Interstitial Oxygen Concentration Research Articles

Effect of Heat Treatment on the Material Property and Cell Viability of Wire Arc Additively Manufactured Ti6Al4 V.

Wire arc additive manufacturing (WAAM) holds promise for producing medium to large industrial components. Application of WAAM in the manufacturing of biomedical materials has not yet been evaluated. The current study addresses two key research questions: first, the suitability of the WAAMed Ti6Al4V alloy for biomedical applications, and second, the effect of Ti6Al4V's constituents (α and β phases) on the cell viability. The WAAMed Ti6Al4V alloy was fabricated (as-deposited: AD) using a metal inert gas (MIG)-based wire arc system using an in-house designed shielding chamber filled with argon. Subsequently, samples were subjected to solution treatment (950 °C for 1 h), followed by aging at 480 °C (T1), 530 °C (T2), and 580 °C (T3) for 8 h and subsequent normalization to ambient conditions. Microstructural analysis revealed ∼45.45% of α'-Ti colonies in the as-deposited samples, reducing to 23.26% postaging at 580 °C (T3). The α-lath thickness and interstitial oxygen content in the sample were observed to be proportional to the aging temperature, peaking at 580 °C (T3). Remarkably, during tribocorrosion analysis in simulated body fluid, the 580 °C-aged T3 sample displayed the lowest corrosion rate (7.9 μm/year) and the highest coefficient of friction (CoF) at 0.58, showing the effect of increasing oxygen content in the alloy matrix. Cell studies showed significant growth at 530 and 580 °C by day 7, correlated with higher oxygen content, while other samples had declining cell density. Additionally, optimal metallurgical property ranges were identified to enhance the Ti6Al4V alloy's biocompatibility, providing crucial insights for biomedical implant development.

Controlling splat boundary network evolution towards the development of strong and ductile cold sprayed refractory metals: The role of powder characteristics

Feedstock powder characteristics such as composition (specific alloying elements and concentrations and impurity levels), microstructure, thickness/composition of surface oxide layers, and particle size distribution play a crucial role in determining the overall mechanical properties of cold sprayed deposits. Herein, we report on two deposits consolidated via cold spray processing from differently-sourced batches of nominally identical elemental refractory powders under identical spraying conditions, which exhibit bending strength and ductility values that differ by more than a factor of two – and with the weakest sample displaying negligible effective ductility. Through chemical, microstructural and micromechanical characterization of both the feedstock powders and cold sprayed deposits, we consider the possible influences of feedstock characteristics on the mechanical performance of cold spray consolidated deposits. It is shown that while differences in interstitial oxygen and hydrogen content may result in differences in the intrinsic yield characteristics of the feedstock material, both feedstocks maintain the ductile behavior required to induce good metallurgical bonding upon impact of optimally sized powder particles. We conclude that the deposits formed from the two feedstock powders are indistinguishable and exhibit high ductility when characterized locally within the relatively undeformed bulk of a single particle or splat. However, the two sprayed deposits show low ductility or brittle behavior when loaded in tension across intersplat boundary domains comprising material that has undergone extensive deformation. In addition, one feedstock incorporates a broader particle size distribution, with a long tail of larger-than-optimal particles. These larger particles are accelerated below the critical impact velocity, resulting in observed imperfect metallurgical bonding at splat interfaces and higher porosity at such intersplat boundaries. This result, combined with the overall differences in the morphology of the intersplat boundary network between the two deposits, explains the difference in macroscopic mechanical behavior. We conclude that accurate control of the powder feedstock particle size distribution is essential for optimizing the mechanical integrity of cold sprayed refractory elements and alloys.

A layered perovskite La2Ni1-xSbxO4+δ-molten carbonate dual-phase membrane for CO2 separation

A new series of layered perovskite K2NiF4 structure La2Ni1-xSbxO4+δ (LNSx, x = 0, 0.025, 0.05) were used to prepare the LNSx-molten carbonate (MC) dual-phase membrane for CO2 separation. Sb doping at the Ni site is expected to enhance CO2 permeability and improve the resistance towards CO2/carbonate corrosion. In this work, the CO2 permeability of the LNSx- MC membrane was investigated for CO2-containing atmospheres with and without oxygen, and correlated with the lattice characteristics, microstructure, chemical bond, and conductivity of LNSx support. The result shows that the introduction of Sb improves the structure symmetry and increases the interstitial oxygen concentration, which is beneficial for oxygen ion transport. The superior CO2 permeability of Sb-doped sample is confirmed by the higher permeation fluxes with value of 0.15 mL min−1 cm−2 at 800 °C of LNS0.025-MC dual-phase membrane in 50% CO2 + 50% N2. In addition, the LNS0.025-MC dual-phase membrane achieves a great enhancement in chemical and structural stability compared to the LNS0. In the simulated flue gas 15% CO2 + 10% O2 + 75% N2, the LNS0.05-based dual phase membrane shows a high permeation flux of 1.07 mL min−1 cm−2 at 800 °C, which is 2 times higher than that of LNS0-based dual-phase membrane.

Solute-solute interactions in dilute Nb-X-O alloys from first principles

Recent efforts to develop Refractory Multi-Principal Element Alloys (RMPEAs) for high temperature applications have led to a renewed interest in elucidating fundamental properties of refractory metals. These metals can dissolve high concentrations of interstitial oxygen to the detriment of their mechanical properties and oxidation resistance. Strategies are therefore sought to control the oxygen solubility of refractory alloys. Even in simple dilute refractory alloys, the underlying mechanisms driving binding energies between substitutional solutes and oxygen is not fully understood. We have used first principles calculations of Nb-X-O alloys to examine the interactions between interstitial oxygen and dilute substitutional solutes X = Al, Si, Sc, Ti, V, Cr, Y, Zr, Mo, Ru, Hf, Ta, W, and Re in BCC Nb. Electronegativity differences drive charge transfer between the Nb matrix and both the substitutional and interstitial solutes. This transfer of charge results in strong electrostatic interactions at short distances that play a key role in determining X-O binding energies. The solute misfit volume, which leads to local straining of the surrounding BCC Nb lattice, is also found to have a strong effect on the X-O binding energies. Finally, we identify a repulsive interaction, of significance for a subset of X-O pairs, that arises from a closed-shell hybridization between localized orbitals on solutes.

Interstitial-oxygen induced and magnetically driven HCP-to-FCC transformation in CoCrFeNiOx high-entropy alloy: a first-principles study

ABSTRACT We report the influences of oxygen interstitials and magnetisms on phase stability and structural transformation of CoCrFeNi high-entropy alloy (HEA) from first-principles calculations. It is found the formation of oxygen interstitials is energetically favourable to occur in face-centred cubic (FCC) CoCrFeNiOx HEA as compared with that in hexagonal close-packed (HCP) one, and at those octahedral sites neighbouring with more Cr or less Ni. Meanwhile, it is determined the HEA prefers FCC over HCP phases when the oxygen concentration exceeds 4.2 and 5.1 at.% with and without considering its magnetisms, respectively. The HCP-to-FCC structural transformation in CoCrFeNiOx HEA could be magnetically driven, accompanied by the significant changes in the atomic magnetic moments in the HEA, particularly with an oxygen interstitial concentration larger than 2.7 at.%. Furthermore, the HCP-to-FCC transformation under hydrostatic pressure in CoCrFeNi and CoCrFeNiOx HEAs is investigated from generalised stacking fault energies, and it is revealed that the synergy effects of oxygen interstitials and magnetisms could facilitate the transformation in CoCrFeNiOx HEA. The coupled interstitials-induced and magnetically driven structural transformation paves a new avenue for the application of HEAs.

Fuzzy-logic indicators for riverbed de-clogging suggest ecological benefits of large wood

Rivers provide dynamic habitats with ecological niches, particularly in their mobile sand, gravel, and cobble riverbed patches that create an active hyporheic zone. Natural or artificial deposition of fine sediment may clog the porous matrix of the hyporheic zone, impairing exchange processes between the subsurface and surface water. Clogging reduces the permeability of the sediment matrix, thus degrading the ecological functionality of the hyporheic zone. Once clogged, the ecological functions may be recovered through active stream restoration, which requires considerate site assessment. To this end, clogging is typically assessed by expert opinion of substrate characteristics including grain size characteristics, porosity, hydraulic conductivity, and interstitial oxygen content. To overcome limitations of expert assessment, such as subjectivity expressed in noisy decision-making, this study introduces a novel fuzzy-logic method based on physically sound rules. The method provides quantitative indicators for clogging and declogging to evaluate the effectiveness of stream restoration. We applied the fuzzy-logic method to test whether the placement of large wood, a common restoration practice, can locally prevent or reduce clogging. Two measurement series from before and after a morphologically effective flood suggested that large wood placements perpendicular to the flow generate elevated amounts of declogging. The tested logs caused a greater amount of declogging within their region of influence than observed at a reference point. The effect was stronger for a log emergent at baseflow. The declogging assessment showed that the novel fuzzy-logic indicators can reasonably overcome subjective judgment by accounting for multi-variate quantitative changes rather than individual parameter trends.

New Family of Interstitial Oxygen Ion Conductor Discovered By High-Throughput Computational Screening

Discovery and design of highly efficient oxygen-active materials which react with, absorb, and transport oxygen is essential for fuel cells and related applications. Currently, the predominant families of oxygen-active materials used in commercial devices are perovskites and fluorites, which diffuse oxygen via a vacancy mechanism and only have adequate oxygen diffusivity and surface exchange at high temperatures (e.g., ~800 ˚C), impeding their use at lower temperatures desirable for more cost-effective and long-lasting device operation. The development of alternative electrolyte/electrode materials with high oxygen ionic conductivity at low temperatures (e.g., room temperature to 400 °C) is of great interest. Interstitial oxygen ion conductors typically have significantly lower migration barriers than even state-of-the-art vacancy-mediated oxygen conductors, which can provide orders of magnitude kinetic enhancement at low temperatures. In addition, the interstitial oxygen defects typically become more thermodynamically favorable as the temperature is lowered, potentially providing an additional boost to the oxygen conductivity at low temperatures from a higher mediating defect concentration. The synergistic combination of low migration barriers and thermodynamically favorable interstitial oxygen content at low temperatures provides the tantalizing possibility that interstitial oxygen conductors may lead to transformative performance improvements in oxygen-active materials.In this work, we developed an approach to discover new interstitial-mediated oxygen conductors by performing high-throughput computational screening of the 34k oxide materials from the Materials Project database and discovered a new structural family of interstitial oxygen diffusers, perrierite-type oxide La4Mn5Si4O22+ 𝜹 (LMS). We used a hierarchy of screening criteria including the geometric free space, thermodynamic stability, synthesizability, redox-active elements, and presence of short diffusion pathways. This approach, based largely on simple, physically intuitive properties, quickly winnowed the field of 34k oxides down to just 345 oxides, an approximate 99% reduction in the search space considered, with essentially no significant computational cost. From this reduced set of promising materials, ab initio simulations were performed to calculate the interstitial oxygen formation energy and migration energy. Our screening has yielded several material families to date, among which the A4B5C4O22+ 𝜹, with La4Mn5Si4O22+ 𝜹 (LMS) as a representative material, was selected for investigation with higher-fidelity DFT hybrid functional calculations and experimental validations. The calculated formation energy of interstitial oxygen is -0.11 eV at a concentration of 2.3% under air condition, indicating that LMS is predicted to be oxygen hyperstoichiometric with an expected composition of La4Mn5Si4O22+0.5 in air. Two separate interstitial and interstitialcy (“kick-out”) diffusion mechanisms are revealed by ab initio molecular dynamics (AIMD) simulation. For the interstitial diffusion pathway, the moves through the channel in between the zigzag-arranged sorosilicate Si2O7 groups, with a barrier of 0.69 eV. For the interstitialcy diffusion pathway, the moves along the corner-sharing Si2O7-MnO2-Si2O7 framework by kicking out the lattice oxygen, with a barrier of 0.74 eV. These results align well with the experimental findings of stable interstitial oxygen content and high oxygen mobility in LMS (Please see a separate poster from Md Sariful Sheikhfor experimental results). This work provides a systematic approach to screening a large number of prospective materials and opens a new avenue of finding promising interstitial oxide ion conducting materials for potential applications in a range of fast oxygen ion conduction-based technologies.

Study of Flow Pattern Defects and Oxidation Induced Stacking Faults in Czochralski Single-Crystal Silicon Growth

This paper emphasizes that the furnace pressure, crucible rotation, and pulling rate have important effects on interstitial oxygen (Oi) concentrations and micro-defects during growth in a Czochralski single-crystal silicon (CZ-Si) growth furnace. Since oxygen in a silicon ingot influences minority carrier lifetime, different set-points of furnace pressure and crucible rotation were controlled to achieve different degrees of Oi. The Oi content has a positive correlation with furnace pressure and crucible rotation. Various numbers of micro-defects were generated under the influence of different pulling rates, owing to the transformation from liquid to solid. The sample also underwent Secco etching and a high-temperature wet oxidation to observe defects caused by the Oi concentration and pulling rate, namely, flow pattern defects (FPDs) and oxidation-induced stacking faults (OISFs). Optical microscopy was employed to confirm the surface topography, and for defect number counting, to observe the correlation between the defects and the minority carrier lifetime. The overall results show that the minority carrier lifetime is mainly dominated by OISFs under high Oi content and FPDs under low Oi content. Therefore, growth using a CZ-Si growth furnace should be carried out with low furnace pressure, low crucible rotation, and low pulling rate to reduce micro-defects.

B-site mixed cationic tetrahedral layer confined the concentration and mobility of interstitial oxygen in mellite family

The subtle difference in the cationic size and covalent bonding between Ga and Ge enables B-site mixed Ga/Ge tetrahedral centers to confine the concentration and mobility of interstitial oxygen in mellite family.

Experimental investigation of Kr diffusion in UO2+x: Slight deviations from stoichiometry, significant effects on diffusion kinetics and mechanisms

Thermo-Desorption Spectrometry (TDS) was employed to study the release of fission gases from a Kr implanted UO2+x during 1050–1300 °C isotherms. The stoichiometry of the sample has been regularly increased by O2 additions in the vacuum setup to cover an hyperstoichiometry x range from ∼1 × 10−6 to ∼0.1. We used an analytical model based on Fick's second law to determine krypton diffusion kinetics (DKr) from the Kr cumulated release profiles. We demonstrate that even little x deviations from stoichiometric UO2 down to the 10−6 order are sufficient to quantitatively enhance fission gas diffusion. This likely explains a fair amount of data scatter in literature for experimental fission gases diffusion rates in (supposedly) perfectly stoichiometric UO2. A model was developed from the experimental results and well-accepted data for UO2 to estimate DKr (and DXe equivalently) as a function of T and x in the ranges of the present study.For moderate hyperstoichiometries, the present results suggest a fission gas diffusion mechanism identical (or similar to the very least) to that largely accepted for stoichiometric UO2, with the increased concentration of oxygen interstitials in the material kinetically enhancing Kr diffusion. At x ≈ 0.001 the diffusion-limiting mechanism changes, materialized by an increase of the activation energy (Ea). This Ea increase seemingly rules out a diffusion of fission gases controlled by VU (U vacancies). Instead, the rise of oxygen interstitial clusters, becoming the dominant type of defects in UO2+x for similar x ≥ 0.001 threshold, makes these defects prime suspects in controlling Kr (and Xe) diffusion in hyperstoichiometric uranium dioxide.

Development of La1.7Ca0.3Ni1-yCuyO4+δ Materials for Oxygen Permeation Membranes and Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells.

The La1.7Ca0.3Ni1-yCuyO4+δ (y = 0.0-0.4) nickelates, synthesized via a solid-state reaction method, are investigated as prospective materials for oxygen permeation membranes and IT-SOFC cathodes. The obtained oxides are single-phase and possess a tetragonal structure (I4/mmm sp. gr.). The unit cell parameter c and the cell volume increase with Cu-substitution. The interstitial oxygen content and total conductivity decrease with Cu-substitution. The low concentration of mobile interstitial oxygen ions results in a limited oxygen permeability of Cu-substituted La1.7Ca0.3NiO4+δ ceramic membranes. However, increasing the Cu content over y = 0.2 induces two beneficial effects: enhancement of the electrochemical activity of the La1.7Ca0.3Ni1-yCuyO4+δ (y = 0.0; 0.2; 0.4) electrodes and decreasing the sintering temperature from 1200 °C to 900 °C. Enhanced electrode activity is due to better sintering properties of the developed materials ensuring excellent adhesion and facilitating the charge transfer at the electrode/electrolyte interface and, probably, faster oxygen exchange in Cu-rich materials. The polarization resistance of the La1.7Ca0.3Ni1.6Cu0.4O4+δ electrode on the Ce0.8Sm0.2O1.9 electrolyte is as low as 0.15 Ω cm2 and 1.95 Ω cm2 at 850 °C and 700 °C in air, respectively. The results of the present work demonstrate that the developed La1.7Ca0.3Ni0.6Cu0.4O4+δ-based electrode can be considered as a potential cathode for intermediate-temperature solid oxide fuel cells.

Preparation of Al and Sm Co-doped Apatite-Type Lanthanum Silicate Electrolyte and analysis of the conductivity mechanism

The contradiction between the increasing demand for energy and the scarcity of traditional fossil energy sources is becoming increasingly acute, and it is urgent to accelerate the development and use of new, more efficient, and environmentally friendly energy sources. Apatite-type lanthanum silicate solid oxide electrolyte materials (La9.33Si6O26, LSO) are widely used in the field of fuel cell electrolytes due to their high ionic conductivity and high density. In this paper, Al and Sm co-doped LSO solid electrolytes were successfully prepared by the urea-nitrate combustion method. SEM images, relative density, and linear shrinkage of Al and Sm co-doped lanthanum silicate electrolytes sintered at different temperatures were compared. The results show that the best sintering temperature is 1500°C. The electrical conductivity of La9.33SmxSi5.5Al0.5O25.75+1.5x was analyzed by EIS. The conductivity of La9.33Sm0.2Si5.5Al0.5O26.05 is 2.56 × 10−4 S·cm−1 when measured at 600°C. The reason Al and Sm co-doping enhances the conductance is that Al doping generates oxygen vacancies and increases the interstitial oxygen (Oi) concentration. Doping of Sm not only increases the concentration of Oi but also reduces the concentration of cation vacancies, thus improving the conductivity of the electrolyte.

The ASi–Sii Defect Model of Light‐Induced Degradation (LID) in Silicon: A Discussion and Review

The ASi–Sii defect model as one possible explanation for light‐induced degradation (LID) in typically boron‐doped silicon solar cells, detectors, and related systems is discussed and reviewed. Starting from the basic experiments which led to the ASi–Sii defect model, the ASi–Sii defect model (A: boron, or indium) is explained and contrasted to the assumption of a fast‐diffusing so‐called “boron interstitial.” An LID cycle of illumination and annealing is discussed within the conceptual frame of the ASi–Sii defect model. The dependence of the LID defect density on the interstitial oxygen concentration is explained within the ASi–Sii defect picture. By comparison of electron paramagnetic resonance data and minority carrier lifetime data related to the assumed fast diffusion of the “boron interstitial” and the annihilation of the fast LID component, respectively, the characteristic EPR signal Si‐G28 in boron‐doped silicon is related to a specific ASi–Sii defect state. Several other LID‐related experiments are found to be consistent with an interpretation by an ASi–Sii defect.

T- and T′-type layered perovskite Ln2CuO4 nanocrystals for enhanced sensing detection of hydrogen peroxide

Nanostructured rare earth cuprates have recently attracted extensive attention as a promising non-noble metal electrocatalyst. However, they are rarely used to construct electrochemical sensors, even no report on hydrogen peroxide detection. Accordingly, two types of layered perovskite Ln2CuO4 nanocrystals with different structures, i.e., T-La2CuO4 and T′-Sm2CuO4 were synthesized from sol-gel method followed by calcining at 600 ℃ in air. Then, these nanomaterials were separately modified on the surface of bare glassy carbon electrode (GCE) by drop coating method, thus assembling efficient non-enzymatic H2O2 electrochemical sensor for the first time. In phosphate buffer solution (pH = 7.0), the La2CuO4/GCE shows high sensitivity (419.6 μA mM−1 cm−2) and low detection limit (160 nM) towards H2O2, which are significantly superior to those of Sm2CuO4/GCE. The difference in electrochemical sensing performance is mainly related to their electrode surface area and conductivity, characteristics of T- and T′-type layered structures, as well as the synergism of interstitial oxygen content and Cu2+/Cu+ redox coupling. In addition, La2CuO4/GCE has satisfactory selectivity and stability, and achieves the detection of trace H2O2 in rat serum, contact lens cleaning solution, tap water and disinfectant, indicating that it has certain practical applications in environmental protection and biological analysis.

Effects of Pre-Annealing on the Radiation Resistance of ZnO Nanorods

Ion implantation is usually used for semiconductor doping and isolation, which creates defects in semiconductors. ZnO is a promising semiconductor and has a variety of applications, such as for use in transparent electronics, optoelectronics, chemical and biological sensors, etc. In this work, ZnO nanorods were grown on Si (100) substrates by the process of chemical bath deposition and then annealed in an O2 atmosphere at 350 and 600 °C for 1 h to introduce different kinds of defects. The as-grown nanorods and the nanorods that annealed were irradiated simultaneously by 180 keV H+ ions at room temperature with a total dose of 8.0×1015 ions/cm2. The radiation effects of the H+ ions, effects of the pre-existed defects on the radiation resistance, and the related mechanisms under irradiation were investigated. The crystal and optical properties of the ZnO nanorods after H+ ion irradiation were found to depend upon the pre-existed defects in the nanorods. The existence of the appropriate concentration of oxygen interstitials in the ZnO nanorods caused them to have good radiation resistance. The thermal effects of irradiation played an important role in the property variation of nanorods. The temperature of the nanorods under 180 keV H+ ion bombardment was around 350 °C.

Deep Learning Models for Data-Driven Laser Induced Breakdown Spectroscopy (LIBS) Analysis of Interstitial Oxygen Impurities in Czochralski-Si Crystals.

Analytical advantages of facile and expeditious spectral data collections from laser-induced breakdown spectroscopy (LIBS) are often offset by the low-accuracy quantitative analyses offered by the technique due to non-equilibrium plasma-matrix interactions. Herein, we developed a one-dimensional (1D) convolutional neural network (CNN) and a least absolute shrinkage and selection operator (LASSO) models for LIBS data analyses to predict trace amounts of interstitial oxygen impurities in commercial Czochralski-silicon (Cz-Si) crystals with known interstitial oxygen concentrations at 0-16 parts per million (ppm). While traditional spectral analyses from O(I) (777.2nm) atomic lines offer poor accuracy, CNN and LASSO analyses generate excellent predictions for the interstitial oxygen concentrations. Specifically, CNN-based spectral analyses uniquely identified systematic alterations in LIBS fingerprints manifested by laser-matter interactions. Our results pave the path for combining facile and voluminous LIBS data collection with deep learning driven high-fidelity data analytics.

Influence of the substitution with rare earth elements on the properties of layered lanthanum nickelate – Part 1: Structure, oxygen transport and electrochemistry evaluation

This study is aimed at studying the properties of La2NiO4+δ (LNO) substituted with rare earth elements to increase its oxygen over-stoichiometry and enhance oxygen transport thus improving electrochemical properties of the related electrodes. Materials of the La1.6Ln0.4NiO4+δ series (where Ln = Pr (LPNO), Nd (LNNO), Sm (LSNO), Eu (LENO), Gd (LGNO)) are synthesized by a nitrate combustion technique and their structural features, oxygen over-stoichiometry, and oxygen transport properties are investigated by different methods such as X-ray diffraction, TGA, temperature programmed isotopic oxygen exchange with C18O2 (TPIE) in a flow reactor. The unit cell volume in the La1.6Ln0.4NiO4+δ series decreases from Pr (V = 188.3 Å3) to Gd (V = 186.7 Å3). According to the TGA data, the LNO value of oxygen over-stoichiometry, δ, is equal to 0.15, while all substituted materials, except LGNO, show higher values: 0.16 for LENO, 0.17 for LSNO and LNNO, and the highest value equal to 0.18 has been revealed for LPNO. Oxygen mobility and surface reactivity are studied by the temperature-programmed isotope exchange of oxygen with C18O2 in a flow reactor. All samples can be characterized by a fast oxygen diffusivity provided by cooperative mechanism of oxygen migration involving both regular and highly mobile interstitial oxygen. Variation of oxygen tracer diffusion coefficient with dopant cation nature is probably associated with interstitial oxygen content. The best characteristics have been acquired for Ln = Eu (D⁎ = 2.4∙10−9 cm2/s at 700 °C). Electrochemical properties of the related La1.6Ln0.4NiO4+δ electrodes are investigated in a contact with a Ce0.8Sm0.2O1.9 solid-state electrolyte. The influence of the temperature of the electrode formation and the effect of the collector layer on the electrode electrochemical activity are considered. The LENO, LPNO and LSNO-based electrodes demonstrate low polarization resistance related to the enhanced oxygen diffusion properties. Substitution with Gd, contrarily, significantly deteriorates electrochemical properties of LNO.

Investigation of orientation, surface morphology, impurity concentration and reflectivity of the multi-crystalline silicon wafers

Multi-crystalline silicon (mc-silicon) ingot was grown using the directional solidification (DS) method. The grown ingot was sliced, and the grain orientations, grain size, surface morphology, and impurities concentration in the wafers were studied. The XRD pattern of as-cut wafers exhibited the formation of a more number of (111) oriented plane in the grown ingot. The scanning electron microscopy images showed the formation of worm-like trenches after the chemical etching of the sliced wafers. FTIR spectra showed the higher carbon concentration on the top wafers and higher oxygen concentration at the bottom wafers. At the central wafer of the middle brick, the calculated carbon and interstitial oxygen concentration result exhibited 4.740 × 1016 and 1.369 × 1017 atoms/cm3, respectively. The impurity concentration of carbon and oxygen is validated with simulation results. The reflectivity spectra revealed low reflectivity for the wafers sliced from the central brick compared to the peripheral brick. The presence of very less impurity concentration and low reflectivity of the middle wafer in the central portion of the ingot enhances the light absorption, which is beneficial for photovoltaic energy generation.

Influence of Point Defects on the Equilibrium Concentration of Interstitial Oxygen in Crystalline Silicon

The effect of excess point defects on the equilibrium concentration of interstitial oxygen for the system of interstitial oxygen/SiO2 precipitates in crystalline Si is theoretically investigated. The expression for the equilibrium concentration of interstitial oxygen in Si modified by the excess point defects is derived. Excess vacancies in Si are found to decrease this concentration, while the excess Si self-interstitials have the opposite effect. The effects of different conditions for the point defect generation on the equilibrium in the system of interstitial oxygen/SiO2 precipitates in crystalline Si are studied.

Virtual experiments of Czochralski growth of silicon using machine learning: Influence of processing parameters on interstitial oxygen concentration

For a process development, it is crucial to know the influence of each process parameter on the process result. However, it is difficult to gauge the influence by experimentally changing only one parameter value owing to constraints of the combination of the parameter values and experimental costs. Machine learning models can predict results that will be obtained under conditions that have not been considered for the experiment. Utilizing a virtual experiment based on a machine learning model, we evaluated the influence of process parameters on the interstitial oxygen (Oi) concentration in Czochralski-grown Si crystals. A dataset for the parameter analysis was constructed, wherein the crucible rotation rate and/or Ar flow rate were systematically changed while maintaining the other parameters at the reference value of an experimental datum. Thereafter, the dataset was input into a neural network model that had been trained with 450 ingot data; consequently, the corresponding Oi concentration was obtained. The evaluated results were consistent with the scientific knowledge previously studied: Oi concentration increases with increasing crucible rotation rate and decreasing Ar flow rate. Furthermore, the two-parameter analysis illustrated a nonlinear relationship between the parameters quantitatively. These approaches demonstrating the Czochralski growth of Si in this study are useful in other crystal growth processes as well.