Defects In Crystalline Structure Research Articles

Facile ligand-regulated synthesis of defective Fe-MOF nanosheets for efficient tetracycline degradation via photoassisted enhanced activation of persulfate

In this work, defective Fe-based metal organic framework (Fe-MOF) were synthesized by a simple and eco-friendly method, in which the benzenetricarboxylic acid (BTC) ligand was partially replaced by cheap terephthalic acid (TPA) to regulate the crystalline morphology, pore structure and ligand defects. At BTC/TPA = 5/3, 4/4 and 3/5 (molar ratio), lamellar crystal (1-Fe-MOF), a mixture of lamellar crystal and nanosheets (2-Fe-MOF), and nanosheets (3-Fe-MOF) were obtained, respectively, which were distinctly different from the octahedral Fe-MOF. In the visible-light-driven persulfate (PS) activation coupled system, 3-Fe-MOF exhibited highest catalytic activity for tetracycline hydrochloride (TCH). 96.5% of TCH was removal within 20 min and the degradation kinetics rate of 0.144 min−1 was 3.5 times higher than that over the intact Fe-MOF. The enhancement in degradation activity was mainly attributed to the emergence of mesoporous structure, exposure of more metal active sites, and accelerated Fe2+/Fe3+ cycling due to more efficient charge separation and electron transfer efficiency, which favored the generation and dominant role of ∙SO4− in TCH degradation. Furthermore, demethylation, deamidation, double-bond oxidation and ring-opening reactions were inferred as the two possible degradation pathways of TCH in 3-Fe-MOF/PS/Vis system. This study provides useful guidance for the design of novel and sustainable MOFs with good application performance and industrialization potential.

MultiSOM: Multi-layer Self Organizing Maps for local structure identification in crystalline structures

Identification of defects in crystalline structures is of vital importance when describing the plastic behavior of metals. Despite the increasing number of tools available in the literature, additional techniques are still required to classify different types of defects. Here we present a novel tool based on Multi-layer Self Organizing Maps (MultiSOM), which can be employed in the identification of vacancies, dislocations and free surfaces at the atomic scale. Three case-studies were analyzed and the performance of MultiSOM was compared to traditional tools, such as common neighbor analysis and polyhedral template matching, revealing that our algorithm is able to identify local structures while other methods are unable to. We demonstrate that excellent results can be obtained for identifying local structural patterns in solids through the MultiSOM framework when combining per-atom properties such as coordination numbers and centrosymmetry parameter; though alone, each property is insufficient. Overall, MultiSOM is an open-source software, that works under the Python programming language with user-selected features.

Mathematical Description for the Hierarchy of Grain-boundary Structures

Polycrystalline materials are ubiquitous, and their macroscopic properties strongly depend on the defects in crystalline structures. Grain boundaries (GBs) are the interfaces between crystal grains, which admit unique atomic arrangements different from those of crystals. It is essential to reveal the polyhedral arrangement in GB atomic structures to identify the origin of structure-property relationships in polycrystalline materials. We found that the GB region can only be packed by the bulk or GB-type polyhedral units with minor variations. Moreover, the GB hierarchy directly follows the distribution of rational numbers that is represented by the Farey diagram. The singular GB is defined to be a GB packed by at the most two types of polyhedral units in a period, and any GB can be packed by the polyhedral units that form the singular GBs. This approach allows us to predict the polyhedral arrangement in any tilt GBs including random GBs.

Electronic structure and electrical conductance properties of two-dimensional arsenin

Arsenene is one of the members of a large group of two-dimensional structures that in the present project, we have investigated the single layer structure and its nanoribbons based on density functional theory. In this study, after calculating the single layer band structure, we discussed the effect of width on the band structure of nanoribbon from the angle of quantum limiting phenomenon. The results show the different effect of quantum limiting phenomenon on different points of each band in the band structure, which is the cause of indirect-direct gap transition due to the reduction of the width of armchair nanoribbon. Also, the electrical conductance properties of arsenene single layer have been obtained by calculating the mobility of load carriers and the effect of uniaxial strain of crystalline structure on them has been investigated. In order to investigate the mobility, crystalline structure defects have been neglected and only phonon dispersion is considered based on Takagi relationship. In this process, the focus is not on the quantitative accuracy of the obtained values for the mobility of load carriers and the existing anisotropy between mobility in the two directions of armchair and zigzag has been the focus of the discussion. The results of the calculations show a significant anisotropy of mobility in the two directions of armchair and zigzag and the effect of uniaxial strain of crystal structure on it. Also, a significant difference between the mobility of electrons and holes in the direction of armchair is one of the key results.

Structural characteristics, impedance spectroscopy, ac-conductivity and dielectric loss studies on RF-magnetron sputtered F doped ZnO (FZO) thin films

The manuscript demonstrates the structural characteristics, impedance spectroscopy, ac-conductivity and dielectric loss studies on F-doped ZnO films grown by RF-magnetron sputtering at TS ∼50 and 125 °C. The electrical impedance spectroscopy enables separately recognizing the contributions of grain and grain-boundary on the electronic properties. The relaxation time distribution on temperature results in the asymmetric and depressed nature of the semi-circular arcs in the Cole-Cole plot and endorses a non-Debye type response under changing electric fields. The negative temperature coefficient of resistance behaviour indicates the semiconducting characteristics. A parallel equivalent circuit model (R || CPE) is designed to fit the semi-circular arc. The grain boundary being more resistive than ZnO-grain, its activation energy appears more significant because of the dynamic disorder characteristics. The ac-conductivity obeys Jonscher power law, and frequency exponent n < 1 suggests hopping of charge carriers with translation motion under ac electric field. The temperature-dependent dc-conductivity follows the Arrhenius behaviour. Sample deposited at higher TS has a greater carrier lifetime due to the improved crystalline structure and lesser defects. Although, the dielectric loss in the form of conduction loss is higher for the low temperature grown sample owing to the relatively effortless movement of charge carriers and formation of dipoles due to its elevated dc conductivity consequent to increased doping.

Assessing the local structure and quantifying defects in Ca4Fe9O17 combining STEM and FAULTS

Defects in crystalline structures play a vital role in their properties, so their proper characterization is essential to understanding and improving the behaviour of the materials.

Nonclassical nonlinear elasticity of crystalline structures.

Hysteretic elastic nonlinearity has been shown to result in a dynamic nonlinear response which deviates from the known classical nonlinear response; hence this phenomenon was termed nonclassical nonlinearity. Metallic structures, which typically exhibit weak nonlinearity, are typically categorized as classical nonlinear materials. This article presents a material model which derives stress amplitude dependent nonlinearity and damping from the mesoscale dislocation pinning and breakaway to show that the lattice defects in crystalline structures can give rise to nonclassical nonlinearity. The dynamic nonlinearity arising from dislocations was evaluated using resonant frequency shift and higher order harmonic scaling. The results show that the model can capture the nonlinear dynamic response across the three stress ranges: linear, classical nonlinear, and nonclassical nonlinear. Additionally, the model also predicts that the amplitude dependent damping can introduce a softening-hardening nonlinear response. The present model can be generalized to accommodate a wide range of lattice defects to further explain nonclassical nonlinearity of crystalline structures.

Luminescence properties and energy transfer processes in LiSrPO4 doped with Pr3+ and co-doped with Na+ and Mg2+

The paper studies the influence of co-doping with alkali metal ions (Na+, Mg2+) on fast interconfigurational 5d-4f luminescence in LiSrPO4 doped with Pr3+. Na+ and Mg2+ ions were introduced in order to provide charge compensation and modify the electronic configuration of the materials. Luminescent properties of the powder samples were investigated using time-resolved pulsed cathodoluminescence and luminescence spectroscopy in the UV-VUV spectral region. The obtained results were compared with those obtained earlier on LiSrPO4:Pr3+ without co-dopants. With introduction of the co-dopants, slight changes in relative luminescence intensity and decay time of Pr3+ ion 4f15d1-4f2 radiative transitions were found. The study revealed a complex interplay between defects of crystalline structure and impurity ions leading to the peculiarities in energy relaxation processes. Energy transfer leading to the delayed recombination processes is responsible for significant afterglow in Pr3+4f15d1-4f2 emission.

Development of scientific ideas on phase and structural transformations in steels for different application

Purposeful control of structural state of steel at every stage of technological chain of steel goods production is necessary for elaboration of effective metallurgical technologies. The purpose of the complex of research and theoretical studies was development of ideas on peculiarities of structure formation of various steel grades. Current conceptions about phase and structural transformations in steels with different contents of carbon and alloying elements considered. For carbon and alloyed steels, the results of the study of the structure of perlite formed at different temperatures summarized; morphology, crystallography and defects of crystalline structure of cementite, processes of its fragmentation, coagulation and spheroidization; crystallography of austenite degradation products; evolution of the structure during cold and hot plastic deformation; carbon redistribution processes prior to and during diffusion-controlled austenite decay presented. For low-carbon low-and sparingly alloyed cold-resistant weldable steels generalized results of investigation of structure-formation processes, alloying relationships, temperature-deformation rolling conditions, parameters of quenching and high-temperature tempering with structure, mechanical properties and performance characteristics of steel plates presented. The elaborated complex of scientific and technical solutions based on the studies enabled to master and digitize production technologies at PJSC “Magnitogorsk steel-works” of new generation steel rolled products intended for ship-building, oil and gas industries, automobile, hardware and construction industries. The new systems of alloying steels of various application, methods of the new generation steels production and automated control of technological processes protected by 27 patents of RF, are widely used in the production activity of PJSC “Magnitogorsk steel-works”.

Effect of heating rate on structure, morphology and photocatalytic properties of TiO2 particles: thermal kinetic and thermodynamic studies

In this study, TiO2 powders were produced via sol–gel route at 500 °C for 2 h with distinct heating rates. TGA-DTA, XRD, SEM, Raman spectroscopy, XPS, UV–vis spectroscopy and photoluminescence characterization techniques were carried out for TiO2 powders. Photocatalytic efficiency of TiO2 powders on degradation of methylene blue (MB) solution was examined in terms of different heating rates. Thermodynamic and non-isothermal kinetic study of TiO2 powders were estimated. TiO2 powders showed anatase phase based on XRD results. Surface morphology of TiO2 powders did not change with different heating rates. It can be concluded that heating rate played important role on band gap and photocatalytic activity. The band gap of the TiO2 particles decreased from 3.25 to 2.95 with increasing heating rate. The photocatalytic activity results exhibit that T1 powders have the highest photocatalytic performances. The kinetic constant and photocatalytic degradation rate were 0.00678 min−1 and 83.48%, respectively. This could be attributed to high crystalline structure and low bulk vacancies or defects. Furthermore, TiO2 powders showed good stability. This study exhibited a new way to enhance the photocatalytic performances of pure TiO2 powders.

FaVAD: A software workflow for characterization and visualizing of defects in crystalline structures

The analysis of defects and defect dynamics in crystalline materials is important for fundamental science and for a wide range of applied engineering. With increasing system size the analysis of molecular-dynamics simulation data becomes non-trivial. Here, we present a workflow for semi-automatic identification and classification of defects in crystalline structures, combining a new approach for defect description with several already existing open-source software packages. Our approach addresses the key challenges posed by the often relatively tiny volume fraction of the modified parts of the sample, thermal motion and the presence of potentially unforeseen atomic configurations (defect types) after irradiation. The local environment of any atom is converted into a rotation-invariant descriptive vector (‘fingerprint’), which can be compared to known defect types and also yields a distance metric suited for classification. Vectors which cannot be associated to known structures indicate new types of defects. As proof-of-concept we apply our method on an iron sample to analyze the defects caused by a collision cascade induced by a 10 keV primary-knock-on-atom. The obtained results are in good agreement with reported literature values. Program summaryProgram Title: Fingerprinting and Visualization Analyzer of Defects (FaVAD).CPC Library link to program files:https://doi.org/10.17632/bmv9kxkzg3.1Developer’s repository link:http://gitlab.mpcdf.mpg.de/NMPP/favad.gitLicensing provisions: GPLv3.Programming language: Python 3, Fortran 90, and C++.Nature of problem: The analysis of damage and damage evolution in crystalline materials is important for fundamental science and for a wide range of applied engineering. Defects in materials on an atomic level are commonly analyzed by Wigner–Seitz or topology Voronoi tessellation based methods. However, these approaches exhibit specific shortcoming, especially at elevated sample temperatures. In order to improve upon that, a more robust and quantifiable identification and classification approach of known as well as of unpredicted defect structures is desirable.Solution method: A fingerprint-like method is proposed to analyze in detail the damage in a material augmented with a probabilistic interpretation. It is based on the calculation of a descriptor vector for each atom in the sample. These vectors represent in a compact form the individual environments of the atoms.For standard types of defects (i.e. interstitial atoms) the corresponding descriptor vectors can be precomputed and used for rapid classification. Unexpected or less common defect types can be identified by applying a principal component analysis to the descriptor vectors. Vacancies in the material are identified by computing the radii of the largest empty spheres which can be embedded into the sample, followed by a thresholding process. This new method is easy to use and requires only modest computational resources.Finally, the classified defects are visualized using the open source software VisIt.Additional comments including restrictions and unusual features: The descriptor vectors are computed using the command line interface of QUIP with the Gaussian Approximation potential (GAP) package. The analysis of the sample is done using Python scripts which make extensive use of the NumPy package. A modified KDTree2 code is employed to calculate the location of single vacancies and voids. The program VisIt is used for the visualization of the classified point defects in the sample. We provide a Dockerfile for automatically creating a portable Docker container which installs all the programs together with a Python script to analyze as an example a damaged iron molecular dynamics sample. A shell script to install the programs locally in a Linux-based server or desktop environment is included also.

Ultrafast dynamics and short-lived carriers in Cu nitride and oxynitride layers

Ultrafast carrier dynamics in copper nitride (Cu3N) have been investigated using femtosecond pump-probe spectroscopy. Cu3N films were prepared on fused SiO2 substrates coated with thin Cu layers under NH3:O2 flow. The obtained differential transmission data revealed discrete maxima in the spectra at different probing energies. Lower energy maxima are attributed to direct bandgap transitions, while transient transmission peaks at higher energies are due to probing defect state transitions in the material. These states originate from crystalline structure defects and are energetically located close to the conduction and valence bands. The recombination times extracted from the data were of the order of few picoseconds which raises the question of how suitable this material is for energy conversion applications. Ultrafast pump-probe spectra obtained at a low temperature of 78 K revealed almost no shifting of the transition energies compared to room temperature spectra, although small differences in decay times were observed due to the absence of thermal effects. Measurements using longer probing wavelengths in the infrared region indicated state filling of defect states within the bandgap for wavelengths between 800 nm and 1400 nm while probing at longer wavelengths (1400–1600 nm) revealed initial free-carrier absorption and re-excitation of carriers to higher energy defect states above the conduction band. In addition, copper oxynitride layers were produced and studied in a similar fashion to investigate the effects of oxygen on the band structure and recombination times.

Disorder engineering in transition metal dichalcogenides toward efficient high current density reduction electrocatalysts

In this perspective, we highlight the importance of nanoscale disorder and mesoscale morphology to enhance the activity and tune the selectivity of group VI transition metal dichalcogenide electrocatalysts toward two paramount reductions reactions as H2 evolution reaction and CO2 reduction. The strategy we propose takes advantage of the metastable nanoscale atomic arrangement of highly disordered and amorphous materials, to overcome the limits of the typical transition metal dichalcogenide crystalline catalysts. For the H2 evolution reaction, going beyond the creation of point defects in crystalline structures in favor of fully amorphous organizations not only increases the per-site activity and active surface area but also improves the conductivity and the reaction kinetics. In addition, the incorporation of nanoscale disorder promotes the formation of complex products in CO2 reduction through reaction pathways inaccessible on other sites. On the other hand, the mesoscale architecture of the catalyst controls mass transport in both the liquid and gas phase, as well as determines the real-world performance of catalysts. We suggest that by exploiting disordered nanoscale organization and controlled mesoscale features, the performances can be drastically improved to reach the state-of-art metallic electrocatalysts.

PHYSICOMECHANICAL PROPERTIES OF COMPOSIT MATERIALS ON BASIS OF COPPER AND POLYOLEFINS

The paper presents the results of a study of the effect of copper concentration on the physicomechanical properties of composites based on high density polyethylene and low density polyethylene. The properties of metal-filled composites, such as ultimate tensile stress, elongation at break, elastic module, melt flow rate, and heat resistance, were studied. Loading of copper into the composition of low density polyethylene contributes to a monotonic increase in the ultimate tensile stress and the elastic module. When copper is loading into the composition of high density polyethylene, on the contrary, a natural decrease in the ultimate tensile stress and elongation at break of the composites is observed. It is shown that when using a compatibilizer, which is polyethylene modified with maleic anhydride, a significant increase in the ultimate tensile stress of high and low density polyethylene composites is observed. A schematic representation of the structure of composites with an interpretation of the probable mechanism of hardening of the material in the presence of a compatibilizer is given. It is shown that the crystallinity of the initial polyethylene has a significant effect on the hardening effect of composites. It is assumed that polyethylene of high density macrochains free of maleic anhydride are involved in the formation of crystalline formations, and small sections of macrosegments containing polar groups are concentrated mainly in amorphous regions and in defects in crystalline structures in the form of passage chains. The concentration of copolymer of polyethylene with maleic anhydride macrosegments in the narrow amorphous space of polyethylene of high density favorably affects the increase in the adhesive forces of interaction on the surface of copper particles, which affects the preservation of the ultimate tensile stress at a relatively high level over a wide range of copper concentrations.

Enhanced Morphology-Dependent Tensile Property and Breakdown Strength of Impact Polypropylene Copolymer for Cable Insulation.

The decrease in electrical properties caused by the toughening of polypropylene (PP) is a difficult problem for the modification of PP used for cable insulation. In this research, an isotactic PP, a cross-linked polyethylene (XLPE) and two impact PP copolymers (IPCs) with an ethylene–propylene rubber phase content of 15 and 30% were prepared to assess the possibility of IPCs to be used as cable insulating material. The tensile properties and breakdown strength were evaluated, meanwhile, the rubber phase content dependence of the crystalline structure, morphology and trap distribution were also investigated. Results show that IPCs with a 15% rubber phase content (IPC15) can achieve the simultaneous improvement of elongation at break and breakdown strength compared with isotactic PP, which can be attributed to the special crystalline structure. According to the results of differential scanning calorimetry (DSC) and FTIR, it is proposed that the lamella thickness of IPC15 is maximal and some ethylene segments exist in PP crystals of IPC15 as crystalline structure defects, which is responsible for this enhanced breakdown strength. The morphology results reveal that rubber microspheres are found to coexist with spherulites, which can promote the relative sliding among lamellas under external force and further results in the increase in the elongation at break.

Preparation of black titanium monoxide nanoparticles and their potential in electromagnetic wave absorption

In this work, black titanium monoxide (TiO) nanoparticles were synthesized by hydrogen assisted magnesium thermal reduction method from nanotube titanic acid (NTA) and their electromagnetic properties were investigated. The black TiO nanoparticles exhibited the optimal reflection loss of −37.7 dB at a thin absorbance layer of 1.2 mm in thickness, which showing a promising candidate in electromagnetic wave absorbing (EA). To explore the mechanism of EA, TiO nanoparticles prepared from the other two initiators (commercial grade TiO and P25 titanium dioxide) was used as a comparison. The results show that the crystalline structure and microscopic defects, which arouse from the formation of TiO in the hydrogen assisted process, affect the electromagnetic performance of Ti-O binary system significantly in addition to their intrinsic effects. We hope this study help to open a new way for the designing of high-performance EA materials.

Физико-механические свойства композитов на основе полиэтилена различных типов и алюминия

The paper presents the results of a study of the effect of aluminum content on the physic-mechanical properties of composites based on high density polyethylene and low density polyethylene. The properties of metal-filled composites, such as ultimate tensile stress, elongation at break, elastic module, melt flow rate, and heat resistance, were studied. According to the data obtained, the loading of aluminum into the composition of low density polyethylene contributes to a monotonic increase in the ultimate tensile stress and the elastic module. When aluminum is loading into the composition of high density polyethylene, on the contrary, a natural decrease in the ultimate tensile stress and elongation at break of the composites is observed. It is shown that when using a compatibilizer, which is polyethylene modified with maleic anhydride, a significant increase in the ultimate tensile stress of high-density polyethylene composites is observed. A schematic representation of the structure of composites with an interpretation of the probable mechanism of hardening of the material in the presence of a compatibilizer is given. It is shown that the crystallinity of the initial polyethylene has a significant effect on the hardening effect of composites. Electron microscopic micrographs of the structure of a filled composite without and with compatibilizer are given. A comparative assessment shows that in the presence of a compatibilizer, aluminum particles are in the bulk of the polymer matrix, i.e. are not in an isolated state. It is assumed that HDPE macrochains free of maleic anhydride (MA) are involved in the formation of crystalline formations, and small sections of macrosegments containing polar groups of MA are concentrated mainly in amorphous regions and in defects in crystalline structures in the form of passage chains. The concentration of PEMA macrosegments containing MA in the narrow amorphous space of HDPE favorably affects the increase in the adhesive forces of interaction on the surface of aluminum particles, which affects the preservation of the ultimate tensile stress at a relatively high level over a wide range of aluminum concentrations.

COMPOSITE CASTINGS WITH DIFFUSION BONDS BETWEEN ELEMENTS

The article is devoted to the current problem of improving foundry competitiveness. With a continuous increase in load, speed, power, temperature, the influence of aggressive environments, and other factors, an adequate increase in the requirements for the operational properties of parts is observed. Composite casting allows us to obtain high-precision castings following all the requirements that apply to them. Composite casting synthesizes individual elements of a part, which can be performed by the most efficient farming methods for a given element, as well as from optimal materials, depending on the requirements for the parts. The main content of the study is the analysis and detailing of the parameters of an economical technology to produce high-precision composite castings with differentiated physical and mechanical properties of their parts and high operational reliability. Considerable attention is paid to contact processes that communicate between elements. In most cases, these are diffusion interactions determined by defects in the crystalline structure. The contact zone should be homogeneous and controllable in geometric parameters and properties in areas where complex physicochemical processes occur under unsteady thermal conditions. The characteristic features of the production of composite castings are highlighted and described, taking into account the choice of elements for each specific case, with the determination of the parameters that determine the relationship between them on specific examples of the preparation of composite castings. The results of the study confirmed stable performance, reduced costs for the manufacture of castings, metal savings (for example, up to 2 kg per cone). The results indicate a high potential of composite casting as a means of increasing the competitiveness of foundry by manufacturing high-precision castings with an increased operational reliability of cast parts.

Stress driven fractionalization of vacancies in regular packings of elastic particles.

Elucidating the interplay of defects and stress at the microscopic level is a fundamental physical problem that has a strong connection with materials science. Here, based on the two-dimensional crystal model, we show that the instability mode of vacancies with varying size and morphology conforms to a common scenario. A vacancy under compression is fissioned into a pair of dislocations that glide and vanish at the boundary. This neat process is triggered by the local shear stress around the vacancy. The remarkable fractionalization of vacancies creates rich modes of interaction between vacancies and other topological defects, and provides a new dimension for mechanical engineering of defects in extensive crystalline structures.

Structure, morphology and adsorption properties of titania shell immobilized onto cobalt ferrite nanoparticle core

A magnetic core-shell adsorbent was synthesized by immobilization of titanium dioxide nanoclusters on the cobalt ferrite nanoparticles. The synthesis was carried out using a modified Pechini sol-gel method with citric acid and ethylene glycol as chelating agents. The structure and morphology of reference TiO2, pristine CoFe2O4 and resulting nanocomposite CoFe2O4@TiO2 were thoroughly characterized using XRD, XRF, BET, SEM, IR spectroscopy and Mössbauer spectroscopy. The obtained spectral data indicate that a shift of electron density from titanium to oxygen atoms takes place. Antistructure modeling suggests that some titanium atoms are entered into the CoFe2O4 spinel structure resulting in defects of crystalline structure. In this way additional adsorption centers arise. The adsorption efficiency of the CoFe2O4@TiO2 nanocomposite was found to be more than twice as high as compared to TiO2 and CoFe2O4 alone. The observed synergistic effect is associated just with the formation of distorted titania nanocrystals. The obtained magnetic nanoadsorbent proved to be efficient in water purification from dichromate anions (83% removal) and Congo Red dye (61% removal).