remain underexplored for ultrafast photomagnetic switching. Herein, we report femtosecond time-resolved K-edge X-ray absorption spectroscopy (TR-XAS) on a Mn(III)-based trinuclear SMM. Exploiting the elemental specificity of XAS, we directly track nuclear dynamics around the metal ions and show that the ultrafast dynamics upon excitation of a crystal-field transition are dominated by a magnetically active Jahn-Teller mode. Our results, supported by simulations, reveal minute bond length changes from 0.01 to 0.05 Å demonstrating the sensitivity of the method. These geometrical changes are discussed in terms of magneto-structural relationships and consequently our results illustrate the importance of TR-XAS for the emerging area of ultrafast molecular magnetism.