Formation Of Structural Defects Research Articles

Evolution of ferroelectric and piezoelectric properties of BiFeO3 ceramics doped with lanthanum and zirconium

In this study, we performed cation substitutions at Bi-site (La3+) and Fe-site (Zr4+) to investigate their possible benefit for the ferroelectric properties of BiFeO3 ceramics. The cations with higher valence (Zr4+) ought to suppress the formation of structural defects during syntheses, such as oxygen vacancies and Fe2+. These defects are responsible for high leakage currents and low breakdown voltages characteristic of the pure BiFeO3. However, doping only with Zr did not improve the ferroelectric properties of bismuth ferrite. These samples were unable to persist electric fields above 30 kV/cm. On the other hand, the increase in lanthanum concentration resulted in improved ferroelectric and piezoelectric properties of the samples, sustaining electric fields above 100 kV/cm. Among the investigated samples, the highest remnant polarization of 24 μC/cm2 and piezoelectric coefficient (d33) of 34 pC/N reached Bi0.85La0.15FeO3 sample at 160 kV/cm. The share of non-ferroelectric contribution to the total polarization of this sample was the lowest (∼ 11 %). When it comes to the co-doped samples, the addition of Zr transformed the behavior from leaky ferroelectric to predominantly leaky dielectric. It indicated that doping with La significantly improved the ferroelectric properties of bismuth ferrite ceramics. In contrast, even a low Zr concentration of 1 mol% could outbalance the influence of much larger La concentrations (10 and 15 mol%).

Phonon spectroscopy and features of low-temperature heat capacity of solid solutions of electrolytes

The kinetic characteristics of thermal frequency phonons in the region of helium temperatures in ceramic samples of the Ce1–xGdxO2–y electrolyte solid solution have been studied. To explain the temperature dependence of the phonon mean free path, we used the previously performed calculations of the energy of vacancy formation in the anion sublattice of a solid solution of zirconium dioxide stabilized by yttrium ZrO2:Y2O3 (YSZ) with a similar crystal structure. It is shown that in the Ce1–xGdxO2–y system under study, the formation of structural defects associated with the presence of vacancies in the anion sublattice with energy Δ = 8.53 K is possible. It has been established that analysis of the temperature dependences of the YSZ heat capacity allows one to trace the degree of disorder (amorphization) of the solid solution depending on its level of stabilization.

Study of Structural Defects Evolution in Fine-Grained Concrete Using Computed Tomography Methods

Introduction. When studying composite materials for construction purposes, it is needed to consider the mechanisms of formation of the structure and properties of modern concretes in the process of strength development. In studies of modern composite materials based on cement binder, there is no information about the development of structural defects and destruction of the material at the initial stages of strength development. This information can be obtained using X-ray computed tomography, a promising method of nondestructive testing of the state of the material. Therefore, the objective of this work was to study the formation and propagation of cracks in samples of fine-grained concrete with different fractional composition of sand due to natural processes of cement shrinkage, as well as the mechanics of destruction of samples of modified fine-grained concrete when applying a compressive load at the early stages of strength development. Materials and Methods. The study used fine-grained concrete mixtures of three compositions with different sand gradation. The tomography samples were made by placing fresh mixtures in polymer cylindrical containers. Tomography of the samples immediately after manufacture, as well as after 8 and 51 days, was performed in a YXLON Cheetah microfocus X-ray machine. The composition with two-fraction sand was modified by mechanical activation of the components, 20×20×20 mm cube samples were made. Further, compression tests were performed at the Instron installation after 3 and 7.5 hours, and then — tomography of the destroyed samples.Results. It was established that the destruction of contact zones depended on the ratio of the size of the fractions. In the presence of a bulk of coarse sand grains in concrete, the destruction of contact zones was more pronounced and had a main mode. When using fine or polyfraction sand, contact zones were destroyed locally and had a visually smaller area. The images of the destroyed modified sample, tested 3 hours after manufacturing, showed clear cracks and indents on the edges, which indicated the elastic-plastic nature of the destruction. In 7.5 hours, the edges of the sample upon destruction were covered with a network of small cracks; inside the sample there were also numerous cracks and microcracks, which indicated brittle fracture. Based on the obtained images of the deformed structure of modified concrete, the mechanism of transition from elastic-plastic destruction of the material to brittle one was clearly visible.Discussion and Conclusion. The studied dependences of the influence of the size of fine aggregate on the mechanisms of formation and propagation of structural defects contribute to the theory of the processes of destruction of fine-grained concretes. The results obtained prove the prospects of using X-ray computed tomography as a method of nondestructive testing of the internal structure of fine-grained concrete, including at the early stages of strength development.

Mechanism of bacteriophage-induced vaterite formation

This study shows how bacterial viruses (bacteriophages, phages) interact with calcium carbonate during precipitation from aqueous solution. Using electron microscopy, epifluorescence microscopy, X-ray diffraction, and image analysis, we demonstrate that bacteriophages can strongly influence the formation of the vaterite phase. Importantly, bacteriophages may selectively bind both amorphous calcium carbonate (ACC) and vaterite, and indirectly affect the formation of structural defects in calcite crystallites. Consequently, the surface properties of calcium carbonate phases precipitating in the presence of viruses may exhibit different characteristics. These findings may have significant implications in determining the role of bacterial viruses in modern microbially-rich carbonate sedimentary environments, as well as in biomedical technologies. Finally, the phage-vaterite system, as a biocompatible material, may serve as a basis for the development of promising drug delivery carriers.

Impact of diatomit on the transport behavior of unmodified and carboxyl-modified nanoplastics in saturated porous media

Due to the extensive use of plastic products and unreasonable disposal, nanoplastics contamination has become one of the important environmental problems that mankind must face. The composition and structure of porous media can determine the complexity and diversity of the transport behavior of nanoplastics. In this study, the influence of diatomite (DIA) on the nanoplastics transport in porous media is investigated by column experiments combined with XDLVO interaction energy and transport model. Results suggest that the recovery rates of unmodified polystyrene nanoparticles (PSNPs) and carboxyl-modified polystyrene nanoparticles (PSNPs-COOH) in the porous media containing DIA decreases compared with that in the pure quartz sand (QS), and the BTCs showed a “blocking” pattern. The presence of DIA inhibits the transport of both PSNPs and PSNPs-COOH, but the inhibition is not significant. This may be because the presence of DIA provides more favorable deposition sites for PSNPs and PSNPs-COOH to some extent. However, since DIA itself carries a certain negative charge, this can only play a role in compressing the double electric layer for PSNPs and PSNPs-COOH with the same negative charge, and cannot destabilize them. The migration capacity of PSNPs and PSNPs-COOH is strongest in the DIA-QS porous media at pH = 7, and is weak at pH = 9 and pH = 5. The inhibition of migration at pH = 9 can be attributed to the dissolution of the DIA surface under alkaline conditions and the formation of pore and defect structures, which provide more deposition sites for PSNPs and PSNPs-COOH. The presence of humic acid (HA) leads to an increase in the mobility of PSNPs and PSNPs-COOH, and the mobility is enhanced with HA concentration. The mobility of PSNPs and PSNPs-COOH in DIA-QS decreases with ionic valence and ionic strength, and PSNPs-COOH is more significantly inhibited compared to PSNPs.

Exploring Defect Dynamics and Twin-Layer Interactions in SiC Crystals through Molecular Simulations.

Silicon carbide (SiC), a third-generation semiconductor material, is pivotal for applications in new energy vehicles, aerospace, and high-speed electronics, owing to its superior properties. This study delves into the twin-induced growth behaviors of SiC crystals through molecular dynamics simulations at temperatures ranging from 2700 to 3200 K. It focuses on the wurtzite and zinc blende SiC structures, revealing dynamic defect behavior during growth, including an initial rise and subsequent decrease in vacancies, with particular emphasis on prevalent defects within zinc blende twin layers. A significant finding is the direct correlation between temperature and growth rates across different SiC structures, highlighting temperature control as essential for optimizing crystal quality. Furthermore, this work contributes to the analysis of the interactions of twin layers and their impact on structural stability and defect formation in SiC crystals. The insights gained here have substantial implications for the semiconductor industry, potentially enhancing device performance by better controlling growth conditions and defect management in SiC-based electronic and optoelectronic devices.

Plastic deformation of the microfibrils in wet polyacrylonitrile fibers induced by the stretching field

AbstractThe plastic deformation of the microfibrils governs the formation and development of orientation, crystallization, and structural defects in polyacrylonitrile (PAN) fibers due to the flow‐fiber coupling effect during stretching process. In this study, we investigated the morphological changes of microfibrils in PAN fibers during wet‐fiber stretching using ultrathin section technology and electron microscopy observation. Their plastic deformation mechanism was also revealed. An interconnected network was formed and separated by the pore/voids during coagulation process. Stretching forces facilitated the plastic deformation of microfibrils, resulted in their elongation and orientation. Moreover, the inter‐fibril distance reduced and pore/void shape and dimensions were changed. The distinct response of microfibril elements under stretching force resulted in skin‐core structures within the fiber. Tensile strength increased from 27 to 382 MPa, while elongation at break decreased from 225% to 28%. Aligned microfibrils exhibited high tensile strength, whereas unoriented microfibrillar networks showed relatively high elongation properties. Additionally, we proposed a relationship between microfibril morphology changes and fiber mechanical properties.

Preparation of N and O doped coal tar pitch based porous carbon for supercapacitor electrode

Coal tar pitch (CTP) is mainly composed of a mixture of polycyclic aromatic hydrocarbons, is almost hydrophobic, and has a low heteroatom content, which limits its surface function. During carbonization, it is prone to condensation and difficult to form pore structures, resulting in poor electrochemical performance for carbon electrode materials. Herein, nitrogen (N) and oxygen (O) doped hierarchical porous carbon (C-ANOCTP) was prepared by HNO3 oxidation and KOH activation using CTP as carbon precursor. The oxidation of HNO3 remarkably increases the hydrophilic functional groups containing N and O on the surface of CTP, improves the hydrophilicity of CTP surface, facilitates the activation process of KOH, promotes the development of carbon material pore structure and the generation of active sites, as well as the formation of defect structures. The specific surface area of C-ANOCTP obtained is 1130 m2/g, with O content of 10.29 at% and N content of 2.37 at%. The specific capacitance of C-ANOCTP in a three-electrode system with 6 M KOH electrolyte is as high as 410.51 F/g at 0.5 A/g. A symmetric supercapacitor is assembled in a 6 M KOH electrolyte using C-ANOCTP as electrode. When the power density is 25 W/kg, the energy density is 10.24 Wh/kg. After 10,000 cycles, the capacitance retention rate is still 90.03% and the coulomb efficiency is 100%. The high N and O content of porous carbon is prepared by simple HNO3 oxidation synergistic KOH activation and low temperature carbonization, which shows excellent electrochemical properties in supercapacitors, making CTP an ideal candidate material for high energy density supercapacitors.

The importance of ammonium and potassium ions under hydrothermal preparation conditions on the structure and corrosion properties of CaP coatings

CaP coatings were hydrothermally deposited on the AZ31 magnesium alloy in rection mixture containing ammonium or potassium ions. CaP coatings were deposited on AZ31 alloy in reaction mixture at pH 5 and 7 with and without EDTA chelating agent. It was found that the ammonium ions present have a negative effect on the quality of the CaP coating deposited from mixture at pH 7 and their presence at neutral environment results in the formation of structural defects in the coatings. At the same time, the presence of ammonium ions suppresses hydrolysis and crystallization of OCP and HAp. However, pH and the presence of EDTA have a more pronounced effect on the structure and phase composition. The coatings deposited in the reaction mixture, containing potassium-based precursors and EDTA, at pH 7 showed the best thermal stability due to the majority of HAp phase. The uniform CaP coating deposited in the reaction mixture containing EDTA and K+ ions at pH 7 also achieved the best corrosion properties due to the absence of structural defects and dense structure.

Reductive Doping Inhibits the Formation of Isomerization-Derived Structural Defects in N-doped Poly(benzodifurandione) (n-PBDF).

Recently, solution-processable n-doped poly(benzodifurandione) (n-PBDF) has been made through in-situ oxidative polymerization and reductive doping, which exhibited exceptionally high electrical conductivities and optical transparency. The discovery of n-PBDF is considered a breakthrough in the field of organic semiconductors. In the initial report, the possibility of structural defect formation in n-PBDF was proposed, based on the observation of structural isomerization from (E)-2H,2'H-[3,3'-bibenzofuranylidene]-2,2'-dione (isoxindigo) to chromeno[4,3-c]chromene-5,11-dione (dibenzonaphthyrone) in the dimer model reactions. In this study, we present clear evidence that structural isomerization is inhibited during polymerization. We reveal that the dimer (BFD1) and the trimer (BFD2) can be reductively doped by several mechanisms, including hydride transfer, forming charge transfer complexes (CTC) or undergoing an integer charge transfer (ICT) with reactants available during polymerization. Once the hydride transfer adducts, the CTC, or the ICT product forms, structural isomerization can be effectively prevented even at elevated temperatures. Our findings provide a mechanistic understanding of why isomerization-derived structural defects are absent in n-PBDF backbone. It lays a solid foundation for the future development of n-PBDF as a benchmark polymer for organic electronics and beyond.

Reductive Doping Inhibits the Formation of Isomerization‐Derived Structural Defects in N‐doped Poly(benzodifurandione) (n‐PBDF)

AbstractRecently, solution‐processable n‐doped poly(benzodifurandione) (n‐PBDF) has been made through in‐situ oxidative polymerization and reductive doping, which exhibited exceptionally high electrical conductivities and optical transparency. The discovery of n‐PBDF is considered a breakthrough in the field of organic semiconductors. In the initial report, the possibility of structural defect formation in n‐PBDF was proposed, based on the observation of structural isomerization from (E)‐2H,2′H‐[3,3′‐bibenzofuranylidene]‐2,2′‐dione (isoxindigo) to chromeno[4,3‐c]chromene‐5,11‐dione (dibenzonaphthyrone) in the dimer model reactions. In this study, we present clear evidence that structural isomerization is inhibited during polymerization. We reveal that the dimer (BFD1) and the trimer (BFD2) can be reductively doped by several mechanisms, including hydride transfer, forming charge transfer complexes (CTC) or undergoing an integer charge transfer (ICT) with reactants available during polymerization. Once the hydride transfer adducts, the CTC, or the ICT product forms, structural isomerization can be effectively prevented even at elevated temperatures. Our findings provide a mechanistic understanding of why isomerization‐derived structural defects are absent in n‐PBDF backbone. It lays a solid foundation for the future development of n‐PBDF as a benchmark polymer for organic electronics and beyond.

A Comprehensive Study of Al2O3 Mechanical Behavior Using Density Functional Theory and Molecular Dynamics.

This study comprehensively investigates Al2O3's mechanical properties, focusing on fracture toughness, surface energy, Young's modulus, and crack propagation. The density functional theory (DFT) is employed to model the vacancies in Al2O3, providing essential insights into this material's structural stability and defect formation. The DFT simulations reveal a deep understanding of vacancy-related properties and their impact on mechanical behavior. In conjunction with molecular dynamics (MD) simulations, the fracture toughness and crack propagation in Al2O3 are explored, offering valuable information on material strength and durability. The surface energy of Al2O3 is also assessed using DFT, shedding light on its interactions with the surrounding environment. The results of this investigation highlight the significant impact of oxygen vacancies on mechanical characteristics such as ultimate strength and fracture toughness, drawing comparisons with the effects observed in the presence of aluminum vacancies. Additionally, the research underscores the validation of fracture toughness outcomes derived from both DFT and MD simulations, which align well with findings from established experimental studies. Additionally, the research underscores the validation of fracture toughness outcomes derived from DFT and MD simulations, aligning well with findings from established experimental studies. The combination of DFT and MD simulations provides a robust framework for a comprehensive understanding of Al2O3's mechanical properties, with implications for material science and engineering applications.

Microstructures and improved properties of Cu–Mo alloys induced by high current pulsed electron beam irradiation

In this paper, a Cu–Mo alloying layer with improved properties was fabricated by high current pulsed electron beam (HCPEB) irradiation. The microstructure of the modified layer was investigated by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The microhardness and friction properties were also measured. After HCPEB irradiation, nano Mo particles, solid solution, and long-period superlattice structures were generated on the surface of Cu–Mo alloys, together with the formation of defect structures. These microstructures led to a significant increase in the surface hardness. The results of sliding wear tests indicated that the HCPEB-irradiated samples exhibited better properties compared with the initial one, which was attributed to the ultrafine Mo particles and the hardened surface.

Insights into structural defect formation in individual InP/ZnSe/ZnS quantum dots under UV oxidation

InP/ZnSe/ZnS quantum dots (QDs) stand as promising candidates for advancing QD-organic light-emitting diodes (QLED), but low emission efficiency due to their susceptibility to oxidation impedes applications. Structural defects play important roles in the emission efficiency degradation of QDs, but the formation mechanism of defects in oxidized QDs has been less investigated. Here, we investigated the impact of diverse structural defects formation on individual QDs and propagation during UV-facilitated oxidation using high-resolution (scanning) transmission electron microscopy. UV-facilitated oxidation of the QDs alters shell morphology by the formation of surface oxides, leaving ZnSe surfaces poorly passivated. Further oxidation leads to the formation of structural defects, such as dislocations, and induces strain at the oxide-QD interfaces, facilitating In diffusion from the QD core. These changes in the QD structures result in emission quenching. This study provides insight into the formation of structural defects through photo-oxidation, and their effects on emission properties of QDs.

Natural formation of linear defect structures in MoS2

Near surface defects can significantly impact the quality of metallic interconnects and other interfaces necessary to create device structures incorporating two-dimensional materials. Furthermore, the impact of such defects can strongly depend on their organization. In this study, we present scanning tunneling microscopy images and tunneling spectroscopy of point and linear defects near the surface of natural MoS2. The point defects share similar structural and electronic characteristics and occur with comparable frequency as subsurface sulfur vacancies observed previously on natural MoS2. The linear defects observed here occur less frequently than the point defects but share the same depth profile and electronic structure. These data indicate that the linear defects are actually a one-dimensional organization of subsurface sulfur vacancies. Our density functional calculations agree with this assessment in that, for sufficient local defect concentrations, it is energetically more favorable for the defects to be organized in a linear fashion rather than as clusters or even isolated single point defects. Given these measurements were taken from naturally formed MoS2, this organization likely occurs during crystal formation. Considering the impact of one-dimensional organization on the local properties of layered materials, and the potential for them to be introduced purposefully during crystal formation, research into the formation mechanism and properties of these defects could enable new paths for defect engineering in MoS2-based systems.

Defect detection by multi-axis infrared process monitoring of laser beam directed energy deposition

Laser beam directed energy deposition (DED-LB) is an attractive additive manufacturing technique to produce versatile and complex 3D structures on demand, apply a cladding, or repair local defects. However, the quality of manufactured parts is difficult to assess by inspection prior to completion, and parts must be extensively inspected post-production to ensure conformance. Consequently, critical defects occurring during the build go undetected. In this work, a new monitoring system combining three infrared cameras along different optical axes capable of monitoring melt pool geometry and vertical displacement throughout deposition is reported. By combining multiple sensor data, an automated algorithm is developed which is capable of identifying the formation of structural features and defects. An intersecting, thin-walled geometry is used to demonstrate the capability of the system to detect process-induced porosity in samples with narrow intersection angles, which is validated using micro-CT observations. The recorded results indicate the root cause of this process-induced porosity at the intersection, and it is shown that advanced toolpath planning can eliminate such defects. The presented methodology demonstrates the value of multi-axis monitoring for identifying both defects and structural features, providing an advancement towards automated detection and alert systems in DED-LB.

Graphene‐Based Lateral Heterojunctions for 2D Integrated Circuits

AbstractA method for patterning single‐layer graphene (SLG) and single‐layer oxidized graphene (SOG) within a continuous atomic layer to form lateral heterojunctions is presented. Raman spectroscopy is employed to investigate the evolution of defect‐related Raman peaks during excimer‐UV irradiation, facilitating the identification of structural changes and defect formation processes. Electrical transport measurements reveal that SOG‐patterned field‐effect transistors (FETs) exhibit varying characteristics depending on the degree of oxidation, thus offering the potential to tailor the electrical properties of graphene devices for specific requirements. Scanning Kelvin probe microscopy measurements reveal the surface potential and work function of the SOG regions compared with those of SLG. The effective functionality of the SOG pattern to operate as a resistor, allowing control of the electrical conductivity in the SOG‐patterned SLG channels, is demonstrated. This capability restricts the current flow while preserving the pristine electrical properties of the graphene channel. Moreover, the SOG pattern can serve as a potential barrier to constructing SLG‐SOG‐patterned integrated circuits, providing exciting opportunities for engineering advanced electronic components. This breakthrough in graphene devices simplifies the fabrication process of graphene‐based FETs and provides the foundation for developing atomically thin integrated circuits for a wide range of applications.

Grazing-incidence synchrotron radiation diffraction studies on irradiated Ce-doped and pristine Y-stabilized ZrO2 at the Rossendorf beamline.

In this work, Ce-doped yttria-stabilized zirconia (YSZ) and pure YSZ phases were subjected to irradiation with 14 MeV Au ions. Irradiation studies were performed to simulate long-term structural and microstructural damage due to self-irradiation in YSZ phases hosting alpha-active radioactive species. It was found that both the Ce-doped YSZ and the YSZ phases had a reasonable tolerance to irradiation at high ion fluences and the bulk crystallinity was well preserved. Nevertheless, local microstrain increased in all compounds under study after irradiation, with the Ce-doped phases being less affected than pure YSZ. Doping with cerium ions increased the microstructural stability of YSZ phases through a possible reduction in the mobility of oxygen atoms, which limits the formation of structural defects. Doping of YSZ with tetravalent actinide elements is expected to have a similar effect. Thus, YSZ phases are promising for the safe long-term storage of radioactive elements. Using synchrotron radiation diffraction, measurements of the thin irradiated layers of the Ce-YSZ and YSZ samples were performed in grazing incidence (GI) mode. A corresponding module for measurements in GI mode was developed at the Rossendorf Beamline and relevant technical details for sample alignment and data collection are also presented.

Framework confinement of multi-metals within silica hollow spheres by one-pot synthesis process

ABSTRACT The control incorporation of metals in silica hollow spheres (SHSs) may bring new functions to silica mesoporous structures for applications including catalysis, sensing, molecular delivery, adsorption filtration, and storage. However, the strategies for incorporating metals, whether through pre-loading in the hollow interior or post-encapsulation in the mesoporous shell, still face challenges in achieving quantitative doping of various metals and preventing metal aggregation or channel blockage during usage. In this study, we explored the doping of different metals into silica hollow spheres based on the dissolution-regrowth process of silica. The process may promote the formation of more structural defects and functional silanol groups, which could facilitate the fixation of metals in the silica networks. With this simple and efficient approach, we successfully achieved the integration of ten diverse metal species into silica hollow sphere (SHS). Various single-metal, dual-metal, triple-metal, and quadruple-metal doped SHSs have been prepared, with the doped metals being stable and homogeneously dispersed in the structure. Based on the structural characterizations, we analyzed the influence of metal types on the morphology features of SHSs. The synergistic effects of multi-metals on the catalysis applications were also studied and compared.

Effect of proton irradiation on optical properties and defect formation in crystals Gd<sub>3</sub>Al<sub>x</sub>Ga<sub>5–x</sub>O<sub>12</sub> (x = 2, 3)

The influence of proton irradiation with a dose of 50 Mrad (Si) on the optical properties and defect formation in crystals of the gadolinium-aluminum-gallium garnet with the substitution of aluminumand gallium in the cationic sublattice: Gd3Al2Ga3O12 (Al: Ga = 2:3) and Gd3Al3Ga2O12 (Al: Ga = 3:2) was studied. After proton irradiation, color of crystals changes: an additional absorption band appears in the transmittance of each crystal in the wavelength range 400–500 nm. This occures due to the formation of induced structural defects as color centers. The refractive indices n(λ) were determined by the Brewster spectrophotometric method and practically did not change for Al:Ga = 2:3 crystals, but significantly increased for Al:Ga = 3:2. There is a noticeable increase in the attenuation of the light in spectral dependences, which also indicates the formation of additional structural defects.