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Results for “Complex oxides”

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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Giant anisotropic magnetoresistance in oxygen-vacancy-ordered epitaxial La 0.5 Sr 0.5 CoO 3–δ films

Recent advances in complex oxide heterostructures have realized extraordinary control over oxygen vacancies ($V_\text{O}$), including strain-tuned $V_\text{O}$ order, and electric-field-controlled transformations between perovskite and $V_\text{O}$-ordered structures. Perovskite cobaltites such as La 1– x Sr x CoO 3–δ provide a prime example, recent work demonstrating that strain engineering of $V_\text{O}$ ordering induces large (~10 7 erg/cm 3 ) perpendicular magnetic anisotropy. Here we show that $V_\text{O}$-ordered epitaxial La 0.5 Sr 0.5 CoO 3–δ films exhibit not only strong magnetic anisotropy, but also a giant form of anisotropic magnetoresistance (AMR). This has magnetic field, temperature, and angular dependencies in quantitative accord with conventional AMR, but with AMR ratios up to an extraordinary 40.3%, 20 times enhanced over bulk cobaltites, and ~10–100 times larger than typical transition metals. This giant AMR has no strong dependence on heteroepitaxial strain (between –2.1% and +1.8%) or thickness, and is instead ascribed to symmetry lowering associated with $V_\text{O}$ ordering. The AMR ratios thus obtained in this work are among the largest reported in the over 160-year history of this phenomenon, despite the absence of heavy elements.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Discerning element and site-specific fluctuations of the charge-orbital order in Fe 3 O 4 below the Verwey transition

Despite countless experimental probes into magnetite's electronic structure across the Verwey transition Fe 3 O 4 , the exact origin of this archetypical metal-insulator transition remains a puzzle. Advanced x-ray diffraction techniques have mostly resolved the monoclinic structure of the insulating phase, including interatomic bond lengths, but the complexity of the charge-orbitally ordered state is difficult to disentangle. Here we combined resonant elastic x-ray scattering and x-ray photon correlation spectroscopy to probe charge-orbital fluctuations in the insulating state of magnetite. By accessing the Bragg forbidden $(00\frac{1}{2})_{c}$ peak at the oxygen K-edge, we complement our previous study on the iron L 3 – edge to reveal the dynamics of the iron 3d and oxygen 2p orbital domains. Our new results reveal a decoupling of the orbital correlation lengths between the oxygen 2p states and site-specific iron 3d states, and we further show charge-orbital domain fluctuations at the iron t 2g orbital sites of trimeron chains. These results also demonstrate an experimental method capable of distinguishing electronic dynamics between the oxygen ligands and the transition metal that underpins emergent behaviors in complex oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Probing the electronic properties of gap states near the surface of n -SrTiO 3-δ / i -Si (001) heterojunctions with high sensitivity

We have measured soft x-ray resonant photoemission for the n–SrTiO 3–δ /i–Si⁡(001) (δ=~0.0003) hybrid semiconductor heterojunction with the goal of probing occupied electronic states in the band gap near the surface. By utilizing both swept energy, angle-integrated and fixed-energy, and angle-resolved spectroscopies, we identify the atomic and orbital character of the in-gap state as well as the different electronic phases that contribute to it. Specifically, we isolate the state associated with trapped charge on the n–SrTiO 3–δ surface that causes surface depletion from the localized gap state resulting from electron correlation effects in the complex oxide. Using an x-ray energy close to select dipole allowed TiL 3 → 3⁢d x-ray absorption resonances results in a 40-fold increase in sensitivity. Furthermore, this feature makes photoemission possible when probing electrons from dopants at concentrations as low as a few hundredths of a percent.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Colloquium : Topological band theory

The first-principles band theory paradigm has been a key player not only in the process of discovering new classes of topologically interesting materials, but also for identifying salient characteristics of topological states, enabling direct and sharpened confrontation between theory and experiment. We begin this review by discussing underpinnings of the topological band theory, which basically involves a layer of analysis and interpretation for assessing topological properties of band structures beyond the standard band theory construct. Methods for evaluating topological invariants are delineated, including crystals without inversion symmetry and interacting systems. The extent to which theoretically predicted properties and protections of topological states have been verified experimentally is discussed, including work on topological crystalline insulators, disorder/interaction driven topological insulators (TIs), topological superconductors, Weyl semimetal phases, and topological phase transitions. Successful strategies for new materials discovery process are outlined. A comprehensive survey of currently predicted 2D and 3D topological materials is provided. This includes binary, ternary and quaternary compounds, transition metal and f-electron materials, Weyl and 3D Dirac semimetals, complex oxides, organometallics, skutterudites and antiperovskites. Also included is the emerging area of 2D atomically thin films beyond graphene of various elements and their alloys, functional thin films, multilayer systems, and ultra-thin films of 3D TIs, all of which hold exciting promise of wide-ranging applications. We conclude by giving a perspective on research directions where further work will broadly benefit the topological materials field

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Genomes of ubiquitous marine and hypersaline Hydrogenovibrio , Thiomicrorhabdus and Thiomicrospira spp. encode a diversity of mechanisms to sustain chemolithoautotrophy in heterogeneous environments: Hydrogenovibrio, Thiomicrorhabdus, Thiomicrospira

Chemolithoautotrophic bacteria from the genera Hydrogenovibrio, Thiomicrorhabdus and Thiomicrospira are common, sometimes dominant, isolates from sulfidic habitats including hydrothermal vents, soda and salt lakes and marine sediments. Their genome sequences confirm their membership in a deeply branching clade of the Gammaproteobacteria. Several adaptations to heterogeneous habitats are apparent. Their genomes include large numbers of genes for sensing and responding to their environment (EAL- and GGDEF-domain proteins and methyl-accepting chemotaxis proteins) despite their small sizes (2.1–3.1 Mbp). An array of sulfur-oxidizing complexes are encoded, likely to facilitate these organisms' use of multiple forms of reduced sulfur as electron donors. Hydrogenase genes are present in some taxa, including group 1d and 2b hydrogenases in Hydrogenovibrio marinus and H. thermophilus MA2-6, acquired via horizontal gene transfer. In addition to high-affinity cbb 3 cytochrome c oxidase, some also encode cytochrome bd-type quinol oxidase or ba 3 -type cytochrome c oxidase, which could facilitate growth under different oxygen tensions, or maintain redox balance. Carboxysome operons are present in most, with genes downstream encoding transporters from four evolutionarily distinct families, which may act with the carboxysomes to form CO 2 concentrating mechanisms. Finally, these adaptations to habitat variability likely contribute to the cosmopolitan distribution of these organisms.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

‘Birth defects’ of photosystem II make it highly susceptible to photodamage during chloroplast biogenesis

High solar flux is known to diminish photosynthetic growth rates, reducing biomass productivity and lowering disease tolerance. Photosystem II (PSII) of plants is susceptible to photodamage (also known as photoinactivation) in strong light, resulting in severe loss of water oxidation capacity and destruction of the water-oxidizing complex (WOC). The repair of damaged PSIIs comes at a high energy cost and requires de novo biosynthesis of damaged PSII subunits, reassembly of the WOC inorganic cofactors and membrane remodeling. Employing membrane-inlet mass spectrometry and O 2 -polarography under flashing light conditions, we demonstrate that newly synthesized PSII complexes are far more susceptible to photodamage than are mature PSII complexes. We examined these ‘PSII birth defects’ in barley seedlings and plastids (etiochloroplasts and chloroplasts) isolated at various times during de-etiolation as chloroplast development begins and matures in synchronization with thylakoid membrane biogenesis and grana membrane formation. We show that the degree of PSII photodamage decreases simultaneously with biogenesis of the PSII turnover efficiency measured by O 2 -polarography, and with grana membrane stacking, as determined by electron microscopy. Our data from fluorescence, Q B -inhibitor binding, and thermoluminescence studies indicate that the decline of the high-light susceptibility of PSII to photodamage is coincident with appearance of electron transfer capability Q$_A^-$ → QB during de-etiolation. This rate depends in turn on the downstream clearing of electrons upon buildup of the complete linear electron transfer chain and the formation of stacked grana membranes capable of longer-range energy transfer.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Effects of cation stoichiometry on electronic and structural properties of LaNiO{sub 3}

LaNiO{sub 3} films with varying La:Ni ratios were deposited onto SrTiO{sub 3} (001) substrates via molecular beam epitaxy to elucidate the effects of cation off-stoichiometry. The physical properties of La-deficient films are found to differ substantially from those of Ni-deficient films, with La-deficient films exhibiting lower electrical resistivities and smaller c-axis parameters than Ni-deficient films. No evidence of secondary phases is observed; however, transmission electron microscopy reveals an abundance of defects, the nature of which differs in lanthanum- and nickel-deficient films. This work illustrates the nontrivial role that cation stoichiometry can play on the functional properties of complex oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Unusual behavior of cuprates explained by heterogeneous charge localization

The discovery of high-temperature superconductivity in cuprates ranks among the major scientific milestones of the past half century, yet pivotal questions regarding the complex phase diagram of these materials remain unanswered. Generally thought of as doped charge-transfer insulators, these complex oxides exhibit pseudogap, strange-metal, superconducting, and Fermi liquid behavior with increasing hole-dopant concentration. Motivated by recent experimental observations, here we introduce a phenomenological model wherein exactly one hole per planar copper-oxygen unit is delocalized with increasing doping and temperature. The model is percolative in nature, with parameters that are highly consistent with experiments. It comprehensively captures key unconventional experimental results, including the temperature and the doping dependence of the pseudogap phenomenon, the strange-metal linear temperature dependence of the planar resistivity, and the doping dependence of the superfluid density. The success and simplicity of the model greatly demystify the cuprate phase diagram and point to a local superconducting pairing mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Nanoscale ferroelastic twins formed in strained LaCoO 3 films

The coexistence and coupling of ferroelasticity and magnetic ordering in a single material offers a great opportunity to realize novel devices with multiple tuning knobs. Complex oxides are a particularly promising class of materials to find multiferroic interactions due to their rich phase diagrams, and are sensitive to external perturbations. Still, there are very few examples of these systems. Here, we report the observation of twin domains in ferroelastic LaCoO 3 epitaxial films and their geometric control of structural symmetry intimately linked to the material’s electronic and magnetic states. A unidirectional structural modulation is achieved by selective choice of substrates having twofold rotational symmetry. This modulation perturbs the crystal field–splitting energy, leading to unexpected in-plane anisotropy of orbital configuration and magnetization. These findings demonstrate the use of structural modulation to control multiferroic interactions and may enable a great potential for stimulation of exotic phenomena through artificial domain engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Extreme tensile strain states in La 0.7 Ca 0.3 MnO 3 membranes

A defining feature of emergent phenomena in complex oxides is the competition and cooperation between ground states. In manganites, the balance between metallic and insulating phases can be tuned by the lattice; extending the range of lattice control would enhance the ability to access other phases. We stabilized uniform extreme tensile strain in nanoscale La 0.7 Ca 0.3 MnO 3 membranes, exceeding 8% uniaxially and 5% biaxially. Uniaxial and biaxial strain suppresses the ferromagnetic metal at distinctly different strain values, inducing an insulator that can be extinguished by a magnetic field. Electronic structure calculations indicate that the insulator consists of charge-ordered Mn 4+ and Mn 3+ with staggered strain-enhanced Jahn-Teller distortions within the plane. This highly tunable strained membrane approach provides a broad opportunity to design and manipulate correlated electron states.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigation of the Current–Voltage Characteristics of New MnO{sub 2}/GaAs(100) and V{sub 2}O{sub 5}/GaAs(100) Heterostructures Subjected to Heat Treatment

Complex oxide films with a thickness of about 200 nm are formed during the thermal oxidation of GaAs with magnetron-deposited V{sub 2}O{sub 5} and MnO{sub 2} nanolayers. The electrical parameters of the films (reverse-bias breakdown voltage and current density) are determined by the method of current–voltage (I–V) characteristics at room temperature in the bias range from –5 to +5 V, and their composition and surface morphology are investigated. It is shown that V{sub 2}O{sub 5} facilitates the more intense (in comparison with MnO{sub 2}) chemical bonding of arsenic at the internal interface with the formation of As{sub 2}O{sub 5}. As a result, thermally oxidized V{sub 2}O{sub 5}/GaAs heterostructures exhibit higher breakdown voltages.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Growth and Structural, Magnetic, and Magnetooptical Properties of ZnO Films Doped with a Fe{sup 57} 3d Impurity

ZnO films obtained by high-frequency magnetron sputtering and doped with a Fe{sup 57} metallic 3d impurity by the diffusion method are studied. The type of local environment of Fe{sup 57} impurity atoms on varying the deposition parameters of ZnO films is determined by Mössbauer spectroscopy. It is established that the ground state of Fe{sup 57} impurity atoms corresponds to metallic iron in the magnetically ordered state and there is a small fraction of Fe{sup 57} atoms with a local environment corresponding to the complex oxide Fe{sub 3}O{sub 4}, having the magnetically ordered state; there is also a fraction of iron atoms in the paramagnetic state. The magnetic and magnetooptical parameters of the films were measured using magnetooptic Kerr effect. The spectral dependences of the polar magnetooptic Kerr effect in ZnO(Fe{sup 57}) films are measured in a photon energy range of 1.5–4.5 eV and simulated by the effective-medium method. It is established that ZnO(Fe{sup 57}) possess an easy-plane magnetic anisotropy with a magnetization lying in the film plane.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Dopant Sensitive Electrolytic Etching of Germanium with High Selectivity

Abstract The enhanced charge carrier mobility and photon absorption compared to silicon make germanium attractive for next-generation photo diodes. However, the complex oxidation behavior of germanium challenges dopant-dependent selective etching that is desired for the fabrication of backside imaging architectures. This report demonstrates electrolytic wet etching of p-doped germanium which proceeds up to 17,500x faster than etching of intrinsic germanium. Homoepitaxially grown layers of germanium were electrolytically etched in potassium hydroxide over a range of biases. Intermittent acquisition of cyclic voltammetry spectra during etching has suppressed the formation of electric double layers, maintained appreciable etch rates, and allowed for in operando process control. The observed etch rates scaled with dopant concentration. An effective etch rate of germanium removal of 2.100±0.044 µm/min was accomplished for a boron dopant concentration of 6E18cm-3. For nominally intrinsic germanium, however, an effective etch rate of only 0.00012±0.00011 µm/min was observed. A series of systematic electrolytic etch experiments have revealed the transfer of 4 electrons per germanium atom removed.

Wood, Joseph G.↗
DOE OSTI2016

Identifying local structural states in atomic imaging by computer vision

Abstract The availability of atomically resolved imaging modalities enables an unprecedented view into the local structural states of materials, which manifest themselves by deviations from the fundamental assumptions of periodicity and symmetry. Consequently, approaches that aim to extract these local structural states from atomic imaging data with minimal assumptions regarding the average crystallographic configuration of a material are indispensable to advances in structural and chemical investigations of materials. Here, we present an approach to identify and classify local structural states that is rooted in computer vision. This approach introduces a definition of a structural state that is composed of both local and nonlocal information extracted from atomically resolved images, and is wholly untethered from the familiar concepts of symmetry and periodicity. Instead, this approach relies on computer vision techniques such as feature detection, and concepts such as scale invariance. We present the fundamental aspects of local structural state extraction and classification by application to simulated scanning transmission electron microscopy images, and analyze the robustness of this approach in the presence of common instrumental factors such as noise, limited spatial resolution, and weak contrast. Finally, we apply this computer vision-based approach for the unsupervised detection and classification of local structural states in an experimental electron micrograph of a complex oxides interface, and a scanning tunneling micrograph of a defect-engineered multilayer graphene surface.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Multiscale dynamics in relaxor ferroelectrics

The multiscale dynamics of complex oxides is illustrated by pairs of mechanical resonances that are excited in the relaxor ferroelectric K1 xLixTaO3 (KLT). These macroscopic resonances are shown to originate in the collective dynamics of piezoelectric polar nanodomains (PND) interacting with the surrounding lattice. Their characteristic Fano lineshapes and rapid evolution with temperature reveal the coherent interplay between the piezoelectric oscillations and orientational relaxations of the PNDs at higher temperature and the contribution of heterophase oscillations near the phase transition. A theoretical model is presented, that describes the evolution of the resonances over the entire temperature range. Similar resonances are observed in other relaxors and must therefore be a common characteristics of these systems.

Toulouse, J.↗
DOE OSTI2018

Advanced Experimental Technique for Radiation Damage Effects in Nuclear Waste Forms: Neutron Total Scattering Analysis

For the past 30 years, the development of durable materials for radionuclide immobilization has been driven by efforts to dispose of wastes generated by the nuclear fuel cycle [National Research Council, ‘Waste Forms Technology and Performance: Final Report’, the National Academies Press, Washington D.C., 2011]. Many materials have been developed, but there still exist large gaps in the knowledge of fundamental modes of waste form degradation in repository environments. An important aspect of waste form science is the behavior of the materials under intense irradiation from decaying actinides and fission products. This irradiation induces a wide range of defects and disorder, the details of which depend on the specific waste form material. At the present time, it is not fully explained how radiation effects will influence the performance of nuclear waste forms and their long-term retention of fission products and actinides under operational conditions. The complex defect behavior and radiation damage must be understood over a range of length scales, from the initial atomic-scale defect structure to the long-range observable material modification. This is particularly challenging and requires advanced characterization techniques. This contribution describes how pair distribution function (PDF) analysis obtained from neutron total scattering experiments can be applied in the research field of waste form science to uniquely characterize radiation effects in a wide range of materials, including crystalline complex oxides and waste glasses. Neutron scattering strength does not have an explicit Z-dependence; this allows access to many low-Z elements, such as oxygen, that cannot be accurately studied with X-rays. In many cases, this can permit a detailed analysis of both cation (often high-Z) and anion (often low-Z) defect behavior. In contrast to traditional crystallography, which relies on long-range order, PDF analysis probes the local defect structure, including changes in site occupation, coordination, and bond distance. This is particularly important when characterizing aperiodic waste glasses with no long-range order at all. In contrast to X-ray characterization which requires very little sample mass (~0.1 mg), neutron characterization (even at state-of-the-art spallation facilities) requires relatively large sample mass (~50 - 100 mg). In conclusion, obtaining this quantity is challenging for studies of irradiated materials, but by tailoring our experimental approach to use high-energy ions (GeV) with very high penetration depth, we are able to produce the required mass.

36 MATERIALS SCIENCE↗