Promising Cr-Doped ZnO Nanorods for Photocatalytic Degradation Facing Pollution

Chromium (Cr)-doped zinc oxide (ZnO) nanorods with wurtzite hexagonal structure were prepared through a thermal decomposition technique. The concentration effect of the Cr doping on the structural, morphological, and optical properties of the ZnO nanorods was established by correlating various measurements: transmission electron microscopy (TEM), photoluminescence (PL), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and several UV-visible studies. The obtained nanorods were investigated as photocatalysts for the photodegradation process of methyl orange (MO), under UV-vis light illumination. Different weights and time intervals were studied. A 99.8% photodegradation of MO was obtained after 100 min in the presence of 1 wt.% Cr III acetate hydroxide and zinc acetate dehydrate “ZnO-Cr1”. The kinetic rate constant of the reaction was found to be equal to 4.451 × 10−2 min−1 via a pseudo-first order rate model. Scavenger radicals demonstrated the domination of OH• radicals by those of O2•− superoxide species during the photodegradation. The interstitial oxygen site Oi is proposed to play a key role in the generation of holes in the valence band under visible irradiation. The ZnO-Cr1 photocatalyst displayed good cycling stability and reusability.

Density Functional Theory Study on Anisotropic Arrangement of Interstitial Oxygen Atoms at (001) Interface of Oxide Precipitates in Si Crystal

The stability of the anisotropic oxygen (O) arrangement at the (001) interface of oxide precipitate (OP) in a Si crystal was analyzed by the density functional theory to understand the OP/Si interfacial structure and the gettering mechanism at the interface at an atomic level. In contrast to the case of the Si bulk, the O atoms align in one Si-Si zig-zag bond to some extent, then start to occupy other Si-Si bonds. After the O atoms are arranged in multiple series in the first interface layer to some extent, those in the second layer become more stable. This trend was confirmed for the second and third layers. The results support the existence of an experimentally observed transition layer with a composition of SiOx (x < 2) at the interface [Kissinger et al., ECS J. Solid State Sci. Technol., 9, 064002 (2020)]. Furthermore, several O alignments at the interface drastically reduce the formation energy of Si vacancies. The vacancies at the OP/Si interface were found to be effective gettering sites for Cu while the dangling bond was found to be an effective gettering site for Ni with a binding energy exceeding 1 eV.

In Situ Evaluation of the Influence of Interstitial Oxygen on the Elastic Modulus of La2NiO4

Lattice defects significantly affect the mechanical properties of crystalline metal oxides. The materials for the components of solid oxide fuel cells (SOFCs) are no exception, and hence understanding of the interplay between lattice defects and the mechanical properties of components is important to ensure the mechanical stability of SOFCs. Herein, we performed an in situ evaluation of the temperature and P(O2) dependence of the elastic moduli of La2NiO4 (LN214), a candidate for the cathode material of SOFCs, using the resonance method to understand the influence of interstitial oxygen on its elastic properties. Above 873 K, both the Young’s and shear moduli of LN214 slightly decreased with increasing P(O2), suggesting that these elastic moduli are correlated with interstitial oxygen concentration and decreased with increasing interstitial oxygen. We analyzed the influence of interstitial oxygen on the Young’s modulus of LN214, based on numerically obtained lattice energy. The P(O2) dependence of the Young’s modulus of LN214 was found to be essentially explained by variation in the c-lattice constant, which was triggered by variation in interstitial oxygen concentration. These findings may contribute to a better understanding of the relationship between lattice defects and mechanical properties, and to the improvement of the mechanical stability of SOFCs.

Li-Ion-Trapping-Induced Degradation Mechanism of Colored State in Tungsten Oxide Electrochromic Films

Aiming to investigate the degradation mechanism of their colored states, tungsten oxide films with different oxygen/tungsten ratio were prepared by direct current reactive magnetron sputtering through adjusting the oxygen partial pressure. After a long-term cycling test, the sample prepared under low oxygen partial pressure (LO#) showed an excellent cycle stability which its optical modulation amplitude remains stable at 23.6%, while the one prepared under high oxygen partial pressure (HO#) exhibited an obvious degradation process of the colored state, leading to the optical modulation amplitude decreased from 34.0% to 18.6% accompanied with a decay of ionic diffusion coefficient and electrode potential, but having an improved coloration efficiency. Combined with various structural characterizations, including SEM, LA-ICP-MS, Raman and XPS, we demonstrate such colored state degradation is attributed to the so-called shallow trap, which corresponds to the irreversible and non-coloring reaction with interstitial oxygen during the insertion of Li+ cations forming superoxides (e.g. LiO2). All these findings not only offer a new insight into the improvement of cyclic stability based on ion-exchange, but also provide a valued information to understanding the physicochemical mechanisms of degradation in electrochromic materials.

Controlling metal–insulator transitions in reactively sputtered vanadium sesquioxide thin films through structure and stoichiometry

We present a study of $$\hbox {V}_{2}\hbox {O}_{3}$$ V 2 O 3 thin films grown on c-plane $$\hbox {Al}_{2}\hbox {O}_{3}$$ Al 2 O 3 substrates by reactive dc-magnetron sputtering. Our results reveal three distinct types of films displaying different metal–insulator transitions dependent on the growth conditions. We observe a clear temperature window, spanning 200 $$^{\circ }$$ ∘ C, where highly epitaxial films of $$\hbox {V}_{2}\hbox {O}_{3}$$ V 2 O 3 can be obtained wherein the transition can be tuned by controlling the amount of interstitial oxygen in the films through the deposition conditions. Although small structural variations are observed within this window, large differences are observed in the electrical properties of the films with strong differences in the magnitude and temperature of the metal–insulator transition which we attribute to small changes in the stoichiometry and local strain in the films. Altering the sputtering power we are able to tune the characteristics of the metal–insulator transition suppressing and shifting the transition to lower temperatures as the power is reduced. Combined results for all the films fabricated for the study show a preferential increase in the a lattice parameter and reduction in the c lattice parameter with reduced deposition temperature with the film deviating from a constant volume unit cell to a higher volume.

High oxide-ion conductivity through the interstitial oxygen site in Ba7Nb4MoO20-based hexagonal perovskite related oxides

Oxide-ion conductors are important in various applications such as solid-oxide fuel cells. Although zirconia-based materials are widely utilized, there remains a strong motivation to discover electrolyte materials with higher conductivity that lowers the working temperature of fuel cells, reducing cost. Oxide-ion conductors with hexagonal perovskite related structures are rare. Herein, we report oxide-ion conductors based on a hexagonal perovskite-related oxide Ba7Nb4MoO20. Ba7Nb3.9Mo1.1O20.05 shows a wide stability range and predominantly oxide-ion conduction in an oxygen partial pressure range from 2 × 10−26 to 1 atm at 600 °C. Surprisingly, bulk conductivity of Ba7Nb3.9Mo1.1O20.05, 5.8 × 10−4 S cm−1, is remarkably high at 310 °C, and higher than Bi2O3- and zirconia-based materials. The high conductivity of Ba7Nb3.9Mo1.1O20.05 is attributable to the interstitial-O5 oxygen site, providing two-dimensional oxide-ion O1−O5 interstitialcy diffusion through lattice-O1 and interstitial-O5 sites in the oxygen-deficient layer, and low activation energy for oxide-ion conductivity. Present findings demonstrate the ability of hexagonal perovskite related oxides as superior oxide-ion conductors.

Simulation of infrared spectra of trace impurities in silicon wafers based on the multiple transmission–reflection infrared method

The content of trace impurities, such as interstitial oxygen and substitutional carbon, in silicon is crucial in determining the mechanical and physical characteristics of silicon wafers. The traditional infrared (IR) method is adopted as a normal means to analyse their concentration at home and abroad, but there are two problems. The first problem is the poor representativeness of a single local sampling point because the impurity distribution in a solid sample is not as uniform as that in a liquid sample. The second problem is that interference fringes appear in the infrared spectra of the sample due to the thin wafer (≤ 300 μm thick). Based on this, controversial issues existed regarding the measured trace impurity concentrations between wafer manufacturers and solar cell assembly businessmen who used silicon sheets made by the former. Therefore, multiple transmission-reflection (MTR) infrared (IR) spectroscopy was proposed to solve the problems mentioned above. In the MTR setup, because light passes through different parts of the silicon chip several times, multiple sampling points make the final result more representative. Moreover, the optical path is lengthened, and the corresponding absorbance is enhanced. In addition to amplification of weak signals, the MTR-IR method can eliminate interference fringes via the integrating sphere effect of its special configuration. The signal-to-noise ratio of the corresponding spectrum is considerably improved due to the aforementioned dual effects. Thus, the accuracy and sensitivity of the detection method for trace impurities in silicon chips are greatly increased. In this study, silicon wafers were placed in the MTR setup, and then, their relative properties at room temperature were investigated. The corresponding theoretical calculation and simulation of infrared spectra of silicon chips were provided. This affords an optional method for the semiconductor material industry to analyse trace impurities in their chips.