Generation Of Structural Defects Research Articles

Ba-leaching-initiated structural destabilization of perovskite Ruthenates during the oxygen evolution reaction

The destabilization of a lattice structure during the oxygen evolution reaction (OER) is one of the most essential aspects for designing and realizing highly efficient electrocatalysts. However, the underlying mechanism of structural evolution or degradation at the microscopic scale on the electrocatalyst surface during the OER has not been elucidated because of the sluggish yet dynamic character of the reaction. To address this issue, the direct observation of the unstable electrocatalytic activity is necessary. In this study, we demonstrate that the structural destabilization of epitaxial cubic perovskite BaRuO3 thin films during the OER originates from Ba leaching, Ru dissolution, and oxygen vacancy. A thin film geometry is adopted to selectively visualize the structural decomposition at the well-defined sample surface. The cubic BaRuO3 thin film initially exhibits high OER activity, which drastically decreases even during the first cyclic voltammetry cycle and is completely lost after the first cycle. The OER activity loss is closely related to the generation of structural defects on the surface, indicating the absence of the Ba and Ru atoms. This study proposes the mechanism underlying the OER activity that can be extended to elucidate the structural destabilization in various Ru- and Ir-based oxide catalysts.

Suppressing the formation of OP4 phase in P2-Structured Na0.67Ni0.1Co0.1Mn0.8O2 by in-situ formed NiF2 layer

The P2-structured sodium transition metal oxides suffer from an irreversible phase transition to OP4, which results in the -1.3 Å shrinking of lattice c and locks the following electrochemical cycles between OP4 and P2’, seriously aggravating the cracking of cathode materials. Therefore, strategies to suppress the phase transition from P2 to OP4 are currently pursued to alleviate the destructively volumetric changes. Here, the DFT calculations reveal that the transition to OP4 phase is not driven by thermodynamical mechanism but is induced by structural defects. To verify this prediction, an in-situ formed NiF2 layer via electrolyte additives is coated on the P2-structured Na0.67Ni0.1Co0.1Mn0.8O2 during initial charging, which mitigates the generation of structural defects from the side reaction of electrolyte with active sites of cathode particles. The sample protected with NiF2 layer presents a continuous, moderate and reversible structural evolution, free from phase P2’. Therefore, the coated sample delivers 230.1 mAh/g at 0.1C and retains 83.4% capacity at 0.5C after 150 cycles, significantly higher than the values, 174.5 mAh/g and 63.4%, respectively, of the pristine materials. This work demonstrates the severe phase transition in P2-type cathode can be effectively alleviated by a simple surface modification.

ЧУТЛИВІ ЕЛЕМЕНТИ ПЕРЕТВОРЮВАЧІВ ТЕМПЕРАТУРИ НА ОСНОВІ ТЕРМОМЕТРИЧНОГО МАТЕРІАЛУ HfNi1-xCuxSn

ЧУТЛИВІ ЕЛЕМЕНТИ ПЕРЕТВОРЮВАЧІВ ТЕМПЕРАТУРИ НА ОСНОВІ ТЕРМОМЕТРИЧНОГО МАТЕРІАЛУ HfNi1-xCuxSn

The impacts of stress on the macromolecular structure of anthracites: Implications for the mechanochemical effects

Despite the vast research studying the influence of stress on the physical structure, little is known whether and how stress works on the chemical structure in coals. In the present study, some insights are given by investigating the macromolecular structure evolution characteristics and mechanism of a Chinese anthracite (Ro,max = 3.6%) during deformation experiments at temperatures of 300–400 °C, confining pressure of 150 MPa, and strain rates of 2.5–20*10−6 s−1. Additional heat treatments (without stress) were also performed at the same temperature range. Revealed by vitrinite reflectance, XRD, and Raman spectroscopy, a smaller and less ordered macromolecular structure was observed within experimental conditions. Upon heating alone, Ro,max and stacking diameter (La) increased together, while stacking height (Lc) and structure ordering (ID/IG and FWHM of D and G peaks) decreased with increasing temperature, indicating structure rearrangement and relaxation. In contrast, the macromolecular structure in deformation experiments showed a two-stage evolution with decreasing strain rate. Stage 1 was characterized by the obvious decreases in Ro,max, La, and Lc, but minor changes in Raman spectra, implying stress might break in-plane and inter-layer chemical bonds at high strain rates. Stage 2 was identified by the relative increases in Ro,max, La, and FWHM of D peak, in combination with Lc, mainly indicating the generation of structural defects at low strain rates allows the aromatic layer to accommodate the stress without breakage. Our results suggest stress can act on the macromolecules directly by breaking or distorting the chemical bonds depending on the strain rate.

Features of Mechanisms of Electrical Conductivity in Semiconductive Solid Solution Lu1 – xScxNiSb

A comprehensive study of the crystal and electronic structures, thermodynamic, electrokinetic, energy, and magnetic properties of the semiconductive solid solution Lu1-xScxNiSb, x = 0 – 0.10, revealed the possibility of doping Sc atoms of different crystallographic sites depending on their concentration. This leads to the generation of structural defects of donor and/or acceptor nature and the appearance of the corresponding energy levels (bands) in the band gap єg. The ratio of ionized donors and acceptors (degree of compensation) determines the position of the Fermi level єF in Lu1-xScxNiSb. The dependence of the rate of generation of energy levels and the position of the Fermi level єF on the impurity concentration Sc, which determines the mechanism of electrical conductivity of Lu1-xScxNiSb, is established. The investigated Lu1-xScxNiSb solid solution is a promising thermoelectric material.

Bamboo-derived carbon material inherently doped with SiC and nitrogen for flexible supercapacitors

• Novel SiC/Pyrrolic-N doped carbon material have been synthesized from bamboo. • Inherent SiO 2 moieties in natural bamboo has been used as a sacrificial template. • The synergy of SiC and Pyrrolic-N has been demonstrated for Faradaic redox reactions. • Natural bamboo-based carbon materials deliver capacitance of 369 F g −1 at 0.5 A g −1 . • Bamboo-based carbon materials deliver 100% capacitance retention after 5000 cycles. It is still challenging to prepare porous carbon materials following a facile, green and universal sacrificial template method from renewable biomass. For this purpose, bio-renewable bamboo is a natural silicon reservoir containing a significant amount of inherent silica that can act as a natural sacrificial template for the formation of porous carbon materials as well as a dopant. Herein, we firstly report the SiC/N dual doped bio-renewable carbon material via a facile, natural sacrificial template method. In this newly developed method, the inherently available SiO 2 nanoparticles have been utilized as the natural sacrificial template for creating the multi-porous architecture as well as for the generation of structural defects in the form of SiC nano-species. Additionally, the inherent nitrogen functional groups give rise to the formation of only pyrrolic-N species after pyrolysis. Furthermore, dual doping of SiC and pyrrolic-N species stimulate the faradaic redox reaction during the charge/discharge process and further increase the rate capability at higher current density with excellent electrochemical stability. Hence, the synergistic effect of SiC and N-pyrrolic dually doped carbon network gives rise to the formation of promising electrode material towards supercapacitors. Benefiting from the above unique features, the supercapacitor with the SNAC-1 electrode material delivers excellent capacitive behavior (369 F g −1 at 0.5 A g −1 ) in 1 M H 2 SO 4 electrolyte with 100% capacitance retention after 5000 charge–discharge cycles. More prominently, the all-solid state, symmetric supercapacitors assembled by SNAC-1 show outstanding capacitance of 162 F g −1 at 0.5 A g −1 and reveal high energy density (∼5.41 W h kg −1 at 0.5 kW kg −1 power density) and excellent cyclic stability. This work provides an ideal sustainable solution from bamboo source to prepare porous SiC/N composites for cost-effective supercapacitor’s electrode materials.

Enhanced Catalytic Performance of Quasi-HKUST-1 for the Tandem Imine Formation.

Copper-based metal-organic framework (Cu3 (BTC)2 (H2 O)3 ]n ⋅nH2 OMeOH (HKUST-1) has been subjected to thermolysis under air atmosphere at different temperatures ranging from 100 to 300 °C. This treatment produces the partial removal of ligands, the generation of structural defects and additional porosity in a controlled way. The resulting defective materials denoted according to the literature as quasi-MOFs, were subsequently employed as heterogeneous catalysts in the one pot synthesis of N-benzylideneaniline from aniline and benzyl alcohol in open air as terminal oxidant at 70 °C under base- and dehydrating agent-free conditions. The Q-HKUST catalysts calcined at 240 °C (QH-240) was the most efficient in the series, promoting imine synthesis. Data from Knoevenagel condensation of malononitrile shows that in QH-240 the distances of Cu ions in HKUST-1 cavities are preserved, increasing the Knoevenagel activity, but a strong rearrangement takes place at 300 °C or above. The unsaturated copper active sites with simultaneous presence of micro- and mesopores in QH-240 are responsible for this excellent catalytic performance. The effective parameters on catalytic activity of QH-240 including deligandation temperature, the amount of catalyst, the ratio of reactants, and reaction temperature as well as the stability and recyclability of the catalyst were also investigated. The possible mechanism used by QH-240 follows alcohol aerobic oxidation and subsequent anaerobic condensation of aldehyde intermediate with aniline.

Cobalt-Based Quasi-Metal–Organic Framework as a Tandem Catalyst for Room-Temperature Open-Air One-Pot Synthesis of Imines

The catalytic activity of MOFs derives in a large extent from defects. To generate these defects, a cobalt-based metal–organic framework TMU-10, [Co6(oba)5(OH)2(H2O)2(DMF)4]n·2DMF has been subjected in the present study to controlled thermal treatment under air at different temperatures ranging from 100 to 700 °C. This treatment produces the removal of ligands, generation of structural defects, and additional porosity in an extent that depends on the conditions of the thermal treatment. The resulting defective materials, denoted according to the literature as quasi-MOFs, were subsequently employed as heterogeneous tandem catalysts in the one-pot synthesis of N-benzylideneaniline from aniline and benzyl alcohol in open air as a terminal oxidant at 60 °C under solvent-, base-, and dehydrating agent-free conditions. The quasi-TMU-10 framework obtained at 300 °C (QT-300) can efficiently promote imine synthesis within 2 h, forming water as the only byproduct. Unsaturated cobalt sites and the presence of micro- and mesopores in QT-300 are responsible for this excellent catalytic performance as tandem catalysts. The influence on QT-300 catalytic activity of catalyst amount, reactant ratio, and reaction temperature was investigated, as well as the stability and recyclability of the catalyst. The one-pot imine formation promoted by QT-300 follows alcohol aerobic oxidation and subsequent anaerobic condensation of the aldehyde intermediate with aniline.

Mechanism of Defect Formation in Zr1 – xVxNiSn Thermoelectric Material

Crystal and electronic structure, transport and energy state characteristics of the Zr1−xVx NiSn (0.01 ≤ x ≤ 0.1) thermoelectric material are investigated in the 80–400 K temperature interval. A mechanism of simultaneous generation of structural defects of the acceptor and donor nature, which determines the electric conductivity of the material, is established. It is shown that energetically expedient is a simultaneous occupation of the 4c position of Ni (3d84s2) atoms by V (3d34s2) atoms, which generates structural defects of the acceptor nature and the impurity acceptor band Ꜫ1A, as well as the 4a position of Zr (4d25s2) atoms, generating structural defects of the donor nature and the impurity donor band Ꜫ2D.

STUDY OF THERMOMETRIC MATERIAL Er1-xScxNiSb. II. EXPERIMENTAL RESULTS

STUDY OF THERMOMETRIC MATERIAL Er1-xScxNiSb. II. EXPERIMENTAL RESULTS

Plasma-Induced Defects Enhance the Visible-Light Photocatalytic Activity of MIL-125(Ti)-NH2 for Overall Water Splitting.

Defect engineering in metal-organic frameworks is commonly performed by using thermal or chemical treatments. Herein we report that oxygen plasma treatment generates structural defects on MIL-125(Ti)-NH2 , leading to an increase in its photocatalytic activity. Characterization data indicate that plasma-treated materials retain most of their initial crystallinity, while exhibiting somewhat lower surface area and pore volume. XPS and FT-IR spectroscopy reveal that oxygen plasma induces MIL-125(Ti)-NH2 partial terephthalate decarboxylation and an increase in the Ti-OH population. Thermogravimetric analyses confirm the generation of structural defects by oxygen plasma and allowed an estimation of the resulting experimental formula of the treated MIL-125(Ti)-NH2 solids. SEM analyses show that oxygen plasma treatment of MIL-125(Ti)-NH2 gradually decreases its particle size. Importantly, diffuse reflectance UV/Vis spectroscopy and valence band measurements demonstrate that oxygen plasma treatment alters the MIL-125(Ti)-NH2 band gap and, more significantly, the alignment of highest occupied and lowest unoccupied crystal orbitals. An optimal oxygen plasma treatment to achieve the highest efficiency in water splitting with or without methanol as sacrificial electron donor under UV/Vis or simulated sunlight was determined. The optimized plasma-treated MIL-125(Ti)-NH2 photocatalyst acts as a truly heterogeneous photocatalyst and retains most of its initial photoactivity and crystallinity upon reuse.

Advances in tailoring the water content in porous carbon aerogels using RT-pulsed fluorination

The present work introduces a safe and efficient fluorination method, called RT-pulsed fluorination, proceeding under pure fluorine gas. The RT-pulsed fluorination enables to modify the surface chemistry of carbon aerogels (CAs), materials which suffer from water trapping into their porosity and their low degree of graphitization, hence limiting their application. This new fluorination route was developed to reach several goals, such as preventing the generation of structural defects, maintaining the tailored porous texture of the aerogel, favoring covalent C–F bonding without promoting CF2 and CF3 groups, and repulsing the water trapping into the porosity. The impact of the RT-pulsed fluorination on the conductivity will be also discussed.

Changes in characteristics of Pt-functionalized RGO nanocomposites by electron beam irradiation for room temperature NO2 sensing

In this study, reduced graphene oxide (RGO) nanosheets were synthesized and then functionalized with Pt nanoparticles (NPs) for gas sensing studies at room temperature. Pt-functionalized RGOs (Pt-RGOs) were irradiated by a 2 MeV electron beam with different doses of 100 and 500 kGy (Pt-RGO-100 and Pt-RGO-500) to study the role of electron beam irradiation (EBI) on properties and NO2 gas sensing characteristics. Different characterization techniques verified the generation of structural defects after EBI. Additionally, NO2 sensing tests at room temperature revealed that the Pt-RGO-100 sensor had the highest response to NO2 gas as well as the shortest response time. We surmise that the improved sensing signal with respect to NO2 gas for Pt-RGO-100 sensor was related to the role of oxygen functional groups. However, decreases in the response for Pt-RGO-500 sensor were related to the creation of reactive oxygen gases that could be adsorbed on the active defects of the RGO by the interaction of electron beams with oxygen species in the ambient air, leading to a decrease of the effective defect sites and decreases of the sensing response. This work suggests progress towards an improved performance of RGO-based gas sensors that can work at low temperature, by using EBI as a clean tool applied at room temperature with Pt-functionalization.

Plasma Treating Mixed Metal Oxides to Improve Oxidative Performance via Defect Generation.

The generation of structural defects in metal oxide catalysts offers a potential pathway to improve performance. Herein, we investigated the effect of thermal hydrogenation and low-temperature plasma treatments on mixed SiO2/TiO2 materials. Hydrogenation at 500 °C resulted in the reduction of the material to produce Ti3+ in the bulk TiO2. In contrast, low temperature plasma treatment for 10 or 20 min generated surface Ti3+ species via the removal of oxygen on both the neat and hydrogenated material. Assessing the photocatalytic activity of the materials demonstrated a 40–130% increase in the rate of formic acid oxidation after plasma treatment. A strong relationship between the Ti3+ content and catalyst activity was established, although a change in the Si–Ti interaction after plasma treating of the neat SiO2/TiO2 material was found to limit performance, and suggests that performance is not determined solely by the presence of Ti3+.

Investigation of Electronic Structure of Zr1-xVxNiSn Semiconductive Solid Solution

The peculiarities of electronic and crystal structures of Zr1-xVxNiSn (x = 0 - 0.10) semiconductive solid solution were investigated. To predict Fermi level εF behavior, band gap εg and electrokinetic characteristics of Zr1-xVxNiSn, the distribution of density of electronic states (DOS) was calculated. The mechanism of simultaneous generation of structural defects of donor and acceptor nature was determined based on the results of calculations of electronic structure and measurement of electrical properties of Zr1-xVxNiSn semiconductive solid solution. It was established that in the band gap of Zr1-xVxNiSn the energy states of the impurity donor εD2 and acceptor εA1 levels (donor-acceptor pairs) appear, which determine the mechanisms of conduction of semiconductor.

Enhancement of catalytic performance over different transition metals modified CeO2 for toluene abatement

Pure CeO2 and CeO2–MOx (M: Mn, Zr and Ni) catalysts were synthesized by the co-precipitation method and evaluated for the oxidation of toluene. The characterization showed that the specific surface area and the porous texture of catalysts were improved due to the doping of transition metal. Besides, the doping of MOx into ceria contributed to the generation of structural defects, which could contribute to the easier storage and release of surface oxygen. Furthermore, the CeO2–MOx (M: Mn, Zr and Ni) catalysts exhibited higher concentration of Ce3+ and surface adsorbed oxygen than pure CeO2, which could correlate with the generation of oxygen vacancies, resulting in the enhancement of redox properties. Hence, CeO2–MnOx exhibited the best apparent catalytic activity of toluene due to its more Ce3+, structural defects and active oxygen species.

Control of nanostructure and pinning properties in solution deposited YBa2Cu3O7\u2212x nanocomposites with preformed perovskite nanoparticles

Solution deposited YBa2Cu3O7−x (YBCO) nanocomposites with preformed nanoparticles represent a promising cost-effective approach for superior critical current properties under applied magnetic fields. Nonetheless, the majority of YBCO nanocomposites with high nanoparticle loads (>20%) suffer from nanoparticle coalescence and degraded superconducting properties. Here, we study the influence of nanoparticle concentration (0–25% mol), size (5 nm–10 nm) and composition (BaHfO3, BaZrO3) on the generation of structural defects in the epitaxial YBCO matrix, key parameter for vortex pinning. We demonstrate that flash-heated superconducting nanocomposites with 20 mol% preformed BaHfO3 or BaZrO3 perovskite secondary phases feature discrete and small (7 nm) nanoparticles and high density of YBa2Cu4O8 (Y248) intergrowths. We identify a synergy between Y248 intergrowth density and small nanoparticles to increase artificial vortex pinning centers. Also, we validate the multideposition process to successfully increase film thickness of epitaxial nanocomposites with competitive critical currents Ic at 77 K.

Nano-Heteroepitaxy: An Investigation of SiGe Nano-Pillars Coalescence

Si/SiGe heterostructures are used in novel device architectures such as stacked nanowires [1] or neuromorphic memories [2]. Epitaxial growth of SiGe on Si is not lattice matched (4.2% difference between Si and Ge), so controlling strain relaxation in thick layers is important. We have recently shown that nano-heteroepitaxy yielded smooth and fully relaxed SiGe layers with a thickness of only a few hundreds of nm [3]. These could then be used as templates for tensile strained Si layers. However, the generation of defects such as stacking faults or twins was inherent to the process itself regardless of the nature of the nano-pillars (Si or SiGe). It is therefore likely that these defects occur during the coalescence process itself, during which adjacent pillars merge in order to form a 2D layer. In this work, we show the characteristics of our SiO2 based nano-template and investigate SiGe nano-pillars at different stages of the coalescence process. We have studied the coalescence of Si0.75Ge0.25 nano-pillars in a 300 mm industrial Reduced Pressure-Chemical Vapour Deposition tool. Dichlorosilane and germane were used to grow these structures at 700°C and a pressure of 20 Torr. The mean growth rate was around 47 nm/min. An integration scheme based on diblock copolymer patterning was used in order to fabricate a nano-template with a honeycomb pattern, with a pitch of 35 nm (see Figure 1). Selective epitaxy using a chlorinated chemistry of SiGe nano-pillars was investigated for different thickness, with a surface preparation based on a Siconi NH3/NF3-based remote plasma treatment [4]. SiGe nano-pillar merging was first examined with Atomic Force Microscopy (see Figure 2). Starting at 30 nm, the shape of the grains takes various forms depending on the number of merging nano-pillars, making the coalescence process heterogeneous in terms of shape evolution. As expected, an increase in average grain diameter and a decrease in the number of grains per unit surface area occurs as the deposited thickness increases (see Figure 3). The coalescence degree (i.e. the inverse of the number of grains) allowed us to predict a full coalescence thickness at ~80 nm. X-Ray Diffraction was performed, with omega-2theta scans performed around in-plane and out-of-plane orders to investigate the structural properties of the nano-pillars at various degrees of coalescence. This showed an increasing macroscopic degree of strain relaxation with thickness, confirming that growth from nano-cavities induces a fast relaxation. Scanning Spreading Resistance Microscopy showed a good sensitivity concerning the electrical activity of the nano-pillars (see Figure 4). At 20 nm, the electrical distinction between nano-pillars and the oxide mask was straightforward. The resistance of individual pillars was otherwise rather uniform. At 35 nm, we detect local resistivity variations within the coalescing nano-pillars, which are likely due to electrically active defects. We used cross-sectional Transmission Electron Microscopy to better understand the generation of structural defects during coalescence. Imaging of the 20 nm thick sample showed that individual nano-pillars were facetted and defect free (see Figure 5). The analysis of the 35 nm thick sample showed various cases ranging from defect free nano-pillar merging to the generation of stacking faults and twinning at the early stages of coalescence (see Figure 6). In conclusion, SiGe nano-pillars coalescence was investigated using a 300 mm industrial Reduced Pressure-Chemical Vapour Deposition tool. An integration scheme based on diblock copolymer patterning was used to provide nanometer-scaled templates for the epitaxy of SiGe nano-pillars. In order to study their merging, growth of nano-pillars with thicknesses ranging from 20 to 35 nm was performed and samples characterized by AFM, XRD, SSRM and TEM. Results showed evolution of grain shape, size and number, and high degrees of macroscopic strain relaxation were obtained even in the emerging nano-pillars. Defects such as stacking faults and twins were identified at the early stages of nano-pillars coalescence.

Near-Infrared Intersubband Photodetection in GaN/AlN Nanowires.

Intersubband optoelectronic devices rely on transitions between quantum-confined electron levels in semiconductor heterostructures, which enables infrared (IR) photodetection in the 1-30 μm wavelength window with picosecond response times. Incorporating nanowires as active media could enable an independent control over the electrical cross-section of the device and the optical absorption cross-section. Furthermore, the three-dimensional carrier confinement in nanowire heterostructures opens new possibilities to tune the carrier relaxation time. However, the generation of structural defects and the surface sensitivity of GaAs nanowires have so far hindered the fabrication of nanowire intersubband devices. Here, we report the first demonstration of intersubband photodetection in a nanowire, using GaN nanowires containing a GaN/AlN superlattice absorbing at 1.55 μm. The combination of spectral photocurrent measurements with 8-band k·p calculations of the electronic structure supports the interpretation of the result as intersubband photodetection in these extremely short-period superlattices. We observe a linear dependence of the photocurrent with the incident illumination power, which confirms the insensitivity of the intersubband process to surface states and highlights how architectures featuring large surface-to-volume ratios are suitable as intersubband photodetectors. Our analysis of the photocurrent characteristics points out routes for an improvement of the device performance. This first nanowire based intersubband photodetector represents a technological breakthrough that paves the way to a powerful device platform with potential for ultrafast, ultrasensitive photodetectors and highly efficient quantum cascade emitters with improved thermal stability.

Features of the band structure and conduction mechanisms of n-HfNiSn heavily doped with Y

The crystalline and electronic structures, energy, kinetic, and magnetic characteristics of n-HfNiSn semiconductor heavily doped with Y acceptor impurity are studied in the ranges: T = 80–400 K, N A Y ≈ 1.9 × 1020–5.7 × 1021 cm–3 (x = 0.01–0.30), and H ≤ 10 kG. The nature of the mechanism of structural defect generation is determined, which leads to a change in the band gap and the degree of semiconductor compensation, the essence of which is the simultaneous reduction and elimination of structural donor-type defects as a result of the displacement of ~1% of Ni atoms from the Hf (4a) site, and the generation of structural acceptor-type defects by substituting Hf atoms with Y atoms at the 4a site. The results of calculations of the electronic structure of Hf1–x Y x NiSn are in agreement with the experimental data. The discussion is performed within the Shklovskii–Efros model of a heavily doped and compensated semiconductor.