T. Haugan

Wright-Patterson Air Force Base, Dayton, Ohio, United States

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Publications (110)190.86 Total impact

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    ABSTRACT: An elastic strain model has been applied in an effort to understand the effect of the lattice strain on the diameter of the BaZrO3 (BZO) nanorods self-assembled into aligned arrays along the c-axis in BZO-doped epitaxial YBa2Cu3O7−δ (YBCO) thin films. The calculated elastic energy of the strained BZO/YBCO composite lattice suggests that the diameter of the nanorods is approximately independent of the doping concentration of BZO as long as the density of the nanorods is sufficiently large. An experimental confirmation was carried out using transmission electron microscopy on YBCO thin films with BZO doping varying from 2% to 6% volume concentration. The diameter of the BZO nanorods was indeed found to be approximately constant in the range of 5.2–5.9 nm. The increase of the doping concentration therefore simply leads to an increase of the nanorod density, which links directly to the matching field of the effective pinning and is consistent with the transport Jc results measured for these samples.
    Superconductor Science and Technology 03/2014; 27(4):044010. · 2.76 Impact Factor
  • IEEE Transactions on Applied Superconductivity 01/2014; PP(99):1-1. · 1.20 Impact Factor
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    ABSTRACT: Multifilament fully stabilized second generation superconductor tapes have been fabricated with filaments widths as small as 180 μm. Each superconducting filament is copper stabilized, with copper thickness up to 30 μm, without compromising the beneficial effect of striations on magnetization AC losses. This has been accomplished by a combination of laser scribing (ablation), post-ablation oxidation, and subsequent selective electroplating of copper. Twelve millimeters wide superconductor tapes divided into 48 filaments with 10 μm thick copper stabilizer is found to meet an AC loss target of 1 W/kA/m in applied alternating magnetic field of 0.075 T at 100 Hz. This technique has a potential to be transferred to a large scale manufacturing of stabilized, low loss multifilament coated conductors.
    Applied Physics Letters 12/2013; 103(25):252603. · 3.52 Impact Factor
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    ABSTRACT: The controlled growth of self-assembled second-phase nanostructures has been shown to be an essential tool for enhancing properties of several composite oxide thin film systems. Here, the role of Y2O3 nanoparticles on the growth of BaZrO3 (BZO) nanorods is investigated in order to understand the mechanisms governing their self-assembly in YBa2Cu3O7–x (YBCO) thin films and to more fully control the resulting defect landscape. By examining the microstructure and current-carrying capacity of BZO-doped YBCO films, it is shown that the nanorod growth dynamics are significantly enhanced when compared to films double-doped with BZO and Y2O3 nanoparticles. The average nanorod length and associated critical current densities are found to increase at a significantly higher rate in the absence of Y2O3 nanoparticles when the growth temperature is increased. Using microstructural data from transmission electron microscopy studies and the response in critical current density, the interactive effects of multiple dopants that must be considered to fully control the defect landscape in oxide thin films are shown.
    Advanced Functional Materials 01/2013; 23(38):4826-4831. · 10.44 Impact Factor
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    ABSTRACT: In this paper, we have searched for superconductivity by measuring ohmic resistivity as a function of temperature in amorphous carbon films deposited by pulsed laser deposition and doped by ion implantation with sulfur and phosphorus ions. The doping concentrations were varied from 0.0003 to 4 Vol% for sulfur and 0.0003 to 1 Vol% for phosphorus. Previous efforts have studied doping of carbon-family materials such as highly oriented pyrolytic graphite, diamond-like carbon, and graphite/graphene, which have yielded critical temperatures lower than 20 K. In this study, amorphous carbon films doped with 2.55×1012 ions/cm2 phosphorus concentration showed a distinct change from semiconducting to metallic behavior and a dramatic 10 000-fold decrease in resistivity below 100 K as compared to undoped films. Sulfur-doped films with 2.55 × 1012 ions/cm2 concentration showed up to a 100-fold decrease in resistivity below 100 K as compared to undoped samples. While evidence of superconductivity was not observed, significant improvements in conductivity were noted below 100 K.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):7000205-7000205. · 1.20 Impact Factor
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    ABSTRACT: We present a design and details of construction of two calorimetric systems that allow us to measure the total loss in high temperature superconducting coils or linear samples carrying alternating current while exposed to a strong alternating magnetic field. This measurement technique is based on the boil-off of liquid nitrogen. The first system is designed to measure ac losses in superconducting coils in self-field generated by AC transport current. The second system contains a permanent magnet rotor and simulates the environment of an electric motor or generator. The sensitivity of the system is such that it can measure low losses from a few milliwatts to several hundred milliwatts, in either a static or dynamic magnetic field.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):4701505-4701505. · 1.20 Impact Factor
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    ABSTRACT: We report the data on magnetization losses and critical current of multifilament copper stabilized coated conductors. Eight centimeters long samples of copper stabilized YBa2Cu3O7-x (YBCO) coated conductors manufactured commercially were subdivided into superconducting filaments by near-IR laser micromachining. The width of the superconducting stripes was varied from 0.2 mm to 0.04 mm. Some of the samples were striated leaving superconducting bridges for current sharing between the filaments. The AC losses were measured at different sweep rates of the magnetic field up to 14 T/s. We will present the results for the hysteresis and coupling losses and discuss the means to reduce the coupling loss by changing the processing parameters of micromachining and by post-ablation treatment.
    IEEE Transactions on Applied Superconductivity 12/2012; · 1.20 Impact Factor
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    ABSTRACT: This work reports a detailed structural study by synchrotron x-ray diffraction of several sets of thick YBa2Cu3O7 layers. The samples represent recent advances in flux-pinning design, containing various concentrations of artificial pinning centers: (i) BaZrO3 nanorods, (ii) BaZrO3 nanoparticles, and (iii) Y2O3 nanoparticles. A statistical analysis was performed in order to separate the effects of defect-induced and intrinsic pinning. We report a statistically significant correlation between the orthorhombic distortion of the YBCO matrix and the pinning strength. Our result implies that the in-plane ordering of oxygen ions in the chain positions accounts for approximately 60% of the pinning force. The strain-induced pinning mechanism analysis, based on the Eshelby model of elastically strained composites, predicts that small YBCO grain size is a critical component of a strong pinning architecture that can enable critical current density values approaching the depairing limit.
    Physical Review B 09/2012; 86(9). · 3.66 Impact Factor
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    ABSTRACT: With research in the area of superconductivity growing, it is no surprise that new efforts are being made to induce superconductivity or increase transition temperatures (Tc) in carbon given its many allotropic forms. Promising results have been published for boron doping in diamond films, and phosphorus doping in highly oriented pyrolytic graphite (HOPG) films show hints of superconductivity.. Following these examples in the literature, we have begun studies to explore superconductivity in thin film carbon samples doped with different elements. Carbon thin films are prepared by pulsed laser deposition (PLD) on amorphous SiO2/Si and single-crystal substrates. Doping is achieved by depositing from (C1-xMx) single-targets with M = B4C and BN, and also by ion implantation into pure-carbon films. Previous research had indicated that Boron in HOPG did not elicit superconducting properties, but we aim to explore that also in thin film carbon and see if there needs to be a higher doping in the sample if trends were able to be seen in diamond films. Higher onset temperatures, Tc , and current densities, Jc, are hoped to be achieved with doping of the thin film carbon with different elements.
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    ABSTRACT: Transmission cables made from high-temperature superconductors have been successfully demonstrated within the electric power grid. These cables carry an ac current of up to 3000 A in a much smaller cross-sectional area than conventional transmission lines, but they are not flexible enough for certain applications that involve very tight cable bends. Certain on-board Air Force applications require 5 MW of dc power transmission at 270 V and current of 18 500 A and would benefit from superconducting transmission in lightweight, flexible cables that would be cooled with helium gas down to about 55 K. To address these needs, we have constructed a 10 mm diameter RE–Ba2Cu3O7 − δ (RE = rare earth) coated conductor cable that is lighter and more flexible than the current generation of superconducting cables, and that has a critical current of 7561 A at 76 K. The cable is expected to have a critical current of more than 20 000 A at 55 K and therefore will likely exceed the requirements for 5 MW on-board power transmission. The cable consists of two electrically insulated phases that can be operated in different modes, which allows us to study the effect of self-field on the cable performance.
    Superconductor Science and Technology 11/2011; 25(1):014003. · 2.76 Impact Factor
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    ABSTRACT: Near-field scanning microwave microscopy (NSMM) provides a unique nondestructive approach for detection of local dissipation with high sensitivity and high spatial resolution. With recently improved NSMM probes of spatial resolution of up to 400 nm ( ~ 10<sup>-6</sup> wavelength), detection of dissipation was achieved on YBCO microbridges at currents more than three orders of magnitude below the Jc ( T ). In this work, we report characterization of the dynamic behavior of low-level dissipation at the grain boundary of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> microbridges as function of time and applied electrical current. On higher-angle grain boundary, the dissipation develops rapidly with increasing current and shows approximately linear dependence on current. On lower-angle grain boundary, nonlinear features were observed and attributed to bi-modal pattern of dissipation evolution of nucleation of isolated hot spots and their evolution. Comparison with the similar NSMM+ IV measurement made on the “bulk” part of the same YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> microbridges on a reduced temperature scale shows higher dissipation on the grain boundary can be mostly attributed to the lower Tc values on grain boundaries.
    IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor
  • Interfaces in Heterogeneous Ceramic Systems: Ceramic Transactions Series, Volume 191, 06/2011: pages 111 - 119; , ISBN: 9781118144084
  • IEEE Transactions on Applied Superconductivity 06/2011; 21(3):3218-3221. · 1.20 Impact Factor
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    ABSTRACT: A correlation between flux-pinning characteristics and stacking faults (SFs) formed by Sm substitution on Y and Ba sites was found in Sm-doped YBa2Cu3O7- (YBCO) films. It was confirmed that 223 type SFs, Y2Ba2Cu3Ox, composed of extra Y and O planes aligned parallel to the ab-planes formed via Sm substitution on the Y site and increased in number with increasing Sm doping on the Ba site. The number density of 223 SFs is correlated strongly with the enhancement in ab-plane correlated flux-pinning, resulting in a sharpening of the H ab peak in the plot of critical current density versus magnetic field orientation.
    Physical Review B 01/2011; 83(22). · 3.66 Impact Factor
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    ABSTRACT: It has been suggested that edge-barrier pinning might cause the critical current density (Jc) in bridged superconducting films to increase. Subsequent work indicated that this edge-barrier effect does not impact bridges larger than 1 μm. However, we provide a theoretical assessment with supporting experimental data suggesting edge-barrier pinning can significantly enhance Jc for bridges of a few microns or even tens of microns thus skewing any comparisons among institutions. As such, when reporting flux pinning and superconductor processing improvements for Jc comparisons, the width of the sample has to be taken into consideration as is currently done with film thickness.
    Applied Physics Letters 12/2010; 97(26):262503-262503-3. · 3.52 Impact Factor
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    ABSTRACT: The thickness dependence of critical current density (Jc) has been investigated in YBa2Cu3O7−x films with BaZrO3 (BZO) nanorods (YBCO/BZO) aligned along the film normal. With the presence of linear defects in the YBCO/BZO films, the thickness dependence of Jc becomes negligible at self field and weak applied magnetic field (H), suggesting these linear defects playing a key role to the elimination of the thickness dependence of Jc. The effect of temperature (T) and H on Jc thickness dependence have been investigated and comparisons have been made between YBCO and YBCO/BZO samples. Since BZO nanorods alignment is greatly influenced by growth temperature, the quantitative difference in terms of nanorod’s density and average length is reflected on Jc angular dependence of H and Jc thickness dependence as thermally assisted flux motion (TAFM) becomes important above a threshold H determined by the BZO nanorod density. With further increasing H, a monotonically increasing Jc vs. thickness trend was observed in YBCO/BZO films, in contrast to an opposite trend when collective pinning is dominant. This result suggests the thickness dependence of Jc is dictated by the microstructure and hence pinning mechanism in YBCO films.
    Journal of Applied Physics 12/2010; 108(11):113911-113911-5. · 2.21 Impact Factor
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    ABSTRACT: Highly splayed BaZrO3 nanorods (BZO-NRs) were generated in YBa2Cu3O7 − δ (YBCO) films doped with 2 vol% BZO on 5° vicinal SrTiO3 (STO) substrates. It was observed that the splay angle of the BZO-NRs around the c-axis increases with film thickness from about 10° at 0.2 µm to 35°–40° at 1 µm. Although the same trend was observed in BZO-NRs in flat YBCO films, the splay angle at a given thickness and its increase with film thickness are significantly smaller. The enhanced dispersion of BZO-NRs in vicinal YBCO/BZO-NR films results in a much reduced strain on the YBCO lattice as compared to its flat counterpart. This led to less disturbed normal-state electron conduction along the ab-plane, higher Tc values and enhanced Jc values due to improved magnetic pinning.
    Superconductor Science and Technology 10/2010; 23(11):115010. · 2.76 Impact Factor
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    ABSTRACT: Edge-barrier pinning in thin superconducting films provides additional pinning over that of the bulk pinning. When using bridges greater than 1 mum to determine the critical current density (Jc) of films, this additional pinning is typically ignored. However, theoretical and experimental data presented here indicate that this pinning enhancement is non-negligible with bridge widths of less than 100 mum and on par with the bulk pinning at a few microns. In the present study, bridges in YBa2Cu3O7-delta (YBCO) thin films were repeatedly narrowed to avoid issues of sample to sample variation. Bridge widths starting at 500 mum and 50 mum were patterned by photolithography with subsequent narrowing performed by photolithography and focused ion beam milling, respectively. Transport Jc was determined after each bridge size. Theoretical analysis follows that of J.R Clem [e.g. Elistratov et al, Phys. Rev. B 66, 220506 (2002)]. Theoretical implications of the narrow bridge effect on Jc(H) and Jc(T) plots are not simple scalar changes. Based on these results presented here, two key points are: 1) Jc data comparison among institutions using different bridge sizes can provide improper conclusions (similarly as not accounting for film thickness), and 2) the Jc(T) and Jc(H) curve shapes are skewed differently for different widths. The implication of these effects will be discussed.
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    ABSTRACT: In pulsed laser deposition of YBa2Cu3O7−δ films, defect introduction into the films tends to anisotropically improve the pinning along the H||c direction due to the columnar growth mode of the process. In Eu-substituted samples, however, even though an increase in critical current density (Jc) in the H||c direction was observed for low fields (H = 0.2 T), the improvement was more notable for the H||ab-plane at both low and higher fields. Herein we present detailed TEM microstructural studies to understand these new trends in Jc(H), which are markedly different than flux pinning increases achieved with other methods, for example, with nanoparticle additions. Threading dislocations, observed in the Eu-substituted samples along the c-axis, account for Jc enhancement with H||c at low field. The enhanced ab-planar pinning in the Eu-substituted samples is attributed to the extensive bending of the {0 0 1} lattice planes throughout the film, and the crystal lattice defects with excess Cu–O planes, that were effective in increasing the Jc for H||ab at both low and high fields.
    Physica C Superconductivity 03/2010; 470:318-322. · 0.72 Impact Factor
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    ABSTRACT: When grown on miscut SrTiO3 substrates, significant microstructural changes are observed in BaZrO3-doped YBa2Cu3O7-x thin films when compared to those on non-vicinal substrates. Scanning Electron Microscopy indicates a surface morphology strongly influenced by the vicinal angle, and an accumulation of BaZrO3 particles is observed near the step edges. Cross-sectional Transmission Electron Microscopy reveals that while the columnar formations of BaZrO3 rods typically seen on non-vicinal substrates are present, a significant increase in planar defects in a 10 vicinal film are observed. The effects observed with increasing miscut angle indicate that the modulated surface provided by the vicinal substrate influences the crystalline quality of the YBCO matrix and BZO columnar formation through the thickness of the film.

Publication Stats

748 Citations
190.86 Total Impact Points


  • 2003–2014
    • Wright-Patterson Air Force Base
      Dayton, Ohio, United States
  • 2004–2011
    • Air Force Research Laboratory
      Washington, Washington, D.C., United States
  • 2006–2010
    • University of Kansas
      • Department of Physics and Astronomy
      Lawrence, Kansas, United States
  • 2009
    • University of Colorado
      Denver, Colorado, United States
    • University of Colorado at Boulder
      • Department of Physics
      Boulder, CO, United States
  • 2005–2007
    • University of Dayton
      Dayton, Ohio, United States
  • 2004–2007
    • California State University, Long Beach
      • Department of Physics & Astronomy
      Long Beach, CA, United States
  • 2000–2003
    • National Institute of Standards and Technology
      • Materials Science and Engineering Division
      Gaithersburg, MD, United States
  • 1992–1996
    • University at Buffalo, The State University of New York
      • Department of Electrical Engineering
      Buffalo, NY, United States