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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 OSTI2022

Tuning Organic Electrochemical Transistor Threshold Voltage using Chemically Doped Polymer Gates

Organic electrochemical transistors (OECTs) have shown promise as transducers and amplifiers of minute electronic potentials due to their large transconductances. Tuning the OECT threshold voltage is important to achieve low-powered devices with amplification properties within the desired operational voltage range. However, traditional design approaches have struggled to decouple channel and materials properties from threshold voltage, thereby compromising on several other OECT performance metrics, such as electrochemical stability, transconductance, and dynamic range. In this work, simple solution-processing methods are utilized to chemically dope polymer gate electrodes, thereby controlling their work function, which in turn tunes the operation voltage range of the OECTs without perturbing their channel properties. Chemical doping of initially air-sensitive polymer electrodes further improves their electrochemical stability in ambient conditions. Thus, OECTs that are simultaneously low-powered and electrochemically resistant to oxidative side reactions under ambient conditions are demonstrated. Furthermore, this approach shows that threshold voltage, which is once interwoven with other OECT properties, can in fact be an independent design parameter, expanding the design space of OECTs.

chemical doping↗
DOE OSTI2024

Tuning the Spin Transition and Carrier Type in Rare-Earth Cobaltates via Compositional Complexity

There is growing interest in material candidates with properties that can be engineered beyond traditional design limits. Compositionally complex oxides (CCO), often called high entropy oxides, are excellent candidates, wherein a lattice site shares more than four cations, forming single-phase solid solutions with unique properties. However, the nature of compositional complexity in dictating properties remains unclear, with characteristics that are difficult to calculate from first principles. Here, in this study, compositional complexity is demonstrated as a tunable parameter in a spin-transition oxide semiconductor La 1- x (Nd, Sm, Gd, Y) x/4 CoO 3 , by varying the population x of rare earth cations over 0.00≤ x≤ 0.80. Across the series, increasing complexity is revealed to systematically improve crystallinity, increase the amount of electron versus hole carriers, and tune the spin transition temperature and on-off ratio. At high a population (x = 0.8), Seebeck measurements indicate a crossover from hole-majority to electron-majority conduction without the introduction of conventional electron donors, and tunable complexity is proposed as new method to dope semiconductors. First principles calculations combined with angle resolved photoemission reveal an unconventional doping mechanism of lattice distortions leading to asymmetric hole localization over electrons. Thus, tunable complexity is demonstrated as a facile knob to improve crystallinity, tune electronic transitions, and to dope semiconductors beyond traditional means.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Uniaxial Strain Tuned Magnetism of the Altermagnet Candidate H-FeS

Altermagnets are a newly recognized class of magnetic materials characterized by compensated spin configurations while still breaking time-reversal symmetry and exhibiting unconventional transport phenomena. Hexagonal FeS (h-FeS) is a recently identified altermagnet candidate that shows a spontaneous anomalous Hall effect (AHE) accompanied by a tiny net magnetization. Here, we show that both the spontaneous AHE and magnetization can be effectively suppressed by an in-plane compressive strain. Since neutron diffraction measurements show that the applied uniaxial strain only modifies the in-plane domain population but does not affect the in-plane magnetic structure, the major effect of the applied strain is to tune the small 𝑐-axis ferromagnetic moment. Our results demonstrate a strong correlation between the tiny net magnetization and the spontaneous AHE in h-FeS, and show that uniaxial strain provides an effective knob to tune both properties in this altermagnet candidate for spintronic applications.

Yao, Weiliang [ORNL]↗
DOE OSTI2020

Hydrostatic and Uniaxial Pressure Tuning of Iron-Based Superconductors: Insights into Superconductivity, Magnetism, Nematicity, and Collapsed Tetragonal Transitions

Iron-based superconductors are well-known for their intriguing phase diagrams, which manifest a complex interplay of electronic, magnetic and structural degrees of freedom. Among the phase transitions observed are superconducting, magnetic, and several types of structural transitions, including a tetragonal-to-orthorhombic and a collapsed-tetragonal transition. In particular, the widely-observed tetragonal-to-orthorhombic transition is believed to be a result of an electronic order that is coupled to the crystalline lattice and is, thus, referred to asnematic transition. Nematicity is therefore a prominent feature of these materials, which signals the importance of the coupling of electronic and lattice properties. Correspondingly, these systems are particularly susceptible to tuning via pressure (hydrostatic, uniaxial, or some combination). We review efforts to probe the phase diagrams of pressure-tuned iron-based superconductors, with a strong focus on our own recent insights into the phase diagrams of several members of this mate-rial class under hydrostatic pressure. These studies on FeSe, Ba(Fe 1-x Co x ) 2 As 2 , Ca(Fe 1-x Co x ) 2 As 2 and CaK(Fe 1-x Ni x ) 4 As 4 were, to a significant extent, made possible by advances of what measurements can be adapted to the use under differing pressure environments. We point out the potential impact of these tools for the study of the wider class of strongly correlated electron systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Differentiating Ligand Tailoring and Cation Incorporation as Strategies for Tuning Heterobimetallic Cerium Complexes

Tuning of redox-active complexes featuring metals with high coordination numbers by incorporation of secondary redox-inactive cations has received far less attention than it deserves. Here, appending moderate steric bulk to a tripodal ligand framework has been tested for its influence on secondary-cation-driven structural and electrochemical tuning of cerium, a lanthanide that tends to adopt high coordination numbers. A quasi -C 3 -symmetric cerium(III) complex denoted [Ce] has been prepared that features pendant benzyloxy groups, and this work demonstrates that this species offers a site capable of binding single Na + or Ca 2+ ions. Electrochemical and UV-visible spectroscopic studies reveal equilibrium binding affinity of [Ce] for Na + in acetonitrile solvent, contrasting with tight binding of all cations in all other previously studied systems of this type. The modulated cation binding can be attributed to the bulky benzyloxy groups, which impact the thermodynamics of cation binding but do not impede the formation of cerium centers with coordination number 8 upon binding of either Na + or Ca2 + . Finally, the Ce(IV/III) reduction potential was found to be tunable under the equilibrium binding conditions, highlighting the potentially significant role that controlled structural changes can play in modulating the solution properties of heterobimetallic complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Tuning Structural and Electronic Configuration of FeN 4 via External S for Enhanced Oxygen Reduction Reaction

The Fe–N–C material represents an attractive oxygen reduction reaction electrocatalyst, and the FeN 4 moiety has been identified as a very competitive catalytic active site. Fine tuning of the coordination structure of FeN 4 has an essential impact on the catalytic performance. Herein, we construct a sulfur‐modified Fe–N–C catalyst with controllable local coordination environment, where the Fe is coordinated with four in‐plane N and an axial external S. The external S atom affects not only the electron distribution but also the spin state of Fe in the FeN 4 active site. The appearance of higher valence states and spin states for Fe demonstrates the increase in unpaired electrons. With the above characteristics, the adsorption and desorption of the reactants at FeN 4 active sites are optimized, thus promoting the oxygen reduction reaction activity. This work explores the key point in electronic configuration and coordination environment tuning of FeN 4 through S doping and provides new insight into the construction of M–N–C‐based oxygen reduction reaction catalysts.

25 ENERGY STORAGE↗
DOE OSTI2024

Cu Based Dilute Alloys for Tuning the C 2+ Selectivity of Electrochemical CO 2 Reduction

Electrochemical CO 2 reduction is a promising technology for replacing fossil fuel feedstocks in the chemical industry but further improvements in catalyst selectivity need to be made. So far, only copper-based catalysts have shown efficient conversion of CO 2 into the desired multi-carbon (C 2+ ) products. This work explores Cu-based dilute alloys to systematically tune the energy landscape of CO 2 electrolysis toward C 2+ products. Selection of the dilute alloy components is guided by grand canonical density functional theory simulations using the calculated binding energies of the reaction intermediates CO*, CHO*, and OCCO* dimer as descriptors for the selectivity toward C 2+ products. Here, a physical vapor deposition catalyst testing platform is employed to isolate the effect of alloy composition on the C 2+ /C 1 product branching ratio without interference from catalyst morphology or catalyst integration. Six dilute alloy catalysts are prepared and tested with respect to their C 2+ /C 1 product ratio using different electrolyzer environments including selected tests in a 100-cm 2 electrolyzer. Consistent with theory, CuAl, CuB, CuGa and especially CuSc show increased selectivity toward C 2+ products by making CO dimerization energetically more favorable on the dominant Cu facets, demonstrating the power of using the dilute alloy approach to tune the selectivity of CO 2 electrolysis.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Tuning the Superconducting Transition Temperature of Co-sputtered Iridium and Platinum Films

A superconducting film with a tunable low transition temperature (Tc) is required in high-resolution Transition-Edge Sensor (TES) detectors, which have applications including dark matter detection, low threshold coherent elastic neutrino nucleus scattering measurement, and X-ray spectroscopy. We have been investigating a new approach to tune the Tc of superconducting thin films fabricated by co-sputtering Iridium and Platinum. The effects of Pt concentration and deposition parameters on the films' structural, electrical, and superconducting properties have been studied. AFM and XRD techniques and low temperature resistance measurements have been utilized for film characterization. By varying the Pt concentration and deposition parameters when co-sputtering, we have successfully achieved controllable tuning of Tc in the range of 30-200 mK. The experimental results demonstrate co-sputtering as a viable method for controlling the Tc of Ir-based thin films that can be applied to fabricating high-resolution TESs.

Yefremenko, V. G.↗
DOE OSTI2024

Fine-tuning catalytic selectivity by modulating catalyst-environment interactions: CO 2 hydrogenation over Pd-based catalysts

Capturing catalytic behaviors under operational conditions is pivotal to gaining a mechanistic understanding and promoting the design of robust catalysts. The challenge lies in the difficulty of monitoring real-time surface dynamics driven by catalyst-environment interactions. Here, in this work, we introduce a framework based on density functional calculations and kinetic modeling. This framework significantly improves the accuracy of theoretical models’ descriptions of experimental observations by quantifying environmental impacts on surface phases and active sites. CO 2 hydrogenation over Pd-based catalysts is taken as a showcase. The observed selectivity variations of Pd and Pd-M bimetallic catalysts strongly correlate with hydrogen coverage maintained under typical CO 2 hydrogenation conditions. By reducing the amount of surface hydrogen, the selectivity tuned effectively from formic acid toward CO and methanol. This study not only deepens the comprehension of dynamics of active sites under active chemical conditions but also introduces an alternative opportunity for catalytic tuning by modulating catalyst-environment interactions.

03 NATURAL GAS↗
DOE OSTI2026

Agentic framework for programmatic crystal structure generation using a fine-tuned worker–supervisor large language model

Platinum group metals (PGMs) underpin many catalytic technologies but face severe supply constraints, motivating the search for alternative materials and computational methods to accelerate discovery. While atomistic simulation tools such as Pymatgen and ASE have streamlined structure manipulation, they require detailed inputs, limiting accessibility for experimentalists and slowing early-stage exploration. Here, in this study, we present an AI-driven agentic framework that orchestrates worker–supervisor large language models (LLMs). The worker translates natural-language prompts of varying abstraction into valid crystallographic structures using a compact LLM fine-tuned with low-rank adaptation on a curated text–code–CIF dataset, emphasizing energy-efficient training. Benchmarking against the baseline CodeGen-350M-mono model shows that fine-tuning reduces hallucination rates from 100% to as low as 5% and improves structural match accuracy to up to 82% for fully specified inputs. Accuracy declines with decreasing prompt detail but remains nontrivial even when only stoichiometry and space group are provided, underscoring the LLM’s capacity for crystallographic inference. The supervisor Claude LLM evaluates the outputs and triggers iterative refinement through the worker’s built-in structure manipulation capabilities (e.g., supercell scaling, strain, vacancy, and substitution operations). We further demonstrate use cases for technologically relevant catalysts, including IrO 2 , pyrochlore Pb 2 Ir 2 O 7 , Ni 2 FeO 4 , and Ni 3 Mo, where the framework generates physically consistent structures that can be refined via geometry optimization. This work introduces a low-energy, language-driven pathway for integrating human and machine intelligence in materials design, paving the way for AI-assisted synthesis planning and high-throughput screening of complex oxides.

AI agent↗
DOE OSTI2022

Tuning transport in graphene oxide membrane with single-site copper ($\mathrm{II}$) cations

Controlling the ion transport through graphene oxide (GO) membrane is challenging, particularly in the aqueous environment due to its strong swelling tendency. Fine-tuning the interlayer spacing and chemistry is critical to create highly selective membranes. We investigate the effect of single-site divalent cations in tuning GO membrane properties. Competitive ionic permeation test indicates that Cu 2+ cations dominate the transport through the 2D channels of GO membrane over other cations (Mg 2+ /Ca 2+ /Co 2+ ). Without/With the single-site M 2+ modifications, pristine GO, Mg-GO, Ca-GO, and Cu-GO membranes show interlayer spacings of ~13.6, 15.6, 14.5, and 12.3 Å in wet state, respectively. The Cu-GO membrane shows a two-fold decrease of NaCl (1 M) permeation rate comparing to pristine GO, Mg-GO, and Ca-GO membranes. In reverse osmosis tests using 1000 ppm NaCl and Na 2 SO 4 as feeds, Cu-GO membrane shows rejection of ~78% and ~94%, respectively, which are 5%–10% higher than its counterpart membranes.

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

Realizing continuous cation order-to-disorder tuning in a class of high-energy spinel-type Li-ion cathodes

Conventional Li-ion cathode materials are dominated by well-ordered structures, in which Li and transition metals occupy distinct crystallographic sites. Here, we show in this paper that profoundly new degrees of freedom for the optimization of electrochemical properties may be accessed if controllable cation disorder is introduced. In a class of high-capacity spinel-type cathode materials, we identify cation to anion ratio in synthesis as a key parameter for tuning the structure continuously from a well-ordered spinel, through a partially ordered spinel, to rocksalt. We find that the varying degree of cation disorder modifies the voltage profile, rate capability, and charge-compensation mechanism in a rational and predictable way. Our results indicate that spinel-type order is most beneficial for achieving high-rate performance as long as the cooperative 8a to 16c phase transition is suppressed, while more rocksalt-like disorder facilitates O redox, which can increase capacity. Our findings reveal an important tuning handle for achieving high energy and power in the vast space of partially ordered cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2025

A sub-5 ps jitter time-to-digital converter ASIC with back-gate delay tuning in 22 nm CMOS

We present the design of a Time-to-Digital Converter (TDC) ASIC together with performance characterization results at cryogenic temperature (6-8 K), and at room temperature using emulated Low-Gain Avalanche Detector (LGAD) signals. The TDC design uses a two-step architecture with a ring-oscillator based counter and a Vernier delay line fine TDC. The TDC is implemented in an FD-SOI process, and back-gate tuning is used not only to correct threshold variation due to cryogenic operation, but also as a novel way to tune TDC delay elements with very little overhead. Using this technique, we demonstrate a design with very low power (0.5 mW) and area (0.003 mm 2 ). We present test results using the Fermilab Constant Fraction Discriminator (FCFD) ASIC to produce discriminated signals from an internal charge injection mechanism that mimics the waveform and signal amplitude of minimum ionizing particles impinging on LGAD sensors. We characterize the time precision of the full system and verify that the TDC ASIC contributes a negligible amount to the total system time precision, fully consistent with the expected jitter contribution of less than 5 ps. In conclusion, the results presented here demonstrate the utility of our TDC for applications in physics and quantum communications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Tuning Point Defects by Elastic Strain Modulates Nanoparticle Exsolution on Perovskite Oxides

Exsolution generates stable and catalytically active metal nanoparticles via phase precipitation out of a host oxide. An ability to control the size and dispersion of the exsolution particles is desirable for design of nanostructured (electro)catalysts. In this work, we demonstrate that tuning point defects by lattice strain affects both the thermodynamics and the kinetics of iron (Fe 0 ) exsolution on La 0.6 Sr 0.4 FeO 3 (LSF) thin film model. By combining in situ surface characterization and ab initio defect modeling, we show oxygen vacancy and Schottky defects to be the primary point defects formed upon Fe0 exsolution. Lattice strain tunes the formation energy, and thus the abundance of these defects, and alters the amount and size of the resulting exsolution particles. In addition, we find that the density of exsolved nanoparticles matches the concentration of oxygen vacancy pairs, thus pointing to the surface oxygen vacancy pairs as preferential nucleation sites for exsolution. The tensile-strained LSF with a facile formation of these critical point defects results in a higher Fe 0 metal concentration, a larger density of nanoparticles, and a reduced particle size at its surfaces. These results provide important mechanistic insights and highlight the role of point-defect engineering in designing nanostructured catalysts in energy and fuel conversion technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Understanding and Tuning the Electronic Properties of Prussian Blue Analogues

Prussian blue analogues (PBAs) have attracted increasing interest owing to their potential applications in various fields such as energy storage and conversion, neuromorphic computing, and magnetic switching. With a general formula of A x M N [M C (CN) 6 ], they feature an open framework that provides abundant channels for diffusion of alkali metal ions A and allows flexible compositional control of transition metal ions M N and M C . The oxidation states of transition metal ions can be tuned by adjusting the amount (x) of alkali ions A. Here, we carried out density functional theory calculations combined with experimental measurements to investigate the effects of transition metal ions, alkali ions, and oxidation states on the electronic properties of PBAs. Our calculations found that the band gaps of PBAs can be tuned from close to 0 eV to more than 4 eV. Experimentally, we introduced the synthesis/characterization of five previously unreported PBAs (M N = Ru, Os; M C = Fe, Ru, and Os) to complete the nine stable M N :M C transition metal combinations in group VIII of the periodic table. The optically measured intervalence charge transfer excitation energies of group VIII PBAs are consistent with calculated band gaps. They demonstrate wide band gap tunability by adjusting transition metals and oxidation states, enabling semiconductor-to-metal transitions for memristor applications and enhancing electronic conductivity for battery applications. In conclusion, this work provides a computational/experimental database of electronic properties versus structural compositions for PBAs.

Electrical conductivity↗
DOE OSTI2022

Tuning the Placement of Pt “Single Atoms” on a Mixed CeO 2 –TiO 2 Support

Defect sites on the oxide supports can be used to anchor and activate "single-atoms" catalysts (SACs). By engineering the anchoring sites for supporting SACs, one can alter their electronic and atomic structures which, in turn, define their activity, selectivity, and stability for catalytic reactions. To create and tune unique sites for Pt SACs on CeO 2 support, in this work, we synthesized a system consisting of CeO 2 decorated on TiO 2 nano-oxides for supporting the Pt SACs and investigated the effect of Pt weight loading. Here, a combination of multiple structural characterization methods including diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) were employed to characterize the distribution of charge states of single atoms and evaluate the heterogeneity of their binding sites. We have found that the placement of Pt atoms can be tuned on a mixed oxide surface by changing the weight loading of Pt.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Tuning Discharge Behavior of Hollandite α-MnO 2 in Hydrated Zinc Ion Battery by Transition Metal Substitution

The tunnel-type hollandite α-MnO 2 is a promising cathode material for rechargeable aqueous zinc-ion batteries (ZIBs) due to its low cost in synthesis and high energy density. However, irreversible structural degradation upon continuous cycling prevents the cathode from being utilized commercially. Herein, density functional theory (DFT) was utilized to conduct a systematic study on tuning the behavior of α-MnO 2 by substituting the Mn ions on the tunnel wall with a transition metal (V or Cr) during the H + -/Zn 2+ -intercalation in hydrated ZIB. Our study revealed that both substituents aid cyclability and capacity retention with Cr outperforming V. In term of discharge voltage, only the Cr-substitution displays clear promotion at the early stage of discharge. The superior performance of substituted Cr 4+ comes from its unique atomic and electronic structures. Upon discharge, it can be reduced to Cr 3+ more readily than Mn 4+ and thereby limits the formation of unstable Mn 3+ or Mn 2+ centers; the formed Cr 3+ is more stable than Mn 3+ and Mn 2+ from the reduction of Mn 4+ ; and Cr 3+ can also greatly stabilize the neighboring Mn ions. Here this study highlights the significant tuning effect of transition metal substitution on the electrochemical and physical performance of α-MnO 2 as a cathode in hydrated ZIBs.

25 ENERGY STORAGE↗
DOE OSTI2021

Tuning the Double Gyroid Phase Window in Block Copolymers via Polymer Chain Conformation Near the Interface

Block copolymer network morphologies have been proven interesting for applications ranging from mechanical to transport and optical properties. The shape of the polymer chain and its ability to stretch across an interface can be used as handles to target these network morphologies. Here, we show that the double gyroid phase window is broadened when there is a flexible segment near the interface and narrowed when a more constrained segment is placed there by using a series of poly(styrene-b-peptoid) block copolymers in which the polypeptoid block chain conformation can be tuned to adopt either a helical or a coil conformation (NRpe 6 vs Npe 6 ). The double gyroid phase is accessed in both block copolymer series, while the phase boundaries are shifted toward larger polypeptoid volume fractions in the helix-forming PS–(NRpe 6 Nmey) series, due to the more compact helix segment (i.e., the helix segment has the same chain volume as its random coil counterpart but occupies less space). The space-filling difference between the helix and coil segment is further confirmed by the smaller domain spacing of PS–(NRpe 6 Nme 39 ) compared to PS–(Npe 6 Nme 36 ) (13.9 nm vs 14.3 nm) despite the former having a longer polypeptoid block. Furthermore, a broadened double gyroid phase window is accessed in the PS–(Npe 6 Nme y ) series that has a flexible coil segment near the interface. These results demonstrate the possibility of tuning the double gyroid phase in linear block copolymers by chain conformation near the interface alone, highlighting chain conformation as a versatile handle in block copolymer design.

36 MATERIALS SCIENCE↗