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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Electrochromic Properties of Perovskite NdNiO 3 Thin Films for Smart Windows

Semiconductors with electrically tunable band gaps are of great interest in controlling transparency to electromagnetic radiation. Thin films of perovskite nickelate NdNiO 3 (NNO), a class of correlated oxides, were deposited on single-crystal (LaAlO 3 (LAO)) and polycrystalline (fluorine-doped tin oxide-coated glass (FTO)) substrates by magnetron sputtering, chemical solution deposition (CSD), and atomic layer deposition (ALD). Their electrochromic behaviors were investigated using a three-electrode setup in basic (KOH solution, pH = 12) electrolyte. During bleaching/coloration process, the proton intercalation/deintercalation and simultaneous electron compensation in the NNO lattice under electrical bias led to crossover of the material between the pristine-conducting phase (Ni 3+ ) and the strongly correlated insulating phase (Ni 2+ ), which serves as the working principle for electrochromic (tunable opacity in the visible range) behavior. Cyclic voltammetry (CV) scans demonstrate that NNO films are electrochemically stable in basic solutions for all three film deposition methods explored here. CV scans at varying rates enabled the extraction of diffusion coefficient of protons in thin film NNO, which is similar to 10 –7 cm 2 s –1 among all films studied. Large light transmittance modulation by bleaching and coloration was observed on films grown on both LAO and FTO substrates, suggesting its potential as an electrochromic material candidate for smart windows and optical shutter applications. Here, porous NNO films obtained by chemical solution deposition tend to demonstrate stronger electrochromic activity than dense films grown by sputtering or ALD.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Evidence of antiferromagnetism in ultrathin metallic (111)-oriented LaNiO 3 films

Antiferromagnets with exotic spin textures promise low-power spintronic devices with extremely high operating frequencies and resistance to external perturbations. In particular, the combination of highly tunable correlated electron physics, as in complex oxides, with metallicity and antiferromagnetism is desirable but exceedingly rare. LaNiO 3 , the lone example of a perovskite nickelate which is metallic across all temperatures, has long been a promising candidate, but the antiferromagnetic metallic state has remained elusive. Here, we demonstrate the emergence of this state in ultrathin films of (111)-oriented LaNiO 3 using a combination of polarized neutron reflectometry, low-energy muon spectroscopy and anomalous Hall effect measurements, and density functional theory calculations with a Hubbard U term. Further, we find a highly strained symmetry-breaking interfacial region which may support canting of the AFM moments leading to a vanishingly small net magnetization at the film-substrate interface, providing a convenient route toward control of the Néel order. Evidence of antiferromagnetic metallic behavior in (111)LNO films highlights the role of crystal symmetry in tuning the novel quantum states in complex oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Synthesis and Photonic Sintering of Proton Conducting Lanthanide Nickelates

Lanthanide nickelate perovskites are known proton conductors at intermediate temperatures (350-600°C). They are attractive targets for proton conducting fuel cells and electrolyzers due to their operational temperature range and their stability in the presence of CO 2 . These materials have the formula LNiO 3 , with the lanthanide L = La, Ce, Pr, Nd, or Sm. Sintering is challenging due to phase transformations that occur at lower temperatures than those required for sintering. In this project, a series of lanthanide nickelate perovskites was synthesized via both a precursor solid solution method and the glycine nitrate process. Powders derived from the precursor solid solution method for LaNiO 3 and NdNiO 3 were sintered at Utility Global Inc. at various temperatures utilizing fast photonic sintering. LaNiO 3 was successfully sintered while maintaining the perovskite phase. NdNiO 3 underwent a phase transformation at all the conditions tested. The stability of the perovskite phase decreases moving right across the lanthanides in the periodic table, while the expected proton conductivity increases. These results will inform further investigations into lanthanide nickelate perovskites toward the goal of producing a free-standing, sintered, proton-conducting membrane.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effects of stoichiometry and epitaxial strain on the stabilization of infinite-layer nickelates

The discovery of superconductivity in infinite-layer nickelates has sparked great interest due to their potential analogy with the unconventional cuprate superconductors. However, investigations of this system have been limited by the challenges in materials control and synthesis driven by substantial thermodynamic instability, making it difficult to reach an experimental consensus. Hence, establishing a robust synthetic route to highly crystalline infinite-layer nickelates is of paramount importance. Here, we present and discuss recent progress on the reproducible two-step synthesis of (Nd,Sr)NiO2 via the stabilization of high-quality perovskite nickelates and the subsequent topotactic transition to the infinite-layer phase. In particular, we discuss the important factors, such as cation stoichiometry and epitaxial strain, which significantly impact the crystallinity of both phases, accompanied by careful structural characterization. These results on robust synthesis can help accelerate the experimental investigation of the intrinsic physical properties of these complex strongly correlated materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High pO2 Flux Growth and Characterization of NdNiO3 Crystals

Single crystals of the perovskite nickelate NdNiO3 with dimensions of up to 50 μm on edge have been successfully grown using the flux method at a temperature of 400 °C and oxygen pressure of 200 bar. The crystals were investigated by a combination of techniques, including high-resolution synchrotron X-ray single-crystal and powder diffraction and physical property measurements such as magnetic susceptibility and resistivity. Resistivity measurements revealed a metal-insulator transition (MIT) at TMIT~180 K with apparent thermal hysteresis; however, no superlattice peaks or peak splitting below TMIT, which corresponds to a structural transition from Pbnm to P21/n, was observed. The successful growth of NdNiO3 crystals at relatively low temperatures and oxygen pressure provides an alternative approach for preparing single crystals of interesting perovskites such as RNiO3 (R = Sm-Lu) and parent phases of superconducting square planar nickelates.

Wang, Xiaoli↗
DOE OSTI2026

Protonic nickelate device networks for spatiotemporal neuromorphic computing

Computation in biological neural circuits arises from the interplay of nonlinear temporal responses and spatially distributed dynamic network interactions. Replicating this richness in hardware has remained challenging, as most neuromorphic devices emulate only isolated neuron- or synapse-like functions. Here we introduce an integrated neuromorphic computing platform in which both nonlinear spatiotemporal processing and programmable memory are realized within a single perovskite nickelate material system. By engineering symmetric and asymmetric hydrogenated NdNiO 3 junction devices on the same wafer, we combine ultrafast, proton-mediated transient dynamics with stable multilevel resistance states. Networks of symmetric NdNiO 3 junctions exhibit emergent spatial interactions mediated by proton redistribution, while each node simultaneously provides short-term temporal memory, enabling nanosecond-scale operation with an energy cost of ~0.2 nJ per input. When interfaced with asymmetric output units serving as reconfigurable long-term weights, these networks allow both feature transformation and linear classification in the same material system. Leveraging these emergent interactions, the platform enables real-time pattern recognition and achieves high accuracy in spoken digit classification and early seizure detection, outperforming temporal-only or uncoupled architectures. These results position protonic nickelates as a compact, energy-efficient, CMOS-compatible platform that integrates processing and memory for scalable intelligent hardware.

Electrical and electronic engineering↗
DOE OSTI2020

Observation of an antiferromagnetic quantum critical point in high-purity LaNiO 3

Amongst the rare-earth perovskite nickelates, LaNiO 3 (LNO) is an exception. While the former have insulating and antiferromagnetic ground states, LNO remains metallic and non-magnetic down to the lowest temperatures. It is believed that LNO is a strange metal, on the verge of an antiferromagnetic instability. Our work suggests that LNO is a quantum critical metal, close to an antiferromagnetic quantum critical point (QCP). The QCP behavior in LNO is manifested in epitaxial thin films with unprecedented high purities. We find that the temperature and magnetic field dependences of the resistivity of LNO at low temperatures are consistent with scatterings of charge carriers from weak disorder and quantum fluctuations of an antiferromagnetic nature. Furthermore, we find that the introduction of a small concentration of magnetic impurities qualitatively changes the magnetotransport properties of LNO, resembling that found in some heavy-fermion Kondo lattice systems in the vicinity of an antiferromagnetic QCP.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Perovskite neural trees

Trees are used by animals, humans and machines to classify information and make decisions. Natural tree structures displayed by synapses of the brain involves potentiation and depression capable of branching and is essential for survival and learning. Demonstration of such features in synthetic matter is challenging due to the need to host a complex energy landscape capable of learning, memory and electrical interrogation. We report experimental realization of tree-like conductance states at room temperature in strongly correlated perovskite nickelates by modulating proton distribution under high speed electric pulses. This demonstration represents physical realization of ultrametric trees, a concept from number theory applied to the study of spin glasses in physics that inspired early neural network theory dating almost forty years ago. We apply the tree-like memory features in spiking neural networks to demonstrate high fidelity object recognition, and in future can open new directions for neuromorphic computing and artificial intelligence.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Quantifying the role of the lattice in metal–insulator phase transitions

Many materials exhibit phase transitions at which both the electronic properties and the crystal structure change. Some authors have argued that the change in electronic order is primary, with the lattice distortion a relatively minor side-effect, and others have argued that the lattice distortions play an essential role in the energetics of the transition. In this paper, we introduce a formalism that resolves this long-standing problem. The methodology works with any electronic structure method that produces solutions of the equation of state determining the electronic order parameter as a function of lattice distortion. We use the formalism to settle the question of the physics of the metal–insulator transitions in the rare-earth perovskite nickelates (RNiO 3 ) and Ruddlesden–Popper calcium ruthenates (Ca 2 RuO 4 ) in bulk, heterostructure, and epitaxially strained thin film forms, finding that electron-lattice coupling is key to stabilizing the insulating state in both classes of materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Photonic Curing of Nickel Oxide Transport Layer and Perovskite Active Layer for Flexible Perovskite Solar Cells: A Path Towards High-Throughput Manufacturing

High-throughput roll-to-roll (R2R) manufacturing of perovskite solar cells (PSCs) is currently limited by thermal processes that take tens of minutes each, translating to impractically long annealing tools at high web speeds. In addition, PSCs are usually made with metal oxide transport layer materials that require high temperatures for thermal annealing. Here, we demonstrate the fabrication of PSCs using photonic curing, instead of thermal annealing, to convert NiO x directly from sol-gel precursors for hole transport layers and to crystallize methylammonium lead iodide (MAPbI 3 ) active layers on flexible Willow ® Glass substrates. Photonic curing uses short, intense pulses of light to process materials at a high speed, hence it is compatible with R2R manufacturing. We achieved power conversion efficiencies (PCEs) of 11.7% in forward-scan and 10.9% in reverse-scan for PSCs made with photonic cured NiO x and MAPbI 3 films. Furthermore, both NiO x and MAPbI 3 films could be processed with a single photonic curing pulse, with a web speed of 5.7 m/min, and still produce PCEs comparable to thermally annealed control samples. Based on the single-pulse photonic curing condition for each film, we project a web speed of 26 m/min, laying a pathway to high-throughput production of perovskite solar modules.

14 SOLAR ENERGY↗
DOE OSTI2021

Probing adsorbates on La1-xSrxNiO3-d surfaces under humid conditions: implications for the oxygen evolution reaction

Earth-abundant nickel-containing perovskite oxides (ANiO3) are highly active materials for the oxygen evolution reaction (OER). The strong nickel-oxygen (Ni-O) covalency, tunable by A-site chemical substitution, contributes to both bulk and surface material properties like the formation of oxygen vacancies (????••) and OER activity. Here we quantify the coverage of OER relevant adsorbates on a series of La1-xSrxNiO3-d (LSNO, 0 = x = 0.5) epitaxial thin films exposed to humid environments by ambient pressure X-ray photoelectron spectroscopy (AP-XPS). While all LSNO film compositions investigated here have comparable hydroxide coverages at the relative humidities (RHs) probed (1.5 x 10-5 – 0.2 %RH), the amount of under-coordinated surface oxygen increases notably with Sr content. We interpret differences in the free energy of adsorption (?Gads,i) of these OER intermediates, inferred from adsorption isotherms, in the context of proposed ????••-mediated OER mechanisms, consistent with the pH-dependent OER activity observed here for LSNO. We find that Sr incorporation enhances the affinity of LSNO surfaces for these under-coordinated oxygen species, in line with calculations in the literature.

Rare-earth nickelates, ambient pressure-X-ray phot↗
DOE OSTI2026

Electrochemical quantification of phosphonic acid passivated surface sites of NiO x for perovskite solar cells

Nickel oxide (NiO x ) is among the few p-type metal oxide semiconductors considered a strong candidate for hole transport layers in halide perovskite solar cells (PSCs). However, its reactivity with perovskite ions poses significant challenges to achieving high efficiency and long-term stability. Here, we investigate passivation of detrimental reactive surface sites on NiO x by carbazole phosphonic acids. We leverage electrochemical cyclic voltammetry (CV) of NiO x electrodes as a proxy measure for the redox activity that afflicts PSCs. From the CVs, we derive a metric, N (units cm −2 ), that relates to the number of redox active sites on NiO x surfaces. We observe a statistically significant negative correlation between PSC efficiency and N-value that indicates PSCs are more efficient on NiO x with lower electrochemical reactivity. The new mechanistic insight into NiO x passivation demonstrates it requires a reducing agent and Brønsted acid combination, providing a broadly applicable approach for evaluating and enhancing the stability and performance of NiO x -based interfaces in photovoltaics.

14 SOLAR ENERGY↗
DOE OSTI2020

Dynamic Lattice Oxygen Participation on Perovskite LaNiO 3 during Oxygen Evolution Reaction

Determining the role of lattice oxygen in the oxygen evolution reaction (OER) is pivotal to understanding reaction mechanisms and predictive design of electrocatalysts based on transition metal oxides. In this work, using well-defined, isotope ( 18 O)-enriched, epitaxial LaNiO 3 thin films as a model system, we show that dynamic lattice oxygen exchange occurs during OER. Additionally, time-of-flight secondary ion mass spectrometry studies reveal that lattice oxygen exchange can affect the top 2 nm of the LaNiO 3 films, but the surface remains crystalline and in the perovskite phase after OER. In addition, cyclic voltammetry and potentiostatic measurements show that OER kinetics are strongly pH dependent, which is different from what is expected from the typical four concerted proton-electron transfer steps, most likely due to the involvement of lattice oxygen. Our findings suggest that the roles of lattice oxygen during OER, and charge transfer mechanisms in such systems, need to be further studied in order to design more efficient and stable electrocatalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Perspective—Emergent Phases in Rare Earth Nickelate Heterostructure

The prediction of high T c superconductivity in layers of LaNiO 3 through orbital engineering has led to extensive research efforts over the last fifteen years. During this period, a plethora of thin films and heterostructures based rare-earth nickelate family with perovskite structure has been synthesized and explored. Here, in this short perspective, we briefly review the complexity of bulk RENiO 3 , spotlighting several recent findings of emergent phenomena in heterostructures containing the interface between RENiO 3 and another transition metal oxide. Finally, we outline potentially interesting future directions linked to time-domain dynamics to harness new Mott and topological phases in artificial structures of RENiO 3 .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗