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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
NASA NTRS1972

Phase transformations and exsolution in lunar and terrestrial calcic plagioclases.

A coarse domain structure had been discovered in plagioclase in an electron microscopic study of lunar rocks reported by Christie et al. (1971). The domain structures are described in more detail, and their significance in the light of current knowledge concerning the crystal structures of the plagioclases is discussed. An exsolution texture is also described. On the basis of the scale of exsolution it appears that the Apollo 11 and 12 basalts examined cooled more rapidly than the Apollo 14 basalt, which in turn cooled more rapidly than the Stillwater rock.

Heuer, A. H.↗
DOE OSTI2019

Electric-field-induced structure and domain texture evolution in PbZrO 3 -based antiferroelectric by in-situ high-energy synchrotron X-ray diffraction

Antiferroelectrics (AFEs) have a great potential for modern electronic devices by virtue of the large strain during the antiferroelectric-to-ferroelectric (AFE-FE) phase transition under external electric fields. Although the fascinating macroscopic properties of AFE materials have been extensively studied, it is still unclear how the underlying structure evolution engenders their defining properties. Here we employ an electric biasing in-situ high-energy synchrotron X-ray diffraction technique to reveal the phase, domain texture, and lattice evolution in a high performance PbZrO 3 -based AFE material. During the reversible AFE-FE transition triggered by electric fields, the evolution of the superstructure for AFE pseudo-tetragonal and FE rhombohedral phase is found to display strong dependence on the angle with respect to the field direction. In contrast to previous prediction, it is found that there is no obvious domain reorientation in the AFE phase, when the system is far away from the AFE-FE transitions. The electric-field-induced FE rhombohedral phase exhibits an unusual microscopic behavior, distinguished from the normal one, presenting small changes in domain texture and lattice strain with electric field, and leading to a small piezoelectric response. The longitudinal, transverse, and volume strains estimated from the XRD peak profiles are well consistent with the macroscopic strain measurements. It is demonstrated that the large strain arises from the structural change associated with anisotropic lattice strain and highly preferential domain reorientation during the AFE-FE transitions. Finally, the AFE-FE switching sequence is constructed based on the present study, which provides a further understating of AFE materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Disentangling ferroelectric domain wall geometries and pathways in dynamic piezoresponse force microscopy via unsupervised machine learning

In this work, domain switching pathways in ferroelectric materials visualized by dynamic piezoresponse force microscopy (PFM) are explored via variational autoencoder, which simplifies the elements of the observed domain structure, crucially allowing for rotational invariance, thereby reducing the variability of local polarization distributions to a small number of latent variables. For small sampling window sizes the latent space is degenerate, and variability is observed only in the direction of a single latent variable that can be identified with the presence of domain wall. For larger window sizes, the latent space is 2D, and the disentangled latent variables can be generally interpreted as the degree of switching and complexity of domain structure. Applied to multiple consecutive PFM images acquired while monitoring domain switching, the polarization switching mechanism can thus be visualized in the latent space, providing insight into domain evolution mechanisms and their correlation with the microstructure.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Resolution of Electronic and Structural Factors Underlying Oxygen-Evolving Performance in Amorphous Cobalt Oxide Catalysts

Non-noble-metal, thin-film oxides are widely investigated as promising materials for catalyzing oxygen evolution reactions (OER). Cobalt oxide thin-films that are electrochemically formed in the presence of borate (CoBi) and phosphate (CoPi) serve as important reference catalysts for assessing correlations between oxyhydroxide domain structures with corresponding electronic properties and OER performance. Here, we present a comparison of CoPi and CoBi thin-film catalysts by a combination of advanced X-ray electronic and vibrational spectroscopies of L-edge synchrotron X-ray absorption (XAS), resonant X-ray emission (RXES), resonant inelastic X-ray scattering (RIXS), resonant Raman (RR) scattering, and high-energy X-ray pair distribution function (PDF) analysis. A detailed spectral analysis is presented and identifies relationships between the OER performance and electronic and molecular-type domain structures. XAS shows that CoBi is composed essentially exclusively of cobalt in octahedral coordination, while CoPi contains approximately 17% tetrahedral Co(II), with the remainder in octahedral coordination. Oxygen-mediated 4 p -3 d hybridization through Co-O-Co bonding was detected by RXES and the inter-site dd excitation was observed by RIXS in CoBi, but not in CoPi. RR shows that CoBi resembles a disordered layered LiCoO 2 -like structure while Co- Pi is amorphous. Distinct domain models in the nanometer range for CoBi and CoPi have been proposed on the basis of the PDF analysis coupled to XAS data. In conclusion, the observed differences provide important implications for the enhancement factors in OEC performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Direct and real time probe of photoinduced structure transition in colossal magnetoresistive material

Here, we report a direct and real time measurement of photoinduced structure phase transition in single crystal La 0.84 Sr 0.16 MnO 3 using femtosecond electron diffraction. The melting of orthorhombic lattice ordering under femtosecond optical excitation is found involving two distinct processes with different time scales, an initial fast melting of orthorhombic phase in about 4 ps and a subsequent slower transformation in 90 ps and longer timescales. Furthermore, the fast process is designated as the initial melting of orthorhombic phase induced by the Mn-O bond change that is most likely driven by the quenching of the dynamic Jahn-Teller distortion following the photo-excitation. We attribute the slow process to the growing of newly formed structure domain from the photo-excited sites to the neighboring non-excited orthorhombic sites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Controlling antiferromagnetic domains in patterned La0.7Sr0.3FeO3 thin films

Transition metal oxide thin films and heterostructures are promising platforms to achieve full control of the antiferromagnetic (AFM) domain structure in patterned features as needed for AFM spintronic devices. In this work, soft x-ray photoemission electron microscopy was utilized to image AFM domains in micromagnets patterned into La0.7Sr0.3FeO3 (LSFO) thin films and La0.7Sr0.3MnO3 (LSMO)/LSFO superlattices. A delicate balance exists between magnetocrystalline anisotropy, shape anisotropy, and exchange interactions such that the AFM domain structure can be controlled using parameters such as LSFO and LSMO layer thickness, micromagnet shape, and temperature. In LSFO thin films, shape anisotropy gains importance only in micromagnets where at least one extended edge is aligned parallel to an AFM easy axis. In contrast, in the limit of ultrathin LSFO layers in the LSMO/LSFO superlattice, shape anisotropy effects dominate such that the AFM spin axes at micromagnet edges can be aligned along any in-plane crystallographic direction.

Lee, Michael S. (ORCID:0000000177852189)↗
NASA NTRS1985

Geometry of miocene extensional deformation, lower Colorado River Region, Southeastern California and Southwestern Arizona: Evidence for the presence of a regional low-angle normal fault

The geometry of Miocene extensional deformation, which changes along a 120 km-long, northeast-trending transect from the southestern Chocolate Mountains, southeastern California, to the Trigo and southern Dome Rock Mountains, southwestern Arizona is discussed. Based upon regional differences in the structural response to extension and estimated extensional strain, the transet can be divided into three northwesterly-trending structural domains. From southwest to northeast, these domains are: (1) southestern Chocolate-southernmost Trigo Mountains; (2) central to northern Trigo Mountains; and (3) Trigo Peaks-southern Dome Rock Mountains. All structures formed during the deformation are brittle in style; fault rocks are composed of gouge, cohesive gouge, and local microbreccia. In each structural domain, exposed lithologic units are composed of Mesozoic crystalline rocks unconformably overlain by Oligocene to Early Miocene volcanic and minor interbedded sedimentary rocks. Breccia, conglomerate, and sandstone deposited synchronously with regional extension locally overlie the volcanic rocks. Extensional deformation largely postdated the main phase of volcanic activity, but rare rhyolitic tuff and flows interbedded with the syndeformational clastic rocks suggest that deformation began during the waning stages of valcanism. K-Ar isotopic ages indicate that deformation occurred in Miocene time, between about 22 and m.y. ago.

Tosdal, R. M.↗
DOE OSTI2018

Visualization and manipulation of magnetic domains in the quasi-two-dimensional material F e 3 GeT e 2

The magnetic domains in two-dimensional layered material Fe 3 GeTe 2 are studied by using a variable-temperature scanning tunneling microscope with a magnetic tip after in situ cleaving of single crystals. A stripy domain structure is revealed in a zero-field-cooled sample below the ferromagnetic transition temperature of 205 K, which is replaced by separate double-walled domains and bubble domains when cooling the sample under a magnetic field of a ferromagnetic Ni tip. The Ni tip can further convert the double-walled domain to a bubble domain pattern as well as move the Neel-type chiral bubble in submicrometer distance. The temperature-dependent evolutions of both zero-field-cooled and field-cooled domain structures correlate well with the bulk magnetization from magnetometry measurements. Furthermore, atomic resolution scanning tunneling images and spectroscopy are acquired to understand the atomic and electronic structures of the material, which are further corroborated by first-principles calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Magnetic properties of two-dimensional nanodots: Ground state and phase transition

We study the effect of perpendicular single-ion anisotropy, −As{sub z}{sup 2}, on the ground-state structure and finite-temperature properties of a two-dimensional magnetic nanodot in presence of a dipolar interaction of strength D. By a simulated annealing Monte Carlo method, we show that in the ground state a vortex core perpendicular to the nanodot plane emerges already in the range of moderate anisotropy values above a certain threshold level. In the giant-anisotropy regime the vortex structure is superseded by a stripe domain structure with stripes of alternate domains perpendicular to the surface of the sample. We have also observed an intermediate stage between the vortex and stripe structures, with satellite regions of tilted nonzero perpendicular magnetization around the core. At finite temperatures, at small A, we show by Monte Carlo simulations that there is a transition from the the in-plane vortex phase to the disordered phase characterized by a peak in the specific heat and the vanishing vortex order parameter. At stronger A, we observe a discontinuous transition with a large latent heat from the in-plane vortex phase to perpendicular stripe ordering phase before a total disordering at higher temperatures. In the regime of perpendicular stripe domains, namely with giant A, there is no phase transition at finite T: the stripe domains are progressively disordered with increasing T. Finite-size effects are shown and discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dynamic Manipulation in Piezoresponse Force Microscopy: Creating Nonequilibrium Phases with Large Electromechanical Response

We discuss how domain walls and topological defects in ferroelectric materials have emerged as a powerful tool for functional electronic devices including memory and logic. Similarly, wall interactions and dynamics underpin a broad range of mesoscale phenomena ranging from giant electromechanical responses to memory effects. Exploring the functionalities of individual domain walls, their interactions, and controlled modifications of the domain structures is crucial for applications and fundamental physical studies. However, the dynamic nature of these features severely limits studies of their local physics since application of local biases or pressures in piezoresponse force microscopy induce wall displacement as a primary response. Here, we introduce an approach for the control and modification of domain structures based on automated experimentation, whereby real-space image-based feedback is used to control the tip bias during ferroelectric switching, allowing for modification routes conditioned on domain states under the tip. This automated experiment approach is demonstrated for the exploration of domain wall dynamics and creation of metastable phases with large electromechanical response.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Roles of Intramolecular and Intermolecular Interactions in Functional Regulation of the Hsp70 J-protein Co-Chaperone Sis1

Unlike other Hsp70 molecular chaperones, those of the eukaryotic cytosol have four residues, EEVD, at heir C-termini. EEVD(Hsp70) binds adaptor proteins of the Hsp90 chaperone system and mitochondrial membrane preprotein receptors, thereby facilitating processing of Hsp70-bound clients through protein folding and translocation pathways. Among J-protein co-chaperones functioning in these pathways, Sis1 is unique, as it also binds the EEVD(Hsp70) motif. However, little is known about the role of the Sis1:EEVD(Hsp70) interaction. We found that deletion of EEVD(Hsp70) abolished the ability of Sis1, but not the ubiquitous J-protein Ydj1, to partner with Hsp70 in in vitro protein refolding. Sis1 co-chaperone activity with Hsp70ΔEEVD was restored upon substitution of a glutamic acid of the J-domain. Structural analysis revealed that this key glutamic acid, which is not present in Ydj1, forms a salt bridge with an arginine of the immediately adjacent glycine-rich region. Thus, restoration of Sis1 in vitro activity suggests that intramolecular interactions between the J-domain and glycine-rich region control co-chaperone activity, which is optimal only when Sis1 interacts with the EEVD(Hsp70) motif. However, we found that disruption of the Sis1:EEVD(Hsp70) interaction enhances the ability of Sis1 to substitute for Ydj1 in vivo. Our results are consistent with the idea that interaction of Sis1 with EEVD(Hsp70) minimizes transfer of Sis1-bound clients to Hsp70s that are primed for client transfer to folding and translocation pathways by their preassociation with EEVD binding adaptor proteins. These interactions may be one means by which cells triage Ydj1- and Sis1-bound clients to productive and quality control pathways, respectively.

Yu, Hyun Young↗
DOE OSTI2014

Magnetic structure and domain conversion of the quasi-2D frustrated antiferromagnet CuCrO{sub 2} probed by NMR

We have carried out {sup 63,65}Cu NMR spectra measurements in a magnetic field up to about 15.5 T on a single crystal of the multiferroic triangular-lattice antiferromagnet CuCrO{sub 2}. The measurements were performed for perpendicular and parallel orientations of the magnetic field with respect to the c axis of the crystal, and the detailed angle dependence of the spectra on the magnetic field direction in the ab plane was studied. The shape of the spectra can be well described in the model of spiral spin structure proposed by recent neutron diffraction experiments. When the field is rotated perpendicular to the crystal c axis, we observed, directly for the first time, a remarkable reorientation of the spin plane simultaneous with rotation of the incommensurate wavevector, by quantitatively deducing the conversion of the energetically less favorable domain to a more favorable one. At high enough fields parallel to the c axis, the data are consistent with either a field-induced commensurate spiral magnetic structure or an incommensurate spiral magnetic structure with a disorder in the c direction, suggesting that high fields may have influence on interplanar ordering.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Revealing ferroelectric switching character using deep recurrent neural networks

The ability to manipulate domains underpins function in applications of ferroelectrics. While there have been demonstrations of controlled nanoscale manipulation of domain structures to drive emergent properties, such approaches lack an internal feedback loop required for automatic manipulation. Here, using a deep sequence-to-sequence autoencoder we automate the extraction of latent features of nanoscale ferroelectric switching from piezoresponse force spectroscopy of tensile-strained PbZr 0.2 Ti 0.8 O 3 with a hierarchical domain structure. We identify characteristic behavior in the piezoresponse and cantilever resonance hysteresis loops, which allows for the classification and quantification of nanoscale-switching mechanisms. Specifically, we identify elastic hardening events which are associated with the nucleation and growth of charged domain walls. This work demonstrates the efficacy of unsupervised neural networks in learning features of a material's physical response from nanoscale multichannel hyperspectral imagery and provides new capabilities in leveraging in operando spectroscopies that could enable the automated manipulation of nanoscale structures in materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Polarization-dependent photoemission electron microscopy for domain imaging of inorganic and molecular materials

Polarization-dependent photoemission electron microscopy (PD-PEEM) exploits spatial variation in the optical selection rules of materials to image domain formation and material organization on the nanoscale. In this Perspective, we discuss the mechanism of PD-PEEM that results in the observed image contrast in experiments and provide examples of a wide range of material domain structures that PD-PEEM has been able to elucidate, including molecular and polymer domains, local electronic structure and defect symmetry, (anti)ferroelectricity, and ferromagnetism. As a result, we discuss challenges and new directions that are possible with this tool for probing domain structure in materials, including investigating the formation of transient ordered states, multiferroics, and the influence of molecular and polymer order and disorder on excited state dynamics and charge transport.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Surface acoustic wave generation and detection in the quantum paraelectric regime of SrTiO 3 -based heterostructures

Strontium titanate (STO), apart from being a ubiquitous substrate for complex-oxide heterostructures, possesses a multitude of strongly coupled electronic and mechanical properties. Surface acoustic wave (SAW) generation and detection offers insight into electromechanical couplings that are sensitive to quantum paraelectricity and other structural phase transitions. Propagating SAWs can interact with STO-based electronic nanostructures, in particular LaAlO 3 /SrTiO 3 (LAO/STO). Here, we report the generation and detection of SAW within LAO/STO heterointerfaces at cryogenic temperatures ( T ≥ 2 K) using superconducting interdigitated transducers. Further, the temperature dependence shows an increase in the SAW quality factor that saturates at T ≈ 8 K. The effect of backgate tuning on the SAW resonance frequency shows the possible acoustic coupling with the ferroelastic domain wall evolution. This method of generating SAWs provides a pathway towards the dynamic tuning of ferroelastic domain structures, which are expected to influence the electronic properties of complex-oxide nanostructures. Devices that incorporate SAWs may in turn help to elucidate the role of ferroelastic domain structures in mediating electronic behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Structure and switching of in-plane ferroelectric nano-domains in strained PbxSr1-xTiO3 thin films

Nanoscale ferroelectrics, the active elements of a variety of nanoelectronic devices, develop denser and richer domain structures than the bulk counterparts. With shrinking device sizes understanding and controlling domain formation in nanoferroelectrics is being intensely studied. Here we show that a precise control of the epitaxy and the strain allows stabilizing a hierarchical domain architecture in PbxSr1-xTiO3 thin films, showing periodic, purely in-plane polarized, ferroelectric nano-domains that can be switched by a scanning probe.

epitaxial thin films↗
DOE OSTI2016

Canted stripe phase evolution due to a spin reorientation transition in Fe films grown on Ag(001) vicinal surface

The evolution of the domain structure with the thickness of bcc Fe films deposited on the Ag(116) vicinal surface is studied by spin-polarized low-energy electron microscopy. We show that a spin reorientation transition proceeds via two mechanisms: continuous rotation of magnetization within the vertical plane perpendicular to the steps and discontinuous reorientation of the in-plane component of magnetization, leading to splitting of the domains. In contrast to previously investigated systems with stripe domains, we reveal that in the case of a vicinal ferromagnetic surface, the domain width increases while changing the orientation of the magnetization from a canted out-of-plane state into an in-plane state. Finally, a theoretical model developed in this work successfully describes the domain structure behavior observed in our experiments and can be equally applied to other ferromagnetic films grown on vicinal surfaces.

domain walls↗
DOE OSTI2019

Atomic and electronic structure of domains walls in a polar metal

Polar metals counterintuitively bring two well-known phenomena into coexistence, namely, bulk polar displacements, and an electronic Fermi surface giving rise to metallic conduction. Furthermore, little is known about the polar domains or domain walls in such materials. Using atomic resolution electron microscopy imaging combined with first principles density functional theory, we show that uncharged head-to-tail walls, and “charged” head-to-head and tail-to-tail walls can exist in the bulk of such crystals of polar metals Ca 3 Ru 2 O 7 , where both structural changes at the wall as well as electrostatic considerations define the wall nature. Significant built-in potentials of 30–170 meV are predicted at such walls.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗