A5090631752- Physics of Superconductivity and Magnetism
- Magnetic and transport properties of perovskites and related materials
- Advanced Condensed Matter Physics
- Electronic and Structural Properties of Oxides
- Iron-based superconductors research
- Superconductivity in MgB2 and Alloys
- ZnO doping and properties
- Semiconductor materials and devices
- Rare-earth and actinide compounds
- Superconducting Materials and Applications
- Advancements in Solid Oxide Fuel Cells
- Magnetic properties of thin films
- HVDC Systems and Fault Protection
- Ferroelectric and Piezoelectric Materials
- Electron and X-Ray Spectroscopy Techniques
- Multiferroics and related materials
- Inorganic Chemistry and Materials
- Advanced X-ray and CT Imaging
- 2D Materials and Applications
- Silicon and Solar Cell Technologies
- Magnesium Alloys: Properties and Applications
- Copper-based nanomaterials and applications
- Nuclear materials and radiation effects
- Aquaculture Nutrition and Growth
- Silicon Nanostructures and Photoluminescence
Oak Ridge National Laboratory
2010-2020
University of Connecticut
2013
Oakland University
2013
University of Houston
2006
Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
2000
University of Naples Federico II
1994-1997
The magnetic structure and phase diagram of the layered ferromagnetic compound ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ has been investigated by a combination synthesis, x-ray neutron diffraction, high-resolution microscopy, magnetization measurements. Single crystals were synthesized self-flux reactions, single-crystal diffraction finds order with moments $1.11(5){\ensuremath{\mu}}_{B}/\mathrm{Fe}$ aligned along $c$ axis at 4 K. These flux-grown have lower Curie temperature...
Using state-of-the-art, aberration-corrected scanning transmission electron microscopy and energy loss spectroscopy with atomic-scale spatial resolution, experimental evidence for an intrinsic electronic reconstruction at the LAO/STO interface is shown. Simultaneous measurements of interfacial density system polarization are crucial establishing highly debated origin 2D gas.
We show that the growth of heterostructure LaGaO3/SrTiO3 yields formation a highly conductive interface. Our samples were carefully analyzed by high resolution electron microscopy, in order to assess their crystal perfection and evaluate abruptness Their carrier density sheet resistance are compared case LaAlO3/SrTiO3 superconducting transition is found. The results open route widening field polar-nonpolar interfaces, pose some phenomenological constrains underlying physics highlight chance...
Oxide self-assembly is a promising bottom-up approach for fabricating new composite materials at the nanometer length scale. Tailoring properties of such systems wide range electronic applications depends on fundamental understanding interfaces between constituent phases. We show that nanoscale strain modulation in self-assembled made high-Tc superconducting films containing nanocolumns BaZrO3 strongly affects oxygen composition superconductor. Our findings explain observed reduction...
REBa2Cu3Ox ((REBCO), RE = rare earth) superconductor tapes with moderate levels of dopants have been optimized for high critical current density in low magnetic fields at 77 K, but they do not exhibit exemplary performance conditions interest practical applications, i.e., temperatures less than 50 K and 2–30 T. Heavy doping REBCO has avoided by researchers thus far due to deterioration properties. Here, we report achievement densities (Jc) above 20 MA/cm2 30 3 T heavily doped (25 mol. %...
Second generation, high-temperature superconducting wires are based on buffered, metallic tape substrates of near single crystal texture. Strong alignment adjacent grains was found to be necessary from previous work that suggested large angle, YBa2Cu3O7−δ [001]-tilt boundaries reduce Jc exponentially with increasing misorientation angle (θ). We pursue the low-θ regime by evaluating grain (GB) and biaxially aligned polycrystalline films utilizing both rolling-assisted textured ion-beam...
Superconducting MgB2 films with Tc=38.6 K were prepared using a precursor-deposition, ex situ postprocessing approach. Precursor of boron, ∼0.5 μm thick, deposited onto Al2O3 (102) substrates by electron-beam evaporation; postanneal at 890 °C in the presence bulk and Mg metal produced highly crystalline films. X-ray diffraction indicated that exhibit some degree c-axis alignment, but are randomly oriented plane. Transport current measurements superconducting properties show high values...
We have formed BaZrO3 nanocolumns and (Gd,Y)2O3 nanoprecipitates in reel-to-reel metal organic chemical vapor deposition (MOCVD) processed (Gd,Y)Ba2Cu3O7−x coated conductors increased the critical currents (Ic) of applied magnetic fields to remarkable levels. A tape 1 m length with 6.5% Zr-additions 30% composition rich both Gd Y showed Ic values 813 A/cm width at (self-field, 77 K) above 186 (1 T, K). The strongly enhanced flux pinning over a wide range field orientations can be attributed...
We report microstructural design via control of BaZrO3 (BZO) defect density in high temperature superconducting (HTS) wires based on epitaxial YBa2Cu3O7-δ (YBCO) films to achieve the highest critical current density, Jc, at different fields, H. find occurrence Jc(H) cross-over between with 1–4 vol% BZO, indicating that optimal BZO doping is strongly field-dependent. The matching Bφ, estimated by number nanocolumns are matched field ranges for which BZO-doped exhibit Jc(H). With incorporation...
Nanodot arrays of Y2O3 were dispersed in thin films YBa2Cu3O7−δ (YBCO) by growing alternating layers these two species using a pulsed laser deposition method. As result, critical current density Jc both applied magnetic field and self-field is enhanced as much an order magnitude, along with significant increase the irreversibility Hirr. High-resolution scanning transmission electron microscopy (STEM) Z -contrast STEM show that nanoparticles are crystalline coherent YBCO matrix. Whereas most...
The influence of Zr doping in (Gd, Y)–Ba–Cu–O ((Gd, Y)BCO) tapes made by metal–organic chemical vapor deposition has been studied with a specific objective uniform and reproducible enhancement in-field critical current (Ic) over long lengths. 50 m 7.5 10 at.% 1 µm thick Y)BCO films have found to exhibit sharply enhanced peak Ic the orientation field parallel c-axis retain 28% their self-field value at 77 K T. BaZrO3 (BZO) nanocolumn density cross-sectional microstructure was increase...
Ba2RENbO6 (RE = rare earth elements including Y) compounds are considered new additives for superior flux-pinning in YBa2Cu3O7-δ (YBCO) films due to their excellent chemical inertness and large lattice mismatches with YBCO. Simultaneous laser ablation of a YBCO target Nb metal foil attached the surface resulted epitaxial growth having columnar defects comprised self-aligned Ba2YNbO6 (BYNO) nanorods parallel c-axis film. Compared pure YBCO, YBCO+BYNO exhibited no Tc reduction as well Jc...
We report rare-earth barium tantalates, ${\text{Ba}}_{2}RE{\text{TaO}}_{6}$ (BRETO, $RE=\text{rare}$ earth elements) as promising pinning additives for superior flux in ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (YBCO) films. BRETO compounds have excellent chemical inertness to and large lattice mismatch with YBCO. This results phase separation strain minimization driven self-assembly of nanocolumns within YBCO $\text{YBCO}+4\text{ }\text{vol}\text{...
The transport characterization in the dark and under light irradiation of three different interfaces—LaAlO 3 /SrTiO , LaGaO novel NdGaO heterostructure—is reported. All them share a perovskite structure, an insulating nature single building blocks, polar/non‐polar character, critical thickness four unit cells for onset conductivity. interface structure charge confinement are probed by atomic‐scale‐resolved electron energy loss spectroscopy showing that, similarly to LaAlO extra electronic...
We use multi-scale techniques to determine the extent of local inhomogeneity and superconductivity in Ca$_{0.86}$Pr$_{0.14}$Fe$_{2}$As$_{2}$ single crystal. The is manifested as a spatial variation praseodymium concentration, density states, superconducting order parameter. show that high-$T_{c}$ emerges from clover-like defects associated with Pr dopants. highest $T_{c}$ observed both tetragonal collapsed phases, its filamentary nature consequence non-uniform distribution develops...
The interplay between magnetism and crystal structures in three CaFe2As2 samples is studied. For the nonmagnetic quenched crystals, different crystalline domains with varying lattice parameters are found phases (orthorhombic, tetragonal collapsed tetragonal) coexist TS = 95 K 45 K. Annealing of crystals at 350°C leads to a strain relief through large (~1.3%) expansion c-parameter small (~0.2%) contraction a-parameter local ~0.2 Å displacements atomic-level. This annealing procedure results...
Abstract Although magnetism originates at the atomic scale, existing spectroscopic techniques sensitive to magnetic signals only produce spectra with spatial resolution on a larger scale. However, recently, it has been theoretically argued that size electron probes customized phase distributions can detect circular dichroism. Here, we report direct experimental real-space detection of dichroism in aberration-corrected scanning transmission microscopy (STEM). Using an size-aberrated probe...
At interfaces between complex oxides it is possible to generate electronic systems with unusual properties, which are not present in the isolated oxides. One important example appearance of superconductivity at interface insulating oxides, although, until now, very low T(c). We report occurrence high T(c) bilayer CaCuO(2)/SrTiO(3), where both constituent insulating. In order obtain a superconducting state, CaCuO(2)/SrTiO(3) must be realized Ca plane CaCuO(2) and TiO(2) SrTiO(3). Only this...
Systematic effects of Zr additions on the structural and flux pinning properties YBa2Cu3O7−δ (YBCO) films deposited by metal–organic chemical vapor deposition (MOCVD) have been investigated. Detailed characterization, conducted coordinated transport, x-ray diffraction, scanning transmission electron microscopy analyses, imaging Raman revealed trends in resulting property/performance correlations these with respect to varying mole percentages (mol%) added Zr. For compositions ≤7.5 mol%, lead...
Magnetoelectric (ME) coupling (αE) in piezoelectric:magnetostrictive composites is mediated through mechanical strain at their interfaces. Incorporating magnetic nanoparticles (NPs) piezoelectric matrix enhances interfacial area between the two phases and therefore large αE can be expected. Here, we present electric ME properties of 3-0 type nanocomposite thin films with various concentrations CoFe2O4 NPs dispersed PbZr0.52Ti0.48O3 (PZT) matrix. Nanocomposite show only a slight reduction...
Heteroepitaxial semiconductor films on low-cost, flexible metal foil templates are a potential route to inexpensive, high-efficiency solar cells. Here, we report epitaxial growth of Si flexible, biaxially-textured Ni-W substrates. A robust buffer architecture comprised multiple oxide layers has been developed grow high quality, heteroepitaxial without any undesired reaction between the film and substrate with single biaxial texture. XRD analysis including ω-scans, φ-scans, pole figures...