Lattice Cohesion Research Articles

Exploring a new creatininium crystalline salt with succinic acid organic counterion: Structural establishment, spectroscopic analysis and theoretical simulation

This study elucidates the structural, vibrational, and electronic properties of a novel proton-transfer system derived from creatinine and succinic acid named bis (creatininium) succinate (I). Fourier maps and geometric evaluations confirm protonation at the imine sites. Spectroscopic analyses, involving both IR and Raman techniques, were conducted, highlighting the vibrational characteristics of key functional groups. The theoretical predictions of structural parameters and vibrational frequencies align well with experimental findings. Frontier Molecular Orbital analysis emphasized the distinct localization of HOMO and LUMO, hinting at potential intramolecular charge transfers. Molecular Electrostatic Potential maps provided a visual testament to regions of electron density and scarcity, offering predictive insights into reactivity. Hirshfeld surface analysis and fingerprint plots further illuminated the intermolecular interactions within the crystal structure, underscoring the significance of hydrogen bonding in lattice cohesion. The results present a comprehensive understanding of the compound's behaviour, potentially impacting fields demanding molecular stability and specificity.

Interstitial concentration effects on incipient plasticity and dislocation behaviors of face-centered cubic FeNiCr multicomponent alloys based on nanoindentation

• The interstitial concentration effects on dislocation behavior and incipient plasticity of a typical equiatomic FeNiCr multicomponent alloy are newly investigated via systematic nano-mechanical experimental study. • The dislocation nucleation of FeNiCr alloy processes in a manner of heterogenous nucleation mode with an activation volume exceeding one single principal atom, by the exchange between primary atoms and vacancies. • Interstitial-atom effects severely suppress the mobility of dislocations in the FeNiCr multicomponent alloys, which hinder the occurrence of pop-ins. • With increasing the concentration of interstitial atoms, both the critical shear stress and activation volume corresponding to the onset of incipient plasticity are enhanced. Interstitial atoms that commonly occupy the octahedral or tetrahedral interstices of face-centered cubic (FCC) lattice, can significantly affect the dislocation behaviors on deformation. Recently, interstitial doping has been applied to tune the mechanical properties of the emerging multicomponent, often termed high-entropy alloys (HEAs) or medium-entropy alloys (MEAs). However, the fundamental mechanisms of the dislocation nucleation and the onset of plasticity of interstitial multicomponent alloys governed by the concentration of interstitial atoms are still unclear. Therefore, in the present work, an instrumented nanoindentation was employed to investigate the interstitial concentration effects of carbon atoms on single FCC-phase equiatomic FeNiCr MEAs during loading. The results show that the pop-in events that denote the onset of incipient plasticity are triggered by the sudden heterogeneous dislocation nucleation via the primary atoms-vacancy exchange with the instant stress field, regardless of the interstitial concentration. Moreover, the measured activation volumes for dislocation nucleation of the FeNiCr MEAs are determined to be increased with the interstitial concentration, which definitely suggests the participation of interstitial atoms in the nucleation process. Besides, it is also found that the average value measured in statistics of the maximum shear stress corresponding to the first pop-in is enhanced with the interstitial concentration. Such scenario can be attributed to the improved local change transfer and lattice cohesion caused by the interstitial atoms with higher concentrations. Furthermore, the significant drag effect of interstitial carbon atoms hinders the mobile dislocations before exhaustion, which severely suppresses the subsequent occurrence of pop-in events in the carbon-doped specimens. The work gives a microscale view of interstitial effects on the mechanical properties of multicomponent alloys, which can further help to develop new interstitial strengthening strategies for structural materials with remarkable performance.

Effect of interstitial oxygen and nitrogen on incipient plasticity of NbTiZrHf high-entropy alloys

In this work, instrumented nanoindentation was employed to investigate the effect of interstitial oxygen or nitrogen addition on the incipient plasticity and dislocation nucleation in a body-centered cubic NbTiZrHf high-entropy alloy (HEA) at loading rates of 10–1000 µN/s. We conducted quantitative statistical analysis and density functional theory (DFT) calculations to identify the role of interstitial oxygen/nitrogen during the onset of plasticity. Synchrotron X-ray diffraction and transmission electron microscopy were also performed to confirm that the oxygen/nitrogen atoms were indeed present as interstitial solutes. These interstitial solutes could increase the critical shear stress required to initiate plasticity, and nitrogen yielded a larger hardening effect than oxygen. The activation volumes were evaluated to be about 2–3 atomic volumes, indicating cooperative migration of multiple atoms during the dislocation nucleation, and neither oxygen nor nitrogen appeared to significantly affect this activation process. Hardness tests were also carried out and the result demonstrated that the enhancement of the critical shear stress for incipient plasticity was not caused by the traditional solid-solution strengthening mechanism. DFT calculations revealed that oxygen/nitrogen interstitials induced local charge transfer and improved the lattice cohesion, which was probably responsible for the enhanced pop-in load/stress in the current interstitially alloyed HEAs.

Noncovalent Se···O Conformational Locks for Constructing High‐Performing Optoelectronic Conjugated Polymers

Noncovalent conformational locks are broadly employed to construct highly planar π-conjugated semiconductors exhibiting substantial charge transport characteristics. However, current chalcogen-based conformational lock strategies for organic semiconductors are limited to S···X (X = O, N, halide) weak interactions. An easily accessible (minimal synthetic steps) and structurally planar selenophene-based building block, 1,2-diethoxy-1,2-bisselenylvinylene (DESVS), with novel Se···O noncovalent conformational locks is designed and synthesized. DESVS unique properties are supported by density functional theory computed electronic structures, single crystal structures, and experimental lattice cohesion metrics. Based on this building block, a new class of stable, structurally planar, and solution-processable conjugated polymers are synthesized and implemented in organic thin-film transistors (TFT) and organic photovoltaic (OPV) cells. DESVS-based polymers exhibit carrier mobilities in air as high as 1.49 cm2 V-1 s-1 (p-type) and 0.65 cm2 V-1 s-1 (n-type) in TFTs, and power conversion efficiency >5% in OPV cells.

An Analysis of Strong Coupling in the High Tc Superconductors

A new McMillan formula is assembled for the High Temperature Superconductors that evidences strong coupling in these materials. The McMillan-Hopfield parameter is calculated in each case, in addition to the Bergmann and Rainer enhancement frequency. The cubic symmetry of the CuO layers and the lattice cohesion and oxygen presence are suggested reasons for the effect.

Rubidium Cerium Sulfate Monohydrate, RbCe(SO4)2.H2O

The title compound crystallized unexpectedly from an aqueous solution of rubidium sulfate and cerium sulfate octahydrate during a study of rubidium lanthanide sulfate tetrahydrates. It has a framework structure comprised of discrete SO4 tetrahedra inter­linked by 9-coordinate Ce polyhedra. Ce bonds to eight sulfate O atoms and a single water molecule. The framework contains large channels parallel to the c axis in which the Rb atoms reside. This framework structure is in contrast to the two-dimensional layered structure exhibited by its tetrahydrate analog where hydrogen bonding plays a key role in lattice cohesion and thermodynamic stability.

Orthorhombic distortion energy for monatomic fcc crystals

The potential energy barrier and the geometry of the volume-conserving orthorhombic distortion for monatomic face-centered cubic (fcc) crystals in the absence of thermal motion have been investigated. It is shown that the orthorhombic transformation path can continuously transform a fcc crystal structure into six neighboring fcc crystal structures. Each of the new fcc lattices is equivalent to the original one but has a different orientation. The only difference of the six new fcc monatomic structures is that all the atoms change one pair of twelve atoms in the first coordination sphere into another pair and the structure has finite shear strains. The height of the potential energy barrier between the two neighboring stable fcc structures is calculated with the Morse and Mie two-body potentials under constant volume expansion or contraction. The barrier height is several times less than the energy corresponding to dilatations (the melting energy) where the lattice cohesion is lost. The total energy difference between body- and face-centered cubic crystal structures is equal to the minimum barrier height for large values of the effective radius of interatomic interaction. For small values of the radius, the minimum barrier height is less than this difference. The growth of the effective radius of the interatomic interaction decreases the height of the energy barrier. The height increases greatly with the volume contraction and decreases with the volume expansion of the fcc structures.

Ultrasonic Investigation of CMSX-6 Superalloy at Low and High Temperatures

The elastic constants C 11 , C 44 and C' have been measured as a function of temperature in a single crystal of CMSX-6 alloy and from these data the bulk, Young's and shear moduli have been deduced, together with the anisotropy factor A and the elastic constant C 12 . The temperature coefficient of the elastic constants C 11 and C 44 becomes gradually more negative on approaching the melting point of the alloy. This softening effect is interpreted in terms of a negative contribution to the elastic stiffness of the material arising from thermal vacancies within the disordered y phase. The anisotropy factor A is found to fall in the typical range of fcc metals and the Cauchy relationship (C 12 = C 44 ) appears to be approximately fulfilled, suggesting that the lattice cohesion is associated with a field of central forces.

Syntheses, thermal behaviour, and spectroscopic and x-ray studies of quinolinium salts of nickel(II), palladium(II) and platinum(II), 1,2-dithiooxalato- S, S′ complexes. Packing and bonding of the quinolinium bis(1,2-dithiooxalato- S, S′)nickelate(II)

Three quinolinium (HC 9H 7N = Hquin) salts of planar inorganic dithiooxalato complexes: (Hquin) 2[Ni(S 2C 2O 2) 2] ( 1, (Hquin) 2[Pd(S 2C 2O 2) 2] ( 2) and (Hquin) 2[Pt(S 2C 2O 2) 2] ( 3) were synthesized and characterized by elemental analysis, IR and UV-vis spectroscopies, thermal analysis (TG, DTG and DTA) and X-ray diffraction techniques. Spectroscopic data support the presence of the aromatic cation and the complex anion. The complexes show a high thermal stability and the thermal studies give evidence that the onset temperatures of their thermal decompositions, the corresponding reaction mechanism and the final solid products are strongly influenced by the atmospheric conditions, as well as the chemical and structural features of the starting compounds. X-ray diffraction analyses show that 2 and 3 are isomorphous with 1, which crystallizes in the monoclinic space group P2 1/ n with Z = 2 so that the anion straddles a crystallographic centre of symmetry. The crystal structure of 1 is built up by layers of quasi-planar [Ni(S 2C 2O 2) 2] 2− complexes (A) and quinolinium cations (C) stacked along the c-axis, following an ⋯ACCACC ⋯ sequence, with alternative interplanar spacings of 3.3–3.8 Å (A ⋯ C) and 3.44 Å (C ⋯ C), which suggest the existence of significant π-π and d z 2 -π interactions between the cations and the complexes' anions. These interactions, together with the electrostatic forces and an extensive network of hydrogen contacts, ensure the lattice cohesion and give the compound a three-dimensional character.

Electronic structure of ZrNi 4P 2 and related compounds with ZrFe 4Si 2-type structure

Extended Huckel molecular orbital and tight-binding band structure calculations have been performed on ZrNi 4 P 2 and then applied through a rigid band model to related compounds with the same ZrFe 4 Si 2 -type structure. The electronic structure has been built up step by step, from fragments, in order to obtain a better understanding of the main interactions which govern the evolution of the lengths of the metal-metal bonds and the lattice cohesion. The role of the 3d metal electron count and that of the ligand matrix are displayed and discussed

Growth of alkali halides by molecular-beam epitaxy.

Alkali halide single crystals are shown to grow well from molecular beams over a wide temperature range \ensuremath{\sim}(0.1--0.5)${\mathit{T}}_{\mathit{m}}$, where ${\mathit{T}}_{\mathit{m}}$ is the melting temperature. Growth characteristics for homoepitaxy and heteroepitaxy, for alloys and superlattices, are discussed and found systematically different from those of metals and semiconductors. The reasons are related here to the type of lattice cohesion.

Thermal Decomposition of Energetic Materials XXIV. A comparison of the crystal structures, IR spectra, Thermolysis and impact sensitivities of nitroguanidine and trinitroethylnitroguanidine

AbstractThe crystal structure of trinitroethylnitroguanidine (TNENG) was determined by X‐ray diffraction for comparison with nitroguanidine (NGu). Pertinent crystal parameters are: orthorhombic, Pbca, a = 14.611 (7) Å, b = 11.973 (5) Å, c = 11.452 (5) Å, V = 2003 (2) Å3, Z = 8, D(calcd) = 1.758 g/cm3, R(F) = 6.30%, R(wF) = 6.58%. A hydrogen bonded network like that present in NGu is largely responsible for the lattice cohesion of TNENG. The IR spectrum of the condensed phase using slow thermolysis, and the gas phase using slow and fast thermolysis, suggests that parallel CN and NN bond fission reactions take place in both TNENG and NGu. The calculated and experimental values of the impact sensitivity of TNENG and NGu are compared. We conclude that the impact sensitivity and the thermal decomposition of TNENG are dominated by the characteristics of the C(NO2)3 group. The intermolecular hydrogen bonding that may desensitize nitroguanidine to impact has essentially no stabilizing effect on TNENG.

Pseudopotential theoretical study of the alkali metals under arbitrary pressure: Density, bulk modulus, and shear moduli.

Milstein and Hill previously derived formulas for computing the bulk and shear moduli, \ensuremath{\kappa}, \ensuremath{\mu}, and \ensuremath{\mu}', at arbitrary pressures, for cubic crystals in which interatomic interaction energies are modeled by pairwise functions, and they carried out the moduli computations using the complete family of Morse functions. The present study extends their work to a pseudopotential description of atomic binding. Specifically: (1) General formulas are derived for determining these moduli under hydrostatic loading within the framework of a pseudopotential model. (2) A two-parameter pseudopotential model is used to describe atomic binding of the alkali metals, and the two parameters are determined from experimental data (the model employs the Heine-Abarenkov potential with the Taylor dielectric function). (3) For each alkali metal (Li, Na, K, Rb, and Cs), the model is used to compute the pressure-versus-volume behavior and, at zero pressure, the binding energy, the density, and the elastic moduli and their pressure derivatives; the theoretical behavior is found to be in excellent agreement with experiment. (4) Calculations are made of \ensuremath{\kappa}, \ensuremath{\mu}, and \ensuremath{\mu}' of the bcc alkali metals over wide ranges of hydrostatic compression and expansion. (5) The pseudopotential results are compared with those of arbitrary\char21{}central-force models (wherein \ensuremath{\kappa}-(2/3)\ensuremath{\mu}=\ensuremath{\mu}'+2P) and with the specific Morse-function results. The pressures, bulk moduli, and zero-pressure shear moduli (as determined for the Morse and pseudopotential models) are in excellent agreement, but important differences appear in the shear moduli under high compressions. The computations in the present paper are for the bcc metals; a subsequent paper will extend this work to include both the bcc and fcc structures, at compressions and expansions where elastic stability or lattice cohesion is, in practice, lost.

Polarization of Molecular ions in NaTCNQ and TTF. TCNQ Crtstals

Abstract Self-consistent electrostatic intersite potentials and atomic charges have been calculated. Lattice cohesion energy for NaTCNQ has been reproduced when polarization of TCNQ- anion in the lattice was taken into account.

Thermodynamics and kinetics of phase transitions in linear polyurethanes from hexa(methylene diisocyanate) and low molecular weight glycoles

Linear polyurethanes based on hexa(methylene diisocyanate) and oligo(ethylene glycoles) were studied using the methods of differential calorimetry, dilatometry and hot-stage microscopy. Thermodynamic analysis of melting and glass transition has shown that urethane groups lower the conformational entropy of melt, which results in a regular increase of bothT m andT g with concentration of these groups in the chain. Energy of intermolecular hydrogen bonding involving urethane groups was estimated by Zhurkov theory to be about 4 kcal/mole. Evidence is presented which suggests that glycole fragments in the crystalline state are “twisted” and depart from the extended conformation. This results not only in the increase of crystalline entropy and lowering of a crystalline packing density, but also in the decrease of a lattice cohesion energy, which then becomes dependent primarily by interactions between di(isocyanate) fragments of the chain crystallizing in the extended conformation. The described effect adequately accounts for the experimentally observed approximate constancy of thermodynamic fusion enthalpies of samples with different lengths of glycole components in the chain, as well as regular change of parametersσ e andG 0 in kinetic equations for the spherulitic growth rate.