Addition Of Oxygen Research Articles

Accelerated oxidation of epoxy thermosets with increased O2 pressure

Polymer oxidation is usually accelerated with temperature, which is therefore applied in nearly every experimental approach dealing with predictive materials aging. Because of this simple approach, we may tend to neglect that the effective concentration of oxygen also acts as a rate multiplier for oxidation. Increasing the oxygen partial pressure in an aging environment accelerates oxidation, and while there is often a near proportional increase initially, the effect of additional oxygen usually transitions to a saturation level at some elevated pressure. This has been theoretically described in the general autoxidation scheme and is well recognized. However, for many materials the exact rate behavior under moderately increased oxygen concentration remains to be established. We therefore review epoxy oxidation and offer a broader overview of its behavior under increased O2 partial pressure. Experimental data are given for a few thermoset materials demonstrating their rate behavior under O2 partial pressure up to 4 atm, meaning approximately 20 times more than under standard atmospheric conditions. Confirmative evidence suggests that epoxy materials will reach saturation oxidation rates only at significantly higher O2 partial pressure. In such a high-pressure regime it is theoretically possible to not only accelerate oxidation, but to transition into a condition where O2 diffusion can be increased without further accelerating the oxidation rate. This can reduce diffusion limited oxidation effects under specific accelerated aging conditions as a combination of temperature and O2 partial pressure.

Fast, Efficient Tailoring Growth of Nanocrystalline Diamond Films by Fine-Tuning of Gas-Phase Composition Using Microwave Plasma Chemical Vapor Deposition.

Nanocrystalline diamond (NCD) films are attractive for many applications due to their smooth surfaces while holding the properties of diamond. However, their growth rate is generally low using common Ar/CH4 with or without H2 chemistry and strongly dependent on the overall growth conditions using microwave plasma chemical vapor deposition (MPCVD). In this work, incorporating a small amount of N2 and O2 additives into CH4/H2 chemistry offered a much higher growth rate of NCD films, which is promising for some applications. Several novel series of experiments were designed and conducted to tailor the growth features of NCD films by fine-tuning of the gas-phase compositions with different amounts of nitrogen and oxygen addition into CH4/H2 gas mixtures. The influence of growth parameters, such as the absolute amount and their relative ratios of O2 and N2 additives; substrate temperature, which was adjusted by two ways and inferred by simulation; and microwave power on NCD formation, was investigated. Short and long deposition runs were carried out to study surface structural evolution with time under identical growth conditions. The morphology, crystalline and optical quality, orientation, and texture of the NCD samples were characterized and analyzed. A variety of NCD films of high average growth rates ranging from 2.1 μm/h up to 6.7 μm/h were successfully achieved by slightly adjusting the O2/CH4 amounts from 6.25% to 18.75%, while that of N2 was kept constant. The results clearly show that the beneficial use of fine-tuning of gas-phase compositions offers a simple and effective way to tailor the growth characteristics and physical properties of NCD films for optimizing the growth conditions to envisage some specific applications.

The Structural Basis of the Activity Cliff in Modafinil-Based Dopamine Transporter Inhibitors.

Modafinil analogs with either a sulfoxide or sulfide moiety have improved binding affinities at the human dopamine transporter (hDAT) compared to modafinil, with lead sulfoxide-substituted analogs showing characteristics of atypical inhibition (e.g., JJC8-091). Interestingly, the only distinction between sulfoxide and sulfide substitution is the presence of one additional oxygen atom. To elucidate why such a subtle difference in ligand structure can result in different typical or atypical profiles, we investigated two pairs of analogs. Our quantum mechanical calculations revealed a more negatively charged distribution of the electrostatic potential surface of the sulfoxide substitution. Using molecular dynamics simulations, we demonstrated that sulfoxide-substituted modafinil analogs have a propensity to attract more water into the binding pocket. They also exhibited a tendency to dissociate from Asp79 and form a new interaction with Asp421, consequently promoting an inward-facing conformation of hDAT. In contrast, sulfide-substituted analogs did not display these effects. These findings elucidate the structural basis of the activity cliff observed with modafinil analogs and also enhance our understanding of the functionally relevant conformational spectrum of hDAT.

Mobility and current boosting of In-Ga-Zn-O thin-film transistors with metal capping layer oxidation

This study investigates the effect of an oxidized Ta capping layer on the boosting of field-effect mobility (μ FE) of amorphous In-Ga-Zn-O (a-IGZO) Thin-film transistors (TFTs). The oxidation of Ta creates additional oxygen vacancies on the a–IGZO channel surface, leading to increased carrier density. We investigate the effect of increasing Ta coverage on threshold voltage (V th), on-state current, μ FE and gate bias stress stability of a-IGZO TFTs. A significant increase in μ FE of over 8 fold, from 16 cm2 Vs−1 to 140 cm2 Vs−1, was demonstrated with the Ta capping layer covering 90% of the channel surface. By partial leaving the a-IGZO uncovered at the contact region, a potential barrier region was created, maintaining the low off-state current and keeping the threshold voltage near 0 V, while the capped region operated as a carrier-boosted region, enhancing channel conduction. The results reported in this study present a novel methodology for realizing high-performance oxide semiconductor devices. The demonstrated approach holds promise for a wide range of next-generation device applications, offering new avenues for advancement in metal oxide semiconductor TFTs.

Reinforced chemical adsorption ability for efficient CO2 electrolysis in solid oxide electrolysis cell via a dual-exsolution strategy

Accelerating sluggish kinetics of CO2 reduction reaction (CO2RR) is of great importance for efficiently converting CO2 into valuable chemical products in solid oxide electrolysis cells (SOECs). Here, a novel dual-exsolution strategy is proposed to enhance CO2 electrolysis properties of La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) cathode. With simultaneously exsolved CoFe alloy and Bi nanoparticles on LSCFN cathodic matrix, the as-prepared SOEC delivers a high current density of 539 mA cm−2 for CO2 electrolysis at 800 °C and 1.5 V, and successfully runs over 170 h without any attenuation. The introduction of Bi exsolution not only promotes CoFe exsolution, provides additional oxygen vacancies, but also greatly boost the kinetics of CO2 adsorption/dissociation/activation. This work offers new insights into tailoring perovskite electrocatalysts for the CO2 electrolysis via dual-exsolution strategy.

Revealing the Mechanism of O<sub>2</sub> and Pressure Effects on the Corrosion of X80 Carbon Steel Under Supercritical CO<sub>2</sub> Conditions

Pipeline transportation is widely used due to its ability to improve the efficiency of CO<sub>2</sub> transportation in Carbon Capture, Utilization, and Storage (CCUS). Within the transport pipelines, CO<sub>2</sub> fluid exists in a supercritical state and often contains various impurity gases such as O<sub>2</sub> and H<sub>2</sub>O, which can easily cause steel corrosion, affecting the safety of pipeline operations. In this investigation, we examine the corrosion behavior of X80 carbon steel within a water-saturated supercritical CO<sub>2</sub> environment utilizing weight loss experiments, electrochemical tests, and surface analysis techniques. Furthermore, we explore the impact of pressure and oxygen on the corrosion process of X80 steel. The results indicated that X80 steel underwent severe corrosion under the experimental conditions, with FeCO<sub>3</sub> as the primary corrosion product. Both the introduction of oxygen and an increase in pressure accelerated the steel's corrosion, and the addition of oxygen led to the formation of a new corrosion product, Fe<sub>2</sub>O<sub>3</sub>. Electrochemical test results showed that changes in pressure did not significantly alter the electrochemical corrosion characteristics of the steel, but the introduction of oxygen decreased the electrochemical reaction resistance of X80 steel. Combined with surface analysis, the following conclusions were drawn: In a 50°C supercritical CO<sub>2</sub> environment, the anode reaction of X80 steel corrosion is the active dissolution of iron, while the cathode reaction involves the dissolution and ionization of CO<sub>2</sub>. Changes in pressure do not alter the corrosion mechanism, but the introduction of oxygen leads to oxygen corrosion reactions in the system, accelerating the anode reaction rate and thus increasing the degree of corrosion.

Clinic-Functional Assessment of Hemoglobin Desaturation by Oxygen in 6-Minute Walk Test Among Patients with Bronchial Asthma

The main purpose of the study is to assess the prevalence and clinical significance of hemoglobin desaturation by oxygen during the 6-minute walk exercise test in patients with bronchial asthma. Material and methods: 75 patients with exacerbation of mixed (48 %) and allergic (52 %) bronchial asthma were examined. Research explored following methods: collecting complaints and anamnesis, physical examination, spirometry, CO-metry of exhaled air to determine carboxyhemoglobin, transcutaneous 2-wave pulse oximetry (at rest and during 6-minute walk exercise test) with spectral analysis and correction for COHb. 6-minute walk exercise test was performed after relief of asthma exacerbation (before discharge from the hospital), assessing the desaturation-distance ratio (the ratio of the area of oxygen desaturation of hemoglobin to the 6-minute walk exercise test distance), O2-GAP index, the dynamics of fatigue and dyspnea before and after 6-minute walk exercise test. In smoking patients (n = 36, 48 %), the smoker index was calculated. Based on oximetry results during the 6-minute walk exercise test, patients were divided into “desaturators” (n = 28, 37 %) and “non-desaturators” (n = 47, 63 %). Results. The findings of the research illustrated that hemoglobin desaturation by oxygen, detected by reducing SpO2 to < 90 % during 6-minute walk exercise test, was associated with the severity of this disease exacerbation, more pronounced impairment of pulmonary ventilation and blood oxygenation, and the demand for longer hospitalization. The prevalence of tobacco smoking and the magnitude of the smoker index in both groups were identical but in “desaturators” we found a higher prevalence of the combination of asthma and COPD compared to “non-desaturators.” The “desaturators” had significantly higher level of desaturation-distance ratio and increased demand for additional oxygen flow to maintain SpO2 at ≥ 88 % during a 6-minute walk test, which indicates a higher “oxygen price” of physical activity in this group of patients. Conclusion. Thus, the high prevalence of the phenomenon of hemoglobin oxygen desaturation during 6-minute walk exercise test in patients with asthma and associated clinic-functional disorders supports the feasibility and clinical significance of conducting a stress test with a 6-minute walk not only in COPD patients, but also in bronchial asthma patients.

Improved resistive switching behavior of defective fluorite structured Sm2Ce2O7 thin film prepared by RF sputtering

The Al/Sm2Ce2O7/ITO (Al/SCO/ITO) structure resistive random access memory (RRAM) was prepared using RF magnetron sputtering, and its resistive switching (RS) behaviors were systematically investigated. The memory exhibited a high switching cycle of 1031, along with set/reset voltages of −1.55/0.53 V and a Ron/Roff ratio exceeding 102. This high performance can be attributed to the presence of intrinsic oxygen vacancies in the defective fluorite structure, accounting for 34.44 % of the vacancies. This vacancy percentage can be increased to 41.97 % by simultaneously transforming Ce4+ to Ce3+ ions through annealing treatment, thereby releasing additional oxygen vacancies. Despite this increase, there remains a sufficient window (Ron/Roff > 10) to distinguish between the high-resistance state (HRS) and low-resistance state (LRS) of the SCO device. Furthermore, the device, when subjected to post-metal annealing (PMA), exhibits a high endurance of up to 1815 cycles, a set/reset voltages of −2.19/1.31 V, a Ron/Roff ratio of >10, and a retention time of over 104 s at 25 °C and 85 °C. However, it is important to note that PMA-treated device requires a higher forming voltage due to the formation of a thicker AlOx layer. This study highlights the potential of Al/SCO/ITO memory devices for RRAM applications.

Exploring tungsten-oxygen vacancy synergy: Impact on leakage characteristics in Hf0.5Zr0.5O2 ferroelectric thin films

The recent discovery of ferroelectric properties in HfO2 has sparked significant interest in the fields of nonvolatile memory and neuromorphic computing. Yet, as device scaling approaches sub-nanometer dimensions, leakage currents present a formidable challenge. While tungsten (W) electrodes are favored over traditional TiN electrodes for their superior strain and interface engineering capabilities, they are significantly hampered by leakage issues. In this study, we elucidate a positive feedback mechanism attributable to W electrodes that exacerbates oxygen vacancy defects, as evidenced by density functional theory computations. Specifically, intrinsic oxygen vacancies facilitate the diffusion of W, which, in turn, lowers the formation energy of additional oxygen vacancies. This cascade effect introduces extra defect energy levels, thereby compromising the leakage characteristics of the device. We introduce a pre-annealing method to impede W diffusion, diminishing oxygen vacancy concentration by 5%. This reduction significantly curtails leakage currents by an order of magnitude. Our findings provide a foundational understanding for developing effective leakage suppression strategies in ferroelectric devices.

Effect of dopant loading and calcination conditions on structural and optical properties of ZrO2 nanopowders doped with copper and yttrium

Undoped, Cu and/or Y doped ZrO2 nanopowders were synthesized with Zr, Y, and Cu nitrates using a co-precipitation approach. Their structural and optical properties were examined regarding dopant content (0.1–8.0 mol.% of CuO and 3–15 mol.% of Y2O3) and calcination conditions (400 °C–1000 °C and, 1,2 or 5 h) through Raman scattering, XRD, TEM, EDS, AES, EPR, UV–vis and FTIR diffused reflectance methods. The results showed that both Cu and Y dopants promoted the appearance of additional oxygen vacancies in ZrO2 host, while the formation of tetragonal and cubic ZrO2 phases was primarily influenced by the Y content, regardless of Cu loading. The bandgap of most of the powders was observed within the 5.45–5.65 eV spectral range, while for those with high Y content it exceeded 5.8 eV. The (Cu,Y)-ZrO2 powders with 0.2 mol.% CuO and 3 mol.% Y2O3 calcined at 600 °C for 2 h demonstrated nanoscaled tetragonal grains (8–12 nm) and a significant surface area covered with dispersed CuxO species. For higher calcination temperatures, the formation of CuZr 2+ EPR centers, accompanied by tetragonal-to-monoclinic phase transformation, was found. For fitting of experimental FTIR reflection spectra, theoretical models with one, five, and seven oscillators were constructed for cubic, tetragonal, and monoclinic ZrO2 phases, respectively. Comparing experimental and theoretical spectra, the parameters of various phonons were determined. It was found that the distinct position of the high-frequency FTIR reflection minimum is a unique feature for each crystalline phase. It was centered at 700–720 cm−1, 790–800 cm−1, and 820–840 cm−1 for cubic, tetragonal, and monoclinic phases, respectively, showing minimal dependence on phonon damping coefficients. Based on the complementary nature of results obtained from structural and optical methods, an approach for monitoring powder properties and predicting catalytic activity can be proposed for ZrO2–based nanopowders.

Unveiling Synergetic Photocatalytic Activity from Heterometallic Ti/Ce Clusters.

Titanium-oxo clusters, with their robust structure and suitable optical and electronic properties, have been widely investigated as photocatalysts. Heterometallic Ti/M-oxo clusters provide additional tunability and functionality, which enable systematic structure-activity investigations to elucidate the reaction mechanisms and improve the catalyst design. Incorporating cerium into Ti-oxo clusters can provide additional redox (CeIV/CeIII) and oxygen harvesting ability, but to date, only a limited number of structurally defined titanium-cerium (Ti/Ce) clusters have been reported due to their synthetic challenges. Herein, we report the synthesis and photocatalytic properties of two structurally defined Ti/Ce-oxo clusters, Ti8Ce2(BA)16 and Ti9Ce4(BA)20, as well as a TiCe-BA cluster with a calculated formula of Ti20Ce9O36(BA)42. Photocatalytic study of these clusters demonstrates that the amount of Ce3+ species greatly impacts its photocatalytic oxidation performance, and their superior photocatalytic reactivity toward aerobic alcohol oxidation can be contributed to the synergistic effects of the multiple radical species generated upon light absorption. This work represents a significant milestone in the construction of stable Ti/Ce-oxo clusters, enriching the current library of known heterometallic Ti/M-oxo clusters, and providing a series of crystalline materials with great promise of photoluminescence and photovoltaic chemistry.

Research on high-carbon ether-based oxygen additives: Catalytic transformation of 2-methylfuran and furfural to ethers via CuMgAlOx catalysts

The surge in aviation fuel consumption has intensified environmental concerns, driving research efforts towards discovering oxygen-enriched additives that can boost their performance. This investigation employs 2-methylfuran and furfural as precursors, undergoing catalytic conversion into high-performance high-carbon ethers. The study initiates by employing Amberlyst-15 resin as a catalyst, converting 2-methylfuran and furfural into a high-carbon polymer (1A). A continuous polymerization process in a fixed-bed reactor highlights the exceptional stability of Amberlyst-15, maintaining a conversion rate of approximately 70 % over 140 h. A kinetics model elucidates the temperature-dependent dynamics of the polymerization reaction. Following this, the polymer undergoes hydrogenation (HDO) using CuMgAlOx catalyst, yielding an ether compound (2A) with a remarkable selectivity of 95.7 % and a carbon yield of 95.5 %. Characterization techniques reveal uniform elemental distribution and a high abundance of mesopores in the CuMgAlOx catalyst, substantiating its superior hydrogenation efficiency. Notably, even after six cycles, the CuMgAlOx catalyst retains an impressive 94.8 % polymer conversion rate, underscoring its exceptional stability.

Regulate local chemical order to achieve high strength and ductility in TiZrNbVAl lightweight high entropy alloys via adding oxygen

TiZrNbVAl lightweight high-entropy alloys (LHEAs) with body-centered cubic (BCC) structure have received extensive attention due to their low density and considerable mechanical properties. And the mechanical properties of these LHEAs can be further improved by adjusting the local chemical order (LCO). Here, we report a strategy for regulating LCOs in TiZrNbVAl LHEAs by adding oxygen. The results showed that the yield strength of LHEA increased from 787.8 MPa to 1029.5 MPa after oxygen addition. Moreover, the microstructure evolution proves that LCOs is conducive to promoting the transition of dislocation from plane slip, which is easy to produce stress concentration, to multistage slip, which improves the homogenizing deformation ability, and increasing the ductility from 12.8 % to 20.9 %, which is an increase of ∼63 %. Our work provides a paradigm for achieving outstanding strength-ductility tradeoff in BCC-LHEAs via O doping.

Measuring flow rate and purity in portable oxygen concentrators

For people with respiratory disorders who need additional oxygen therapy, oxygen concentrators are vital medical equipment. By concentrating oxygen from the ambient air, they function to give the user a greater flow of oxygen-enriched air. The application of lithium zeolite for oxygen concentration in POCs is the most intense part of this work. One kind of zeolite material that may selectively absorb nitrogen from the air to increase oxygen concentration is lithium zeolite. The capacity, effectiveness, and dependability of a POC fitted with lithium zeolite are all examined in this study, along with its overall performance. The findings show that lithium zeolite, which has benefits including high oxygen purity and low energy consumption, is a potential material for use in POCs. The results of this study aid in the creation of POCs for oxygen therapy that are more effective and efficient. This study suggests utilizing an Arduino microcontroller and an HX710B air pressure sensor to measure the oxygen flow rate in a POC. The POC’s oxygen flow channel incorporates the HX710B sensor to monitor pressure variations, which the Arduino uses to translate into flow rate readings. To verify the accuracy and dependability of the system, its performance is assessed under different flow rate scenarios. Lithium zeolites are well-known for having a high selectivity for nitrogen adsorption, which can enhance the concentrator’s oxygen separation process’s effectiveness. Lithium-zeolite-based oxygen concentrators may have a lower environmental effect than standard concentrators.

Topochemical behavior of ferrocene embedded in V2O5·nH2O with weak hydrogen bonding enhancing ammonium-ion storage

Aqueous ammonium ion batteries (AAIBs) are garnering increasing attention due to their utilization of abundant resources, cost-effectiveness, safety, and unique energy storage mechanism. The pursuit of high-performance cathode materials has become a pressing issue. In this study, we propose and synthesize ferrocene-embedded hydrated vanadium pentoxide (Fer/VOH) for implementation in AAIBs. The inclusion of ferrocene serves to expand the interlayer spacing, mitigate interlayer forces, and introduce the electron-rich environment characteristic of ferrocene. This augmentation facilitates the creation of additional oxygen vacancies, substantially enhancing the capacity and efficiency of ammonium ion storage. Notably, our investigation reveals that the incorporation of ferrocene attenuates the hydrogen bonding interactions associated with ammonium ions, rendering them more amenable to the interlayer embedding and release processes. Building upon these advantages, Fer/VOH exhibits a specific capacity of 313 mAh/g at a current density of 0.2 A/g, representing the highest reported performance among vanadium oxides utilized in AAIBs to date. Even after 2000 charge/discharge cycles at a current density of 2 A/g, Fer/VOH maintains a reversible specific capacity of 89 mAh/g, with a capacity retention rate of 54.8%. This study confirms the viability of Fer/VOH as a cathode material for AAIBs and offers a novel approach to enhancing the electrical conductivity and diminishing the hydrogen bonding forces in vanadium oxide intercalation through the embedding of electron-rich species and positronic groups.

Does coronavirus disease 2019 history alone increase the risk of postoperative pulmonary complications after surgery? Prospective observational study using serology assessment.

Concern exists about the increasing risk of postoperative pulmonary complications in patients with a history of coronavirus disease 2019 (COVID-19). We conducted a prospective observational study that compared the incidence of postoperative pulmonary complications in patients with and without a history of COVID-19. From August 2022 to November 2022, 244 adult patients undergoing major non-cardiac surgery were enrolled and allocated either to history or no history of COVID-19 groups. For patients without a history of confirming COVID-19 diagnosis, we tested immunoglobulin G to nucleocapsid antigen of SARS-CoV-2 for serology assessment to identify undetected infection. We compared the incidence of postoperative pulmonary complications, defined as a composite of atelectasis, pleural effusion, pulmonary edema, pneumonia, aspiration pneumonitis, and the need for additional oxygen therapy according to a COVID-19 history. After excluding 44 patients without a COVID-19 history who were detected as seropositive, 200 patients were finally enrolled in this study, 100 in each group. All subjects with a COVID-19 history experienced no or mild symptoms during infection. The risk of postoperative pulmonary complications was not significantly different between the groups according to the history of COVID-19 (24.0% vs. 26.0%; odds ratio, 0.99; 95% confidence interval, 0.71-1.37; P-value, 0.92). The incidence of postoperative pulmonary complications was also similar (27.3%) in excluded patients owing to being seropositive. Our study showed patients with a history of no or mild symptomatic COVID-19 did not show an increased risk of PPCs compared to those without a COVID-19 history. Additional precautions may not be needed to prevent PPCs in those patients.

Unlocking ethane production in photocatalytic methanol reforming based on a novel carbon–carbon coupling mechanism

Photocatalytic methanol reforming represents a promising solution to energy and environmental challenges, yet the CO2 by-product poses significant environmental concerns. Recent advancements enhance the economic and environmental sustainability of this process by yielding valuable by-products like ethylene and ethylene–glycol. However, synthesizing ethane (C2H6), a crucial material, remains unattainable through this reaction, with an unclear mechanism. Herein, we synthesized oxygen-deficient two-dimensional TiO2 nanosheets to achieve ethane production via methanol reforming. Through theoretical calculations and in situ characterization, we unveil a novel carbon–carbon (C–C) coupling mechanism driving ethane production. It is discovered that methanol preferentially adsorbs on the oxygen vacancies of the defective TiO2 surface, forming methoxy radicals (*CH3O), facilitating C–C coupling for ethane formation. Furthermore, prolonged hydrogenation creates additional oxygen vacancies, leading to more adjacent oxygen vacancies. This results in more neighboring *CH3O, facilitating C–C coupling and elevating C2H6 production. Our study clarifies ethane production feasibility in photocatalytic methanol reforming, providing valuable references for future research.

(Invited) Role of Oxidant Gas for Atomic Layer Deposition of HfxZr1−XO2 Thin Films on Ferroelectricity of Metal-Ferroelectric-Metal Capacitors

We fabricated 400°C-annealed TiN/HfxZr1−xO2 (HZO)/TiN metal–ferroelectric–metal (MFM) capacitors using H2O and O2 plasma as oxidant gases of thermal (TH) and plasma-enhanced atomic layer deposition (PE-ALD), respectively, for HZO films. The PE-ALD film formed a more ferroelectric orthorhombic phase compared with the TH-ALD case. Therefore, the MFM capacitor with the PE-ALD film showed higher remanent polarization and dielectric constant. For the PE-ALD case, moreover, an oxygen-rich interfacial layer (O-rich-IL) was formed between the HZO film and TiN-bottom electrode during the ALD process. Thus, the MFM capacitor with the PE-ALD film showed less degradation of switching polarization during field cycling compared with the TH-ALD case, because an O-rich-IL should prevent the interface reaction and formation of additional oxygen vacancies in the PE-ALD film during field cycling. Based on these results, it is important to consider the selection of an ALD oxidant gas for the fabrication of HZO-based MFM capacitors.

Full-Field Deformation Study of Ti–25Nb, Ti–25Nb–0.3O and Ti–25Nb–0.7O Shape Memory Alloys During Tension Using Digital Image Correlation

A Ti–25Nb shape memory alloy (SMA) exhibits shape memory effect associated with stress-induced martensitic transformation from β to α″ phase. Addition of oxygen stabilizes the β phase and changes stress–strain response. Oxygen-added Ti–25Nb SMAs show a more distinct superelastic behavior. In this work, digital image correlation (DIC) was applied to investigate for the first time full-field deformation of Ti–25Nb, Ti–25Nb–0.3O and Ti–25Nb–0.7O (at. pct) SMAs. The specimens were subjected to loading–unloading tensile tests to study local and global mechanical characteristics related to activity of particular deformation mechanisms of the SMAs. Strain and strain rate fields were quantitatively compared at selected stages of each SMA’s deformation. It was found that the Ti–25Nb SMA exhibits a macroscopically localized Lüders-type deformation associated with the stress-induced phase transformation, whereas Ti–25Nb–0.3O and Ti–25Nb–0.7O SMAs show more discrete types of deformation related to activity of interstitial oxygen atoms. As a consequence, at particular stages of deformation, local values of strain rate of Ti–25Nb SMA were significantly higher than those of average strain rate. The results obtained in this paper provide a better understanding of the deformation mechanism in the oxygen-added Ti–25Nb based SMAs.

Toward an understanding of the role of structural organization and point defects in the formation of functional pure and Tm3+-doped (Ca3-xSrx)(VO4)2 for diode-pumped and SRS lasers

Whitlockite-type polycrystalline and single-crystal (Ca3−xSrx)(VO4)2 solid solutions were successfully obtained by solid-state synthesis and Czochralski method, respectively. Synchrotron powder X-ray diffraction allowed to reveal actual compositions of polycrystalline (Ca3−xSrx)(VO4)2 solid solutions with х = 0.3, 0.54, 0.9, 1.2, 1.35 refined by Rietveld method, which are slightly different from the initial ones. Synchrotron X-ray single-crystal diffraction analysis of Czochralski-grown undoped (Ca1.8Sr1.2)(VO4)2 (CSVO) revealed its actual composition (Ca2.982(11)Sr0.031)(VО4)2. Difference between initial and refined compositions is analyzed and discussed. In the CSVO structure, Sr2+ ions partially occupy monocapped Ca2 and two-capped Ca3 trigonal prismatic sites and Ca2+ ions are in the Ca5 and Ca5A sites, forming two independent strongly distorted tetrahedral Ca5O4 and octahedral Ca5AO6 oxygen environments. Synchrotron X-ray single-crystal diffraction analysis together with X-ray absorption spectroscopic study of (Сa2.4Sr0.6)(VO4)2 doped with 0.5 and 1.0 wt% Tm2O3 (СSVO:0.5Tm and CSVO:1.0Tm) allowed to establish the absence of cations in the Ca5A site, the localization of Sr2+ ions in the Ca2 and Ca3 sites and additionally in octahedral Ca4 site together with Tm3+ ions, forming an individual eight-coordinated environment, in the refined compositions (Ca2.776(7)Sr0.210(4)Tm3+0.008(1))(VO4)2 and (Ca2.855(7)Sr0.140(7)Tm3+0.009(1)□0.022(7))(VO4)2, respectively, with vacancies (marked by a square,□) in the two-capped Ca1 trigonal prismatic site in the CSVO:1.0Tm structure. Additional interstitial oxygen, participating in the formation of the Tm3+ environment, found in the residual electron density, together with vacancies in the Ca1 site provides electroneutrality to CSVO:0.5Tm and CSVO:1.0Tm crystals. Several structural models of the coordination environment of Tm3+ ions were analyzed and the most correct one was proposed.