Ambient Oxygen Pressure Research Articles

Mist-CVD-derived Hf0.55Zr0.45O2 ferroelectric thin films post-annealed by rapid thermal annealing

We have newly applied Rapid Thermal Annealing (RTA) for the post-annealing of mist chemical-vapor-deposition (CVD)-derived Hf1−xZrxO2 (HZO) thin films. A ferroelectric polarization-electric field (P–E) curve was confirmed typically with noticeable polarization reversal currents. These ferroelectric properties of the HZO thin films provided quantitative estimation for Pr and Ec of ∼20 µC/cm2 and 1–1.5 MV/cm, respectively, compared to those reported from other growth methods, such as atomic-layer-deposition (ALD). It was revealed that the background leakage should be further reduced in a mist-CVD HZO film compared to those by ALD recently reported. The origin of the leakage was strongly related to the oxygen vacancy (Vo) generated in the film and near the HZO/bottom electrode interface. Nonetheless, it was found effective to use atmospheric pressure in air or oxygen in the post-RTA process for reducing leakage. In general, endurance behaviors for the mist-CVD HZO film revealed similar to those for samples prepared by other methods for both “wake-up” and “fatigue” phenomena, showing that the mist-CVD HZO film endured up to 2 × 109 counts. Finally, we expect that the mist-CVD HZO thin film would become a candidate for fabricating large-scale integration-oriented ferroelectric devices due to the intrinsic merits of the method.

Thermal laser evaporation of elemental metal sources in oxygen

Thermal laser epitaxy (TLE) is a novel film growth technique capable of fabricating ultrapure films of many material systems. For growing oxide films with TLE, the impact of source oxidation on the evaporation rate is a central issue, which, however, has not yet been explored systematically. Here, we report a systematic, experimental study of the role of source oxidation on source evaporation at various oxygen pressures and source temperatures in TLE. The volatility of the oxidized metal sources affects the source evaporation rate. When the oxidized metal source is more volatile than the metal, the source evaporation rate increases with the oxygen supply. In a strongly oxidizing environment, stable oxides with lower volatility tend to form and decrease the evaporation rate of the source. Increasing the laser power—and thereby the source temperature—tends to prevent the formation of stable oxides. At even higher source temperatures, the metal vapor pressure can dominate the oxide vapor pressure even in a high oxygen pressure atmosphere. A power-law relation between deposition rate and oxidizing gas pressure is found in case the formation and evaporation of volatile oxides of the elemental source material dominates the total evaporation process. The exponent of this law is a measure of the relevance of source oxidation for the evaporation of the source.

Symmetric Supercapacitor Based on Nitrogen-Doped and Plasma-Functionalized 3D Graphene

Nitrogen-doped, 3-dimensional graphene (N3DG), synthesized as a one-step thermal CVD process, was further functionalized with atmospheric pressure oxygen plasma. Electrodes were fabricated and tested based on the functionalized N3DG. Their characterization included scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Brunauer–Emmet–Teller (BET), and electrochemical measurements. The tested electrodes revealed a 208% increase in the specific capacitance compared to pristine 3D graphene electrodes in a three-electrode configuration. The performed doping and plasma treatment enabled an increase in the electrode‘s surface area by 4 times compared to pristine samples. Furthermore, the XPS results revealed the presence of nitrogen and oxygen functional groups in the doped and functionalized material. Symmetric supercapacitors assembled from the functionalized 3D graphene using aqueous and organic electrolytes were compared for electrochemical performance. The device with ionic electrolyte EMIMB4 electrolyte exhibited a superior energy density of 54 Wh/kg and power density of 1224 W/kg. It also demonstrated a high-cyclic stability of 15,000 cycles with a capacitance retention of 107%.

Prediction of severe pancreatitis in a population with low atmospheric oxygen pressure

To establish the severity of pancreatitis, there are many scoring systems, the most used are the Marshall and APACHE II systems, each one has advantages and disadvantages; but with good relation regarding mortality and prediction of complications. In populations with low barometric pressures produced by a decrease in atmospheric pressure, there is a decrease in partial pressure of oxygen, in these cases scores which take arterial oxygen partial pressure as one of their variables, may be overestimated. A diagnostic trial study was designed to evaluate the performance of APACHE II, Marshall and BISAP in a city 2640 m above sea level. A ROC analysis was performed to estimate the AUC of each of the scores, to evaluate the performance in predicting unfavorable outcomes (defined as the need for percutaneous drainage, surgery, or mortality) and a non-parametric comparison was made between the AUC of each of the scores with the DeLong test. From January 2018 to December 2019, data from 424 patients living in Bogota, with a diagnosis of gallstone pancreatitis was collected consecutively in a hospital in Bogota, Colombia. The ROC analysis showed AUC for predicting adverse outcomes for APACHE II in 0.738 (95% CI 0.647–0.829), Marshall in 0.650 (95% CI 0.554–0.746), and BISAP in 0.744 (95% CI 0.654–0.835). The non-parametric comparison to assess whether there were differences between the different AUC of the different scores showed that there is a statistically significant difference between Marshall and BISAP AUC to predict unfavorable outcomes (p=0.032). The mortality in the group of patients studied was 5.8%. We suggest the use of BISAP to predict clinical outcomes in patients with a diagnosis of biliary pancreatitis in populations with decreased atmospheric pressure because it is an easy-to-use tool and does not require arterial oxygen partial pressure for its calculation.

Experimental and numerical investigation on flow condensation process of oxygen jet in crossflow of liquid oxygen

The mixing and condensation process of gaseous oxygen jet in liquid oxygen flow in the outlet pipeline of oxidizer booster pump in liquid rocket engine are studied. In the present study, experiments are performed to investigate oxygen jet condensation in crossflow of liquid oxygen in a vertical pipe. The image of the test section is obtained by visualization device and processed by digital image technology. A computational fluid dynamics (CFD) model is developed to simulate the mixing and condensation process based on multiphase VOF model and Lee phase change model. The experimental results show that, under the current operating conditions, gaseous oxygen forms a crooked jet plume at the outlet of orifices, and then the gas phase gradually condenses, forming discontinuous bubbles downstream. The effects of Reynolds number of liquid oxygen, oxygen mass flux, ambient pressure and liquid oxygen temperature on the gas distribution and axial condensation length are investigated accordingly. The mass transfer coefficient r=10000s−1 which has been verified by the experiment of oxygen jet in liquid oxygen crossflow is obtained and the predicted gas distribution by CFD simulation is in good agreement with the experimental data. The experimental dimensionless axial condensation length is in the rage of 7.3 to 18.2, and a correlation of dimensionless axial condensation length has been modified. Besides, the dimensionless axial condensation length predicted by simulation is less than 13% comparing with experiment. The averaged heat transfer coefficients obtained in experiment and simulation are around 13.89–26.04 kW/(m2K) and 12-67kW/(m2K), which is much lower than the average heat transfer coefficient in the DCC of water. The results of the present investigation will be helpful in designing the pipeline between pumps in liquid rocket engine.

An investigation of the characteristics of oxygen sensors using a Nd1+xBa2−xCu3Oy-based ceramics rod

A hot spot, which is a glowing orange local area, appears in REBa2Cu3Oy (RE: rare earth) ceramic rods when a voltage exceeding a certain value is applied at room temperature. After a hot spot appears, the current changes according to the partial pressure of oxygen in the ambient atmosphere, acting as an oxygen sensor without the need for a heating system. In this study, the moisture resistance and oxygen-sensing characteristics of 5 mol% Nd2BaCuO5-added Nd1+xBa2−xCu3Oy (x = 0–0.8) rods were investigated by preparing ceramic rods via a solid-state reaction at 960 °C. The moisture resistance improved at x ≥ 0.4. In the case of x ≤ 0.4, the current increased as the voltage increased, reached its peak value, and subsequently decreased. Finally, the current increased monotonically with increasing voltage at x ≥ 0.6. Furthermore, the sensitivity to gas was not strongly affected by the changes in x. The characteristics are discussed from the viewpoint of the heat balance in the rod and lattice defects of the material.

Direct Synthesis of 3-Aryl Substituted Isocoumarins and Phthalides through Palladium Acetate Catalyzed C(sp2 )-H Activation in Ionic Liquids.

A novel Pd-catalysed oxidative coupling between benzoic acids and vinylarenes or acrylates to furnish isocoumarins and phthalides is reported. The reaction proceeds smoothly in molten tetrabutylammonium acetate via a selective C-H bond activation, with very low percentage of ligand-free palladium acetate as the catalyst, under atmospheric pressure of oxygen. Sub-stoichiometric amount of copper acetate is also required as a reoxidant for the palladium.

Independent Effects Of Hypoxia And Altitude On Human Physiology

PURPOSE: Decreased fraction of inspired oxygen (FiO2) is often used to simulate the atmospheric partial pressure of oxygen decreases experienced during high altitude sojourns. Therefore, we aimed to independently investigate hypoxia and altitude by isolating oxygen concentration and barometric pressure. METHODS: 18 subjects completed 3 trials (sea level, hypoxia, altitude). 90-minute duration and intensity matched hypoxic stimuli were induced via decreased FiO2 or 4,200 m ascent. Relative tissue oxygenation change and cardiovascular variables were measured during rest and a 3-minute step-test. RESULTS: Muscle oxygenated hemoglobin (O2Hb) and muscle deoxygenated hemoglobin (HHb) were not different across environments during rest or exercise (p > 0.339) with alterations noted during rest to exercise transitions (p < 0.001). Resting brain O2Hb at hypoxia and altitude were lower than sea level (p < 0.012), but not different than each other (p = 0.278). Exercising brain O2Hb was lower at altitude than sea level (p = 0.007) similarly trending compared to hypoxia (p = 0.066). Exercising brain O2Hb was not different between hypoxia and sea level (p = 0.158). Brain HHb at hypoxia and altitude were higher than sea level (p < 0.001), but not different than each other (p = 0.158). Exercise HR at hypoxia (141 ± 4 beats·min-1) and altitude (141 ± 3 beats·min-1) were lower than sea level (127 ± 44 beats·min-1, p < 0.002), but not different than each other (p > 0.208). Exercise stroke volume at altitude (109.6 ± 4.1 mL) was higher than hypoxia (97.8 ± 3.3 mL) and sea level (99.8 ± 3.9 mL, p < 0.010) with no differences between hypoxia and sea level (p = 0.481). Exercise cardiac output at hypoxia (13.8 ± 0.6 L) and altitude (15.5 ± 0.7 L) were greater than sea level (12.6 ± 0.5 L, p < 0.006) with altitude greater than hypoxia (p = 0.001). CONCLUSIONS: During acute hypoxic stimuli, skeletal muscle maintains oxygenation while the brain does not. Tissue oxygenation may be mediated by environmentally driven cardiovascular compensation. FiO2 decreases may not satisfactorily simulate all physiological outcomes experienced during altitude induced barometric pressure decreases. Funding: Department of Defense United States Army Medical Research and Materiel Command (DOD USAMRMC: W81XWH-15-2-0075).

Enhancing Resin Cement Adhesion to Zirconia by Oxygen Plasma-Aided Silicatization.

The combinations of alumina particle air abrasion (AA) and a 10-methacryloyloxyidecyl-dihyidrogenphosphate (MDP) primer and a tribochemical silica coating (TSC) and a silane–base primer are contemporary pre-cementation treatments for zirconia restorations for bonding with resin cements. However, the stability of zirconia resists the mechanical or chemical preparations. The purpose of this study was to develop an atmospheric-pressure oxygen plasma (OP)-aided silicatization method to enhance the adhesion of resin cements to zirconia. Zirconia discs were prepared to receive surface treatments of different combinations: (1) AA or TSC (2) with or without OP treatment, and (3) a chemical primer (no primer, silane, or a silane–MDP mixture). The surface morphology, hydrophilicity, and chemical compositions were characterized, and the resin–zirconia bond strengths were examined either after 24 h or a thermocycling test. The results indicated that the OP treatment after the TSC facilitated the homogeneous distribution of silane and crosslinking of silica particles, and effectively improved the hydrophilicity. The OP increased the O and Si and reduced the C elemental contents, while the combination of TSC, OP, and silane induced SiOx generation. Among the groups, only the TSC-OP–silane treatment effectively enhanced the bond strength and maintained the adhesion after thermocycling. With these results, the OP aided the silicatization protocol effectively, generated silane crosslinking, and resulted in superior resin–zirconia bond strength and durability compared to the current treatments.

Gold Nanoparticles Supported on Poly(2,6‐dimethyl‐1,4‐phenylene oxide) as Robust, Selective and Cost‐Effective Catalyst for Aerobic Oxidation and Direct Oxidative Esterification of Alcohols

AbstractA new catalytic system based on gold nanoparticles (AuNPs) incarcerated in poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) matrix has been synthesized and successfully tested in aerobic oxidation of alkyl alcohols. PPO is a cheap and commercially available polymer, showing nanoporous morphology, high glass transition temperature (Tg =220 °C), semi‐crystallinity, excellent thermal stability, and interesting chemo‐physical properties. The synthesis of the AuNPs‐PPO catalyst is simple, cost‐effective and allows a fine control of the gold concentration, as well as an optimal dispersion of 7–8 nm sized AuNPs in the polymer matrix. AuNPs‐PPO is an efficient, robust and selective catalyst active in the aerobic oxidation and oxidative esterification of alcohols in water under mild reaction conditions (35 °C, atmospheric pressure of oxygen). The testing of AuNPs‐PPO in aerobic oxidation of 1‐phenylethanol to acetophenone, as a benchmark reaction, highlighted that this gold catalyst exhibits activity values among the highest so far reported for polymer‐supported AuNPs under mild reaction conditions. The oxidation of primary alcohols, such as benzyl and cinnamyl alcohols, could be addressed to the corresponding aldehyde or carboxylate derivatives. Alkyl cinnamates were obtained with efficiency in the one‐pot aerobic oxidation of cinnamyl alcohol in the presence of alkyl alcohols, such as n‐butanol or n‐hexanol. The role of the polymer matrix and the reaction conditions on both activity and selectivity of the AuNPs‐PPO catalyst were also investigated and discussed.

Desulfurization of molten steel with molten slag using the electrochemical method

The desulfurization in metallurgical process is electrochemical reaction in nature. Desulfurization using the electrochemical method was proposed with the CaO-MgO-Al2O3 molten slag covering molten steel. Effect of an applied external DC voltage, which varied from 0 to 8V, was discussed. The results indicated that sulfur in molten steel could be removed effectively with applied external voltage. According to the mechanism analyses of the desulfurization under the applied external voltage, kinetics formulae were developed, and the model calculated results that were in agreement with the experimental values. The transfer coefficient of sulfur in molten slag under electromigration conditions was approximately 2.09?10-5 m?s-1?V-1. The desulfurization of molten steel with molten slag can be promoted by increasing the applied voltage, reducing the partial pressure of atmospheric oxygen, strengthening the stirring intensity of the reaction system, and optimizing the composition and properties of the slag.

Efectos de la variación en la presión de oxígeno ambiental sobre el movimiento dentario ortodóntico.

Objective: To evaluate the effects of variation in ambient oxygen pressure on orthodontic tooth movement in guinea pigs. Material and Methods: Seventy-two guinea pigs randomly distributed into two groups (A and B) were evaluated in the study. All specimens were fitted with orthodontic appliances to distalize maxillary incisors. Group A was controlled under conditions of oxygen pressures at sea level (150 masl, 157 mm Hg) and Group B under conditions of oxygen pressures at altitude (3405 masl, 107 mm Hg). The clinical (distance between the distal-incisal angles of the maxillary incisors), biochemical (serum alkaline phosphatase), and histopathological characteristics (osteoblast and osteocyte count) were evaluated before placing the orthodontic devices and after 24 and 72 hours. Results: In the clinical evaluation, the distance between the distal-incisal angles of the maxillary incisors, on day one and three, was significantly higher in group B compared to group A (p=0.002 and p=0.001, respectively). In the biochemical evaluation, the level of serum alkaline phosphatase on the first and third days was significantly higher in group B compared to group A (p=0.001 and p=0.001, respectively). In the histopathological evaluation, the osteoblasts and osteocytes count on day one and three was significantly higher in group B compared to group A (p&lt;0.05). Conclusion: Oxygen pressure at high altitude positively influenced orthodontic tooth movement in guinea pigs, improving its clinical, biochemical, and histopathological characteristics.

Reversible Manipulation of Photoconductivity Caused by Surface Oxygen Vacancies in Perovskite Stannates with Ultraviolet Light.

Programmable optoelectronic devices call for the reversible control of the photocarrier recombination process by in-gap states in oxide semiconductors. However, previous approaches to produce oxygen vacancies as a source of in-gap states in oxide semiconductors have hampered the reversible formation of oxygen vacancies and their related phenomena. Here, a new strategy to manipulate the 2D photoconductivity from perovskite stannates is demonstrated by exploiting spatiallyselective photochemical reaction under ultraviolet illumination at room temperature. Remarkably, the ideal trap-free photocurrent of air-illuminated BaSnO3 (≈200pA) is reversibly switched into three orders of magnitude higher photocurrent of vacuum-illuminated BaSnO3 (≈335nA) with persistent photoconductivity depending on ambient oxygen pressure under illumination. Multiple characterizations elucidate that ultraviolet illumination of BaSnO3 under low oxygen pressure induces surface oxygen vacancies as a result of surface photolysis combined with the low oxygen-diffusion coefficient of BaSnO3 ; the concentrated oxygen vacancies are likely to induce a two-step transition of photocurrent response by changing the characteristics of in-gap states from the shallow level to the deep level. These results suggest a novel strategy that uses light-matter interaction in a reversible and spatiallyconfined way to manipulate functionalities related to surface defect states, for the emerging applications using newly discovered oxide semiconductors.

Experimental investigation of the methane combustion assisted by atmospheric pressure oxygen microwave plasma torch

The atmospheric-pressure oxygen microwave plasma is employed to enhance the methane combustion in the jet-diffusion combustor. The plasma-assisted combustion (PAC) is compared with natural combustion without plasma application in terms of the flame morphology, flame temperature, and combustion efficiency. It is found experimentally that the oxygen plasma assistance in combustion is prominent in lean oxygen condition, and the active species generated in the microwave plasma torch contribute to the combustion process more dominantly than the flame temperature change caused by heating of oxygen microwave plasma. The combustion degree of CH4 in PAC is much more enhanced in lean oxygen combustion, and the exhaust gas in combustion is effectively controlled with the use of the oxygen microwave plasma torch.

Field measurements of vehicle pollutant emissions in road tunnels at different altitudes

Many previous studies have focused on air quality in road tunnels, which is a major concern for ventilation design. However, few researchers have investigated the air quality in tunnels in high-altitude areas. The ambient environment in high-altitude areas featuring low oxygen content and ambient pressure can influence the vehicle pollutant emissions inside the tunnels. As a result, field measurements were carried out considering environmental parameters and gaseous pollutant concentrations in four road tunnels at different altitudes to determine exact vehicle emissions. Results show that ambient pressure is closely related to the altitude and that the oxygen content will decrease when the altitude increases due to the lower air density. The air velocity induced by the vehicle fleet is only affected by the traffic parameters and not influenced by the air density. The CO and NO emission factors in test tunnels at different altitudes were calculated according to pollutant mass balance models. We can conclude that an environment featuring low oxygen content and ambient pressure in high-altitude areas contributes to incomplete combustion of the engines and performance degradation of the catalytic converter, which leads to higher toxic pollutant emissions inside the tunnels. In this study, the CO and NO emission factors were 0.701 and 0.403 g km−1 vehicle-1 respectively at an altitude of 500 m, which then increased to 1.567 and 0.886 g km−1 vehicle-1, respectively, at an altitude of 3850 m. The NO altitude coefficient is introduced, similar to the CO altitude coefficient in the guidelines, to reflect the influence of altitude on the NO emission factor, and we can determine that the impact of altitude on the CO emission factor is greater. We hope our work will provide a reference for road tunnel ventilation design in high-altitude areas.

The role of oxygen vacancies on SnO2 in improving formaldehyde competitive adsorption: A DFT study with an experimental verification

The synthesis of metal oxides enriched with oxygen vacancies is beneficial for improving the gas-sensing properties of metal-oxide-based chemoresistive sensors. Density functional theory (DFT) calculations were performed to investigate the mechanism of adsorption of formaldehyde and acetone vapors on oxygen-vacancy-enriched SnO2. The ambient humidity and oxygen pressure were also considered in the calculations. The results indicated that oxygen vacancies play an important role in formaldehyde adsorption. The adsorption energy of formaldehyde on the reduced (110) surface was four times higher than that on the stoichiometric (110) surface, which was in turn, much higher than that of acetone. The presence of water molecules weakened the affinity of the adsorbed species for the SnO2 surface; however, the inhibition capacity varied. The formaldehyde molecules combined with the oxygen atom in the hydroxyl group to form dioxymethylene during adsorption, which mitigates the weakening effect. Oxygen-vacancy-enriched SnO2 was prepared to verify the validity of the DFT calculations.

Effect of Atmospheric Pressure Oxygen Plasma treatment on Bonding Characteristics of Basalt Fibre Reinforced Concrete

In this research work, the bonding characteristics of plasma treated basalt fibres were analysed by employing the fibre pull-out test. 80 samples were prepared with two different spans of basalt fibres (such as 25 mm and 50 mm) and four levels of embedded length (10, 15, 20 and 25) inside standard M20 grade concrete. Debonding and bonding characteristics of the plasma treated fibres were compared with raw basalt fibres through the fibre pull-out test. The plasma treated and raw basalt fibres were characterised through Field emission scanning electron microscope (FESEM) and Fourier transform infrared (FTIR) analysis. It was observed that confirmation of the presence of hydroxyl groups on the basalt fibre surface was realised through the FTIR test and that there was higher adsorption of concrete particles by the plasma treated basalt fibres through FESEM. The de bonding and fibre pull-out energy of the plasma treated basalt fibres were improved by about 9% and 10% compared with 25 mm and 50 mm raw basalt fibres. From the observation above, it can be stated that the surface modification of basalt fibre may lead to a change in the debonding and pull-out energy level.

Effects of Ambient Pressure on Burning Characteristics of Gasoline: A Pilot Study

A fire can pose a significant threat to a building’s occupants and leads to property damage. The burning characteristics usually determine the severity of the accident. Environments in high-altitude areas feature low oxygen content and ambient pressure, which can influence the burning characteristics of combustibles. In this paper, a series of field experiments were conducted to investigate the burning characteristics of gasoline at different altitudes considering heat release rate (HRR), flame height, and smoke release rate. Results show that the combustion process can be divided into three stages: initial stage, stable stage, and attenuation stage. Lower oxygen content and ambient pressure reduce the HRR; for example, the HRR at an altitude of 4150 m is nearly half at an altitude of 500 m, contributing to a lower smoke release rate. The HRR is proportional to 1.3 power of atmospheric pressure, and a fitting equation was brought out in this paper. Flame height increases with the increase in altitude due to the demand for more oxygen during the combustion process since the oxygen content is low in high-altitude areas.

Ozone Production in Cylindrical Co-axial Double Dielectric Barrier Discharge Ozone Generator

This study developed an ozone generator of a double co-axial cylindrical dielectric barrier discharge system with air, argon, and oxygen as the working gases. The discharge was produced by using a high voltage power supply of 0 - 18 kV and a line frequency of 50 Hz. The flow rate of air, argon, and oxygen was varied from 1 to 6 L/min. A comparison of O3 generation in air, argon, and oxygen using brass as a central electrode was conducted and it was found that O3 concentration was higher in the case of oxygen than in the air and in argon gases environment for given fixed discharge time, applied voltage, and diameter of the brass electrode. This study revealed that the concentration of ozone increased along with the increase in the applied voltage for constant discharge time and gas flow rate. The O3 concentration also increased with the increase in the discharge time at fixed applied voltage and gas flow rate; however, the concentration decreased with the increase in the gas flow rate at fixed discharge time, applied voltage, and diameter of the electrode. A small reactor with a large inner electrode generated a high concentration of O3. Yet, a reactor with a small diameter, there seemed to have an optimum inner electrode diameter. The glass tube reactor of the internal diameter of 18 mm and the brass electrode of diameter 8 mm were utilized in this study. The ozone concentration was higher for oxygen as feed gas than both in the air and in argon and the O3 concentration was also higher in the air than in argon at fixed discharge time, applied voltage, and diameter of ozone generator. HIGHLIGHTS Ozone concentration increases with increasing applied voltage and discharge time but concentration decreases with increasing gas flow rates Low cost ozone can be produced in DBD reactor at atmospheric pressure Oxygen can be used as feed gas to generate high concentration of ozone than other gases inside DBD generator Optimization of central electrode diameter and gap space inside DBD reactor can help to increase ozone concentration, yield, and efficiency Proper choice of central high voltage electrode also can play the important role for the generation of ozone in DBD chamber GRAPHICAL ABSTRACT

Role of oxygen vacancies on the low-temperature dielectric relaxor behavior in epitaxial Ba0.85Ca0.15Ti0.9Zr0.1O3 thin films

Dielectric relaxation in ferroelectric perovskites can result from different inherent chemical and charge disorders within their crystal structures. Despite several theories on dielectric relaxations, the relationship between the concentration of oxygen vacancy (${V}_{\mathrm{O}}$) and dielectric relaxation has not been studied in perovskite oxide thin films. In this work, we report a systematic investigation on the influence of the ${V}_{\mathrm{O}}^{\ensuremath{'}}\mathrm{s}$ on the dielectric relaxation of ${\mathrm{Ba}}_{0.85}{\mathrm{Ca}}_{0.15}{\mathrm{Ti}}_{0.9}{\mathrm{Zr}}_{0.1}{\mathrm{O}}_{3}$ (BCZT) epitaxial thin films grown with ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ (LSMO) top and bottom electrodes on single-crystal ${\mathrm{SrTiO}}_{3}$ (100) substrates using pulsed laser deposition. The ambient oxygen pressures during film growth were systematically varied to control the concentration of ${V}_{\mathrm{O}}$ in the epitaxial BCZT thin films. Low ambient oxygen pressure was found to enhance the tetragonality of the BCZT films and a systematic decrease in the tetragonality was observed at high oxygen pressure conditions as evidenced from x-ray diffraction (XRD) studies. Temperature dependent XRD analyses indicated a low-temperature anomaly near $\ensuremath{\sim}160\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in the BCZT/LSMO heterostructures. Low-temperature dielectric measurements revealed relaxor dielectric response with broad frequency dependence of the dielectric constant. It is proposed that the low-temperature dielectric relaxation is possibly caused by dipolar clusters that are formed by the aggregation of correlated ${V}_{\mathrm{O}}$-induced dipolar defects within the films deposited under different ambient oxygen pressures. High-resolution transmission electron microscopy suggested the presence of the nanometer-sized ${V}_{\mathrm{O}}$ clusters as represented by the structural defects of average diameters of $\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ in the BCZT films grown at variable ambient oxygen pressure. Activation energies of the aforesaid dipolar clusters, obtained from the Vogel-Fulcher fitting of the dielectric dispersion, showed a gradual increase in magnitude, as well as decreasing freezing temperatures, with decreasing concentrations of ${V}_{\mathrm{O}}$ in the BCZT films. From the theoretical analysis of the experimental data, it is postulated that the presence of the ${V}_{\mathrm{O}}$-induced dipolar defects affects the low-temperature dielectric relaxation in the BCZT thin films. This work significantly extends the understanding of ${V}_{\mathrm{O}}$-mediated dielectric relaxor behavior in complex perovskite oxide films.