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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Toward ultrafast, ultra-stable imaging arrays: Superlattice doping to enhance the performance of backside-illuminated 3D-hybridized silicon photodetectors

In this paper, the authors report the latest results on their development of superlattice-doped, thinned, backside-illuminated (BSI), 3D-integrated photodiode detectors—a step toward their ultimate goal of demonstrating ultrafast, ultrastable CMOS imaging arrays. As with most silicon-based photodetectors, backside-illumination and backside surface passivation are keys to achieve the highest performance capability. The two-dimensional (2D) doping technique developed at the Jet Propulsion Laboratory (JPL) has proved to result in a highly efficient, highly stable detector response when combined with a variety of detectors. Here, JPL's 2D-doping has been combined with Sandia's BSI photodetectors hybridized with custom fanout wafer via copper Direct Bond Interconnect (DBI®), a technology that is rapidly becoming industry standard for BSI CMOS imaging arrays. The prototype detectors were packaged and evaluated with respect to their response to low energy electrons. The authors find that the responsivity of 2D-doped BSI detectors is higher than devices prepared using other surface passivation techniques (i.e., ion implantation). The success of the work described herein verifies that the 2D-doping processes previously developed for Sandia's frontside-illuminated photodetectors are generally applicable to BSI detectors and demonstrates for the first time that JPL's 2D-doping process is compatible with the Cu-DBI® technology.

Jewell, April D.↗
DOE OSTI2023

Quantifying carrier dynamics and PL characterization of antimony-doped CdTe and CdSeTe

Our team has achieved ~20% doping activation of CdSeTe with antimony (Sb), whose shallow acceptor level makes it a viable alternative to As.1,2 Arsenic (As)-doped graded CdSeTe photovoltaics have achieved record efficiencies of 22.3%. Remaining challenges include doping activation of only ~2% in polycrystalline films and radiative voltage losses of ~100 mV. Here we use (transient) terahertz and photoluminescence spectroscopy of CdTe:Sb and CdSeTe:Sb to show sufficiently long bulk lifetimes to enable high-efficiency devices. Early results also indicate dominant bandgap emission in CdSeTe:Sb and a lack of potential fluctuations with Sb-doping that have proven detrimental for As-doped films. While more work is needed, these results show significant promise for Sb doping.

14 SOLAR ENERGY↗
DOE OSTI2023

High Quality Doping of GaN Through Transmutation Processing

This project led to several outstanding achievements: - Computational modeling of nuclear reactions, including estimates of the production ratio and doping concentration using TALYS 1.96 based on nuclear reactions in GaN induced by gamma-ray and protons. For photonuclear transmutation doping, simulations proved that Zn/Ge ratio with 40 MeV is higher than the other energies. - Proton transmutation doping was shown to be a potential nuclear source to fabricate p-type gallium-based semiconductor materials, examined during new irradiations with Oak Ridge National Laboratory and Brookhaven National Laboratory (in 200 MeV H - –Linac). - Patent disclosure to the University of Missouri-Columbia about healing effects in GaN by radiations. - Zn-doped p-type GaN through photonuclear transmutation doping process. - The PIs made an oral presentation on the p-type characteristics of Zn-doped GaN at the Materials Research Society Fall meeting in Boston. - The last irradiation process was in progress in collaboration with Argonne National Laboratory.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Quantifying carrier dynamics and PL characterization of antimony-doped CdTe and CdSeTe

Our team has achieved ~20% doping activation of CdSeTe with antimony (Sb), whose shallow acceptor level makes it a viable alternative to As.1,2 Arsenic (As)-doped graded CdSeTe photovoltaics have achieved record efficiencies of 22.3%. Remaining challenges include doping activation of only ~2% in polycrystalline films and radiative voltage losses of ~100 mV. Here we use (transient) terahertz and photoluminescence spectroscopy of CdTe:Sb and CdSeTe:Sb to show sufficiently long bulk lifetimes to enable high-efficiency devices. Early results also indicate dominant bandgap emission in CdSeTe:Sb and a lack of potential fluctuations with Sb-doping that have proven detrimental for As-doped films. While more work is needed, these results show significant promise for Sb doping.

14 SOLAR ENERGY↗
DOE OSTI2025

Demonstrate new plasticity models for doped UO 2 that capture dislocation mechanisms

In light water reactors, fuel vendors are investigating the use of dopants to modify the properties of UO 2 pellets, with the goal of improving pellet-cladding mechanical interactions during operation. Dopants are expected to ‘soften’ the pellets; that is, the doped pellets have higher plastic deformation than conventional UO 2 . This leads to a reduction in the severity of mechanical pellet-cladding interactions, helping to reduce the hoop strain on the cladding. By minimizing the strain exerted by the pellet on the cladding, it is anticipated that cladding performance under accident conditions can be enhanced (i.e., lowering the risk of burst during a LOCA). Dopants such as chromium (Cr) promote grain growth during pellet fabrication, leading to larger grains; therefore, understanding the link between chemistry, microstructure and mechanical deformation (enhanced creep rates) behavior of UO 2 is critical to helping operators further substantiate the benefits of doping UO 2 . Historically, the nuclear energy industry has relied on empirical models to make assessments of performance. Compared to empirical models, mechanistic physics-based models provide benefits, such as, fewer data points for validation and better extrapolation where experimental data is scarce or non-existent. In this report, Bayesian inference techniques have been applied to a previously developed lower length-scale-informed diffusional creep model. The objective is to i) infer lower-length-scale parameter distributions from available experiment and then ii) determine the uncertainties in the measurable quantity (in this case creep rates) after propagating the inferred lower length scale parameter uncertainties. The approach requires many evaluations of the model, which becomes computationally insurmountable; therefore, a neural-network model is trained to data obtained by sampling the full model over the most important parameters. This neural-network is then used in the Bayesian inference approach to determine probability distributions in the parameter values that represent the uncertainty in the model given what is known from the experiments (posterior). A significant reduction compared to conservative initial (prior) uncertainties is achieved through inference against the experimental data, demonstrating the efficacy of this approach. Furthermore, by accounting for uncertainties in the experimental conditions and sample non-stoichiometry, it is possible to resolve apparent discrepancies in experimental measurements within a self-consistent grain boundary (Coble) creep model that is sensitive to chemistry. This work has been written up and submitted to Nuclear Technology for a special issue on accelerated fuel qualification (AFQ). This uncertainty quantification (UQ) work not only improves the diffusional model, while accounting for uncertainty, but also establishes a framework which can readily be applied to the mechanistic models of dislocation deformation developed in this study. The most likely values from the Bayesian analysis are incorporated into our UO 2 diffusional creep model and a lower length scale-informed irradiation UO 2 creep mechanistic model to generate a dataset. This dataset has been provided to our INL collaborators for training an artificial neural network surrogate model, which will be implemented in the BISON fuel performance code to assess how the results differ from those currently obtained using a fully empirical model and that of using the nominal (uncalibrated) atomic scale parameters in our mechanistic model. Plastic deformation (creep and glide) in UO 2 is a complex phenomenon, governed by multiple underlying processes such as local defect concentrations, applied stresses, and microstructural characteristics. Consequently, there is a need for a meso-scale model with polycrystalline resolution capable of extrapolating to large grain sizes applicable to doped UO 2 , where data is limited and the model can help bridge the knowledge gap. By integrating atomistic data into the polycrystal LApx code, it becomes possible to predict dislocation climb and glide plasticity that simple analytical models cannot accurately represent. The application of atomic-scale data within LApx demonstrated the importance of climb and glide mechanisms in reproducing high-stress UO 2 behavior. Behaviors such as this are crucial to capture and implement in BISON, as parts of the fuel pellet can reach temperatures where glide can occur before pellet cracking. This model which captures dislocation based mechanisms for UO 2 is then used to stand up the doped model accounting for larger grain sizes. It was found that larger grain sizes can lead to enhanced deformation rates in the glide regime, and therefore can help with the pellet cladding mechanical interaction. Therefore if the fuel pellet reaches conditions (stress/temperature) where glide is active, the enhanced creep rates for larger grains in the glide regime (doped UO 2 ) can help with pellet cladding mechanical interactions. Plastic deformation in UO 2 involves multiple mechanisms, including diffusional creep, dislocation climb, and glide. This milestone contains two parts: (1) UQ of a pre-existing lower length scale informed mechanistic diffusional creep model, and (2) development of a new LApx based model for dislocation-mediated creep mechanisms in UO 2 , with application to large-grain doped UO 2 .

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Computational Fermi Level Engineering and Doping-Type Conversion of Ga2O3 Via Three-Step Processing

Ga2O3 is being actively explored for power electronics, deep-ultraviolet optoelectronics, and other applications due to its ultra-wide bandgap and low projected fabrication cost of large-size and high-quality crystals. N-type doping of Ga2O3 can be achieved and tuned, but p-type doping faces fundamental obstacles due to deep character of acceptor levels and polaron transport of resulting holes. However, successful engineering of Ga2O3 based devices requires critical control of doping density, Fermi level position, and free carrier concentration, providing opportunities for predictive process simulation. We use first-principles defect theory and defect equilibrium calculations to simulate a 3-step growth-annealing-quench protocol for hydrogen assisted Mg doping in Ga2O3, taking into account the hydrogen-oxygen-water gas phase equilibrium. We predict type conversion to a net p-type regime following O-rich annealing after growth under reducing conditions in the presence of H2. This process is similar to the Mg acceptor activation by H removal in GaN. We show that there is an optimal temperature that maximizes the net acceptor density during the equilibrium annealing step for a given Mg doping level. Quenching of non-equilibrium annealed samples then results in a Fermi level EF below mid-gap down to about EV +1.5 eV, creating a significant number of uncompensated neutral MgGa0 acceptors. The resulting free hole concentration in quenched samples is very low (109 – 1012 cm-3) due to deep energy level of these Mg acceptors, but this type converted Ga2O3 material can create a significant built-in field in a p-n junction with an adjoining n-type material. Additionally, the electron concentration is greatly suppressed in such acceptor-doped Ga2O3, which could enable the use as a current blocking layer to fabricate normally-off (enhancement-mode) vertical Ga2O3 based metal-oxide-semiconductor field effect transistors (MOSFETs), and as a guard ring for edge termination in MOSFETs and Schottky barrier diodes (SBDs) with increased breakdown voltage.

CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS,M↗
DOE OSTI2022

Process for preparing doped lithium lanthanum zirconium oxide

A process for preparing doped-lithium lanthanum zirconium oxide (doped-LLZO) is described herein. The method involves dry doping of a co-precipitated lanthanum zirconium oxide (LZO) precursor. Dry doping is a process in which a dry powdered dopant is ground and mixed with a pre-prepared co-precipitated LZO precursor and a lithium salt to provide a LLZO precursor composition, which is subsequently calcined to form a doped-LLZO. The process described herein comprises calcining a dry, powdered (e.g., micron, sub-micron or nano-powdered) mixture of a co-precipitated LZO precursor, a dopant salt or oxide, and a lithium salt under an oxygen-containing atmosphere at a temperature in the range of about 500 to about 1100° C., and recovering the doped-LLZO after calcining.

Durham, Jessica L.↗
DOE OSTI2022

Effective Selective Area Doping for GaN Vertical Power Transistors Enabled by Innovative Materials Engineering

GaN vertical power transistors have emerged as promising candidates for future high efficiency high power electronic applications, with the potential to outperform conventional GaN lateral power devices in terms of power, breakdown, and avalanche characteristics. However, the development of current GaN vertical power transistors is seriously hindered by the poor materials performance of selective area doped p-n junctions. A mechanistic understanding of these fundamental materials issues is essential in order to achieve high performance selective area doped p-n junctions and consequently to advance the GaN vertical power transistor technology. To address this challenge, we carried out a comprehensive research program that advance fundamental knowledge in the selective area doping for GaN materials, and which will lead to the development of high performance GaN vertical power transistors. First, we developed innovative fabrication processes, including novel surface etching, surface passivation, and metalorganic chemical vapor deposition (MOCVD) growth, which provided enhanced opportunities for solving the unique challenges of selective area doping in GaN materials. Second, we performed a fundamental materials study using powerful characterization methods including transmission electron microscopy (TEM), ultraviolet (UV-), x-ray and angle-resolved photoelectron spectroscopy (UPS/XPS/ARPES), electron holography, and cathodoluminescence (CL); Third, we investigated several related issues, including Mg incorporation, polarization effects in carrier transport, and non-ideal material effects, which have rarely been explored so far. At the end of this project, we successfully demonstrated (1) fundamental understanding of selective area etching, regrowth, and doping of GaN, and associated knowledge on defects, interface, and breakdown properties. (2) Effective etch and regrowth processing recipes to achieve etch/regrowth GaN p-n diodes with very low leakage of 3.5 nA at 600 V, which meets the ARPA-E target. (2) High performance vertical GaN p-n didoes and vertical junction termination extension (JTE) devices with breakdown voltage of ~ 2 kV, and breakdown electric field of ~ 3.5 MV/cm, which are close to the performance limit of GaN. The successful outcome has resulted in new fundamental understandings in the selective area doping and regrowth process for GaN, which will lead to groundbreaking GaN vertical transistors for high performance next generation power electronics.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2020

Leveraging Sequential Doping of Semiconducting Polymers to Enable Functionally Graded Materials for Organic Thermoelectrics

With the ability to modulate electronic properties through molecular doping coupled with ease in processability, semiconducting polymers are at the forefront in enabling organic thermoelectric devices for thermal energy management. In contrast to uniform thermoelectric material properties, an alternative route focuses on functionally graded materials (FGMs) where one spatially controls and optimizes transport properties across the length of a thermoelectric material. While primarily studied in the context of inorganic materials, the concept of FGMs for organic thermoelectrics has not been explored. Herein, we introduce how molecular doping of semiconducting polymers enables spatial compositional control of thin-film FGMs. Specifically, we utilize sequential vapor doping of poly[2,5-bis(3-tetradecylthiophen-2-yl) thieno [3,2-b]thiophene] (PBTTT) with the small molecule acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) to fabricate the simplest form of FGMs – double- segmented thin films. The two thin-film segments are of equal length (7.5 mm), but each set to different doping levels. Our study focuses on understanding the thermoelectric properties (Seebeck coefficient, α, and electronic conductivity, σ) and structural properties (through X-ray scattering, UV-vis-NIR spectroscopy, and Raman spectroscopy) within and across the two segments. We observe the presence of a small diffuse interfacial region of 0.5 – 1 mm between the two segments where the doping level and transport properties vary continuously. Despite the diffuse interface, the measured effective Seebeck coefficient (αeff) across the two segments is simply the average of α within each segment. Importantly, this experimental result is consistent with reported mathematical models describing αeff in graded thermoelectric materials. Finally, our results demonstrate the facile fabrication and characterization of functionally graded organic thermoelectric materials, providing guidelines for further development on more complex FGMs.

36 MATERIALS SCIENCE↗
DOE OSTI2025

P-Type Doping of Mixed Tin–Lead Halide Perovskites Using Electron Transfer to Mo(tfd-COCF3) 3 and F 4 TCNQ

Mixed tin-lead halide perovskites are emerging as promising candidates to address the toxicity issues of lead-based perovskites and to provide additional bandgap tunability for optoelectronic applications. Electron-transfer doping offers a prospective pathway to modulate electronic properties of metal-halide perovskites, while not disturbing the underlying crystal structure. However, limited research exists comparing molecular dopants for these systems. Here, our study investigates the p-type electron-transfer doping of the mixed tin-lead halide perovskite MAPb 0.5 Sn 0.5 I 3 (MA = methylammonium) using a sequential deposition approach (perovskite film followed by dopant incorporation) and the molecular dopants F 4 TCNQ and Mo(tfd-COCF 3 ) 3 . Up to 3 orders of magnitude higher carrier density and up to 2 orders of magnitude greater conductivity are achieved relative to the undoped samples, with F 4 TCNQ and Mo(tfd-COCF 3 ) 3 demonstrating similar doping efficiencies (associated with the ratio of mobile charges added to the number of dopant molecules incorporated) of 0.031(3) % and 0.024(3) %, respectively. Differences in the doping effectiveness for a given molarity doping solution likely follow from variations in dopant incorporation within the film during the spin coating deposition step.

14 SOLAR ENERGY↗
DOE OSTI2022

DFT simulation of conductivity of the p-type doped and charge-injected cis-polyacetylene

Semiconducting conjugated polymers (CPs) have shown great potential in organic solar cells and organic field-effect transistors (OFETs), due to their tunable electronic and optical properties. In this study, we compare computational predictions of electronic and optical properties of ensembles of cis-polyacetylene (cis-PA) multiple oligomers in two different forms (a) undoped cis-PA and (b) cis-PA doped by phosphorous fluoride (PF¯ 6 ) via density functional theory (DFT) with hybrid functionals. The comparison of undoped cis-PA under the constraint of injected charge carrier and cis-PA doped by PF¯ 6 shows that either doping or injection provides very similar features in electronic structure and optical properties. Doped and injected are similar to each other and different from the pristine, undoped PA. Computed results also indicate that the injection of charge carriers and adding p-type doping into the semiconducting CP model both greatly affect the conductivity. Furthermore, these observations provide a better understanding and practical use of the properties of polyacetylene films for flexible electronic applications.

74 ATOMIC AND MOLECULAR PHYSICS↗
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 OSTI2025

Co‐Doping Approach for Enhanced Electron Extraction to TiO 2 for Stable Inorganic Perovskite Solar Cells

Inorganic perovskite CsPbI 3 solar cells hold great potential for improving the operational stability of perovskite photovoltaics. However, electron extraction is limited by the low conductivity of TiO 2 , representing a bottleneck for achieving stable performance. In this study, a co‐doping strategy for TiO 2 using Nb(V) and Sn(IV), which reduces the material's work function by 80 meV compared to Nb(V) mono‐doped TiO 2 , is introduced. To gain fundamental understanding of the processes at the interfaces between the perovskite and charge‐selective layer, transient surface photovoltage measurements are applied, revealing the beneficial effect of the energetic and structural modification on electron extraction across the CsPbI 3 /TiO 2 interface. Using 2D drift‐diffusion simulations, it is found that co‐doping reduces the interface hole recombination velocity by two orders of magnitude, increasing the concentration of extracted electrons by 20%. When integrated into n–i–p solar cells, co‐doped TiO 2 enhances the projected T S80 lifetimes under continuous AM1.5G illumination by a factor of 25 compared to mono‐doped TiO 2 . This study provides fundamental insights into interfacial charge extraction and its correlation with operational stability of perovskite solar cells, offering potential applications for other charge‐selective contacts.

14 SOLAR ENERGY↗
DOE OSTI2020

Growth and Characterization of Arsenic-Doped CdTe 1-x Se x Single Crystals Grown by the Cd-Solvent Traveling Heater Method

The photovoltaic performance of CdTe solar cells is mainly limited by low doping and short minority carrier lifetime. Group-V element doping and Se-alloying have a significant impact on tuning these fundamental CdTe properties. In this paper, we report the growth of p-type As-doped, Cd-rich CdTe 1-x Se x single crystals using metallic Cd as the solvent in the traveling-heater method. The structural and electrical properties of CdTe1-xSex are examined for different Se concentrations. CdTe 1-x Se x single crystals (0 ≤ x ≤ 0.5) with zincblende structure indicate homogeneous composition. The 10 17 cm-3 As-doping activation efficiency can be maintained at close to 50% for x ≤ 0.2. Se alloying leads to bulk minority carrier lifetime exceeding 30 ns for samples doped near 1017 cm -3 . These results help us to overcome the current roadblocks in device performance.

14 SOLAR ENERGY↗
DOE OSTI2022

Reverse water-gas shift: Na doping of m-ZrO 2 supported Pt for selectivity control

Reverse water-gas shift (RWGS) is a vital step in producing syngas for the chemical conversion of CO 2 to liquid transportation fuels and chemicals. Na-doping of m-ZrO 2 supported Pt catalysts allowed selectivity control by systematically increasing the ratio of relative rates of r CO /r CH4 . This was achieved by facilitating the formation of formate intermediate species, which precedes CO formation, and by suppressing the metallic Pt 0 active sites responsible for CH 4 formation. Here, a 2.5%Na-2%Pt/m-ZrO 2 catalyst was first tested for the forward water-gas shift (FWGS) reaction and found to have 50% higher CO conversion at 285°C compared to the undoped catalyst. Results of DRIFTS spectroscopy of adsorbed CO confirmed a formate ν(CH) band shift to lower wavenumbers (2870–2802 cm —1 ) with the addition of Na and more rapid forward formate decomposition in steam to H 2 and carbonate species, the precursor to CO 2 . This is consistent with C-H bond breaking being the rate limiting step of a FWGS mechanism occurring at the metal-support junction. Consistent with this, DRIFTS of RWGS in 4%CO 2 + 60%H 2 showed more facile formation of formate for the Na-doped catalyst and, once again, the ν(CH) band was shifted to lower wavenumbers (2874–2803 cm —1 ) with Na-doping. In addition, Na doping resulted in a systematic decrease in the Pt-carbonyl band in DRIFTS of adsorbed CO as well as DRIFTS of in-situ RWGS reaction tests, suggesting that Na blocked a fraction of on-top Pt sites, breaking up ensembles of Pt 0 responsible for methanation. The selectivity of the 2.5%Na-doped catalyst, unlike its undoped counterpart, was remarkably resistant to methanation (e.g., selectivity < 0.2% CH 4 with pressures of up to 20 bar).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

High-efficiency perovskite photovoltaic modules achieved via cesium doping

Perovskite solar modules have been attracting increasing attention due to their market potential, yet publications concerned with theintrinsic scale-up potential of different perovskite compositions remain relatively scarce. On the other hand, while great success is being made towards improving the power conversion efficiency (PCE) of perovskite solar cells (PSCs) by cesium cation (Cs + ) doping of the perovskite, more attention is being paid to the perovskite phase stabilization effect of Cs + doping, and less to other properties that are critical to understand and futher improve the PSC's. In this work, moderately-Cs-doped MAPbI 3 was employed as a model perovskite material in order to exclude the phase stabilization effect. Our systematic study revealed the influence of Cs + in organic-inorganic hybrid perovskites on the crystal structure, crystallization process, trap state density, band structure and charge (i.e., ions or photo-carriers) transport. Markedly, it has been observed that Cs + doping can greatly increase the carrier diffusion length in the perovskite films, thus improving the potential to scale-up PSC's.The PCE of small area devices (0.09 cm 2 ) was increased to 21.72% from 19.73%, with decreased hysteresis behavior and increased operational stability (T85 = 1000 h) after Cs + doped, where T85 refers to the retention of 85% of the initial PCE. Moreover, a PCE of 21.08% was obtained for a Cs + -containing perovskite module with an active area > 30 cm 2 , which demonstrates a better "reproducibility" than the reference sample (MAPbI3-based perovskite modules, PCE = 18.26%).

14 SOLAR ENERGY↗
DOE OSTI2020

Cr-doped U 3 Si 2 composite fuels under steam corrosion

Dense Cr-doped U 3 Si 2 composite fuels were manufactured by spark plasma sintering, and the effects of Cr addition on mechanical properties and oxidation resistance were investigated. Furthermore, dynamic oxidation testing by thermogravimetric analysis revealed significantly improved oxidation resistance of U 3 Si 2 with minimal doping of 3 wt% Cr. The onset oxidation temperature increased to above 550 °C in air and ~520 °C in steam conditions for the 5 wt% and 10 wt% Cr-doped composites. Steam corrosion testing under 360 °C for 24 hours indicated well-maintained pellet integrity without pulverization for the 10 wt% Cr-doped U 3 Si 2 pellet which only showed minor surface oxidation. The first promising results open up the possibility of designing and manufacturing metal additive-doped U 3 Si 2 composite fuels with significantly-improved corrosion resistance as a potential candidate for accident tolerant fuels.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Nitrogen: A promising doping strategy for high-performance ovonic threshold switching selectors

The Ovonic Threshold Switching (OTS) selector serves as an essential component in the development of three-dimensional high-density memory integration technology. Nevertheless, the state-of-the-art high-performance OTS materials usually contain toxic elements such as arsenic (As), posing significant risks to both environmental and human health. Nitrogen (N), which belongs to the same group as arsenic (As), has emerged as a highly promising alternative for As doping. However, the underlying mechanisms that govern N-based OTS materials have not yet been extensively investigated. In this study, we delve into the effects of N doping on the structural, bonding, and electronic properties of amorphous GeSe (a-GeNSe) by ab initio molecular dynamics simulations to bridge the knowledge gap. Our findings indicate that upon N doping in a-GeSe, the formation of robust Ge-N bonds, along with N-centered tetrahedral and triangular structures, resulting in the sluggish atomic movement that enhances the thermal stability and endurance of a-GeNSe. The OTS characteristics are significantly influenced by the material’s electronic band structure, and thus the relatively slow performance drift can be attributed to the stabilization of mid-gap states, a result of N doping which effectively slows down the aging process of chalcogenide glass. Moreover, the increased mobility gap in a-GeNSe raises the threshold voltage (V th ), making it more compatible with commercially available phase-change memory materials. Furthermore, our findings reveal the extensive impact of the N element on a typical OTS material and offer valuable perspectives for alternative doping strategies that could potentially supplant As practices.

36 MATERIALS SCIENCE↗