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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Effect of interstitial impurities on the field dependent microwave surface resistance of niobium

Previous work has demonstrated that the radio frequency surface resistance of niobium resonators is dramatically reduced when nitrogen impurities are dissolved as interstitial in the material. This effect is attributed to the lowering of the Mattis-Bardeen surface resistance with increasing accelerating field; however, the microscopic origin of this phenomenon is poorly understood. Meanwhile, an enhancement of the sensitivity to trapped magnetic field is typically observed for such cavities. In this paper, we conduct a systematic study on these different components contributing to the total surface resistance as a function of different levels of dissolved nitrogen, in comparison with standard surface treatments for niobium resonators. Adding these results together, we are able to show which is the optimum surface treatment that maximizes the Q-factor of superconducting niobium resonators as a function of expected trapped magnetic field in the cavity walls. These results also provide insights on the physics behind the change in the field dependence of the Mattis-Bardeen surface resistance, and of the trapped magnetic vortex induced losses in superconducting niobium resonators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

First-principles multiple-barrier diffusion theory. The case study of interstitial diffusion in CdTe

The diffusion of particles in solid-state materials generally involves several sequential thermal-activation processes. However, presently, diffusion coefficient theory only deals with a single barrier, i.e., it lacks an accurate description to deal with multiple-barrier diffusion. Here, we develop a general diffusion coefficient theory for multiple-barrier diffusion. Using our diffusion theory and first-principles calculated hopping rates for each barrier, we calculate the diffusion coefficients of Cd, Cu, Te, and Cl interstitials in CdTe for their full multiple-barrier diffusion pathways. As a result, we found that the calculated diffusivity agrees well with the experimental measurement, thus justifying our theory, which is general for many other systems.

36 MATERIALS SCIENCE↗
DOE OSTI2016

The effect of interstitial carbon on the mechanical properties and dislocation substructure evolution in Fe 40.4 Ni 11.3 Mn 34.8 Al 7.5 Cr 6 high entropy alloys

A systematic study of the effects of up to 1.1 at. % carbon on the mechanical properties and evolution of the dislocation substructure in a series of a high entropy alloys (HEA) based on Fe40.4Ni11.3Mn34.8Al7.5Cr6 is presented. Transmission electron microscopy (TEM), synchrotron X-ray diffraction (XRD) and atom probe tomography (APT) were used to show that all the alloys are single-phase f.c.c. random solid solutions. The lattice constant, determined from synchrotron XRD measurements, increases linearly with increasing carbon concentration, which leads to a linear relationship between the yield strength and the carbon concentration. The dislocation substructures, as determined by a TEM, show a transition from wavy slip to planar slip and, at higher strains, and from cell-forming structure (dislocations cells, cell blocks and dense dislocation walls) to non-cell forming structure (Taylor lattice, microbands and domain boundaries) with the addition of carbon, features related to the increase in lattice friction stress. The stacking fault energy (measured via weak-beam imaging of the separation of dislocation partials) decreases with increasing carbon content, which also contributes to the transition from wavy slip to planar slip. The formation of non-cell forming structure induced by carbon leads to a high degree of strain hardening and a substantial increase in the ultimate tensile strength. The consequent postponement of necking due to the high strain hardening, along with the plasticity accommodation arising from the formation of microbands and domain boundaries, result in an increase of ductility due to the carbon addition. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Dislocation structures↗
DOE OSTI2018

First-principles investigation of native interstitial diffusion in Cr2O3

First principles density functional theory (DFT) investigation of native interstitials and the associated self-diffusion mechanisms in a-Cr2O3 reveals that interstitials are more mobile than vacancies of corresponding species. Cr interstitials occupy the unoccupied Cr sublattice sites that are octahedrally coordinated by 6 O atoms, and O interstitials form a dumbbell configuration orientated along the [221] direction (diagonal) of the corundum lattice. Calculations predict that neutral O interstitials are predominant in O-rich conditions and Cr interstitials in +2 and +1 charge states are the dominant interstitial defects in Cr-rich conditions. Similar to that of the vacancies, the charge transition levels of both O and Cr interstitials are located deep within the bandgap. Transport calculations reveal a rich variety of interstitial diffusion mechanisms that are species, charge, and orientation dependent. Cr interstitials diffuse preferably along the diagonal of corundum lattice in a two step process via an intermediate defect complex comprising a Cr interstitial and an adjacent Cr Frenkel defect in the neighboring Cr bilayer. This mechanism is similar to that of the vacancy mediated Cr diffusion along the c-axis with intermediate Cr vacancy and Cr Frenkel defect combination. In contrast, O interstitials diffuse via bond switching mechanism. O interstitials in -1 and -2 charge states have very high mobility compared to neutral O interstitials.

Medasani, Bharat K.↗
DOE OSTI2021

Small uranium and oxygen interstitial clusters in UO 2 : An empirical potential study

The aggregation of defect clusters in UO 2 under irradiations creates dislocation loops and cavities, which in turn contribute to swelling of the fuels, leading to detrimental pellet-clad mechanical interactions. The kinetics of the defect clusters, however, have received less attention and are not well understood. As such, using two interatomic potentials, the Morelon potential and a many-body model by Cooper, Rushton, and Grimes (CRG), the energetics and kinetics of small uranium interstitial clusters, with and without bound oxygen interstitials, are investigated with molecular dynamics and accelerated molecular dynamics simulations. For the single bound anti-Schottky interstitial cluster (U i 2O i ), both potentials find the interstitialcy migration mechanism to be a low barrier migration mechanism. However, for the CRG potential, an oxygen Frenkel pair assisted interstitial cluster migration mechanism with a lower migration barrier is identified during accelerated molecular dynamics simulations. For the Morelon potential, the interstitial clusters have geometrically compact structures, and small interstitial clusters (two and three anti-Schottky clusters) are more mobile than the single bound anti-Schottky interstitial cluster; for the CRG potential, the interstitial clusters have geometrically non-compact structures, yielding a more complex energy landscape. The rapid migration of interstitials and interstitial clusters are important for the irradiation response of UO 2 and correlates well with the very low barriers reported in a few historic experimental studies.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

Understanding and design of interstitial oxygen conductors

Highly efficient oxygen-active materials that react with, absorb, and transport oxygen is essential for fuel cells, electrolyzers and related applications. While vacancy-mediated oxygen-ion conductors have long been the focus of research, they are limited by high migration barriers at intermediate temperatures (400–600 °C), which hinder their practical applications. In contrast, interstitial oxygen conductors exhibit significantly lower migration barriers enabling higher ionic conductivity at lower temperatures. This review systematically examines both well-established and recently identified families of interstitial oxygen-ion conductors, focusing on how their unique structural motifs such as corner-sharing polyhedral frameworks, isolated polyhedral, and cage-like architectures, facilitate low migration barriers through interstitial and/or interstitialcy diffusion mechanisms. A central discussion of this review focuses on the evolution of design strategies, from targeted donor doping, element screening, to physical-intuition descriptor material screening and machine learning approach, which leverage computational tools to explore vast chemical spaces in search for new interstitial conductors. The success of these strategies demonstrates that a significant, largely unexplored space remains for discovering high-performing interstitial oxygen conductors. Crucial features enabling high-performance interstitial oxygen diffusion include the availability of electrons for oxygen reduction and sufficient structural flexibility with accessible volume for interstitial accommodation and migration. This review concludes with a forward-looking perspective, proposing a knowledge-driven methodology that integrates current understanding with data-centric approaches to identify promising interstitial oxygen conductors outside traditional search paradigms. These approaches are expected to significantly accelerate the development of high-performance interstitial oxygen conductors for a variety of oxygen-active applications, ultimately paving the way for more efficient and sustainable energy technologies.

Interstitial oxygen conductors↗
DOE OSTI2014

SU-F-19A-12: Split-Ring Applicator with Interstitial Needle for Improved Volumetric Coverage in HDR Brachytherapy for Cervical Cancer

Purpose: To evaluate volumetric coverage of a Mick Radionuclear titanium Split-Ring applicator (SRA) with/without interstitial needle compared to an intracavitary Vienna applicator (VA), interstitial-intracavitary VA, and intracavitary ring and tandem applicator (RTA). Methods: A 57 year-old female with FIGO stage IIB cervical carcinoma was treated following chemoradiotherapy (45Gy pelvic and 5.4Gy parametrial boost) with highdose- rate (HDR) brachytherapy to 30Gy in 5 fractions using a SRA. A single interstitial needle was placed using the Ellis Interstitial Cap for the final three fractions to increase coverage of left-sided gross residual disease identified on 3T-MRI. High-risk (HR) clinical target volume (CTV) and intermediate-risk (IR) CTV were defined using axial T2-weighted 2D and 3D MRI sequences (Philips PET/MRI unit). Organs-at-risks (OARs) were delineated on CT. Oncentra planning system was used for treatment optimization satisfying GEC-ESTRO guidelines for target coverage and OAR constraints. Retrospectively, treatment plans (additional 20 plans) were simulated using intracavitary SRA (without needle), intracavitary VA (without needle), interstitial-intracavitary VA, and intracavitary RTA with this same patient case. Plans were optimized for each fraction to maintain coverage to HR-CTV. Results: Interstitial-intracavitary SRA achieved the following combined coverage for external radiation and brachytherapy (EQD2): D90 HR-CTV =94.6Gy; Bladder-2cc =88.9Gy; Rectum-2cc =65.1Gy; Sigmoid-2cc =48.9Gy; Left vaginal wall (VW) =103Gy, Right VW =99.2Gy. Interstitial-intracavitary VA was able to achieve identical D90 HR-CTV =94.6Gy, yet Bladder-2cc =91.9Gy (exceeding GEC-ESTRO recommendations of 2cc<90Gy) and Left VW =120.8Gy and Right VW =115.5Gy. Neither the SRA nor VA without interstitial needle could cover HR-CTV adequately without exceeding dose to Bladder-2cc. Conventional RTA was unable to achieve target coverage for the HR-CTV >80Gy without severely overdosing OARs. Conclusion: The Ellis Interstitial Cap for the SRA offered superior dosimetric coverage as compared to the interstitialintracavitary VA. This represents the first reported use for this devise, and further investigation is warranted.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

A curved pathway for oxygen interstitial diffusion in aluminum

Here, the diffusion of interstitial oxygen (O) in fcc aluminum (Al) has been studied using first-principles and the diffusion coefficient has been calculated. Whereas interstitial atoms in fcc systems are typically found to hop directly between interstitial centres, the diffusion pathway for interstitial O in fcc Al was calculated to have a curved minimum energy pathway with an energy barrier of 0.95 eV. The barrier was found to be off-centre of a neighboring octahedral site. Also unlike the majority of fcc metals, O prefers to sit in the tetrahedral interstitial site as opposed to the octahedral site. The calculated O diffusion coefficient is on the same order of magnitude of the diffusion coefficient of O in other fcc metals. The preferred interstitial site, diffusion pathway and vacancy binding energy were found to be related to the bond length of O with neighboring Al atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Interstitial hydrogen enhances the mobility of some grain boundaries in tungsten

Segregation of interstitials at a grain boundary (GB) is known to generally lower its mobility. This phenomenon, called 'solute-drag', has important ramifications on the process of recrystallization and microstructural evolution. Here, we present predictions from molecular dynamics (MD) simulations which demonstrate that interstitial hydrogen in tungsten can in fact increase the mobility of some GBs which exhibit shear coupling. Assuming a disconnection-based mechanism, activation energies and pre-factors for disconnection nucleation are predicted from simulations of shear-coupled motion. In GBs where enhanced mobility is predicted, interstitial H reduces both the activation energy and the pre-factor for disconnection nucleation, thus effectively increasing the mobility. For GBs with diminished mobility, MD predicts that presence of interstitial H reduces the pre-factor and, in some cases, increases the activation energy. The reduction in the activation energy inferred from MD simulations are confirmed by nudged elastic band calculations. Temperature-dependent structural transitions are observed for some GBs, and the effect of interstitial H is found to change with the changes in structure. The effect of interstitial H is predicted to be complex and highly variable, providing some plausible explanations for experimental observations on the recrystallization of tungsten in presence of H-loaded plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Phase-field modeling of dislocation–interstitial interactions

The mechanical behavior of body-centered cubic (BCC) materials can be dramatically affected by the presence of interstitial solute atoms. Here we present a new phase-field dislocation dynamics formulation to include the diffusion of interstitials. Short-range interactions are accounted for by a concentration-dependent lattice energy, and long-range interactions are accounted for by modifications to the elastic energy. The interstitial diffusion law introduces gradients that require methods for minimizing Gibbs oscillations, which is done via a modified Green’s function. The formulation is general to any solute-solvent system and is applied here to Nb-O as a model system, whose interstitial parameters are obtained from ab initio calculations. The effect of O on the core structures of Nb edge and screw dislocations is calculated. The diffusion of O to form interstitial atmospheres around dislocation cores is simulated, as well as the critical stresses required for dislocations to break away or cross slip from these atmospheres. Future applications of the method to simulate complex interstitial embrittlement mechanisms are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Electrochemical Doping of Halide Perovskites by Noble Metal Interstitial Cations

Abstract Metal halide perovskites are an attractive class of semiconductors, but it has proven difficult to control their electronic doping by conventional strategies due to screening and compensation by mobile ions or ionic defects. Noble‐metal interstitials represent an under‐studied class of extrinsic defects that plausibly influence many perovskite‐based devices. In this work, doping of metal halide perovskites is studied by electrochemically formed Au + interstitial ions, combining experimental data on devices with a computational analysis of Au + interstitial defects based on density functional theory (DFT). Analysis suggests that Au + cations can be easily formed and migrate through the perovskite bulk via the same sites as iodine interstitials (I i + ). However, whereas I i + compensates n‐type doping by electron capture, the noble‐metal interstitials act as quasi‐stable n‐dopants. Experimentally, voltage‐dependent, dynamic doping by current density–time ( J–t ), electrochemical impedance, and photoluminescence measurements are characterized. These results provide deeper insight into the potential beneficial and detrimental impacts of metal electrode reactions on long‐term performance of perovskite photovoltaic and light‐emitting diodes, as well as offer an alternative doping explanation for the valence switching mechanism of halide‐perovskite‐based neuromorphic and memristive devices.

14 SOLAR ENERGY↗
DOE OSTI2018

Electronic Structure of HgBa{sub 2}CuO{sub 4+δ} with Self-organized Interstitial Oxygen Wires in the Hg Spacer Planes

While recent experiments have found that at optimum doping for the highest critical temperature in HgBa{sub 2}CuO{sub 4+y} (Hg1201) the oxygen interstitials (O-i) are not homogeneously distributed but form one-dimensional atomic wires, there are no available information of its electronic structure considering self-organized O-i atomic wires. Here we report the calculated electronic structure of HgBa{sub 2}CuO{sub 4+y} where oxygen interstitials form atomic wires along (1,0,0) crystal direction in the Hg layer. We find that at optimum doping for superconductivity the chemical potential is tuned near an electronic topological Lifshitz transition for the appearing of a second quasi 1D Fermi surface. A first large Fermi surface coexists with a second incipient quasi one-dimensional (1D) Fermi surface related with atomic wires of oxygen interstitials. Increasing oxygen doping the chemical potential is driven to the band edge of the second 1D-band giving a peak in the density-of-states. The new 1D electronic states are confined near the oxygen interstitial wires with a small spread only on nearby sites. Spin-polarized calculations show that the magnetic response is confined in the oxygen-poor domains free of oxygen interstitials wires and it is quite insensitive to the density of O-i wires.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Chemical complexity suppresses interstitial solute segregation to screw dislocation cores in the bcc NbTaTiHfZr high-entropy alloy

Recent reports suggest that interstitial solute additions to body-centered cubic (bcc) high-entropy alloys (HEAs) may enhance their mechanical properties. However, details of interactions between interstitial atoms and dislocations in these HEAs remain incompletely understood. Using first-principles calculations, we examine the energetics of C, N, and O interstitial solutes in elemental bcc metals and NbTaTiHfZr, focusing on their segregation in screw dislocation cores. We examine two types of core sites and show that the low-energy configuration and associated segregation energy depend on the transition metal group. In NbTaTiHfZr, we find that chemical complexity substantially suppresses interstitial segregation in dislocation cores, as fluctuations in bulk solute energies induce energetically favorable sites that disfavor segregation to core sites. Local chemical order further enhances this effect by promoting solute clustering away from dislocation cores. These findings reveal fundamental differences between the behavior of interstitial atoms in elemental metals and HEAs, with implications for high-temperature plasticity and dynamic strain aging.

Body-centered cubic transition metals↗
DOE OSTI2024

Thermal and dynamic partition of dumbbell interstitials in complex concentrated alloys

Complex concentrated alloys (CCAs) are promising candidates for applications in extreme conditions, such as irradiation where interstitial mediated diffusion is important. In CCAs with N principal elements, $\frac{N(N+1)}{2}$ types of dumbbell interstitials exist. Currently, there is no way to predict the thermal partition (fractional concentration at equilibrium) and the dynamic partition (fractional time an interstitial spends during diffusion) of each type of dumbbell interstitial. To mitigate this issue, this work proposes a theoretical model for computing the equilibrium concentrations and thermal partition of dumbbell interstitials in CCAs and validates the model using grand canonical Monte Carlo simulations. Lattice kinetic Monte Carlo simulations show that the thermal partition is equivalent to the dynamic partition, and both are governed by composition and formation energies of dumbbells. As a result, the model proposed provides a foundation for understanding radiation enhanced diffusion and induced segregation in CCAs under irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Computational discovery of fast interstitial oxygen conductors

New highly oxygen-active materials may enhance many energy-related technologies by enabling efficient oxygen-ion transport at lower temperatures, for example, below ~400 °C. Interstitial oxygen conductors have the potential to realize such performance but have received far less attention than vacancy-mediated conductors. Here, in this study, we combine physically motivated structure and property descriptors, ab initio simulations and experiments to demonstrate an approach to discover new fast interstitial oxygen conductors. Multiple new families were found, which adopt completely different structures from known oxygen conductors. From these families, we synthesized and studied oxygen kinetics in La 4 Mn 5 Si 4 O 22+δ , a representative member of the perrierite/chevkinite family. We found that La 4 Mn 5 Si 4 O 22+δ has higher oxygen-ion conductivity than the widely used yttria-stabilized ZrO 2 , and among the highest surface oxygen exchange rates at the intermediate temperature of known materials. The fast oxygen kinetics is the result of simultaneously active interstitial and interstitialcy diffusion pathways. We propose that the essential features for forming an effective interstitial oxygen conductor are the availability of electrons and structural flexibility, enabling a sufficient accessible volume. This work provides a powerful approach for understanding and discovering new interstitial oxygen conductors.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Interstitial proton transport through defective MXenes

Proton transport across nanometer-thick membranes in an aqueous medium is important for applications in energy and molecular sieving. Recently, Hu et al. [Nature 516(7530), 227–230 (2014)] experimentally demonstrated proton tunneling through 2D materials like graphene and hexagonal boron nitride, opening up a wide range of applications in hydrogen-based technologies such as fuel cells. Here, we demonstrate proton transport in an aqueous medium across a 2D cubic Ti 2 C membrane, a representative defective MXene, from ab initio molecular dynamics simulations. We observe bidirectional translocation of protons, which occurs through the interstitial vacancies in the surface. We show from our simulations that water dissociates on the membrane and the dissociated proton moves into the interstitial sites in the membrane. The proton hops from interstitial-to-interstitial and transports across the membrane. Here, we also show that this interstitial proton transport is associated with an induced electric field that is modulated with bidirectional transport of protons across the membrane.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗