Interstitial Nitrogen Research Articles

Marine sediment nitrogen isotopes and their implications for the nitrogen cycle in the sulfate-methane transition zone

IntroductionRecent work has proposed that the nitrogen isotopes in marine sediments can be impacted by anaerobic oxidation of methane (AOM), since nitrogen uptake by anaerobic methanotrophic archaea (ANME) modifies the nitrogen isotope compositions of bulk sediment. Thus, unraveling the AOM-driven nitrogen cycle in the sulfate-methane transition zone (SMTZ) becomes significant. Additional study of the nitrogen cycle between sediment and interstitial water in SMTZ is needed.MethodsTo better understand the nitrogen cycle in the SMTZ, we analyzed NH4+ concentrations of interstitial water and nitrogen isotopes of sediment in the core GC10 from the southwestern Taiwan Basin in the South China Sea.ResultsThe defined SMTZ is located at 560–830 cmbsf, based on methane and sulfate concentrations, as well as TS/TOC ratios, δ13CTIC and δ34S values. In the SMTZ, the NH4+ concentration decreases, the δ15NTN shows a negative excursion, δ15Ndecarb displays a positive excursion.DiscussionsNH4+ concentration decrease is interpreted by sulfate-reducing ammonium oxidation (SRAO). The δ15NTN shows negative excursion, which is most likely interpreted to N2 (δ15N=0‰) released from SRAO that was fixed into marine sediment via ANME nitrogen fixation. The δ15Ndecarb shows a negative correlation with NH4+ concentrations, indicating that it was controlled by organic matter decomposition. In the SMTZ, the methane competes with organic matter for becoming the substrate of sulfate reduction bacteria, which possibly decreases the organic matter degradation rate and causes δ15Ndecarb relative positive excursion. Although δ15Ndecarb is controlled by organic matter degradation, δ15NTN still reveals a negative excursion in the SMTZ. This likely indicates that nitrogen uptake by ANME/AOM microbial consortiums mainly modifies the nitrogen isotope of soluble nitrogen in the SMTZ.ConclusionsThis study indicates unique geochemistry processes in SMTZ will modify nitrogen characteristics in sediment/interstitial water, and the latter can serve as a proxy for AOM.

Effect of interstitial carbon and nitrogen on corrosion of FeCoCrNi multi-principal element alloys made by selective laser melting

The corrosion behaviors of selective laser melted (SLMed) FeCoCrNi multi-principal element alloys (MPEAs) with carbon or nitrogen addition in 0.5 M H2SO4 solution were investigated. Both C and N addition refined the grains and introduced a heterogeneous structure in SLMed FeCoCrNi MPEA, but they had opposite effects on the corrosion behavior. The doped carbon participated as nano-sized carbides in SLMed MPEA, and localized galvanic corrosion occurred, degrading the corrosion resistance. The doped nitrogen was gathered with chromium and formed CrN chemical clusters in SLMed MPEA, and a protective passive film with a higher Cr2O3/Cr(OH)3 ratio formed, which improved corrosion resistance.

Effect of nitrogen content on the mechanical properties and deformation behaviors of ferritic-pearlitic steels

The effect of nitrogen content (0.001 wt%, 0.009 wt%, 0.017 wt%) on the microstructure, mechanical properties and deformation behaviors of a medium-carbon ferritic-pearlitic steel is investigated in this study. The addition of nitrogen is shown to have little effect on the ferrite-pearlite microstructure and only marginally coarsens it because austenite grain growth is promoted. Although nitrogen is a strong element for solid solution strengthening, nitrogen addition only marginally improves the strength of the steel and has little effect on the ductility because fine Fe3N phases are precipitated during the tensile process. The toughness of the steel is markedly decreased by the addition of nitrogen because the dislocation locking effect caused by interstitial nitrogen atoms is enhanced. When the nitrogen content increases from 0.001 wt% to 0.017 wt%, the yield-point phenomenon in the tensile process is first strengthened and then weakened. The yield-point phenomenon is closely related to the dislocation behaviors in proeutectoid ferrite, and the different yield-point phenomena under different nitrogen contents are related to the dislocation locking effect caused by interstitial nitrogen atoms and to the dislocation pinning effect caused by Fe3N phases.

Theoretical and experimental investigation of the electronic and optical properties of pure and interstitial nitrogen -doped (TiO2)n cluster

The structural and electronic properties of pure and nitrogen-doped TiO2 nanoclusters are investigated using density functional theory with vibrational modes. We performed numerical simulation using two methods based on theories at the Quantum Espresso/PBE and Gaussian/B3LYP/631G (d) levels. The properties of a single nitrogen-doped (TiO2)n nanocluster are also computed in this study. In both cases, interstitial and substitutional Nitrogen doping at all accessible sites was examined. For the experiment, Supersonic Cluster Beam Deposition (SCBD) was used to create pure and nitrogen-doped TiO2 films of nanocluster assemblies. Atomic force microscopy, X-ray photoelectron spectroscopy (XPS), UV–Vis spectroscopy, and Raman techniques were used to characterize these samples. The binding energies (Np, O2s, Ti 2p1/2, and Ti 2p3/2) of N-doped TiO2 were estimated using XPS spectral results. The UV–Vis measurement confirmed the previously stated reasoning about the quantum size effect on the band gap of the pure and nitrogen doped TiO2 nanocluster. The theoretical vibrational modes frequencies are calculated using the B3LYP/6-31G (d) functional via the Gaussian16 code's implementation algorithm. The good agreement between simulation and experimental results implies that a significant advantage of interstitial over substitutional positions. N–O vibration modes appeared in interstitial doped TiO2, and each vibration was dependent on a different cluster structure.

Interactions between irradiation defects and nitrogen in [formula omitted]‐Fe: an integrated experimental and theoretical study

This paper aims at clarifying, by means of an integrated experimental and theoretical approach, the properties of the interaction between interstitial nitrogen (N) and irradiation generated lattice defects in α-Fe. For this purpose, N-doped and pure Fe specimens were irradiated at low temperature by high energy protons. The evolution of radiation defects and their interaction with N was monitored by electrical resistivity measurements during post-irradiation annealing. In parallel, density functional theory (DFT) was employed to study the properties of N solutes, vacancies and their mutual interaction in the Fe matrix. The DFT results were confronted to the experiment via kinetic rate theory modelling, employed to quantitatively simulate the measured resistivity evolution. One of the most important results is the experimental validation of the theoretically predicted strong binding energy of vacancy-N complexes, which reconciles previous discrepancies. Furthermore, a quantitative interpretation is provided of how irradiation competes with nitride precipitation.

The [formula omitted] (n=1,2) defect in Si from a Density Functional Theory perspective

Nitrogen constitutes a significant defect in silicon (Si) as it can affect its mechanical properties. Substitutional nitrogen defects can be created from interstitial nitrogen defects during cooling of the crystal. In turn, the substitutional nitrogen atoms can form micro-defects in Si, most important of which are the interstitial oxygen atoms since they have an impact on a device’s characteristics. In the present paper, we study the structure of the defect clusters in Si consisting of substitutional nitrogen and interstitial oxygen atoms. We find that the most stable structure is the one containing two interstitial oxygen atoms, while the presence of these interstitials results to narrow-gap semiconductors.

Realization of volatile and non-volatile resistive switching with N-TiO2 nanorod arrays based memristive devices through compositional control

It is attractive to manipulate the volatile and non-volatile resistive switching behaviors of memristors to create genuine neuromorphic systems such as artificial neural networks (ANNs) and spiking neural networks (SNNs). To investigate the above behaviors, nitrogen has been introduced into TiO2 nanorod arrays (TiO2 NRAs) by hydrothermal processing. X-ray photoelectron spectroscopy (XPS) analysis shows that both lattice and interstitial nitrogen are incorporated into the TiO2 NRAs. Nitrogen doped TiO2 NRAs (N-TiO2 NRAs) based memristive devices with different contents of lattice nitrogen were investigated systematically. The results show that non-volatile restive switching is achieved at up to a relative lattice nitrogen content of 21%, with volatile switching behavior above this value. The volatile memristive devices show similar spiking and decay features to the Leaky Integrate-and-Fire (LIF) model. The lifetime of the decay process of the volatile devices rang from 0.029 to 1.835 s. The longest lifetime is obtained when the relative content of lattice nitrogen is about 70%. The volatile behavior is related to the large defect concentration, caused by nitrogen doping. The proposed nitrogen engineered memristive devices could pave the way to achieving a physical neuromorphic system.

Site-Selective Nitrogen-Doped α-MnO2 for Catalytic Oxidation of Carcinogenic HCHO in Indoor Air

Developing high-efficiency formaldehyde (HCHO) catalytic oxidation catalysts is of significance and practicability for indoor air decontamination. It is generally considered that anionic doping is a traditional strategy to regulate the reaction activity of catalyst materials. However, one of the concerns worth exploring is the recognition of doping sites and their impact on catalytic performance. Herein, nitrogen atoms are successfully introduced into the MnO2 structure by high-temperature calcination with urea as the nitrogen source for the first time. By regulating the usage of urea, nitrogen atoms are selectively and successfully doped into the interstitial sites and substitutional sites. Furthermore, the effect of nitrogen-doped MnO2 on the catalytic oxidation of HCHO is studied in detail. Results indicate that nitrogen doping can promote the formation of oxygen vacancies, strengthen the activation of adsorbed O2, and enhance the adsorption of HCHO, which is conducive to catalytic decomposition of HCHO. Importantly, nitrogen doping at various doping sites has a considerable effect on catalytic decomposition activity. Although both interstitial and substitutional nitrogen doping can boost the decomposition performance of HCHO, the interstitial sites are the most suitable doping sites in the α-MnO2 lattice. The chemical environment around the interstitial sites is favorable for the creation of oxygen vacancies, as well as the adsorption/activation of HCHO and O2. Interstitial nitrogen doping can dramatically increase the HCHO catalytic activity of α-MnO2, and the complete catalytic decomposition temperature is reduced from 130 to 90 °C at the condition of GHSV = 90 L/gcat·h. This study provides a facile and effective method for site-selective nitrogen-doping and an in-depth understanding of its effect on catalytic activity.

Hole traps related to nitrogen displacement in p-type GaN grown by metalorganic vapor phase epitaxy on freestanding GaN

This work investigated deep levels in p-type GaN originating from intrinsic point defects, using deep level transient spectroscopy (DLTS) to examine homoepitaxial GaN p+–p−–n+ junction diodes grown via metalorganic vapor-phase epitaxy. Following exposure to an electron beam with an energy of 137 keV that generated nitrogen vacancies (VN) and nitrogen interstitials (NI), a peak due to EHa hole traps (at 0.52 eV) was observed in DLTS spectra. The injection of minority carriers resulting from applying a forward bias generated signals for EHb (0.5 eV) and EHc (0.8 eV) hole traps while decreasing the EHa signal and increasing the net accepter concentration. The generation of EHa traps can likely be attributed to VN (3+/+) or NI (2+/+) defects based on the results of first-principles calculations. The EHb and EHc hole traps may have been associated with complex defects, including those that generated EHa traps, because these two traps appeared as the concentration of EHa traps decreased.

Developing dual-textured titanium (Ti) extrudates via utilizing the β transus in commercially pure Ti

In contrast with titanium (Ti) alloys, the α+β region for commercially pure Ti is neglectable. Therefore, its β transus (Tβ) can be regarded as a watershed for β-Ti and α-Ti. Utilizing this characteristic, we fabricated dual-textured Ti extrudates through a powder metallurgy route via manipulating the hot extrusion temperature. The crystallographic texture along extrusion direction (ED) was analyzed. Different from the sole <1010>//ED texture throughout the entire extrudate in previous studies, our extrudates exhibited unique dual-textured microstructure. The firstly extruded portion manifested <0001>//ED and <1011>//ED, whereas the rest extrudate displayed <1010>//ED. This was attributed to the realtime extrusion temperature of each location in comparison with Tβ. On the other hand, the last portion of the extrudate contained much more interstitial nitrogen and oxygen, which led to extremely high strength via solid solution strengthening. This was resulted from a combination effect of diffusion-controlled element absorbing and material flow during extrusion. Our findings may open up a new direction in developing high-performance materials with variable microstructure and mechanical properties for medical applications like neoarthrosis.

DFT Investigation of Substitutional and Interstitial Nitrogen-Doping Effects on a ZnO(100)-TiO2(101) Heterojunction.

Density Functional Theory (DFT) calculations have been performed to investigate the structural and electronic properties of the ZnO(wurtzite)-ATiO2(anatase) heterojunction in the absence and presence of substitutional, interstitial nitrogen (N) doping and oxygen vacancies (OV). We report a detailed study of the interactions between the two nonpolar ZnO and TiO2 surfaces and on the role of N-doping and oxygen vacancies, which are decisive for improving the photocatalytic activity of the heterojunction. Our calculations show that substitutional N-doping is favored in the ATiO2 portion, whereas the interstitial one is favored in the ZnO region of the interface. Both substitutional and interstitial N-doped sites (i) induce gap states that act as deep electronic traps improving the charge separation and delaying electron-hole recombination, (ii) facilitate the OV formation causing a decrease in the formation energy (E FORM), and (iii) do not affect the band alignment when compared to the undoped analogue system. The presented results shed light on the N-doping effect on the electronic structure of the ZnO(100)-TiO2(101) heterojunction and how N-doping improves its photocatalytic properties.

Microstructure and strengthening mechanisms of tantalum prepared using laser melting deposition

Laser melting deposition (LMD) additive manufacturing process has been attractive to the fabrications of pure tantalum due to the advantage of fast near net shaping of complex shaped components. In the present study, the LMD process has been applied to the fabrication of tantalum using two kinds of powders with different interstitial contents. The microstructure, chemistry, and mechanical properties of the LMD samples have been investigated to understand the strengthening mechanisms. The results show that the tantalum samples have near full dense, and large columnar grains with the growth direction slightly deviated from the deposition direction. The LMD tantalum can have high hardness of up to 300 HV, mainly due to the solid solution strengthening of nitrogen and oxygen interstitials. With relative low interstitial contents of about 400 ppm, the LMD tantalum can have ductile properties, showing ultimate tensile strength above 400 MPa, and elongations of about 14–16%, which are comparable to the properties of cold-worked tantalum. The present work suggests the LMD tantalum could have potential usages in the industry fields.

Phosphonium ionic liquid-promoted Ce-doped nitrogen-rich TiO2 for degradation gaseous pollutant under visible light irradiation

Altering physicochemical properties of TiO2 based on modifying the cation and anion structure of ionic liquids (ILs) is of great interests for environment. Up to date, the research involving IL-assisted synthesis of TiO2 was focused on imidazolium IL, and much less attention was devoted to IL with other structures. Hence, strategy for preparation of TiO2 in phosphonium IL is presented to control the growth of TiO2 nanocrystals. The as-prepared noble cerium-doped nitrogen-rich phosphonium IL-TiO2 photocatalyst with assisted by tributyl(propyl)phosphonium tetrafluoroborate exhibits a higher specific surface area and smaller crystallite size, which is conducive to the production of more and faster active substance, such as hydroxyl oxygen. When evaluated for photocatalysis of gaseous toluene under visible light irradiation, the sample manifests high degradation rate and efficiency, as well as excellent recycling performance due to the existence of superoxide radical produced by the Ce3+/Ce4+ redox reaction. The introduction of phosphonium IL and Ce greatly enhanced charge separation efficiency and promoted production of active substances. Nitrogen also existed in the form of interstitial nitrogen and substituted nitrogen improves its response to visible light. This work shows promising application of phosphonium IL for highly enhanced TiO2 photocatalytic performance.

High-throughput nitride and interstitial nitrogen analysis in ferritic/martensitic steels via time-of-flight secondary ion mass spectrometry

The following work focuses on characterizing nitrogen in several modified alloys of the precipitation strengthened ferritic/martensitic steel HT9 (12Cr-1MoWV (wt%)). Alloy HT9 is a candidate material for fuel rod cladding and ductwork in the core of the Versatile Test Reactor and other next-generation nuclear fast reactors. Nitrogen content has been shown to have a significant effect on irradiated properties in alloy HT9. To explore that theory, a more comprehensive assessment of the location of nitrogen must be performed; however, locating nano-precipitates, such as nitrides and light interstitial elements like nitrogen in steel, has proven difficult. To begin answering questions surrounding the location of nitrogen, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was employed as a primary analysis technique, together with extensive transmission electron microscopy, internal friction testing, and thermodynamic simulations, providing verification and context to trends found in the ToF-SIMS data. For the first time, ToF-SIMS was demonstrated to reliably measure relative differences in the vanadium carbonitride precipitate volume fraction across several chemistries and heat treatments of ferritic/martensitic steels. Additionally, associating matrix elements (iron and chromium) to nitrogen-containing ion clusters significantly reduced the ‘matrix effect that biases nitrogen detection towards nitride precipitates, providing a potential, high-throughput method for the measurement of relative interstitial nitrogen content in steels with ToF-SIMS. • ToF-SIMS provided a new high-throughput analysis method for microalloy precipitate and microstructure design. • ToF-SIMS was employed for semi-quantitative, bulk detection and measurement of nitrides and interstitial nitrogen in steel. • S/TEM provided a quantitative comparison of nitride content, while internal friction testing provided a semi-quantitative comparison of interstitial N.

Transition metal carbides and nitrides as catalysts for thermochemical reactions

Transition metal carbides and nitrides (TMCs and TMNs) have attracted much attention due to their unique physical and chemical properties brought by the incorporation of interstitial carbon and nitrogen into the crystal lattice of the parent metals. Recent advances in utilizing TMCs and TMNs have revealed their intriguing catalytic properties in many industrially important reactions, including heteroatom removal, CO2 activation, alcohol reforming, and water–gas shift reactions. The promising activity, selectivity, and stability of TMCs and TMNs, either as catalysts or as supports for other metals, are often attributed to their strong interactions with the adsorbates, tunable surface properties, as well as the synergy with supported metals. This review summarizes the synthesis and characterization of TMC and TMN model surfaces and powder catalysts, and uses several case studies to demonstrate their unique catalytic properties in these important reactions. A discussion is also provided regarding the challenges and opportunities associated with the utilization of TMCs and TMNs in thermocatalysis.

Tensile and fatigue crack growth behavior of commercially pure titanium produced by laser powder bed fusion additive manufacturing

The effects of build orientation and post heat treatments on the tensile and fatigue crack growth (FCG) behavior of commercially pure titanium (CP-Ti) manufactured by laser powder bed fusion (LPBF) using grade 2 powder were examined. Two orthogonal build orientations were used in conjunction with hot isostatic pressing (HIP) both above (950 °C) and below (730 °C) the β-transus temperature and property comparisons were also made to commercially available wrought material. The HIP treatments coarsened the α grain structure, reduced the tensile strength, and increased the fatigue crack growth threshold. The LPBF materials were generally stronger and more fatigue resistant than the wrought material due higher interstitial oxygen and nitrogen content. Additionally, higher tensile strength values were found for one build orientation with higher nitrogen content that was attributed to the different thermal histories during LPBF. However, the build orientation effect was not observed for the FCG behavior of the LPBF material and the FCG resistance at low growth rates were mainly controlled by the grain size. This was in sharp contrast to the wrought material which showed strong anisotropy in the microstructure sensitive fatigue crack growth regime due to strong crystallographic texture. At higher growth rates, FCG became microstructure insensitive when the cyclic plastic zone size became of similar order of magnitude to the grain size. • Fatigue crack growth rates measured for laser powder bed fusion CP-Ti. • Interstitial pickup during fabrication raised tensile strength and fatigue resistance. • Microstructure sensitive growth when cyclic plastic zone - grain size ratio is ≲1–4. • α'/α lath thickness and interstitial content controlled fatigue crack growth rates. • Build orientation had negligible effect on fatigue crack growth.

Identification of the Nitrogen Interstitial as Origin of the 3.1 eV Photoluminescence Band in Hexagonal Boron Nitride

Nitrogen interstitials () have the lowest formation energy among intrinsic defects of hexagonal boron nitride (hBN) under n‐type and N‐rich conditions. Using an optimized hybrid functional, which reproduces the gap and satisfies the generalized Koopman's condition, an configuration is found, which is lower in energy than the ones reported so far. The (0/–) charge transition level is also much deeper, so acts as a very efficient compensating center in n‐type samples. Its calculated photoluminescence (PL) at 3.0 eV agrees well with the position of an N‐sensitive band measured at 3.1 eV. It is also found that the nitrogen vacancy () cannot be the origin of the three‐boron‐center (TBC) electron paramagnetic resonance (EPR) center and in thermal equilibrium it is even unlikely to exist in n‐type samples.

Influence of Nitrogen Incorporation Sites on Structural and Optical Properties of Sputtered TiO2-N Thin Films with Improved Visible Light Activity

The influence of deposition and annealing parameters on optical, structural and photocatalytic properties of N-doped titanium-dioxide (TiO2) thin films have been studied. Anatase and anatase-rutile crystalline phase mixture TiO2 thin films were obtained depending on the reactive direct current (DC) sputtering and annealing conditions. Deposition in the nitrogen atmosphere produced N-doped TiO2 thin films with energy gap values shifted towards visible region in comparison with thin TiO2 films deposited without nitrogen in the atmosphere. The role of substitutional and interstitial nitrogen atoms incorporated in obtained crystalline structures during the deposition was shown important and was reflected in the efficiency of photocatalysis. It was found that thin TiO2 films with more substitutional incorporated nitrogen exhibits better photocatalytic properties. These results could be of importance towards achieving controlled synthesis of N-doped TiO2 thin films with desired structural and optical properties, especially with improved photo-activity in the visible part of the solar spectrum.

Preparation of N-I co-doped TiO2 supported on activated carbon photocatalyst for efficient photocatalytic reduction of Cr(Ⅵ) ions

Photocatalytic reduction of Cr(Ⅵ) is a safe, economical and clean method. In this study, a series of photocatalysts based on N-I co-doped TiO2 supported on activated carbon (denoted as x/yNIT@AC-z, N-I/Ti = x/y, calcination temperature = z °C) were synthesized, characterized and utilized for Cr(Ⅵ) photocatalytic reduction. Results of characterization revealed that all the prepared TiO2 existed in the form of monocrystalline tetragonal anatase phase with the particle size of 20 nm. Among them, 1/2NIT@AC-350 exhibited the highest photocatalytic performance. 1/2NIT@AC-350 showed a narrow band gap of 2.77 eV, which was chiefly because of the role of defect levels caused by pentavalent iodine, interstitial and substitutional nitrogen. 1/2NIT@AC-350/UV light/citric acid system exhibited the complete removal of 50 mg/L Cr(Ⅵ), over four successive reuse cycles without any obvious decrease in its photocatalytic reduction capability. In addition, the activated carbon in 1/2NIT@AC-350 provided a high concentration reaction environment for TiO2 via electrostatic attraction, which makes the photocatalyst possess a strong photocatalytic reaction driving force even at low concentration. Cr(Ⅵ) was also successfully removed in an actual water matrix (Yangtze river). This study provides a promising demonstration for the treatment of environmental pollutants, especially for Cr(Ⅵ) in wastewater effluents.

Pressure-induced disordering of site occupation in iron–nickel nitrides

Controlled disordering of substitutional and interstitial site occupation at high pressure can lead to important changes in the structural and physical properties of iron–nickel nitrides. Despite important progress that has been achieved, structural characterization of ternary Fe–Ni–N compounds remains an open problem owing to the considerable technical challenges faced by current synthetic and structural approaches for fabrication of bulk ternary nitrides. Here, iron–nickel nitride samples are synthesized as spherical-like bulk materials through a novel high-pressure solid-state metathesis reaction. By employing a wide array of techniques, namely, neutron powder diffraction, Rietveld refinement methods combined with synchrotron radiation angle-dispersive x-ray diffraction, scanning electron microscopy/energy dispersive x-ray spectroscopy, and transmission electron microscopy, we demonstrate that high-temperature and high-pressure confinement conditions favor substitutional and interstitial site disordering in ternary iron–nickel nitrides. In addition, the effects of interstitial nitrogen atoms and disorderly substituted nickel atoms on the elastic properties of the materials are discussed.