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Results for “Interstitial doping”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Suppressing ion migration in metal halide perovskite via interstitial doping with a trace amount of multivalent cations

Cations with suitable sizes to occupy an interstitial site of perovskite crystals have been widely used to inhibit ion migration and promote the performance and stability of perovskite optoelectronics. However, such interstitial doping inevitably leads to lattice microstrain that impairs the long-range ordering and stability of the crystals, causing a sacrificial trade-off. Here, we unravel the evident influence of the valence states of the interstitial cations on their efficacy to suppress the ion migration. Incorporation of a trivalent neodymium cation (Nd 3+ ) effectively mitigates the ion migration in the perovskite lattice with a reduced dosage (0.08%) compared to a widely used monovalent cation dopant (Na + , 0.45%). As a result, the photovoltaic performances and operational stability of the prototypical perovskite solar cells are enhanced with a trace amount of Nd 3+ doping while minimizing the sacrificial trade-off.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Promoting reversibility of layered potassium cathode through interstitial doping

With the increasing needs for large-scale and low-cost energy storage devices, Mn-based layered oxide cathodes have achieved considerable researching interests for potassium-ion batteries owing to their high energy density, abundant resource and low toxicity. However, their developments are challenged by the absence of suitable cathode materials to tolerate large-sized K-ion insertion/extraction and the presence of Jahn-Teller distortion of Mn 3+ . To address this issue, here we present a strategy of embedding boron into interstitial tetrahedral sites to obtain a P3-K 0.5 Mn 0.8 Co 0.2 B 0.1 O 2 cathode. Strong B-O covalent bonds facilitate the construction of robust orthorhombic framework and alleviate the undesired elongation of Mn-O bonds, contributing to excellent electrochemical performance. In addition, boron ions are verified to promote the formation of a homogeneous cathode electrolyte interphase layer, improving interfacial stability and realizing highly reversible cycling in a wide voltage range (1.4-4.3 V). This strategy provides a new pathway towards the development of high-performance cathode materials for potassium-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Materials Science of the Interstitial Doping Process

Particle accelerators are an increasingly important tool for frontier science. Growing initial and operating costs are a significant barrier for upgrades and for new machines. While everything matters, the major cost contributor is the SRF cavities and their ancillary facilities (e.g., cryoplant). Accordingly, the accelerator science community devotes much R&D effort to improving their energy efficiency (increased Q o ) and gradient (E acc ). While improved gradient is at the forefront for certain machines (ILC), improved quality factor has broader impact, benefitting all SRF applications. An important opportunity for accelerator science and technology to move forward arose in the course of building the LCLS-II, the second generation Linac Coherent Light Source at SLAC. At more or less the same time, researchers at Fermilab discovered that introducing a small amount of nitrogen to the niobium surface could improve the mid-range quality factor as much as three-fold. A firm resolution of how nitrogen confers its benefit attracts much current research interest. The key elements of the “nitrogen doping” process were vacuum bake at 800 °C, brief exposure to mTorr of nitrogen at several hundred degrees followed by electropolish (EP) to remove several microns from the surface to eliminate unwanted nitrides: While the process as a whole was novel, the comprising unit operations are familiar to the accelerator community. It was judged reasonable to adopt it as a cost-reduction technology for LCLS-II. Researchers carried out a program of varying process parameters and measuring performance in single-cell cavities, leading to a consensus stable protocol for the project. The transition to vendor fabrication and multiple niobium sources has presented unforeseen challenges of performance variation evidently not connected to anything that could be incorporated in a purchase specification. Moving beyond the high temperature N-doping process above, researchers reported a simplified process consisting entirely of tens of hours anneal in a N atmosphere at low temperatures (~120°C – 160°C) after 800 °C UHV bake. These processes typically yield a few-nm doped layer while the high temperature process yields at least a few to many micron doped layer. Even more recently, oxygen has been used to dope instead of nitrogen which leaves a few-µm O-alloyed layer upon vacuum annealing for 300 °C for ~3 hours. The investigation of these materials is just beginning, but the process simplification they may offer is surely attractive. The very low quantity of material that appears to be significant in the “infusion” process indicates the need for very careful control of gas species available for diffusion into the surface during low temperature treatment, both for process control and research to characterize the underlying dynamics. Oxygen alloying offers the further opportunity to utilize the decomposition of the surface native oxide as the dopant source. It is necessary to understand and (thus) manage this process. We have been supported by the Department of Energy Offices of High Energy Physics and Nuclear Physics to pursue this goal.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Methods of controllable interstitial oxygen doping in niobium

A method for vacuum heat treating Nb, such as is used in superconducting radio frequency cavities, to engineer the interstitial oxygen profile with depth into the surface to conveniently optimize the low-temperature rf surface resistance of the material. An example application is heating of 1.3 GHz accelerating structures between 250-400° C. to achieve a very high quality factor of 5×1010 at 2.0 K. With data supplied by secondary ion mass spectrometry measurements, application of oxide decomposition and oxygen diffusion theory was applied to quantify previously unknown parameters crucial in achieving the oxygen alloy concentration profiles required to optimize the rf surface resistance. RF measurements of vacuum heat treated Nb superconducting radio frequency cavities confirmed the minimized surface resistance (higher Q0) previously expected only from 800° C. diffusive alloying with nitrogen.

Palczewski, Ari D.↗
DOE OSTI2021

Controlling magnetostructural transition and magnetocaloric effect in multi-component transition-metal-based materials

Proper coupling between structural and magnetic transitions is critical for the emergence and control of magnetocaloric effects in solids. We examine the influence of minor substitutional doping (replacing Mn by Cr and Al by Sn) and interstitial doping with B on the magnetic, structural, and magnetocaloric properties of recently discovered Mn 0.5 Fe 0.5 NiSi 0.94 Al 0.06 alloy exhibiting a giant magnetocaloric effect near room temperature. We demonstrate that magnetocaloric properties of the base compound can be controlled and, in some cases, improved by chemical substitutions. First-principles computations elucidate how small changes in the composition affect properties in this family of compounds and, thus, provide useful guidance for the selection of suitable doping elements for such materials. Here the magnetic-field-induced entropy change measured for Mn 0.5 Fe 0.5 NiSi 0.94 Al 0.06 B 0.005 is –22 J/kg K near room temperature for the applied magnetic field of 2 T, and it is among the highest known values for this class of materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Influence of heterovalent doping on tetrahedral N interstitial formation in dilute GaAsN alloys

Dilute alloying of GaAs with N enables bandgap tuning for near-infrared to mid-infrared optoelectronic devices. However, non-substitutional N incorporation has been linked to lower absorption and emission efficiencies in dilute-nitride-alloy-based devices, especially in those containing heterovalent dopants. Here, in this work, we examine the influence of heterovalent dopants on N incorporation mechanisms in dilute GaAs 1−x N x alloys with N composition intentionally below the threshold composition for the formation of tetrahedral N interstitials (N tetra ) in undoped GaAs 1−x N x . For undoped GaAs 1−x N x , 20% of the N incorporates in non-substitutional sites, as (N-N) As and (N-As) split interstitials. Interestingly, Si dopants induce the formation of N tetra , while Be doping has a negligible effect on the interstitial type. Although elastic interactions due to opposite signs of the misfit volumes of N tetra and N As contribute to N tetra incorporation above a threshold N composition, Si dopants reduce the threshold composition, due to the Fermi level-dependent stability of N tetra .

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ab initio prediction of FeCr sigma (001)/FCC Fe(111) interfacial energy: Effect of interfacial doping of C, B, and N

Interfacial energy plays a crucial role for high-temperature material systems in determining their microstructure evolution and mechanical properties. Optimizing the interfacial energy through doping can improve the stability, performance, and overall functionality of these materials. Here, the present study delivers theoretical investigation on the sigma FeCr (001)//FCC Fe (111) interfacial energy using ab initio methods, focusing on the implications of interfacial doping with important interstitial elements carbon (C), boron (B), and nitrogen (N). The calculated interfacial energy without doping is 0.183J/m 2 . Upon doping, notable reductions in interfacial energy were observed. Doping with B decreased the interfacial energy to 0.046J/m 2 , with single C doping to 0.126J/m 2 , with two C doping to 0.098J/m 2 , and with a single N doping to 0.071J/m 2 . These findings not only shed light on the atomistic origin for the effect of stabilizing the microstructure of stainless steel at elevated temperatures by interstitial doping, but also present a systematic, thorough ab initio approach to predict interfacial doping properties and guide alloy design to enhance the performance and stability.

FeCr sigma phase↗
DOE OSTI2021

Interstitial Nature of Mn 2+ Doping in 2D Perovskites

Halide perovskites doped with magnetic impurities (such as the transition metals Mn 2+ , Co 2+ , Ni 2+ ) are being explored for a wide range of applications beyond photovoltaics, such as spintronic devices, stable light-emitting diodes, single-photon emitters, and magneto-optical devices. However, despite several recent studies, there is no consensus on whether the doped magnetic ions will predominantly replace the octahedral B-site metal via substitution or reside at interstitial defect sites. Here, by performing correlated nanoscale X-ray microscopy, spatially and temporally resolved photoluminescence measurements, and magnetic force microscopy on the inorganic 2D perovskite Cs 2 PbI 2 Cl 2 , we show that doping Mn 2+ into the structure results in a lattice expansion. The observed lattice expansion contrasts with the predicted contraction expected to arise from the B-site metal substitution, thus implying that Mn 2+ does not replace the Pb 2+ sites. Photoluminescence and electron paramagnetic resonance measurements confirm the presence of Mn 2+ in the lattice, while correlated nano-XRD and X-ray fluorescence track the local strain and chemical composition. Density functional theory calculations predict that Mn 2+ atoms reside at the interstitial sites between two octahedra in the triangle formed by one Cl – and two I – atoms, which results in a locally expanded structure. These measurements show the fate of the transition metal dopants, the local structure, and optical emission when they are doped at dilute concentrations into a wide band gap semiconductor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Tunable structural and magnetic properties of NiAs-type Mn x Sb (1.00≤x≤1.30) compounds

Mn-based alloys can exhibit a variety of magnetic properties related to their tunable exchange interactions. Here, structural and magnetic properties of hexagonal NiAs-type Mn x Sb (1.00≤x≤1.30) compounds are studied with a combination of X-ray diffraction, neutron diffraction, and magnetic measurements. It is found that the magnetization, Curie temperature, and magnetocrystalline anisotropy of Mn x Sb compounds can be tuned by controlling Mn concentration and doping at interstitial (2d) sites. With increasing Mn concentration, magnetic moments of Mn atoms decrease and deviate gradually from the ab-plane to the c-axis for 1.20≤x≤1.22 at room temperature, which leads to a decrease of the Curie temperature T c and the spin reorientation temperature T SR . By doping with nonmagnetic elements, a substantial room-temperature magnetocaloric effect without magnetic hysteresis was achieved for Mn 1.12 Zr 0.1 Sb compound, which is highly beneficial to the practical magnetic refrigeration application.

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 OSTI2024

Stabilization of the Active Ruthenium Oxycarbonate Phase for Low-Temperature CO 2 Methanation

Interstitial carbon-doped RuO 2 catalyst with the newly reported ruthenium oxycarbonate phase is a key component for low-temperature CO 2 methanation. However, a crucial factor is the stability of interstitial carbon atoms, which can cause catalyst deactivation when removed during the reaction. In this work, the stabilization mechanism of the ruthenium oxycarbonate active phase under reaction conditions is studied by combining advanced operando spectroscopic tools with catalytic studies. Three sequential processes: carbon diffusion, metal oxide reduction, and decomposition of the oxycarbonate phase and their influence by the reaction conditions, are discussed. We present how the reaction variables and catalyst composition can promote carbon diffusion, stabilizing the oxycarbonate catalytically active phase under steady-state reaction conditions and maintaining catalyst activity and stability over long operation times. In addition, insights into the reaction mechanism and a detailed analysis of the catalyst composition that identifies an adequate balance between the two phases, i.e., ruthenium oxycarbonate and ruthenium metal, are provided to ensure an optimum catalytic behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Enhanced Phase Stability of Sm 2 (Fe, Al) 17 C x

Aluminum doping can improve the phase stability of metastable compound Sm 2 Fe 17 C x with a high carbon content (x > 1.5). We investigated the preferential site substitution of Al, chemical bonding, and structural stability in Sm 2 (Fe,Al) 17 C 3 using first-principle calculations. Our results reveal a strong correlation between the preferential substitution of Fe by Al and the atomic site chemical environment, which affects the overall phase stability. Specifically, Al preferentially occupies the 9d site in Sm 2 (Fe,Al) 17 C 3 . At the same time, Al prefers the site 6c in its parent phase Sm 2 (Fe,Al) 17 . Partial replacement of Fe with Al leads to a more negative formation energy, indicating enhanced thermodynamic stability. Crystal Orbital Hamilton Population (COHP) and Crystal Orbital Bond Index (COBI) analysis suggest that insertion of carbon weakens the bonding strength of Sm-Fe (18f) and Sm-Fe (18h), resulting in metastability of Sm 2 Fe 17 C x . Doping Al strengthens Al-Fe, Al-Sm, Sm-Fe (18f, 18h) and Fe–C bonding in Sm 2 (Fe,Al) 17 C 3 , as revealed by calculated COHP and COBI. These effects contribute to improved phase stability in the Al-doped 2:17 interstitial compound.

chemical bonding↗
DOE OSTI2022

Investigating the Anomalous Frequency Variations Near $T_c$ of Nb SRF Cavities

We report recent studies on the anomalous frequency variations of 1.3 GHz Nb SRF cavities near the transition temperature Tc and use them to investigate the underlying physics of state-of-the-art surface treatments. One such feature, a dip in frequency, correlates directly with the quality factor at 16 MV/m and the anti-Q slope that arise in cavities with dilute concentrations of N interstitial in the RF layer achieved via N-doping and mid temperature baking. For N interstitial, we find that the dip magnitude and Tc follow exponential relationships with the electronic mean free path. We present the first observation of the frequency dip near Tc in a cavity baked at 200 C in-situ for 11 hours, which is concurrent with the anti-Q slope, and may be driven by oxygen diffused from the native oxide, thus suggesting the possibility of ‘‘O-doping.’’ We also investigate the conductivities of two cavities that display different resonant frequency behaviors near Tc and suggest that the anti-Q slope and frequency dip phenomena may occur in the presence of interstitial N or possibly O that inhibit the formation of proximity coupled Nb nano-hydrides.

43 PARTICLE ACCELERATORS↗
NASA NTRS1996

Observations of Dynamic Strain Aging in Polycrystalline NiAl

Dynamic strain aging has been investigated at temperatures between 77 and 1100 K in eight polycrystalline NiAl alloys. The 0.2% offset yield stress and work hardening rates for these alloys generally decreased with increasing temperature. However, local plateaus or maxima were observed in conventional purity and carbon doped alloys at intermediate temperatures (600-900 K). This anomalous behavior was not observed in low interstitial high-purity, nitrogen doped, or in titanium doped materials. Low or negative strain rate sensitivities (SRS) were also observed in all eight alloys in this intermediate temperature range. Coincident with the occurrence of negative SRS was the occurrence of serrated flow in conventional purity alloys containing high concentrations of Si in addition to C. These phenomena have been attributed to dynamic strain aging (DSA). Chemical analysis of the alloys used in this study suggests that the main species causing strain aging in polycrystalline NiAl is C but indicate that residual Si impurities can enhance the strain aging effect.

Weaver, M. L.↗