Search

Progressive optimization of the surface passivation of Si solar cells requires access to the elemental composition and chemical bonding characteristics of ultrathin layers and buried interfaces on textured or structured surfaces. The passivation of the rear side of passivated emitter and rear solar cells, for instance, can be realized through AlOx/SiNx stacks, which are known to provide an additional field effect passivation on top of the chemical surface passivation. Herein, transmission electron microscopy is used at locally prepared cross‐sections of such stacks. Electron energy loss spectroscopy is used to extract depth‐resolved information of elemental composition and chemical bonding at nanometer scale. With this, the interfacial excess O fraction, which is crucial for the field effect passivation, is successfully determined for the first time for AlOx passivation layer systems on industrially produced Si solar cells. [ABSTRACT FROM AUTHOR]

• Numerical model is developed to investigate oxy-coal combustion in novel swirl burner. • Flame properties and flame type change significantly at different oxygen excess values. • Carbon monoxide decreases and nitrogen oxides increase with increase of oxygen excess. • Burner is able for stable work with similar flame shape in both combustion modes. • Carbon monoxide and nitrogen oxides are lower during oxy-fuel than air combustion. Oxy-fuel combustion is the most promising carbon capture and storage technology, which eliminates carbon dioxide emissions into the atmosphere and also decreases nitrogen oxides emissions thereby lowering global warming potential. In order to implement oxy-fuel combustion technology in full scale power plants, its costs, mainly connected with the amount of pure oxygen produced, must be lowered. The main hypothesis is that it is possible to maintain similar velocity and heat transfer distribution while maintaining stable and efficient burner operation during both combustion technologies modifying burner aerodynamics. Excess oxygen is chosen as a representative parameter of burner's performance and investigation is carried out for four different oxy-fuel burner oxygen excess ratios (λ: 0.8, 0.98, 1.07, and 1.24) together with reference air combustion case. This study suggests a workflow, based on semi-industrial experimental investigations and computational fluid dynamics model composed of advanced sub-models for different combustion phases for development of real scale dual-mode coal swirl burners able for efficient operation during both combustion regimes. The results show that the temperature in near-burner zone and nitrogen oxides emissions increase, while carbon monoxide emissions decrease with the increase of burner oxygen excess ratio, and stable combustion with similar velocity and temperature distributions for both combustion modes is achieved for oxygen excess ratio of 1.07, with decrease in nitrogen oxides and carbon monoxide emissions during oxy-fuel combustion. The performed study demonstrates that it is possible to choose the appropriate burner settings regarding nitrogen oxides and carbon monoxide emissions and burner's ability to operate stably in both air and oxy-fuel combustion modes. [ABSTRACT FROM AUTHOR]

Abstract Bulk CuAlO 2 compound has been widely studied as a p-type metal oxide semiconductor material due to the simplicity in its synthesis and use of inexpensive raw materials. The Fe doping in CuAlO 2 has been demonstrated to enhance the electrical conductivity. An in-depth analysis of the effect of Fe doping in CuAlO 2 on the carrier concentration improvement was revealed. Delafossite CuAl 1−x Fe x O 2 powders with x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.30 were synthesized by a solid-state reaction method. The X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) studies were used to measure the atomic-ion concentrations and the oxidation state of each element. The variations of carrier concentration corresponded with a ratio of Cu2+/Cu1+ in CuAlO 2. We found that the increase of Cu2+/Cu1+ was caused by double effects through divalent metal ions (Fe2+) doping and excess oxygen (O 2−δ) in CuAlO 2. The maximum carrier concentration of 8.09 × 1017 cm−3 was obtained for the CuAlO 2 sample at Fe content of 10 at.%. Highlights • XPS and XAS are used to identify CuAl 1−x Fe x O 2 for understanding in-depth mechanism. • Fe doping improves interstitial O 2 and surface oxygen adsorption capability of CuAlO 2. • The variations of carrier concentration caused by double effects, Fe2+ and O 2+δ [ABSTRACT FROM AUTHOR]

This work presents the role of excess oxygen in CuFeO 2.06 compounds on thermoelectric and optical properties. The CuFeO 2.06 specimens were synthesized by solid state reaction method. X-ray diffraction technique has confirmed the CuFeO 2 structure for the specimens. In particularly, CuFeO 2.06 specimen revealed the structural extension of lattice parameter: a and c . Also, the specimen found increasing excess oxygen of approximately 3% as a resulted enhancement of mixed valence state of Cu + and Cu 2+ ions. XPS showed mixed valence state of the Cu + /Cu 2+ ions, and Fe 3+ and Fe 2+ ions was also found in the CuFeO 2.06 specimen. Mixed valence states contributed the co-existence of hole and electron carriers for conduction. Consequently, electrical conductivity of the CuFeO 2.06 specimen increased up to 23 S/cm at 873 K. Also, increasing Seebeck coefficient was shown to be approximately 302 μV/K at 873 K. The CuFeO 2.06 specimen was found power factor to be approximately 2.1 × 10 −4 W/m∙K 2 at 873 K. The indirect optical gap of CuFeO 2.06 (2.40 eV) was lower than that of the CuFeO 2 (2.60 eV). Thus, thermoelectric and optical properties were governed by an existence of excess oxygen. [ABSTRACT FROM AUTHOR]

We have investigated the structure, magnetic, and electrical properties, and the resistance switching effect (RSE) of La2NiO $_{{ {4+\delta }}} compounds with different excess oxygen levels of \delta = 0.004 - 0.031 . Our results showed the structure changes from tetragonal I4/mmm to orthorhombic Fmmm when reducing \delta value from 0.011 to 0.006. The M(H) curves measured at several temperatures exhibit a coexistence of the weak ferromagnetic and antiferromagnetic interactions. Two shoulders on M(T) curves related to the spin and charge ordering have also been observed. These ordering temperatures depend strongly on \delta ) and low ( RL ) values. The resistance change ratio of the samples defined as 100% \times [RH - RL]/RL is found to be about 18%–57%, which depends on the value of $\delta $ in the samples. [ABSTRACT FROM AUTHOR]

Mixed ionic and electronic conducting K2NiF4-type oxide, Nd2Ni1-xCuxO4+δ (x=0~1) powders were synthesized by solid state reaction technique and solid oxide fuel cells consisting of a Nd2Ni1-xCuxO4+δ cathode, a Ni-YSZ anode and ScSZ as an electrolyte were fabricated. The effect of copper substitution for nickel on the electrical and electrochemical properties was examined. Small amount of copper doping (x=0.2) resulted in the increased electrical conductivity and decreased polarization resistance. It appears that this phenomenon was associated with the high mean valence of nickel and copper and the resulting excess oxygen (δ). It was found that power densities of the cell with the Nd2Ni1-xCuxO4+δ (x=0.1 and 0.2) cathode were higher than that of the cell with the Nd2NiO4+δ cathode. [ABSTRACT FROM AUTHOR]

Highlights: [•] Excess oxygen has significant impact on crystal structure of Nd2NiO4+δ ceramics. [•] Temperature-stable giant dielectric responses are observed in both ceramics. [•] The small polaronic hopping model is confirmed in oxygen excess ceramics. [ABSTRACT FROM AUTHOR]

Abstract: Pr1.91Ni0.71Cu0.24Ga0.05O4 (PNCG) thin film with few 100 nm thickness was prepared on polycrystalline MgO substrate with pulsed laser deposition (PLD) method. The prepared film was dense and uniform, and formation of Pr2NiO4 phase was observed after a post annealing treatment. Electrical conductivity was significantly changed in the film and increase in conductivity was observed when the film thickness was 320 nm. However, the conductivity decreased with decreasing the film thickness less than 300 nm and Hall coefficient measurements suggested that the electronic hole concentration increased, however its mobility decreased in PNCG film because of the expanded lattice. Increased conductivity in the PNCG film with 320 nm could be explained by the increased amount of electronic hole and its high mobility. XPS measurement also showed that Pr and Ni were an oxidized state comparing with that in bulk and so excess oxygen may be introduced in the PNCG thin film by charge compensation. [Copyright &y& Elsevier]

Abstract: In the paper, a new approach to the combustion control by introducing the parallel type air–fuel combustion control and cross-limiting type (or lead-lag type) combustion control technique designed in one control system in a boiler is presented. This new approached combustion control system is designed in such way that controlled the air–fuel ratio in furnace in parallel way for small steam demand variation and in cross-limiting way for high steam demand variation. This approach does not require any extra field instrumentation or modified process parameter. All original instruments are used to measure the process parameters for combustion control and final control elements controlled the process. It is shown that air and fuel flow can be successfully optimized for the required steam demand by new designed combustion control. The accurate air–fuel ratio obtained in the proposed technique also minimizes some problems of the conventional system like incomplete combustion during sudden load change, boiler stuck-up problem and bump problem. The complete derivation of the required mathematical models is reported in the paper. Performance of three boilers incorporated with the proposed system is observed for a long period and the performance report is presented. A very efficient performance in three boilers has been observed. [Copyright &y& Elsevier]

Abstract: Various supported Pt catalysts (Pt/WO3/CeO2/ZrO2; Pt/ZrO2, Pt/CeO2, Pt/CeZrO, Pt/WO3/ZrO2, and Pt/WO3/CeZrO) were prepared and characterized, and their characteristics of catalytic reductions of NO by CO with or without oxygen were investigated. TPR and CO-TPD showed that Pt/CeO2 and Pt/CeZrO could be easily reduced by CO while the reduction by CO was inhibited with the introduction of WO3 in the case of Pt/WO3/CeZrO. According to NO-TPD, NO reduction could not proceed over the catalysts (Pt/WO3/CeZrO, Pt/ZrO2, Pt/WO3/ZrO2) to remain in an oxidized state even after reduction by CO, but NO reduction was possible over Pt/CeO2 and Pt/CeZrO catalysts when reduced by CO. For NO+CO reaction without oxygen, those easily reducible catalysts (Pt/CeO2 and Pt/CeZrO) exhibited better catalytic performances. With excess oxygen, however, Pt/WO3/CeZrO and Pt/WO3/ZrO2 catalysts exhibited higher NO conversions to N2 and N2O especially at a low temperature. The acidity from ZrO2 and WO3 in Pt/WO3/CeO2/ZrO2 catalysts should play an important role on their NO conversion only in the presence of excess oxygen. [Copyright &y& Elsevier]

Abstract: This study examined the reduction of NO x by H2 over a Pt/Al2O3 catalyst coated onto a monolith as a function of temperature. The formation of N2O began at a low temperature due to the chemisorption of NO on Pt metal and its resulting oxidation at the Pt active sites. The formation of N2 was possible at higher temperatures because at the high temperatures, the reaction rate for N2 formation was higher than the reaction rate for N2O formation. The formation of NO2 was predominant above 150°C due to the excessive oxidation activity of the catalyst. The formation of N2O at low temperatures and that of N2 at high temperatures were found to be strongly related to the Pt loading and the temperature range in which the reductive activity was obtained, respectively. Therefore, both reductive conditions and an adequate reaction temperature are important factors for the selective formation of N2 from the reduction of NO on a Pt catalyst. The temperature-dependent change in the oxidation state of Pt during the reduction of NO was also examined to determine the mechanism for the reduction of NO x by H2. In addition, the reaction conditions for the selective reduction of NO x to N2 were determined. [Copyright &y& Elsevier]

We have fabricated truly single-crystal BSCCO thin films of the quality of traveling-solvent-floating-zone single crystals by using a double side cleaving technique. The thicknesses of the cleaved thin films thus obtained ranges from 20 nm to 100 nm. These films are found to adsorb or desorb oxygen very easily at a relatively low annealing temperature of 200 to 300°C. When a cleaved film is annealed in Argon at 300°C for 10 mm, it changes to an insulator without any trace of superconducting transition. When this film is subsequently annealed in oxygen at 300°C, it exhibits a sharp superconducting transition at about 90 K. When the film is subjected to these process repeatedly, the film changes from an insulator to a superconductor quite reversibly. We have measured in-plane resistivity and the Hall coefficient systematically in a wide doping range for this thin film BSCCO single crystals. [ABSTRACT FROM AUTHOR]

Abstract: Defect chemistry plays an important role in the p-type conductivity of transparent CuAlO2 thin films. Presence of excess oxygen atoms within the crystallites sites or interstitial sites is responsible for the enhanced hole-conductivity of p-CuAlO2+ x thin films. These excess oxygen atoms within the films were induced by post-deposition annealing of the films in oxygen atmosphere. Composition analyses of the films confirmed the presence of nonstoichiometric (excess) oxygen within the films. With increase in the post-deposition annealing time, more and more oxygen atoms were intercalated within the p-CuAlO2+ x thin films. Electrical conductivity measurements of the films indicated that with increase in the excess oxygen contents within the films, the p-type conductivity also increased. This observation supports the origin of p-type conduction in CuAlO2+ x thin films due to excess oxygen atoms. [Copyright &y& Elsevier]

We have prepared single-crystalline CaCuO2 thin films with infinite layer structure by pulsed laser deposition and investigated their optical properties by light absorption and Raman scattering. We find that oscillator strength of the charge transfer excitations decreases with increasing the lattice parameter c. On the other hand, two-magnon Raman scattering is insensitive to the lattice parameter. These results indicate that excess oxygen incorporated under the relatively strong oxidative condition supplies localized holes into the CuO2 planes. Furthermore, the excess oxygen relaxes selection rule of the phononic Raman scattering in the infinite layer compounds. [Copyright &y& Elsevier]

To explore the behavior of excess oxygen in uranium dioxide (UO 2+x), we have investigated the energetics of oxygen interstitial clusters using density function theory (DFT+U). The calculations are based on transverse 3k antiferromagnetic UO 2+x with a P a 3 ¯ configuration. The spin-orbit coupling increases the possibility of capturing the ground state of UO 2 without special control. The size of the simulation boxes significantly impacts the formation energies and thus the clustering energies of defects, especially for large oxygen interstitial clusters with charge states. The interactions between two negatively charged oxygen interstitials as a function of distance in UO 2+x demonstrate that the oxygen interstitials prefer a split di-interstitial configuration for distances less than 0.5 nm, but the mono-interstitial is the preferred configuration for distances greater than 0.6 nm. Cube-octahedral clusters are metastable and may relax to split-type clusters. The clustering energies of oxygen interstitial clusters imply that the interstitials are more prone to cluster for Fermi levels close to the valence band, while the clustering becomes energetically unfavorable at Fermi levels beyond the mid band gap. The Bader charge analysis indicates that neighboring uranium ions to the oxygen interstitials can oxidize to a +5 valence state. [ABSTRACT FROM AUTHOR]

Internal oxidation of dilute silver alloys containing Al, Mg, Zn, Cu, and Sn was studied in air at temperatures between 573 K and 1173 K. Electrical resistivity, gravimetric, and gas-extraction measurements were made. The general trend of the resistivity is that it increases upon oxidation at lower temperatures and the resistivity decreases at higher temperatures in all of these alloys except Ag-Mg, in which it increases even at 1173 K. The increase in resistivity is considered to be related to the formation of clusters having excess oxygen. A detailed investigation was performed on Ag-Al alloys. The O/Al ratio in the clusters in Ag-2.2 at.% Al is much higher on oxidation at 773 K than for stoichiometric AlO at 1173 K. The clusters release the excess oxygen on subsequent annealing at high temperatures, and decompose to stable AlO at 1173 K. [ABSTRACT FROM AUTHOR]

Insulator-to-metal transition in Ca 2 RuO 4 has drawn keen attention because of its sensitivity to various stimulation and its potential controllability. Here, we report a direct observation of Fermi surface, which emerges upon introducing excess oxygen into an insulating Ca 2 RuO 4 , by using angle-resolved photoemission spectroscopy. Comparison between energy distribution curves shows that the Mott insulating gap is closed by eV-scale spectral-weight transfer with excess oxygen. Momentum-space mapping exhibits two square-shaped sheets of the Fermi surface. One is a hole-like α sheet around the corner of a tetragonal Brillouin zone, and the other is an electron-like β sheet around the Γ point. The electron occupancies of the α and β bands are determined to be n α = 1. 6 and n β = 0. 6 , respectively. Our result indicates that the insulator-to-metal transition occurs selectively in d x z and d y z bands and not yet in d x y band. This orbital selectivity is most likely explained in terms of the energy level of d x y , which is deeper for Ca 2 RuO 4 + δ than for Ca 1.8 Sr 0.2 RuO 4. Consequently, we found substantial differences from the Fermi surface of other ruthenates, shedding light on a unique role of excess oxygen among the metallization methods of Ca 2 RuO 4. • Direct observation of the Fermi surface emerging from a ruthenate Mott insulator. • Metallic electronic states can be induced by a small amount of excess oxygen. • Our result opens a new way to understand and control the metal–insulator transition. [ABSTRACT FROM AUTHOR]

The catalytic performance of a series of La-Fe/AC catalysts was studied for the selective catalytic reduction (SCR) of NO by CO. With the increase in La content, the Fe2+/Fe3+ ratio and amount of surface oxygen vacancies (SOV) in the catalysts increased; thus the catalytic activity improved. Incorporating the promoters to La3-Fe1/active carbon (AC) catalyst could affect the catalyst activity by changing the electronic structure. The increase in Fe2+/Fe3+ ratio after the promoter addition is possibly due to the extra synergistic interaction of M (Mn and Ce) and Fe through the redox equilibrium of M3+ + Fe3+ ↔ M4+ + Fe2+. This phenomenon could have improved the redox cycle, enhanced the SOV formation, facilitated NO decomposition, and accelerated the CO-SCR process. The presence of O2 enhanced the formation of the C(O) complex and improved the activation of the metal site. Mn@La3-Fe1/AC catalyst revealed an excellent NO conversion of 93.8% at 400 °C in the presence of 10% oxygen. The high catalytic performance of MnOx and double exchange behavior of Mn3+ and Mn4+ can increase the number of SOV and improve the catalytic redox properties. [ABSTRACT FROM AUTHOR]

• CuFeO 2+δ has been rapidly synthesized by microwave-assisted hydrothermal method. • The sample has high quality as well as contains elevated concentrations of excess O. • The formation mechanism is based on the non-equilibrium hydrothermal synthesis. • CuFeO 2+δ exhibits half-metallic ferromagnetism and multiple band gaps. • Non-stoichiometric CuFeO 2+δ compounds have potential applications in solar energy conversion. As an alternative to high-temperature oxidation, the present study demonstrates a new approach to the intercalation of excess O into 3R-delafossite CuFeO 2 , based on a non-equilibrium hydrothermal synthesis. At lower temperatures, or during the initial stage of this hydrothermal reaction, a large amount of excess O remains between the self-assembled block layers, owing to the incomplete reduction of propionaldehyde in the hydrothermal process. This work not only confirmed the presence of this excess O and quantified the excess O concentrations, but also established the mechanism by which non-stoichiometric CuFeO 2+δ is generated, on the basis of experimental observations and theoretical calculations. Normally, highly crystalline CuFeO 2+δ prepared using the conventional hydrothermal process only contains low levels of excess O, but the present work shows that this problem can be mitigated by employing a microwave-assisted hydrothermal reaction. This technique can rapidly synthesize high quality 3R-delafossite CuFeO 2+δ containing elevated concentrations of excess O. Electronic structures calculated based on density functional theory showed that CuFeO 2+δ should exhibit half-metallic ferromagnetism and multiple band gaps. Systematic experimental characterization and theoretical calculations were used to elucidate the manner in which excess O significantly affects the microstructure of this material, while enhancing the electrical, optical and electrochemical properties of CuFeO 2. As a result of these enhancements, this material is suitable for the improvement of solar energy conversion. Photoelectrochemical trials and data from the photocatalytic performances confirm these properties, suggesting that non-stoichiometric 3R-delafossite CuFeO 2+δ compounds have potential applications in solar energy conversion. [ABSTRACT FROM AUTHOR]

As one of the most promising carbon capture technologies for coal-fired power plants, oxy-coal combustion has attracted wide interests during the last two decades. In comparison to atmospheric oxy-fuel combustion, pressurized oxy-fuel combustion has the potential to further reduce the energy penalties caused by the carbon capture and storage and improve the net power plant efficiency. Although many researchers have investigated the NO x emissions of atmospheric oxy-coal combustion, the NO x emission behaviors under pressurized oxy-coal combustion conditions are much less understood and further comprehensive experimental investigations with continuous fuel-feeding pressurized oxy-coal combustion systems are needed in order to fill this knowledge gap. In the present study, a series of oxy-coal combustion experiments were conducted in a 30 kW th pressurized fluidized bed combustor. The effects of combustion pressure, bed temperature and excess oxygen on the NO x emissions were investigated systematically. The experimental results have shown that an increase in combustion pressure from 0.1 MPa to 0.4 MPa leads to a significant reduction in NO x emissions. An increase in bed temperature or excess oxygen results in higher NO x emissions under the higher combustion pressure conditions, which is consistent with what is observed under the atmospheric pressure combustion condition. Besides, it is found that the promoting effect of temperature increase on NO x emissions under the higher combustion pressures is weaker than that under the atmospheric pressure. • The NO x emissions of pressurized oxy-coal combustion are investigated. • An increase in pressure reduces the NO x emissions of oxy-combustion significantly. • An increase in temperature or excess oxygen leads to the higher NO x emission. • The promoting effect of temperature increase on NO x is weaker under high pressures. • The NO x emissions are closely related to the CO concentration in the flue gas. [ABSTRACT FROM AUTHOR]

Amorphous oxide semiconductors (AOSs) have been commercialized since 2012 as thin‐film transistor (TFT) backplanes in flat‐panel displays. This review first provides a brief history and current status of AOS technology, and then introduces electronic defects in AOSs reported to date that are critically important for understanding and controlling the instability of TFTs that is the most serious issue in the development of the AOS technology. In particular, it is important to know that many AOS defects are related to oxygen and hydrogen impurities, though oxygen is the major constituent of AOS and hydrogen is not intentionally incorporated. Instability issues and their underlying mechanisms are also discussed in relation to these defects. Amorphous oxide semiconductors are currently employed in several flat‐panel displays, including large‐sized organic light‐emitting diode televisions. This paper reviews the defects in AOSs reported to date as well as provides a brief history and current status of AOS technology. TFT instability issues, their underling mechanisms, and optimum fabrication conditions are discussed in relation to these defects. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the temperature dependence of the in-plane resistivity and the Hall coefficient for high-quality single crystal Bi2Sr2CaCu2O8+δ (Bi2212) in a wide doping range. Doping is controlled by successive annealing treatments from a nearly optimally doped region to an insulating region systematically. It is found that the residual resistivity increases notably with decreasing doping and undergoes the superconductor–insulator (SI) transition when the residual resistivity becomes ∼1mΩcm, which corresponds to the universal sheet resistance h/4e 2. In addition, the Hall coefficient at which superconductivity disappears is found to be very small compared with the La- or Y-based system. These results imply that the transition temperature is anomalously suppressed in the underdoped region of Bi2212 while the SI transition is of the same origin for various systems. [Copyright &y& Elsevier]

The ceramic La2CuO4+δ with excess oxygen is found to have two superconducting phases, whose transition temperatures are 32 K (36 K) of the low Tc phase and 45 K of the high Tc phase, respectively. In this paper we report the normal state susceptibilities of the two kinds of almost single superconducting phases. The susceptibility of the high Tc phase was found to be similar to that of optimally doped (LaSr)2CuO4. The susceptibility gradually decreased with decreasing temperature from 300 K. On the other hand, in the low Tc phase, the first large susceptibility peak suggesting some antiferromagnetic ordering was observed at about 260 K, and then the second small peak at about 215 K. In the preliminary measurements, the susceptibility of the powdered low Tc phase showed a Curie-type increase from about 215 K down to the superconducting transition temperature. [Copyright &y& Elsevier]