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Sample records for quality mgb2 thin

  1. Preparation of variable-thickness MgB 2 thin film bridges by AFM nanolithography

    NASA Astrophysics Data System (ADS)

    Gregor, M.; Plecenik, A.; Plecenik, T.; Tomasek, M.; Kus, P.; Micunek, R.; Stefecka, M.; Zahoran, M.; Grancic, B.; Kubinec, M.; Gasparik, V.

    2006-03-01

    In this paper we focus our attention on preparation of superconducting MgB2 thin films and variable-thickness MgB2 thin film bridges using the Atomic Force Microscope nanolithographic technique. Microstructures and their following variable-thickness bridges were prepared on nonsuperconducting MgB thin films. Final structures were annealed in argon atmosphere at temperature 680 °C and exhibit transition to the superconducting state Tcon = 33 K and zero critical temperature Tc0 = 30.5 K. Critical current density jc (4.2 K) measured on the bridge was higher than 106 A/cm2.

  2. Characterization of off-axis MgB2 epitaxial thin films for planar junctions

    NASA Astrophysics Data System (ADS)

    Iavarone, M.; Karapetrov, G.; Menzel, A.; Komanicky, V.; You, H.; Kwok, W. K.; Orgiani, P.; Ferrando, V.; Xi, X. X.

    2005-12-01

    Using scanning tunneling spectroscopy, we perform a full mapping of the quasiparticle density of states of magnesium diboride (MgB2) epitaxial thin films grown on (110) yttrium stabilized zirconia (YSZ) by hybrid physical-chemical vapor deposition. The films have critical temperatures of 40 K. X-ray measurements show an epitaxial MgB2 growth having the c-axis tilted by 32° with respect to the normal to the substrate, consistent with the atomic force microscopy images of the sample. Scanning tunneling spectroscopy clearly finds that the spectroscopic peak associated to the π gap is reduced on most of the film surface and the feature representative of the σ gap is present, with different intensity, on the majority of the sample's surface, which is consistent with x-ray measurements.

  3. l/f Noise in the Superconducting Transition of a MgB2 Thin Film

    NASA Technical Reports Server (NTRS)

    Lakew, B.; Aslam, S.; Jones, H.; Stevenson, T.; Cao, N.

    2010-01-01

    The noise voltage spectral density in the superconducting transition of a MgB2 thin film on a SiN-coated Si thick substrate was measured over the frequency range 1 Hz-to-1 KHz. Using established bolometer noise theory the theoretical noise components due to Johnson, 1/f(excess) and phonon noise are modeled to the measured data. It is shown that for the case of a MgB2 thin film in the vicinity of the mid-point of transition, coupled to a heat sink via a fairly high thermal conductance (approximately equal to 10(sup -1) W/K)) that the measured noise voltage spectrum is 1/f limited and exhibits lit dependence with a varying between 0.3 and 0.5 in the measured frequency range. At a video frame rate frequency of 30 Hz the measured noise voltage density in the film is approximately equal to 61 nV /the square root of HZ, using this value an upper limit of electrical NEP approximately equal to 0.67pW / the square root of Hz is implied for a practical MgB2 bolometer operating at 36.1 K.

  4. Development of hot-electron THz bolometric mixers using MgB2 thin films

    NASA Astrophysics Data System (ADS)

    Cunnane, Daniel; Kawamura, Jonathan; Karasik, Boris S.; Wolak, Matthaeus A.; Xi, X. X.

    2014-07-01

    Terahertz high-resolution spectroscopy of interstellar molecular clouds greatly relies on hot-electron superconducting bolometric (HEB) mixers. Current state-of-the-art receivers use mixer devices made from ultrathin (~ 3-5 nm) films of NbN with critical temperature ~ 9-11 K. Such mixers have been deployed on a number of groundbased, suborbital, and orbital platforms including the HIFI instrument on the Hershel Space Observatory. Despite its good sensitivity and well-established fabrication process, the NbN HEB mixer suffers from the narrow intermediate frequency (IF) bandwidth ~ 2-3 GHz and is limited to operation at liquid Helium temperature. As the heterodyne receivers are now trending towards "high THz" frequencies, the need in a larger IF bandwidth becomes more pressing since the same velocity resolution for a Doppler shifted line at 5 THz requires a 5-times greater IF bandwidth than at 1 THz. Our work is focusing on the realization of practical HEB mixers using ultrathin (10-20 nm) MgB2 films. They are prepared using a Hybrid Physical-Chemical Vapor Deposition (HPCVD) process yielding ultrathin films with critical temperature ~ 37-39 K. The expectation is that the combination of small thickness, high acoustic phonon transparency at the interface with the substrate, and very short electron-phonon relaxation time may lead to IF bandwidth ~ 10 GHz or even higher. SiC continues to be the most favorable substrate for MgB2 growth and as a result, a study has been conducted on the transparency of SiC at THz frequencies. FTIR measurements show that semi-insulating SiC substrates are at least as transparent as Si up to 2.5 THz. Currently films are passivated using a thin (10 nm) SiO2 layer which is deposited ex-situ via RF magnetron sputtering. Micron-sized spiral antenna-coupled HEB mixers have been fabricated using MgB2 films as thin as 10 nm. Fabrication was done using contact UV lithography and Ar Ion milling, with E-beam evaporated Au films deposited for the

  5. High critical current density and enhanced irreversibility field in superconducting MgB2 thin films

    NASA Astrophysics Data System (ADS)

    Eom, C. B.; Lee, M. K.; Choi, J. H.; Belenky, L. J.; Song, X.; Cooley, L. D.; Naus, M. T.; Patnaik, S.; Jiang, J.; Rikel, M.; Polyanskii, A.; Gurevich, A.; Cai, X. Y.; Bu, S. D.; Babcock, S. E.; Hellstrom, E. E.; Larbalestier, D. C.; Rogado, N.; Regan, K. A.; Hayward, M. A.; He, T.; Slusky, J. S.; Inumaru, K.; Haas, M. K.; Cava, R. J.

    2001-05-01

    The discovery of superconductivity at 39K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. This compound has twice the transition temperature of Nb3Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has already been demonstrated. One possible drawback, however, is that the magnetic field at which superconductivity is destroyed is modest. Furthermore, the field which limits the range of practical applications-the irreversibility field H*(T)-is approximately 7T at liquid helium temperature (4.2K), significantly lower than about 10T for Nb-Ti (ref. 6) and ~20T for Nb3Sn (ref. 7). Here we show that MgB2 thin films that are alloyed with oxygen can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding an H* value at 4.2K greater than 14T. In addition, very high critical current densities at 4.2K are achieved: 1MAcm-2 at 1T and 105Acm-2 at 10T. These results demonstrate that MgB2 has potential for high-field superconducting applications.

  6. Upper Threshold Fields of Dendritic Flux Jumps in Gold-Coated MgB2 Thin Films

    NASA Astrophysics Data System (ADS)

    Choi, Eun-Mi; Lee, Hyun-Sook; Lee, Jae Yeap; Lee, Sung-Ik; Olsen, Å. A. F.; Yurchenko, V. V.; Shantsev, D. V.; Johansen, T. H.; Kim, Hyeong-Jin; Cho, Moo-Hyun

    We measured the magneto-optical images (MOIs) and the magnetic hysteresis (M - H) curves of c-axis-oriented MgB2 thin films to investigate the flux penetration in the form of dendritic avalanches. In order to understand the role of the thermal effects, we prepared Au-coated MgB2 thin films with different thicknesses of gold. While the MOI provides a spatially resolved flux pattern, the M - H curve presents global and average information about the flux noise associated with avalanches. These two types of measurements complement each other. The upper threshold field, above which the flux noise disappears, was determined from the M-H curves while the lower threshold field was determined from both the M - H curves and the MO images. The field range where the flux penetrates via avalanches is found to be smaller for thicker gold layers. These results are important for many superconducting applications.

  7. Enhancement of Jc in MgB2 thin films on Si substrate with pinning centers introduced by deposition in O2 atmosphere

    NASA Astrophysics Data System (ADS)

    Haruta, M.; Fujiyoshi, T.; Kajita, R.; Yonekura, K.; Sueyoshi, T.; Doi, T.; Kitaguchi, H.; Awaji, S.; Watanabe, K.

    2007-10-01

    As-grown MgB2 thin films on Si substrates with high Jc under magnetic fields were prepared by electron-beam evaporation. The value of Jc has been enhanced by the deposition of MgB2 thin film in an O2 atmosphere. The MgB2 thin film deposited in the O2 atmosphere (O2-doped film) has exhibited considerably higher Jc in magnetic fields among MgB2 thin films reported before. It has been found that the high Jc of the O2-doped film is attributable to the flux pinning with grain boundaries strengthened by an introduction of MgO along grain boundaries. In a high magnetic field, a peculiar behavior of E-J characteristics where E-J curves vary in two stages was observed. This behavior also originates from the flux pinning with strengthened grain boundaries.

  8. Upper critical field and anisotropy in carbon alloyed MgB2 thin films

    NASA Astrophysics Data System (ADS)

    Li, Qi; Ferrando, Valeria; Chen, Jun; Pogrebnyakov, Alexej; Redwing, Joan; Xi, Xiaoxing; Gurevich, Alex; Larbalestier, David; Betts, J. B.; Mielke, C. H.

    2006-03-01

    We have studied the upper critical field and its anisotropy γ of C-alloyed MgB2 thin films grown on (0001) SiC single crystal substrates by hybrid physical-chemical vapor deposition (HPCVD). Different concentrations of C were introduced during the deposition, which increased the residual resistivity systematically but did not affect Tc seriously. The upper critical field was found to increase to above 60 T for H parallel to the ab plane and up to ˜ 40T for H parallel to the c axis with even moderate amounts of C doping. Moreover, we show that Hc2 stays at these levels in a wide range of C doping. The Hc2 anisotropy was found to decrease as the C concentration increases. The Hc2(T) curves for both H ab and H c directions were explained by a theoretical model of dirty limit two band superconductivity, which takes into account different scattering rates in π and σ bands, as well as interband scattering. The differences in the Hc2(T) and γ(T) for different samples can be explained by the differences of the relative scattering rates in each band which make it possible to adjust the π and σ scattering such that Hc2 perpendicular to ab can attain almost 20T at 20K.

  9. Microscopic Study of Dendritic Avalanches in MgB2 Thin Films of Various Widths

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Yeap; Lee, Hyun-Sook; Lee, Hu-Jong; Choi, Eun-Mi; Kang, Won-Nam; Lee, Sung-Ik

    2010-04-01

    To understand the features of a dendritic avalanche, we prepared the eight sets of MgB2 thin films with rectangular shapes of 3 mm [length L] × w [width], where w = 0.2 to 1.6 mm; the samples were in the long-length limit of w < L. Magneto-optical images (MOIs) of the first few dendrite patterns, which were distributed sparsely, were taken at applied fields below 35 mT at a temperature of 4 K. The key features of the present measurements are as follows: (1) the number of branches and the area of the dendrites increase with increasing w; (2) the change in the flux density (CFD) from before to after the jump at the edge of the samples increased with increasing w; (3) the applied magnetic flux density of the first few appearances of dendrites decreased with increasing of the w; (4) the real initial penetration flux density at the sample’s edge was about 20 mT, regardless of w; (5) the critical current densities obtained from the MOI were almost the same for all samples, which implies that Bean’s critical model works quite well.

  10. Epitaxial MgB2 thin films on ZrB2 buffer layers: structural characterization by synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Ferrando, V.; Tarantini, C.; Bellingeri, E.; Manfrinetti, P.; Pallecchi, I.; Marré, D.; Plantevin, O.; Putti, M.; Felici, R.; Ferdeghini, C.

    2004-12-01

    Structural and superconducting properties of magnesium diboride thin films grown by pulsed laser deposition on zirconium diboride buffer layers were studied. We demonstrate that the ZrB2 layer is compatible with the MgB2 two step deposition process. Synchrotron radiation measurements, in particular anomalous diffraction measurements, allowed us to separate MgB2 peaks from ZrB2 ones and revealed that both layers have a single in plane orientation with a sharp interface between them. Moreover, the buffer layer avoids oxygen contamination from the sapphire substrate. The critical temperature of this film is near 37.6 K and the upper critical field measured at the Grenoble High Magnetic Field Laboratory up to 20.3 T is comparable with the highest ones reported in literature.

  11. Microstructures and superconducting properties of high performance MgB2 thin films deposited from a high-purity, dense Mg-B target

    PubMed Central

    Li, G.Z.; Susner, M.A.; Bohnenstiehl, S.D.; Sumption, M.D.; Collings, E.W.

    2015-01-01

    High quality, c-axis oriented, MgB2 thin films were successfully grown on 6H-SiC substrates using pulsed laser deposition (PLD) with subsequent in situ annealing. To obtain high purity films free from oxygen contamination, a dense Mg-B target was specially made from a high temperature, high pressure reaction of Mg and B to form large-grained (10~50 µm) MgB2. Microstructural analysis via electron microscopy found that the resulting grains of the film were composed of ultrafine columnar grains of 19–30 nm. XRD analysis showed the MgB2 films to be c-axis oriented; the a-axis and c-axis lattice parameters were determined to be 3.073 ± 0.005 Å and 3.528 ± 0.010 Å, respectively. The superconducting critical temperature, Tc,onset, increased monotonically as the annealing temperature was increased, varying from 25.2 K to 33.7 K. The superconducting critical current density as determined from magnetic measurements, Jcm, at 5 K, was 105 A/cm2 at 7.8 T; at 20 K, 105 A/cm2 was reached at 3.1 T. The transport and pinning properties of these films were compared to “powder-in-tube” (PIT) and “internal-infiltration” (AIMI) processed wires. Additionally, examination of the pinning mechanism showed that when scaled to the peak in the pinning curve, the films follow the grain boundary, or surface, pinning mechanism quite well, and are similar to the response seen for C doped PIT and AIMI strands, in contrast to the behavior seen in undoped PIT wires, in which deviations are seen at high b (b = B/Bc2). On the other hand, the magnitude of the pinning force was similar for the thin films and AIMI conductors, unlike the values from connectivity-suppressed PIT strands. PMID:26417117

  12. Microstructures and superconducting properties of high performance MgB2 thin films deposited from a high-purity, dense Mg-B target.

    PubMed

    Li, G Z; Susner, M A; Bohnenstiehl, S D; Sumption, M D; Collings, E W

    2015-12-01

    High quality, c-axis oriented, MgB2 thin films were successfully grown on 6H-SiC substrates using pulsed laser deposition (PLD) with subsequent in situ annealing. To obtain high purity films free from oxygen contamination, a dense Mg-B target was specially made from a high temperature, high pressure reaction of Mg and B to form large-grained (10~50 µm) MgB2. Microstructural analysis via electron microscopy found that the resulting grains of the film were composed of ultrafine columnar grains of 19-30 nm. XRD analysis showed the MgB2 films to be c-axis oriented; the a-axis and c-axis lattice parameters were determined to be 3.073 ± 0.005 Å and 3.528 ± 0.010 Å, respectively. The superconducting critical temperature, Tc,onset , increased monotonically as the annealing temperature was increased, varying from 25.2 K to 33.7 K. The superconducting critical current density as determined from magnetic measurements, Jcm , at 5 K, was 10(5) A/cm(2) at 7.8 T; at 20 K, 10(5) A/cm(2) was reached at 3.1 T. The transport and pinning properties of these films were compared to "powder-in-tube" (PIT) and "internal-infiltration" (AIMI) processed wires. Additionally, examination of the pinning mechanism showed that when scaled to the peak in the pinning curve, the films follow the grain boundary, or surface, pinning mechanism quite well, and are similar to the response seen for C doped PIT and AIMI strands, in contrast to the behavior seen in undoped PIT wires, in which deviations are seen at high b (b = B/Bc2 ). On the other hand, the magnitude of the pinning force was similar for the thin films and AIMI conductors, unlike the values from connectivity-suppressed PIT strands.

  13. Superconducting screening on different length scales in high-quality bulk MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Horvat, J.; Soltanian, S.; Pan, A. V.; Wang, X. L.

    2004-10-01

    High-quality bulk MgB2 exhibits a structure of voids and agglomeration of crystals on different length scales. Because of this, the superconducting currents percolate between the voids in the ensuing structure. Magnetic measurements reveal that the superconducting currents circulate on at least three different length scales, of ˜1μm, ˜10μm, and whole of the sample (˜millimeter). Each of these screenings contributes to the measured irreversible magnetic moment (Δm ). The analysis of the field dependence of Δm for samples of subsequently decreasing size showed that the critical current obtained using the simple critical state model is erroneous. This leads to the artifact of the sample size-dependent critical current density Jc and irreversibility field. Our data analysis enables the separation of the contribution of each of the screening currents to Δm. The field dependence of each of the currents follows a stretched exponential form. The currents flowing around whole of the sample give a dominant contribution to Δm in the intermediate fields (1T

  14. Effect of two bands on critical fields in MgB2 thin films with various resistivity values

    NASA Astrophysics Data System (ADS)

    Ferrando, V.; Manfrinetti, P.; Marré, D.; Putti, M.; Sheikin, I.; Tarantini, C.; Ferdeghini, C.

    2003-09-01

    Upper critical fields of four MgB2 thin films were measured up to 28 T at Grenoble High Magnetic Field Laboratory. The films were grown by pulsed laser deposition and showed critical temperatures ranging between 29.5 and 38.8 K and resistivities at 40 K varying from 5 to 50 μΩ cm. The critical fields in the perpendicular direction turned out to be in the 13 24 T range while they were estimated to be in 42 57 T range for ab planes. In contrast to the prediction of the BCS theory, we did not observe any saturation at low temperatures: a linear temperature dependence is exhibited even at lowest temperatures at which we made the measurements. Moreover, the critical field values seemed not to depend on the normal state resistivity value. In this paper, we analyze these data considering the multiband nature of superconductivity in MgB2. We will show how the scattering mechanisms that determine critical fields and resistivity can be different.

  15. Energy gap, penetration depth, and surface resistance of MgB2 thin films determined by microwave resonator measurements

    NASA Astrophysics Data System (ADS)

    Jin, B. B.; Klein, N.; Kang, W. N.; Kim, Hyeong-Jin; Choi, Eun-Mi; Lee, Sung-Ik; Dahm, T.; Maki, K.

    2002-09-01

    We have measured the temperature dependence of the microwave surface impedance Zs=Rs+iωμ0λ of two c-axis oriented MgB2 films employing dielectric resonator techniques. The temperature dependence of the magnetic-field penetration depth λ determined by a sapphire dielectric resonator at 17.9 GHz can be well fitted from 5 K close to Tc by the standard BCS integral expression assuming the reduced energy gap Δ(0)/kTc to be as low as 1.13 and 1.03 for the two samples. For the penetration depth at zero temperatures, values of 102 and 107 nm were determined from the fit. Our results clearly indicate the s-wave character of the order parameter. A similar fit of the penetration depth data was obtained with an anisotropic s-wave BCS model. Within this model we had to assume a prolate order parameter, having a large gap value in the c-axis direction and a small gap within the ab plane. This is in contrast to recent fits of the anisotropic s-wave model to upper critical-field data, where an oblate order parameter had to be used, and raises interesting questions about the nature of the superconducting state in MgB2. A rutile dielectric resonator was employed to obtain the temperature dependence of Rs with high accuracy. Below about Tc/2, Rs(T)-Rs(5 K) exhibits an exponential temperature dependence with a reduced energy gap consistent with that determined from the penetration depth data. The Rs value at 4.2 K was found to be as low as 19 μΩ at 7.2 GHz, which is comparable with a high-temperature superconducting copper oxide thin film.

  16. Pinning in high performance MgB2 thin films and bulks: Role of Mg-B-O nano-scale inhomogeneities

    NASA Astrophysics Data System (ADS)

    Prikhna, Tatiana; Shapovalov, Andrey; Eisterer, Michael; Shaternik, Vladimir; Goldacker, Wilfried; Weber, Harald W.; Moshchil, Viktor; Kozyrev, Artem; Sverdun, Vladimir; Boutko, Viktor; Grechnev, Gennadiy; Gusev, Alexandr; Kovylaev, Valeriy; Shaternik, Anton

    2017-02-01

    The comparison of nano-crystalline MgB2 oxygen-containing thin film (140 nm) and highly dense bulk materials showed that the critical current density, Jc, depends on the distribution of Mg-B-O nano-scale inhomogeneities. It has been shown that MgB2 bulks with high Jc in low (∼106 A/cm2 in 0-1 T at 10 K) and medium magnetic fields contain MgB0.6-0.8O0.8-0.9 nano-inclusions, where δTc or a combined δTc (dominant) / δl pinning mechanism prevails, while in bulk MgB2 with high Jc in high magnetic fields (Birr(18.5 K) = 15 T, Bc2(0 K) = 42.1 T) MgB1.2-2.7O1.8-2.5 nano-layers are present and δl pinning prevails. The structure of oxygen-containing films with high Jc in low and high magnetic fields (Jc (0 Т) = 1.8 × 107 А/сm2 and Jc (5 Т) = 2 × 106 А/сm2 at 10 К) contains very fine oxygen-enriched Mg-B-O inhomogeneities and δl pinning is realized. The results of DOS calculations in MgB2-xOx cells for x = 0, 0.125, 0.25, 0.5, 1 demonstrate that all compounds are conductors with metal-like behaviour. In the case of ordered oxygen substitution for boron the binding energy, Eb, does not increase sufficiently as compared with that for MgB2, while when oxygen atoms form zigzag chains the calculated Eb is even lower (Eb = -1.15712 Ry).

  17. Enhancement of the critical current density in FeO-coated MgB2 thin films at high magnetic fields

    PubMed Central

    Surdu, Andrei E; Hamdeh, Hassan H; Al-Omari, I A; Sellmyer, David J; Socrovisciuc, Alexei V; Prepelita, Andrei A; Koparan, Ezgi T; Yanmaz, Ekrem; Ryazanov, Valery V; Hahn, Horst

    2011-01-01

    Summary The effect of depositing FeO nanoparticles with a diameter of 10 nm onto the surface of MgB2 thin films on the critical current density was studied in comparison with the case of uncoated MgB2 thin films. We calculated the superconducting critical current densities (J c) from the magnetization hysteresis (M–H) curves for both sets of samples and found that the J c value of FeO-coated films is higher at all fields and temperatures than the J c value for uncoated films, and that it decreases to ~105 A/cm2 at B = 1 T and T = 20 K and remains approximately constant at higher fields up to 7 T. PMID:22259764

  18. Upper critical field and Raman spectra of MgB2 thin films irradiated with low energy oxygen ion

    NASA Astrophysics Data System (ADS)

    Wang, J.; Zhuang, C. G.; Li, J.; Wang, Y. Z.; Feng, Q. R.; Zheng, D. N.

    2009-11-01

    The structure, upper critical field, and Raman spectrum of epitaxial MgB2 thin films irradiated by 300 keV O2+ ions have been investigated. Lattice parameter c expands after irradiation. There is a significant increase in upper critical field in the moderately irradiated films, while the critical temperature is reduced slightly. The values of critical field at zero temperature exhibit a maximum for samples with a moderate irradiation level for the applied magnetic field both perpendicular and parallel to the film surface. The temperature dependence of the anisotropy parameter, which is defined as the ratio of the upper critical field with the field parallel to the film surface and perpendicular to the film surface, reveals that oxygen ion irradiation mainly affects the σ band at a low irradiation level. With increasing irradiation level, π band scattering is strongly enhanced, and finally both bands are in the dirty limit. A broad peak centered around 570 cm-1 is observed in the Raman spectrum of the unirradiated films, and the peak position has a visible redshift in the irradiated samples. In particular, high-frequency spectral structures appear and become dominant, while the E2g broad band diminishes gradually with increasing irradiation fluence. The results are discussed by considering the disorder-induced change in carrier scattering within and between the σ and π bands and a violation of the Raman selection rules due to oxygen ion irradiation.

  19. MgB2 Thin-Film Bolometer for Applications in Far-Infrared Instruments on Future Planetary Missions

    NASA Technical Reports Server (NTRS)

    Lakew, B.; Aslam, S.; Brasunas, J.; Cao, N.; Costen, N.; La, A.; Stevenson, T.; Waczynski, A.

    2012-01-01

    A SiN membrane based MgB2 thin-film bolometer, with a non-optimized absorber, has been fabricated that shows an electrical noise equivalent power of 256 fW/square root Hz operating at 30 Hz in the 8.5 - 12.35 micron spectral bandpass. This value corresponds to an electrical specific detectivity of 7.6 x 10(exp 10) cm square root Hz/W. The bolometer shows a measured blackbody (optical) specific detectivity of 8.8 x 10(exp 9) cm square root Hz/W, with a responsivity of 701.5 kV/W and a first-order time constant of 5.2 ms. It is predicted that with the inclusion of a gold black absorber that a blackbody specific detectivity of 6.4 x 10(exp 10) cm/square root Hz/W at an operational frequency of 10 Hz, can be realized for integration into future planetary exploration instrumentation where high sensitivity is required in the 17 - 250 micron spectral wavelength range.

  20. Cabling of Thin MgB2 Strands for High-Current Conductors with Reduced AC Losses

    NASA Astrophysics Data System (ADS)

    Schlachter, S. I.; Braun, U.; Drechsler, A.; Goldacker, W.; Holúbek, T.; Kling, A.; Schmidt, C.

    2010-04-01

    Since the discovery of superconductivity in MgB2 many efforts have been undertaken to improve the current carrying capacity of mono- or multifilament MgB2 conductors. However, even though MgB2 conductors can be produced in geometries which easily allow twisting or cabling, the reduction of ac losses has often played a minor role, even though many technical superconductor applications like transformers, rotating machinery, and ramped magnets require conductors with low AC losses. In this paper we present short cables together with measured AC-losses applying a simple cabling technique. Coupling losses of the cables with strands having a single component stainless steel (SS) sheath are negligible. The lower apparent measured losses of cables with Nb/Cu/SS sheaths may be explained by magnetic shielding of the Nb layer and by a systematic problem of the magnetization method for samples containing diamagnetic and ferromagnetic components.

  1. First-principles study of the superconductivity in MgB2 bulk and in its bilayer thin film based on electron-phonon coupling

    NASA Astrophysics Data System (ADS)

    Morshedloo, T.; Roknabadi, M. R.; Behdani, M.

    2015-02-01

    In this paper, phonon-mediated superconductivity has been investigated in MgB2 bulk structure and bilayer thin film by using first-principles calculations. The electronic band structure, total and partial density of states (DOS and PDOS), phonon dispersion, isotropic Eliashberg function α2F(ω), and electron-phonon coupling have been calculated within the framework of density functional theory (DFT). Our results indicate that holes at the top of boron σ bands mainly and holes in the boron π band partially contribute to formation of coupled holes in superconductivity state. The density of states at the Fermi energy level is increased for MgB2 bilayer with respect to its bulk structure. According to the phonon dispersion and Eliashberg function curves, coupling considerably occurs between holes at the top of the boron σ band by means of optical phonon mode for both structures. This phonon mode has the E2g symmetry at the Г point. We obtain electron-phonon coupling constants of 0.74 and 0.91 for bulk and bilayer structures, respectively. By using the Allen-Dynes formula, we estimate superconducting transition temperature TC of 40 K for bulk and 48 K for the thin film.

  2. Time-Resolved Photoexcitation of the Superconducting Two-Gap State in MgB2 Thin Films

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Khafizov, M.; Satrapinsky, L.; Kúš, P.; Plecenik, A.; Sobolewski, Roman

    2003-11-01

    Femtosecond pump-probe studies show that carrier dynamics in MgB2 films is governed by the sub-ps electron-phonon (e-ph) relaxation present at all temperatures, the few-ps e-ph process well pronounced below 70K, and the sub-ns superconducting relaxation below Tc. The amplitude of the superconducting component versus temperature follows the superposition of the isotropic dirty gap and the three-dimensional π gap dependences, closing at two different Tc values. The time constant of the few-ps relaxation exhibits a double divergence at temperatures corresponding to the Tc's of the two gaps.

  3. Fabrication and superconducting properties of multifilamentary MgB2 conductors for AC purposes: twisted tapes and wires with very thin filaments

    NASA Astrophysics Data System (ADS)

    Malagoli, A.; Bernini, C.; Braccini, V.; Fanciulli, C.; Romano, G.; Vignolo, M.

    2009-10-01

    In order to use MgB2 conductors for AC applications, research and development efforts have to be carried out on their architecture and sheath material to minimize the AC losses. This paper will present the fabrication and characterization of two types of ex situ powder-in-tube processed pure MgB2 conductors with properties making them good candidates for AC industrial applications: a multifilamentary tape with 12 filaments with a twisting pitch down to 17 mm and a 361-filament wire with an average single-filament size of about 30 µm. Concerning the twisted tapes we will present values of critical current density of about 105 A cm-2 at 4.2 K and 2 T and we will show that it is possible to achieve a proper compromise between the tape size, the twisting pitch length and the critical current density to face a reduction of the critical current density as a consequence of the strain on the filaments. Concerning the 361-multifilamentary wire we will show appreciable values of critical current density of about 5 × 104 A cm-2 at 4.2 K and 2.5 T which, together with the advantages given by the high number of very thin filaments and the non-magnetic matrix, could justify their employment.

  4. Thickness dependence of Jc (0) in MgB2 films

    NASA Astrophysics Data System (ADS)

    Chen, Yiling; Yang, Can; Jia, Chunyan; Feng, Qingrong; Gan, Zizhao

    2016-06-01

    MgB2 superconducting films, whose thicknesses range from 10 nm to 8 μm, have been fabricated on SiC substrates by hybrid physical-chemical vapor deposition (HPCVD) method. It is the first time that the Tc and the Jc of MgB2 films are studied on such a large scale. It is found that with the increasing of thickness, Tc elevates first and then keeps roughly stable except for some slight fluctuations, while Jc (5 K, 0 T) experiences a sharp increase followed by a relatively slow fall. The maximum Jc (5 K, 0 T) = 2.3 × 108 A cm-2 is obtained for 100 nm films, which is the experimental evidence for preparing high-quality MgB2 films by HPCVD method. Thus, this work may provide guidance on choosing the suitable thickness for applications. Meanwhile, the films prepared by us cover ultrathin films, thin films and thick films, so the study on them will bring a comprehensive understanding of MgB2 films.

  5. Development of a liquid hydrogen transfer pump system with MgB2 wires

    NASA Astrophysics Data System (ADS)

    Kajikawa, Kazuhiro; Kuga, Hirotsugu; Inoue, Takuro; Watanabe, Kazuki; Uchida, Yushi; Nakamura, Taketsune; Kobayashi, Hiroaki; Hongo, Motoyuki; Kojima, Takayuki; Taguchi, Hideyuki; Naruo, Yoshihiro; Wakuda, Tsuyoshi; Tanaka, Kazuhide

    An electric pump composed of an MgB2 motor is combined with superconducting level sensors using thin CuNi-sheathed MgB2 wires to transfer liquid hydrogen. An impeller is attached to the lower end of a rotating shaft on the MgB2 motor and covered with an outer casing to form a centrifugal pump. Then, the MgB2 motor and impeller are placed vertically inside a cryostat with an infill of liquid hydrogen. A glass Dewar vessel is prepared to receive the liquid hydrogen transferred from the cryostat containing the MgB2 motor. The MgB2 sensors are used not only to detect the level of liquid hydrogen but also to control the electric pump on the basis of their pre-estimated calibration curves. By using the assembled pump system, the liquid hydrogen is successfully transferred from the cryostat to the glass Dewar vessel via a transfer tube.

  6. Fabrication of superconducting MgB2 nanostructures by an electron beam lithography-based technique

    NASA Astrophysics Data System (ADS)

    Portesi, C.; Borini, S.; Amato, G.; Monticone, E.

    2006-03-01

    In this work, we present the results obtained in fabrication and characterization of magnesium diboride nanowires realized by an electron beam lithography (EBL)-based method. For fabricating MgB2 thin films, an all in situ technique has been used, based on the coevaporation of B and Mg by means of an e-gun and a resistive heater, respectively. Since the high temperatures required for the fabrication of good quality MgB2 thin films do not allow the nanostructuring approach based on the lift-off technique, we structured the samples combining EBL, optical lithography, and Ar milling. In this way, reproducible nanowires 1 μm long have been obtained. To illustrate the impact of the MgB2 film processing on its superconducting properties, we measured the temperature dependence of the resistance on a nanowire and compared it to the original magnesium diboride film. The electrical properties of the films are not degraded as a consequence of the nanostructuring process, so that superconducting nanodevices may be obtained by this method.

  7. Superconducting MgB2 flowers: growth mechanism and their superconducting properties

    NASA Astrophysics Data System (ADS)

    Seong, Won Kyung; Ranot, Mahipal; Lee, Ji Yeong; Yang, Cheol-Woong; Lee, Jae Hak; Oh, Young Hoon; Ahn, Jae-Pyoung; Kang, Won Nam

    2016-04-01

    We report for the first time the growth and the systematic study of the growth mechanism for flower-like MgB2 structures fabricated on the substrates for solid-state electronics by the hybrid physical-chemical vapor deposition (HPCVD) technique. The MgB2 flower has a width of 30 μm and a height of 10 μm. The superconductivity of MgB2 flowers was confirmed by a magnetization measurement, and the transition temperature is 39 K, which is comparable with high-quality bulk samples. The excellent current-carrying capability was demonstrated by MgB2 flowers. To understand the nucleation and growth mechanism of MgB2 flowers a very systematic study was performed by a high-resolution transmission electron microscope (HRTEM) and atom probe (AP) microscopy. The HRTEM revealed that the seed grain of a MgB2 flower has a [101¯0] direction, and the flower is composed of micro-columnar MgB2 grains having pyramidal tips and which are grown along the (0001) plane. A clear understanding of the growth mechanism for MgB2 flowers could lead to the growth of other low-dimensional MgB2 structures for superconducting electronic devices.

  8. EBSD analysis of MgB2 bulk superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Schmauch, J.; Inoue, K.; Muralidhar, M.; Berger, K.; Noudem, J.

    2016-04-01

    The grain orientation, the texture and the grain boundary misorientations are important parameters for the understanding of the magnetic properties of the bulk MgB2 samples intended for super-magnet applications. Such data can be provided by electron backscatter diffraction (EBSD) analysis. However, as the grain size (GS) of the MgB2 bulks is preferably in the 100-200 nm range, the common EBSD technique working in reflection operates properly only on highly dense samples. In order to achieve a reasonably good Kikuchi pattern quality on all samples, we apply here the newly developed transmission EBSD (t-EBSD) technique to several bulk MgB2 samples. This method requires the preparation of TEM slices by means of focused ion-beam milling, which are then analyzed within the SEM, operating with a specific sample holder. We present several EBSD mappings of samples prepared with different techniques and at various reaction temperatures.

  9. Recent developments in melt processed Gd-123 and MgB2 materials at RTRI

    NASA Astrophysics Data System (ADS)

    Muralidhar, M.; Fukumoto, Y.; Ishihara, A.; Suzuki, K.; Tomita, M.; Koblischka, M. R.; Yamamoto, A.; Kishio, K.

    2014-01-01

    In this contribution we will report on the current status, recent developments in GdBa2Cu3Oy "Gd-123" and MgB2 material processing, characterization, and applications at the Railway Technical Research Institute (RTRI). Batch-processing of Gd-123 bulk material grown in air was performed using novel thin film Nd-123 seeds grown on MgO crystals. In this way, we are able to fabricate materials with good quality, and uniform performance. We examined the technology of the uniform performance of the large 45 mm diameter, single grain Gd-123 bulks for use in application of NMR. For this purpose, four 5 mm thick pieces are cut vertically from a single grain Gd-123 material and the magnetic field distribution is measured using a scanning hall sensor. We found that all four pieces are single domain and exhibit a quite uniform field distribution. Furthermore, the batch-processed bulk materials are used for the construction of a chilled Maglev vehicle. On the other hand, to optimize the trapped field performance of bulk MgB2 material, several samples were prepared by solid state reaction at different temperatures ranging from 750 to 950 °C in pure argon atmosphere. X-ray diffraction results indicated that single phase and homogenous MgB2 bulks are produced when sintering them around 775 °C. Further, atomic force microscopy (AFM) and scanning electron microscopy (SEM) indicated that an uniform grain size results by controlling the processing temperature. So, higher trapped fields can be achieved in sintered MgB2 material.

  10. MgB2UltrathinFilms Fabricated by Hybrid Physical Chemical Vapor Deposition and Subsequent Ion Milling

    NASA Astrophysics Data System (ADS)

    Acharya, Narendra; Wolak, Matthaeus; Tan, Teng; Cunnane, Daniel; Karasik, Boris; Xi, Xiaoxing

    Hot electron bolometer (HEB) mixers are a great tool for measuring high-resolution spectroscopy at Terahertz frequencies. MgB2offers a higher critical temperature (39 K) compared to commonly used Nb and NbN and boasts a shorter intrinsic electron-phonon relaxation time, giving rise to a broader intermediate frequency (IF) bandwidth. We have fabricated high quality ultrathin MgB2films using hybrid physical-chemical vapor deposition (HPCVD) and employing ion milling to achieve thickness down to 2 nm. The thinnest achieved films show high Tc of 28 K with residual resistivity below 28 µ Ωcm and high critical current Jcof 1x106 A/cm2at 20 K. As a result of the employed low angle ion milling process, the films remain well connected even after being thinned down since the initial thick films offer a better connectivity than as-grown thin films. The established process offers a way to realize MgB2 based HEB mixers of extremely low thickness and therefore small local oscillator power requirements and increased IF bandwidth.

  11. Concurrent doping effect of Ti and nano-diamond on flux pinning of MgB 2

    NASA Astrophysics Data System (ADS)

    Zhao, Y.; Ke, C.; Cheng, C. H.; Feng, Y.; Yang, Y.; Munroe, P.

    2010-11-01

    Nano-diamond and titanium concurrently doped MgB2 nanocomposites have been prepared by solid state reaction method. The effects of carbon and Ti concurrent doping on Jc-H behavior and pinning force scaling features of MgB2 have been investigated. Although Tc was slightly depressed, Jc of MgB2 have been significantly improved by the nano-diamond doping, especially in the high field region. In the mean time, the Jc value in low field region is sustained though concurrent Ti doping. Microstructure analysis reveals that when nano-diamond was concurrently doped with titanium in MgB2, a unique nanocomposite in which TiB2 forms a thin layer surrounding MgB2 grains whereas nano-diamond particles were wrapped inside the MgB2 grains. Besides, nano-diamond doping results in a high density stress field in the MgB2 samples, which may take responsibility for the Δκ pinning behavior in the carbon-doped MgB2 system.

  12. Application of superconducting magnesium diboride (MGB2) in superconducting radio frequency cavities

    NASA Astrophysics Data System (ADS)

    Tan, Teng

    The superconductivity in magnesium diboride (MgB2) was discovered in 2001. As a BCS superconductor, MgB2 has a record-high Tc of 39 K, high Jc of > 107 A/cm2 and no weak link behavior across the grain boundary. All these superior properties endorsed that MgB2 would have great potential in both power applications and electronic devices. In the past 15 years, MgB2 based power cables, microwave devices, and commercial MRI machines emerged and the next frontier are superconducting radio frequency (SRF) cavities. SRF cavities are one of the leading accelerator technologies. In SRF cavities, applied microwave power generates electrical fields that accelerate particle beams. Compared with other accelerator techniques, SRF cavity accelerators feature low loss, high acceleration gradients and the ability to accelerate continuous particle beams. However, current SRF cavities are made from high-purity bulk niobium and work at 2 K in superfluid helium. The construction and operational cost of SRF cavity accelerators are very expensive. The demand for SRF cavity accelerators has been growing rapidly in the past decade. Therefore, a lot of effort has been devoted to the enhancement of the performance and the reduction of cost of SRF cavities. In 2010, an acceleration gradient of over 50 MV/m has been reported for a Nb-based SRF cavity. The magnetic field at the inner surface of such a cavity is ~ 1700 Oe, which is close to the thermodynamic critical field of Nb. Therefore, new materials and technologies are required to raise the acceleration gradient of future SRF cavity accelerators. Among all the proposed approaches, using MgB2 thin films to coat the inner surface of SRF cavities is one of the promising tactics with the potential to raise both the acceleration gradient and the operation temperature of SRF cavity accelerators. In this work, I present my study on MgB2 thin films for their application in SRF cavities. C-epitaxial MgB2 thin films grown on SiC(0001) substrates

  13. Superconductivity in MgB 2

    NASA Astrophysics Data System (ADS)

    Akimitsu, Jun; Muranaka, Takahiro

    2003-05-01

    We recently discovered that the intermetallic compound magnesium diboride (MgB2) exhibits the highest superconducting transition temperature (Tc=39 K) of all the metallic superconductors. In this paper we report on the basic superconducting characteristics of MgB2 and the current status of the research for the unanswered problem in this superconductivity. Especially, we review the several reports for the superconducting gap (Δ) by the spectroscopic measurements. Moreover we introduce the research into its anisotropic parameter (γ), which is important for the understanding of this superconducting states in this material.

  14. MgB2 ultrathin films fabricated by hybrid physical chemical vapor deposition and ion milling

    NASA Astrophysics Data System (ADS)

    Acharya, Narendra; Wolak, Matthäus A.; Tan, Teng; Lee, Namhoon; Lang, Andrew C.; Taheri, Mitra; Cunnane, Dan; Karasik, Boris. S.; Xi, X. X.

    2016-08-01

    In this letter, we report on the structural and transport measurements of ultrathin MgB2 films grown by hybrid physical-chemical vapor deposition followed by low incident angle Ar ion milling. The ultrathin films as thin as 1.8 nm, or 6 unit cells, exhibit excellent superconducting properties such as high critical temperature (Tc) and high critical current density (Jc). The results show the great potential of these ultrathin films for superconducting devices and present a possibility to explore superconductivity in MgB2 at the 2D limit.

  15. Evaluations of MgB2 Coatings on 2'' Copper Discs for Superconducting Radio Frequency Applications

    NASA Astrophysics Data System (ADS)

    Withanage, Wenura; Tan, Teng; Lee, Namhoon; Banjade, Huta; Eremeev, Grigory; Welander, Paul; Valente-Feliciano, Anne-Marie; Kustom, Robert; Wolak, Matthäus; Nassiri, Alireza; Xi, Xiaoxing

    We propose that coating the inner walls of copper RF cavities with superconducting MgB2 (Tc = 39 K) can result in a viable alternative to the already established niobium-based SRF technology. This approach improves the thermal conductivity, allows for operation at higher temperatures, and reduces the need for large helium refrigeration, thereby resulting in lower operational costs. For our studies, we grew MgB2 films via hybrid physical chemical vapor deposition (HPCVD) on 2'' Cu substrates. Since Mg and Cu readily form an alloy at higher temperatures, the HPCVD setup was modified in order to achieve lower deposition temperatures, minimize alloy formation, and provide high quality MgB2 films. This method yielded MgB2 coatings on 2'' Cu discs with transition temperatures around 38 K. The samples were characterized with regards to their RF attributes and showed similar performance in comparison to Nb reference samples. The presented results show that MgB2 coated copper can be a suitable alternative for use in SRF cavities.

  16. Characterization of MgB2 Superconducting Hot Electron Bolometers

    NASA Technical Reports Server (NTRS)

    Cunnane, D.; Kawamura, J. H.; Wolak, M. A.; Acharya, N.; Tan, T.; Xi, X. X.; Karasik, B. S.

    2014-01-01

    Hot-Electron Bolometer (HEB) mixers have proven to be the best tool for high-resolution spectroscopy at the Terahertz frequencies. However, the current state of the art NbN mixers suffer from a small intermediate frequency (IF) bandwidth as well as a low operating temperature. MgB2 is a promising material for HEB mixer technology in view of its high critical temperature and fast thermal relaxation allowing for a large IF bandwidth. In this work, we have fabricated and characterized thin-film (approximately 15 nanometers) MgB2-based spiral antenna-coupled HEB mixers on SiC substrate. We achieved the IF bandwidth greater than 8 gigahertz at 25 degrees Kelvin and the device noise temperature less than 4000 degrees Kelvin at 9 degrees Kelvin using a 600 gigahertz source. Using temperature dependencies of the radiation power dissipated in the device we have identified the optical loss in the integrated microantenna responsible as a cause of the limited sensitivity of the current mixer devices. From the analysis of the current-voltage (IV) characteristics, we have derived the effective thermal conductance of the mixer device and estimated the required local oscillator power in an optimized device to be approximately 1 microwatts.

  17. Fabrication of superconducting nanowires from ultrathin MgB2 films via focused ion beam milling

    NASA Astrophysics Data System (ADS)

    Zhang, Chen; Wang, Da; Liu, Zheng-Hao; Zhang, Yan; Ma, Ping; Feng, Qing-Rong; Wang, Yue; Gan, Zi-Zhao

    2015-02-01

    High quality superconducting nanowires were fabricated from ultrathin MgB2 films by a focused ion beam milling technique. The precursor MgB2 films in 10 nm thick were grown on MgO substrates by using a hybrid physical-chemical vapor deposition method. The nanowires, in widths of about 300-600 nm and lengths of 1 or 10 μm, showed high superconducting critical temperatures (Tc's) above 34 K and narrow superconducting transition widths (ΔTc's) of 1-3 K. The superconducting critical current density Jc of the nanowires was above 5 × 107 A/cm2 at 20 K. The high Tc, narrow ΔTc, and high Jc of the nanowires offered the possibility of making MgB2-based nano-devices such as hot-electron bolometers and superconducting nanowire single-photon detectors with high operating temperatures at 15-20 K.

  18. Fabrication and superconducting properties of MgB2 composite wiresby the PIT method

    NASA Astrophysics Data System (ADS)

    Feng, Y.; Zhao, Y.; Pradhan, A. K.; Zhou, L.; Zhang, P. X.; Liu, X. H.; Ji, P.; Du, S. J.; Liu, C. F.; Wu, Y.; Koshizuka, N.

    2002-01-01

    Dense MgB2/Cu wires with Ta as a buffer layer were successfully fabricated by the powder-in-tube (PIT) method. The microstructure was investigated by optical microscopy. Magnetization measurements were carried out by using a superconducting quantum interference device (SQUID) magnetometer at magnetic fields up to 7 T from 5 K to 35 K. The transition temperature of the MgB2 wire is around 38.4 K and the irreversibility field is 6.6 T at 5 K. The critical current density as high as 105 A cm-2 (5 K, self-field) and 104 A cm-2 (20 K, 1 T) has been obtained. The results suggest that the powder-in-tube (PIT) process is promising in preparing high-quality MgB2 wires.

  19. MICROSTRUCTURE OF SUPERCONDUCTING MGB(2).

    SciTech Connect

    ZHU,Y.; LI,Q.; WU,L.; VOLKOV,V.; GU,G.; MOODENBAUGH,A.R.

    2001-07-12

    Recently, Akimitsu and co-workers [1] discovered superconductivity at 39 K in the intermetallic compound MgB{sub 2}. This discovery provides a new perspective on the mechanism for superconductivity. More specifically, it opens up possibilities for investigation of structure/properties in a new class of materials. With the exceptions of the cuprate and C{sub 60} families of compounds, MgB{sub 2} possesses the highest superconducting transition temperature T{sub c}. Its superconductivity appears to follow the BCS theory, apparently being mediated by electron-phonon coupling. The coherence length of MgB{sub 2} is reported to be longer than that of the cuprates [2]. In contrast to the cuprates, grain boundaries are strongly coupled and current density is determined by flux pinning [2,3]. Presently, samples of MgB{sub 2} commonly display inhomogeneity and porosity on the nanoscale, and are untextured. In spite of these obstacles, magnetization and transport measurements show that polycrystalline samples may carry large current densities circulating across many grains [3,4]. Very high values of critical current densities and critical fields have been recently observed in thin films [5,6]. These attributes suggest possible large scale and electronic applications. The underlying microstructure can be intriguing, both in terms of basic science and in applied areas. Subsequent to the discovery, many papers were published [1-13], most dealing with synthesis, physical properties, and theory. There have yet been few studies of microstructure and structural defects [11, 14]. A thorough understanding of practical superconducting properties can only be developed after an understanding of microstructure is gained. In this work we review transmission electron microscopy (TEM) studies of sintered MgB{sub 2} pellets [14]. Structural defects, including second phase particles, dislocations, stacking faults, and grain boundaries, are analyzed using electron diffraction, electron

  20. Fabrication and radio frequency test of large-area MgB2 films on niobium substrates

    NASA Astrophysics Data System (ADS)

    Ni, Zhimao; Guo, Xin; Welander, Paul B.; Yang, Can; Franzi, Matthew; Tantawi, Sami; Feng, Qingrong; Liu, Kexin

    2017-04-01

    Magnesium diboride (MgB2) is a promising candidate material for superconducting radio frequency (RF) cavities because of its higher transition temperature and critical field compared with niobium. To meet the demand of RF test devices, the fabrication of large-area MgB2 films on metal substrates is needed. In this work, high quality MgB2 films with 50 mm diameter were fabricated on niobium by using an improved HPCVD system at Peking University, and RF tests were carried out at SLAC National Accelerator Laboratory. The transition temperature is approximately 39.6 K and the RF surface resistance is about 120 μΩ at 4 K and 11.4 GHz. The fabrication processes, surface morphology, DC superconducting properties and RF tests of these large-area MgB2 films are presented.

  1. Phase 1 Final Technical Report - MgB2 Synthesis for High Field Performance

    SciTech Connect

    Mohit Bhatia; Peter McIntyre

    2009-11-02

    Accelerator Technology Corp. (ATC) has successfully completed its Phase 1 effort to devel-op rf plasma torch synthesis of MgB2 superconducting powder. The overall objective is to de-velop a way to introduce homogeneous alloying of C and SiC impurities into phase-pure MgB2. Several groups have attained remarkable benefits from such alloying in raising the upper critical field Hc2 from ~14 T to ~30 T (bulk) and ~50 T (thin films). But no one has succeeded in pro-ducing that benefit homogeneously, so that current transport in a practical powder-in-tube (PIT) conductor is largely the same as without the alloying. ATC has conceived the possibility of attaining such homogeneity by passing aerosol suspen-sions of reactant powders through an rf plasma torch, with each reactant transported on a stream-line that heats it to an optimum temperature for the synthesis reaction. This procedure would uniquely access non-equilibrium kinetics for the synthesis reaction, and would provide the possi-bility to separately control the temperature and stoichiometry of each reactant as it enters the mixing region where synthesis occurs. It also facilitates the introduction of seed particles (e.g. nanoscale SiC) to dramatically enhance the rate of the synthesis reaction compared to gas-phase synthesis in rf plasma reported by Canfield and others. During the Phase 1 effort ATC commissioned its 60 kW 5 MHz rf source for a manufactur-ing-scale rf plasma torch. This effort required repair of numerous elements, integration of cooling and input circuits, and tuning of the load characteristics. The effort was successful, and the source has now been tested to ~full power. Also in the Phase 1 effort we encountered a subsidiary but very important problem: the world is running out of the only present supply of phase-pure amorphous boron. The starting boron powder must be in the amorphous phase in order for the synthesis reaction to produce phase-pure MgB2. Even small contamination with crystalline

  2. Magnesium diboride thin films and devices

    NASA Astrophysics Data System (ADS)

    Cui, Yi

    Magnesium diboride (MgB2) is a binary compound superconductor with a superconducting transition temperature Tc of ˜40 K. MgB2 has two conduction bands: a two-dimensional sigma band and a three-dimensional pi band with weak interband scattering. The two gap superconductivity in MgB2 gives rise to many interesting physical properties not possible in other superconductors. The relatively high Tc combined with phonon mediated superconductivity and relatively long coherence length makes MgB2 promising for electronics applications like rapid single flux quantum (RSFQ) logics and superconducting quantum interference devices (SQUID). The high current density and record-high upper critical field in pure or alloyed MgB2 are also attractive to a variety of high field applications including cryogen-free Magnetic Resonance Imaging (MRI) systems. MgB2 may also be used in RF cavity coatings due to its low surface resistance and in photo detection due to its fast photoresponse coupled with relatively high Tc. High quality epitaxial thin films are produced by the hybrid physical-chemical vapor deposition (HPCVD) technique. The HPCVD MgB2 thin films have the highest Tc and lowest resistivity with sharp transition of all MgB2 materials reported. The HPCVD MgB2 material is free of dendritic flux jumps due to its low resistivity. The root-mean-square (RMS) surface roughness of HPCVD MgB2 films can be ˜1 nm when ˜1% of nitrogen is added to the hydrogen carrier gas during the growth. The stability of MgB2 films in water is studied; it is found that degradation can be prevented by a thin (10 nm) MgO layer deposited on the film surface. The Tc is enhanced by tensile strain due to the Volmer-Weber growth mode and the mismatches between MgB2 and the substrate in the lattice constants and the coefficients of thermal expansion. High quality superconductor-insulator-superconductor Josephson tunnel junctions were made with various barrier formation techniques. The junction critical current

  3. Microstructure and superconducting properties of nanocarbon-doped internal Mg diffusion-processed MgB2 wires fabricated using different boron powders

    NASA Astrophysics Data System (ADS)

    Xu, Da; Wang, Dongliang; Li, Chen; Yuan, Pusheng; Zhang, Xianping; Yao, Chao; Dong, Chiheng; Huang, He; Ma, Yanwei; Oguro, Hidetoshi; Awaji, Satoshi; Watanabe, Kazuo

    2016-04-01

    MgB2/Nb/Monel monofilament wires were fabricated using four different boron powders by an internal Mg diffusion (IMD) process. The microstructure, morphology and the critical current density (J c) of the used boron powders and the formative MgB2 layers were analyzed and compared. It was found that the purity and particle size of the boron powder influence the superconducting properties of MgB2 wires; further that the optimized heat-treatment condition also depends on the quality of the boron powder. The highest J c was obtained in the MgB2 layer made using amorphous boron (AB) powder, although a certain amount of voids existed in the superconducting layer. The IMD-processed MgB2 layer fabricated using high-purity boron (HB) powder had also a high J c compared with the powder-in-tube (PIT) process and a few unreacted boron particles remained in it. MgB2 wire fabricated using low-purity boron (LB) powder had a high cost-performance ratio compared with the others, which is expected to allow the fabrication of large-scale and low-cost superconducting wires for practical application. However, the enhancement of the J c was not found in the MgB2 layer manufactured using the ball-milled LB (MLB) powder as expected due to the increased percentage of impurity.

  4. Intrinsic flux pinning mechanisms in different thickness MgB2 films

    NASA Astrophysics Data System (ADS)

    Yang, C.; Ni, Z. M.; Guo, X.; Hu, H.; Wang, Y.; Zhang, Y.; Feng, Q. R.; Gan, Z. Z.

    2017-03-01

    MgB2 films in four thickness (60 nm, 200nm, 600nm and 1μm) have been fabricated by hybrid physical-chemical vapor deposition technique (HPCVD). By measuring the magnetization hysteresis loops and the resistivity, we have obtained the transport and magnetic properties of the four films. After that, the pinning mechanisms in them were discussed. Comparing the pinning behaviors in these ultrathin films, thin films and thick films, it was found that there exist different pinning types in MgB2 films of different thickness. In combination with the study of the surface morphology, cross-section and XRD results, we concluded that MgB2 films had different growth modes in different growth stages. For thin films, films grew along c axis, and grain boundaries acted as surface pinning. While for thick films, films grew along c axis at first, and then changed to a-b axis growth. As a result, the a-b axis grains acted as strong volume pinning.

  5. Al addition effect of bulk MgB 2 superconductor

    NASA Astrophysics Data System (ADS)

    Shinohara, K.; Ikeda, H.; Yoshizaki, R.

    2007-10-01

    The properties of transport and magnetization have been investigated for bulk MgB2Alx superconductor with Al addition (x = 0, 0.5, 1 wt%). MgB2 bulk samples sintered at different temperatures at 650-740 °C were prepared in the undoped state. The temperature and applied field dependencies of resistivity and magnetization were measured for the samples. The sample sintered at 690 °C exhibited the highest critical current density (Jc) and the lowest resistivity. This undoped sample was chosen as a criterion sample, and the effect of Al addition on the MgB2 bulk was studied from the transport and magnetization properties in a magnetic field. For MgB2Alx bulk samples sintered at 690 °C, the resistivity increased and Jc decreased as amount of Al was increased.

  6. Magnetic lenses using different MgB2 bulk superconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Z. Y.; Choi, S.; Matsumoto, S.; Teranishi, R.; Giunchi, G.; Figini Albisetti, A.; Kiyoshi, T.

    2012-02-01

    A magnetic lens allows the concentration of magnetic fields using the diamagnetism of superconductors. The important features of the magnetic lens are a tapered inner diameter from which the magnetic flux is extruded and a slit to suppress the circumference current that shields the magnetic flux. This concept was experimentally confirmed through the use of GdBaCuO bulks and a stack of NbTi/Nb/Cu sheets. We refer to this arrangement as a magnetic lens. The Mg-reactive liquid infiltration (Mg-RLI) process developed by Edison SpA is suitable for the production of large and high-density MgB2 bulks. Three MgB2 bulk magnetic lenses, each with a different microstructure, were fabricated following the Mg-RLI process. The properties of the MgB2 magnetic lenses were measured in a cryocooler system as well as in liquid helium. The results confirmed that the MgB2 bulk magnetic lenses could concentrate a magnetic field and that their field concentration properties were greatly affected by the temperature and the external field. In addition, the microstructure of the MgB2 bulk also had an influence on the magnetic properties at different external fields. The results indicated that the MgB2 lens might be utilized as a field amplifier in intermediate fields.

  7. Anomalous flux flow resistivity in the two-gap superconductor MgB2

    NASA Astrophysics Data System (ADS)

    Shibata, A.; Matsumoto, M.; Izawa, K.; Matsuda, Y.; Lee, S.; Tajima, S.

    2003-08-01

    The flux flow resistivity ρf associated with purely viscous motion of vortices in high-quality MgB2 was measured by microwave surface impedance. Flux flow resistivity exhibits unusual field dependence with strong enhancement at low field, which is markedly different to conventional s-wave superconductors. A crossover field which separates two distinct flux flow regimes having different ρf slopes was clearly observed in H‖ab plane. The unusual H dependence indicates that two very differently sized superconducting gaps in MgB2 manifest in the vortex dynamics and almost equally contribute to energy dissipation. The carrier scattering rate in two different bands is also discussed with the present results, compared to heat-capacity and thermal-conductivity results.

  8. Effect of cold high pressure deformation on the properties of ex situ MgB2 wires

    NASA Astrophysics Data System (ADS)

    Kulich, M.; Flükiger, R. L.; Senatore, C.; Tropeano, M.; Piccardo, R.

    2013-10-01

    A substantially different behaviour was observed between MgB2 wires produced either by in situ or ex situ processing after applying the recently developed technique of cold high pressure densification (or CHPD). In contrast to in situ wires, where densification at 1.5 GPa on binary and ternary alloyed in situ MgB2 wires causes an enhancement of mass density and a strong enhancement of Jc, ex situ wires up to 2 GPa show only a negligible enhancement of the MgB2 mass density, while a considerable enhancement of Jc is still observed. In both cases, this reflects an enhancement of grain connectivity, however in ex situ wires, the enhancement of Jc is connected to the partial disruption of the oxide layer around each MgB2 powder particle, in contrast to the enhancement of Jc in situ wires, which is correlated to a smaller void fraction and a larger contact area between neighbouring grains. It is well known that Jc of ex situ wires decreases after longer exposition times when exposed to air prior to annealing; after several months Jc falls to values ≤50% of the original value. After cold pressing, we have found that Jc of the same wire exceeded the original values, even after exposing the unreacted wire for >1 year to air. A lower electrical resistivity is measured on pressed ex situ MgB2 wires, which confirms the improvement of grain connectivity due to the breakage of the oxide layers. Thus, the application of high pressure at room temperature allows us to recover the values of Jc for ex situ wires even after they have been degraded either by low quality MgB2 precursors or by prolonged ageing of the already formed wire prior to the final heat treatment. The limits of the Jc enhancement in ex situ wires are discussed.

  9. Characterization of MgB2 Conductors for Coil Development

    NASA Astrophysics Data System (ADS)

    Aslanoglu, Z.; Arda, L.; Akin, Y.; Sumption, M. D.; Tomsic, M.; Hascicek, Y. S.

    2004-06-01

    The effects of the heat treatment conditions on microstructure and the transport critical current density of MgB2 wires, which were fabricated by the Continuous Tube Forming and Filling (CTFF) process, have been investigated. Two types of MgB2 conductors, Fe/MgB2 and Cu/MgB2, were studied. It was found that the sheath materials affect the optimum annealing profile of MgB2 conductor. The annealing temperature for Cu/MgB2 conductors was lower than that for the Fe/MgB2 conductors. The critical current density, Jc was measured to be 1.1×105 A/cm2 at 20 K in-self field for Cu/MgB2 conductor of 1.25 mm in diameter. The processing, microstructure and superconducting properties are presented.

  10. MgB2-Based Bolometer Array for Far Infra-Red Thermal Imaging and Fourier Transform Spectroscopy Applications

    NASA Technical Reports Server (NTRS)

    Lakew, B.; Aslam, S.; Brasunas, J.

    2012-01-01

    The mid-superconducting critical temperature (T(sub c) approximately 39 K) of the simple binary, intermetallic MgB, [1] makes it a very good candidate for the development of the next generation of electrooptical devices (e.g. [2]). In particular, recent advances in thin film deposition teclmiques to attain higb quality polycrystalline thin film MgB, deposited on SiN-Si substrates, with T(sub c) approximately 38K [3] coupled with the low voltage noise performance of the film [4] makes it higbly desirable for the development of moderately cooled bolometer arrays for integration into future space-bourne far infra-red (FIR) spectrometers and thermal mappers for studying the outer planets, their icy moons and other moons of interest in the 17-250 micrometer spectral wavelength range. Presently, commercially available pyroelectric detectors operating at 300 K have specific detectivity, D(*), around 7 x 10(exp 8) to 2 x 10(exp 9) centimeters square root of Hz/W. However, a MgB2 thin film based bolometer using a low-stress (less than 140 MPa) SiN membrane isolated from the substrate by a small thermal conductive link, operating at 38 K, promises to have two orders of magnitude higher specific detectivity [5][6].

  11. Influence of nano-Cu additive on MgB2 phase formation, processing temperature, and transport properties

    NASA Astrophysics Data System (ADS)

    Varghese, Neson; Vinod, K.; Rahul, S.; Devadas, K. M.; Thomas, Syju; Pradhan, S.; Syamaprasad, U.

    2011-02-01

    Pure and nano-Cu doped MgB2/Fe superconducting wires were prepared by in situ powder-in-tube method at different temperatures (550-675 °C). The phase formation, microstructure, and transport critical current density of the wires were investigated as a function of the heat-treatment temperature. A small amount of nano-Cu addition (2.5 wt %) was found to dramatically decrease the reaction temperature of magnesium and boron, forming MgB2 without any degradation in the transport critical current. From x-ray diffraction and scanning electron microscopy analyses, it was found that the added Cu form a reacted phase Mg2Cu with Mg which melts at around 550 °C. This liquid phase helps the formation of MgB2 at a significant lower temperature with improved grain connectivity, grain size, and density. All Cu doped samples heat treated in the range of 550-650 °C exhibited a transport JC quite comparable to that of the pure sample processed at 650 °C, which shows that high quality MgB2 conductors can be produced even at 550 °C with minor Cu doping.

  12. MgB2 tunnel junctions with native or thermal oxide barriers

    NASA Astrophysics Data System (ADS)

    Singh, R. K.; Gandikota, R.; Kim, J.; Newman, N.; Rowell, J. M.

    2006-07-01

    MgB2 tunnel junctions (MgB2/barrier/MgB2) were fabricated using a native oxide grown on the bottom MgB2 film as the tunnel barrier. Such barriers therefore survive the deposition of the second electrode at 300°C, even over junction areas of ˜1mm2. Studies of such junctions and those of the type MgB2/native or thermal oxide/metal (Pb, Au, or Ag) show that tunnel barriers grown on MgB2 exhibit a wide range of barrier heights and widths.

  13. Sintering time dependence of iron diffusion in MgB2 and its effect on superconducting properties

    NASA Astrophysics Data System (ADS)

    Ulgen, Asaf Tolga; Belenli, Ibrahim

    2017-02-01

    We have investigated the effects of the iron diffusion on the crystal structure and superconducting properties of pelletised magnesium diboride (MgB2) bulk samples employing X-ray diffraction (XRD), critical transition temperature, and room temperature resistivity measurements. The Fe diffusion into MgB2 bulk pellets upon sintering at 900°C has been studied for sintering time durations of 15 minutes, 30 minutes, 1 hour, 2 hours, and 4 hours. We have carried out XRD and room temperature resistivity determinations along the depth starting from iron coated surface by successive removal of thin layers from the surface mechanically. Sintering time dependence of the Fe diffusion coefficients has been calculated from depth profiles of lattice parameter c and room temperature resistivity values. It has been found that the Fe diffusion coefficient decreases with increasing sintering time.

  14. Active Protection of an MgB2 Test Coil

    PubMed Central

    Park, Dong Keun; Hahn, Seungyong; Bascuñán, Juan; Iwasa, Yukikazu

    2011-01-01

    This paper presents results of a study, experimental and computational, of a detect-and-activate-the-heater protection technique applied to a magnesium diboride (MgB2) test coil operated in semi-persistent mode. The test coil with a winding ID of 25 cm and wound with ~500-m long reacted MgB2 wire was operated at 4.2 K immersed in a bath of liquid helium. In this active technique, upon the initiation of a “hot spot” of a length ~10 cm, induced by a “quench heater,” a “protection heater” (PH) of ~600-cm long planted within the test coil is activated. The normal zone created by the PH is large enough to absorb the test coil’s entire initial stored energy and still keeps the peak temperature within the winding below ~260 K. PMID:22081754

  15. Attempts at doping indium in MgB2

    NASA Astrophysics Data System (ADS)

    Grivel, J.-C.

    2016-12-01

    Indium (In) doped MgB2 polycrystalline samples were prepared by solid-liquid phase reaction in Ar. After reaction at 800 °C, less than 1 at.% Mg was replaced by In in the MgB2 phase, without significant influence on its lattice parameters and only a slight decrease of its superconducting transition temperature. For all studied In concentrations in the nominal composition, the formation of InMg was evidenced by X-ray diffraction. The critical current density and accommodation field of the wires are decreased in the samples containing In. The flux pinning mechanism can be described by surface pinning in both the doped and undoped samples.

  16. Experimental Investigation of MGB2 Switching with Magnetic Pulses

    NASA Astrophysics Data System (ADS)

    Ishmael, S. A.; Leveque, J.; Netter, D.; Meinke, R. B.; Masson, P. J.

    2010-04-01

    Superconducting machines require DC current excitation in the rotor usually achieved using brushless exciters relying on solid state components for current rectification. The use of solid state components limits the amount of current allowable and imposes a large inductance in the rotor. MgB2 allows for "close to" superconducting splicing enabling development of large current rotors where solid state devices could be advantageously replaced by superconducting switches and used with a flux pump excitation system. For certain applications, such as a synchronous condenser, the dynamics of the excitation system is important as well as imposing fast switching and fast recovery. Switches driven by magnetic pulses are expected to exhibit a very limited temperature increase leading to fast recovery and also to contribute to very good system dynamics. This paper covers the experimental investigation of the response of MgB2 conductors subjected to magnetic pulses. The dependence of the resistance vs. J/Jc and operating temperature are discussed.

  17. MgB2 magnetometer with a directly coupled pick-up loop

    NASA Astrophysics Data System (ADS)

    Portesi, C.; Mijatovic, D.; Veldhuis, D.; Brinkman, A.; Monticone, E.; Gonnelli, R. S.

    2006-05-01

    In this work, we show the results obtained in the fabrication and characterization of an MgB2 magnetometer with a directly coupled pick-up loop. We used an all in situ technique for fabricating magnesium diboride films, which consists of the co-evaporation of B and Mg by means of an e-gun and a resistive heater respectively. Consequently, we realized the superconducting device, which incorporates two nanobridges as weak links in a superconducting loop. The nanobridges were realized by focused ion beam milling; they were 240 nm wide and had a critical current density of 107 A cm-2. The magnetometer was characterized at different temperatures and also measurements of the noise levels have been performed. The device shows Josephson quantum interference up to 20 K and the calculated effective area at low temperatures was 0.24 mm2. The transport properties of the magnetometer allow determining fundamental materials properties of the MgB2 thin films, such as the penetration depth.

  18. Fine-Filament MgB2 Superconductor Wire

    NASA Technical Reports Server (NTRS)

    Cantu, Sherrie

    2015-01-01

    Hyper Tech Research, Inc., has developed fine-filament magnesium diboride (MgB2) superconductor wire for motors and generators used in turboelectric aircraft propulsion systems. In Phase I of the project, Hyper Tech demonstrated that MgB2 multifilament wires (<10 micrometers) could reduce alternating current (AC) losses that occur due to hysteresis, eddy currents, and coupling losses. The company refined a manufacturing method that incorporates a magnesium-infiltration process and provides a tenfold enhancement in critical current density over wire made by a conventional method involving magnesium-boron powder mixtures. Hyper Tech also improved its wire-drawing capability to fabricate fine multifilament strands. In Phase II, the company developed, manufactured, and tested the wire for superconductor and engineering current density and AC losses. Hyper Tech also fabricated MgB2 rotor coil packs for a superconducting generator. The ultimate goal is to enable low-cost, round, lightweight, low-AC-loss superconductors for motor and generator stator coils operating at 25 K in next-generation turboelectric aircraft propulsion systems.

  19. Enhancement of the critical current density and flux pinning of MgB2 superconductor by nanoparticle SiC doping

    NASA Astrophysics Data System (ADS)

    Dou, S. X.; Soltanian, S.; Horvat, J.; Wang, X. L.; Zhou, S. H.; Ionescu, M.; Liu, H. K.; Munroe, P.; Tomsic, M.

    2002-10-01

    Doping of MgB2 by nano-SiC and its potential for the improvement of flux pinning were studied for MgB2-x)(SiCx/2 with x=0, 0.2, and 0.3 and for 10 wt % nano-SiC-doped MgB2 samples. Cosubstitution of B by Si and C counterbalanced the effects of single-element doping, decreasing Tc by only 1.5 K, introducing intragrain pinning centers effective at high fields and temperatures, and significantly enhancing Jc and Hirr. Compared to the undoped sample, Jc for the 10 wt % doped sample increased by a factor of 32 at 5 K and 8 T, 42 at 20 K and 5 T, and 14 at 30 K and 2 T. At 20 K and 2 T, the Jc for the doped sample was 2.4 x105 A/cm2, which is comparable to Jc values for the best Ag/Bi-2223 tapes. At 20 K and 4 T, Jc was twice as high as for the best MgB2 thin films and an order of magnitude higher than for the best Fe/MgB2 tapes. The magnetic Jc is consistent with the transport Jc which remains at 20 000 A/cm2 even at 10 T and 5 K for the doped sample, an order of magnitude higher than the undoped one. Because of such high performance, it is anticipated that the future MgB2 conductors will be made using a formula of MgBxSiyCz instead of pure MgB2.

  20. Thermal study of a cryogen-less MgB2 cavity

    NASA Astrophysics Data System (ADS)

    Holzbauer, J. P.; Nassiri, A.

    2014-12-01

    Recent efforts towards production of high-quality magnesium diboride (MgB2) coatings have raised the possibility of producing usable accelerating cavities. Work continues to reliably produce films of sufficient quality over the large, complex surface area of an accelerating cavity, but this technology would open many interesting technical opportunities. One of these is to replace the traditionally required liquid helium cryogenic systems with a dry system based on cryocoolers. This is made possible by the much higher Tc of MgB2, allowing operation closer to 30 K where cryocooler efficiency becomes competitive with alternative systems. This removes the need for pressure vessels in the cryomodule as well as internal distribution systems, greatly simplifying cryomodule design and fabrication. The lack of uniform cooling over the cavity surface, however, complicates behavior by coupling RF losses, heat leak, and cooling design in a way not seen in traditional SRF cavities. In this paper, these complexities are explored, including realistic cryocooler performance, temperature dependant RF losses, and standard thermal management challenges.

  1. In situ Pulsed Laser Deposition of C-Axis Oriented MgB2 Films and Their Characterization

    NASA Technical Reports Server (NTRS)

    Shinde, Sanjay; Lakew, Brook; Ogale, S. B.; Kulkarni, V. N.; Kale, S. N.; Venkatesan, T.

    2004-01-01

    The recent discovery of an intermetallic superconductor MgB2 has renewed interest in the area of superconductivity not only because of fundamental understanding of superconductivity but also due to its potential applicability in devices such as thermal detectors. Considerable amount of research has been devoted to obtain MgB2 films by an all in situ growth technique. We have grown MgB2 thin films by an all in situ pulsed laser deposition process from pure B and Mg targets. Ultrathin layers of B and Mg were deposited in a multilayer configuration. Hundreds of such Mg-B bilayers with a capping Mg layer on the top were deposited on sapphire substrate. These depositions were done in high vacuum (approx. 10(exp -7) Torr) and at room temperature. After deposition, such a configuration was annealed at high temperature for a short time in a forming gas (4% H2 in Ar). The best films, obtained by this procedure, showed superconducting transition temperature approx. 30 K. These films have been characterized by x-ray diffraction, Rutherford Backscattering Spectrometry, AC susceptibility-, resistivity- (with and without magnetic field) and 1/f noise-measurements. The physical properties of these films will be presented and discussed.

  2. Fast creation of dense MgB2 phase in wires made by IMD process

    NASA Astrophysics Data System (ADS)

    Kováč, P.; Hušek, I.; Melišek, T.; Kopera, L.; Kulich, M.

    2016-10-01

    Single-core MgB2 wires have been made by internal magnesium diffusion (IMD) into boron process. Heat treatments were performed at variable periods (4-90 min) for two adjusted temperatures 635 °C and 650 °C, with an overshoot of ≈20 °C after 5 min. Critical currents of differently treated MgB2/Ti/GlidCop wires have been measured and related with the MgB2 layers. The fast creation MgB2 compound has been observed after 8 min annealing at both temperatures and showing the critical current maxima. The less uniform MgB2 containing cracks was created for longer annealing periods (≥10 min), which resulted in lowered critical currents and worsened thermal stability. The fast creation of dense MgB2 allows it to utilize a continual and short heat treatment process for high current density wires made by IMD.

  3. Al-doped MgB2 materials studied using electron paramagnetic resonance and Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Bateni, Ali; Erdem, Emre; Repp, Sergej; Weber, Stefan; Somer, Mehmet

    2016-05-01

    Undoped and aluminum (Al) doped magnesium diboride (MgB2) samples were synthesized using a high-temperature solid-state synthesis method. The microscopic defect structures of Al-doped MgB2 samples were systematically investigated using X-ray powder diffraction, Raman spectroscopy, and electron paramagnetic resonance. It was found that Mg-vacancies are responsible for defect-induced peculiarities in MgB2. Above a certain level of Al doping, enhanced conductive properties of MgB2 disappear due to filling of vacancies or trapping of Al in Mg-related vacancy sites.

  4. Broadband MgB2 Hot-Electron Bolometer THz Mixers Operating up to 20 K

    NASA Astrophysics Data System (ADS)

    Novoselov, Evgenii; Cherednichenko, Sergey

    2017-01-01

    We discuss performance of submicron size hot-electron bolometer mixers made from thin MgB2 superconducting films. With a superconducting transition temperature of ∼30 K, such terahertz (THz) mixers can operate with high sensitivity at temperatures up to 20 K. Due to very small dimensions local oscillator power requirements are rather low. In the intermediate frequency band of 1-3 GHz, the double sideband receiver noise temperature is 1600 K at 10 K operation temperature, 2000 K at 15 K, 2500-3000 K at 20 K. The gain bandwidth of such devices is 6 GHz and the noise bandwidth is estimated to be 6-8 GHz.

  5. Physical property characterization of bulk MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Awana, V. P. S.; Vajpayee, A.; Mudgel, M.; Ganesan, V.; Awasthi, A. M.; Bhalla, G. L.; Kishan, H.

    2008-04-01

    We report synthesis, structure/micro-structure, resistivity under magnetic field [ρ(T)H], Raman spectra, thermoelectric power S(T), thermal conductivity κ(T), and magnetization of ambient pressure argon annealed polycrystalline bulk samples of MgB2, processed under identical conditions. The compound crystallizes in hexagonal structure with space group P6/mmm. Transmission electron microscopy ( TEM) reveals electron micrographs showing various types of defect features along with the presence of 3 4 nm thick amorphous layers forming the grain boundaries of otherwise crystalline MgB2. Raman spectra of the compound at room temperature exhibited characteristic phonon peak at 600 cm-1. Superconductivity is observed at 37.2 K by magnetic susceptibility χ(T), resistivity ρ(T), thermoelectric power S(T), and thermal conductivity κ(T) measurements. The power law fitting of ρ(T) give rise to Debye temperature (ΘD) at 1400 K which is found consistent with the theoretical fitting of S(T), exhibiting Θ D of 1410 K and carrier density of 3.81 × 1028/m3. Thermal conductivity κ(T) shows a jump at 38 K, i.e., at Tc, which was missing in some earlier reports. Critical current density (Jc) of up to 105 A/cm2 in 1 2 T (Tesla) fields at temperatures (T) of up to 10 K is seen from magnetization measurements. The irreversibility field, defined as the field related to merging of M(H) loops is found to be 78, 68 and 42 kOe at 4, 10 and 20 K respectively. The superconducting performance parameters viz. irreversibility field (Hirr) and critical current density Jc(H) of the studied MgB2 are improved profoundly with addition of nano-SiC and nano-diamond. The physical property parameters measured for polycrystalline MgB2 are compared with earlier reports and a consolidated insight of various physical properties is presented.

  6. Andreev reflections on a MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Aswal, D. K.; Sen, Shashwati; Gadkari, S. C.; Singh, Ajay; Gupta, S. K.; Gupta, L. C.; Bajpai, A.; Nigam, A. K.

    2002-07-01

    An Andreev-reflection study of MgB2/Ag planar junctions as a function of temperature and magnetic field is reported. The differential resistance (dV/dI) versus voltage (V) characteristics exhibited a distinct double minimum feature. This, together with a comparison of Blonder-Tinkham-Klapwijk theory of isotropic superconductor, indicates that data are not consistent with the weak-coupling BCS theory. This is further supported by unusual temperature and magnetic-field dependence of the tunneling characteristics. The results are discussed using various existing theories.

  7. Low-noise THz MgB2 Josephson mixer

    NASA Astrophysics Data System (ADS)

    Cunnane, Daniel; Kawamura, Jonathan H.; Acharya, Narendra; Wolak, Matthäus A.; Xi, X. X.; Karasik, Boris S.

    2016-09-01

    The potential applications for high frequency operation of the Josephson effect in MgB2 include THz mixers, direct detectors, and digital circuits. Here we report on MgB2 weak links which exhibit the Josephson behavior up to almost 2 THz and using them for low-noise heterodyne detection of THz radiation. The devices are made from epitaxial film grown in the c-axis direction by the hybrid physical-chemical vapor deposition method. The current in the junctions travels parallel to the surface of the film, thus making possible a large contribution of the quasi-two-dimensional σ-gap in transport across the weak link. These devices are connected to a planar spiral antenna with a dielectric substrate lens to facilitate coupling to free-space radiation for use as a detector. The IcRn product of the junction is 5.25 mV, giving confirmation of a large gap parameter. The sensitivity of the mixer was measured from 0.6 THz to 1.9 THz. At a bath temperature of over 20 K, a mixer noise temperature less than 2000 K (DSB) was measured near 0.6 THz.

  8. A 2-D Array of Superconducting Magnesium Diboride (MgB2) Far-IR Thermal Detectors for Planetary Exploration

    NASA Technical Reports Server (NTRS)

    Lakew, Brook

    2009-01-01

    A 2-D array of superconducting Magnesium Diboride(MgB2) far IR thermal detectors has been fabricated. Such an array is intended to be at the focal plane of future generation thermal imaging far-IR instruments that will investigate the outer planets and their icy moons. Fabrication and processing of the pixels of the array as well as noise characterization of architectured MgB2 thin films will be presented. Challenges and solutions for improving the performance of the array will be discussed.

  9. High Upper Critical Field and Irreversibility Field in MgB2 Coated-Conductor Fibers

    DTIC Science & Technology

    2016-06-13

    for MgB2 by sputtering on Hastelloy 9 and by electroplating on stainless steel .10 These works have gener- ated Hc2 and Hirr values similar to those of...wires because it is brittle and costly, MgB2 coatings can be made on inexpensive and strong metallic wires such as stainless steel .10,26 Therefore

  10. Experimental characterization of the constitutive materials of MgB2 multi-filamentary wires for the development of 3D numerical models

    NASA Astrophysics Data System (ADS)

    Escamez, Guillaume; Sirois, Frédéric; Tousignant, Maxime; Badel, Arnaud; Granger, Capucine; Tixador, Pascal; Bruzek, Christian-Éric

    2017-03-01

    Today MgB2 superconducting wires can be manufactured in long lengths at low cost, which makes this material a good candidate for large scale applications. However, because of its relatively low critical temperature (less than 40 K), it is necessary to operate MgB2 devices in a liquid or gaseous helium environment. In this context, losses in the cryogenic environment must be rigorously minimized, otherwise the use of a superconductor is not worthy. An accurate estimation of the losses at the design stage is therefore mandatory in order to allow determining the device architecture that minimizes the losses. In this paper, we present a complete a 3D finite element model of a 36-filament MgB2 wire based on the architecture of the Italian manufacturer Colombus. In order for the model to be as accurate as possible, we made a substantial effort to characterize all constitutive materials of the wire, namely the E–J characteristics of the MgB2 filaments and the electric and magnetic properties (B‑H curves) of nickel and monel, which are the two major non-superconducting components of the wire. All properties were characterized as a function of temperature and magnetic field. Limitations of the characterization and of the model are discussed, in particular the difficulty to extract the maximum relative permeability of nickel and monel from the experimental data, as well as the lack of a thin conductive layer model in the 3D finite element method, which prevents us from taking into account the resistive barriers around the MgB2 filaments in the matrix. Two examples of numerical simulations are provided to illustrate the capabilities of the model in its current state.

  11. Magnetic flux noise in MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Khare, Neeraj; Singh, D. P.; Gupta, Ajai K.

    2008-05-01

    Magnetic flux noise in MgB2 polycrystalline sample is measured using a high-TC rf-superconducting quantum interference device in the temperature range of 6-40K. A small magnetic field (˜200mG ) was applied while cooling the sample. The flux noise exhibits 1/fα type of behavior with α ˜1.0-1.3 and shows enhanced noise around 24 and 37K. The flux noise seems to originate from thermally activated vortex hopping. The large magnetic noise at 24K indicates the presence of larger density of pinning sites with energies ˜0.061eV leading to enhanced magnetic fluctuations at temperatures much below TC.

  12. Substitution Effects on MgB2 Superconductivity

    NASA Astrophysics Data System (ADS)

    Liu, Juan; Zhao, Yuan; Yi, Lin

    2008-02-01

    With the help of supercell method, the first-principle calculations were performed for the study of doping crystal Mg1-xAlxB2 and Mg(B1-yCy)2. Analyzing the variations of the charge distribution and the partial densities of states, we found that the compounds with doping Al to MgB2 compound and/or replacing boron by carbon exhibit new covalent bond effects and unexpected electronic properties, related to superconductivity. The study of the density of states indicates that superconductivity decreases with the increase of Al fraction and carbon concentration. There exists a transition of superconductor to non-superconductor with the change of Al doping fraction. The substitution of boron by carbon results in the decrease of the transition temperature since the decrease of the electron concentration and the lattice constant. The theoretical predictions agree with experimental observations.

  13. Superconductivity of MgB2: covalent bonds driven metallic.

    PubMed

    An, J M; Pickett, W E

    2001-05-07

    A series of calculations on MgB2 and related isoelectronic systems indicates that the layer of Mg2+ ions lowers the nonbonding B pi ( p(z)) bands relative to the bonding sigma ( sp(x)p(y)) bands compared to graphite, causing sigma-->pi charge transfer and sigma band doping of 0.13 holes/cell. Because of their two dimensionality the sigma bands contribute strongly to the Fermi level density of states. Calculated deformation potentials of gamma point phonons identify the B bond stretching modes as dominating the electron-phonon coupling. Superconductivity driven by sigma band holes is consistent with the report of destruction of superconductivity by doping with Al.

  14. MgB2 superconductors with abnormally improved Jc sintered after autoxidation of milled original powders

    NASA Astrophysics Data System (ADS)

    Ma, Zongqing; Liu, Yongchang; Huo, Jie; Gao, Zhiming

    2009-12-01

    An autoxidation treatment of short-time milled original powders was introduced for the synthesis of MgB2 superconductors and the critical current density Jc of the sintered MgB2 bulks was measured. It is unusually found that the undoped MgB2 bulks sintered with those autoxided milled original powder exhibit abnormally excellent Jc (above 1×104 A cm-2 even at 3.5 T, 20 K). Combined with the investigation of sintering process, it was found that the autoxidation treatment of the milled powders affects the subsequent sintering process dramatically and finally leads to the formation of MgB2 nanocrystalline with lots of dislocation and self-generated MgO nanoinclusions embedded in them. This unique microstructure brought up a significant improvement of Jc at high fields. Besides, the formation mechanism of this unique microstructure during the sintering process was also discussed in detail. It suggested that the MgO preformed by the reaction between Mg and B2O3 in the interface between Mg particles and B particles might serve as nuclei for the heterogeneous nucleation of the MgB2 phase and finally be included in the MgB2 grains as they grew up. The present method provides possible windows for the development of practical MgB2 superconductors without adopting expensive nanodopants.

  15. Phase transitions in a MgB2 granular BCS superconductor in weak magnetic fields

    NASA Astrophysics Data System (ADS)

    Derevyanko, V. V.; Sungurov, M. S.; Sukhareva, T. V.; Finkel', V. A.; Shakhov, Yu. N.

    2017-02-01

    The character of temperature dependences of the electric conductivity of MgB2 granular BCS superconductors at temperatures of 35-45 K in external magnetic fields H ext of up to 2 kOe is studied. An increase in the superconducting transition width Δ T c with an increase in Hext is found. The presence of a system of weak links in MgB2-based granular superconductors is established. On the basis of experimental data, MgB2 granular superconductor is assigned to two-level superconducting systems and the H-T phase diagram is constructed.

  16. Low-temperature Mechanical Properties of Bulk MgB2 Fabricated by Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Murakami, A.; Teshima, H.; Naito, T.; Fujishiro, H.; Kudo, T.; Iwamoto, A.

    Mechanical properties ina MgB2superconducting bulk sample,whose packing ratio is 92%,fabricated by hot isostatic pressing (HIP)areevaluated at 77 K through bending tests.The fracture strength at 77 K is higher than at room temperature. From the bending test result at 77 K, the fracture strength of ideal bulk MgB2,whose packing ratio is 100%,is estimated. The fracture strength at very low temperature of the HIP bulk MgB2is also estimated from the bending test results at 77 K and room temperature.

  17. Improving magnetic properties of MgB2 bulk superconductors by synthetic engine oil treatment

    NASA Astrophysics Data System (ADS)

    Taylan Koparan, E.; Savaskan, B.; Yanmaz, E.

    2016-08-01

    The present study focuses on the effects of standby time of the MgB2 samples immersed in synthetic engine oil on the critical current density (Jc(H)), magnetic field dependence of the pinning force density fp(b) and Tc performances of MgB2 bulk superconductors. Synthetic engine oil was used as a product which is cheap and a rich carbon source. Manufactured MgB2 pellet samples were immersed at different standby time of 30 min, 120 min, 300 min and 1440 min in synthetic engine oil after the first heating process. Finally, MgB2 samples immersed in synthetic engine oil were sintered at 1000 °C and kept for 15 min in Ar atmosphere. The critical current density of all of MgB2 samples immersed at different standby time in engine oil in whole field range was better than that of the pure MgB2 sample because of the number of the pinning centers. The MgB2 sample immersed at 300 min standby time in synthetic engine oil has the best performance compared to other samples. The Jc value for the pure sample is 2.0 × 103 A/cm2, whereas for the MgB2 sample immersed at 300 min standby time in engine oil the Jc is enhanced to 4.8 × 103A/cm2 at 5 K and 3 T. The superconducting transition temperature (Tc) did not change with the increasing standby time of the samples in synthetic engine oil at all. The best diamagnetic property was obtained from the sample which kept in synthetic engine oil for 300 min. Synthetic engine oil treatment results in remarkable improvement of the critical current density and pinning force performances of MgB2 superconductors. It was found that all MgB2 samples have a different pinning property at different measuring temperatures. Using synthetic engine oil as a product which is cheap and a rich carbon source in MgB2 bulk superconductors makes MgB2 samples immersed in synthetic engine oil a good candidate for industrial applications.

  18. Superior homogeneity of trapped magnetic field in superconducting MgB2 bulk magnets

    NASA Astrophysics Data System (ADS)

    Ishihara, A.; Akasaka, T.; Tomita, M.; Kishio, K.

    2017-03-01

    Homogeneity of trapped magnetic field in radial and circumferential directions of high temperature superconducting bulk magnets, MgB2 (T c ˜38.3 K) and YBa2Cu3O y (T c ˜91.5 K), have been measured. In polycrystalline MgB2 bulks, the circularity of trapped magnetic field in a cylindrical disk is over 97% at 20-32.5 K, while that of YBa2Cu3O y was ˜87% at 77 K. Magnetic field distribution of MgB2 bulk was satisfactorily homogeneous and these measurements suggest MgB2 bulks with highly efficient cryocoolers should be very useful for novel high field permanent magnet applications.

  19. In situ synthesis of superconducting MgB2 fibers within a magnesium matrix

    NASA Astrophysics Data System (ADS)

    DeFouw, John D.; Dunand, David C.

    2003-07-01

    Composite wires, consisting of several hundred continuous MgB2 fibers embedded within an Mg matrix, are produced by a casting method, whereby liquid Mg is pressure infiltrated into a preform of aligned B fibers which are subsequently reacted in situ to form MgB2 fibers. Despite defects in the form of small, unreacted B islands and radial cracks from volume expansion, the MgB2 fibers exhibit superconducting properties (Tc=39 K and Jc=360 kA/cm2 at 5 K) comparable to the best results published for bulk MgB2. The fibers are cylindrical and straight, allowing high packing densities within a mechanically tough, thermally dissipating, electrically conductive Mg matrix. The process is scalable to continuous lengths of superconducting Mg/MgB2 wires.

  20. Superconducting characteristics of short MgB2 wires of long level sensor for liquid hydrogen

    NASA Astrophysics Data System (ADS)

    Takeda, M.; Inoue, Y.; Maekawa, K.; Matsuno, Y.; Fujikawa, S.; Kumakura, H.

    2015-12-01

    To establish the worldwide storage and marine transport of hydrogen, it is important to develop a high-precision and long level sensor, such as a superconducting magnesium diboride (MgB2) level sensor for large liquid hydrogen (LH2) tanks on board ships. Three 1.7- m-long MgB2 wires were fabricated by an in situ method, and the superconducting characteristics of twenty-four 20-mm-long MgB2 wires on the 1.7-m-long wires were studied. In addition, the static level-detecting characteristics of five 500-mm-long MgB2 level sensors were evaluated under atmospheric pressure.

  1. Ex situ MgB2 barrier behavior of monofilament in situ MgB2 wires with Glidcop® sheath material

    NASA Astrophysics Data System (ADS)

    Kario, A.; Morawski, A.; Häßler, W.; Nenkov, K.; Schubert, M.; Herrmann, M.; Ringsdorf, B.; Schlachter, S. I.; Goldacker, W.; Holzapfel, B.; Schultz, L.

    2010-11-01

    Cost-effective MgB2 wires are highly sought after to replace the widely used NbTi conductors in superconducting magnets, e.g. for magnetic resonance imaging (MRI). One method of choice for lowering conductor costs is to use a less expensive barrier and sheath material. From this point of view copper is a good candidate for the sheath, and additionally has other advantageous properties, e.g. the best electrical and thermal conductivity at operating temperature. One major disadvantage of copper is its high chemical reactivity. This material reacts fast with magnesium and forms Mg-Cu alloys, removing the starting element necessary for MgB2 formation. To prevent this reaction, a special coaxial architecture was applied using ex situ MgB2 powder as a chemical barrier between the copper sheath and the in situ MgB2 powder core. The Glidcop® (dispersed strengthened copper) sheathed MgB2 wires with an ex situ barrier have been fabricated by the conventional powder in tube (PIT) method. Besides avoiding the reaction of Mg and Cu, the barrier also contributes to the superconducting core fraction and increases the filling factor up to 50%. The Glidcop® sheathed wires with an ex situ MgB2 commercial powder used as a barrier have been successfully drawn to a diameter of 1.2 mm and then a pressure-assisted heat treatment was applied. For our case of specified in situ and ex situ powders the pressure-assisted preparation of at least 0.15 GPa was found to be important for the densification of the ex situ barrier.

  2. Lightweight MgB2 superconducting 10 MW wind generator

    NASA Astrophysics Data System (ADS)

    Marino, I.; Pujana, A.; Sarmiento, G.; Sanz, S.; Merino, J. M.; Tropeano, M.; Sun, J.; Canosa, T.

    2016-02-01

    The offshore wind market demands a higher power rate and more reliable turbines in order to optimize capital and operational costs. The state-of-the-art shows that both geared and direct-drive conventional generators are difficult to scale up to 10 MW and beyond due to their huge size and weight. Superconducting direct-drive wind generators are considered a promising solution to achieve lighter weight machines. This work presents an innovative 10 MW 8.1 rpm direct-drive partial superconducting generator using MgB2 wire for the field coils. It has a warm iron rotor configuration with the superconducting coils working at 20 K while the rotor core and the armature are at ambient temperature. A cooling system based on cryocoolers installed in the rotor extracts the heat from the superconducting coils by conduction. The generator's main parameters are compared against a permanent magnet reference machine, showing a significant weight and size reduction. The 10 MW superconducting generator concept will be experimentally validated with a small-scale magnetic machine, which has innovative components such as superconducting coils, modular cryostats and cooling systems, and will have similar size and characteristics as the 10 MW generator.

  3. High critical currents in iron-clad superconducting MgB2 wires.

    PubMed

    Jin, S; Mavoori, H; Bower, C; van Dover, R B

    2001-05-31

    Technically useful bulk superconductors must have high transport critical current densities, Jc, at operating temperatures. They also require a normal metal cladding to provide parallel electrical conduction, thermal stabilization, and mechanical protection of the generally brittle superconductor cores. The recent discovery of superconductivity at 39 K in magnesium diboride (MgB2) presents a new possibility for significant bulk applications, but many critical issues relevant for practical wires remain unresolved. In particular, MgB2 is mechanically hard and brittle and therefore not amenable to drawing into the desired fine-wire geometry. Even the synthesis of moderately dense, bulk MgB2 attaining 39 K superconductivity is a challenge because of the volatility and reactivity of magnesium. Here we report the successful fabrication of dense, metal-clad superconducting MgB2 wires, and demonstrate a transport Jc in excess of 85,000 A cm-2 at 4.2 K. Our iron-clad fabrication technique takes place at ambient pressure, yet produces dense MgB2 with little loss of stoichiometry. While searching for a suitable cladding material, we found that other materials dramatically reduced the critical current, showing that although MgB2 itself does not show the 'weak-link' effect characteristic of the high-Tc superconductors, contamination does result in weak-link-like behaviour.

  4. Direct evidence for two-band superconductivity in MgB2 single crystals from directional point-contact spectroscopy in magnetic fields.

    PubMed

    Gonnelli, R S; Daghero, D; Ummarino, G A; Stepanov, V A; Jun, J; Kazakov, S M; Karpinski, J

    2002-12-09

    We present the results of the first directional point-contact spectroscopy experiments in high-quality MgB2 single crystals. Because of the directionality of the current injection into the samples, the application of a magnetic field allowed us to separate the contributions of the sigma and pi bands to the total conductance of our point contacts. By using this technique, we were able to obtain the temperature dependency of each gap independent of the other. The consequent, strong reduction of the error on the value of the gap amplitude as a function of temperature allows a stricter test of the predictions of the two-band model for MgB2.

  5. A new scaling relation for n-AlN doped superconducting MgB2

    NASA Astrophysics Data System (ADS)

    Tripathi, D.; Dey, T. K.

    2013-09-01

    The scaling behavior of nano-aluminum nitride added polycrystalline MgB2 superconductor is discussed. A series of polycrystalline MgB2 samples with different amounts of nanosized AlN addition are synthesized by solid reaction. All the synthesized pellets are subjected to x-ray diffraction, field emission gun scanning electron microscopy (FEG-SEM), and transmission electron microscopy (TEM) to examine their micro-structural features. A marginal decrease in lattice parameters of pure MgB2 with AlN nanoparticles addition is observed. Surface morphology reveals randomly oriented hexagonal MgB2 grains decorated with AlN nanoparticles between the grain boundaries and also scattered on the grain surface. For higher concentration, n-AlN agglomerates are visible. Resistivity data confirm a decrease in superconducting transition temperature (Tc) from 38.5 to 37 K and increase in transition width (ΔTc) with increased loading of n-AlN in MgB2. The critical current density (Jc) of the pellets at 4, 10, 20, and 30 K is evaluated from the magnetization data between ±6 T and is explained well in the framework of collective pinning model. The normalized pinning force density of n-AlN doped MgB2 at various temperatures indicates an excellent scaling with respect to Hn (the field corresponding to which Fp drops to half of its maximum value) as the scaling field. A new scaling expression derived, using the expression of field dependence of Jc proposed by "collective pinning model" in small bundle regime, demonstrates an excellent agreement with the measured normalized pinning force density (viz., Fp/Fpmax vs. hn) of the AlN nanoparticles doped MgB2 superconductors.

  6. TOPICAL REVIEW: The widely variable resistivity of MgB2 samples

    NASA Astrophysics Data System (ADS)

    Rowell, John M.

    2003-06-01

    In this brief review, I consider a rather mundane property of MgB2, namely its resistivity as a function of temperature. It turns out that a comparison of resistivity data for a wide variety of samples, from single crystals to films, wires and polycrystalline bulk, is surprisingly informative. The majority of samples of MgB2 exhibit resistivities that are much higher than the low values that are seen in a relatively small number of single crystals, bulk samples and films. In many cases, the resistivity is increased over the single crystal values by orders of magnitude. Even at these high values, there is often still a metallic temperature dependence of the resistivity, and surprisingly, Tc is often at or near the bulk value of 39 K. The resistivity increase has been ascribed to a reduction in the effective current-carrying cross-sectional area of the sample. If this loss of cross-sectional area is the dominant factor contributing to the increase in resistivity of MgB2 samples, then the critical current density must be decreased by the same loss in the effective area. Comparisons of the MgB2 resistivity with the properties of disordered 'cluster compound' superconductors, of HTS materials and of granular Al (heavily contaminated with oxygen), show similarities between the MgB2 behaviour and the results of the HTS and Al studies. I discuss various effects that might contribute to the reduction in effective sample area in MgB2 samples, to the increase in resistivity and to a reduction in Jc. I speculate that a Josephson junction model of the grain boundaries in MgB2 might apply to samples with extremely high resistivities. Alternatively, it has been suggested that the two-band nature of MgB2 can result in an unusual behaviour of its resistivity and Tc as the material changes from the 'clean' to 'dirty' limits. I conclude that measurements of both the resistivity and the transport critical current density in a wide variety of bulk and film samples would be very useful, as would a study of the resistivity and Jc changes as a function of irradiation damage in MgB2 bulk and films of initially low resistivity.

  7. The phase analysis of spark plasma sintered MgB2 after ball milling.

    PubMed

    Kang, Deuk-Kyun; Kim, Dong-Woong; Kim, Cheol-Jin; Ahn, In-Shup

    2010-01-01

    Mg and amorphous B powders below 10 and 3 micro meter were used as raw materials, and mixed by planetary-mill for 9 hours at argon atmosphere. MgB2 bulk was fabricated at the various temperatures by Spark Plasma Sintering. In the sintering process, mixed powders were sintered in graphite mold, at the pressure of 55 Mpa. The fabricated MgB2 samples were evaluated with XRD, EDS, FE-SEM, PPMS. MgB2, MgO and Fe phases were observed from XRD result. In the results, MgO and Fe were impurity which may affect superconducting properties of MgB2 samples, and it's distribution could be confirmed from EDS mapping result. In order to confirm the formation of MgB2 phase, DTA was used as heating rate of 10 degrees C/min at Ar atmosphere from room temperature to 1200 degrees C. In the PPMS result, the Tc (critical temperature) was about 21 K, and the density of spark plasma sintered samples increased to 1.87 g/cm3 by increasing sintering temperature.

  8. Low-temperature synthesis of MgB2 via powder metallurgy processing

    NASA Astrophysics Data System (ADS)

    Birol, Yucel

    2016-12-01

    Ball-milled Mg/B2O3 powder blends reveal interpenetrating layers of deformed magnesium and boron oxide grains that are increasingly refined with increasing milling time. Boron oxide is reduced by Mg and MgO thus formed reacts with the remaining B2O3 to produce Mg3(BO3)2 during ball milling for 30 min. Both B2O3 and Mg3(BO3)2 react with Mg to produce MgB2 upon further ball milling. An annealing treatment can be employed when ball milling is performed for less than 1 h as thermal exposure of the ball-milled Mg/B2O3 powder blends also leads to the formation of MgB2. The above reactions take place between 500 and 700 °C when the Mg/B2O3 powder blend is ball milled for 30 min, and between 450 and 550 °C, after ball milling for 1 h. This is a very attractive route owing to processing temperatures where the volatility of Mg is no longer a problem.

  9. Effects of Metal Powder Addition in Ni-Sheathed PIT MgB2 Tapes

    NASA Astrophysics Data System (ADS)

    Tachikawa, K.; Yamada, Y.; Katagiri, K.; Kumakura, H.; Iwamoto, A.; Watanabe, K.

    2004-06-01

    The effect of different metal powder additions on the transport current and stress/strain performance of ex-situ processed MgB2 tapes with Ni sheath has been studied. The metal powder added to the core exhibits elongated morphology after the fabrication. The addition of low melting point metal powder, e.g. In and Sn, produces an appreciable increase in the Jc of MgB2 core. An addition of 10 vol% In enhances Jc by a factor of 6 to 7 after the combination of rolling and annealing at 200 °C, up to the order of 105 A/cm2 at 0.5 T and 4.2 K. An addition of 10 vol% Sn enhances Jc by a factor of ˜ 3. The In and Sn additions also appreciably increase the n-value of the current-voltage transition. Both In and Sn metals infiltrate into gaps between MgB2 grains, improving the linkage of the grains. Current may transfer through the impregnated metal by the proximity effect. Furthermore, the metal powder addition appreciably improves the strain tolerance in MgB2 tapes. The low melting point metal powder addition is a relatively simple and easy approach to yield better transport current and stress/strain performance in ex-situ MgB2 tapes.

  10. Critical current density and grain connectivity of Bi-2223 added MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Tripathi, D.; Dey, T. K.

    2014-04-01

    Polycrystalline MgB2 with addition of 0, 1, 3, and 5 wt. % of Bi-2223(Bi1.8Pb0.26Sr2Ca2Cu3O10+x) powder has been synthesized by solid reaction process. The effect of Bi-2223 addition on current transport and superconducting properties of polycrystalline MgB2 superconductor is discussed. Four probe DC resistivity measurement shows that low level of Bi-2223 addition hardly affects the superconducting transition temperature, Tc of MgB2. The modified Bloch- Gruneisen (B-G) analysis of normal state resistivity data reveals a decrease in intergrain connectivity and increase in intragrain connectivity of MgB2 by Bi-2223 addition. The critical current density of present set of samples is estimated from M- H hysteresis loop in the light of Bean's model. MgB2 added with 1 wt. % of Bi- 2223 added gives the best performance (˜ 2 times enhancement in Jc) amongst the studied samples.

  11. Copper sheath MgB 2 wires fabricated by an in situ PIT method

    NASA Astrophysics Data System (ADS)

    Shimura, S.; Machi, T.; Murakami, M.; Koshizuka, N.; Mochizuki, K.; Ishikawa, I.; Shibata, N.

    2004-10-01

    We investigated the applicability of Cu as sheath materials for MgB 2 wires prepared by in situ PIT (powder-in-tube) method in comparison with stainless steal. Since the critical current density of MgB 2 increases with TiH 2 doping, we prepared TiH 2 doped MgB 2 Cu sheath wires 40 m in length and ∅ 1.0 mm or 0.5 × 1.0 mm 2 in cross section by rotary swaging, drawing, and two-axial rolling under cold working. We then annealed the samples at 600-850 °C for 1-2 h in Ar gas atmosphere. The critical current of TiH 2 (6%) doped MgB 2/Cu short sample annealed at 650 °C reached 208 A ( Jc=230 kA/cm 2) at 4.2 K and self-field. We also fabricated several coils using these wires. The Ic value was ∼100 A at 4.2 K for a coil prepared with use of a 5 m length wire. These results suggest that it is possible to fabricate Cu sheathed MgB 2 wires with good performance by using the in situ PIT method.

  12. Preferentially grown nanostructured MgB2C2: A new material for lightening applications

    NASA Astrophysics Data System (ADS)

    Singh, Paviter; Singh, Kulwinder; Kaur, Manpreet; Kaur, Harpreet; Singh, Bikmramjeet; Kaur, Gurpreet; Kaur, Manjot; Kumar, Manjeet; Kaur, Kamalpreet; Bala, Rajni; Kumar, Akshay

    2017-03-01

    Nanostructured MgB2C2 is a promising candidate as functional material. High Temperature synthesis conditions were the limitations for its exploitation in materials research. Present study deals with the synthesis of specifically oriented nanostructured MgB2C2 at relatively low temperature by solvothermal route. The synthesis conditions are modified to grow these nanostructures in least dense plane (002). Optical properties are explored for the first time. XRD analysis confirms the formation of MgB2C2 phase. Morphological analysis (Transmission/Scanning Electron Microscopy) indicated that the synthesized material is in nano range. Photoluminescence study shows that the synthesized material emits light in visible spectrum when excited at 380 nm. The quantum efficiency of synthesized material calculated by De Mello's method is approximately 23% which makes the material efficient enough for lightening applications.

  13. Three-dimensional MgB2-type superconductivity in hole-doped diamond.

    PubMed

    Boeri, Lilia; Kortus, Jens; Andersen, O K

    2004-12-03

    We substantiate by numerical and analytical calculations that the recently discovered superconductivity below 4 K in 3% boron-doped diamond is caused by electron-phonon coupling of the same type as in MgB2, albeit in three dimensions. Holes at the top of the zone-centered, degenerate sigma-bonding valence-band couple strongly to the optical bond-stretching modes. The increase from two to three dimensions reduces the mode softening crucial for T(c) reaching 40 K in MgB2. Even if diamond had the same bare coupling constant as MgB2, which could be achieved with 10% doping, T(c) would be only 25 K. Superconductivity above 1 K in Si (Ge) requires hole doping beyond 5% (10%).

  14. Superconductivity of MgB 2 with embedded multiwall carbon nanotube

    NASA Astrophysics Data System (ADS)

    Kim, J. H.; Yeoh, W. K.; Xu, X.; Dou, S. X.; Munroe, P.; Rindfleisch, M.; Tomsic, M.

    2006-11-01

    We studied the effects of MgB2 with embedded multiwall carbon nanotubes (MWCNTs) on the crystallinity, lattice parameters, critical current density (Jc), upper critical field (Hc2), irreversibility field (Hirr), and microstructure of MgB2. Fe sheathed un-doped and MWCNT doped MgB2 wires were fabricated by the powder-in-tube (PIT) method and sintered at the high sintering temperatures of 900 °C. We observed that for the MWCNT doped sample high temperature sintering resulted in depressed crystallinity, shrinkage of the a-lattice parameter, higher Jc up to 12 T, and lower critical temperature (Tc) values. Specifically, MWCNT doped samples sintered at 900 °C exhibited excellent Jc, ∼104 A cm-2 up to 9 T at 4.2 K. This can be explained by lattice distortion and poor crystallinity due to carbon (C) substitution from the MWCNT.

  15. Suppression of superconductivity in epitaxial MgB2 ultrathin films

    NASA Astrophysics Data System (ADS)

    Zhang, Chen; Wang, Yue; Wang, Da; Zhang, Yan; Liu, Zheng-Hao; Feng, Qing-Rong; Gan, Zi-Zhao

    2013-07-01

    MgB2 ultrathin films have potential to make sensitive superconducting devices such as superconducting single-photon detectors working at relatively high temperatures. We have grown epitaxial MgB2 films in thicknesses ranging from about 40 nm to 6 nm by using the hybrid physical-chemical vapor deposition method and performed electrical transport measurements to study the thickness dependence of the superconducting critical temperature Tc. With reducing film thickness d, although a weak depression of the Tc has been observed, which could be attributed to an increase of disorder (interband impurity scattering) in the film, the Tc retains close to the bulk value of MgB2 (39 K), being about 35 K in the film of 6 nm thick. We show that this result, beneficial to the application of MgB2 ultrathin films and in accordance with recent theoretical calculations, is in contrast to previous findings in MgB2 films prepared by other methods such as co-evaporation and molecular-beam epitaxy, where a severe Tc suppression has been observed with Tc about one third of the bulk value in films of ˜5 nm thick. We discuss this apparent discrepancy in experiments and suggest that, towards the ultrathin limit, the different degrees of Tc suppression displayed in currently obtained MgB2 films by various techniques may arise from the different levels of disorder present in the film or different extents of proximity effect at the film surface or film-substrate interface.

  16. Low-Temperature Synthesis of Superconducting Nanocrystalline MgB 2

    DOE PAGES

    Lu, Jun; Xiao, Zhili; Lin, Qiyin; ...

    2010-01-01

    Magnesium diboride (MgB 2 ) is considered a promising material for practical application in superconducting devices, with a transition temperature near 40 K. In the present paper, nanocrystalline MgB 2 with an average particle size of approximately 70 nm is synthesized by reacting LiBH 4 with MgH 2 at temperatures as low as 450 ° C. This synthesis approach successfully bypasses the usage of either elemental boron or toxic diborane gas. The superconductivity of the nanostructures is confirmed by magnetization measurements, showing a superconducting critical temperature of 38.7 K.

  17. Preparation of MgB2 superconducting microbridges by focused ion beam direct milling

    NASA Astrophysics Data System (ADS)

    Zhang, Xuena; Li, Yanli; Xu, Zhuang; Kong, Xiangdong; Han, Li

    2017-01-01

    MgB2 superconducting microbridges were prepared by focused ion beam (FIB) direct milling on MgB2 films. The surface topography of the microbridges were observed using SEM and AFM and the superconductivity was measured in this paper. Lots of cracks and holes were found near the milled area. And the superconducting transition temperature was decreased a lot and the bridges prepared were not superconducting due to ion damage after milled with large dose. Through these works, we explored the effect regular of FIB milling and experimental parameters on the performance of microbridges.

  18. Transport behavior and critical current densities in MgB2 wires

    NASA Astrophysics Data System (ADS)

    Pradhan, A. K.; Feng, Y.; Zhao, Y.; Koshizuka, N.; Zhou, L.; Zhang, P. X.; Liu, X. H.; Ji, P.; Du, S. J.; Liu, C. F.

    2001-09-01

    We report on the transport and magnetization properties of MgB2 wires fabricated by a powder-in-tube (PIT) technique. Temperature and magnetic-field-dependent resistivity displays a high conductivity and upper critical field Hc2 generally observed in dense samples. The electronic mass anisotropy γ≈1.3±0.15 predicts some texturing in the wire. Our data on transition temperature TC, Hc2, and both magnetic and transport critical current density Jc indicate that MgB2 can be manufactured in a wire form using a PIT technique and required engineering Jc can be achieved on further optimization.

  19. Effect of heat-treatment temperatures on density and porosity in MgB 2 superconductor

    NASA Astrophysics Data System (ADS)

    Liu, C. F.; Yan, G.; Du, S. J.; Xi, W.; Feng, Y.; Zhang, P. X.; Wu, X. Z.; Zhou, L.

    2003-04-01

    The density, porosity, and microstructures of MgB 2 samples are very important factors for transition critical current density. The effect of heat-treatment temperatures on density and porosity in MgB 2 superconductors has been investigated. The open porosity increases with increasing heat-treatment temperatures, but close porosity decreases. The calculated theory densities from the lattice parameters of the measured samples are 2.6-2.63 g/cm 3. The average measured total porosity (including open and close porosity) is about 50%.

  20. Preparation and properties of amorphous MgB2/MgO superstructures: Model disordered superconductor

    NASA Astrophysics Data System (ADS)

    Siemons, W.; Steiner, M. A.; Koster, G.; Blank, D. H. A.; Beasley, M. R.; Kapitulnik, A.

    2008-05-01

    In this paper, we introduce a unique method for fabricating MgB2/MgO multilayers and demonstrate the potential for using them as a new model for disordered superconductors. In this approach, we control the annealing of the MgB2 to yield an interesting new class of disordered (amorphous) superconductors with relatively high transition temperatures. The multilayers appear to exhibit quasi-two-dimensional superconductivity with controlled anisotropy. We discuss the properties of the multilayers as the thickness of the components of the bilayers vary.

  1. Tunneling spectroscopy and magnetization measurements of the superconducting properties of MgB2

    NASA Astrophysics Data System (ADS)

    Sharoni, Amos; Felner, Israel; Millo, Oded

    2001-06-01

    Cryogenic scanning tunneling microscopy and magnetization measurements were used to study the superconducting properties of MgB2. The magnetization measurements show a sharp superconductor transition at Tc=39 K, in agreement with previous works. The tunneling spectra exhibit BCS-like gap structures, with gap parameters in the range of 5 to 7 meV, yielding a ratio of 2Δ/kBTc~3-4. This suggests that MgB2 is a conventional BCS s-wave superconductor, either in the weak-coupling or in the ``intermediate-coupling'' regime.

  2. Development of 2-D Array of Superconducting Magnesium Diboride (MgB2) for Far-IR Investigations of the Outer Planets and Icy Moons

    NASA Astrophysics Data System (ADS)

    Lakew, Brook

    2009-09-01

    A 2-D array of superconducting Magnesium Diboride(MgB2) far -IR thermal detectors has been fabricated. Such an array is intended to be at the focal plane of future generation thermal imaging far-IR instruments that will investigate the outer planets and their icy moons. Fabrication and processing of the pixels of the array as well as noise characterization of architectured MgB2 thin films will be presented. Challenges and solutions for improving the performance of the array will be discussed.

  3. An innovative technique to synthesize C-doped MgB2 by using chitosan as the carbon source

    NASA Astrophysics Data System (ADS)

    Bovone, G.; Vignolo, M.; Bernini, C.; Kawale, S.; Siri, A. S.

    2014-02-01

    Here, we report a new technique to synthesize carbon-doped MgB2 powder. Chitosan was innovatively used as the carbon source during the synthesis of boron from boron oxide. This allowed the introduction of local defects, which later on served as pinning centers in MgB2, in the boron lattice itself, avoiding the traditional and time consuming ways of ex situ MgB2 doping (e.g. ball milling). Two volume percentages of C-doping have been tried and its effect on the superconducting properties, evaluated by magnetic and transport measurements, are discussed here. Morphological analysis by scanning electron microscopy revealed nano-metric grains’ distribution in the boron and MgB2 powder. Mono-filamentary MgB2 wires have been fabricated by an ex situ powder-in-tube technique by using the thus prepared carbon-doped MgB2 and pure MgB2 powders. Transport property measurements on these wires were made and compared with MgB2 wire produced using commercial boron.

  4. RAPID COMMUNICATION: Formation of MgB2 at ambient temperature with an electrochemical process: a plausible mechanism

    NASA Astrophysics Data System (ADS)

    Jadhav, A. B.; Subhedar, K. M.; Hyam, R. S.; Talaptra, A.; Sen, Pintu; Bandyopadhyay, S. K.; Pawar, S. H.

    2005-06-01

    The binary intermetallic MgB2 superconductor has been synthesized by many research groups. However, the mechanism of its formation is not clearly understood. In this communication, a comprehensive mechanism of the formation of MgB2 from Le Chatelier's principle of equilibrium reaction has been explained both for solid-state reaction and electrodeposition methods.

  5. Flux jump behaviors and mechanism of FeTi doped MgB2 at 5 K

    NASA Astrophysics Data System (ADS)

    Lee, H. B.; Kim, G. C.; Kim, Y. C.; Ahmad, D.

    2015-08-01

    This study examined the flux jump behaviors of Fe-doped MgB2 according to content of FeTi particles at 5 K, at which flux jump has been shown to be more frequent. The samples were synthesized in a stainless steel tube with Mg, B and FeTi particles. The motives of flux jump in MgB2 superconductors are over-moving fluxes around the defects and the low heat capacity of MgB2. MgB2 was doped with FeTi particles to overcome these vulnerable points of MgB2. The flux jump of MgB2 decreased with increasing content of doped FeTi particles. On the other hand, excessive doping of FeTi resulted in a decrease of diamagnetic properties and the flux pinning effects together. It is concluded that FeTi particles in MgB2 do not block the flux jump itself, but the propagation of flux jump of MgB2.

  6. Development of magnesium diboride (MgB 2) wires and magnets using in situ strand fabrication method

    NASA Astrophysics Data System (ADS)

    Tomsic, Michael; Rindfleisch, Matthew; Yue, Jinji; McFadden, Kevin; Doll, David; Phillips, John; Sumption, Mike D.; Bhatia, Mohit; Bohnenstiehl, Scot; Collings, E. W.

    2007-06-01

    Since 2001 when magnesium diboride (MgB 2) was first reported to have a transition temperature of 39 K, conductor development has progressed to where MgB 2 superconductor wire in kilometer-long piece-lengths has been demonstrated in magnets and coils. Work has started on demonstrating MgB 2 wire in superconducting devices now that the wire is available commercially. MgB 2 superconductors and coils have the potential to be integrated in a variety of commercial applications such as magnetic resonance imaging, fault current limiters, transformers, motors, generators, adiabatic demagnetization refrigerators, magnetic separation, magnetic levitation, energy storage, and high energy physics applications. This paper discusses the progress on MgB 2 conductor and coil development in the last several years at Hyper Tech Research, Inc.

  7. Effect of deformation with Bridgman anvils on the structure, hardness, and critical current of a massive MgB2-based sample

    NASA Astrophysics Data System (ADS)

    Akshentsev, Yu. N.; Degtyarev, M. V.; Pilyugin, V. P.; Krinitsina, T. P.; Kuznetsova, E. I.; Blinova, Yu. V.; Sudareva, S. V.; Romanov, E. P.

    2015-05-01

    The structure and properties of synthesized massive MgB2-based samples subjected to deformation with Bridgman anvils have been studied. Deformation results in the formation of fine-grained structure of the MgB2 phase, enhancement of interconnection of grains, complete disappearance of friable MgB2-phase areas, and abrupt increase in the microhardness.

  8. A Superconducting Joint Technique for MgB2 Round Wires

    PubMed Central

    Yao, Weijun; Bascuñán, Juan; Hahn, Seungyong; Iwasa, Yukikazu

    2009-01-01

    This paper describes a technique to superconductively splice multifilament MgB2 wires. To date the technique has achieved joints capable of carrying a superconducting current of 200 A at 10 K in self field. Joints details, as well as testing methods and results are presented here. PMID:20671806

  9. The doping effect of multiwall carbon nanotube on MgB2/Fe superconductor wire

    NASA Astrophysics Data System (ADS)

    Kim, J. H.; Yeoh, W. K.; Qin, M. J.; Xu, X.; Dou, S. X.

    2006-07-01

    We evaluated the doping effect of two types of multiwall carbon nanotubes (CNTs) with different aspect ratios on MgB2/Fe monofilament wires. Relationships between microstructure, magnetic critical current density (Jc), critical temperature (Tc), upper critical field (Hc2), and irreversibility field (Hirr) for pure and CNT doped wires were systematically studied for sintering temperature from 650to1000°C. As the sintering temperature increased, Tc for short CNT doped sample slightly decreased, while Tc for long CNT doped sample increased. This indicates better reactivity between MgB2 and short CNT due to its small aspect ratio, and substitution of carbon (C) from short CNT for boron (B) occurs. In addition, short CNT doped samples sintered at high temperatures of 900 and 1000°C exhibited excellent Jc, and this value was approximately 104A /cm2 in fields up to 8T at 5K. This suggests that short CNT is a promising carbon source for MgB2 superconductor with excellent Jc. In particular, inclusion of nanosized MgO particles and substitution of C into the MgB2 lattice could result in strong flux pinning centers.

  10. Coexistence of covalent and metallic bonding in the boron intercalation superconductor MgB2

    NASA Astrophysics Data System (ADS)

    Belashchenko, K. D.; Schilfgaarde, M. Van; Antropov, V. P.

    2001-09-01

    Chemical bonding and electronic structure of MgB2, a boron-based newly discovered superconductor, is studied using self-consistent band-structure techniques. Analysis of the transformation of the band structure for the hypothetical series of graphite-primitive graphite-primitive graphitelike boron-intercalated boron, shows that the band structure of MgB2 is graphitelike, with π bands falling deeper than in ordinary graphite. These bands possess a typically delocalized and metallic, as opposed to covalent, character. The in-plane σ bands retain their two-dimensional (2D) covalent character, but exhibit a metallic hole-type conductivity. The coexistence of 2D covalent in-plane and three-dimensional (3D) metallic-type interlayer conducting bands is a peculiar feature of MgB2. We analyze the 2D and 3D features of the band structure of MgB2 and related compounds, and their contributions to conductivity.

  11. Temperature dependence of superconducting gap and penetration depth for MgB2

    NASA Astrophysics Data System (ADS)

    Karakaya, Seniye; Ozbas, Omer

    2012-09-01

    In this study, we have investigated both the temperature dependence of magnetic penetration depth and superconducting energy gap for magnesium diboride (MgB2) by considering several models such as Bardeen-Cooper-Schrieffer (BCS), two fluids and two band Eliashberg model. These models are compared with each others and available literature results. Several studies reported that MgB2 has two different superconducting gaps. That is, the multi-band superconductor MgB2 exhibits two dimensional (2D) σ-band and three-dimensional (3D) π-band superconductivity and have the remarkably high critical temperature (Tc= 39K) all of the metallic superconductors. So, recently it has attracted great attention. The superconductivity in MgB2 has been analyzed by using two band Eliashberg model. We also have calculated the temperature dependence of the superconducting gaps (Δσ and Δπ) and compared them with the available experimental data and the other theoretical predictions.

  12. Rational design of MgB2 conductors toward practical applications

    NASA Astrophysics Data System (ADS)

    Patel, Dipak; Hossain, Md Shahriar Al; Motaman, Ashkan; Barua, Shaon; Shahabuddin, Mohammed; Kim, Jung Ho

    2014-09-01

    We report the research progress that has been made on developing rational MgB2 superconducting conductors toward practical applications. Owing to the poor performance of the critical current density (Jc) of bare MgB2, various techniques have been developed to overcome this obstacle. Among these, chemical doping has proved to be the most effective way to enhance the superconducting properties, such as Jc and the irreversibility field (Birr). More than a hundred different forms of dopants have been investigated over the past 13 years. Among these, the most effective dopants have been identified to be silicon carbide, carbon, and malic acid. The best results, Birr of 22 T and Jc of 40,000 A cm-2 at 4.2 K and 10 T, have been reported for malic acid treated MgB2 conductors, which have matched the benchmark performance of commercial low temperature superconductor wire such as Nb-Ti. This work will review and discuss the progress on MgB2 conductor development over the past few years at the University of Wollongong and Hyper Tech Research, Inc.

  13. Point pinning centers in SiC doped MgB2 wires after HIP

    NASA Astrophysics Data System (ADS)

    Gajda, D.; Zaleski, A.; Morawski, A.; Cetner, T.; Thong, C. J.; Rindfleisch, M. A.

    2016-08-01

    In this study we show that dominant point pinning mechanisms in SiC doped MgB2 wires can be obtained by annealing in high isostatic pressure. The results indicate that the point pinning centers increase the critical current density in medium and high magnetic fields, but not at low magnetic fields. In addition, our study shows that dominant pinning mechanism changes from point to surface type with increase of magnetic fields. An MgB2 wire heat treated in a high pressure of 1.4 GPa shows a high critical current density of 100 A mm-2 in 13 T at 4.2 K. Scanning electron microscope studies show that high isostatic pressure increases the density of the MgB2 material, eliminates voids, allows for small Si precipitates and homogeneous distribution of Si precipitates. Transport measurements E - B and E - I show that the MgB2 wires manufactured by Hyper Tech Research did not heat up after transition into a normal state. This is important for applications in coils.

  14. High-performance dense MgB2 superconducting wire fabricated from mechanically milled powder

    NASA Astrophysics Data System (ADS)

    Kodama, Motomune; Suzuki, Takaaki; Tanaka, Hideki; Okishiro, Kenji; Okamoto, Kazutaka; Nishijima, Gen; Matsumoto, Akiyoshi; Yamamoto, Akiyasu; Shimoyama, Jun-ichi; Kishio, Kohji

    2017-04-01

    Owing to the relatively high critical temperature and the low manufacturing cost, MgB2 superconducting wires are promising for liquid helium-free superconducting applications. Today, commercially available MgB2 wires are manufactured by either an in situ or ex situ powder-in-tube process, the in situ process being more effective to obtain high critical current density. In in situ-processed wires, however, the critical current density is seriously suppressed by the high porosity of MgB2 filaments. To resolve this problem, we propose an innovative method of using precursor powder prepared by mechanical milling of magnesium, boron, and coronene powders. This precursor powder has a metal–matrix–composite structure, in which boron particles are dispersed in a magnesium matrix. The plastic deformation of the precursor powder through wire processing leads to compact packing, and a dense MgB2 filament is generated after heat treatment. As a result, the limitation of critical current density that occurs for the typical in situ process is overcome, and the practical critical current density of 103 A mm‑2 is obtained at 10 K and 6.1 T, at 15 K and 4.8 T, and at 20 K and 3.3 T.

  15. Strongly connected ex situ MgB2 polycrystalline bulks fabricated by solid-state self-sintering

    NASA Astrophysics Data System (ADS)

    Tanaka, Hiroya; Yamamoto, Akiyasu; Shimoyama, Jun-ichi; Ogino, Hiraku; Kishio, Kohji

    2012-11-01

    The transport current carrying capacity of ex situ processed MgB2 is expected to be greatly enhanced if a strong intergrain connectivity can be realized. Although percolation theory predicts that ex situ MgB2 samples should have a high connectivity of over 30% due to their high bulk density (P ≈ 75%), the reported connectivities of ex situ MgB2 bulks and wires are generally less than 10%. This is presumably because ex situ MgB2 has a much weaker intergrain connectivity than in situ MgB2. It is well known that heat treatment after cold working of ex situ MgB2 improves the connectivity and the critical current density. However, it is currently unclear whether such heat treatment induces self-sintering that results in the formation of necks, the elimination of pores, and an increase in contact area. In the present study, we investigated the microstructure, normal-state electrical connectivity, and critical current density of ex situ MgB2 polycrystalline bulks prepared by systematically varying the sintering conditions under low pressure. Samples heated at a high temperature of ˜900 °C for a long period showed an increased packing factor, a larger intergrain contact area, and a significantly enhanced electrical connectivity, all of which indicate solid-state self-sintering of MgB2. Sintered ex situ MgB2 bulks from a laboratory-made ball-milled powder exhibited a greatly enhanced connectivity of 28%, which is the highest connectivity of pressureless ex situ MgB2 bulks, wires, and tapes. Surprisingly, grain growth did not occur during long-duration (˜100 h) sintering in the sintered ex situ MgB2 bulks. This is in marked contrast to in situ processed MgB2 samples, for which significant grain growth occurred during heat treatment at ˜900 °C, producing grains that are several tens of times larger than the initial boron grains. Consequently, the critical current density as a function of the external magnetic field at 20 K progressively improved with sintering due to the relatively small grain size and good intergrain connectivity. We thus conclude that solid-state self-sintering is an effective approach for producing strongly connected, dense ex situ MgB2 polycrystals without grain growth.

  16. Effect of Non-substitutional Hole Doping on the Tc of MgB2

    NASA Astrophysics Data System (ADS)

    Ma, Danhao; Adu, Kofi; Sumanasekera, Gamini; Hess, Dustin; Terrones, Mauricio

    2015-03-01

    We report, for the first time, an increase in the superconducting critical temperature, TC of MgB2 by a nonsubstitutional hole-doping of the MgB2 structure using minute, single-wall carbon nanotube (SWCNT) inclusions. We varied the SWCNT concentration from 0.05wt% to 5wt% and investigated the temperature-dependent resistivity and TEP from 5K to 300K. We used micro-Raman spectroscopy, field-emission scanning electron microscopy, and x-ray diffraction to analyze the interfacial interactions between the SWCNTs and the MgB2 grains. We obtained an increase in TC from 33.0 to 37.8K (ΔT = 4.8K) which is attributed to charge transfer from the MgB2 structure to the SWCNT structure. The charge transfer phenomenon is confirmed by micro-Raman analysis of the phonon states of the SWCNT tangential band frequency in the composites. We determined the charge transfer per carbon atom to be 0.0023/C, 0.0018/C and 0.0008/C for 0.05wt%, 0.5wt% and 5wt% SWCNT inclusions, respectively, taking into account the contributions from the softening of the lattice constant and the nonadiabatic (dynamic) effects at the Fermi level. This report provides an experimental, alternative pathway to hole-doping of MgB2 without appealing to chemical substitution. This Work is Supported by Penn State Altoona Undergraduate Research Sponsored Program and Penn State Materials Research Institute, University Park.

  17. Elimination of bubbles and improvement of the superconducting properties in MgB2 films annealed using electron beam

    NASA Astrophysics Data System (ADS)

    Xu, Zhuang; Kong, Xiangdong; Han, Li; Pang, Hua; Wu, Yue; Gao, Zhaoshun; Li, Xiaona

    2017-03-01

    MgB2 superconducting films can be readily obtained using the electron-beam annealing method. However, many bubbles existing in the film severely damage the surface morphology, which is known as the deleterious current-limiting mechanism. Based on morphology images and energy-dispersive spectroscopy spectra, we found that, during the annealing process, solid Mg-rich layers evaporate to form Mg vapour in the precursor film, resulting in bubbles in the film. By reducing the cycle thickness of the precursor film, we obtained MgB2 films with better properties. The root-mean-square surface roughness was 2.7 nm over a 10 × 10 μm area for a 100 nm-thick film, and the critical current density at 20 K was increased to 3.8 × 106 A cm‑2. These MgB2 films are suitable for fabricating MgB2 superconducting devices.

  18. High trapped fields in bulk MgB2 prepared by hot-pressing of ball-milled precursor powder

    NASA Astrophysics Data System (ADS)

    Fuchs, G.; Häßler, W.; Nenkov, K.; Scheiter, J.; Perner, O.; Handstein, A.; Kanai, T.; Schultz, L.; Holzapfel, B.

    2013-12-01

    Bulk superconducting MgB2 samples, 20 mm in diameter, were prepared by hot-pressing of ball-milled Mg and B powders using fine-grained boron powders. High maximum trapped fields of B0 = 5.4 T were obtained at 12 K in one of the investigated trapped field magnets (height 8 mm) at the centre of the bulk surface. Investigating the temperature dependence of the trapped field for short MgB2 samples (height ≤1.6 mm), trapped fields of up to B0 = 3.2 T at 15 K were achieved. These high trapped fields are related to extremely high critical current densities of up to 106 A cm-2 at 15 K, indicating strong pinning due to nanocrystalline MgB2 grains. Expected trapped field data for long trapped field magnets prepared from the available MgB2 material are estimated.

  19. Relaxation and pinning in spark-plasma sintered MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Jirsa, M.; Rames, M.; Koblischka, M. R.; Koblischka-Veneva, A.; Berger, K.; Douine, B.

    2016-02-01

    The model of thermally activated relaxation developed and successfully tested on high-T c superconductors (Jirsa et al 2004 Phys. Rev. B 70 0245251) was applied to magnetic data of a bulk spark-plasma sintered MgB2 sample to elucidate its magnetic relaxation behavior. MgB2 and the related borides form a superconductor class lying between classical and high-T c superconductors. In accord with this classification, the relaxation phenomena were found to be about ten times weaker than in cuprates. Vortex pinning analyzed in terms of the field dependence of the pinning force density indicates a combined pinning by normal point-like defects and by grain surfaces. An additional mode of pinning at rather high magnetic fields (of still unknown origin) was observed.

  20. Effects of glucose doping on the MgB2 superconductors using cheap crystalline boron

    NASA Astrophysics Data System (ADS)

    Parakkandy, Jafar Meethale; Shahabuddin, Mohammed; Shah, M. Shahabuddin; Alzayed, Nasser S.; Qaid, Salem A. S.; Madhar, Niyaz Ahmad; Ramay, Shahid M.; Shar, Muhammad Ali

    2015-12-01

    We report the effect of glucose (C6H12O6) doping on the structural and electromagnetic properties of MgB2 superconductor fabricated by dry mixing using planetary ball milling. Herein, as-prepared bulk polycrystalline Mg (B1-xCx) 2 samples with different doping levels (x = 0, 2, 4, and 6 at. %) were systematically studied by X-ray diffraction, magnetic and resistivity measurements, and microstructure analysis. When carbon doped, the reduction in critical transition temperature and shrinkage in a-lattice were obviously observed. This resulted in structural distortion of the MgB2 lattice, and thereby, enhanced an impurity scattering. In addition to these, upper critical field and high-field critical current densities were also enhanced. On the other hand, both pinning force and low-field critical current density are decreased. The high field enhancement and low field degradation are due to increase in impurity scattering and decrease in pinning force respectively.

  1. Critical current densities and irreversibility fields of MgB 2 bulks

    NASA Astrophysics Data System (ADS)

    Kumakura, H.; Takano, Y.; Fujii, H.; Togano, K.; Kito, H.; Ihara, H.

    2001-11-01

    We prepared two MgB 2 bulks by applying conventional sintering and high-pressure sintering methods, and compared the current carrying properties. Jc obtained by the resistive method was larger than that obtained by the magnetic method. Jc- B curves obtained by the resistive method showed no history effect. These results indicate that most of the superconducting currents flowing in the MgB 2 bulks were intergrain (transport) currents and intragrain currents were negligibly small. The high-pressure sintered sample with smaller grain size showed smaller field dependence of Jc and higher Birr than the conventionally sintered sample with larger grain size. This behavior can be explained by the grain boundary flux pinning.

  2. Improved chemical stability of Ti-doped MgB2 in water

    NASA Astrophysics Data System (ADS)

    Zhao, Y.; Cheng, C. H.; Machi, T.; Koshizuka, N.; Murakami, M.

    2002-04-01

    We investigated the degradation of critical current density (Jc) and irreversibility field (Hirr) of pure and Ti-doped MgB2 bulks by exposing the samples to water for a total of 10, 48, 100, and 124 h. We found that both Jc and Hirr of the samples were degraded by exposure to water, in various degrees depending on the doping level. In the same exposure duration, the Ti-doped samples exhibited a less sensitivity to water, which was confirmed by the less degradation of Jc and Hirr. Our results demonstrate that Ti doping is not only effective in improving the superconducting properties of MgB2 but also in enhancing its chemical stability against water.

  3. Retention of two-band superconductivity in highly carbon-doped MgB2

    NASA Astrophysics Data System (ADS)

    Schmidt, H.; Gray, K. E.; Hinks, D. G.; Zasadzinski, J. F.; Avdeev, M.; Jorgensen, J. D.; Burley, J. C.

    2003-08-01

    Tunneling data on MgB1.8C0.2 show a reduction in the energy gap of the π bands by nearly a factor of 2 from undoped MgB2 that is consistent with the Tc reduction, but inconsistent with the expectations of the dirty limit. Dirty-limit theory for undoped MgB2 predicts a single gap about three times larger than measured and a reduced Tc comparable to that measured. Our heavily doped samples exhibit a uniform dispersion of C suggestive of significantly enhanced scattering, and we conclude that the retention of two-band superconductivity in these samples is caused by a selective suppression of interband scattering.

  4. Saturation and intrinsic dynamics of fluxons in NbTi and MgB2

    NASA Astrophysics Data System (ADS)

    Chamberlin, R. V.; Newman, N.; Gandikota, R.; Singh, R. K.; Moeckly, B. H.

    2007-03-01

    The authors measured the remanent magnetization of superconducting NbTi and MgB2 as a function of time after removing an applied field. At similar reduced temperatures, the density of magnetic flux quanta (fluxons) is found to relax faster in NbTi than in MgB2. Nearer the transition, the relaxation rate in both materials exhibits a saturation that is independent of the initially applied field. This saturation occurs when the distance between fluxons is comparable to the London penetration depth. The temperature dependence of the saturation and time dependence of the relaxation can be characterized by the Anderson-Kim model [Rev. Mod. Phys. 36, 39 (1964)] for fluxon dynamics.

  5. Disorder induced evolution of two energy gaps in MgB2

    NASA Astrophysics Data System (ADS)

    Kim, Yong-Jihn

    2007-03-01

    We study disorder effect on MgB2 superconductivity using the two band model by Suhl, Matthias, and Walker. We stress the importance of the Cooper pair size effect in the response of the BCS superconductor to the perturbation: the bounded Cooper pairs see the impurities within the range of the coherence length. This effect will undermine the initial decrease of the Tc and the big energy gap due to disorder, until the resistance ratio reaches about ˜3. For the resistance ratio less than 3, weak localization starts to decouple electrons and phonons, leading to the significant decrease of both the Tc and the big gap. In particular, we trace the evolution of two energy gaps of MgB2 as a function of disorder. Estimating the inter-band scattering rate from the experimental data, we compare our calculations with experiments. We also calculate the transition temperature, Tc as a function of the resistance ratio.

  6. AC losses of single-core MgB2 wires with different metallic sheaths

    NASA Astrophysics Data System (ADS)

    Kováč, J.; Šouc, J.; Kováč, P.; Hušek, I.

    2015-12-01

    AC losses of single-core MgB2 superconductors with different metallic sheaths (Cu, GlidCop, stainless steel and Monel) have been measured and analyzed. These wires were exposed to external magnetic field with frequencies 72 and 144 Hz and amplitudes up to 0.1 T at temperatures ranged from 18 to 40 K. The obtained results have shown that applied metallic sheath can affect the measured AC loss considerably. In the case of GlidCop and Stainless Steel a negligible small effect of metallic sheath was observed. Strong contribution of eddy currents has been found in the wire with well conductive copper sheath. In the case of Monel sheath, the hysteresis loss of magnetic sheath is dominated and AC loss of MgB2 core is practically not visible.

  7. Strong interaction between electrons and collective excitations in the multiband superconductor MgB2

    DOE PAGES

    Mou, Daixiang; Jiang, Rui; Taufour, Valentin; ...

    2015-04-08

    We use a tunable laser angle-resolved photoemission spectroscopy to study the electronic properties of the prototypical multiband BCS superconductor MgB2. Our data reveal a strong renormalization of the dispersion (kink) at ~65meV, which is caused by the coupling of electrons to the E2g phonon mode. In contrast to cuprates, the 65 meV kink in MgB2 does not change significantly across Tc. More interestingly, we observe strong coupling to a second, lower energy collective mode at a binding energy of 10 meV. As a result, this excitation vanishes above Tc and is likely a signature of the elusive Leggett mode.

  8. Feasibility study of a MgB2 superconducting magnetic cloak

    DOE PAGES

    Giunchi, Giovanni; Turrioni, Daniele; Kashikhin, Vladimir; ...

    2016-04-01

    The magnetic shielding capability of bulk MgB2 hollow cylinders can be fruitfully combined with an external paramagnetic sheath, to tailor the shape of the external magnetic flux lines. By appropriate selection of the external sheath permeability and thickness, it is possible to leave the magnetic flux lines unaltered by the shield (cloaking effect). Preliminary measurements have been performed at 4.2 K on shielding capability of bulk cylinders, which are subjected to axial and transversal magnetic fields up to 5 T. Furthermore, the cloaking conditions have been modeled to find the optimized thickness to realize the cloaking effect. The MgB2 materialmore » of the superconducting shield is also optimized to avoid low-temperature flux jumps, without losing its shielding capability.« less

  9. The distribution of elements in sequentially prepared MgB2 on SiC buffered Si substrate and possible pinning mechanisms

    NASA Astrophysics Data System (ADS)

    Chromik, Š.; Nishida, A.; Štrbík, V.; Gregor, M.; Espinós, J. P.; Liday, J.; Durný, R.

    2013-03-01

    MgB2 thin films are prepared by sequential evaporation of boron and magnesium bilayers on SiC buffered Si substrates followed by an in situ annealing. Precursor Mg-B bilayers are deposited by electron beam evaporation at room temperature. The amount of B is varied so as to result in different thickness (15 nm and 50 nm) of stoichiometric MgB2 final film after an in situ reaction with the excess Mg top layer in the vacuum. We show the distribution of the elements through the film. X-ray photoelectron spectroscopy analyses have shown that carbon is not free in the films (except the surface of the film) and silicon is in the compound form, too. In the case of the 15 nm thick films we see a strong interdiffusion of the elements (C, B) and we observe a suppression of TC of the film to 20 K. We register different slope of the H(T) dependence - the lowest temperature value of H for the 15 nm thick film exceeds the one for the 50 nm thick film in spite of lower TC. We suppose that δl pinning mechanism is dominant for the 15 nm thick film.

  10. Ship Propulsion Motor Employing Bi-2223 and MgB2 Superconductors

    NASA Astrophysics Data System (ADS)

    Kalsi, Swarn

    Compact and light weight direct-drive machines in large rating are desired as ship propulsion motors, and as generators for off-shore wind farm applications. A key goal for such machines is to be shipped to the site as fully assembled units. In order to achieve this goal, it is essential to construct both rotor and stator windings also using high-temperature superconducting (HTS) materials. Two commercially available HTS conductors are Bi-2223 (Bi2Sr2Ca2Cu3O) HTS with a critical temperature of about 110 K, and Magnesium Diboride (MgB2) with a critical temperature of about 40 K. The MgB2, available in small diameter wires, is suitable for manufacturing stator coils operating in high AC magnetic field environment. This chapter presents a concept design for a 40 MW, 120-RPM ship propulsion motor employing Bi-2223 for field winding and MgB2 for stator winding. Ambient temperature magnetic iron is employed on the rotor and the stator. The field winding consists of race track shaped Bi-2223 coils operating at 35 K. The stator winding, made up of MgB2 race track coils, operates at 20 K. Available off-the-shelf cryo-coolers are used for cooling all coils. The concept 40 MW motor is expected to be about 3 m in diameter, 2.3 m in axial length, and weigh around 80,000 kg. The design approach discussed here could also be used for designing large rating generators for wind farm applications.

  11. A MgB2 12.5 kVA superconductor transformer

    NASA Astrophysics Data System (ADS)

    Hascicek, Y. S.; Akin, Y.; Baldwin, T. W.; Rindfleisch, M. M.; Yue, J.; Sumption, M. D.; Tomsic, M.

    2009-06-01

    A 12.5 kVA, MgB2 superconductor transformer was designed as five alternating stacked coils between the primary and the secondary windings. Hyper Tech Research Inc. (Hyper Tech) manufactured multifilament MgB2 superconductor wire by using a patented process called the continuous tube filling and forming (CTFF) process. The CTFF MgB2 conductor was insulated with yttrium-stabilized zirconia (YSZ) using the chemical solution coating process. An all-copper former was designed and fabricated with an OD of 71 mm, ID of 42 mm and heights of 12 mm and 8 mm for primary and secondary coils, respectively. Two primary and three secondary coils were fabricated using the sol-gel insulated MgB2 wire using the W&R coil technology. One of the primary coils was tested at 4.2 K which showed better than 250 A engineering critical current. These five coils were then stacked as in the design in alternating fashion and connected and instrumented for testing. The transformer was cooled in He gas first then in liquid helium. The tests showed that the individual coils, the primary and the secondary windings performed better than the design currents. Also the open-circuit tests of the transformer showed that 1:1 transfer was achieved. This article was originally submitted for the special issue 'Selected papers from the International Conference on Superconductivity and Magnetism (ICSM2008) (Side, Turkey, 25-29 August 2008)', Superconductor Science and Technology, volume 22, issue 3.

  12. Vortex core shrinkage in a two gap superconductor: Application to MgB 2

    NASA Astrophysics Data System (ADS)

    Graser, S.; Gumann, A.; Dahm, T.; Schopohl, N.

    2007-09-01

    As a model for the vortex core in MgB2 we study a two band model with a clean σ band and a dirty π band. We present calculations of the vortex core size in both bands as a function of temperature and show that there exists a Kramer-Pesch effect in both bands even though only one of the bands is in the clean limit. We present calculations for different π band diffusivities and coherence lengths.

  13. Magnetic relaxation and lower critical field in MgB2 wires

    NASA Astrophysics Data System (ADS)

    Y, Feng; G, Yan; Y, Zhao; Pradhan, A. K.; F, Liu C.; X, Zhang P.; L, Zhou

    2003-09-01

    Magnetic relaxation behaviour, critical current density Jc and lower critical field Hc1 have been investigated in MgB2/Ta/Cu wires. It is found that Jc and Hc1 decrease linearly with temperature in the whole temperature region below Tc. The relaxation rate is very small and has a weak temperature dependence compared to high-Tc superconductors. Also, the pinning potential is much larger and the temperature and field dependences of the pinning potential are briefly discussed.

  14. Metallurgical phases and their magnetism at the interface of nanoscale MgB2/Fe layered structures.

    PubMed

    Sahoo, B; Keune, W; Kuncser, V; Becker, H-W; Röhlsberger, R

    2011-11-30

    We report on the characterization of metallurgical phases and their magnetism at the interfaces of nanoscale MgB(2)/Fe layered structures. MgB(2)/(57)Fe multilayers with varying layer thicknesses were prepared by vacuum deposition and investigated, before and after annealing by electrical resistance measurements, x-ray diffraction and (57)Fe conversion-electron Mössbauer spectroscopy (CEMS) down to 5 K. Interfacial Fe-B phases, such as Fe(2)B, were identified by CEMS. A superparamagnetic-to-ferromagnetic transition is observed with increasing (57)Fe film thickness. Ultrahigh vacuum annealing at 500 °C of the multilayers leads to strong diffusion of Fe atoms into the boundary regions of the MgB(2) layers. MgB(2) in the as-grown multilayers is non-superconducting. Structural disorder and the effect of Fe interdiffusion contribute to the suppression of superconductivity in the MgB(2) films of all the as-grown multilayers and the thinner annealed multilayers. However, an annealed MgB(2)/(57)Fe/MgB(2) trilayer with thicker (500 Å) MgB(2) layers is observed to be superconducting with an onset temperature of 25 K. At 5 K, the annealed trilayer can be conceived as being strongly chemically modulated, consisting of two partially Fe-doped superconducting MgB(2) layers separated by an interdiffused weakly magnetic Fe-B interlayer, which is characterized by a low hyperfine magnetic field B(hf) of ∼11 T. This chemically modulated layer structure of the trilayer after annealing was verified by Rutherford backscattering.

  15. Metallurgical phases and their magnetism at the interface of nanoscale MgB2/Fe layered structures

    NASA Astrophysics Data System (ADS)

    Sahoo, B.; Keune, W.; Kuncser, V.; Becker, H.-W.; Röhlsberger, R.

    2011-11-01

    We report on the characterization of metallurgical phases and their magnetism at the interfaces of nanoscale MgB2/Fe layered structures. MgB2/57Fe multilayers with varying layer thicknesses were prepared by vacuum deposition and investigated, before and after annealing by electrical resistance measurements, x-ray diffraction and 57Fe conversion-electron Mössbauer spectroscopy (CEMS) down to 5 K. Interfacial Fe-B phases, such as Fe2B, were identified by CEMS. A superparamagnetic-to-ferromagnetic transition is observed with increasing 57Fe film thickness. Ultrahigh vacuum annealing at 500 °C of the multilayers leads to strong diffusion of Fe atoms into the boundary regions of the MgB2 layers. MgB2 in the as-grown multilayers is non-superconducting. Structural disorder and the effect of Fe interdiffusion contribute to the suppression of superconductivity in the MgB2 films of all the as-grown multilayers and the thinner annealed multilayers. However, an annealed MgB2/57Fe/MgB2 trilayer with thicker (500 Å) MgB2 layers is observed to be superconducting with an onset temperature of 25 K. At 5 K, the annealed trilayer can be conceived as being strongly chemically modulated, consisting of two partially Fe-doped superconducting MgB2 layers separated by an interdiffused weakly magnetic Fe-B interlayer, which is characterized by a low hyperfine magnetic field Bhf of ˜11 T. This chemically modulated layer structure of the trilayer after annealing was verified by Rutherford backscattering.

  16. Flux jumps in high-J c MgB2 bulks during pulsed field magnetization

    NASA Astrophysics Data System (ADS)

    Fujishiro, H.; Mochizuki, H.; Naito, T.; Ainslie, M. D.; Giunchi, G.

    2016-03-01

    Pulsed field magnetization (PFM) of a high-J c MgB2 bulk disk has been investigated at 20 K, in which flux jumps frequently occur for high pulsed fields. Using a numerical simulation of the PFM procedure, we estimated the time dependence of the local magnetic field and temperature during PFM. We analyzed the electromagnetic and thermal instability of the high-J c MgB2 bulk to avoid flux jumps using the time dependence of the critical thickness, d c(t), which shows the upper safety thickness to stabilize the superconductor magnetically, and the minimum propagation zone length, l m(t), to obtain dynamical stability. The values of d c(t) and l m(t) change along the thermally-stabilized direction with increasing temperature below the critical temperature, T c. However, the flux jump can be qualitatively understood by the local temperature, T(t), which exceeds T c in the bulk. Finally, possible solutions to avoid flux jumps in high-J c MgB2 bulks are discussed.

  17. Influence of nanocrystalline boron precursor powder on superconductivity in MgB2 bulk.

    PubMed

    Zhang, Yun; Lu, Cheng; Zhou, Sihai; Joo, Jinho

    2009-12-01

    In this report, high-purity nanocrystalline boron powders processed by ball-milling were used as the precursor powders to fabricate MgB2 superconductor. The transport properties and the critical current density in the samples made from ball-milled boron powders and as-supplied boron powders were investigated. It was found that the ball-milled boron powders led to a significant enhancement of the critical current density in MgB2 sintered at 650 degrees C. The reason can be attributed to the small MgB2 grain size caused by the ball-milled boron precursor powders. The resistivity of the samples made from the ball-milled boron powder was lower than that of the sample from as-supplied boron powder. As the sintering temperature increased, both resistivity and upper critical field decreased in the samples using the ball-milled boron powders as a precursor. Poor connectivity and large strain are responsible for the high resistivity.

  18. Effect of fabrication route on density and connectivity of MgB2 filaments

    NASA Astrophysics Data System (ADS)

    Viljamaa, J.; Kováč, P.; Hušek, I.; Melišek, T.; Štrbík, V.; Dobročka, E.

    2010-06-01

    Series of samples was manufactured to test the effect of fabrication route on the density of the polycrystalline core, the connectivity between MgB2 grains and also the critical current density of undoped MgB2 conductors. All the samples had titanium sheaths and were manufactured using the Powder-in-Tube method. The Ti tubes were filled with either in situ, ex situ, or 60%-40% mixture of in situ and ex situ powders. After powder packing, the samples went through different deformation steps such as rotary swaging, two-axial rolling, pressing, cold isostatic pressing, or some combination of these, to form monofilamentary tapes. The core density was qualitatively estimated by measuring the Vickers microhardness from several locations of the ceramic filament. The changes in connectivity, or effective cross-section, were evaluated by performing resistivity measurements on the MgB2 cores after removal of the metallic sheath. The Jc characteristics were measured at 4.2 K and at variable external magnetic flux densities.

  19. Investigation on the levitation force behaviour of malic acid added bulk MgB2 superconductors

    NASA Astrophysics Data System (ADS)

    Savaskan, B.; Taylan Koparan, E.; Celik, S.; Ozturk, K.; Yanmaz, E.

    2014-07-01

    The effects of malic acid addition (from 0 to 15 wt% of the total MgB2) on the levitation force properties of bulk MgB2 have been investigated. All samples were prepared from magnesium powder, amorphous boron powder, malic acid (C4H6O5) and toluene (C7H8) by using two-step solid state reaction method. Vertical and lateral levitation force measurements that are under both zero-field-cooled (ZFC) and field-cooled (FC) regimes were carried out at different temperatures of 24, 28 and 32 K for samples with various adding level. It was found that the reasonable malic acid adding has a positive impact on the levitation properties. At 24 K and 28 K, the 4 wt% and 6 wt% malic acid added samples exhibits a higher levitation force than pure sample. In the case of the optimally additive 4 wt% sample, the maximum levitation force corresponds to 18.60 N, whereas the pure sample shows 16.95 N at 24 K for ZFC regime. In this study the enhancing effect of malic acid adding on the levitation force properties of MgB2 has been first time investigated and reported.

  20. Superior high-field current density in slightly Mg-deficient MgB2 tapes

    NASA Astrophysics Data System (ADS)

    Jiang, C. H.; Nakane, T.; Kumakura, H.

    2005-12-01

    A series of Fe-clad MgxB2 tapes with x varying from 0.5 to 1.2 was prepared by the in situ powder-in-tube method. Slightly Mg-deficient samples showed higher Jc in high magnetic fields, whereas samples with stoichiometric Mg or a slight excess of Mg exhibited better Jc in the low-field region. The sample with x =0.9 showed the best Jc in the applied magnetic field. The MgB2 core was porous in Mg-deficient tapes but with smaller grain sizes than the samples with a slight Mg excess due to insufficient grain growth. Some fine nanometer size grains were also observed in the B-rich samples. The enhanced grain boundary pinning due to the smaller grain size may explain the superior high-field Jc property of the slightly Mg-deficient MgB2 tapes. Our results indicate that preparing MgB2 samples with a slight excess of Mg may not be advantageous when developing devices for high-field applications.

  1. Superconducting properties of adipic-acid-doped bulk MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Vajpayee, Arpita; Awana, V. P. S.; Bhalla, G. L.; Bhobe, P. A.; Nigam, A. K.; Kishan, H.

    2009-01-01

    We report the effect of adipic acid (C6H10O4) doping on lattice parameters, microstructure, critical temperature (Tc), current density (Jc) and irreversibility field (Hirr) for an MgB2 superconductor. Actual carbon (C) substitution level for boron (B) is estimated to be from 0.40 at.% to 2.95 at.% for different doping levels. A reduction in Tc from 38.43 to 34.93 K and in lattice parameter a from 3.084(3) Å to 3.075(6) Å is observed for the 10 wt% C6H10O4 doped sample in comparison to pristine MgB2. This is an indication of C substitution at boron sites, with the C coming from the decomposition of C6H10O4 at the time of reaction. Interestingly the doped samples have resulted in significant enhancement of Jc and Hirr. All the doped samples exhibit the Jc value of the order of 104 A cm-2 at 5 K and 8 T, which is higher by an order of magnitude as compared to the undoped sample. This result indicates that C6H10O4 is a promising material for MgB2 for obtaining the excellent Jc values under higher magnetic fields.

  2. Solid cryogen: a cooling system for future MgB2 MRI magnet.

    PubMed

    Patel, Dipak; Hossain, Md Shahriar Al; Qiu, Wenbin; Jie, Hyunseock; Yamauchi, Yusuke; Maeda, Minoru; Tomsic, Mike; Choi, Seyong; Kim, Jung Ho

    2017-03-02

    An efficient cooling system and the superconducting magnet are essential components of magnetic resonance imaging (MRI) technology. Herein, we report a solid nitrogen (SN2) cooling system as a valuable cryogenic feature, which is targeted for easy usability and stable operation under unreliable power source conditions, in conjunction with a magnesium diboride (MgB2) superconducting magnet. The rationally designed MgB2/SN2 cooling system was first considered by conducting a finite element analysis simulation, and then a demonstrator coil was empirically tested under the same conditions. In the SN2 cooling system design, a wide temperature distribution on the SN2 chamber was observed due to the low thermal conductivity of the stainless steel components. To overcome this temperature distribution, a copper flange was introduced to enhance the temperature uniformity of the SN2 chamber. In the coil testing, an operating current as high as 200 A was applied at 28 K (below the critical current) without any operating or thermal issues. This work was performed to further the development of SN2 cooled MgB2 superconducting coils for MRI applications.

  3. The size effect on the magnetic levitation force of MgB2 bulk superconductors

    NASA Astrophysics Data System (ADS)

    Savaskan, B.; Koparan, E. T.; Güner, S. B.; Celik, S.; Yanmaz, E.

    2016-12-01

    In this study, the size effect on the magnetic levitation performance of disk-shaped MgB2 bulk superconductors and permanent magnets was investigated. MgB2 samples with varying diameters of 13 mm, 15 mm and 18 mm, each of which were 2 g in mass, were prepared by two-step solid state reaction method. Vertical levitation force measurements under both zero-field-cooled (ZFC) and field-cooled (FC) regimes were carried out at different temperatures of 20, 24 and 28 K. It was determined that the levitation force of the MgB2 strongly depends on both the diameters of the sample and the permanent magnet. In ZFC regime, the maximum levitation force value for the permanent magnet and the sample 18 mm in diameters reached to the 8.41 N at 20 K. In addition, in FC regime, attractive and repulsive force increased with increasing diameters of the sample and the permanent magnet. In that, the sample with 18 mm in diameter showed the highest attractive force value -3.46 N at 20 K and FC regime. The results obtained in this study are very useful in magnetic levitation devices as there is no detailed study on the size of superconductors and permanent magnets.

  4. Magnetization AC losses in MgB2 wires made by IMD process

    NASA Astrophysics Data System (ADS)

    Kováč, J.; Šouc, J.; Kováč, P.; Hušek, I.

    2015-01-01

    Magnetization AC losses of MgB2 superconductors with one and four filaments made by an internal magnesium diffusion (IMD) into boron process were measured and analyzed. For AC loss measurement a system based on a calibration-free method was used. Short samples of MgB2 wires were exposed to an external magnetic field with amplitudes up to 0.07 T, frequencies up to 1200 Hz, and a temperature range between 15 K and 40 K. A strong effect of eddy current losses was found in single-core wire containing pure copper sheath, which was proved by the same wire measurement after Cu etching. The impact of coupling current losses in non-twisted four-filament wire and the decoupling effect after twisting were observed. Coupling current losses in a low-frequency region were effectively reduced in agreement with theoretical assumption. The degradation of transport currents due to torsion stress by twisting was taken into account and the normalized AC losses of MgB2 wires made by IMD and powder-in-tube processes were compared. It appears that the IMD process is more perspective for AC applications due to much higher current densities and smaller degradation of current-carrying capability by twisting.

  5. Solid cryogen: a cooling system for future MgB2 MRI magnet

    PubMed Central

    Patel, Dipak; Hossain, Md Shahriar Al; Qiu, Wenbin; Jie, Hyunseock; Yamauchi, Yusuke; Maeda, Minoru; Tomsic, Mike; Choi, Seyong; Kim, Jung Ho

    2017-01-01

    An efficient cooling system and the superconducting magnet are essential components of magnetic resonance imaging (MRI) technology. Herein, we report a solid nitrogen (SN2) cooling system as a valuable cryogenic feature, which is targeted for easy usability and stable operation under unreliable power source conditions, in conjunction with a magnesium diboride (MgB2) superconducting magnet. The rationally designed MgB2/SN2 cooling system was first considered by conducting a finite element analysis simulation, and then a demonstrator coil was empirically tested under the same conditions. In the SN2 cooling system design, a wide temperature distribution on the SN2 chamber was observed due to the low thermal conductivity of the stainless steel components. To overcome this temperature distribution, a copper flange was introduced to enhance the temperature uniformity of the SN2 chamber. In the coil testing, an operating current as high as 200 A was applied at 28 K (below the critical current) without any operating or thermal issues. This work was performed to further the development of SN2 cooled MgB2 superconducting coils for MRI applications. PMID:28251984

  6. Solid cryogen: a cooling system for future MgB2 MRI magnet

    NASA Astrophysics Data System (ADS)

    Patel, Dipak; Hossain, Md Shahriar Al; Qiu, Wenbin; Jie, Hyunseock; Yamauchi, Yusuke; Maeda, Minoru; Tomsic, Mike; Choi, Seyong; Kim, Jung Ho

    2017-03-01

    An efficient cooling system and the superconducting magnet are essential components of magnetic resonance imaging (MRI) technology. Herein, we report a solid nitrogen (SN2) cooling system as a valuable cryogenic feature, which is targeted for easy usability and stable operation under unreliable power source conditions, in conjunction with a magnesium diboride (MgB2) superconducting magnet. The rationally designed MgB2/SN2 cooling system was first considered by conducting a finite element analysis simulation, and then a demonstrator coil was empirically tested under the same conditions. In the SN2 cooling system design, a wide temperature distribution on the SN2 chamber was observed due to the low thermal conductivity of the stainless steel components. To overcome this temperature distribution, a copper flange was introduced to enhance the temperature uniformity of the SN2 chamber. In the coil testing, an operating current as high as 200 A was applied at 28 K (below the critical current) without any operating or thermal issues. This work was performed to further the development of SN2 cooled MgB2 superconducting coils for MRI applications.

  7. MgB2 -based negative refraction index metamaterial at visible frequencies: Theoretical analysis

    NASA Astrophysics Data System (ADS)

    Kussow, Adil-Gerai; Akyurtlu, Alkim; Semichaevsky, Andrey; Angkawisittpan, Niwat

    2007-11-01

    The presented metamaterial consists of the matrix (magnesium diboride MgB2 in a normal state, at room temperature) with randomly (or regularly) embedded spherical nanoparticles of a polaritonic crystal, SiC. The calculations demonstrate explicitly that the metamaterial exhibits negative refraction index behavior with low losses for a scattered wave. The result stands for both random and regular distributions of SiC nanoparticles inside the MgB2 matrix. This favorable situation stems from the Drude-like behavior of both the low-energy, p2(ωp2≈1.9eV) , and the high-energy, p1(ωp1≈6.3eV) , plasmon modes of MgB2 with plasmon losses, γ⩽0.25eV . The effective medium parameters were calculated in the framework of the extended theories of Maxwell-Garnett [Philos. Trans. R. Soc. London, Ser. A 203, 385 (1904)] and Lewin [Proc. Inst. Electr. Eng. 94, 65 (1947)], and the obtained results are validated via ab initio finite difference time domain simulations.

  8. Critical currents of Rutherford MgB2 cables compacted by two-axial rolling

    NASA Astrophysics Data System (ADS)

    Kopera, L.; Kováč, P.; Kulich, M.; Melišek, T.; Rindfleisch, M.; Yue, J.; Hušek, I.

    2017-01-01

    Two types of Rutherford cables made of two strand layers of commercial MgB2 wires manufactured by Hyper Tech Research, Inc. have been made. Flat rectangular cables consisting of 12 single-core MgB2/Nb/Cu10Ni, or 6-filaments MgB2/Nb/Cu strands, both of diameter 390 mewm, were assembled using a back-twist cabling machine with transposition length of 20 mm. In order to analyze impact of the cable compaction on critical currents, cables were two-axially rolled, each by a single step reduction of 3.5%-29.7% to thickness range of 0.775-0.62 mm. It was found that by increasing the packing factor (PF) of cable above 0.79, the critical current begins to increase. It is improved nearly two times up to the PF limit 0.89. Compaction over the PF limit introduced cable degradation and decrease of critical current. Bending tests applied to cables showed that critical current degradation starts below the bending diameter 120 mm for 6-filaments Cu sheath and 70 mm for single-core Cu10Ni sheath cable. Tensile tests showed similar irreversible strain values for the both types of cables. Rutherford cables assembled of single-core strands are promising for low field (2.7-4 T) applications where low bending diameters are required.

  9. The influence of HIP on the homogeneity, Jc, Birr, Tc and Fp in MgB2 wires

    NASA Astrophysics Data System (ADS)

    Gajda, D.; Morawski, A.; Zaleski, A.; Kurnatowska, M.; Cetner, T.; Gajda, G.; Presz, A.; Rindfleisch, M.; Tomsic, M.

    2015-01-01

    Unreacted MgB2 wires were made at Hyper Tech Research, USA by a continuous tube forming and filling method using mixtures of Mg and B with and without SiC powder additions. All of the wires underwent hot isostatic pressure (HIP) treatment at the Institute of High Pressure. The first part of the wire was annealed at a pressure of 1 GPa, and the second part was annealed at 0.1 MPa. In this work, we show the influence of high pressure on critical current density (Jc), pinning force (Fp), critical temperature (Tc), irreversible magnetic fields (Birr) and the Fp scaling and microstructure of MgB2 wires. The results obtained indicate that after annealing at high pressure, the MgB2 wires show increases of Jc and Fp in high magnetic fields (8 T-12 T); in SiC doped MgB2 wires, Fpmax shifts to higher magnetic fields. We also compared the Jc of the doped and undoped MgB2 wires (without HIP and with HIP). The scanning electron microscope (SEM) results show that HIP increases the density of MgB2 material and improves its uniformity.

  10. Temperature effect on microstructure and electromagnetic performance of polycarbosilane and sugar-doped MgB2 wires

    NASA Astrophysics Data System (ADS)

    Shcherbakov, A. V.; Horvat, J.; Shcherbakova, O. V.; Novosel, N.; Babić, E.; Dou, S. X.

    2010-06-01

    The effect of processing temperature on structural and superconducting properties of 10 wt.% sugar- and 10 wt.% PCS-doped MgB2 wires is systematically investigated. It is demonstrated that these dopants significantly enhance the electromagnetic performance of Fe-clad MgB2 superconductor and increase its potential for practical application. The enhancement of in-field critical current density (Jc(Ba)) and upper critical field (Bc2) is due to formation of a large amount of lattice defects caused by impurities and C substitution into the MgB2 crystal lattice. High temperature sintering of sugar-doped sample results in as high Bc2 value as 37 T (at 5 K), which correlates with higher level of C substitution into MgB2 crystal lattice in this sample. In contrast, for PCS doped MgB2 wire higher Bc2 value (32 T at 5 K) is observed at lower sintering temperatures. In spite of the fact that the level of C in the crystal lattice and Bc2 value are higher in the sugar doped MgB2 sample, this sample has lower Jc(Ba) when compared to the sample with PCS addition. We speculate that it is due to a higher level of MgO impurities in the sugar doped sample (18.6 wt.% compared to 9.15 wt.% in the PCS doped sample), which results in the dissipation of supercurrent flowing through this sample.

  11. Measurement of the penetration depth and coherence length of MgB 2 in all directions using transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Loudon, J. C.; Yazdi, S.; Kasama, T.; Zhigadlo, N. D.; Karpinski, J.

    2015-02-01

    We demonstrate that images of flux vortices in a superconductor taken with a transmission electron microscope can be used to measure the penetration depth and coherence length in all directions at the same temperature and magnetic field. This is particularly useful for MgB 2, where these quantities vary with the applied magnetic field and values are difficult to obtain at low field or in the c direction. We obtained images of flux vortices from a MgB 2 single crystal cut in the a c plane by focused ion beam milling and tilted to 45∘ with respect to the electron beam about the crystallographic a axis. A new method was developed to simulate these images that accounted for vortices with a nonzero core in a thin, anisotropic superconductor and a simplex algorithm was used to make a quantitative comparison between the images and simulations to measure the penetration depths and coherence lengths. This gave penetration depths Λa b=100 ±35 nm and Λc=120 ±15 nm at 10.8 K in a field of 4.8 mT. The large error in Λa b is a consequence of tilting the sample about a and had it been tilted about c , the errors on Λa b and Λc would be reversed. Thus obtaining the most precise values requires taking images of the flux lattice with the sample tilted in more than one direction. In a previous paper [J. C. Loudon et al., Phys. Rev. B 87, 144515 (2013), 10.1103/PhysRevB.87.144515], we obtained a more precise value for Λa b using a sample cut in the a b plane. Using this value gives Λa b=107 ±8 nm, Λc=120 ±15 nm, ξa b=39 ±11 nm, and ξc=35 ±10 nm, which agree well with measurements made using other techniques. The experiment required two days to conduct and does not require large-scale facilities. It was performed on a very small sample, 30 ×15 μ m and 200-nm thick, so this method could prove useful for superconductors where only small single crystals are available, as is the case for some iron-based superconductors.

  12. Measurement of the Penetration Depth and Coherence Length of MgB2 in All Directions Using Transmission Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Loudon, James; Yazdi, S.; Kasama, T.; Zhigadlo, N. D.; Karpinski, J.

    2015-03-01

    We demonstrate that images of flux vortices in a superconductor taken with a transmission electron microscope can be used to measure simultaneously the penetration depth and coherence length in all directions at the same temperature and magnetic field. This is particularly useful for MgB2 where these quantities vary with the applied magnetic field and values are difficult to obtain at low field or in the c direction. We obtained images of flux vortices from a sample cut in the ac plane by focussed ion beam milling and compared these with simulations which accounted for flux vortices with a non-zero core in a thin, anisotropic superconductor. This gave penetration depths Λab = 100 +/- 35 nm, Λc = 120 +/- 15 nm and coherence lengths ξab = 41 +/- 13 nm and ξc = 34 +/- 10 nm at 10.8 K in a field of 4.8 mT. The implications of these values for type-1.5 superconductivity will be discussed.

  13. The Levitation Characteristics of MGB2 Plates on Tracks of Permanent Magnets

    NASA Astrophysics Data System (ADS)

    Perini, E.; Bassani, E.; Giunchi, G.

    2010-04-01

    The bulk MgB2 can be manufactured in large plates by an innovative process: the reactive liquid Mg infiltration (Mg-RLI). According to this process it is possible to produce, even at lab scale, plates of 10÷20 cm in lateral dimensions. The superconducting material resulting is very dense and, even if it is in polycrystalline form, it levitates with respect to Permanent Magnets (PM), like the textured YBCO samples, up to 35 K. In order to control the levitation forces and stiffnesses of an MgB2 plate (10×10×1 cm3) moving with respect to a track of PM's (NdFeB bars arranged in 4 lines according to an Halbach disposition and separated by Iron flux concentrators), we have used an instrumented Cryogenic Levitation Apparatus (CLA). We have studied different kind of movements of the PM's track with respect to the MgB2 plate. First, we consider the vertical movement, assumed z direction, which describes the properly levitation characteristics. Secondly, we consider two kinds of lateral movements of the track, assumed x direction, with the long size of the magnets either perpendicular or parallel to the movement direction. The resulting configurations simulate the main movements that a superconducting levitating vehicle will do in a real track, either of axial or of guidance type. The levitation axial forces, measured in Field Cooling or Zero Field Cooling conditions, indicate that at the distance between superconducting plate and PM's of 4 mm it is possible to have an overall levitating pressure of 7 N/cm2.

  14. Properties of hydrostatically extruded in situ MgB2 wires doped with SiC

    NASA Astrophysics Data System (ADS)

    Pachla, W.; Morawski, A.; Kovác, P.; Husek, I.; Mazur, A.; Lada, T.; Diduszko, R.; Melisek, T.; Strbík, V.; Kulczyk, M.

    2006-01-01

    In situ nano-SiC doped MgB2 wires were fabricated from MgH2 and B powders. Hydrostatic extrusion, followed by rotary swaging and two-axial rolling, were applied as the forming processes. The critical current Jc of MgB2 wires, made from MgH2 and B powders, was significantly improved by nano-SiC doping. Nano-SiC doping substantially increased the upper critical (irreversibility) field Bc 2 above 20 T. The maximum Jc values were measured for samples having 6 at.% SiC in low field and for those having 12 at.% SiC in high field, above 10 T. During the final sintering at 670 °C, the SiC decomposed and formed an Si-rich layer at the inner circumference of the Fe sheath. The composition of the core of SiC doped wires is more inhomogeneous in comparison to undoped ones, with MgO, Mg2Si and probably Mg2SiO4 as the major segregated phases. Strong segregation of Si within the MgB2 core was also observed. The highest Tc-mid = 39.3 K was measured for undoped wire. For the optimal SiC doping amount ~6 at.%, at high field, there was no difference in Jc between hydrostatically extruded and hydrostatically extruded plus two-axially rolled wire. This can be attributed to the beneficial effect of hydrostatic extrusion, which causes higher density of the core in comparison to traditional deformation processes.

  15. Strong-coupling s-wave Superconductor MgB2 : ^11B NMR Study

    NASA Astrophysics Data System (ADS)

    Kotegawa, Hisashi; Ishida, Kenji; Kitaoka, Yoshio; Muranaka, Takahiro; Nakagawa, Norimasa; Takagiwa, Hiroyuki; Akimitsu, Jun

    2002-03-01

    We report nuclear magnetic resonance (NMR) results on the recently discovered superconductor MgB_2. This binary compound exhibits a remarkably high superconducting (SC) transition temperature, Tc of ~40K, and thus attracts a great deal of attention. Numerous theoretical and experimental approaches have been performed in order to investigate SC characteristics in this compound. We have investigated a SC gap structure of MgB2 through the measurement of ^11B nuclear spin-lattice relaxation time, T_1. ^11(1/T_1T) is independent of the temperature (T) in the normal state, and decreases exponentially in the SC state, accompanied with a tiny coherence peak just below T_c. The T dependence of 1/T_1T in the SC state can be accounted for by an s-wave SC model with a large gap size of 2Δ /k_BTc ~ 5 which suggests to be in a strong-coupling regime. We carried out the measurement in Al-doped Mg_1-xAl_xB_2. 1/T1 in the SC state revealed that the size in SC gap is not changed by substituting Al for Mg. The reduction in Tc is shown to be due to the decrease of N(E_F). According to the McMillan equation, the experimental relation between Tc and the relative change in N(E_F) allowed us to estimate a characteristic phonon frequency ω ~ 700K and an electron-phonon coupling constant λ ~ 0.87. These results suggest that the high-Tc superconductivity in MgB2 is mediated by the strong electron-phonon coupling with high-frequency phonons.

  16. Thermal Transport of MgB2 Superconductors:. Interplay Between Electron and Lattice-Impurity Scattering

    NASA Astrophysics Data System (ADS)

    Varshney, Dinesh; Nagar, M.; Choudhary, K. K.

    We use the Kubo model to calculate the lattice contribution to the thermal conductivity (κph) in MgB2 superconductors. The theory is formulated when heat transfer is limited by the scattering of phonons from defects, grain boundaries, charge carriers, and phonons. The lattice thermal conductivity in normal state of MgB2 superconductors dominates and is an artifact of strong phonon-impurity and -phonon scattering mechanism. Later on, the electronic contribution to the thermal conductivity (κe) is calculated within relaxation time approximation for π and σ band carriers with s wave symmetry. Such an estimate sets an upper bound on κe and is about 30% of the total heat transfer at room temperature. The validity of the Wiedemann Franz law is also examined and an enhanced Lorenz number is obtained. Both these channels for heat transfer are clubbed and κtot develops a broad peak at about 120 K, before falling off at higher temperatures weakly. The anomalies reported are well-accounted in terms of the scattering mechanism by phonon and electron with impurities. It is shown that the behavior of the thermal conductivity is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between electron and lattice contributions. The contribution of carriers toward κ is substantial and is due to the fact that the carriers are condensed and do not carry entropy. We include comparisons with other theoretical calculations on κe and available experimental data. The numerical analysis of heat transfer in the metallic phase of MgB2 shows similar results as those revealed from experiments.

  17. Second-phase segregation and micro strain/lattice parameter dependent transition temperature in polycrystalline MgB2

    NASA Astrophysics Data System (ADS)

    Cai, Qi; Liu, Yongchang; Guo, Qianying; Ma, Zongqing; Li, Huijun

    2016-10-01

    Un-doped, metal-doped, and carbon-doped MgB2 samples were prepared by furnace cooling and quenching to investigate the second phase behavior and the resultant critical current density J c performance under different heat treatment processes, which is infrequently mentioned, and to explore the strain/lattice parameter dependence of the superconducting transition temperature. To release the residual stress, quenching induced second-phase segregation in these MgB2 samples shows a negative effect on the J c. Nevertheless, the dislocations and the lattice distortion assisted the enhancement of the high-field J c in the un-doped and metal-doped MgB2 samples, which indicated that quenching could be technically applied for the fabrication of metal-sheathed MgB2 wires and tapes to obtain excellent J c. After evaluating the micro strain and the lattice parameters’ (c and a for hexagonal lattice) variation, a dome was observed in the illustration of the strain/lattice parameter c/a dependence of T c, which differed from the reported linear relation in previous work. This suggests that the c/a ratio and the strain may be the predominant parameters for scaling of the superconducting dome width in the superconducting phase diagram of MgB2.

  18. Estimation of critical current density and grain connectivity in superconducting MgB 2 bulk using Campbell’s method

    NASA Astrophysics Data System (ADS)

    Ni, B.; Morita, Y.; Liu, Z.; Liu, C.; Himeki, K.; Otabe, E. S.; Kiuchi, M.; Matsushita, T.

    2008-09-01

    Many recent reports on the critical current density ( Jc) in superconducting MgB 2 bulks indicated that improving the grain connectivity is important, since the obtained Jc values were generally much lower than those in other metallic superconductors and it was ascribed to the poor connectivity between grains in polycrystalline MgB 2. In this study, we focused on the estimation of the global critical current density, super-current path, grain connectivity and their relationships with the faults volume fraction in the MgB 2 bulks prepared by a modified PIT (powder in tube) method. Campbell’s method was applied for the purpose of obtaining the penetrating AC flux profile and the characteristic of AC magnetic field vs. penetration depth from the sample’s surface. A computer simulation on the penetrating AC flux profile in MgB 2 bulks with randomly distributed voids, oxidized grains and other faults was also carried out. Jc obtained by Campbell’s method turned out to be smaller than that obtained from the SQUID measurement, implying that the global super-current was reduced by the existence of various faults and the lack of the electrical connectivity. It was verified that the relationship between the global critical current characteristics and the faults contained in MgB 2 samples can be quantitatively clarified by comparing the simulated critical current densities and other factors with the experimental results.

  19. Negligible effect of grain boundaries on the supercurrent density in polycrystalline MgB 2

    NASA Astrophysics Data System (ADS)

    Kim, Kijoon H. P.; Kang, W. N.; Kim, Mun-Seog; Jung, C. U.; Kim, Hyeong-Jin; Choi, Eun-Mi; Park, Min-Seok; Lee, Sung-Ik

    2002-04-01

    We used dc magnetization and transport measurement to estimate the superconducting critical current densities ( Jc) of polycrystalline MgB 2 sintered under high temperature and high pressure. We measured the current-voltage ( I-V) characteristics and found the existence of a vortex-glass phase in the field-temperature ( H-T) plane. This is notable in that the vortex-glass phase can be observed even in a polycrystalline specimen, which suggests that the supercurrent is not sensitive to the grain boundaries. Moreover, the transport (intergrain) Jc seems to be comparable to a magnetic (intragrain) Jc.

  20. Angle-resolved magnetotransport studies in anisotropic MgB2 single crystals

    NASA Astrophysics Data System (ADS)

    Pradhan, A. K.; Tokunaga, M.; Shi, Z. X.; Takano, Y.; Togano, K.; Kito, H.; Ihara, H.; Tamegai, T.

    2002-04-01

    We report the angle-resolved magnetotransport measurements on MgB2 single crystals that exhibit moderate anisotropy (γ) in upper critical fields with γ=2.6+/-0.1. Unusual ``kink'' features in resistivity are observed, which appear most clearly for field parallel to the c axis. We discuss the origin of the ``kink'' features in relation with the vortex-lattice melting and the recently proposed model of two-gap superconductivity. The influences of anisotropy on superconducting properties including the kink features are also demonstrated.

  1. Isotope effect on electron-phonon interaction in the multiband superconductor MgB2

    DOE PAGES

    Mou, Daixiang; Manni, Soham; Taufour, Valentin; ...

    2016-04-07

    We investigate the effect of isotope substitution on the electron-phonon interaction in the multiband superconductor MgB2 using tunable laser-based angle-resolved photoemission spectroscopy. The kink structure around 70 meV in the σ band, which is caused by electron coupling to the E2g phonon mode, is shifted to higher binding energy by ~3.5 meV in Mg10B2 and the shift is not affected by superconducting transition. Furthermore, these results serve as the benchmark for investigations of isotope effects in known, unconventional superconductors and newly discovered superconductors where the origin of pairing is unknown.

  2. Micro-SQUIDs based on MgB2 nano-bridges for NEMS readout

    NASA Astrophysics Data System (ADS)

    Lolli, L.; Li, T.; Portesi, C.; Taralli, E.; Acharya, N.; Chen, K.; Rajteri, M.; Cox, D.; Monticone, E.; Gallop, J.; Hao, L.

    2016-10-01

    We show the results obtained from the fabrication and characterisation of MgB2 loops with two nano-bridges as superconducting weak links. These ring structures are made to operate as superconducting quantum interference devices and are investigated as readout system for cryogenics NEMS resonators. The nano-constrictions are fabricated by EBL and ion beam milling. The SQUIDs are characterised at different temperatures and measurements of the noise levels have been performed. The devices show high critical current densities and voltage modulations under applied magnetic field, close to the critical temperatures.

  3. Band Structure Simulations of the Photoinduced Changes in the MgB2:Cr Films

    PubMed Central

    Kityk, Iwan V.; Fedorchuk, Anatolii O.; Ozga, Katarzyna; AlZayed, Nasser S.

    2015-01-01

    An approach for description of the photoinduced nonlinear optical effects in the superconducting MgB2:Cr2O3 nanocrystalline film is proposed. It includes the molecular dynamics step-by-step optimization of the two separate crystalline phases. The principal role for the photoinduced nonlinear optical properties plays nanointerface between the two phases. The first modified layers possess a form of slightly modified perfect crystalline structure. The next layer is added to the perfect crystalline structure and the iteration procedure is repeated for the next layer. The total energy here is considered as a varied parameter. To avoid potential jumps on the borders we have carried out additional derivative procedure.

  4. Enhanced critical fields and superconducting properties of pre-doped B powder-type MgB2 strands

    NASA Astrophysics Data System (ADS)

    Susner, M. A.; Yang, Y.; Sumption, M. D.; Collings, E. W.; Rindfleisch, M. A.; Tomsic, M. J.; Marzik, J. V.

    2011-01-01

    Conventional doping methods that directly add C or a C-bearing species to Mg + B powder have the disadvantage of adding C inhomogeneously, yielding either under-reacted regions or, in some cases, secondary phases which may be either beneficial or detrimental. Alternatively, pre-doped B powder provides a more homogeneous distribution of the C dopant in MgB2. In this work, powders containing varying amounts of C were used to produce in situ MgB2 strands which showed high values of Bc2, Birr and transport Jc (104 A cm - 2 at 13.3 T). Compared to SiC-added and malic-acid-treated strands the pre-doped MgB2 showed high values of Birr primarily due to more efficient C substitution into the B sublattice and a concomitant increase in transport Jc.

  5. The microstructures and superconducting properties of MgB 2 bulks prepared by a high-energy milling method

    NASA Astrophysics Data System (ADS)

    Wu, Y. F.; Lu, Y. F.; Li, J. S.; Chen, S. K.; Yan, G.; Pu, M. H.; Li, C. S.; Zhang, P. X.

    2007-12-01

    We succeeded in the synthesis of high-Jc MgB2 bulks via high energy ball-milling of elemental Mg and B powder at ambient temperatures. The mixed powder was ball-milled for 1-10 h and the completed reaction was achieved by subsequent annealing. The correlations among synthesis parameters, microstructures and superconducting properties in MgB2 bulks were investigated. Samples were characterized by X-ray diffraction and scanning electron microscope, and the magnetization properties were examined by a superconducting quantum interfere device magnetometer. The highest Jc, approximately 2.3 × 105 A/cm2 (15 K, 3 T), was obtained for samples milled for 5 h and sintered at 750 °C for 1 h. It is even comparable with SiC-doped MgB2 bulks made by Dou's group, which had exhibited the strongest reported flux pinning and the highest Jc in high field to date.

  6. Vortex Lattice Metastability and Power Law Dynamics in MgB2

    NASA Astrophysics Data System (ADS)

    Rastovski, Catherine; Kuhn, S. J.; Smith, K.; Eskildsen, M. R.; Debeer-Schmitt, L.; Dewhurst, C. D.; Gannon, W. J.; Zhigadlo, N. D.; Karpinski, J.

    2014-03-01

    Previous small-angle neutron scattering (SANS) studies of the vortex lattice (VL) of MgB2 with H ∥ c found a triangular VL which undergoes a field-driven 30° reorientation transition, forming three distinct ground state phases. A high degree of metastability exists between the VL phases of MgB2 that cannot be attributed to vortex pinning and may be a result of the jamming of VL domains [C. Rastovski et al., Phys. Rev. Lett. 111, 107002 (2013)]. To further investigate the effect of vortex motion on the metastable to ground state VL transition, we applied a small AC magnetic field parallel or perpendicular to the vortices to ``shake'' the lattice. The metastable VL volume fraction decreased with a two-step power law dependence on the number of applied AC cycles. The slow and then fast power law decay of the metastable state may indicate first nucleation and then growth of ground state VL domains. This work was supported by the Department of Energy, Basic Energy Sciences under Award No. DE-FG02-10ER46783.

  7. Trapped Magnetic Field Properties of MgB2 Bulks Doped with Ti

    NASA Astrophysics Data System (ADS)

    Naito, Tomoyuki; Yoshida, Takafumi; Fujishiro, Hiroyuki

    We have studied the trapped magnetic field properties on doped MgB2 bulk with Ti (nominal content was Mg:Ti =0.9:0.1 and 0.8:0.2). The trapped magnetic field, BT, was enhanced by approximately 1.3 times from 2.6 T of the pristine bulk to 3.5 T of the Ti-doped bulks at 15 K. The extrapolated BT(T) curve reached 5 T below 4.2 K, indicating that 5 T class bulk magnet can be realized using MgB2 with Ti-doping. The critical current density, Jc, under the magnetic field was also enhanced by Ti-doping, therefore, an irreversibility field, Birr, of the Ti-doped bulks exceeded 5 T at 20 K. Ti and TiB2 impurities confirmed by the pow- der X-ray diffraction acted as the pinning centers and resulted in the enhancement of the trapped field and the critical current density.

  8. High transport critical current density in Cu-clad multifilament MgB2 tape

    NASA Astrophysics Data System (ADS)

    Liu, C. F.; Du, S. J.; Yan, G.; Fu, B. Q.; Feng, Y.; Ji, P.; Wang, J. R.; Liu, X. H.; Zhang, P. X.; Wu, X. Z.; Zhou, L.; Cao, L. Z.; Ruan, K. Q.; Wang, C. Y.; Li, X. G.; Zhou, G. E.; Zhang, Y. H.

    2002-05-01

    Cu-clad multifilament MgB2 tapes with Ta or NbZr buffer have been fabricated by using a powder-in-tube (PIT). Mg+2B mixture powder was used as the central conductor core in single filament with Cu sheath and Ta or NbZr buffer wall. The composite tapes with 18 filaments were heat-treated in pure Ar atmosphere at 600-1000 °C for 1-10 h, and reacted in-situ to form MgB2. The phase composition and microstructure in the samples were examined by using X-ray diffraction and optical microscopy. Transport critical current was measured by a standard four-probe technique at different magnetic fields and temperatures. The sample with 18 filaments and NbZr buffer shows a high transport critical current density of 8×104 A/cm2 (10 K, 0 T) and 1.36×104 A/cm2 (10 K, 1 T).

  9. Strongly linked current flow in polycrystalline forms of the superconductor MgB2

    NASA Astrophysics Data System (ADS)

    Larbalestier, D. C.; Cooley, L. D.; Rikel, M. O.; Polyanskii, A. A.; Jiang, J.; Patnaik, S.; Cai, X. Y.; Feldmann, D. M.; Gurevich, A.; Squitieri, A. A.; Naus, M. T.; Eom, C. B.; Hellstrom, E. E.; Cava, R. J.; Regan, K. A.; Rogado, N.; Hayward, M. A.; He, T.; Slusky, J. S.; Khalifah, P.; Inumaru, K.; Haas, M.

    2001-03-01

    The discovery of superconductivity at 39K in magnesium diboride, MgB2, raises many issues, a critical one being whether this material resembles a high-temperature copper oxide superconductor or a low-temperature metallic superconductor in terms of its behaviour in strong magnetic fields. Although the copper oxides exhibit very high transition temperatures, their in-field performance is compromized by their large anisotropy, the result of which is to restrict high bulk current densities to a region much less than the full magnetic-field-temperature (H-T) space over which superconductivity is found. Moreover, the weak coupling across grain boundaries makes transport current densities in untextured polycrystalline samples low and strongly sensitive to magnetic field. Here we report that, despite the multiphase, untextured, microscale, subdivided nature of our MgB2 samples, supercurrents flow throughout the material without exhibiting strong sensitivity to weak magnetic fields. Our combined magnetization, magneto-optical, microscopy and X-ray investigations show that the supercurrent density is mostly determined by flux pinning, rather than by the grain boundary connectivity. Our results therefore suggest that this new superconductor class is not compromized by weak-link problems, a conclusion of significance for practical applications if higher temperature analogues of this compound can be discovered.

  10. Continuous- and batch-processed MgB 2/Fe strands--transport and magnetic properties

    NASA Astrophysics Data System (ADS)

    Collings, E. W.; Lee, E.; Sumption, M. D.; Tomsic, M.; Wang, X. L.; Soltanian, S.; Dou, S. X.

    2003-04-01

    The tube filling/forming powder-in-tube (PIT) technique was employed at Hyper Tech Research for the continuous processing of MgB 2/Fe composite strand. Demonstration lengths of up to 70 m of 1.2 mm diameter precursor strand--an Fe-clad Mg + B elemental powder mixture--have so far been produced. Short samples of this strand, heat treated for 3-30 min/800-950 °C, have yielded transport critical current densities ( Jc) of 2-3×10 4 A/cm 2 at 4 K/4 T, 4×10 4 A/cm 2 at 4 K/2 T, and at 4 K in self field an extrapolated Jc of at least 2×10 5 A/cm 2. Batch-processed PIT MgB 2/Fe strands and tapes were made at the University of Wollongong’s Institute for Superconducting and Electronic Materials. These were the focus of magnetization- and magnetic-shielding studies. Depending on the thickness of the Fe sheath, the superconducting core could be completely shielded at low fields (e.g. below 2 kOe). Taking this into account, the magnetic Jc is extracted, and found to be comparable to the extrapolated transport value.

  11. Dynamic and Structural Studies of Metastable Vortex Lattice Domains in MgB2

    NASA Astrophysics Data System (ADS)

    de Waard, E. R.; Kuhn, S. J.; Rastovski, C.; Eskildsen, M. R.; Leishman, A.; Dewhurst, C. D.; Debeer-Schmitt, L.; Littrell, K.; Karpinski, J.; Zhigadlo, N. D.

    Small-angle neutron scattering (SANS) studies of the vortex lattice (VL) in the type-II superconductor MgB2 have revealed an unprecedented degree of metastability that is demonstrably not due to vortex pinning, [C. Rastovski et al . , Phys. Rev. Lett. 111, 107002 (2013)]. The VL can be driven to the GS through successive application of an AC magnetic field. Here we report on detailed studies of the transition kinetics and structure of the VL domains. Stroboscopic studies of the transition revealed a stretched exponential decrease of the metastable volume fraction as a function of the number of applied AC cycles, with subtle differences depending on whether the AC field is oriented parallel or perpendicular to the DC field used to create the VL. We speculate the slower transition kinetics for the transverse AC field may be due to vortex cutting. Spatial studies include scanning SANS measurements showing the VL domain distribution within the MgB2 single crystal as well as measurements of VL correlation lengths. This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Award DE-FG02-10ER46783.

  12. Numerical modeling of MgB2 conductors for high power AC transmission

    NASA Astrophysics Data System (ADS)

    Grilli, F.; Chervyakov, A.; Zermeno, V.; Marian, A.; Grasso, G.; Goldacker, W.; Rubbia, C.

    2014-09-01

    Cables made of MgB2 superconductors are currently explored as a viable solution for transporting high electrical power in the AC regime. In order to be competitive against the DC solution, the cables need to have an acceptable level of AC losses. In this contribution, we discuss the main aspects relevant for designing a cable with a sufficiently low AC loss level. To this end, we perform finite-element-method (FEM) simulations to determine the current and field distributions and calculate the AC losses of such cable configuration. For current capacities of 2-5 kA (peak), power cables are assembled from a relatively small number of MgB2 strands. The performance of such cables strongly depends on the current and field distributions, which are in turn influenced by the number and the arrangement of the superconducting components and also by the magnetic properties of supporting materials. Numerical simulations can help to test different cable configurations and provide important insights for optimizing the cable's design. The numerical model includes the field dependence of the superconductor's critical current density Jc(B) as well as the non-linear properties of magnetic materials.

  13. Flux motion and isotropic effects in MgB2 near the critical temperature

    NASA Astrophysics Data System (ADS)

    Olutaş, M.; Kiliç, A.; Kiliç, K.; Altinkök, A.

    2012-11-01

    The anisotropic behaviour of polycrystalline MgB2 was studied in details by means of angle dependent magnetovoltage measurements ( V- θ curves) at the temperatures near the critical temperature T c, where θ is the angle between the external magnetic field H and the transport current I. The measurement of V- θ curves was carried out at fixed temperatures below T c for different values of H and I in a range of θ = -20° -200°. Magnetovoltage measurements ( V- H curves) were performed for perpendicular and parallel orientations of H with respect to I, i.e., the V ⊥- H curves for ěc H bot ěc I and V ∥- H curves for ěc Hallel ěc I . The analysis of V- θ curves does not give any agreement with V( θ) sin2( θ) or any modified angular relationship, so that the measured dissipation is nearly independent of the angle between H and I. The isotropic effects observed in MgB2 were discussed in the frame of the continuum approximation, the discrete case and the flux line cutting associated with the double critical state model derived in the literature. Finally, it is concluded that structural disorder induced isotropic effects can explain the isotropic angular dissipation observed in V- θ, I- V and V- H curves.

  14. Phase Formation and Superconductivity of Fe-TUBE Encapsulated and Vacuum-Annealed MgB2

    NASA Astrophysics Data System (ADS)

    Singh, K. P.; Awana, V. P. S.; Shahabuddin, Md.; Husain, M.; Saxena, R. B.; Nigam, Rashmi; Ansari, M. A.; Gupta, Anurag; Narayan, Himanshu; Halder, S. K.; Kishan, H.

    We report optimization of the synthesis parameters viz. heating temperature (TH), and hold time (thold) for vacuum-annealed (10-5 Torr) and LN2 (liquid nitrogen) quenched MgB2 compound. These are single-phase compounds crystallizing in the hexagonal structure (space group P6/mmm) at room temperature. Our XRD results indicated that for phase-pure MgB2, the TH for 10-5 Torr annealed and LN2-quenched samples is 750°C. The right stoichiometry i.e., MgB2 of the compound corresponding to 10-5 Torr and TH of 750°C is found for the hold time (thold) of 2.30 hours. With varying thold from 1-4 hours at fixed TH (750°C) and vacuum (10-5 Torr), the c-lattice parameter decreases first and later increases with thold (hours) before a near saturation, while the a-lattice parameter first increases and later decreases beyond a thold of 2.30 hours. The c/a ratio versus thold plot showed an inverted bell-shaped curve, touching the lowest value of 1.141, which is the reported value for perfect stoichiometry of MgB2. The optimized stoichimetric MgB2 compound exhibited superconductivity at 39.2 K with a transition width of 0.6 K. In conclusion, the synthesis parameters for phase pure stoichimetric vacuum-annealed MgB2 compound are optimized and are compared with widely-reported Ta tube encapsulated samples.

  15. Effects of Bi-2212 addition on the levitation force properties of bulk MgB2 superconductors

    NASA Astrophysics Data System (ADS)

    Taylan Koparan, E.; Savaskan, B.; Guner, S. B.; Celik, S.

    2016-02-01

    We present a detailed investigation of the effects of Bi2Sr2Ca1Cu2O8+κ (Bi-2212) adding on the levitation force and magnetic properties of bulk MgB2 obtained by hot press method. The amount of Bi-2212 was varied between 0 and 10 wt% (0, 2, 4, 6, 10 wt%) of the total MgB2. Moreover, we present MgB2 bulk samples fabricated by using different production methods including hot pressing method to our knowledge. All samples were prepared by using elemental magnesium (Mg) powder, amorphous nano-boron (B) powder and Bi-2212 powder which are produced by hot press method. As a result of hot press process, compact pellet samples were manufactured. The vertical and lateral levitation force measurements were executed at the temperatures of 20, 24 and 28 K under zero-field-cooled (ZFC) and field-cooled (FC) regimes for samples with various adding levels. At 24 K and 28 K under ZFC regime, the 2 wt% Bi-2212 added sample exhibits a higher vertical levitation force than the pure sample. Bi-2212 added MgB2 samples compared to the pure sample have lower attractive force values in FC regime. The magnetic field dependence of the critical current density J c was calculated from the M-H loops for Bi-2212 added MgB2 samples. The 2 wt% Bi-2212 added sample has the best levitation and critical current density performance compared to other samples. The critical temperature ( T c ) has slightly dropped from 37.8 K for the pure MgB2 sample to 36.7 K for the 10 wt% of Bi-2212 added sample. The transition temperature slightly decreases when Bi-2212 adding level is increased.

  16. Sugar as an optimal carbon source for the enhanced performance of MgB2 superconductors at high magnetic fields

    NASA Astrophysics Data System (ADS)

    Shcherbakova, O. V.; Pan, A. V.; Wang, J. L.; Shcherbakov, A. V.; Dou, S. X.; Wexler, D.; Babić, E.; Jerčinović, M.; Husnjak, O.

    2008-01-01

    In this paper we report the results of an extended study of the effect of sugar doping on the structural and electromagnetic properties of MgB2 superconductors. High values of the upper critical field (Bc2) of 36 T and the irreversibility field (Birr) of 27 T have been estimated at the temperature of 5 K in a bulk MgB2 sample with the addition of 10 wt% of sugar. The critical current density (Jc(Ba)) of sugar-doped samples has been significantly improved in the high field region. The value of transport Jc has reached as high as 108 A m-2 at 10 T and 5 K for Fe-sheathed sugar-doped MgB2 wire. The analysis of the pinning mechanism in the samples investigated indicated that dominant vortex pinning occurs on the surface type of pinning defects, such as grain boundaries, dislocations, stacking faults etc, for both pure and doped MgB2. In sugar-doped samples, pinning is governed by numerous crystal lattice defects, which appear in MgB2 grains as a result of crystal lattice distortion caused by carbon substitution for boron and nano-inclusions. The drastically improved superconducting properties of sugar-doped samples are also attributed to the highly homogeneous distribution and enhanced reactivity of this dopant with host Mg and B powders. The results of this work suggest that sugar is the optimal source of carbon for doping MgB2 superconductor, especially for application at high magnetic fields.

  17. Design, manufacturing and tests of first cryogen-free MgB2 prototype coils for offshore wind generators

    NASA Astrophysics Data System (ADS)

    Sarmiento, G.; Sanz, S.; Pujana, A.; Merino, J. M.; Iturbe, R.; Apiñaniz, S.; Nardelli, D.; Marino, I.

    2014-05-01

    Although renewable sector has started to take advantage of the offshore wind energy recently, the development is very intense. Turbines reliability, size, and cost are key aspects for the wind industry, especially in marine locations. A superconducting generator will allow a significant reduction in terms of weight and size, but cost and reliability are two aspects to deal with. MgB2 wire is presented as one promising option to be used in superconducting coils for wind generators. This work shows the experimental results in first cryogen-free MgB2 prototype coils, designed according to specific requirements of TECNALIA's wind generator concept.

  18. Analysis of the levitation force of pure and starch/polystyrene/MWCNT added bulk MgB2 superconductors using frozen image model under zero field cooling condition

    NASA Astrophysics Data System (ADS)

    Tripathi, D.; Dey, T. K.

    2016-04-01

    The measurement of superconducting levitation force between permanent magnet and polycrystalline samples of pure and MgB2 added with starch, polystyrene (PS) and multiwall carbon nanotube (MWCNT) have been performed under zero field cooling (ZFC) condition at 20 K in both descending and ascending modes. For this, the bulk pellets were synthesized by conventional solid state sintering technique. The XRD data indicate well developed MgB2 phase. However, a decrease in lattice parameter 'a = b' have been observed for doped MgB2 samples. Superconducting transition temperature of MgB2 also decreases with starch/PS/MWCNT addition. Unlike MWCNT, the addition of starch/polystyrene is found to enhance the levitation force of MgB2 superconductor. The levitation force between PM and investigated pellets in ZFC condition is explained well in terms of the updated version of modified frozen image model and the magnetic moment originated due to vertical motion of the superconductors have been estimated. It may be noted that except for MWCNT, addition of starch/PS in MgB2 improves the magnetic moment generated by vertical movement of pure MgB2. However, this improvement is more pronounced for 1 wt.% of PS added MgB2, which indicates more flux trapping and hence better levitation properties in 1 wt.% of PS added MgB2. The vertical stiffness estimated for pure and starch/PS/MWCNT doped MgB2 samples indicate that the levitation force are more sensitive in the region close to the PM.

  19. Demonstration of a Conduction Cooled React and Wind MgB2 Coil Segment for MRI Applications.

    PubMed

    Kim, H S; Kovacs, C; Rindfleisch, M; Yue, J; Doll, D; Tomsic, M; Sumption, M D; Collings, E W

    2016-06-01

    This study is a contribution to the development of technology for an MgB2-based, cryogen-free, superconducting magnet for an MRI system. Specifically, we aim to demonstrate that a react and wind coil can be made using high performance in-situ route MgB2 conductor, and that the conductor could be operated in conduction mode with low levels of temperature gradient. In this work, an MgB2 conductor was used for the winding of a sub-size, MRI-like coil segment. The MgB2 coil was wound on a 457 mm ID 101 OFE copper former using a react-and-wind approach. The total length of conductor used was 330 m. The coil was epoxy impregnated and then instrumented for low temperature testing. After the initial cool down (conduction cooling) the coil Ic was measured as a function of temperature (15-30 K), and an Ic of 200 A at 15 K was measured.

  20. Demonstration of a Conduction Cooled React and Wind MgB2 Coil Segment for MRI Applications

    PubMed Central

    Kim, H. S.; Kovacs, C.; Rindfleisch, M.; Yue, J.; Doll, D.; Tomsic, M.; Sumption, M. D.; Collings, E. W.

    2016-01-01

    This study is a contribution to the development of technology for an MgB2-based, cryogen-free, superconducting magnet for an MRI system. Specifically, we aim to demonstrate that a react and wind coil can be made using high performance in-situ route MgB2 conductor, and that the conductor could be operated in conduction mode with low levels of temperature gradient. In this work, an MgB2 conductor was used for the winding of a sub-size, MRI-like coil segment. The MgB2 coil was wound on a 457 mm ID 101 OFE copper former using a react-and-wind approach. The total length of conductor used was 330 m. The coil was epoxy impregnated and then instrumented for low temperature testing. After the initial cool down (conduction cooling) the coil Ic was measured as a function of temperature (15-30 K), and an Ic of 200 A at 15 K was measured. PMID:27857508

  1. Further progresses in the development of large MgB2 Superconducting Coils for the Ignitor Experiment

    NASA Astrophysics Data System (ADS)

    Tumino, A.; Grasso, G.; Coppi, B.

    2013-10-01

    Intermediate temperature superconducting cables have been adopted for the fabrication of the largest poloidal field coils of the Ignitor experiment. This is an important step toward achieving better duty cycles in Ignitor-like machines with innovative magnet technologies compared to traditional superconductors. The commercially available MgB2 strands manufactured by Columbus Superconductors can achieve the target specifications for the considered coils, about 5 meters of outer diameter and maximum field on the conductor below 5 T. These cables are also compatible with the Ignitor cryogenic system, which is designed to cool the machine at about 30 K, although MgB2 may use colder gas at 10 K. The preliminary cable design includes about 300 MgB2 multifilamentary strands of 1 mm in diameter and a copper tube for the He-gas flow in the center. Recently we have succeeded in the development of MgB2 strands with a further improvement in design and electrical properties for cable application. Reaching of a higher critical current density and better current sharing properties between the different strands is allowed by the newest design. The implementation of this progress in wire performance and its impact on the coil design will be discussed. US DOE partly sponsored.

  2. Superconductivity in MgPtSi: An orthorhombic variant of MgB2

    NASA Astrophysics Data System (ADS)

    Kudo, Kazutaka; Fujimura, Kazunori; Onari, Seiichiro; Ota, Hiromi; Nohara, Minoru

    2015-05-01

    A ternary compound, MgPtSi, was synthesized by solid-state reaction. An examination of the compound by powder x-ray diffraction revealed that it crystallizes in the orthorhombic TiNiSi-type structure with the P n m a space group. The structure comprises alternately stacked layers of Mg and PtSi honeycomb network, which is reminiscent of MgB2, and the buckling of the honeycomb network causes orthorhombic distortion. Electrical and magnetic studies revealed that MgPtSi exhibited superconductivity with a transition temperature of 2.5 K. However, its isostructural compounds, namely, MgRhSi and MgIrSi, were not found to exhibit superconductivity.

  3. Thermal conductivity in large residual resistance ratio MgB2 wire

    NASA Astrophysics Data System (ADS)

    Pope, A. L.; Tritt, T. M.; Canfield, P. C.; Bud'ko, S. L.; Liebenberg, D. H.

    2003-05-01

    We measured the thermal conductivity in MgB2 wires, with Tc=39.5 K, in both the superconducting and normal state regimes between 10-70 K. As expected, the thermal conductivity is increased for this sample, which has a residual resistance ratio (RRR) of about 32, as compared with earlier measurements on bulk samples with much lower RRR values. Over the measured temperature range, this more metallic material exhibits a temperature dependence of the thermal conductivity in the superconducting state that is different from that in previous reports and can be ascribed primarily to defect scattering. Unusual results are presented for the magnetic field dependence of the thermal conductivity around Tc for fields up to 9 T.

  4. Stoichiometry dependence of superconductivity and microstructure in mechanically alloyed MgB2

    NASA Astrophysics Data System (ADS)

    Perner, O.; Eckert, J.; Häßler, W.; Fischer, C.; Acker, J.; Gemming, T.; Fuchs, G.; Holzapfel, B.; Schultz, L.

    2005-03-01

    The correlations among stoichiometry variation, preparation route, and microstructure as well as superconducting properties were investigated in MgB2 bulk samples. We demonstrate that the different initial weight ratios of Mg and B between Mg0.9B2 and Mg1.1B2 are only slightly shifted towards Mg depletion during the mechanical alloying preparation at room temperature followed by a short annealing step. The samples with Mg surplus show the highest critical temperature Tc˜36K, highest critical current density Jc˜1.5×106A/cm2 at 7.5 K in self-field, and a homogeneous microstructure. In contrast, the Mg-depleted samples exhibit a rather porous and multiphase microstructure with a broad grain size distribution. A direct correlation of stoichiometry variation and superconducting properties was not found, but rather a strong influence of the Mg content on lattice strain and grain connectivity.

  5. Surface superconductivity of dirty two-band superconductors: applications to MgB2.

    PubMed

    Gorokhov, Denis A

    2005-02-25

    The minimal magnetic field H(c2) destroying superconductivity in the bulk of a superconductor is smaller than the magnetic field H(c3) needed to destroy surface superconductivity if the surface of a superconductor coincides with one of the crystallographic planes and is parallel to the external magnetic field. While for a dirty single-band superconductor the ratio of H(c3) to H(c2) is a universal temperature-independent constant 1.6946, for dirty two-band superconductors this is not the case. I show that in the latter case the interaction of the two bands leads to a novel scenario with the ratio H(c3)/H(c2) varying with temperature and taking values larger and smaller than 1.6946. The results are applied to MgB(2) and compared with recent experiments (A. Rydh, cond-mat/0307445).

  6. Structural and AC loss study for pure and doped MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Hansdah, J. S.; Sarun, P. M.

    2015-06-01

    Superconducting polycrystalline bulk MgB2 samples doped with n-C, n-Y2O3 and n-Ho2O3 were prepared by powder-in-sealed (PIST) method. XRD measurement shows the influence of dopants on phase and lattice parameters of samples. The ac susceptibility measurement reveals ac loss and activation energy of the samples. Nano-C doped sample shows less ac loss in all frequency (208 Hz - 999 Hz) among the doped samples; whereas n-Ho2O3 doped sample shows highest ac loss. The activation energy is high for rare earth (n-Y2O3 and n-Ho2O3) doped samples as compare to n-C doped samples which reveals the enhancement in flux-pinning properties of these materials.

  7. Intra-wire resistance and AC loss in multi-filamentary MgB2 wires

    NASA Astrophysics Data System (ADS)

    Zhou, C.; Offringa, W.; Bergen, A.; Wessel, W. A. J.; Krooshoop, H. J. G.; Dhallé, M.; Sumption, M. D.; Collings, E. W.; Rindfleisch, M.; Tomsic, M.; ten Kate, H. H. J.; Nijhuis, A.

    2013-02-01

    Intra-wire resistance and AC loss of various multi-filamentary MgB2 wires with filaments surrounded by Nb barriers have been measured and analyzed. The intra-wire resistance is measured with a direct four-probe voltage-current method at various temperatures. The AC loss is acquired by both vibrating sample magnetometer (VSM) and magnetization measurements at 4.2 K. With the aid of finite element method simulations, the filament-to-matrix contact resistance and effective transverse resistivity are derived from direct intra-wire resistance measurements. The effective transverse resistivity values are in good agreement with those analytically derived from the AC coupling loss measurements. Surprisingly, very high values of filament-to-matrix contact resistivity are found, being 2 or 3 orders higher than commonly found for NbTi or Nb3Sn wires.

  8. AC losses and transverse resistivity in filamentary MgB 2 tape with Ti barriers

    NASA Astrophysics Data System (ADS)

    Polák, M.; Demenčík, E.; Hušek, I.; Kopera, L.; Kováč, P.; Mozola, P.; Takács, S.

    2011-07-01

    We measured and analyzed AC losses of MgB 2 tape with 19 filaments surrounded by Ti barriers and embedded in copper stabilization, exposed to external magnetic field with frequencies from 30 mHz up to 1.4 Hz and amplitudes up to 0.8 T at 4.2 K. Using the measured frequency dependence of the total AC losses we determined the contribution of hysteresis and coupling losses. The transverse resistivity determined from the coupling losses is considerably higher than that corresponding to the resistivity of copper stabilization before the tape processing due to diffusion of Ti. From the measured penetration field critical current densities were determined using results of theories for circular as well as rectangular filaments.

  9. Physical property characterization of Fe-tube encapsulated and vacuum annealed bulk MgB 2

    NASA Astrophysics Data System (ADS)

    Awana, V. P. S.; Rawat, Rajeev; Gupta, Anurag; Isobe, M.; Singh, K. P.; Vajpayee, Arpita; Kishan, H.; Takayama-Muromachi, E.; Narlikar, A. V.

    2006-08-01

    We report the phase formation, and present a detailed study of magnetization and resistivity under magnetic field of MgB 2 polycrystalline bulk samples prepared by the Fe-tube encapsulated and vacuum (10 -5 Torr) annealed (750 ∘C) route. Zero-field-cooled magnetic susceptibility (χ) measurements exhibited a sharp transition to the superconducting state with a sizeable diamagnetic signal at 39 K (Tc). The measured magnetization loops of the samples, despite the presence of flux jumps, exhibited a stable current density (Jc) of around 2.4×10 5 A/cm 2 in up to 2 T (Tesla) field and at temperatures (T) up to 10 K. The upper critical field is estimated from resistivity measurements in various fields and shows a typical value of 8 T at 21 K. Further, χ measurements at an applied field of 0.1 T reveal a paramagnetic Meissner effect (PME) that is briefly discussed.

  10. Effect of La doping on microstructure and critical current density of MgB2

    NASA Astrophysics Data System (ADS)

    Shekhar, Chandra; Giri, Rajiv; Tiwari, R. S.; Rana, D. S.; Malik, S. K.; Srivastava, O. N.

    2005-09-01

    In the present study, La-doped MgB2 superconductors with different doping levels (Mg1-xLaxB2; x = 0.00, 0.01, 0.03 and 0.05) have been synthesized by the solid-state reaction route at ambient pressure. Effects of La doping have been investigated in relation to microstructural characteristics and superconducting properties, particularly intragrain critical current density (Jc). The microstructural characteristics of the as-synthesized Mg(La)B2 compounds were studied employing the transmission electron microscopic (TEM) technique. The TEM investigations reveal inclusion of LaB6 nanoparticles within the MgB2 grains, which provide effective flux pinning centres. The evaluation of intragrain Jc through magnetic measurements on the fine powdered version of the as-synthesized samples reveal that Jc values of the samples change significantly with the doping level. The optimum result on Jc is obtained for Mg0.97La0.03B2 at 5 K Jc reaches ~1.4 × 107 A cm-2 in self-field, ~2.1 × 106 A cm-2 at 1 T, ~2.5 × 105 A cm-2 at 2.5 T and ~1.8 × 104 A cm-2 at 4.5 T. The highest value of intragrain Jc in the Mg0.97La0.03B2 superconductor has been attributed to the inclusion of LaB6 nanoparticles, which are capable of providing effective flux pinning centres.

  11. Electrical resistivity, Debye temperature, and connectivity in heavily doped bulk MgB2 superconductors

    NASA Astrophysics Data System (ADS)

    Susner, M. A.; Bhatia, M.; Sumption, M. D.; Collings, E. W.

    2009-05-01

    The measured transport critical current densities, Jc, of MgB2 superconductors fall short of their intrinsic Jcs on account of the grain boundary blockage, sausaging, and porosity seen in most powder-processed wire samples. Hence, it becomes important to understand and to be able to measure the degree of what can be referred to as "connectivity" in order to be able to assess the highest attainable Jc in a given class of samples. In this paper connectivity is determined with the aid of normal state resistivity in an extension of the model originally proposed by Rowell. The normal-state resistivity temperature dependence is fitted to a standard Bloch-Grüneisen (B-G) equation in the range 50-300 K. Such an approach leads not only to a connectivity parameter but also to other useful data: the actual intragrain residual resistivity (indirectly related to the upper critical field) and a resistively determined Debye temperature, θR. The latter quantity, coupled to the transition temperature, Tc, provides a measure (by way of the McMillan formula) of the electron-phonon coupling constant, usually designated λ. The B-G-based connectivity model was applied to our own experimental data on binary and heavily doped MgB2 samples as well as published resistivity data. To complete the study, low temperature specific heat measurements, performed on binary and doped bulk samples provided calorimetrically determined Debye temperatures, θD, for comparison to the resistively determined values and excellent agreement was found. Calorimetric measurements also probed the homogeneity of the doped samples in terms of the roundness of the electronic specific heat jump near Tc.

  12. Fabrication of MgB 2 nanobridge dc SQUIDs by focused ion beam

    NASA Astrophysics Data System (ADS)

    Hong, Sung-Hak; Lee, Soon-Gul; Kyung Seong, Won; Nam Kang, Won

    2010-12-01

    We have studied fabrication of MgB2 intragrain nanobridge dc SQUIDs by a focused ion beam (FIB) patterning technique. Not only the nanobridges as Josephson elements but the SQUID loop was patterned by FIB. The beam voltage was 30 kV and the beam current was 0.9 nA for the SQUID loop and 1.5 pA for the nanobridges. Each bridge had a nominal width and length of about 100 nm and a thickness of 650 nm. The SQUID loop had a 3 μm × 3 μm hole with a 2 μm average linewidth. The zero-field superconducting transition temperature (Tc) of the SQUID was 37 K. Current-voltage (I-V) characteristics of the SQUID showed large excess currents at all temperatures with a small portion of a resistively-shunted-junction (RSJ) component which increases as temperature approaches Tc. At low temperatures, the I-V curves exhibit a large heating effect with a second transition step, which is believed to be due to the transition of a grain boundary near the nanobridge. The SQUID showed well-behaving modulation properties at all temperatures with a modulation depth of more than 30 μV at 33.5 K and 110 μV at 15 K. These results together with our previous results on the intergrain nanobridge dc SQUID suggest that fabrication of dc SQUIDs based on FIB-patterned MgB2 nanobridges is highly tolerant of fabrication conditions.

  13. Experimental studies of the quench behaviour of MgB2 superconducting wires for fault current limiter applications

    NASA Astrophysics Data System (ADS)

    Ye, Lin; Majoros, M.; Campbell, A. M.; Coombs, T.; Astill, D.; Harrison, S.; Husband, M.; Rindfleisch, M.; Tomsic, M.

    2007-07-01

    Various MgB2 wires with different sheath materials provided by Hyper Tech Research Inc., have been tested in the superconducting fault current limiter (SFCL) desktop tester at 24-26 K in a self-field. Samples 1 and 2 are similarly fabricated monofilamentary MgB2 wires with a sheath of CuNi, except that sample 2 is doped with SiC and Mg addition. Sample 3 is a CuNi sheathed multifilamentary wire with Cu stabilization and Mg addition. All the samples with Nb barriers have the same diameter of 0.83 mm and superconducting fractions ranging from 15% to 27% of the total cross section. They were heat-treated at temperatures of 700 °C for a hold time of 20-40 min. Current limiting properties of MgB2 wires subjected to pulse overcurrents have been experimentally investigated in an AC environment in the self-field at 50 Hz. The quench currents extracted from the pulse measurements were in a range of 200-328 A for different samples, corresponding to an average engineering critical current density (Je) of around 4.8 × 104 A cm-2 at 25 K in the self-field, based on the 1 µV cm-1 criterion. This work is intended to compare the quench behaviour in the Nb-barrier monofilamentary and multifilamentary MgB2 wires with CuNi and Cu/CuNi sheaths. The experimental results can be applied to the design of fault current limiter applications based on MgB2 wires. This work is supported by Rolls-Royce plc and the UK Department of Trade and Industry (DTI).

  14. The synthesis of lamellar nano MgB2 grains with nanoimpurities, flux pinning centers and their significantly improved critical current density.

    PubMed

    Ma, Zongqing; Liu, Yongchang; Cai, Qi

    2012-03-21

    MgB(2) superconductors with unique microstructures were rapidly fabricated at low temperatures, and exhibited significantly improved critical current density (J(c)). According to the microstructure observations, the prepared samples consisted of lamellar nano MgB(2) grains with many embedded nanoimpurities (about 10 nm). The formation of these lamellar nano MgB(2) grains is associated with the presence of a local Mg-Cu liquid at sintering temperatures as low as 575 °C. The ball milling treatment of the original powders also plays a positive role in the growth of lamellar grains. Based on an analysis of the relationship between resistivity and temperature, the lamellar nano MgB(2) grains in the prepared sample possess better grain connectivity than the typical morphology of MgB(2) samples prepared by traditional high-temperature sintering. Furthermore, the presence of many nano MgB(2) grain boundaries and nano impurities in the prepared sample can obviously increase the flux pinning centers in accordance with the analysis of flux pinning behavior. Both factors mentioned above contribute to the significant improvement in J(c) from low field to relative high field. The method developed in the present work is an effective and low-cost way to further enhance J(c) in MgB(2) superconductors across a wide range of applied magnetic fields without using expensive nanometer-sized dopants.

  15. Estimation of π and σ band contributions in the normal state electrical conductivity of (Bi, Pb)-2223 added MgB2 superconductors

    NASA Astrophysics Data System (ADS)

    Tripathi, D.; Dey, T. K.

    2015-06-01

    Temperature dependence of the normal state electrical resistivity of polycrystalline MgB2 added with 0, 0.5, 1, 3 and 5 wt. % of (Bi, Pb)-2223 (Bi1.8Pb0.26Sr2Ca2Cu3O10+x) superconducting powder have been investigated in the light of two band approach based on π and σ bands of MgB2 superconductor. The scattering rates (γσ, γπ) and residual resistivity (ρ0σ,ρ0π) of each band are estimated for the investigated samples. Our observation for pure MgB2 shows much higher scattering rate in π bands, as compared to σ bands and hence indicates 'dirty' nature of the samples. However, the addition of 2223 in MgB2 is found to enhance the scattering rate in both bands, but the enhancement is more pronounced in π bands as compared to σ bands. Contribution of each individual band towards the total electrical conductivity of 2223 added MgB2 pellets are separated. Our analysis confirms that σ band contribution shows a small increase with 2223 addition and reaches nearly 89% for 5 wt. % 2223 added MgB2 polycrystalline pellets. The electron-phonon coupling constant (λ) of pure and 2223 added MgB2 pellets calculated using Mc-Millan expression is found to be nearly invariant with 2223 addition.

  16. The effect of geometry of composite MgB 2/stainless-steel (SS) wires fabricated by PIT process on the superconducting properties

    NASA Astrophysics Data System (ADS)

    Song, K. J.; Kim, S. W.; Park, C.; Joo, J. H.; Choi, S. J.; Ko, R. K.; Ha, H. S.; Ha, D. W.; Oh, S. S.

    2004-08-01

    Single-, multi-, and two kinds of coaxial-filament composite MgB 2/SS-SS (stainless steel for both outer and inner tubes) and MgB 2/SS-Cu (stainless steel for outer tube and copper for inner tube) wires were successfully fabricated using powder-in-tube (PIT) process with swaging only. The effect of the geometries of the MgB 2 PIT wires has been studied comparatively. The isothermal magnetizations M( H) for both the sintered and the as-rolled single-, multi-, and coaxial-filament MgB 2 wires were measured at temperatures between 5 and 50 K in fields up to 5 T. The critical current density was estimated by the M( H) data using Bean model. The coaxial-filament composite MgB 2 wires showed much better Jc than both the single- and the multi-filament composite ones. The results of this study show that the superconducting properties of the MgB 2 PIT wires/tapes can improve by employing better geometries such as the coaxial-filament composite MgB 2/SS-SS wires.

  17. High critical current density and improved flux pinning in bulk MgB2 synthesized by Ag addition

    NASA Astrophysics Data System (ADS)

    Shekhar, Chandra; Giri, Rajiv; Tiwari, R. S.; Srivastava, O. N.; Malik, S. K.

    2007-02-01

    In the present investigation, we report a systematic study of Ag admixing in MgB2 prepared by solid-state reaction at ambient pressure. All the samples in the present investigation have been subjected to structural/ microstructural characterization employing x-ray diffraction and transmission electron microscopic (TEM) techniques. The magnetization measurements were performed by physical property measurement system. The TEM investigations reveal the formation of MgAg nanoparticles in Ag admixed samples. These nanoparticles may enhance critical current density due to their size (˜5-20nm ) which is compatible with the coherence length of MgB2 (˜5-6nm ). In order to study the flux pinning effect of Ag admixing in MgB2, the evaluation of intragrain critical current density (Jc) has been carried out through magnetic measurements on the fine powdered version of the as synthesized samples. The optimum result on intragrain Jc is obtained for 10at.% Ag admixed sample at 5K. This corresponds to ˜9.23×107A /cm2 in self-field, ˜5.82×107A/cm2 at 1T, ˜4.24×106A/cm2 at 3.6T, and ˜1.52×105A/cm2 at 5T. However, intragrain Jc values for MgB2 sample without Ag admixing are ˜2.59×106, ˜1.09×106, ˜4.53×104, and 2.91×103A /cm2 at 5K in self-field, 1T, 3.6T, and 5T, respectively. The high value of intragrain Jc for Ag admixed MgB2 superconductor has been attributed to the inclusion of MgAg nanoparticles into the crystal matrix of MgB2, which are capable of providing effective flux pinning centers. A feasible correlation between microstructural features and superconducting properties has been put forward.

  18. Effect of Dy2O3 doping on phase formation and properties of MgB2 wires made by the modified internal magnesium diffusion process

    NASA Astrophysics Data System (ADS)

    Brunner, B.; Rosová, A.; Kováč, P.; Reissner, M.; Dobročka, E.

    2017-02-01

    A series of single-core MgB2 wires was produced by the modified internal magnesium diffusion process, starting with a Mg tube filled with carbon predoped boron powder, which resulted in an extractable MgB2 core allowing thorough investigation of superconducting properties. Carbon contained in the boron powder enhances critical current density (J c), however, it also reduces the reactivity of boron and thus acts as a MgB2 growth inhibitor. In order to compensate this negative effect, Dy2O3 nanopowder was added into boron powder and the composites were subjected to heat-treatment at increased temperature for a longer time. By this approach, the reactivity of carbon predoped boron was substantially improved, yielding wires with an increased amount of MgB2 of high phase purity with enhanced J c.

  19. Low noise terahertz MgB2 hot-electron bolometer mixers with an 11 GHz bandwidth

    NASA Astrophysics Data System (ADS)

    Novoselov, E.; Cherednichenko, S.

    2017-01-01

    Terahertz (THz) hot-electron bolometer mixers reach a unique combination of low noise, wide noise bandwidth, and high operation temperature when 6 nm thick superconducting MgB2 films are used. We obtained a noise bandwidth of 11 GHz with a minimum receiver noise temperature of 930 K with a 1.63 THz Local Oscillator (LO), and a 5 K operation temperature. At 15 K and 20 K, the noise temperature is 1100 K and 1600 K, respectively. From 0.69 THz to 1.63 THz, the receiver noise increases by only 12%. Device current-voltage characteristics are identical when pumped with LOs from 0.69 THz up to 2.56 THz, and match well with IVs at elevated temperatures. Therefore, the effect of the THz waves on the mixer is totally thermal, due to absorption in the π conduction band of MgB2.

  20. Enhancement of critical current of SiC and malic acid codoped MgB2/Fe wires

    NASA Astrophysics Data System (ADS)

    Li, W. X.; Chen, R. H.; Xu, X.; Hu, Y. M.; Zhu, M. Y.; Li, Y.; Dou, S. X.

    2015-09-01

    The influences of microstructure, connectivity, and disorder on the critical current density, Jc, are discussed to clarify the different mechanisms of Jc(H) in different magnetic field ranges for in situ and combined in situ/ex situ MgB2/Fe wires with nano SiC and malic acid codoping. Sintering temperature plays a very important role in the electromagnetic properties at different temperatures and under various magnetic fields. Connectivity, upper critical field, Hc2, and irreversibility field, Hirr, are studied to demonstrate the mechanism of Jc dependence on magnetic field. The combined in situ/ex situ process is proved to be a promising technique for fabrication of practical MgB2 wires.

  1. Correlation between critical current density and n-value in MgB 2/Nb/Monel superconductor wires

    NASA Astrophysics Data System (ADS)

    Kim, J. H.; Dou, S. X.; Matsumoto, A.; Choi, S.; Kiyoshi, T.; Kumakura, H.

    2010-11-01

    Field and temperature dependences of critical current density (Jc) and n-value were evaluated from un-doped and carbon doped MgB2 wires, supplied by the Hyper Tech Research, Inc. In order to explore the possibility of persistent current mode, the variation of n-values for the different MgB2 conductors was studied in more detail. It was observed that the n-value decreased gradually with an increasing magnetic field and operating temperature. From the power-law relationship between the Jc and the n-value, n ∝ Jcm, we found that there was a strong relationship, m = 0.371, for both wires at 4.2 and 20 K. On the basis of our experiments, a larger Jc led to a higher n-value, whether there was doping or not.

  2. Persistence of metastable vortex lattice domains in MgB2 in the presence of vortex motion.

    PubMed

    Rastovski, C; Schlesinger, K J; Gannon, W J; Dewhurst, C D; DeBeer-Schmitt, L; Zhigadlo, N D; Karpinski, J; Eskildsen, M R

    2013-09-06

    Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.

  3. Persistence of Metastable Vortex Lattice Domains in MgB2 in the Presence of Vortex Motion

    SciTech Connect

    Rastovski, Catherine; Schlesinger, Kimberly; Gannon, William J; Dewhurst, Charles; Debeer-Schmitt, Lisa M; Zhigadlo, Nikolai; Karpinski, Janusz; Eskildsen, Morten

    2013-01-01

    Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.

  4. Investigation on the AC loss characteristics of MgB 2 wires by using a conduction cooling device

    NASA Astrophysics Data System (ADS)

    Jin, H. B.; Li, Z.; Ryu, K.

    2011-11-01

    In this study, we have experimentally investigated the AC loss characteristics of MgB2 wires with matrix of Fe and Cu by using a conduction cooling device. We fabricated the conduction cooling device to cool MgB2 wires down to 4 K. We also developed our unique test method, which is called AC pulse technique, to evaluate their AC loss characteristics within few hundred milliseconds. The test results show that the AC loss of the Fe/MgB2 wire is mainly generated in the ferromagnetic Fe matrix. Its AC loss is ten times larger than that of the Cu/MgB2 wire. In this paper, the evaluation technique of AC loss by using the conduction cooling device is described and the test results are discussed.

  5. Electromagnetic properties and microstructures of in situ MgB2 wires made from three types of boron powders

    NASA Astrophysics Data System (ADS)

    Kodama, Motomune; Kotaki, Hiroshi; Yamamoto, Hiroyuki; Iwane, Tomohiro; Tanaka, Kazuhide; Tanaka, Hideki; Okishiro, Kenji; Okamoto, Kazutaka; Nishijima, Gen; Matsumoto, Akiyoshi; Kumakura, Hiroaki; Yamamoto, Akiyasu; Shimoyama, Jun-ichi; Kishio, Kohji

    2016-10-01

    In powder-in-tube processed MgB2 wires, the choice of boron powder as a starting material crucially affects their performance. In this paper, we prepared in situ MgB2 wires from three types of boron powders in various heat-treatment conditions and investigated their electromagnetic properties and microstructures. Their critical current density, J c, varied over a wide range from sample to sample. The difference in J c is understood to be caused by the effect of changes in the electrical connectivity, K, and intrinsic residual resistivity, ρ 0. Here, K represents the effective cross-sectional area for current, and ρ 0 reflects the degree of the charge carrier scattering caused by lattice defects. It was found that the use of boron powder with a large specific surface area leads to a large degree of lattice defects in MgB2 grains and enhances ρ 0, resulting in improving J c. The boron powder produced by thermal decomposition of B2H6 has a large specific surface area. Hence, this boron powder is the most suitable as a starting material for MgB2. Meanwhile, dry pulverization of low-cost boron powder, which is largely produced by active-metal reduction of B2O3, is also effective to increase its specific surface area without introducing impurities, resulting in the enhancement of J c in the entire magnetic field region. This finding broadens the choice of boron powder and contributes to realizing superconducting applications with excellent balance between performance and cost.

  6. Structure and stability of superconducting core of single-core MgB2/Cu,Nb tube composite with a high critical current

    NASA Astrophysics Data System (ADS)

    Krinitsina, T. P.; Kuznetsova, E. I.; Blinova, Yu. V.; Rakov, D. N.; Belotelova, Yu. N.; Sudareva, S. V.; Degtyarev, M. V.; Romanov, E. P.

    2014-06-01

    The core of a single-core MgB2/Cu,Nb composite, which has been prepared by the ex-situ technique and exhibits a high critical current equal to 427 A (at 0 T and 4.2 K, j c ≥ 105 A/cm2), has been studied using various structural methods. Two kinds of MgB2 crystals were observed; those of the first kind is large, highly dense crystals characterized by a low oxygen content (2-8 at %) and the others are fine, weakly coupled crystallites characterized by high oxygen content (4-21 at %). To perform a comparative analysis of the structures, we have also studied an MgB2 bulk sample synthesized at 1000°C. It was found that two phases with the same lattice are formed; they differ in the magnesium and boron contents (within the homogeneity range), impurity oxygen content and microstructure as well but differ slightly in the lattice parameters. The two-phase state of MgB2 bulk sample is due to the mechanism of its formation, which includes the melting of magnesium, the dissolution of solid boron in it, and the crystallization of MgB2 from the melt with the formation of dendrite-like structure characterized by corresponding redistribution of components and impurities. To a certain degree, the two-phase structure of MgB2 bulk sample is inherited by the MgB2/Cu,Nd composite prepared by ex-situ technique (annealing of composite at 700°C). It was shown that oxygen in the MgB2 compound is the destabilizing factor and leads to the transformation of the superconductor into MgO.

  7. Calorimetric AC loss measurement of MgB2 superconducting tape in an alternating transport current and direct magnetic field

    NASA Astrophysics Data System (ADS)

    See, K. W.; Xu, X.; Horvat, J.; Cook, C. D.; Dou, S. X.

    2012-11-01

    Applications of MgB2 superconductors in electrical engineering have been widely reported, and various studies have been made to define their alternating current (AC) losses. However, studies on the transport losses with an applied transverse DC magnetic field have not been conducted, even though this is one of the favored conditions in applications of practical MgB2 tapes. Methods and techniques used to characterize and measure these losses have so far been grouped into ‘electrical’ and ‘calorimetric’ approaches with external conditions set to resemble the application conditions. In this paper, we present a new approach to mounting the sample and employ the calorimetric method to accurately determine the losses in the concurrent application of AC transport current and DC magnetic fields that are likely to be experienced in practical devices such as generators and motors. This technique provides great simplification compared to the pickup coil and lock-in amplifier methods and is applied to a long length (˜10 cm) superconducting tape. The AC loss data at 20 and 30 K will be presented in an applied transport current of 50 Hz under external DC magnetic fields. The results are found to be higher than the theoretical predictions because of the metallic fraction of the tape that contributes quite significantly to the total losses. The data, however, will allow minimization of losses in practical MgB2 coils and will be used in the verification of numerical coil models.

  8. AC losses in high pressure synthesized MgB2 bulk rings measured by a transformer method

    NASA Astrophysics Data System (ADS)

    Meerovich, V.; Sokolovsky, V.; Prikhna, T.; Gawalek, W.; Habisreuther, T.

    2013-03-01

    Recently developed manufacturing technologies use high pressure and various doping additions to prepare bulk MgB2-based materials with a high critical current density measured by the magnetization method. We use a contactless transformer method, which is based on studying the superconductor response to an induced transport current, to measure AC losses in bulk MgB2 rings synthesized under high pressure. The obtained dependence of the losses on the primary current (applied magnetic field) is fitted by a power law with an exponent of ˜2.1 instead of the cubic dependence predicted by Bean’s model and power law electric field-current density (E-J) characteristics with a large exponent. An unusually strong dependence of the AC losses on the frequency is also observed. It is shown that the E-J characteristic of bulk MgB2 is well fitted by the dependence used in the extended critical state model based on account of the viscous vortex motion in the flux flow regime. Numerical simulation using this E-J characteristic gives current and frequency AC loss dependences that agree well with the experimental results.

  9. Experimental study of magnetization AC loss in MgB2 wires and cables with non-magnetic sheath

    NASA Astrophysics Data System (ADS)

    Kováč, Ján; Šouc, Ján; Kováč, Pavol; Hušek, Imrich; Gömöry, Fedor

    2013-12-01

    The influence of MgB2 wires design on the magnetization AC loss was studied. AC loss in external AC magnetic field perpendicular to the wire axis was measured in the temperature range from 18 K up to 40 K and at the frequencies of 72 Hz and 144 Hz, respectively. For this purpose the experimental apparatus combining magnetization measurement system and non-magnetic vacuum vessel with two-stage crycooler for sample cooling has been used. To clarify the influence of wire architecture on the AC loss in non-magnetic GlidCop sheathed MgB2 composites experiments on a single-core, 30-filament un-twisted and also twisted samples were performed. MgB2 cables containing 7 mono-core strands and 30 filament strands were also measured. While in the cable containing single core strands the hysteresis loss was dominant, in the un-twisted wire and the cable with un-twisted filaments the coupling loss prevailed. The effect of decoupling was observed in all twisted filamentary wires. The obtained results show that in 7 strands cable the AC loss of strands is crucial to the overall AC loss of a cable.

  10. Superconducting tunnel junctions on MgB2 using MgO and CaF2 as a barrier

    NASA Astrophysics Data System (ADS)

    Sakoda, Masahito; Aibara, Masato; Mede, Kazuya; Kikuchi, Motoyuki; Naito, Michio

    2016-11-01

    We report the fabrication of superconducting tunnel junctions, both of superconductor-insulator-normal metal (SIN) and superconductor-insulator-superconductor (SIS), on MgB2 using MgO and CaF2 as a barrier. The SIN junctions fabricated using an MgO barrier showed excellent quasi-particle characteristics, including a large superconducting gap (Δ) of 2.5-3 meV and a low zero-bias conductance. We have also fabricated SIS junctions with an MgO barrier, but the quasi-particle characteristics of the SIS junctions are not as good as those of the SIN junctions, namely a reduced superconducting gap and a high zero-bias conductance. It appears that top MgB2 electrodes do not grow well on an MgO barrier, which is also suggested from in-situ RHEED observation. The SIN junctions fabricated using a CaF2 barrier showed less sharp quasi-particle characteristics than using an MgO barrier. However, the SIS junctions using a CaF2 barrier showed a fairly large IcRN value at 4.2 K over 1 mV and also exhibited finite Josephson current up to almost the film's Tc (∼30 K). The RHEED observation revealed that top MgB2 electrodes grow well on a CaF2 barrier.

  11. Transport critical current density of Fe sheath MgB 2 tapes sintered at different temperatures

    NASA Astrophysics Data System (ADS)

    Ruan, K. Q.; Li, H. L.; Yu, Y.; Wang, C. Y.; Cao, L. Z.; Liu, C. F.; Du, S. J.; Yan, G.; Feng, Y.; Wu, X.; Wang, J. R.; Liu, X. H.; Zhang, P. X.; Wu, X. Z.; Zhou, L.

    2003-04-01

    Fe sheath MgB 2 tapes sintered at 650, 750, 850 and 950 °C, respectively, for 2 h in a high purity argon gas were prepared using the powder-in-tube method. Transport critical current densities of tapes were measured in the fields up to 10 T from 4 to 30 K. Both tapes sintered at 850 and 950 °C completely lost the capacity of carrying superconducting current over the temperature range from 4 to 30 K. Compared to a tape sintered at 650 °C, an improvement in the in-field critical current density Jc and irreversibility field μ0H*( T) was observed in a tape sintered at 750 °C. At 20 K, the Jc value was ∼1.32×10 5 A/cm 2 in self-field and the μ0H* value 4.2 T for the tape sintered at 750 °C, whereas the Jc in self-field and μ0H* values were ∼5.9×10 4 A/cm 2 and 2.8 T for that sintered at 650 °C.

  12. Electric transport measurements on bulk, polycrystalline MgB2 samples prepared at various reaction temperatures

    NASA Astrophysics Data System (ADS)

    Wiederhold, A.; Koblischka, M. R.; Inoue, K.; Muralidhar, M.; Murakami, M.; Hartmann, U.

    2016-03-01

    A series of disk-shaped, bulk MgB2 superconductors (sample diameter up to 4 cm) was prepared in order to improve the performance for superconducting super-magnets. Several samples were fabricated using a solid state reaction in pure Ar atmosphere from 750 to 950oC in order to determine the optimum processing parameters to obtain the highest critical current density as well as large trapped field values. Additional samples were prepared with added silver (up to 10 wt.-%) to the Mg and B powder. Magneto-resistance data and I/V-characteristics were recorded using an Oxford Instruments Teslatron system. From Arrhenius plots, we determine the TAFF pinning potential, U 0. The I/V-characteristics yield detailed information on the current flow through the polycrystalline samples. The current flow is influenced by the presence of pores in the samples. Our analysis of the achieved critical currents together with a thorough microstructure investigation reveals that the samples prepared at temperatures between 775°C and 805°C exhibit the smallest grains and the best connectivity between them, while the samples fabricated at higher reaction temperatures show a reduced connectivity and lower pinning potential. Doping the samples with silver leads to a considerable increase of the pinning potential and hence, the critical current densities.

  13. Selected properties of GlidCop® sheathed MgB2 wires

    NASA Astrophysics Data System (ADS)

    Kováč, P.; Melišek, T.; Kopera, L.; Kováč, J.; Hušek, I.

    2012-09-01

    GlidCop® sheathed MgB2 wires containing 1-30 filaments have been manufactured by a powder-in-tube process. Two materials (Nb or Ti) have been used for barriers protecting the filaments against the diffusion of copper. Different deformations (drawing, rolling, rotary swaging and isostatic pressing) have been applied to the 30-filament wires prior to the final heat treatment. Critical current densities, Jc, were measured at low external magnetic fields including the self-field and at temperatures from 4.2 to 20 K by a short pulse currents. This allows a detailed pinning force analysis to be made, which has not been done up to now from the transport current data. The resistance of 1-30 filament wires against axial tensile stress has also been examined at 4.2 K. It was found that filament density influences not only the transport Jc but also the resistance to tension stress. While an increased filament density improves Jc the opposite effect has been found for resistance to axial tension. AC losses measured by a calibration-free technique of non-twisted wires have shown the dominant effect of the filament architecture and critical current densities.

  14. Carbon doping of MgB 2 by toluene and malic-acid-in-toluene

    NASA Astrophysics Data System (ADS)

    Bohnenstiehl, S. D.; Susner, M. A.; Yang, Y.; Collings, E. W.; Sumption, M. D.; Rindfleisch, M. A.; Boone, R.

    2011-02-01

    The decomposition of malic acid (C 4H 6O 5) in the presence of Mg and B was studied using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) which revealed that malic acid reacted with Mg but not B. Also, the addition of toluene (C 7H 8) to dissolve malic acid followed by subsequent drying resulted in no reaction with Mg, indicating that the malic acid had decomposed during the dissolution/drying stage. The total carbon contributed by toluene versus a toluene/5 wt.% malic acid mixture was measured using a LECO CS600 carbon analyzer. The toluene sample contained ∼0.4 wt.% C while the toluene/malic acid mixture had ∼1.5 wt.% C, demonstrating that the toluene contributed a significant amount of carbon to the final product. Resistivity measurements on powder-in-tube MgB 2 monofilamentary wires established that the toluene/malic acid doped sample had the highest B c2. However, the toluene-only sample had the highest transport J c over most of the magnetic field range (0-9 T), equaled only by that of toluene/malic-acid sample in fields above 9 T.

  15. Plasma synthesized doped B powders for MgB 2 superconductors

    NASA Astrophysics Data System (ADS)

    Marzik, J. V.; Suplinskas, R. J.; Wilke, R. H. T.; Canfield, P. C.; Finnemore, D. K.; Rindfleisch, M.; Margolies, J.; Hannahs, S. T.

    2005-07-01

    Gas phase plasma synthesis methods have been used to prepare nano-scale particles of C doped boron powder that are well suited for powder-in-tube (PIT) fabrication of superconducting wire. Mixtures of H2, BCl3, and CH4 gas are injected into an induction plasma where doped boron powder is formed and collected on a stainless steel screen. The particles typically are ∼20 nm in size and collect into lacy agglomerates in the 1-50 μm size range. Pressed pellets of these powders heated in a Mg atmosphere are transformed to the MgB2 phase at temperatures ranging from 600 °C to 1200 °C. Critical current densities, Jc, at 5 K run from about 106 A/cm2 at self-field to 4 × 104 A/cm2 at 7 T. At 20 K, Jc ranges from 5 × 105 A/cm2 at self-field to about 104 A/cm2 at 3 T. Samples of pure B powder and B with 7.4%C powder were prepared as PIT wires having a combination Fe inner jacket and a cupro-nickel outer jacket. These PIT Jc values are lower than, but comparable to the pressed pellet values. The PIT samples can be reacted in times on the order of 10 min and still exhibit greater than 105 A/cm2 at 5 K and 2 T.

  16. Avalanche of flux jumps in polycrystalline MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Felner, I.; Awana, V. P. S.; Mudgel, Monika; Kishan, H.

    2007-05-01

    Dc magnetization studies were carried out on a polycrystalline MgB2 superconductor, which was synthesized at 750°C in Fe tube encapsulation under a vacuum of 10-5Torr. Zero resistances at H =0 and 8T are obtained at 38 and 22K, respectively. The material possesses a sharp diamagnetic transition in the zero-field-cooled branch, whereas the field-cooled branch exhibits the paramagnetic-Meissner-effect-like phenomenon below Tc, indicating strong pinning in this compound. The critical current density at 20K and 2T, estimated by the Bean model is higher than 105A/cm2. Due to the strong pinning, we observed the presence of flux avalanches below H =2T at temperatures below 20K. The magnetization M(H ) grows (as usual) slowly with H and falls sharply to near zero moment value, and further grows again in a common way. The flux avalanches were seen quite symmetric in both increasing/decreasing the field in all four quadrants of the M(H ) loops. The dynamics behavior of sinusoidal-like symmetric reproducible flux avalanches is discussed.

  17. AC losses in monofilamentary MgB2 round wire carrying alternating transport currents

    NASA Astrophysics Data System (ADS)

    Kajikawa, K.; Kawano, T.; Osaka, R.; Nakamura, T.; Sugano, M.; Takahashi, M.; Wakuda, T.

    2010-04-01

    AC losses in a monofilamentary MgB2 round wire with niobium and copper metal sheaths and carrying alternating transport currents are evaluated at several temperatures and frequencies. First, the transport current losses are observed electrically using a lock-in amplifier. Experimental results show that the AC losses decrease with an increase in the temperature if the amplitude of the transport current normalized by the corresponding critical current is maintained constant. On the other hand, the AC losses increase slightly with the frequency. Next, the AC losses are calculated numerically by a finite difference method. The numerical results for the superconductor filament show a good agreement with the results of the conventional theoretical expression formulated using the Bean model over a wide range of current amplitudes. It is also found that the AC losses in the niobium sheath are negligible whereas those in the copper sheath are comparable with those in the superconductor. On the basis of the numerical calculations, an expression is analytically derived for estimating the eddy current loss occurring in a metal sheath. The derived expression well reproduces the AC loss properties of both the copper and niobium sheaths.

  18. Preparation of SiC doped In-Situ MgB2 mono- and 7-filamentary wires by continuous tube forming and filling technique

    NASA Astrophysics Data System (ADS)

    Ma, L.; Suo, H. L.; Zhang, Z. L.; Gao, T. Y.; Liu, M.; Zhao, Y.; Zhou, M. L.; Flükiger, R.

    2008-02-01

    Long lengths of in-situ SiC doped MgB2/Fe mono- filamentary wires with high critical current densities and 7- filamentary MgB2/Nb/Cu/Fe wires with better thermal stability have been fabricated by either continuous tube forming & filling (CTFF) technique or combining both powder in tube (PIT) and CTFF process, respectively. Particular efforts were made in view of the optimization of the manufacturing and annealing processes of the wires. The as obtained wires were sintered under a vacuum furnace at different sintering temperatures and the optimized sintering of the MgB2 wires were investigated by the analysis of optical microscope, XRD, SEM, and the transport Jc measurements. The Jc value in a 8 at.% SiC doped MgB2/Fe mono- filamentary wire is more than 104A/cm2 at 4.2 K and a field of 11 T. While in doped 7- filamentary wire, the similar Jc value (104A/cm2) is obtained at 4.2 K and a field of 7.5 T. Moreover, the n factors are determined to be 33 and 10 at 11 T in the mono- and 7- filamentary MgB2wires with SiC doping, respectively, indicating the possibility to use the as fabricated MgB2 wires in the persistent mode for fields from 0.5 T to 10 T at 4.2 K.

  19. Intrawire resistance, AC loss and strain dependence of critical current in MgB2 wires with and without cold high-pressure densification

    NASA Astrophysics Data System (ADS)

    Zhou, C.; Gao, P.; Krooshoop, H. J. G.; Dhallé, M.; Sumption, M. D.; Rindfleisch, M.; Tomsic, M.; Kulich, M.; Senatore, C.; Nijhuis, A.

    2014-07-01

    The intrawire resistance and alternating current (AC) loss of two MgB2 wires with filaments surrounded by Nb barriers have been measured and analyzed. Relatively high values of filament-to-matrix contact resistivity are found in the MgB2 wires; the values are two or three orders higher than those commonly found in NbTi or Nb3Sn wires. Considering the high porosity of the MgB2 filaments, cold high-pressure densification has been applied on the two MgB2 wires to investigate its impact on intrawire resistance and AC loss. The intrawire resistance is measured with a direct four-probe voltage-current method at various temperatures. The AC loss is measured by vibrating sample magnetometer measurements at 4.2 K. In addition to the intrawire resistance measurements, the critical current of MgB2 wires before and after densification is measured with a U-shaped bending spring at 4.2 K as function of axial strain. The critical current in densified MgB2 wires is found to be higher than that in the same wire without densification; it is also less sensitive to the applied axial strain.

  20. Evaluation of Young’s modulus of MgB2 filaments in composite wires for the superconducting links for the high-luminosity LHC upgrade

    NASA Astrophysics Data System (ADS)

    Sugano, Michinaka; Ballarino, Amalia; Bartova, Barbora; Bjoerstad, Roger; Gerardin, Alexandre; Scheuerlein, Christian

    2016-02-01

    MgB2 wire is a promising superconductor for the superconducting links for the high-luminosity upgrade of the large Hadron collider at CERN. The mechanical properties of MgB2 must be fully quantified for the cable design, and in this study, we evaluate the Young’s modulus of MgB2 filaments in wires with a practical level of critical current. The Young’s moduli of MgB2 filaments by two different processes, in situ and ex situ, were compared. Two different evaluation methods were applied to an in situ MgB2 wire, a single-fiber tensile test and a tensile test after removing Monel. In addition, the Young’s modulus of the few-micron-thick Nb-Ni reaction layer in an ex situ processed wire was evaluated using a nanoindentation testing technique to improve the accuracy of analysis based on the rule of mixtures. The Young’s moduli of the in situ and ex situ MgB2 wires were in the range of 76-97 GPa and no distinct difference depending on the fabrication process was found.

  1. Effects of Magnetic and Non-Magnetic Impurities in MgB2: A Point-Contact Study of Single Crystals

    NASA Astrophysics Data System (ADS)

    Daghero, D.

    2007-03-01

    We studied the effects of chemical substitutions, either magnetic (Mn) or non-magnetic (Al, C), on the energy gaps of MgB2 by means of directional point-contact spectroscopy (PCS) in state-of-the-art single crystals. Here we discuss two noticeable cases, i.e. Mg1-xMnxB2 crystals with x up to 0.015, and Mg1-xAlxB2 crystals with x up to 0.32. In both cases, we used a pressure-less PCS technique in which a thin Au wire is put in contact with the side surface of the crystal by means of a small drop of Ag paint. The gaps δσ and δπ were obtained through a two-band Blonder-Tinkham-Klapwijk (BTK) fit of the Andreev-reflection conductance curves of the resulting contacts. Both in Mn- and Al-doped MgB2, the gaps decrease on decreasing the critical temperature of the contacts, Tc^A (at which the Andreev-reflection structures disappear), but remain clearly distinct down to Tc^A˜10 K. Once analysed within the two-band Eliashberg theory, the δσ and δπ vs. Tc^A curves give information about the effects of Mn and Al substitutions on the different scattering channels (interband and intraband, magnetic or non-magnetic). It turns out that the main effect of Mn is to increase the spin-flip scattering within the σ band (with smaller contributions from either the π-π or the σ-π channels), as also confirmed by first-principle bandstructure calculations. In the case of Al, the band-filling effect is largely dominant. An increase in non-magnetic interband scattering is possible, but small enough not to give rise to gap merging. In collaboration with G.A. Ummarino, A. Calzolari, M. Tortello, D. Delaude, R.S. Gonnelli, Dipartimento di Fisica and CNISM, Politecnico di Torino, Italy; V.A. Stepanov, P.N. Lebedev Physical Institute, RAS, Moscow, Russia; N.D. Zhigadlo, J. Karpinski, Laboratory for Solid State Physics, ETHZ, Zurich, Switzerland; and S. Massidda, Dipartimento di Fisica, Universitàdi Cagliari, Italy.

  2. AC susceptibility analysis on MgB2 bulk and Ti-sheathed wire superconductors

    NASA Astrophysics Data System (ADS)

    Çiçek, Özlem; Yetiş, Hakan; Gencer, Ali

    2014-09-01

    We report a comparative study for bulk MgB2 superconductors and monofilamentary Ti/MgB2 wires as functions of the boron powder purity, average particle size of magnesium, and applied pressure. The structural and magnetic characterizations of the bulk samples were performed by means of XRD and AC susceptibility measurements, respectively. We found that the applied pressure did not cause any significant change on the onset transition temperature Tc,onset and transition width. This is also confirmed by the calculation of the lattice parameters. On the other hand, Tc,onset values were measured as 37.3 K, 38.0 K, and 38.6 K for the samples prepared from the precursor boron powders with purities of 95.2%, ⩾95%, and >98%, respectively. However Mg-particle size (Mg1: AlfaAesar Mg powder, avg. par. size: -325 mesh, purity: 99.8%; Mg2: SigmaAldrich Mg powder, avg. par. size: 20-230 mesh, purity: 98%) did not affect the Tc,onset but increasing the Mg particle size caused a significant broadening at the superconducting transition width for all precursor boron powder purity levels. Magnetization measurements showed that the critical current density of Ti/MgB2 wire prepared from AlfaAesar Mg powder (avg. par. size: -325 mesh) and Aldrich B powder (amorphous, purity ⩾ 95%) is greater than that of prepared by SigmaAldrich Mg powder (avg. par. size: 20-230 mesh) and Pavezyum B powder (amorphous, avg. par. size: 0,3 μm (max), purity > 98%) as 2.6 × 105 A/cm2 and 1.4 × 105 A/cm2 at T = 10 K and μ0H = 0.5 T, respectively. In addition, SigmaAldrich Mg and Pavezyum B wire sample has a lower pinning force, Fp, value at each temperature.

  3. Effect of field cooling heights on the levitation force of pure and starch/polystyrene/MWCNT added bulk MgB2 superconductors

    NASA Astrophysics Data System (ADS)

    Tripathi, D.; Dey, T. K.

    2014-12-01

    A series of MgB2 pellets with and without addition of carbon from different sources (viz. starch, polystyrene and carbon nanotubes) have been synthesized by solid state reaction under argon atmosphere. XRD analysis indicates a decrease in lattice parameters of MgB2 with addition of starch, polystyrene (PS) and MWCNT and confirms substitution of carbon in boron sites. The presence of nanosized carbon inclusions between the grain boundaries in the present set of samples is evident in TEM photographs. Resistivity data confirms a decrease in superconducting transition temperature (Tc0) for MgB2 doped with starch/PS/MWCNT. The effect of different field cooling heights (HIFC) at 20 K on maximum levitation force (FMLF) and maximum attractive force (FMAF) of pure MgB2 and MgB2 doped with starch/PS/MWCNT have been investigated. Except for MWCNT, doping of starch and PS in MgB2 is found to improve FMLF and FMAF and the best result is obtained for MgB2 doped with 1 wt.% PS. Levitation force measured as a function of decreasing initial field cooling height indicates exponential dependence of both maximum levitation force (FMLF) and maximum attractive force (FMAF). However, the gap distance between PM and the sample (H0AF and HMAF) corresponding to maximum attractive force (FMAF) and zero attractive force (F0AF) varies linearly and their difference remains constant. This constancy in (HMAF - H0AF) is understood in terms of constant reduction rate of magnetic flux density between H0AF and HMAF.

  4. Influence of Metal Diboride and Dy2O3 Additions on Microstructure and Properties of MgB2 Fabricated at High Temperatures and under Pressure

    PubMed Central

    Yang, Y.; Sumption, M. D.; Collings, E. W.

    2016-01-01

    High temperatures and under pressure (HTP) processing has been used to study the effects of chemical doping in MgB2. ZrB2, TiB2 and NbB2 were selected as additives since, like MgB2, they have an AlB2-type structure and similar lattice parameters. Dy2O3 was selected as it has been reported to generate nanoscale, secondary intragrain phases in MgB2. While C is known to enter the B-sublattice readily, attempts to dope Zr and other elements onto the Mg site have been less successful due to slow bulk diffusion, low solubility in MgB2, or both. We have used high-temperature, solid-state sintering (1500 °C), as well as excursions through the peritectic temperature (up to 1700 °C), to investigate both of these limitations. Bulk MgB2 samples doped with MB2 (M = Zr, Ti and Nb) and Dy2O3 additions were synthesized and then characterized. Lattice distortion and high densities of crystal defects were observed in the MgB2 grains around nano-sized MB2 inclusions, this highly defected band contributed to a large increase in Bc2 but was not large enough to increase the irreversibility field. In contrast, distributed intragrain precipitates were formed by Dy2O3 additions which did not change the lattice parameters, Tc, Tc distribution or Bc2 of MgB2, but modified the flux pinning. PMID:27406904

  5. Peculiarities of high-pressure and hot-pressing manufacture of MgB2-based blocks with high critical currents for electrical machines

    NASA Astrophysics Data System (ADS)

    Prikhna, T. A.; Gawalek, W.; Savchuk, Ya M.; Sergienko, N. V.; Moshchil, V. E.; Wendt, M.; Habisreuther, T.; Dub, S. N.; Melnikov, V. S.; Kozyrev, A. V.; Schmidt, Ch; Dellith, J.; Litzkendorf, D.; Nagorny, P. A.; Dittrich, U.; Sverdun, V. B.; Kovalev, L. K.; Penkin, V. T.; Goldacker, W.; Rozenberg, O. A.; Noudem, J.

    2008-02-01

    Structure and properties of MgB2-based materials in the form of cylinders, rings, quadratic and rectangular blocks manufactured using high-pressure (2 GPa), hot-pressing (30 MPa), hot isostatic pressing (0.1 GPa), and atmospheric pressure (with predensification by broaching) from different types of B and MgB2 are considered. The blocks have been synthesized from Mg and B or sintered from MgB2 at 800 - 1100 °C (with and without additions of Ti or Ta). The inclusions of higher borides (with stoichiometry near MgB12 in the high pressure-manufactured magnesium diboride or near MgB7 in the hot-pressing-synthesized material) can effect critical current density: higher amount and finer dispersion of the above inclusions are observed in the materials with higher critical currents. Samples synthesized (at 4 GPa) from the MgB12 stoichiometric mixture of Mg and B that, according to the SEM microprobe analysis, contained MgB12 (more than 50 %) and MgO phases and, according to X-ray analysis, along with the above phases some amount of MgB2 demonstrated superconducting behavior. From high-pressure synthesized MgB2 blocks the first reluctance-type superconductive electromotor (1,3 kW) has been constructed and successfully tested.

  6. A defect detection method for MgB2 superconducting and iron-based Ba(Fe,Co)2As2 wires

    NASA Astrophysics Data System (ADS)

    Gajda, D.; Morawski, A.; Zaleski, A.; Yamamoto, A.; Cetner, T.

    2016-04-01

    In this article, a method allowing for the detection of damage in iron-based superconducting bulks and MgB2 wires is presented. MgB2 wires were made of in situ material with ex situ MgB2 barrier. The iron superconductor studied was Ba(Fe,Co)2As2. This material was surrounded by Nb barrier and placed inside an iron tube. All samples were annealed in the isostatic pressure of 1 GPa. Transport measurements were made using a four-contact probe. The transition of Nb and ex situ MgB2 barrier from superconducting into resistive state (first transition) was observed at a temperature range from 5 K to 10 K and can be attributed to damage in either the Nb or ex situ MgB2 barrier in these samples. For samples with a damaged barrier, it was not possible to determine the critical current density of the wires. The analysis indicates that annealing at 1 GPa leads to the Ba(Fe,Co)2As2 material with critical temperatures of 27 K and 21.5 K at upper critical flux density (Bc2) of 14 T.

  7. A multiscale and multiphysics model of strain development in a 1.5 T MRI magnet designed with 36 filament composite MgB2 superconducting wire

    NASA Astrophysics Data System (ADS)

    Amin, Abdullah Al; Baig, Tanvir; Deissler, Robert J.; Yao, Zhen; Tomsic, Michael; Doll, David; Akkus, Ozan; Martens, Michael

    2016-05-01

    High temperature superconductors such as MgB2 focus on conduction cooling of electromagnets that eliminates the use of liquid helium. With the recent advances in the strain sustainability of MgB2, a full body 1.5 T conduction cooled magnetic resonance imaging (MRI) magnet shows promise. In this article, a 36 filament MgB2 superconducting wire is considered for a 1.5 T full-body MRI system and is analyzed in terms of strain development. In order to facilitate analysis, this composite wire is homogenized and the orthotropic wire material properties are employed to solve for strain development using a 2D-axisymmetric finite element analysis (FEA) model of the entire set of MRI magnet. The entire multiscale multiphysics analysis is considered from the wire to the magnet bundles addressing winding, cooling and electromagnetic excitation. The FEA solution is verified with proven analytical equations and acceptable agreement is reported. The results show a maximum mechanical strain development of 0.06% that is within the failure criteria of -0.6% to 0.4% (-0.3% to 0.2% for design) for the 36 filament MgB2 wire. Therefore, the study indicates the safe operation of the conduction cooled MgB2 based MRI magnet as far as strain development is concerned.

  8. Effect of carbon substitution on low magnetic field AC losses in MgB 2 single crystals

    NASA Astrophysics Data System (ADS)

    Ciszek, M.; Rogacki, K.; Karpiński, J.

    2011-11-01

    The DC magnetization and AC magnetic susceptibilities were measured for MgB2 single crystals, unsubstituted and carbon substituted with the composition of Mg(B0.94C0.06)2. AC magnetic losses were derived from the AC susceptibility data as a function of the AC amplitude and the DC bias magnetic field. From the DC magnetization loops critical current densities were derived as a function of temperature and DC field. Results show that the substitution with carbon decreases critical current densities at low external magnetic fields, in contrast to the well known effect of an increase of the critical current densities at higher magnetic fields.

  9. The influence of heating rate on superconducting characteristics of MgB2 obtained by spark plasma sintering technique

    NASA Astrophysics Data System (ADS)

    Aldica, G.; Burdusel, M.; Popa, S.; Enculescu, M.; Pasuk, I.; Badica, P.

    2015-12-01

    Superconducting bulks of MgB2 were obtained by the Spark Plasma Sintering (SPS) technique. Different heating rates of 20, 100, 235, 355, and 475 °C/min were used. Samples have high density, above 95%. The onset critical temperature Tc, is about 38.8 K. There is an optimum heating rate of ∼100 °C/min to maximize the critical current density Jc0, the irreversibility field Hirr, the product (Jc0 x μ0Hirr), and to partially avoid formation of undesirable flux jumps at low temperatures. Significant microstructure differences were revealed for samples processed with low and high heating rates in respect to grain boundaries.

  10. Improvement of critical properties of undoped, multifilamentary MgB2 wires in Nb/Cu after annealing under high gas pressure

    NASA Astrophysics Data System (ADS)

    Cetner, T.; Morawski, A.; Adamczyk, K.; Rindfleisch, M.; Tomsic, M.; Zaleski, A.; Gajda, D.; Presz, A.

    2012-09-01

    Raw MgB2 wires have been manufactured by Hyper Tech Inc. Each of their 18 cores contained undoped in situ powder surrounded by an Nb barrier and placed in a Cu sheath, and cores were coated in a common Monel sheath. Wires of diameters 0.63 and 0.83 mm were annealed under high argon pressure (up to 1 GPa). Parameters of such HIP process (temperature, time, and pressure) were varied in order to determine their optimal values. Superconducting properties of such samples were investigated by means of four-probe critical current j c measurement. Bitter magnet producing magnetic field up to 14 T was used. It provided place for samples 70 mm long in parallel field and 20 mm long in perpendicular field. Results include critical current j c and pinning force density F p dependencies on magnetic field as well as Kramer plots. Critical current of 104 A/cm 2 was achieved at 12 T magnetic field. SEM pictures of wire cross sections were also taken to determine quality of Nb barrier and microstructure of superconducting material.

  11. Reactive spark plasma sintering of MgB2 in nitrogen atmosphere for the enhancement of the high-field critical current density

    NASA Astrophysics Data System (ADS)

    Badica, P.; Burdusel, M.; Popa, S.; Pasuk, I.; Ivan, I.; Borodianska, H.; Vasylkiv, O.; Kuncser, A.; Ionescu, A. M.; Miu, L.; Aldica, G.

    2016-10-01

    High density bulks (97%-99%) of MgB2 were prepared by spark plasma sintering (SPS) in nitrogen (N2) atmosphere for different heating rates (10, 20 and 100 °C min-1) and compared with reference samples processed in vacuum and Ar. N2 reacts with MgB2 and forms MgB9N along the MgB2 grain boundaries. The high-field critical current density is enhanced for the sample processed in N2 with a heating rate of 100 °C min-1. At 2-35 K, this sample shows the strongest contribution of the grain boundary pinning (GBP). All samples are in the point pinning (PP) limit and by increasing temperature the GBP contribution decreases.

  12. Electrical and structural properties of MgB2 films prepared by sequential deposition of B and Mg on the NbN-buffered Si(100) substrate

    NASA Astrophysics Data System (ADS)

    Chromik, Š.; Gaži, Š.; Štrbík, V.; Španková, M.; Vávra, I.; Beňačka, Š.; van der Beek, C. J.; Gierlowski, P.

    2004-10-01

    We introduce a simple method of a MgB2 film preparation using a sequential electron-beam evaporation of B-Mg bilayer (followed by in-situ annealing) on the NbN-buffered Si(100) substrate. The transmission electron microscopy analyses confirm a growth of homogeneous nanogranular MgB2 films without the presence of crystalline MgO. A sensitive measurement of temperature dependence of microwave losses shows a presence of intergranular weak links close to the superconducting transition only. The MgB2 films obtained, about 200-nm thick, exhibit a maximum zero resistance critical temperature of 36K and a critical current density of 3×107A /cm2 at 13.2K.

  13. Proposal of new structure of MgB 2 wires with low AC loss for stator windings of fully superconducting motors located in iron core slots

    NASA Astrophysics Data System (ADS)

    Kajikawa, K.; Osaka, R.; Kuga, H.; Nakamura, T.; Wakuda, T.

    2011-11-01

    The new structure of MgB2 monofilamentary wires for stator windings of fully superconducting motors is proposed to reduce their AC losses in iron core slots for the application of an alternating transport current. In order to validate the proposed structure of wire for loss reduction, numerical calculations are carried out by means of a finite element method using edge elements formulated with a self-field due to currents induced in an analysis region. It is assumed that the voltage-current characteristics of the MgB2 superconductor are given by Bean's critical state model, in which the critical current density is independent of the local magnetic field. The influences of wire structures on the AC losses are discussed quantitatively toward the optimum design of stator windings in fully superconducting motors with the MgB2 wires.

  14. Limiting factors of normal-state conductivity in superconducting MgB2: an application of mean-field theory for a site percolation problem

    NASA Astrophysics Data System (ADS)

    Yamamoto, Akiyasu; Shimoyama, Jun-ichi; Kishio, Kohji; Matsushita, Teruo

    2007-07-01

    Normal-state conductivity in polycrystalline MgB2 bulk samples having a systematically varied packing factor was studied. The packing factor dependence of phonon term resistivity Δρ(T) = ρ(T)-ρ0 was found to be well explained by the three-dimensional site percolation model. The low packing density of the samples and the wet impurity phases at grain boundaries are suggested to be the main causes of poor electrical connectivity in MgB2. Our model enables quantitative evaluations of the intrinsic resistivity inside the grains, the fraction of the active grains that can carry current and the anisotropy of the grains in polycrystalline samples. The model predicts that the anomaly suppressed connectivity in rather weak-link-free MgB2 can be understood under a scenario of a percolation problem.

  15. Electron Spin Resonance of MgB2 : test of the Elliott relation in the normal state

    NASA Astrophysics Data System (ADS)

    Lobo, R. P. S. M.; Elsen, M.; Monod, P.; Cava, R. J.

    2003-03-01

    The Elliott relation states that, for the conduction electrons in a normal metal, the ratio of the thermal spin relaxation rate to the thermal ordinary collision rate is equal to the square of their g shift: (g - 2.0023)^2. This is well verified for simple metals and originates from the presence of the intrinsic spin orbit potential of the metal. For conduction electrons, the spin lifetime is measured as the inverse of the spin resonance linewidth. By careful measurement of the temperature dependance of the linewidth of the conduction electron spin resonance of MgB2 fine powder between 50 K and 600 K at 9.5 GHz and simultaneoous determination of the position of the line center to better than 1% of the linewidth, we tested the validity of the Elliott relation. An original feature occurs in the case of MgB2 where the linewidth of the spin resonance no longer increases above about 300 K in contrast to the resistivity. This apparent paradox is lifted, within experimental error, by the simultaneous temperature dependance of the g factor observed to vary from 2.0010 10-4 at 150 K to 2.0020 10-4 at 600 K. This decrase of the g shift with increase of temperature could be related to the onset of a thermal mixing of the different Fermi surface sheets.

  16. Transport critical current of MgB2 wires: pulsed current of varying rate compared to direct current method

    NASA Astrophysics Data System (ADS)

    See, K. W.; Xu, X.; Horvat, J.; Cook, C. D.; Dou, S. X.

    2011-10-01

    The measurement of transport critical current (Ic) for MgB2 wires and tapes has been investigated with two different techniques, the conventional four-probe arrangement with direct current (DC) power source, and a tailored triangle pulse at different rates of current change. The DC method has been widely used and practiced by various groups, but suffers from inevitable heating effects when high currents are used at low magnetic fields. The pulsed current method has no heating effects, but the critical current can depend on the rate of the current change (dI/dt) in the pulse. Our pulsed current measurements with varying dI/dt show that the same values of Ic are obtained as with the DC method, but without the artifacts of heating. Our method is particularly useful at low field regions which are often inaccessible by DC methods. We also performed a finite element method (FEM) analysis to obtain the time dependent heat distribution in MgB2 due to the electric potential produced at the current contacts to the superconducting sample and its gradient around the contacts. This gradient is defined as the current transfer length (CTL) of the samples and leads to Joule heating of the wire near the contacts. The FEM results provide further evidence of the limitation of the DC method in obtaining high transport critical current.

  17. Effect of Mg/B ratio on the superconductivity of MgB2 bulk with SiC addition

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Dou, S. X.; Lu, C.; Zhou, S. H.; Li, W. X.

    2010-03-01

    To improve the self-field critical current density (Jc) and critical temperature (Tc) in SiC-doped MgB2 , optimization of the nominal Mg/B mixing ratio has been performed. The effects of the nominal Mg/B mixing ratio (x:2) on the superconductivity, Raman spectra, current transport properties, and flux pinning mechanisms in MgB2 with 10 wt.% SiC doping were investigated systematically, with x varied from 1 to 1.2. It has been found that the sample with the Mg/B ratio of 1.15:2 exhibited the best Jc performance for all fields (0-8.5 T), and its Tc was also enhanced. The optimized Mg/B ratio diminished the interband scattering caused by Mg or B vacancies, and in turn, increased Tc . The connectivity and disorder were increased in the Mg1.15B2 sample. Both of these were responsible for the improved Jc under all the fields examined.

  18. Evaluation of persistent-mode operation in a superconducting MgB2 coil in solid nitrogen

    NASA Astrophysics Data System (ADS)

    Patel, Dipak; Hossain, Md Shahriar Al; See, Khay Wai; Qiu, Wenbin; Kobayashi, Hiroki; Ma, Zongqing; Kim, Seong Jun; Hong, Jonggi; Park, Jin Yong; Choi, Seyong; Maeda, Minoru; Shahabuddin, Mohammed; Rindfleisch, Matt; Tomsic, Mike; Xue Dou, Shi; Kim, Jung Ho

    2016-04-01

    We report the fabrication of a magnesium diboride (MgB2) coil and evaluate its persistent-mode operation in a system cooled by a cryocooler with solid nitrogen (SN2) as a cooling medium. The main purpose of SN2 was to increase enthalpy of the cold mass. For this work, an in situ processed carbon-doped MgB2 wire was used. The coil was wound on a stainless steel former in a single layer (22 turns), with an inner diameter of 109 mm and height of 20 mm without any insulation. The two ends of the coil were then joined to make a persistent-current switch to obtain the persistent-current mode. After a heat treatment, the whole coil was installed in the SN2 chamber. During operation, the resultant total circuit resistance was estimated to be <7.4 × 10-14 Ω at 19.5 K ± 1.5 K, which meets the technical requirement for magnetic resonance imaging application.

  19. A persistent-mode 0.5 T solid-nitrogen-cooled MgB2 magnet for MRI

    NASA Astrophysics Data System (ADS)

    Ling, Jiayin; Voccio, John P.; Hahn, Seungyong; Qu, Timing; Bascuñán, Juan; Iwasa, Yukikazu

    2017-02-01

    This paper presents construction details and test results of a persistent-mode 0.5 T MgB2 magnet developed at the Francis Bitter Magnet Laboratory, MIT. The magnet, of 276 mm inner diameter and 290 mm outer diameter, consisted of a stack of eight solenoidal coils with a total height of 460 mm. Each coil was wound with monofilament MgB2 wire, equipped with a persistent-current switch and terminated with a superconducting joint, forming an individual superconducting loop. Resistive solder joints connected the eight coils in series. The magnet, after being integrated into a testing system, immersed in solid nitrogen, was operated in a temperature range of 10-13 K. A two-stage cryocooler was deployed to cool a radiation shield and the cold mass that included mainly ˜60 kg of solid nitrogen and the magnet. The solid nitrogen was capable of providing a uniform and stable cryogenic environment to the magnet. The magnet sustained a 0.47 T magnetic field at its center persistently in a range of 10-13 K. The current in each coil was inversely calculated from the measured field profile to determine the performance of each coil in persistent-mode operation. Persistent-current switches were successfully operated in solid nitrogen for ramping the magnet. They were also designed to absorb magnetic energy in a protection mechanism; its effectiveness was evaluated in an induced quench.

  20. Field cooling of a MgB2 cylinder around a permanent magnet stack: prototype for superconductive magnetic bearing

    NASA Astrophysics Data System (ADS)

    Perini, E.; Giunchi, G.

    2009-04-01

    The behaviour of bulk superconductors as levitators of permanent magnets (PMs) has been extensively studied for the textured YBCO high-temperature superconductor material, in the temperature range lower than 77 K, obtaining extremely high trapped fields but also experiencing limitations on the mechanical characteristics of the material and on the possibility to produce large objects. Alternatively, bulk MgB2, even if it is superconducting at lower temperatures, has fewer mechanical problems, when fully densified, and presents stable magnetization in the temperature range between 10 and 30 K. With the reactive Mg-liquid infiltration technique we have produced dense MgB2 bulk cylinders of up to 65 mm diameter and 100 mm height. This kind of cylinder can be consider as a prototype of a passive magnetic bearing for flywheels or other rotating electrical machines. We have conductively cooled one of these superconducting cylinders inside a specially constructed cryostat, and the levitation forces and stiffness, with respect to axial movements of various arrangements of the PM, have been measured as a function of the temperature below Tc. We verified the very stable characteristics of the induced magnetization after several cycles of relative movements of the PM and the superconducting cylinder.

  1. Conceptual designs of conduction cooled MgB2 magnets for 1.5 and 3.0 T full body MRI systems

    NASA Astrophysics Data System (ADS)

    Baig, Tanvir; Amin, Abdullah Al; Deissler, Robert J.; Sabri, Laith; Poole, Charles; Brown, Robert W.; Tomsic, Michael; Doll, David; Rindfleisch, Matthew; Peng, Xuan; Mendris, Robert; Akkus, Ozan; Sumption, Michael; Martens, Michael

    2017-04-01

    Conceptual designs of 1.5 and 3.0 T full-body magnetic resonance imaging (MRI) magnets using conduction cooled MgB2 superconductor are presented. The sizes, locations, and number of turns in the eight coil bundles are determined using optimization methods that minimize the amount of superconducting wire and produce magnetic fields with an inhomogeneity of less than 10 ppm over a 45 cm diameter spherical volume. MgB2 superconducting wire is assessed in terms of the transport, thermal, and mechanical properties for these magnet designs. Careful calculations of the normal zone propagation velocity and minimum quench energies provide support for the necessity of active quench protection instead of passive protection for medium temperature superconductors such as MgB2. A new ‘active’ protection scheme for medium T c based MRI magnets is presented and simulations demonstrate that the magnet can be protected. Recent progress on persistent joints for multifilamentary MgB2 wire is presented. Finite difference calculations of the quench propagation and temperature rise during a quench conclude that active intervention is needed to reduce the temperature rise in the coil bundles and prevent damage to the superconductor. Comprehensive multiphysics and multiscale analytical and finite element analysis of the mechanical stress and strain in the MgB2 wire and epoxy for these designs are presented for the first time. From mechanical and thermal analysis of our designs we conclude there would be no damage to such a magnet during the manufacturing or operating stages, and that the magnet would survive various quench scenarios. This comprehensive set of magnet design considerations and analyses demonstrate the overall viability of 1.5 and 3.0 T MgB2 magnet designs.

  2. High temperature and low field regime vortex phase diagram of in-situ prepared stainless steel sheathed MgB2 tapes

    NASA Astrophysics Data System (ADS)

    Rajput, Suchitra

    2017-04-01

    A magnetic field-temperature vortex phase diagram has been proposed for MgB2 on the basis of magnetoresistance studies performed on an in-situ prepared stainless steel sheathed MgB2 tapes. Thermally activated flux flow (TAFF) behavior is analyzed using Arrhenius relation. Low dissipative part of magnetoresistance with temperature is well described by vortex glass theory. Above critical region, the resistive behavior is influenced by fluctuation conductivity. In addition, a considerable vortex liquid region below HC2 is also observed but TAFF region is found to be quite narrow.

  3. Thermochemical analysis of magnesium diboride thin film synthesis and its application to Josephson junction fabrication

    NASA Astrophysics Data System (ADS)

    Kim, Jihoon

    MgB2 is an unusual binary metallic superconductor in that it has a transition temperature of almost twice that of other metallic compounds and possesses two superconductor gaps. It has proven to be difficult to fabricate in thin film form, predominantly as a result of the high volatility of Mg. In this thesis, critical factors involved in MgB2 thin film growth and the synthesis of multilayer MgB2 Josephson junctions have been studied. The thermochemistry of MgB2 thin film growth has been investigated. The low Mg sticking coefficient at temperatures over 300°C prevents high temperature synthesis with traditional vacuum growth methods. However, as a result of the large kinetic barrier to MgB2 decomposition, metastable growth and subsequent thermal processing is possible. The Mg sticking coefficient is found to be strongly dependent upon B flux. High Mg and B fluxes make it possible to extend the processing window to elevated temperatures by enhancing the Mg sticking coefficient. A transition temperature of 37˜38K was achieved using molecular beam epitaxy (MBE). For the fabrication of Josephson junctions, various barrier layers including native oxide, boron, AIN, and thermal oxide were explored. Cross-bridge junction structures were fabricated using shadow masks. Repeatable tunneling characteristics were observed from metal/native oxide/MgB2 junctions. MgB 2 energy gaps and density of states, as well as the barrier's height and thickness, have been inferred from tunneling conductance measurements. MgB2/native oxide or boron/MgB2 junctions with 1mm 2 areas were fabricated and also exhibited tunneling characteristics. The junctions produced with the cross geometry process have a Josephson coupling energy that is too small compared to the thermal energy to exhibit supercurrent as a result of the junction's large size and high resistance. To overcome this limitation, planar type junctions were prepared using conventional microfabrication techniques. MgB2,/AlN/MgB2 and

  4. Effect of boron particle size on microstructure and superconducting properties of in-situ Cu addition MgB2 multifilamentary wire

    NASA Astrophysics Data System (ADS)

    Hishinuma, Y.; Kikuchi, A.; Shimada, Y.; Hata, S.; Takeuchi, T.; Yamada, S.; Sagara, A.

    2014-05-01

    In previous studies, the secondary (impurity and non-reactive) phase and voids were observed in MgB2 matrix after the heat treatment, and then these are the lowering factors of critical current density (Jc) property. In order to improve Jc property by microstructure control of MgB2 matrix, the fine elemental boron powder as the raw material was carried out using the high-speed vibrated milling with tungsten carbide (WC) jar. The average particle size of metal boron powder was decreased from 1.14 μm to 0.20 μm by the high-speed vibrated milling. The various fine particle boron powders as the function of milling time were also prepared, and in-situ Cu addition MgB2 multifilamentary wires using these fine boron powders were fabricated. Critical transition temperature (Tc) value of Cu addition MgB2 wire using fine boron powder obtained to about 37 K. No change of the Tc property by the different particle sized boron powders was confirmed. In this paper, the comparisons of microstructure and superconducting properties between the different boron particle sizes were investigated.

  5. Significant improvement in the critical current density of MgB2 bulks in situ sintered at low temperature by excess Mg addition

    NASA Astrophysics Data System (ADS)

    Ma, Zongqing; Liu, Yongchang; Cai, Qi; Yu, Liming

    2014-01-01

    MgB2 bulks with excess Mg addition were rapidly synthesized by sintering at low temperature in present work. It is found that even after ball milling treatment of original powders, the reaction between Mg and B during subsequent low temperature sintering process was uncompleted within 5 h and there is still some residual Mg. On the other hand, the presence of residual Mg can make the sintering microstructure more homogeneous and dense, and also reduce lattice defects and mechanical strains. All the factors are contributed to the improvement of the grain connectivity in the samples with excess Mg addition sintered at low temperature compared to the reference MgB2 sample sintered at high temperature. Hence, Jc of these prepared samples is enhanced significantly across the whole measured fields. Especially, at 20 K, 2 T, the value of Jc in the 5 h-sintered MgB2 bulk with Mg addition is above 1 × 105 A cm-2. The technique developed in present work is an effective and low-cost way to further enhance Jc in the MgB2 superconductors without using expensive nanometer-size dopants.

  6. Structure, grain connectivity and pinning of as-deformed commercial MgB2 powder in Cu and Fe/Cu sheaths

    NASA Astrophysics Data System (ADS)

    Kovác, P.; Husek, I.; Pachla, W.; Melisek, T.; Diduszko, R.; Fröhlich, K.; Morawski, A.; Presz, A.; Machajdik, D.

    2002-07-01

    Single-core MgB2 wires and tapes have been made by the powder-in-tube (PIT) method using commercial MgB2 powder (Alfa Aesar). Composites have been made using the two-axial rolling process in Cu and/or Fe/Cu sheaths. Alternative deformations by wire drawing, rotary swaging and cold isostatic pressing have been applied to PIT wires and tapes. Current-voltage characteristics and transport current densities in the self-field and in the external field were measured. It was found that the grain connectivity of ex situ MgB2 is affected by the applied sheath and the mode of deformation. Two-axial rolling has generated the highest powder density resulting in the best grain connectivity. The highest transport current densities of 8700 A cm-2 and 55 830 A cm-2 were measured for Cu and Fe/Cu sheathed square wires, respectively. Cold isostatic pressing at 1.5 GPa has increased current density and n-exponent, which suggests an improvement in grain connectivity. It was found that the external pressure improves the inter-grain connectivity but decreases the pinning in MgB2 cores.

  7. Strong competition between the δl and δTc flux pinning mechanisms in MgB2 doped with carbon containing compounds

    NASA Astrophysics Data System (ADS)

    Ghorbani, S. R.; Wang, Xiao-Lin; Hossain, M. S. A.; Yao, Q. W.; Dou, S. X.; Lee, Sung-IK; Chung, K. C.; Kim, Y. K.

    2010-06-01

    The transport and magnetic properties of 10 wt % malic acid and 5 wt % nanocarbon doped MgB2 have been studied by measuring the resistivity (ρ), critical current density (jc), connectivity factor (AF), irreversibility field (Hirr), and upper critical field (Hc2). The pinning mechanisms are studied in terms of the collective pinning model. It was found that both mean free path (δl) and critical temperature (δTc) pinning mechanisms coexist in both doped MgB2. For both the malic acid and nanocarbon doped samples, the temperature dependence of the crossover field, which separates the single vortex and the small bundle pinning regime, Bsb(T ), shows that the δl pinning mechanism is dominant for temperatures up to t(T /Tc)=0.7 but the δTc pinning mechanism is dominant for t >0.7. This tendency of coexistence of the δl and the δTc pinning mechanism is in strong contrast with the pure MgB2, in which the δTc pinning mechanism is dominant over a wide temperature range below Tc. It was also observed that the connectivity factor, active cross-sectional area fraction (AF), are 0.11 and 0.14 for the nanocarbon and the malic acid doped MgB2, respectively, indicating that there are still rooms for further improving jc performance.

  8. Improved critical current density in ex situ processed MgB2 tapes by the size reduction of grains and crystallites by high-energy ball milling

    NASA Astrophysics Data System (ADS)

    Fujii, Hiroki; Ishitoya, Akira; Itoh, Shinji; Ozawa, Kiyoshi; Kitaguchi, Hitoshi

    2017-03-01

    We have fabricated Fe-sheathed MgB2 tapes through an ex situ process in a powder-in-tube (PIT) technique using powders ball milled under various conditions. Although the ex situ processed wires and tapes using the high-energy ball milled MgB2 powders have been studied and the decrease of grain and crystallite sizes of MgB2 and the critical current density (Jc) improvement of those conductors were reported so far, the use of filling powders milled at a higher rotation speed than previously reported further decreases the crystallite size and improves the Jc properties. The improved Jc values at 4.2 K and 10 T were nearly twice as large as those previously reported. Those milled powders and hence as-rolled tapes easily receive contamination in air. Thus, the transport Jc properties are easily deteriorated and scattered unless the samples are handled with care. The optimized heat treatment temperature (Topt) of those tape samples at which best performance in the Jc property is obtained decreases by more than 100 °C, compared with that of tapes using the as-received MgB2 powder.

  9. Uniform transport performance of a 100 m-class multifilament MgB2 wire fabricated by an internal Mg diffusion process

    NASA Astrophysics Data System (ADS)

    Wang, Dongliang; Xu, Da; Zhang, Xianping; Yao, Chao; Yuan, Pusheng; Ma, Yanwei; Oguro, Hidetoshi; Awaji, Satoshi; Watanabe, Kazuo

    2016-06-01

    A 100 m long six-filament MgB2 wire was successfully fabricated using an internal magnesium diffusion (IMD) process. We investigated the transport properties and the uniformity of this long multifilament IMD wire. The MgB2 layer and the sub-filament region are regular, and the J c values have a fairly homogenous distribution throughout the wire, suggesting that there were no obvious defects along the length of the wire. The uniformity problem of long multifilament IMD MgB2 wires can be mitigated by optimizing the starting composite parameters, multifilament geometry, fabricating process and annealing conditions. A layer J c as high as 1.2 × 105 A cm-2 at 4.2 K and 8 T was obtained, which was comparable with the highest reported value for a short multifilament IMD wire. The transport layer J c, non-barrier J c and J e values are independent of the wire diameter. In addition, the analysis of the stress-strain characteristics and the n value of the IMD wire is also presented. These results indicate that the long multifilament IMD-processed MgB2 superconducting wire is suitable for practical applications.

  10. Numerical simulation of quench protection for a 1.5 T persistent mode MgB2 conduction-cooled MRI magnet

    NASA Astrophysics Data System (ADS)

    Deissler, Robert J.; Baig, Tanvir; Poole, Charles; Amin, Abdullah; Doll, David; Tomsic, Michael; Martens, Michael

    2017-02-01

    The active quench protection of a 1.5 T MgB2 conduction-cooled MRI magnet operating in persistent current mode is considered. An active quench protection system relies on the detection of the resistive voltage developed in the magnet, which is used to trigger the external energizing of quench heaters located on the surfaces of all ten coil bundles. A numerical integration of the heat equation is used to determine the development of the temperature profile and the maximum temperature in the coil at the origin, or ‘hot spot’, of the quench. Both n-value of the superconductor and magnetoresistance of the wire are included in the simulations. An MgB2 wire manufactured by Hyper Tech Research, Inc. was used as the basis to model the wire for the simulations. With the proposed active quench protection system, the maximum temperature was limited to 200 K or less, which is considered low enough to prevent damage to the magnet. By substituting Glidcop for the Monel in the wire sheath or by increasing the thermal conductivity of the insulation, the margin for safe operation was further increased, the maximum temperature decreasing by more than 40 K. The strain on the MgB2 filaments is calculated using ANSYS, verifying that the stress and strain limits in the MgB2 superconductor and epoxy insulation are not exceeded.

  11. Momentum dependence of the superconducting gap and in-gap states in MgB2 multiband superconductor

    DOE PAGES

    Mou, Daixiang; Jiang, Rui; Taufour, Valentin; ...

    2015-06-29

    We use tunable laser-based angle-resolved photoemission spectroscopy to study the electronic structure of the multiband superconductor MgB2. These results form the baseline for detailed studies of superconductivity in multiband systems. We find that the magnitude of the superconducting gap on both σ bands follows a BCS-like variation with temperature with Δ0 ~ 7meV. Furthermore, the value of the gap is isotropic within experimental uncertainty and in agreement with a pure s-wave pairing symmetry. We observe in-gap states confined to kF of the σ band that occur at some locations of the sample surface. As a result, the energy of thismore » excitation, ~ 3 meV, was found to be somewhat larger than the previously reported gap on π Fermi sheet and therefore we cannot exclude the possibility of interband scattering as its origin.« less

  12. Fermi surface topology and the upper critical field in two-band superconductors: application to MgB2.

    PubMed

    Dahm, T; Schopohl, N

    2003-07-04

    Recent measurements of the anisotropy of the upper critical field B(c2) on MgB2 single crystals have shown a puzzling strong temperature dependence. Here, we present a calculation of the upper critical field based on a detailed modeling of band structure calculations that takes into account both the unusual Fermi surface topology and the two gap nature of the superconducting order parameter. Our results show that the strong temperature dependence of the B(c2) anisotropy can be understood as an interplay of the dominating gap on the sigma band, which possesses a small c-axis component of the Fermi velocity, with the induced superconductivity on the pi-band possessing a large c-axis component of the Fermi velocity. We provide analytic formulas for the anisotropy ratio at T=0 and T=T(c) and quantitatively predict the distortion of the vortex lattice based on our calculations.

  13. Experimental study of the AC magnetization loss in MgB2 superconducting wires at different temperatures

    NASA Astrophysics Data System (ADS)

    Kováč, Ján; Šouc, Ján; Kováč, Pavol

    2012-05-01

    The temperature and external AC magnetic field dependence of AC magnetization losses of MgB2 wires were studied. Temperature was varied from 18 K to 40 K and external magnetic field of frequencies 72 Hz and 144 Hz from 8 mT to 70 mT with orientation perpendicular to the wire axis. To clarify the influence of the wire construction on AC loss, single and six filament untwisted samples of length ∼50 mm were examined. For this purpose unique experimental apparatus created by the combination of original calibration-free measuring system designed for ac magnetization loss measurement and non-magnetic vacuum vessel with two-stage cryocooler for sample cooling was used. It was found, that for monofilament sample hysteretic AC losses was dominated in comparison to untwisted six-filaments sample, where coupling losses confirmed by frequency dependence were dominated.

  14. Method for producing high quality thin layer films on substrates

    DOEpatents

    Strongin, M.; Ruckman, M.; Strongin, D.

    1994-04-26

    A method for producing high quality, thin layer films of inorganic compounds upon the surface of a substrate is disclosed. The method involves condensing a mixture of preselected molecular precursors on the surface of a substrate and subsequently inducing the formation of reactive species using high energy photon or charged particle irradiation. The reactive species react with one another to produce a film of the desired compound upon the surface of the substrate. 4 figures.

  15. Method for producing high quality thin layer films on substrates

    DOEpatents

    Strongin, Myron; Ruckman, Mark; Strongin, Daniel

    1994-01-01

    A method for producing high quality, thin layer films of inorganic compounds upon the surface of a substrate is disclosed. The method involves condensing a mixture of preselected molecular precursors on the surface of a substrate and subsequently inducing the formation of reactive species using high energy photon or charged particle irradiation. The reactive species react with one another to produce a film of the desired compound upon the surface of the substrate.

  16. A 0.6 T/650 mm RT Bore Solid Nitrogen Cooled MgB2 Demonstration Coil for MRI-a Status Report.

    PubMed

    Bascuñán, Juan; Lee, Haigunan; Bobrov, Emmanuel S; Hahn, Seungyong; Iwasa, Yukikazu; Tomsic, Mike; Rindfleisch, Matt

    2006-06-01

    Aiming to demonstrate feasibility and practicality of a low cost superconducting MRI magnet system targeted for use in small hospitals, rural communities and underdeveloped countries, MIT-Francis Bitter Magnet Laboratory has developed a 0.6 T/650 mm room temperature bore demonstration coil wound with multifilament MgB2 conductor and cooled via an innovative cryogenic design/operation. The coil is to be maintained cold by solid nitrogen kept in the solid state by a cryocooler. In the event of a power failure the cryocooler is automatically thermally decoupled from the system. In this paper we present details of the MgB2 conductor, winding process, and preliminary theoretical analysis of the current-carrying performance of the conductively cooled coils in zero background field and over the 10-30 K temperature range.

  17. Comparison of critical current density in SiC-doped in situ MgB2 coils and straight wire samples processed by HIP

    NASA Astrophysics Data System (ADS)

    Gajda, D.; Morawski, A.; Zaleski, A.; Cetner, T.; Małecka, M.; Presz, A.; Rindfleisch, M.; Tomsic, M.; Thong, C. J.; Surdacki, P.

    2013-11-01

    Unreacted MgB2 wires fabricated from SiC-doped precursor material by Hyper Tech Research, Inc. have been used to make small-diameter (14 mm) superconducting coils. All coils made of 500 mm length wires were subjected to hot isostatic pressure (HIP) treatment. The critical current density (Jc) parameters of coils were compared to straight samples characteristics. Both types of samples have been measured in perpendicular magnetic field configuration for Jc and pinning force density (Fp) evaluation. No significant Jc difference between the long wires on coils and straight wires was found. These results suggest that the critical current (Ic) for coils can be determined for straight samples (25 mm). SEM analysis indicated that a small diameter of the coil does not influence the structure of in situ MgB2 wire.

  18. A 0.6 T/650 mm RT Bore Solid Nitrogen Cooled MgB2 Demonstration Coil for MRI—a Status Report

    PubMed Central

    Bascuñán, Juan; Lee, Haigunan; Bobrov, Emmanuel S.; Hahn, Seungyong; Iwasa, Yukikazu; Tomsic, Mike; Rindfleisch, Matt

    2014-01-01

    Aiming to demonstrate feasibility and practicality of a low cost superconducting MRI magnet system targeted for use in small hospitals, rural communities and underdeveloped countries, MIT-Francis Bitter Magnet Laboratory has developed a 0.6 T/650 mm room temperature bore demonstration coil wound with multifilament MgB2 conductor and cooled via an innovative cryogenic design/operation. The coil is to be maintained cold by solid nitrogen kept in the solid state by a cryocooler. In the event of a power failure the cryocooler is automatically thermally decoupled from the system. In this paper we present details of the MgB2 conductor, winding process, and preliminary theoretical analysis of the current-carrying performance of the conductively cooled coils in zero background field and over the 10–30 K temperature range. PMID:25580068

  19. Highly enhanced in-field critical current density of MgB 2 superconductor by combined addition of burned rice husk and nano Ho 2O 3

    NASA Astrophysics Data System (ADS)

    Vinod, K.; Varghese, Neson; Sundaresan, A.; Syamaprasad, U.

    2010-04-01

    With the aim of improving flux pinning and in-field critical current density [ JC( H)], two physically and chemically different additives - burned rice husk (BRH) and nano Ho 2O 3 were introduced into in situ MgB 2 superconductor. The effects of the above two additives were studied individually and combinedly. Ho 2O 3 decomposed and reacted with B to form HoB 4, without any substitution. BRH caused considerable amount of C substitution at B site and formed Mg 2Si and Mg 2C 3 secondary phases. Addition of Ho 2O 3 improved the JC( H) only marginally, but BRH improved the JC( H) strongly. Combined addition of Ho 2O 3 with BRH was found to be much more effective than their solo addition for the enhancement of JC( H) of MgB 2.

  20. Graphite coating effects on the critical current characteristics of MgB 2/Cu wires fabricated by an in situ PIT method

    NASA Astrophysics Data System (ADS)

    Shimura, S.; Machi, T.; Nakao, K.; Koshizuka, N.; Tanaka, S.; Mochizuki, K.; Shibata, N.; Ushio, K.

    2005-10-01

    In order to improve the critical current characteristics of Cu sheathed MgB2 wires, we studied the carbon doping and coating effects on JC of wires prepared by an in situ powder-in-tube (PIT) method. Raw materials of Mg and B powders were mixed with a certain amount of MgB2 powder to increase the core density of wires in the heat treated samples. The pellets of these mixed powders were inserted into Cu sheaths and manufactured into wires by rotary swaging, two-axial rolling and drawing under cold-working. The wires were finally heat treated at 600 °C for 2 h in Ar gas atmosphere. The critical current IC of short samples of graphite 5 at.% doped MgB2/Cu with diameter of 1.0 mm reached 548 A (JC = 440 kA/cm2) at 4.2 K in self-field. The reaction of Mg with Cu decreased for graphite coating samples compared with non-coating ones. We obtained high performance MgB2/Cu wires by doping of diamond and graphite powder in the in situ PIT method. We found that the graphite coating on the inside surface of Cu sheath was effective for suppressing the reaction of Mg with Cu sheath. We also fabricated solenoid coils by wind and react method heat treated under the above conditions. The IC value was 230 A at 4.2 K for a coil produced by using a 16 m wire. This coil generated a magnetic field of 0.42 T at liquid He temperature.

  1. Critical current densities and n-values of MgB2 strands over a wide range of temperatures and fields

    NASA Astrophysics Data System (ADS)

    Li, G. Z.; Yang, Y.; Susner, M. A.; Sumption, M. D.; Collings, E. W.

    2012-02-01

    Transport measurements of critical current density, Jct, in monocore powder-in-tube MgB2 strands have been carried out at temperatures, T, of from 4.2 to 40 K, and in transverse fields, B, of up to 14 T. Processing methods used were conventional continuous tube forming/filling (CTFF) and internal magnesium diffusion (IMD). Strands with several powder compositions were measured, including binary (undoped) MgB2, 2% carbon doped MgB2, and 3% carbon doped MgB2. Magnetization loops (M-B) were also measured, and magnetic critical current density, Jcm, values extracted from them. The transport, Jct(B) and magnetic, Jcm(B), critical current densities were compared. Also studied was the influence of doping on the resistively measured irreversibility field, Birr, and upper critical field, Bc2. Critical current densities, Jct, and n-values were extracted from transport measurements and were found to be universally related (for all B and T) according to n\\propto {J}_{{ct}}^{m} in which m = 0.52 ± 0.11. Likewise n was found to be related to B according to n ∝ B-p with a T-dependent p in the range of about 0.08-0.21. Further analysis of the field (B) and temperature (T) dependences of n-value resulted in an expression that enabled n(B,T), for all B and T, to be estimated for a given strand based on the results of transport Jct(B) measurements made at one arbitrarily chosen temperature.

  2. Update on the Fabrication and Performance of 2-D Arrays of Superconducting Magnesium Diboride (MgB2) Thermal Detectors for Outer-Planets Exploration

    NASA Technical Reports Server (NTRS)

    Lakew, Brook; Aslam, S.

    2011-01-01

    Detectors with better performance than the current thermopile detectors that operate at room temperature will be needed at the focal plane of far-infrared instruments on future planetary exploration missions. We will present an update on recent results from the 2-D array of MgB2 thermal detectors being currently developed at NASA Goddard. Noise and sensitivity results will be presented and compared to thermal detectors currently in use on planetary missions.

  3. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Pressure and Doping Effects on Critical Temperature in MgB2 and Nonmagnetic Borocarbides within Two-Band Eliashberg Theory

    NASA Astrophysics Data System (ADS)

    Askerzade, I. N.

    2010-06-01

    Critical temperature of Mg1-xAlxB2, MgB2-xCx are calculated using two-band Eliashberg theory in intermediate e-ph coupling. Analytical calculations are conducted for different values of doping parameters x in this compounds. Pressure effects on critical temperature in MgB2 and nonmagnetic borocarbide YNi2B2C are also investigated. Results is compared with available experimental data and good agreement is achieved.

  4. Thermodynamic stability of transition metals on the Mg-terminated MgB2 (0001) surface and their effects on hydrogen dissociation and diffusion

    NASA Astrophysics Data System (ADS)

    Wang, Yongli; Michel, Kyle; Zhang, Yongsheng; Wolverton, C.

    2015-04-01

    The hydrogenation of MgB2 is a critical step in the reversibility of several well-known hydrogen storage reactions. Of the many processes that must occur during rehydrogenation, at least two of them take place near the surface: the dissociation of H2 molecules and the subsequent diffusion of atomic hydrogen. Using first-principles calculations, we determine the energetic barriers for these processes on the ideal Mg-terminated MgB2 (0001) surface, as well as on surfaces containing transition metal dopants (Sc-Zn, Y-Cd, Pt, and Au). The calculated dissociation barrier for H2 on the clean surface is 0.89 eV, and the surface diffusion barrier is 0.17 eV. However, we find examples of dopants that significantly decrease the activation barrier for the dissociation of H2 . Our calculations suggest that Ni, Cu, and Pd are good catalytic candidates for the surface processes involved in MgB2 rehydrogenation.

  5. Magnetic field dependent stability and quench behavior and degradation limits in conduction-cooled MgB2 wires and coils

    PubMed Central

    Ye, Liyang; Cruciani, Davide; Xu, Minfeng; Mine, Susumu; Amm, Kathleen; Schwartz, Justin

    2015-01-01

    Long lengths of metal/MgB2 composite conductors with high critical current density (Jc), fabricated by the power-in-tube (PIT) process, have recently become commercially available. Owing to its electromagnetic performance in the 20 K – 30 K range and relatively low cost, MgB2 may be attractive for a variety of applications. One of the key issues for magnet design is stability and quench protection, so the behavior of MgB2 wires and magnets must be understood before large systems can emerge. In this work, the stability and quench behavior of several conduction-cooled MgB2 wires are studied. Measurements of the minimum quench energy and normal zone propagation velocity are performed on short samples in a background magnetic field up to 3 T and on coils in self-field and the results are explained in terms of variations in the conductor architecture, electrical transport behavior, operating conditions (transport current and background magnetic field) and experimental setup (short sample vs small coil). Furthermore, one coil is quenched repeatedly with increasing hot-spot temperature until Jc is decreased. It is found that degradation during quenching correlates directly with temperature and not with peak voltage; a safe operating temperature limit of 260 K at the surface is identified. PMID:25883414

  6. Superconductivity, critical current density, and flux pinning in MgB2-x(SiC)x/2 superconductor after SiC nanoparticle doping

    NASA Astrophysics Data System (ADS)

    Dou, S. X.; Pan, A. V.; Zhou, S.; Ionescu, M.; Wang, X. L.; Horvat, J.; Liu, H. K.; Munroe, P. R.

    2003-08-01

    We investigated the effect of SiC nanoparticle doping on the crystal lattice structure, critical temperature Tc, critical current density Jc, and flux pinning in MgB2 superconductor. A series of MgB2-x(SiC)x/2 samples with x=0-1.0 were fabricated using an in situ reaction process. The contraction of the lattice and depression of Tc with increasing SiC doping level remained rather small most likely due to the counterbalancing effect of Si and C co-doping. The high level Si and C co-doping allowed the creation of intragrain defects and highly dispersed nanoinclusions within the grains which can act as effective pinning centers for vortices, improving Jc behavior as a function of the applied magnetic field. The enhanced pinning is mainly attributable to the substitution-induced defects and local structure fluctuations within grains. A pinning mechanism is proposed to account for different contributions of different defects in MgB2-x(SiC)x/2 superconductors.

  7. Numerical study on the quench propagation in a 1.5 T MgB2 MRI magnet design with varied wire compositions

    NASA Astrophysics Data System (ADS)

    Poole, Charles; Baig, Tanvir; Deissler, Robert J.; Doll, David; Tomsic, Michael; Martens, Michael

    2016-04-01

    To reduce the usage of liquid helium in MRI magnets, magnesium diboride (MgB2), a high temperature superconductor, has been considered for use in a design of conduction cooled MRI magnets. Compared to NbTi wires the normal zone propagation velocity (NZPV) in MgB2 is much slower leading to a higher temperature rise and the necessity of active quench protection. The temperature rise, resistive voltage, and NZPV during a quench in a 1.5 T main magnet design with MgB2 superconducting wire was calculated for a variety of wire compositions. The quench development was modeled using the Douglas-Gunn method to solve the 3D heat equation. It was determined that wires with higher bulk thermal conductivity and lower electrical resistivity reduced the hot-spot temperature rise near the beginning of a quench. These improvements can be accomplished by increasing the copper fraction inside the wire, using a sheath material (such as Glidcop) with a higher thermal conductivity and lower electrical resistivity, and by increasing the thermal conductivity of the wire’s insulation. The focus of this paper is on the initial stages of quench development, and does not consider the later stages of the quench or magnet protection.

  8. Magnetic field dependent stability and quench behavior and degradation limits in conduction-cooled MgB2 wires and coils

    NASA Astrophysics Data System (ADS)

    Ye, Liyang; Cruciani, Davide; Xu, Minfeng; Mine, Susumu; Amm, Kathleen; Schwartz, Justin

    2015-03-01

    Long lengths of metal/MgB2 composite conductors with high critical current density (Jc), fabricated by the powder-in-tube process, have recently become commercially available. Owing to its electromagnetic performance in the 20-30 K range and relatively low cost, MgB2 may be attractive for a variety of applications. One of the key issues for magnet design is stability and quench protection, so the behavior of MgB2 wires and magnets must be understood before large systems can emerge. In this work, the stability and quench behavior of several conduction-cooled MgB2 wires are studied. Measurements of the minimum quench energy and normal zone propagation velocity are performed on short samples in a background magnetic field up to 3 T and on coils in self-field and the results are explained in terms of variations in the conductor architecture, electrical transport behavior, operating conditions (transport current and background magnetic field) and experimental setup (short sample versus small coil). Furthermore, one coil is quenched repeatedly with increasing hotspot temperature until Jc is decreased. It is found that degradation during quenching correlates directly with temperature and not with peak voltage; a safe operating temperature limit of 260 K at the surface is identified.

  9. Magnetic field dependent stability and quench behavior and degradation limits in conduction-cooled MgB2 wires and coils.

    PubMed

    Ye, Liyang; Cruciani, Davide; Xu, Minfeng; Mine, Susumu; Amm, Kathleen; Schwartz, Justin

    2015-03-01

    Long lengths of metal/MgB2 composite conductors with high critical current density (Jc), fabricated by the power-in-tube (PIT) process, have recently become commercially available. Owing to its electromagnetic performance in the 20 K - 30 K range and relatively low cost, MgB2 may be attractive for a variety of applications. One of the key issues for magnet design is stability and quench protection, so the behavior of MgB2 wires and magnets must be understood before large systems can emerge. In this work, the stability and quench behavior of several conduction-cooled MgB2 wires are studied. Measurements of the minimum quench energy and normal zone propagation velocity are performed on short samples in a background magnetic field up to 3 T and on coils in self-field and the results are explained in terms of variations in the conductor architecture, electrical transport behavior, operating conditions (transport current and background magnetic field) and experimental setup (short sample vs small coil). Furthermore, one coil is quenched repeatedly with increasing hot-spot temperature until Jc is decreased. It is found that degradation during quenching correlates directly with temperature and not with peak voltage; a safe operating temperature limit of 260 K at the surface is identified.

  10. Interplay of ballistic and diffusive superconductivity in the vortex core in the model two-band system MgB2

    NASA Astrophysics Data System (ADS)

    Tanaka, K.; Eschrig, M.; Agterberg, D. F.

    2007-03-01

    A revived interest in multi-band superconductivity has emerged due to the unexpected and interesting simultaneous presence of diffusive and ballistic bands in the superconductor MgB2. Motivated by recent experimental data on the vortex state in MgB2 obtained by scanning tunneling spectroscopy, we theoretically study the intriguing effects of superconductivity in a diffusive band (`π band') induced by superconductivity in a ballistic band (`σ band'). We apply a unique model that has been developed recently [1] for describing such a system, based on coupled Eilenberger and Usadel equations. Results are presented for the spatial variation of the order parameter, the current density, and the vortex core spectrum in the two bands. A particularly interesting result emerging from our studies is the possibility of additional bound states near the gap edge in the `strong' σ band, which arise from hybridization with the `weak' π band. The development of such gap-edge bound states is examined for various sets of physical parameters that are relevant for MgB2. We will also discuss the induced Kramer-Pesch effect in the π band and magnetic-field dependence of vortex core size. [1] K. Tanaka, D. F. Agterberg, J. Kopu, M. Eschrig, Phys. Rev. B 73, 220501(R) (2006).

  11. Hysteresis losses in MgB2 superconductors exposed to combinations of low AC and high DC magnetic fields and transport currents

    NASA Astrophysics Data System (ADS)

    Magnusson, N.; Abrahamsen, A. B.; Liu, D.; Runde, M.; Polinder, H.

    2014-11-01

    MgB2 superconductors are considered for generator field coils for direct drive wind turbine generators. In such coils, the losses generated by AC magnetic fields may generate excessive local heating and add to the thermal load, which must be removed by the cooling system. These losses must be evaluated in the design of the generator to ensure a sufficient overall efficiency. A major loss component is the hysteresis losses in the superconductor itself. In the high DC - low AC current and magnetic field region experimental results still lack for MgB2 conductors. In this article we reason towards a simplified theoretical treatment of the hysteresis losses based on available models in the literature with the aim of setting the basis for estimation of the allowable magnetic fields and current ripples in superconducting generator coils intended for large wind turbine direct drive generators. The resulting equations use the DC in-field critical current, the geometry of the superconductor and the magnitude of the AC magnetic field component as parameters. This simplified approach can be valuable in the design of MgB2 DC coils in the 1-4 T range with low AC magnetic field and current ripples.

  12. Improved transport properties and connectivity of in situ MgB 2 wires obtained by Cold High Pressure Densification (CHPD)

    NASA Astrophysics Data System (ADS)

    Flükiger, R.; Hossain, M. S. A.; Senatore, C.; Rindfleisch, M.

    2011-11-01

    The critical current density, Jc, of in situ MgB2 wires with C4H6O5 (malic acid) has been strongly enhanced by means of Cold High Pressure Densification (CHPD) at pressures up to 2.5 GPa prior to reaction. An increase in Jc by factors 2 and 8 was observed at 4.2 and 20 K, regardless of the applied field. Densified wires were found to exhibit a higher homogeneity due to enhanced connectivity. In addition, a higher C content was found, as shown by the lattice parameter change, the decrease of Tc, the shift of the calorimetric Tc distribution and a reduced anisotropy in tapes obtained from the same wires. The higher C content in densified wires is responsible for the observed enhancement of Birr by more than 1 T, up to 11 T at 20 K. Almost isotropic Jc values were obtained for C4H6O5 added square wires of 1 × 0.6 mm2 cross section, the values of Jc(4.2 K) = 1 × 104 A/cm2 for fields // and ⊥ to the wider surface being obtained at 13.8 and 13.1 T (1 μV/cm criterion), the values for 20 K being 6.4 and 6.2 T, respectively. The method was successfully applied to mono- and multifilamentary wires with lengths up to several meters, suggesting applicability for industrial lengths.

  13. Influence of the carbon substitution on the critical current density and AC losses in MgB2 single crystals

    NASA Astrophysics Data System (ADS)

    Ciszek, M.; Rogacki, K.; Oganisian, K.; Zhigadlo, N. D.; Karpinski, J.

    2010-12-01

    The DC magnetization and AC complex magnetic susceptibilities were measured for MgB2 single crystals, unsubstituted and carbon substituted with the composition of Mg(B0.94C0.05)2. The measurements were performed in AC and DC magnetic fields oriented parallel to the c-axis of the crystals. From the DC magnetization loops and the AC susceptibility measurements, critical current densities ( J c were derived as a function of temperature and the DC and AC magnetic fields. Results show that the substitution with carbon decreases J c ) at low magnetic fields, opposite to the well known effect of an increase of J c at higher fields. AC magnetic losses were derived from the AC susceptibility data as a function of amplitude and the DC bias magnetic field. The AC losses were determined for temperatures of 0.6 and 0.7 of the transition temperature T c , so close to the boiling points of LH2 and LNe, potential cooling media for magnesium diboride based composites. The results are analyzed and discussed in the context of the critical state model.

  14. Fluxoid jump coupled high critical current density of nano-Co3O4 doped MgB2

    NASA Astrophysics Data System (ADS)

    Awana, V. P. S.; Isobe, M.; Singh, K. P.; Takayama-Muromachi, E.; Kishan, H.

    2006-06-01

    Polycrystalline MgB2 samples, with added 0, 2, 4 and 6% nano-Co3O4, synthesized by vacuum (10-5 Torr) annealing at 750 °C for two and a half hours each, are found to be nearly single phase with the presence of only a small quantity of Mg/MgO in the pristine sample in addition to the Co2O3 in the doped compounds. All the samples exhibited clear and sharp diamagnetic transitions at around 38 K, in zero-field-cooled (ZFC) magnetic susceptibility measurements with a sizeable signal. The field-cooled (FC) measurements, though having sharp transitions, showed a very small signal, indicating a high level of pinning centres in these samples. Further, some of the doped samples exhibited the paramagnetic Meissner effect (PME) in an applied field of 5 Oe. The critical current density (Jc), estimated by invoking Bean's model for the pristine compound, increases by nearly an order of magnitude for 2% and 4% nano-Co3O4 doping and then decreases sharply for the 6% sample at nearly all studied temperatures and applied fields. Further, the increased Jc (~108 A cm-2) is coupled with fluxoid jumps (T<=20 K and H<=1 T). Fluxoid jumps are not seen in the relatively low Jc pristine or 6% sample. This means that the fluxoid jumps are intrinsic only to the high-Jc samples.

  15. Induced Kramer-Pesch effect in a two-gap superconductor: Application to MgB2

    NASA Astrophysics Data System (ADS)

    Gumann, A.; Graser, S.; Dahm, T.; Schopohl, N.

    2006-03-01

    The size of the vortex core in a clean superconductor is strongly temperature dependent and shrinks with decreasing temperature, decreasing to zero for T→0 . We study this so-called Kramer-Pesch effect both for a single-gap superconductor and for the case of a two-gap superconductor using parameters appropriate for magnesium diboride. Usually, the Kramer-Pesch effect is absent in the dirty limit. Here, we show that the Kramer-Pesch effect exists in both bands of a two-gap superconductor even if only one of the two bands is in the clean limit and the other band in the dirty limit, a case appropriate for MgB2 . In this case an induced Kramer-Pesch effect appears in the dirty band. Besides numerical results we also present an analytical model for the spatial variation of the pairing potential in the vicinity of the vortex center that allows a simple calculation of the vortex core radius even in the limit T→0 .

  16. Plasma Synthesized Doped Boron Nanopowder for MgB2 Superconductors

    SciTech Connect

    James V. Marzik

    2012-03-26

    Under this program, a process to synthesize nano-sized doped boron powder by a plasma synthesis process was developed and scaled up from 20 gram batches at program start to over 200 grams by program end. Over 75 batches of boron nanopowder were made by RF plasma synthesis. Particle sizes were typically in the 20-200 nm range. The powder was synthesized by the reductive pyrolysis of BCl{sub 3} in hydrogen in an RF plasma. A wide range of process parameters were investigated including plasma power, torch geometry, gas flow rates, and process pressure. The powder-in-tube technique was used to make monofilament and multifilament superconducting wires. MgB{sub 2} wire made with Specialty Materials plasma synthesized boron nanopowder exhibited superconducting properties that significantly exceeded the program goals. Superconducting critical currents, J{sub c}, in excess of 10{sup 5} A cm{sup -2} at magnetic fields of 8 tesla were reproducibly achieved. The upper critical magnetic field in wires fabricated with program boron powder were H{sub c2}(0) = 37 tesla, demonstrating the potential of these materials for high field magnet applications. T{sub c} in carbon-doped MgB{sub 2} powder showed a systematic decrease with increasing carbon precursor gas flows, indicating the plasma synthesis process can give precise control over dopant concentrations. Synthesis rates increased by a factor of 400% over the course of the program, demonstrating the scalability of the powder synthesis process. The plasma synthesis equipment at Specialty Materials has successfully and reproducibly made high quality boron nanopowder for MgB{sub 2} superconductors. Research and development from this program enabled Specialty Materials to successfully scale up the powder synthesis process by a factor of ten and to double the size of its powder pilot plant. Thus far the program has been a technical success. It is anticipated that continued systematic development of plasma processing parameters, dopant

  17. A comprehensive study of the pinning mechanisms of MgB2 wires treated with malic acid and their relationships with lattice defects

    NASA Astrophysics Data System (ADS)

    Motaman, A.; Hossain, M. S. A.; Xu, X.; See, K. W.; Chung, K. C.; Dou, S. X.

    2013-08-01

    The effects of sintering temperature on the lattice parameters, structural strain, critical temperature (Tc), critical current density (Jc), irreversibility field (Birr), upper critical field (Bc2), and resistivity (ρ) of MgB2 wires treated with 10 wt.% malic acid (C4H6O5) are investigated in this paper. The a-lattice parameter of the sample treated with malic acid was drastically reduced, to 3.0745 Å, as compared to those for the undoped samples. Reduction in the a-lattice parameter is related to crystalline imperfections arising from carbon substitution—as confirmed by x-ray diffraction and Raman spectra—which play a vital role in enhancing Jc, Bc2 and Birr. We have also analyzed the pinning mechanisms, and concluded that flux pinning is dominated by point and correlated pinning at lower and higher magnetic fields, respectively, for the carbon-doped samples sintered at both 700 and 900 ° C. The degree of flux pinning enhancement and the ratio RHH (Bc2/Birr) have been estimated to guide us towards further enhancement of Jc. We argue that δℓ and δTc pinning mechanisms, based on variation of the mean free path (ℓ) and the critical temperature, respectively, coexist in the MgB2 wires treated with malic acid, regardless of the sintering temperature. The δℓ pinning is predominant at lower operating temperatures, and δTc pinning starts close to Tc, which means that spatial variation in the charge carrier mean free path is the main mechanism responsible for the flux pinning in the MgB2 wires treated with malic acid that were sintered at 700 and 900 ° C.

  18. Comparative study of mono- and multi-filament MgB2 wires with different boron powders and malic acid addition

    NASA Astrophysics Data System (ADS)

    Kim, J. H.; Heo, Yoon-Uk; Matsumoto, A.; Kumakura, H.; Rindfleisch, M.; Tomsic, M.; Dou, S. X.

    2010-07-01

    We evaluated the effects of different boron (B) powders and of malic acid (C4H6O5) addition on the critical current density (Jc) of mono- and multi-filament MgB2 wires. We found that Jc of the wires made from the amorphous B showed the best performance. Low sintering processing keeps the grain size small, which leads to strong flux pinning. From transmission electron microscopy (TEM) observations, we confirmed that the crystalline B powders supplied by SMI and Tangshan had a β-rhombohedral structure as a main phase. These two powders also had numerous defects, such as twin and stacking faults inside the powder particles. However, these defects are not enough to promote the full reaction between magnesium (Mg) and B crystalline powder when sintered at low temperatures, and brings about low Jc values. Even though the morphologies of the two crystalline B powders appeared somewhat different, Jc for the two wires had similar quantitative values. For the malic acid doped wires, Jc of the wire made from the amorphous B was estimated to be above 100 000 A cm - 2 at 6 T and 4.2 K. This value is comparable to the low temperature superconductor Nb-Ti. In addition, the Jc was 25 000 A cm - 2 at 10 T and 4.2 K. This performance is the best Jc reported so far in in situ processed MgB2 wires. Interestingly, the low-field Jc performance of malic acid doped wire fabricated with crystalline B is higher than that of the pure wire fabricated with amorphous B. At 20 K, enhanced performance of Jc by malic acid doping is much higher than that of the pure MgB2 wire. The Jc at 5 T and 20 K was estimated to be 13 000 A cm - 2.

  19. The Effect of High-energy Ball Milling on the Microstructure and Properties of Ti-doped MgB2 Bulks and Wires

    NASA Astrophysics Data System (ADS)

    Yang, F.; Yan, G.; Wang, Q. Y.; Xiong, X. M.; Li, S. Q.; liu, G. Q.; Feng, J. Q.; Pang, Y. C.; Li, C. S.; Feng, Y.; Zhang, P. X.

    MgB2 bulks were prepared by high-energy ball milling of Mg, B and Ti powders at ambient temperatures. The mixed powders were ball-milled for 0-10 h using a ball-to-powder mass ratio of 10 and sintered at 750 °C for 2 h. The phase and microstructure of MgB2 were characterized by means of X-ray diffraction (XRD) and Scanning electron microscope (SEM). XRD results reveal the appearance of a small amount of MgO impurity, and the relative percentage composition of MgO phase is gradually increased with prolonged the milling time. It proved that the sample milled 5 h has the best homogeneity in grain size. The milled 5 h powders were further processed to wires. The wire samples were fabricated by the in-situ powder-in-tube (PIT) method. The mechanical properties were analyzed by stress-strain measurements at room temperature and the superconducting behaviors are investigated by electrical tests at 4.2 K. The critical engineering current Ic reaches above 330 A (Jce exceeding 2.2×104 A/cm2) at 4.2 K and 2 T.

  20. High temperature heat treatment on boron precursor and PIT process optimization to improve the Jc performance of MgB2-based conductors

    NASA Astrophysics Data System (ADS)

    Vignolo, M.; Bovone, G.; Bernini, C.; Palenzona, A.; Kawale, S.; Romano, G.; Siri, A. S.

    2013-10-01

    The promising results reported in our previous works led us to think that the production process of boron plays a crucial role in MgB2 synthesis. A new method for boron preparation has been developed in our laboratory. This particular process is based on magnesiothermic reaction (Moissan’s process) with the addition of an initial step that gives boron powder with nano-metric grain size. In this paper we report our efforts regarding optimization of the powder-in-tube (PIT) method for these nano-metric powders, and the resolution of problems previously highlighted such as the difficulty in powder packaging and the high friction phenomena occurring during cold working. This increases cracking during the tape and wire manufacture, leading to failure. Packaging problems are related to the amorphous nature of boron synthesized in our laboratory, so a crystallization treatment was applied to improve the crystallinity of the boron. To prevent excessive friction phenomena we synthesized non-stoichiometric MgB2 and used magnesium as lubricant. Our goal is the Jc improvement, but a global physical-chemical characterization was also made to analyse the improvement given by our treatments: this characterization includes x-ray diffraction, ρ(T) measurement, and SEM imaging, besides magnetic and transport Jc measurements.

  1. Influence of crystalline boron powders on superconducting properties of C-doped internal Mg diffusion processed MgB2 wires

    NASA Astrophysics Data System (ADS)

    Wang, Dongliang; Zhang, Xianping; Tang, Shaopu; Xu, Da; Yao, Chao; Dong, Chiheng; Xu, Zhongtang; Ma, Yanwei; Oguro, Hidetoshi; Awaji, Satoshi; Watanabe, Kazuo

    2015-10-01

    Monofilament MgB2/Fe wires or tapes were fabricated with two different purity crystalline boron powders, using internal magnesium diffusion (IMD) and in situ powder-in-tube (PIT) processes. To evaluate which method was more insensitive to the purity of the boron powders, a sensitivity factor was used. It was found that the IMD process was less sensitive to the purity of the boron powders, compared to the PIT method. Furthermore, J c values of the IMD-processed wires were higher than those of the PIT-processed samples. The reduced porosity and hence the increased density in the IMD-processed samples was thought to be the main reason. Although a number of B-rich particles remained in the MgB2 region, a layer J c as high as 4.8 × 104 A cm-2 at 4.2 K and 10 T was still obtained in the IMD-processed wire, which was comparable to that of IMD-processed wires fabricated using amorphous boron powders.

  2. Scattering effect of the well-ordered MgB4 impurity phase in two-step sintered polycrystalline MgB2 with glycine addition

    NASA Astrophysics Data System (ADS)

    Cai, Qi; Liu, Yongchang; Guo, Qianying; Ma, Zongqing

    2017-04-01

    Glycine-doped MgB2 bulk was prepared by two-step sintering in this study, first at 750 °C and then 900 °C. The MgB4 particles are induced to precipitate where the dislocations concentrated after C substitution or along the steps of screw dislocation during crystal growth, forming ordered MgB4 arrays throughout the MgB2 grain. By means of atomic force microscope, the detected magnetic domains are arranged in agreement with the ordered MgB4 particles after the measurement of magnetic hysteresis loop, which supported that the nano-scale MgB4 domain structure brought strong scattering effects and indicated that atomic force microscopy could test the role of the impurities. As a result, the extrapolating upper critical field H c2(0 K) is enhanced to 22.8 T for the sample with ordered MgB4, while only 18.1 T for the un-doped sample underwent the same sintering program. Besides, carbon substitution contributed to the enhancement of H c2 as well.

  3. Mathematical model to determine the dimensions of superconducting cylindrical coils with a given central field - the case study for MgB2 conductors with isotropic Ic(B) characteristic

    NASA Astrophysics Data System (ADS)

    Pitel, Jozef; Melišek, Tibor; Tropeano, Matteo; Nardelli, Davide; Tumino, Andrea

    2016-08-01

    In this work, we present a mathematical model which enables to design cylindrical coils with a given central field, made of the superconducting conductor with isotropic Ic(B) characteristic. The model results in a computer code that enables to find out the coil dimensions, and to calculate the coil parameters such as critical current, maximum field in the winding and field non-uniformity on the coil axis. The Ic(B) characteristic of the conductor is represented by the set of data measured in discrete points. This approach allows us to express the Ic(B) as a function linearized in parts. Then, it is possible to involve the central field of the coil, coil dimensions, and parameters of the conductor, including its Ic(B) characteristic, in one equation which can be solved using ordinary numerical non-linear methods. Since the coil dimensions and conductor parameters are mutually linked in one equation with respect to a given coil central field, it is possible to analyze an influence of one parameter on the other one. The model was applied to three commercially available MgB2/Ni/Cu conductors produced by Columbus Superconductors. The results of simulations with the Ic(B) data at 20 K illustrate that there exists a set of winding geometries that generate a required central field, changing from a disc shape to long thin solenoid. Further, we analyze how the thickness of stabilizing copper influences the coil dimensions, overall conductor length, coil critical current, maximum field in the winding. An influence of the safety coefficient in operating current on coil dimensions and other above mentioned parameters is studied as well. Finally, we compare the coil dimensions, overall conductor length as well as coil critical current and maximum field in the winding if the value of required central field changes between 1 and 3 T.

  4. Effect of cold isostatic pressing on the transport current of filamentary MgB2 wire made by the IMD process

    NASA Astrophysics Data System (ADS)

    Kováč, P.; Hušek, I.; Pachla, W.; Melišek, T.; Kulich, M.; Rosová, A.; Kopera, L.

    2016-07-01

    This work describes the effect of cold isostatic pressing applied to as-drawn filamentary wires in a GlidCop and/or Cu sheath made by the internal magnesium diffusion process. Critical currents of as-drawn and isostatically pressed wires at high pressures up to 2.0 GPa followed by heat treatment at 640 °C for 40 min were measured. The obtained results show an improvement in boron powder density resulting in an increase of the critical current of MgB2 layers. The engineering current density increases by 4-13 times after the high-pressure treatment, and is influenced by the density of the boron powder and by the mechanical strength of the outer sheath.

  5. The effect of used deformation, metal sheath and heat treatment on the I-V curve of ex situ MgB 2 composite

    NASA Astrophysics Data System (ADS)

    Kováč, P.; Hušek, I.; Melišek, T.

    2004-01-01

    Current-voltage characteristics of MgB 2 composite wires made of ex situ process using Cu, Fe and stainless steel (SS) sheaths have been measured at 4.2 K in the self-field and external magnetic field between 2 and 4 T. It was found that the used mode of deformation (drawing, rotary swaging and two-axial rolling) influences the slope of I-V curve due to affected grain connectivity. Final heat treatment at 950 °C/0.5 h improves grain connectivity apparently, which results in I-V characteristic with very high n-exponents. The n-exponents of multi-core wires measured in external field are apparently lower due to a current sharing among the non-uniform filaments surrounded by high resistance matrix.

  6. The roles of CHPD: superior critical current density and n-value obtained in binary in situ MgB2 cables

    NASA Astrophysics Data System (ADS)

    Hossain, M. S. A.; Motaman, A.; Barua, S.; Patel, D.; Mustapic, M.; Kim, J. H.; Maeda, M.; Rindfleisch, M.; Tomsic, M.; Cicek, O.; Melisek, T.; Kopera, L.; Kario, A.; Ringsdorf, B.; Runtsch, B.; Jung, A.; Dou, S. X.; Goldacker, W.; Kovac, P.

    2014-09-01

    A binary magnesium diboride (MgB2) cable has been assembled by braiding six Nb/Monel sheathed monofilament strands around a central copper stabilizer for improving the operational environment. The total critical current (Ic) of the braided cable is obtained by multiplying the Ic of six single wires, without any dissipation. In this work, various mechanical deformations, i.e., swaging, two-axial rolling, groove rolling, and cold high-pressure densification (CHPD) at 1.8 GPa have been applied to the 6-stranded cable to obtain additional densification. The highest critical current density at both 4.2 and 20 K has been achieved in this work through the CHPD treated cable due to higher filament mass density. The present results are promising in view of the cable, particularly in power applications at industrial lengths that pave the way to seeking an optimal protocol to meet a practical functionality.

  7. Observation of Well-ordered Metastable Vortex Lattice Phases in Superconducting MgB2 Using Small-Angle Neutron Scattering

    SciTech Connect

    Das, Pinaki; Rastovski, Catherine; O'Brien, Timothy; Schlesinger, Kimberly; Dewhurst, Charles; Debeer-Schmitt, Lisa M; Zhigadlo, Nikolai; Karpinski, Janusz; Eskildsen, Morten

    2012-01-01

    The vortex lattice (VL) symmetry and orientation in clean type-II superconductors depends sensitively on the host material anisotropy, vortex density and temperature, frequently leading to rich phase diagrams. Typically, a well-ordered VL is taken to imply a ground-state configuration for the vortex-vortex interaction. Using neutron scattering we studied the VL in MgB2 for a number of field-temperature histories, discovering an unprecedented degree of metastability in connection with a known, second-order rotation transition. This allows, for the first time, structural studies of a well-ordered, nonequilibrium VL. While the mechanism responsible for the longevity of the metastable states is not resolved, we speculate it is due to a jamming of VL domains, preventing a rotation to the ground-state orientation.

  8. Experimental research of high field pinning centers in 2% C doped MgB2 wires at 20 K and 25 K

    NASA Astrophysics Data System (ADS)

    Gajda, D.; Morawski, A.; Zaleski, A. J.; Häßler, W.; Nenkov, K.; Małecka, M.; Rindfleisch, M. A.; Hossain, M. S. A.; Tomsic, M.

    2016-09-01

    High field pinning centers in MgB2 doped with 2 at. % carbon under a low and a high hot isostatic pressures have been investigated by transport measurements. The field dependence of the transport critical current density was analyzed within the different pinning mechanisms: surface pinning, point pinning, and pinning due to spatial variation in the Ginzburg-Landau parameter (Δκ pinning). Research indicates that a pressure of 1 GPa allows similar pinning centers to Δκ pinning centers to be obtained. This pinning is very important, because it makes it possible to increase the critical current density in high magnetic fields at 20 K and 25 K. Our results indicate that the δTc and δl pinning mechanisms, which are due to a spatial variation in the critical temperature (Tc) and the mean free path, l, respectively, create dislocations. The high density of dislocations with inhomogeneous distribution in the structure of the superconducting material creates the δl pinning mechanism. The low density of dislocations with inhomogeneous distribution creates the δTc pinning mechanism. Research indicates that the hot isostatic pressure process makes it possible to obtain a high dislocation density with a homogeneous distribution. This allows us to obtain the δTc pinning mechanism in MgB2 wires. In addition, a high pressure increases the crossover field from the single vortex to the small vortex bundle regime (Bsb) and improves the δTc pinning mechanism. Our research has proved that a high pressure significantly increases the crossover field from the small bundle to the thermal regime (Bth), with only a modest decrease in Tc of 1.5 K, decreases the thermal fluctuations, increases the irreversibility magnetic field (Birr) and the upper critical field (Bc2) in the temperature range from 4.2 K to 25 K, and reduces Birr and Bc2 above 25 K.

  9. Effect of two different treatments for reducing grape yield in Vitis vinifera cv Syrah on wine composition and quality: berry thinning versus cluster thinning.

    PubMed

    Gil, M; Esteruelas, M; González, E; Kontoudakis, N; Jiménez, J; Fort, F; Canals, J M; Hermosín-Gutiérrez, I; Zamora, F

    2013-05-22

    The influence of two treatments for reducing grape yield, cluster thinning and berry thinning, on red wine composition and quality were studied in a Vitis vinifera cv Syrah vineyard in AOC Penedès (Spain). Cluster thinning reduced grape yield per vine by around 40% whereas berry thinning only reduced it by around 20%. Cluster thinning grapes had higher soluble solids content than control grapes, and their resultant wines have greater anthocyanin and polysaccharide concentrations than the control wine. Wine obtained from berry thinning grapes had a higher total phenolic index, greater flavonol, proanthocyanidin, and polysaccharide concentrations, and lower titratable acidity than the control wine. Wines obtained from both treatments were sufficiently different from the control wine to be significantly distinguished by a trained panel in a triangular test. Even though both treatments seem to be effective at improving the quality of wine, berry thinning has the advantage because it has less impact on crop yield reduction.

  10. Photoluminescence-based quality control for thin film absorber layers of photovoltaic devices

    DOEpatents

    Repins, Ingrid L.; Kuciauskas, Darius

    2015-07-07

    A time-resolved photoluminescence-based system providing quality control during manufacture of thin film absorber layers for photovoltaic devices. The system includes a laser generating excitation beams and an optical fiber with an end used both for directing each excitation beam onto a thin film absorber layer and for collecting photoluminescence from the absorber layer. The system includes a processor determining a quality control parameter such as minority carrier lifetime of the thin film absorber layer based on the collected photoluminescence. In some implementations, the laser is a low power, pulsed diode laser having photon energy at least great enough to excite electron hole pairs in the thin film absorber layer. The scattered light may be filterable from the collected photoluminescence, and the system may include a dichroic beam splitter and a filter that transmit the photoluminescence and remove scattered laser light prior to delivery to a photodetector and a digital oscilloscope.

  11. The effect of carbon doping on the upper critical field (Hc2) and resistivity of MgB2 by using sucrose (C12H22O11) as the carbon source

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Zhou, S. H.; Lu, C.; Konstantinov, K.; Dou, S. X.

    2009-01-01

    In this work, sucrose was doped into MgB2 samples to act as a carbon source. The sintering temperature varied from 850 to 1050 °C. The effects of sucrose doping and sintering temperature on the lattice parameters, microstrain, critical temperature (Tc), resistivity, and upper critical field (Hc2) have been investigated in detail. It has been found that sucrose doping results in a small depression in Tc and high resistivity, while the Hc2 performance is improved. The best performance was shown in the sucrose-doped sample sintered at 850 °C. The reason for the enhancement of Hc2 is likely to be disorder caused by C substitution for B and/or diffusion of C atoms in the MgB2 lattice as interstitial atoms.

  12. Scalable fabrication of high-quality, ultra-thin single crystal diamond membrane windows

    NASA Astrophysics Data System (ADS)

    Piracha, Afaq Habib; Ganesan, Kumaravelu; Lau, Desmond W. M.; Stacey, Alastair; McGuinness, Liam P.; Tomljenovic-Hanic, Snjezana; Prawer, Steven

    2016-03-01

    High quality, ultra-thin single crystal diamond (SCD) membranes that have a thickness in the sub-micron range are of extreme importance as a materials platform for photonics, quantum sensing, nano/micro electro-mechanical systems (N/MEMS) and other diverse applications. However, the scalable fabrication of such thin SCD membranes is a challenging process. In this paper, we demonstrate a new method which enables high quality, large size (~4 × 4 mm) and low surface roughness, low strain, ultra-thin SCD membranes which can be fabricated without deformations such as breakage, bowing or bending. These membranes are easy to handle making them particularly suitable for fabrication of optical and mechanical devices. We demonstrate arrays of single crystal diamond membrane windows (SCDMW), each up to 1 × 1 mm in dimension and as thin as ~300 nm, supported by a diamond frame as thick as ~150 μm. The fabrication method is robust, reproducible, scalable and cost effective. Microwave plasma chemical vapour deposition is used for in situ creation of single nitrogen-vacancy (NV) centers into the thin SCDMW. We have also developed SCD drum head mechanical resonator composed of our fully clamped and freely suspended membranes.High quality, ultra-thin single crystal diamond (SCD) membranes that have a thickness in the sub-micron range are of extreme importance as a materials platform for photonics, quantum sensing, nano/micro electro-mechanical systems (N/MEMS) and other diverse applications. However, the scalable fabrication of such thin SCD membranes is a challenging process. In this paper, we demonstrate a new method which enables high quality, large size (~4 × 4 mm) and low surface roughness, low strain, ultra-thin SCD membranes which can be fabricated without deformations such as breakage, bowing or bending. These membranes are easy to handle making them particularly suitable for fabrication of optical and mechanical devices. We demonstrate arrays of single crystal diamond

  13. Thin-slice vision: inference of confidence measure from perceptual video quality

    NASA Astrophysics Data System (ADS)

    Hameed, Abdul; Balas, Benjamin; Dai, Rui

    2016-11-01

    There has been considerable research on thin-slice judgments, but no study has demonstrated the predictive validity of confidence measures when assessors watch videos acquired from communication systems, in which the perceptual quality of videos could be degraded by limited bandwidth and unreliable network conditions. This paper studies the relationship between high-level thin-slice judgments of human behavior and factors that contribute to perceptual video quality. Based on a large number of subjective test results, it has been found that the confidence of a single individual present in all the videos, called speaker's confidence (SC), could be predicted by a list of features that contribute to perceptual video quality. Two prediction models, one based on artificial neural network and the other based on a decision tree, were built to predict SC. Experimental results have shown that both prediction models can result in high correlation measures.

  14. Fabrication of high-quality single-crystal Cu thin films using radio-frequency sputtering

    PubMed Central

    Lee, Seunghun; Kim, Ji Young; Lee, Tae-Woo; Kim, Won-Kyung; Kim, Bum-Su; Park, Ji Hun; Bae, Jong-Seong; Cho, Yong Chan; Kim, Jungdae; Oh, Min-Wook; Hwang, Cheol Seong; Jeong, Se-Young

    2014-01-01

    Copper (Cu) thin films have been widely used as electrodes and interconnection wires in integrated electronic circuits, and more recently as substrates for the synthesis of graphene. However, the ultra-high vacuum processes required for high-quality Cu film fabrication, such as molecular beam epitaxy (MBE), restricts mass production with low cost. In this work, we demonstrated high-quality Cu thin films using a single-crystal Cu target and radio-frequency (RF) sputtering technique; the resulting film quality was comparable to that produced using MBE, even under unfavorable conditions for pure Cu film growth. The Cu thin film was epitaxially grown on an Al2O3 (sapphire) (0001) substrate, and had high crystalline orientation along the (111) direction. Despite the 10−3 Pa vacuum conditions, the resulting thin film was oxygen free due to the high chemical stability of the sputtered specimen from a single-crystal target; moreover, the deposited film had >5× higher adhesion force than that produced using a polycrystalline target. This fabrication method enabled Cu films to be obtained using a simple, manufacturing-friendly process on a large-area substrate, making our findings relevant for industrial applications. PMID:25169804

  15. Beware of poor-quality MgO substrates: A study of MgO substrate quality and its effect on thin film quality

    NASA Astrophysics Data System (ADS)

    Schroeder, J. L.; Ingason, A. S.; Rosén, J.; Birch, J.

    2015-06-01

    Magnesium oxide (MgO) substrates are widely used for fundamental research of a large variety of materials. Our motivation is to make the research community aware of poor-quality MgO substrates. We acquired thirty MgO substrates from six different vendors and demonstrate that 'single-crystal' MgO substrates are not always single crystal, but can consist of multiple domains. These multiple-domain MgO substrates can have a significant impact on research results as demonstrated by a one-to-one correlation between the domain structure of MgO substrates and titanium nitride (TiN) thin films (i.e. poor-quality MgO substrates result in poor-quality TiN films). Poor-quality MgO substrates are shown to be a widespread problem with over 70% of the evaluated substrates exhibiting multiple domains, essentially disqualifying them as substrates for epitaxy. MgO substrate vendors and researchers are encouraged to work together to resolve the problem of inconsistent MgO substrate quality and the research community is encouraged to perform quality control of MgO substrates prior to thin film deposition. Quality control by vendors and/or researchers can be achieved by acquiring X-ray diffraction omega-phi maps in batch processes, as detailed in this paper. We also propose a simple quality grading system to differentiate MgO substrates of varying quality.

  16. Influence of oxygen on the quality of the PZT thin films prepared by IBS

    NASA Astrophysics Data System (ADS)

    Horodyska, Petra; Hlubucek, Jiri; Zidek, Karel; Vaclavik, Jan

    2016-11-01

    Pb(Zr,Ti)O3 (PZT) is a ferroelectric material interesting for its high dielectric constant and piezoelectric response. PZT thin films can be prepared by various methods, e.g. pulsed laser deposition, chemical vapor deposition, sol-gel and, most frequently, sputtering. Though the magnetron sputtering is used more frequently, PZT thin films can be prepared also by ion-beam sputtering (IBS). In this paper we study the deposition process of PZT thin films in our IBS system with a possibility of ion-beam assisted deposition (IBAD), which has the advantage that more energy can be added to the growing layer. We show how in our system the resulting layers, mainly their quality, the Pb content, which is important for the creation of the perovskite crystal structure, and the resulting crystal structure are influenced by the oxygen flux during the deposition for the samples grown on the silicon substrate with and without an intermediate Ti seeding layer.

  17. Rapid and semi-analytical design and simulation of a toroidal magnet made with YBCO and MgB2 superconductors

    DOE PAGES

    Dimitrov, I. K.; Zhang, X.; Solovyov, V. F.; ...

    2015-07-07

    Recent advances in second-generation (YBCO) high-temperature superconducting wire could potentially enable the design of super high performance energy storage devices that combine the high energy density of chemical storage with the high power of superconducting magnetic storage. However, the high aspect ratio and the considerable filament size of these wires require the concomitant development of dedicated optimization methods that account for the critical current density in type-II superconductors. In this study, we report on the novel application and results of a CPU-efficient semianalytical computer code based on the Radia 3-D magnetostatics software package. Our algorithm is used to simulate andmore » optimize the energy density of a superconducting magnetic energy storage device model, based on design constraints, such as overall size and number of coils. The rapid performance of the code is pivoted on analytical calculations of the magnetic field based on an efficient implementation of the Biot-Savart law for a large variety of 3-D “base” geometries in the Radia package. The significantly reduced CPU time and simple data input in conjunction with the consideration of realistic input variables, such as material-specific, temperature, and magnetic-field-dependent critical current densities, have enabled the Radia-based algorithm to outperform finite-element approaches in CPU time at the same accuracy levels. Comparative simulations of MgB2 and YBCO-based devices are performed at 4.2 K, in order to ascertain the realistic efficiency of the design configurations.« less

  18. Development of plasma assisted thermal vapor deposition technique for high-quality thin film

    NASA Astrophysics Data System (ADS)

    Lee, Kang-Il; Choi, Yong Sup; Park, Hyun Jae

    2016-12-01

    The novel technique of Plasma-Assisted Vapor Deposition (PAVD) is developed as a new deposition method for thin metal films. The PAVD technique yields a high-quality thin film without any heating of the substrate because evaporated particles acquire energy from plasma that is confined to the inside of the evaporation source. Experiments of silver thin film deposition have been carried out in conditions of pressure lower than 10-3 Pa. Pure silver plasma generation is verified by the measurement of the Ag-I peak using optical emission spectroscopy. A four point probe and a UV-VIS spectrophotometer are used to measure the electrical and optical properties of the silver film that is deposited by PAVD. For an ultra-thin silver film with a thickness of 6.5 nm, we obtain the result of high-performance silver film properties, including a sheet resistance <20 Ω sq-1 and a visible-range transmittance >75%. The PAVD-film properties show a low sheet resistance of 30% and the same transmittance with conventional thermal evaporation film. In the PAVD source, highly energetic particles and UV from plasma do not reach the substrate because the plasma is completely shielded by the optimized nozzle of the crucible. This new PAVD technique could be a realistic solution to improve the qualities of transparent electrodes for organic light emission device fabrication without causing damage to the organic layers.

  19. Development of plasma assisted thermal vapor deposition technique for high-quality thin film.

    PubMed

    Lee, Kang-Il; Choi, Yong Sup; Park, Hyun Jae

    2016-12-01

    The novel technique of Plasma-Assisted Vapor Deposition (PAVD) is developed as a new deposition method for thin metal films. The PAVD technique yields a high-quality thin film without any heating of the substrate because evaporated particles acquire energy from plasma that is confined to the inside of the evaporation source. Experiments of silver thin film deposition have been carried out in conditions of pressure lower than 10(-3) Pa. Pure silver plasma generation is verified by the measurement of the Ag-I peak using optical emission spectroscopy. A four point probe and a UV-VIS spectrophotometer are used to measure the electrical and optical properties of the silver film that is deposited by PAVD. For an ultra-thin silver film with a thickness of 6.5 nm, we obtain the result of high-performance silver film properties, including a sheet resistance <20 Ω sq(-1) and a visible-range transmittance >75%. The PAVD-film properties show a low sheet resistance of 30% and the same transmittance with conventional thermal evaporation film. In the PAVD source, highly energetic particles and UV from plasma do not reach the substrate because the plasma is completely shielded by the optimized nozzle of the crucible. This new PAVD technique could be a realistic solution to improve the qualities of transparent electrodes for organic light emission device fabrication without causing damage to the organic layers.

  20. High quality thin films of thermoelectric misfit cobalt oxides prepared by a chemical solution method

    NASA Astrophysics Data System (ADS)

    Rivas-Murias, Beatriz; Manuel Vila-Fungueiriño, José; Rivadulla, Francisco

    2015-07-01

    Misfit cobaltates ([Bi/Ba/Sr/Ca/CoO]nRS[CoO2]q) constitute the most promising family of thermoelectric oxides for high temperature energy harvesting. However, their complex structure and chemical composition makes extremely challenging their deposition by high-vacuum physical techniques. Therefore, many of them have not been prepared as thin films until now. Here we report the synthesis of high-quality epitaxial thin films of the most representative members of this family of compounds by a water-based chemical solution deposition method. The films show an exceptional crystalline quality, with an electrical conductivity and thermopower comparable to single crystals. These properties are linked to the epitaxial matching of the rock-salt layers of the structure to the substrate, producing clean interfaces free of amorphous phases. This is an important step forward for the integration of these materials with complementary n-type thermoelectric oxides in multilayer nanostructures.

  1. High quality thin films of thermoelectric misfit cobalt oxides prepared by a chemical solution method

    PubMed Central

    Rivas-Murias, Beatriz; Manuel Vila-Fungueiriño, José; Rivadulla, Francisco

    2015-01-01

    Misfit cobaltates ([Bi/Ba/Sr/Ca/CoO]nRS[CoO2]q) constitute the most promising family of thermoelectric oxides for high temperature energy harvesting. However, their complex structure and chemical composition makes extremely challenging their deposition by high-vacuum physical techniques. Therefore, many of them have not been prepared as thin films until now. Here we report the synthesis of high-quality epitaxial thin films of the most representative members of this family of compounds by a water-based chemical solution deposition method. The films show an exceptional crystalline quality, with an electrical conductivity and thermopower comparable to single crystals. These properties are linked to the epitaxial matching of the rock-salt layers of the structure to the substrate, producing clean interfaces free of amorphous phases. This is an important step forward for the integration of these materials with complementary n-type thermoelectric oxides in multilayer nanostructures. PMID:26153533

  2. Growth and optical characteristics of high-quality ZnO thin films on graphene layers

    SciTech Connect

    Park, Suk In; Tchoe, Youngbin; Baek, Hyeonjun; Hyun, Jerome K.; Yi, Gyu-Chul E-mail: gcyi@snu.ac.kr; Heo, Jaehyuk; Jo, Janghyun; Kim, Miyoung; Kim, Nam-Jung E-mail: gcyi@snu.ac.kr

    2015-01-01

    We report the growth of high-quality, smooth, and flat ZnO thin films on graphene layers and their photoluminescence (PL) characteristics. For the growth of high-quality ZnO thin films on graphene layers, ZnO nanowalls were grown using metal-organic vapor-phase epitaxy on oxygen-plasma treated graphene layers as an intermediate layer. PL measurements were conducted at low temperatures to examine strong near-band-edge emission peaks. The full-width-at-half-maximum value of the dominant PL emission peak was as narrow as 4 meV at T = 11 K, comparable to that of the best-quality films reported previously. Furthermore, the stimulated emission of ZnO thin films on the graphene layers was observed at the low excitation energy of 180 kW/cm{sup 2} at room temperature. Their structural and optical characteristics were investigated using X-ray diffraction, transmission electron microscopy, and PL spectroscopy.

  3. Effect of combined addition of nano-SiC and nano-Ho2O3 on the in-field critical current density of MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Varghese, Neson; Vinod, K.; Chattopadhyay, M. K.; Roy, S. B.; Syamaprasad, U.

    2010-01-01

    MgB2 superconducting samples added with nano-Ho2O3 (n-Ho2O3) and/or nano-SiC (n-SiC) have been prepared by an in situ solid state reaction method to investigate and compare the combined and individual effects of n-SiC and n-Ho2O3 on a crystal structure, critical temperature (TC), and critical current density (JC) of MgB2. All the doped samples exhibit significantly enhanced in-field JC and the codoped sample with 2.5 wt % n-Ho2O3 and 5 wt % n-SiC gives the best performance in in-field JC, and the enhancement is around 100 times and 2 times greater than the undoped and monodoped n-SiC samples, respectively, at 5 K and 8 T. For the n-SiC added sample, lattice distortions due to C substitution on the B site and the formation of reacted phase Mg2Si as flux pinners cause enhanced JC up to the maximum field studied (8 T). While in the n-Ho2O3 added sample, a reacted phase HoB4 having a strong magnetic moment forms, without any substitution at the Mg or B site, which acts as a flux pinner in order to enhance the in-field JC. Accordingly the best codoped sample exhibits these combined benefits of n-SiC and n-Ho2O3 in MgB2 superconductor.

  4. Evaporative thinning: a facile synthesis method for high quality ultrathin layers of 2D crystals.

    PubMed

    Huang, Yi-Kai; Cain, Jeffrey D; Peng, Lintao; Hao, Shiqiang; Chasapis, Thomas; Kanatzidis, Mercouri G; Wolverton, Christopher; Grayson, Matthew; Dravid, Vinayak P

    2014-10-28

    The palette of two-dimensional materials has expanded beyond graphene in recent years to include the chalcogenides among other systems. However, there is a considerable paucity of methods for controlled synthesis of mono- and/or few-layer two-dimensional materials with desirable quality, reproducibility, and generality. Here we show a facile top-down synthesis approach for ultrathin layers of 2D materials down to monolayer. Our method is based on controlled evaporative thinning of initially large sheets, as deposited by vapor mass-transport. Rather than optimizing conditions for monolayer deposition, our approach makes use of selective evaporation of thick sheets to control the eventual thickness, down to a monolayer, a process which appears to be self-stopping. As a result, 2D sheets with high yield, high reproducibility, and excellent quality can be generated with large (>10 μm) and thin (∼ 1-2 nm) dimensions. Evaporative thinning promises to greatly reduce the difficulty involved in isolating large, mono- and few-layers of 2D materials for subsequent studies.

  5. Josephson effect in Nb/Al2O3/Al/MgB2 large-area thin-film heterostructures

    NASA Astrophysics Data System (ADS)

    Carapella, G.; Martucciello, N.; Costabile, G.; Ferdeghini, C.; Ferrando, V.; Grassano, G.

    2002-04-01

    We report the demonstration of dc and ac Josephson effects in Nb/Al2O3/Al/MgB2 thin-film heterostructure. The heterostructure exhibits moderately hysteretic current-voltage characteristic with a dc Josephson current branch and regular microwave-induced Shapiro steps. From conductance spectrum, a gap of about 2 meV at 7.7 K is estimated for the proximized surface of MgB2 electrode.

  6. Combined Effect of Upper Critical Field and Flux Pinning on Enhancing Critical Current Density of In-situ MgB2/Fe Tapes with Various Carbon Sources Simultaneously Doped

    NASA Astrophysics Data System (ADS)

    Pan, Xifeng; Matsumoto, Akiyoshi; Kumakura, Hiroaki; Zhao, Yong; Yan, Guo; Feng, Yong

    2012-01-01

    MgB2/Fe tapes with various forms of mono- and co-doped C sources were prepared by an in-situ powder-in-tube (PIT) method to study the effect of different C sources on the transport critical current density Jc behavior of MgB2. A remarkable Jc improvement at 4.2 K under higher fields and a significant increase in the actual content of C substitution for B were achieved for the tapes with various C sources co-doped. For these co-doped tapes, both enhanced Hc2 and flux pinning properties are responsible for their Jc improvement in this work. Comparing the 4 wt % C9H11NO doped tape with the 20 wt % malic acid doped tape, the latter possesses much better in-field Jc performance at 4.2 K and 10 T and sharper field dependence of Jc, which suggests that the flux pinning plays a crucial role in determining its Jc behavior.

  7. Fabrication of high quality nanocrystalline Cd(1-x)ZnxS thin films for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Verma, Urvashi; Thakur, Vikas; Rajaram, P.; Shrivastava, A. K.

    2013-02-01

    Nanocrystalline Cd(1-x)ZnxS thin films were prepared by spray pyrolysis technique. XRD studies showed that the films are polycrystalline and possess the hexagonal structure. The preferred crystallographic orientation of crystallites changes gradually from (002) to (101) with the increase in Zn composition. The AFM studies showed that the surface of the film is highly smooth and uniformly covered with the CdZnS nanoparticles. UV-VIS studies confirm the high quality of films. The band edge of these films is blue-shifted with the increase in Zn composition.

  8. Increased Optoelectronic Quality and Uniformity of Hydrogenated p-InP Thin Films

    SciTech Connect

    Wang, Hsin-Ping; Sutter-Fella, Carolin M.; Lobaccaro, Peter; Hettick, Mark; Zheng, Maxwell; Lien, Der-Hsien; Miller, D. Westley; Warren, Charles W.; Roe, Ellis T.; Lonergan, Mark C.; Guthrey, Harvey L.; Haegel, Nancy M.; Ager, Joel W.; Carraro, Carlo; Maboudian, Roya; He, Jr-Hau; Javey, Ali

    2016-07-12

    The thin-film vapor-liquid-solid (TF-VLS) growth technique presents a promising route for high quality, scalable, and cost-effective InP thin films for optoelectronic devices. Toward this goal, careful optimization of material properties and device performance is of utmost interest. Here, we show that exposure of polycrystalline Zn-doped TF-VLS InP to a hydrogen plasma (in the following referred to as hydrogenation) results in improved optoelectronic quality as well as lateral optoelectronic uniformity. A combination of low temperature photoluminescence and transient photocurrent spectroscopy was used to analyze the energy position and relative density of defect states before and after hydrogenation. Notably, hydrogenation reduces the relative intragap defect density by 1 order of magnitude. As a metric to monitor lateral optoelectronic uniformity of polycrystalline TF-VLS InP, photoluminescence and electron beam induced current mapping reveal homogenization of the grain versus grain boundary upon hydrogenation. At the device level, we measured more than 260 TF-VLS InP solar cells before and after hydrogenation to verify the improved optoelectronic properties. Hydrogenation increased the average open-circuit voltage (VOC) of individual TF-VLS InP solar cells by up to 130 mV and reduced the variance in VOC for the analyzed devices.

  9. Chemical Vapor Deposition Synthesized Atomically Thin Molybdenum Disulfide with Optoelectronic-Grade Crystalline Quality.

    PubMed

    Bilgin, Ismail; Liu, Fangze; Vargas, Anthony; Winchester, Andrew; Man, Michael K L; Upmanyu, Moneesh; Dani, Keshav M; Gupta, Gautam; Talapatra, Saikat; Mohite, Aditya D; Kar, Swastik

    2015-09-22

    The ability to synthesize high-quality samples over large areas and at low cost is one of the biggest challenges during the developmental stage of any novel material. While chemical vapor deposition (CVD) methods provide a promising low-cost route for CMOS compatible, large-scale growth of materials, it often falls short of the high-quality demands in nanoelectronics and optoelectronics. We present large-scale CVD synthesis of single- and few-layered MoS2 using direct vapor-phase sulfurization of MoO2, which enables us to obtain extremely high-quality single-crystal monolayer MoS2 samples with field-effect mobility exceeding 30 cm(2)/(V s) in monolayers. These samples can be readily synthesized on a variety of substrates, and demonstrate a high-degree of optoelectronic uniformity in Raman and photoluminescence mapping over entire crystals with areas exceeding hundreds of square micrometers. Because of their high crystalline quality, Raman spectroscopy on these samples reveal a range of multiphonon processes through peaks with equal or better clarity compared to past reports on mechanically exfoliated samples. This enables us to investigate the layer thickness and substrate dependence of the extremely weak phonon processes at 285 and 487 cm(-1) in 2D-MoS2. The ultrahigh, optoelectronic-grade crystalline quality of these samples could be further established through photocurrent spectroscopy, which clearly reveal excitonic states at room temperature, a feat that has been previously demonstrated only on samples which were fabricated by micro-mechanical exfoliation and then artificially suspended across trenches. Our method reflects a big step in the development of atomically thin, 2D-MoS2 for scalable, high-quality optoelectronics.

  10. Significant enhancement of the in-field critical current density of the MgB2 superconductor through codoping of nano-TiC with nano-SiC

    NASA Astrophysics Data System (ADS)

    Vinod, K.; Varghese, Neson; Roy, S. B.; Syamaprasad, U.

    2009-05-01

    Nanoparticles of two carbides, SiC and TiC, having different reactivities with the Mg/B are doped into the MgB2 system. These carbides are added in mono-and codoping conditions through the in situ solid state reaction, and the structural and superconducting properties are studied. The results show distinct modifications in the structural and superconducting properties by the two dopants. SiC causes considerable C substitution at the B site and the formation of intragrain inclusions, whereas TiC remains unreacted and does not cause any substitution. The codoped samples show significantly enhanced JC(H) performance compared to the undoped and monodoped samples. Compared to the undoped sample, the enhancement of JC is more than two orders of magnitude at 15 K for fields >7 T for the best sample. The results of JC(H) performance of the samples are discussed.

  11. The enhanced Jc and Birr of in situ MgB2 wires and tapes alloyed with C4H6O5 (malic acid) after cold high pressure densification

    NASA Astrophysics Data System (ADS)

    Hossain, M. S. A.; Senatore, C.; Flükiger, R.; Rindfleisch, M. A.; Tomsic, M. J.; Kim, J. H.; Dou, S. X.

    2009-09-01

    Cold high pressure densification, a method recently introduced at GAP in Geneva, was applied for improving the transport critical current density, Jc, and the irreversibility field, Birr, of monofilamentary in situ MgB2 wires and tapes alloyed with 10 wt% C4H6O5 (malic acid). Tapes densified at 1.48 GPa exhibited after reaction an enhancement of Jc from 2 to 4 × 104 A cm-2 at 4.2 K/10 T and from 0.5 to 4 × 104 A cm-2 at 20 K/5 T, while the Birr was enhanced from 19.3 to 22 T at 4.2 K and from 7.5 to 10.0 T at 20 K. Cold densification also caused a strong enhancement of B(104), the field at which Jc takes the value 1 × 104 A cm-2. For tapes subjected to 1.48 GPa, B(10^{4})^{\\parallel } and B(10^{4})^{ \\perp } at 4.2 K were found to increase from 11.8 and 10.5 T to 13.2 and 12.2 T, respectively. Almost isotropic conditions were obtained for rectangular wires with aspect ratios a/b<2 subjected to 2.0 GPa, where B(10^{4})^{\\parallel }=12.7 and B(10^{4})^{ \\perp }=12.5 T were obtained. At 20 K, the wires exhibited an almost isotropic behavior, with B(10^{4})^{\\parallel }=5.9 T and B(10^{4})^{ \\perp }=5.75 T, Birr(20 K) being ~10 T. These values are equal to or higher than the highest values reported so far for isotropic in situ wires with SiC or other carbon based additives. Further improvements are expected on optimizing the cold high pressure densification process, which has the potential for fabrication of MgB2 wires of industrial lengths.

  12. Improvement of Crystallographic Quality of Electroplated Copper Thin-Film Interconnections for Through-Silicon Vias

    NASA Astrophysics Data System (ADS)

    Suzuki, Ken; Murata, Naokazu; Saito, Naoki; Furuya, Ryosuke; Asai, Osamu; Miura, Hideo

    2013-04-01

    The relationship between the electrical properties and crystallographic quality (crystallinity) of electroplated copper thin-film interconnections was investigated. The crystallinity of the grains and grain boundaries of the interconnections was evaluated on the basis of the image quality (IQ) value obtained by electron back-scatter diffraction (EBSD) analysis. The electrical properties of the interconnections vary markedly depending on their crystallinity. The crystallinity also changed markedly as functions of electroplating conditions and the annealing temperature after electroplating. Although the electro migration (EM) resistance of the annealed interconnection was improved, stress-induced migration (SM) was activated by a high residual stress after annealing. To improve electrical reliability without heat treatment after electroplating, the effects of the seed layer under the interconnections on the crystallinity were investigated. As a result, the crystallinity was improved by changing the seed layer from Cu to Ru. In addition, the decrease in current density during electroplating also improved the crystallinity. Therefore, both introducing the Ru seed layer and decreasing the current density during electroplating are effective for developing highly reliable copper interconnections.

  13. Improving the assembly speed, quality, and tunability of thin conductive multilayers.

    PubMed

    Gittleson, Forrest S; Kohn, David J; Li, Xiaokai; Taylor, André D

    2012-05-22

    While inhomogeneous thin conductive films have been sought after for their flexibility, transparency, and strength, poor control in the processing of these materials has restricted their application. The versatile layer-by-layer assembly technique allows greater control over film deposition, but even this has been hampered by the traditional dip-coating method. Here, we employ a fully automated spin-spray layer-by-layer system (SSLbL) to rapidly produce high-quality, tunable multilayer films. With bilayer deposition cycle times as low as 13 s (~50% of previously reported) and thorough characterization of film conductance in the near percolation region, we show that SSLbL permits nanolevel control over film growth and efficient formation of a conducting network not available with other methods of multilayer deposition. The multitude of variables from spray time, to spin rate, to active drying available with SSLbL makes films generated by this technique inherently more tunable and expands the opportunity for optimization and application of composite multilayers. A comparison of several polymer-CNT systems deposited by both spin-spray and dip-coating exemplifies the potential of SSLbL assembly to allow for rapid screening of multilayer films. Ultrathin polymer-CNT multilayers assembled by SSLbL were also evaluated as lithium-ion battery electrodes, emphasizing the practical application of this technique.

  14. Some aspects over the quality of thin films deposited on special steels used in hydraulic blades

    NASA Astrophysics Data System (ADS)

    Tugui, C. A.; Vizureanu, P.; Iftimie, N.; Steigmann, R.

    2016-08-01

    The experimental research involved in this paper consists in the obtaining of superior physical, chemical and mechanical properties of stainless steels used in the construction of hydraulic turbine blades. These properties are obtained by deposition of hard thin films in order to improve the wear resistance, increasing the hardness but maintaining the tenacious core of the material. The chosen methods for deposition are electrospark deposition because it has relatively low costs, are easy to obtain, the layers have a good adherence to support and the thickness can be variable in function of the established conditions and the pulsed laser deposition because high quality films can be obtained at nanometric precision. The samples will be prepared for the analysis of the structure using optical method as well as for the obtaining of the optimal roughness for the deposition. The physical, chemical and mechanical properties will be determined after deposition using SEM and EDX, in order to emphasize the structure film-substrate and repartition of the deposition elements on the surface and in transversal section. The non-destructive testing has emphasized the good adherence between deposited layer and the metallic support, due to double deposition, spallation regions doesn't appear.

  15. High-quality EuO thin films the easy way via topotactic transformation

    DOE PAGES

    Mairoser, Thomas; Mundy, Julia A.; Melville, Alexander; ...

    2015-07-16

    Epitaxy is widely employed to create highly oriented crystalline films. A less appreciated, but nonetheless powerful means of creating such films is via topotactic transformation, in which a chemical reaction transforms a single crystal of one phase into a single crystal of a different phase, which inherits its orientation from the original crystal. Topotactic reactions may be applied to epitactic films to substitute, add or remove ions to yield epitactic films of different phases. Here we exploit a topotactic reduction reaction to provide a non-ultra-high vacuum (UHV) means of growing highly oriented single crystalline thin films of the easily over-oxidizedmore » half-metallic semiconductor europium monoxide (EuO) with a perfection rivalling that of the best films of the same material grown by molecular-beam epitaxy or UHV pulsed-laser deposition. Lastly, as the technique only requires high-vacuum deposition equipment, it has the potential to drastically improve the accessibility of high-quality single crystalline films of EuO as well as other difficult-to-synthesize compounds.« less

  16. High-quality EuO thin films the easy way via topotactic transformation

    SciTech Connect

    Mairoser, Thomas; Mundy, Julia A.; Melville, Alexander; Hodash, Daniel; Cueva, Paul; Held, Rainer; Glavic, Artur; Schubert, Jürgen; Muller, David A.; Schlom, Darrell G.; Schmehl, Andreas

    2015-07-16

    Epitaxy is widely employed to create highly oriented crystalline films. A less appreciated, but nonetheless powerful means of creating such films is via topotactic transformation, in which a chemical reaction transforms a single crystal of one phase into a single crystal of a different phase, which inherits its orientation from the original crystal. Topotactic reactions may be applied to epitactic films to substitute, add or remove ions to yield epitactic films of different phases. Here we exploit a topotactic reduction reaction to provide a non-ultra-high vacuum (UHV) means of growing highly oriented single crystalline thin films of the easily over-oxidized half-metallic semiconductor europium monoxide (EuO) with a perfection rivalling that of the best films of the same material grown by molecular-beam epitaxy or UHV pulsed-laser deposition. Lastly, as the technique only requires high-vacuum deposition equipment, it has the potential to drastically improve the accessibility of high-quality single crystalline films of EuO as well as other difficult-to-synthesize compounds.

  17. High-quality EuO thin films the easy way via topotactic transformation

    PubMed Central

    Mairoser, Thomas; Mundy, Julia A.; Melville, Alexander; Hodash, Daniel; Cueva, Paul; Held, Rainer; Glavic, Artur; Schubert, Jürgen; Muller, David A.; Schlom, Darrell G.; Schmehl, Andreas

    2015-01-01

    Epitaxy is widely employed to create highly oriented crystalline films. A less appreciated, but nonetheless powerful means of creating such films is via topotactic transformation, in which a chemical reaction transforms a single crystal of one phase into a single crystal of a different phase, which inherits its orientation from the original crystal. Topotactic reactions may be applied to epitactic films to substitute, add or remove ions to yield epitactic films of different phases. Here we exploit a topotactic reduction reaction to provide a non-ultra-high vacuum (UHV) means of growing highly oriented single crystalline thin films of the easily over-oxidized half-metallic semiconductor europium monoxide (EuO) with a perfection rivalling that of the best films of the same material grown by molecular-beam epitaxy or UHV pulsed-laser deposition. As the technique only requires high-vacuum deposition equipment, it has the potential to drastically improve the accessibility of high-quality single crystalline films of EuO as well as other difficult-to-synthesize compounds. PMID:26177710

  18. Experimental and modeling studies of the hybrid physical-chemical vapor deposition of superconducting magnesium diboride thin films

    NASA Astrophysics Data System (ADS)

    Lamborn, Daniel Ray

    source and increased substrate size. MgB2 film growths in this configuration were achieved, with comparable film properties from the original configuration; however the process had poor reproducibility and low growth rates. Boron film growth experiments and numerical modeling, incorporating the previously developed chemistry model showed that there is substantial B2H6 depletion upstream of the substrate and indicated that this configuration was not an optimal design. An impinging jet reactor configuration was then designed to reduce parasitic deposition upstream of the substrate, yet maintain the independent temperature control of the substrate and Mg source. Numerical modeling was used to explore process parameters for boron thin film growth and provide a guide for growth experiments. Initial experiments showed that a balance needed to be established between the loss of B2H6 and the gas-phase nucleation of Mg particles from cold-finger effects induced by the inlet jet flow. Superconducting MgB2 films were successfully grown in the impinging jet reactor that a Tc of 39.8 K and critical current density greater than 2x106 A/cm2 at zero magnetic field. The impinging jet configuration introduced a large degree of flexibility in MgB2 deposition with thin axis oriented films deposited at low jet flow rates with improved uniformity and thick coatings with growth rates in excess of 100 mum/hr at higher jet flow rates.

  19. Blowpipe Mineralogy for Physics/Environment: Highest-Possible-Tc SuperConductor (Beyond: (but via!!!) MgB2, Cuprates, Pnictides) Quest; BOTH PERMANENT FOREVER Carb-IDES SOLID-State Sequestration AND Drought(s)-Elimination

    NASA Astrophysics Data System (ADS)

    Segler, Kurt; Williams, Wendell; Siegel, Edward

    2011-03-01

    Detailed are old blowpipe new applications: charcoal-block reduction of borates to yield ("N-NW" of MgB2) Overhauser-[PR 35,1,411(1987); Intl.J.Mod.Phys.1, 2 & 4, 927(1987)]-"land" predicted high-EST-POSSIBLE Tc SC "LiD2"; very-early: Siegel[Phys.Stat.Sol.(a)11,45(1972);Semiconductors.and Insulators 5: 39,47,62(1979)] carb-IDES SOLID-state phase-TRANSITIONED CHEMICALLY-REDOX"-REACTED STABLE PERMANENT LONG-term NOT "CO2" BUT C-sequestration: PROFITABLE "Grab and Sell" TRUMPS "cap and trade"!!!; Mott alloying/vertical metal-insulator transitions in "borax-(GLASS)-beads"; and very-earlySiegel [{3rd Intl.Conf.Alt.Energy }(1980)-vol.5/p.459!!!] "FLYING-WATER" Hindenberg-effect (H2-UP;H2O-DOWN) via Hydrogen-maximal-Archimedes-buoyancy "chemical-rain-in-pipelines", only via Siegel proprietary "magnetic-hydrogen-valve"(MHV): Renewables-Hydrogen-Water flexible versatile agile scaleable retrofitable integrated operating-system for PERMANENT drought(s)-elimination FOREVER!!!

  20. Superconducting properties of very high quality NbN thin films grown by high temperature chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hazra, D.; Tsavdaris, N.; Jebari, S.; Grimm, A.; Blanchet, F.; Mercier, F.; Blanquet, E.; Chapelier, C.; Hofheinz, M.

    2016-10-01

    Niobium nitride (NbN) is widely used in high-frequency superconducting electronics circuits because it has one of the highest superconducting transition temperatures ({T}{{c}}˜ 16.5 {{K}}) and largest gap among conventional superconductors. In its thin-film form, the T c of NbN is very sensitive to growth conditions and it still remains a challenge to grow NbN thin films (below 50 nm) with high T c. Here, we report on the superconducting properties of NbN thin films grown by high-temperature chemical vapor deposition (HTCVD). Transport measurements reveal significantly lower disorder than previously reported, characterized by a Ioffe-Regel parameter ({k}{{F}}{\\ell }) ˜ 12. Accordingly we observe {T}{{c}}˜ 17.06 {{K}} (point of 50% of normal state resistance), the highest value reported so far for films of thickness 50 nm or less, indicating that HTCVD could be particularly useful for growing high quality NbN thin films.

  1. Silver doping: A potential means to grow high quality YBa{sub 2}Cu{sub 3}O{sub 7-x} thin films on bare sapphire

    SciTech Connect

    Kumar, D.; Satyalakshmi, K.M.; Manoharan, S.S.

    1995-10-01

    High quality Ag-doped YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) thin films have been grown by laser ablation on < {bar 1}012 > bare sapphire. This work demonstrates that Ag-doping can be used as very convenient means to realize good quality YBCO films on highly coveted sapphire substrates for microwave applications of high T{sub c} thin films.

  2. Optical properties of high quality Cu{sub 2}ZnSnSe{sub 4} thin films

    SciTech Connect

    Luckert, F.; Hamilton, D. I.; Yakushev, M. V.; Martin, R. W.; Beattie, N. S.; Zoppi, G.; Moynihan, M.; Forbes, I.; Karotki, A. V.; Mudryi, A. V.; Grossberg, M.; Krustok, J.

    2011-08-08

    Cu{sub 2}ZnSnSe{sub 4} thin films, fabricated on bare or molybdenum coated glass substrates by magnetron sputtering and selenisation, were studied by a range of techniques. Photoluminescence spectra reveal an excitonic peak and two phonon replicas of a donor-acceptor pair (DAP) recombination. Its acceptor and donor ionisation energies are 27 and 7 meV, respectively. This demonstrates that high-quality Cu{sub 2}ZnSnSe{sub 4} thin films can be fabricated. An experimental value for the longitudinal optical phonon energy of 28 meV was estimated. The band gap energy of 1.01 eV at room temperature was determined using optical absorption spectra.

  3. Use of space ultra-vacuum for high quality semiconductor thin film growth

    NASA Technical Reports Server (NTRS)

    Ignatiev, A.; Sterling, M.; Sega, R. M.

    1992-01-01

    The utilization of space for materials processing is being expanded through a unique concept of epitaxial thin film growth in the ultra-vacuum of low earth orbit (LEO). This condition can be created in the wake of an orbiting space vehicle; and assuming that the vehicle itself does not pertub the environment, vacuum levels of better than 10 exp -14 torr can be attained. This vacuum environment has the capacity of greatly enhancing epitaxial thin film growth and will be the focus of experiments conducted aboard the Wake Shield Facility (WSF) currently being developed by the Space Vacuum Epitaxy Center (SVEC), Industry, and NASA.

  4. High quality transparent conductive Ag-based barium stannate multilayer flexible thin films.

    PubMed

    Wu, Muying; Yu, Shihui; He, Lin; Yang, Lei; Zhang, Weifeng

    2017-12-01

    Transparent conductive multilayer thin films of silver (Ag)-embedded barium stannate (BaSnO3) structures have been deposited onto flexible polycarbonate substrates by magnetron sputtering at room temperature to develop an indium free transparent flexible electrode. The effect of thicknesses of Ag mid-layer and barium stannate layers on optical and electrical properties were investigated, and the mechanisms of conduction and transmittance were discussed. The highest value of figure of merit is 25.5 × 10(-3) Ω(-1) for the BaSnO3/Ag/BaSnO3 multilayer flexible thin films with 9 nm thick silver mid-layer and 50 nm thick barium stannate layers, while the average optical transmittance in the visible range from 380 to 780 nm is above 87%, the resistivity is 9.66 × 10(-5) Ω · cm, and the sheet resistance is 9.89 Ω/sq. The change rate of resistivity is under 10% after repeated bending of the multilayer flexible thin films. These results indicate that Ag-based barium stannate multilayer flexible thin films can be used as transparent flexible electrodes in various flexible optoelectronic devices.

  5. Fabrication of high quality, thin Ge-on-insulator layers by direct wafer-bonding for nanostructured thermoelectric devices

    NASA Astrophysics Data System (ADS)

    Veerappan, Manimuthu; Mukannan, Arivanandhan; Salleh, Faiz; Shimura, Yosuke; Hayakawa, Yasuhiro; Ikeda, Hiroya

    2017-03-01

    A simple means of fabricating thin Ge-on-insulator (GOI) layers with a strong bond at the Ge/SiO2 interface through direct wafer-bonding is described. In this work, high quality Ge/SiO2 bonding was achieved under ambient air and at room temperature as a result of the extremely hydrophilic bonding surfaces obtained by chemical treatment prior to direct bonding. Based on the results of this work, the first-ever bonding mechanism between ammonium hydroxide treated Ge and SiO2/Si wafer surfaces is proposed. In addition, strain generated during post-annealing as a consequence of the significant thermal-expansion mismatch between Ge and SiO2 was gradually relieved by applying a multistep-cooling process. Structural characteristics of the thin GOI layer were analyzed by cross-sectional scanning electron microscopy, Raman spectroscopy, x-ray diffraction and transmission electron microscopy. It was determined that direct wafer-bonding followed by polishing could produce a GOI layer as thin as 156 nm, with sub-nm surface roughness.

  6. Improving the surface structure of high quality Sr2FeMoO6 thin films for multilayer structures

    NASA Astrophysics Data System (ADS)

    Angervo, I.; Saloaro, M.; Tikkanen, J.; Huhtinen, H.; Paturi, P.

    2017-02-01

    Two sets of Sr2FeMoO6 thin films were prepared with pulsed laser deposition and the effect of the laser fluence and the deposition temperature was investigated. The Sr2FeMoO6 thin films showed clear evidence of impurity phases when the laser fluence was altered. Phase pure films resulted through the whole temperature range between 900 °C and 1050 °C when a proper laser fluence was used. Films fabricated at lower deposition temperatures resulted with smaller surface roughnesses around 5 nm, higher Curie temperatures and with relatively high saturation magnetization values. The Curie temperature was determined from the minimum of the first order derivative and results showed the highest values of 350 K and above. The films with the highest Curie temperature reached zero magnetization above 400 K. The results indicate that both high microstructural and high magnetic quality Sr2FeMoO6 thin films can be obtained with a deposition temperature between 900 °C and 950 °C. This provides better fabrication parameters for the upcoming SFMO multilayer structures.

  7. Electronic Properties of High-Quality Epitaxial Topological Dirac Semimetal Thin Films.

    PubMed

    Hellerstedt, Jack; Edmonds, Mark T; Ramakrishnan, Navneeth; Liu, Chang; Weber, Bent; Tadich, Anton; O'Donnell, Kane M; Adam, Shaffique; Fuhrer, Michael S

    2016-05-11

    Topological Dirac semimetals (TDS) are three-dimensional analogues of graphene, with linear electronic dispersions in three dimensions. Nanoscale confinement of TDSs in thin films is a necessary step toward observing the conventional-to-topological quantum phase transition (QPT) with increasing film thickness, gated devices for electric-field control of topological states, and devices with surface-state-dominated transport phenomena. Thin films can also be interfaced with superconductors (realizing a host for Majorana Fermions) or ferromagnets (realizing Weyl Fermions or T-broken topological states). Here we report structural and electrical characterization of large-area epitaxial thin films of TDS Na3Bi on single crystal Al2O3[0001] substrates. Charge carrier mobilities exceeding 6,000 cm(2)/(V s) and carrier densities below 1 × 10(18) cm(-3) are comparable to the best single crystal values. Perpendicular magnetoresistance at low field shows the perfect weak antilocalization behavior expected for Dirac Fermions in the absence of intervalley scattering. At higher fields up to 0.5 T anomalously large quadratic magnetoresistance is observed, indicating that some aspects of the low field magnetotransport (μB < 1) in this TDS are yet to be explained.

  8. Quality Factor and Microslipping of Fatigue Cracks in Thin Plates at Resonant Vibration

    NASA Technical Reports Server (NTRS)

    Wincheski, B.; Namkung, M.; Fulton, J. P.

    1993-01-01

    Resonant vibrations have been stimulated in thin metal plates using a non-contacting electromagnetic driver. A sinusoidal force was applied in a swept frequency fashion and the resulting surface displacements were monitored through the use of an acoustic microphone. It has been found that the presence of a fatigue crack in the sample causes a broadening of the second resonance peak. The Q factors of the resonance curves were determined and are directly correlated with the presence of fatigue cracks in the samples. The broadening of the curves is explained in terms of a microslipping at the crack face walls which reduces the amplitude of the resonant vibration by increasing the damping of the system. A comparison is made between the resonance characteristics of fatigue damaged and notched samples, where the stiffness of the two systems is nearly constant while the interaction between crack face walls is eliminated in the latter.

  9. The Nonprofit Advantage: Producing Quality in Thick and Thin Child Care Markets

    ERIC Educational Resources Information Center

    Cleveland, Gordon; Krashinsky, Michael

    2009-01-01

    Nonprofit child care centers are frequently observed to produce child care which is, on average, of higher quality than care provided in commercial child care centers. In part, this nonprofit advantage is due to different input choices made by nonprofit centers--lower child--staff ratios, better-educated staff and directors, higher rates of…

  10. Thin-film fixed-bed reactor for solar photocatalytic inactivation of Aeromonas hydrophila: influence of water quality

    PubMed Central

    2012-01-01

    Background Controlling fish disease is one of the major concerns in contemporary aquaculture. The use of antibiotics or chemical disinfection cannot provide a healthy aquaculture system without residual effects. Water quality is also important in determining the success or failure of fish production. Several solar photocatalytic reactors have been used to treat drinking water or waste water without leaving chemical residues. This study has investigated the impact of several key aspects of water quality on the inactivation of the pathogenic bacterium Aeromonas hydrophila using a pilot-scale thin-film fixed-bed reactor (TFFBR) system. Results The level of inactivation of Aeromonas hydrophila ATCC 35654 was determined using a TFFBR with a photocatalytic area of 0.47 m2 under the influence of various water quality variables (pH, conductivity, turbidity and colour) under high solar irradiance conditions (980–1100 W m-2), at a flow rate of 4.8 L h-1 through the reactor. Bacterial enumeration were obtained through conventional plate count using trypticase soy agar media, cultured in conventional aerobic conditions to detect healthy cells and under ROS-neutralised conditions to detect both healthy and sub-lethally injured (oxygen-sensitive) cells. The results showed that turbidity has a major influence on solar photocatalytic inactivation of A. hydrophila. Humic acids appear to decrease TiO2 effectiveness under full sunlight and reduce microbial inactivation. pH in the range 7–9 and salinity both have no major effect on the extent of photoinactivation or sub-lethal injury. Conclusions This study demonstrates the effectiveness of the TFFBR in the inactivation of Aeromonas hydrophila under the influence of several water quality variables at high solar irradiance, providing an opportunity for the application of solar photocatalysis in aquaculture systems, as long as turbidity remains low. PMID:23194331

  11. High-Quality Solution-Processed Silicon Oxide Gate Dielectric Applied on Indium Oxide Based Thin-Film Transistors.

    PubMed

    Jaehnike, Felix; Pham, Duy Vu; Anselmann, Ralf; Bock, Claudia; Kunze, Ulrich

    2015-07-01

    A silicon oxide gate dielectric was synthesized by a facile sol-gel reaction and applied to solution-processed indium oxide based thin-film transistors (TFTs). The SiOx sol-gel was spin-coated on highly doped silicon substrates and converted to a dense dielectric film with a smooth surface at a maximum processing temperature of T = 350 °C. The synthesis was systematically improved, so that the solution-processed silicon oxide finally achieved comparable break downfield strength (7 MV/cm) and leakage current densities (<10 nA/cm(2) at 1 MV/cm) to thermally grown silicon dioxide (SiO2). The good quality of the dielectric layer was successfully proven in bottom-gate, bottom-contact metal oxide TFTs and compared to reference TFTs with thermally grown SiO2. Both transistor types have field-effect mobility values as high as 28 cm(2)/(Vs) with an on/off current ratio of 10(8), subthreshold swings of 0.30 and 0.37 V/dec, respectively, and a threshold voltage close to zero. The good device performance could be attributed to the smooth dielectric/semiconductor interface and low interface trap density. Thus, the sol-gel-derived SiO2 is a promising candidate for a high-quality dielectric layer on many substrates and high-performance large-area applications.

  12. The Quality Issue of the Parts Blanked from Thin Silicon Sheets

    NASA Astrophysics Data System (ADS)

    Mucha, Jacek; Jaworski, Jan

    2017-03-01

    In this paper, the wear mechanism of punches made of M3:2 and M2 steel sheet which are used in blanking process of the rotor part of the low-power asynchronous motor was presented. The influence of additional TiN coating on the punch flank surface degradation intensity was described. The punch wear influence on the hardness changes close the material intersection surface was determined. The research results indicate that the tool durability ensures the quality of parts blanked from electrotechnical steel. The results will allow for selection of new tools materials for this type of tools which are used in difficult tribological conditions.

  13. Enhanced optoelectronic quality of perovskite thin films with hypophosphorous acid for planar heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Pathak, Sandeep; Sakai, Nobuya; Stergiopoulos, Thomas; Nayak, Pabitra K.; Noel, Nakita K.; Haghighirad, Amir A.; Burlakov, Victor M.; Dequilettes, Dane W.; Sadhanala, Aditya; Li, Wenzhe; Wang, Liduo; Ginger, David S.; Friend, Richard H.; Snaith, Henry J.

    2015-11-01

    Solution-processed metal halide perovskite semiconductors, such as CH3NH3PbI3, have exhibited remarkable performance in solar cells, despite having non-negligible density of defect states. A likely candidate is halide vacancies within the perovskite crystals, or the presence of metallic lead, both generated due to the imbalanced I/Pb stoichiometry which could evolve during crystallization. Herein, we show that the addition of hypophosphorous acid (HPA) in the precursor solution can significantly improve the film quality, both electronically and topologically, and enhance the photoluminescence intensity, which leads to more efficient and reproducible photovoltaic devices. We demonstrate that the HPA can reduce the oxidized I2 back into I-, and our results indicate that this facilitates an improved stoichiometry in the perovskite crystal and a reduced density of metallic lead.

  14. Enhanced optoelectronic quality of perovskite thin films with hypophosphorous acid for planar heterojunction solar cells.

    PubMed

    Zhang, Wei; Pathak, Sandeep; Sakai, Nobuya; Stergiopoulos, Thomas; Nayak, Pabitra K; Noel, Nakita K; Haghighirad, Amir A; Burlakov, Victor M; deQuilettes, Dane W; Sadhanala, Aditya; Li, Wenzhe; Wang, Liduo; Ginger, David S; Friend, Richard H; Snaith, Henry J

    2015-11-30

    Solution-processed metal halide perovskite semiconductors, such as CH3NH3PbI3, have exhibited remarkable performance in solar cells, despite having non-negligible density of defect states. A likely candidate is halide vacancies within the perovskite crystals, or the presence of metallic lead, both generated due to the imbalanced I/Pb stoichiometry which could evolve during crystallization. Herein, we show that the addition of hypophosphorous acid (HPA) in the precursor solution can significantly improve the film quality, both electronically and topologically, and enhance the photoluminescence intensity, which leads to more efficient and reproducible photovoltaic devices. We demonstrate that the HPA can reduce the oxidized I2 back into I(-), and our results indicate that this facilitates an improved stoichiometry in the perovskite crystal and a reduced density of metallic lead.

  15. Influence of Clearance and Punch Velocity on the Quality of Pure Thin Copper Sheets Blanked Parts

    NASA Astrophysics Data System (ADS)

    Zakariya Lubis, Didin; Mahardika, Muslim

    2016-11-01

    Research on the influence of clearance and punch velocity to determine the quality of the punched edge were conducted. This study uses pure copper sheet material with the clearance variation of 2.5, 5, 7.5 and 10%. Punch velocity is based on the ability of about Micro Punch CNC machine which is 100 and 2600 mm/min. At highest speed with a clearance of 2.5%, sheared zone is of about 395 pm or 79% of the material thickness. It can be concluded that the punch velocity gives positive influence on the sheared zone in copper. Basically the ideal outcome of the sheared edge of punching result is having rollover and small burr and contain at least 75% of the shear zone. This can be achieved with a clearance of 2.5%.

  16. Enhanced optoelectronic quality of perovskite thin films with hypophosphorous acid for planar heterojunction solar cells

    DOE PAGES

    Zhang, Wei; Pathak, Sandeep; Sakai, Nobuya; ...

    2015-11-30

    Solution-processed metal halide perovskite semiconductors, such as CH3NH3PbI3, have exhibited remarkable performance in solar cells, despite having non-negligible density of defect states. A likely candidate is halide vacancies within the perovskite crystals, or the presence of metallic lead, both generated due to the imbalanced I/Pb stoichiometry which could evolve during crystallization. Herein, we show that the addition of hypophosphorous acid (HPA) in the precursor solution can significantly improve the film quality, both electronically and topologically, and enhance the photoluminescence intensity, which leads to more efficient and reproducible photovoltaic devices. We demonstrate that the HPA can reduce the oxidized I2 backmore » into I-, and our results indicate that this facilitates an improved stoichiometry in the perovskite crystal and a reduced density of metallic lead.« less

  17. Enhanced optoelectronic quality of perovskite thin films with hypophosphorous acid for planar heterojunction solar cells

    PubMed Central

    Zhang, Wei; Pathak, Sandeep; Sakai, Nobuya; Stergiopoulos, Thomas; Nayak, Pabitra K.; Noel, Nakita K.; Haghighirad, Amir A.; Burlakov, Victor M.; deQuilettes, Dane W.; Sadhanala, Aditya; Li, Wenzhe; Wang, Liduo; Ginger, David S.; Friend, Richard H.; Snaith, Henry J.

    2015-01-01

    Solution-processed metal halide perovskite semiconductors, such as CH3NH3PbI3, have exhibited remarkable performance in solar cells, despite having non-negligible density of defect states. A likely candidate is halide vacancies within the perovskite crystals, or the presence of metallic lead, both generated due to the imbalanced I/Pb stoichiometry which could evolve during crystallization. Herein, we show that the addition of hypophosphorous acid (HPA) in the precursor solution can significantly improve the film quality, both electronically and topologically, and enhance the photoluminescence intensity, which leads to more efficient and reproducible photovoltaic devices. We demonstrate that the HPA can reduce the oxidized I2 back into I−, and our results indicate that this facilitates an improved stoichiometry in the perovskite crystal and a reduced density of metallic lead. PMID:26615763

  18. Enhanced optoelectronic quality of perovskite thin films with hypophosphorous acid for planar heterojunction solar cells

    SciTech Connect

    Zhang, Wei; Pathak, Sandeep; Sakai, Nobuya; Stergiopoulos, Thomas; Nayak, Pabitra K.; Noel, Nakita K.; Haghighirad, Amir A.; Burlakov, Victor M.; deQuilettes, Dane W.; Sadhanala, Aditya; Li, Wenzhe; Wang, Liduo; Ginger, David S.; Friend, Richard H.; Snaith, Henry J.

    2015-11-30

    Solution-processed metal halide perovskite semiconductors, such as CH3NH3PbI3, have exhibited remarkable performance in solar cells, despite having non-negligible density of defect states. A likely candidate is halide vacancies within the perovskite crystals, or the presence of metallic lead, both generated due to the imbalanced I/Pb stoichiometry which could evolve during crystallization. Herein, we show that the addition of hypophosphorous acid (HPA) in the precursor solution can significantly improve the film quality, both electronically and topologically, and enhance the photoluminescence intensity, which leads to more efficient and reproducible photovoltaic devices. We demonstrate that the HPA can reduce the oxidized I2 back into I-, and our results indicate that this facilitates an improved stoichiometry in the perovskite crystal and a reduced density of metallic lead.

  19. Molecular solution approach to synthesize electronic quality Cu2ZnSnS4 thin films.

    PubMed

    Yang, Wenbing; Duan, Hsin-Sheng; Cha, Kitty C; Hsu, Chia-Jung; Hsu, Wan-Ching; Zhou, Huanping; Bob, Brion; Yang, Yang

    2013-05-08

    Successful implementation of molecular solution processing from a homogeneous and stable precursor would provide an alternative, robust approach to process multinary compounds compared with physical vapor deposition. Targeting deposition of chemically clear, high quality crystalline films requires specific molecular structure design and solvent selection. Hydrazine (N2H4) serves as a unique and powerful medium, particularly to incorporate selected metallic elements and chalcogens into a stable solution as metal chalcogenide complexes (MCC). However, not all the elements and compounds can be easily dissolved. In this manuscript, we demonstrate a paradigm to incorporate previously insoluble transitional-metal elements into molecular solution as metal-atom hydrazine/hydrazine derivative complexes (MHHD), as exemplified by dissolving of the zinc constituent as Zn(NH2NHCOO)2(N2H4)2. Investigation into the evolution of molecular structure reveals the hidden roadmap to significantly enrich the variety of building blocks for soluble molecule design. The new category of molecular structures not only set up a prototype to incorporate other elements of interest but also points the direction for other compatible solvent selection. As demonstrated from the molecular precursor combining Sn-/Cu-MCC and Zn-MHHD, an ultrathin film of copper zinc tin sulfide (CZTS) was deposited. Characterization of a transistor based on the CZTS channel layer shows electronic properties comparable to CuInSe2, confirming the robustness of this molecular solution processing and the prospect of earth abundant CZTS for next generation photovoltaic materials. This paradigm potentially outlines a universal pathway, from individual molecular design using selected chelated ligands and combination of building blocks in a simple and stable solution to fundamentally change the way multinary compounds are processed.

  20. Enhanced quality thin film Cu(In,Ga)Se.sub.2 for semiconductor device applications by vapor-phase recrystallization

    DOEpatents

    Tuttle, John R.; Contreras, Miguel A.; Noufi, Rommel; Albin, David S.

    1994-01-01

    Enhanced quality thin films of Cu.sub.w (In,Ga.sub.y)Se.sub.z for semiconductor device applications are fabricated by initially forming a Cu-rich, phase-separated compound mixture comprising Cu(In,Ga):Cu.sub.x Se on a substrate to form a large-grain precursor and then converting the excess Cu.sub.x Se to Cu(In,Ga)Se.sub.2 by exposing it to an activity of In and/or Ga, either in vapor In and/or Ga form or in solid (In,Ga).sub.y Se.sub.z. Alternatively, the conversion can be made by sequential deposition of In and/or Ga and Se onto the phase-separated precursor. The conversion process is preferably performed in the temperature range of about 300.degree.-600.degree. C., where the Cu(In,Ga)Se.sub.2 remains solid, while the excess Cu.sub.x Se is in a liquid flux. The characteristic of the resulting Cu.sub.w (In,Ga).sub.y Se.sub.z can be controlled by the temperature. Higher temperatures, such as 500.degree.-600.degree. C., result in a nearly stoichiometric Cu(In,Ga)Se.sub.2, whereas lower temperatures, such as 300.degree.-400.degree. C., result in a more Cu-poor compound, such as the Cu.sub.z (In,Ga).sub.4 Se.sub.7 phase.

  1. Enhanced quality thin film Cu(In,Ga)Se[sub 2] for semiconductor device applications by vapor-phase recrystallization

    DOEpatents

    Tuttle, J.R.; Contreras, M.A.; Noufi, R.; Albin, D.S.

    1994-10-18

    Enhanced quality thin films of Cu[sub w](In,Ga[sub y])Se[sub z] for semiconductor device applications are fabricated by initially forming a Cu-rich, phase-separated compound mixture comprising Cu(In,Ga):Cu[sub x]Se on a substrate to form a large-grain precursor and then converting the excess Cu[sub x]Se to Cu(In,Ga)Se[sub 2] by exposing it to an activity of In and/or Ga, either in vapor In and/or Ga form or in solid (In,Ga)[sub y]Se[sub z]. Alternatively, the conversion can be made by sequential deposition of In and/or Ga and Se onto the phase-separated precursor. The conversion process is preferably performed in the temperature range of about 300--600 C, where the Cu(In,Ga)Se[sub 2] remains solid, while the excess Cu[sub x]Se is in a liquid flux. The characteristic of the resulting Cu[sub w](In,Ga)[sub y]Se[sub z] can be controlled by the temperature. Higher temperatures, such as 500--600 C, result in a nearly stoichiometric Cu(In,Ga)Se[sub 2], whereas lower temperatures, such as 300--400 C, result in a more Cu-poor compound, such as the Cu[sub z](In,Ga)[sub 4]Se[sub 7] phase. 7 figs.

  2. 7 CFR 29.3648 - Thin Leaf (C Group).

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... tolerance. C4L Fair Quality Light-brown Thin Leaf. Mature, thin, close leaf structure, rough, lean in oil... tolerance. C5L Low Quality Light-brown Thin Leaf Underripe, thin, close leaf structure, rough, lean in oil... tolerance. C4F Fair Quality Medium-brown Thin Leaf. Mature, thin, close leaf structure, rough, lean in...

  3. 7 CFR 29.3648 - Thin Leaf (C Group).

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... tolerance. C4L Fair Quality Light-brown Thin Leaf. Mature, thin, close leaf structure, rough, lean in oil... tolerance. C5L Low Quality Light-brown Thin Leaf Underripe, thin, close leaf structure, rough, lean in oil... tolerance. C4F Fair Quality Medium-brown Thin Leaf. Mature, thin, close leaf structure, rough, lean in...

  4. 7 CFR 29.3648 - Thin Leaf (C Group).

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... tolerance. C4L Fair Quality Light-brown Thin Leaf. Mature, thin, close leaf structure, rough, lean in oil... tolerance. C5L Low Quality Light-brown Thin Leaf Underripe, thin, close leaf structure, rough, lean in oil... tolerance. C4F Fair Quality Medium-brown Thin Leaf. Mature, thin, close leaf structure, rough, lean in...

  5. 7 CFR 29.3648 - Thin Leaf (C Group).

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... tolerance. C4L Fair Quality Light-brown Thin Leaf. Mature, thin, close leaf structure, rough, lean in oil... tolerance. C5L Low Quality Light-brown Thin Leaf Underripe, thin, close leaf structure, rough, lean in oil... tolerance. C4F Fair Quality Medium-brown Thin Leaf. Mature, thin, close leaf structure, rough, lean in...

  6. 7 CFR 29.3648 - Thin Leaf (C Group).

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... tolerance. C4L Fair Quality Light-brown Thin Leaf. Mature, thin, close leaf structure, rough, lean in oil... tolerance. C5L Low Quality Light-brown Thin Leaf Underripe, thin, close leaf structure, rough, lean in oil... tolerance. C4F Fair Quality Medium-brown Thin Leaf. Mature, thin, close leaf structure, rough, lean in...

  7. High- and Mid-temperature Superconducting Sensors for Far IR/Sub-mm Applications in Space

    NASA Technical Reports Server (NTRS)

    Lakew, Brook; Brasunas, J. C.

    2004-01-01

    In this review paper an overview of the potential applications of high Tc (approx. 90 K) superconductors (HTS) and mid-Tc (approx. 39 K) superconductors (MTS) thin films in far IR/Sub-mm thermal detectors is presented. HTSs (YBCO, GdBCO etc.) were discovered in the late 80s while superconductivity in MgB2, an MTS, was discovered in 2001. The sharp transition in transport properties of HTS has allowed the fabrication of composite infrared thermal detectors (bolometers) with better figures of merit than thermopile detectors - thermopiles are currently on board the CIRS instrument on the Cassini mission to Saturn. The potential for developing even more sensitive sensors for IR/Sub-mm applications using MgB2 thin films is assessed. Current MgB2 thin film deposition techniques and film quality are reviewed.

  8. High quality nitrogen-doped zinc oxide thin films grown on ITO by sol-gel method

    NASA Astrophysics Data System (ADS)

    Pathak, Trilok Kumar; Kumar, Vinod; Purohit, L. P.

    2015-11-01

    Highly transparent N-doped ZnO thin films were deposited on ITO coated corning glass substrate by sol-gel method. Ammonium nitrate was used as a dopant source of N with varying the doping concentration 0, 0.5, 1.0, 2.0 and 3.0 at%. The DSC analysis of prepared NZO sols is observed a phase transition at 150 °C. X-ray diffraction pattern showed the preferred (002) peak of ZnO, which was deteriorated with increased N concentrations. The transmittance of NZO thin films was observed to be ~88%. The bandgap of NZO thin films increased from 3.28 to 3.70 eV with increased N concentration from 0 to 3 at%. The maximum carrier concentration 8.36×1017 cm-3 and minimum resistivity 1.64 Ω cm was observed for 3 at% N doped ZnO thin films deposited on glass substrate. These highly transparent ZnO thin films can be used as a window layer in solar cells and optoelectronic devices.

  9. Influence of Mn contents in 0Cr18Ni10Ti thin wall stainless steel tube on TIG girth weld quality

    NASA Astrophysics Data System (ADS)

    Liu, Bo

    2017-03-01

    Three kinds of cold worked 0Cr18Ni10Ti thin wall stainless steel tubes with the manganese contents of 1.27%, 1.35% and 1.44% and the cold worked 0Cr18Ni10Ti stainless steel end plug with manganese content of 1.35% were used for TIG girth welding in the present investigation. The effect of different manganese contents in stainless steel tube on weld quality was studied. The results showed that under the same welding conditions, the metallographic performance of the girth weld for the thin wall stainless steel tube with the manganese element content 1.44% welded with end plug was the best. Under the appropriate welding conditions, the quality of the girth weld increased with the increase of the manganese content till 1.44%. It was found that in the case of the Mn content of 1.44%, and under the proper welding condition the welding defects, such as welding cracks were effectively avoided, and the qualified weld penetration can be obtained.. It is concluded that the appropriate increase of the manganese content can significantly improve the TIG girth weld quality of the cold worked 0Cr18Ni10Ti stainless steel tube.

  10. Effects of Thinning and a Wildfire on Sediment Production Rates, Channel Morpholgy, and Water Quality in the Upper South Platte River Watershed

    NASA Astrophysics Data System (ADS)

    Libohova, Z.; MacDonald, L. H.; Entwistle, D.

    2012-12-01

    The Upper South Platter River watershed is the primary source of Denver's water supply. There has been increasing concern over the potential adverse effects of large wildfires on runoff, erosion, and water quality, and this has led to extensive forest thinning projects to reduce the potential for high-severity wildfires. The initial goal of this project was to evaluate the effects of thinning at the hillslope scale using sediment fences and the small catchment scale by installing flumes and periodically monitoring water quality and channel morphology. The hillslope measurements began in mid-2001, and the flumes were installed in early summer 2002. In 2001 only 3 of the 40 hillslopes produced sediment. In June 2002, the Hayman fire burned half of the study sites. Mean percent ground cover decreased from 90% to 6% in the sites burned at high severity, and the soils were strongly water repellent from the surface to a depth of 6 or 9 cm. The first two storms of 11 and 17 mm caused extensive rilling in the formerly unchannelled swales and extensive downstream gullying. Erosion rates averaged 7.5 Mg ha-1 in the dry summer of 2002 and 10.7 Mg ha-1 in the wet summer of 2003. Thinning in the remaining unburned swales decreased the mean vegetative cover from 15% to 7% and increased the mean percent bare soil from 8% to 16%. However, 75% ground cover meant that no sediment was generated from any of the thinned or the control hillslopes from 2002 through 2006. At the small watershed scale, the observed high water marks were as much as 1.4 m above the estimated bankfull stage. The Saloon Gulch flume was completely buried by the post-fire deposition, and the nearly continuous deposition in the Brush Creek flume precluded accurate flow measurements. Potassium, magnesium, calcium, chloride and nitrate concentrations approximately doubled after the fire. Turbidity increased substantially, while the pH remained unchanged. These results clearly show the dramatic difference between

  11. Flexible thin-layer dielectric barrier discharge plasma treatment of pork butt and beef loin: effects on pathogen inactivation and meat-quality attributes.

    PubMed

    Jayasena, Dinesh D; Kim, Hyun Joo; Yong, Hae In; Park, Sanghoo; Kim, Kijung; Choe, Wonho; Jo, Cheorun

    2015-04-01

    The effects of a flexible thin-layer dielectric barrier discharge (DBD) plasma system using a sealed package on microbial inactivation and quality attributes of fresh pork and beef were tested. Following a 10-min treatment, the microbial-load reductions of Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella Typhimurium were 2.04, 2.54, and 2.68 Log CFU/g in pork-butt samples and 1.90, 2.57, and 2.58 Log CFU/g in beef-loin samples, respectively. Colorimetric analysis showed that DBD-plasma treatment did not significantly affect L* values (lightness) of pork and beef samples, but lowered a* values (redness) significantly after 5- and 7.5-min exposures. The plasma treatment significantly influenced lipid oxidation only after a 10-min exposure. The texture of both types of meat was unaffected by plasma treatment. All sensory parameters of treated and non-treated samples were comparable except for taste, which was negatively influenced by the plasma treatment (P < 0.05). This thin-layer DBD-plasma system can be applied to inactivate foodborne pathogens. The observed minor deterioration of meat quality might be prevented by the use of hurdle technology.

  12. Modelling and optimization of cut quality during pulsed Nd:YAG laser cutting of thin Al-alloy sheet for straight profile

    NASA Astrophysics Data System (ADS)

    Sharma, Amit; Yadava, Vinod

    2012-02-01

    Thin sheets of aluminium alloys are widely used in aerospace and automotive industries for specific applications. Nd:YAG laser beam cutting is one of the most promising sheetmetal cutting process for cutting sheets for any profile. Al-alloy sheets are difficult to cut by laser beam because of its highly reflective nature. This paper presents modelling and optimization of cut quality during pulsed Nd:YAG laser cutting of thin Al-alloy sheet for straight profile. In the present study, four input process parameters such as oxygen pressure, pulse width, pulse frequency, and cutting speed and two output parameters such as average kerf taper ( Ta) and average surface roughness ( Ra) are considered. The hybrid approach comprising of Taguchi methodology (TM) and response surface methodology (RSM) is used for modelling whereas multi-objective optimization is performed using hybrid approach of TM and grey relational analysis (GRA) coupled with entropy measurement methodology. The entropy measurement methodology is employed for the calculation of weight corresponding to each quality characteristic. The results indicate that the hybrid approaches applied for modelling and optimization of the LBC process are reasonable.

  13. Improving the structural quality and electrical resistance of SrTiO{sub 3} thin films on Si (001) via a two-step anneal

    SciTech Connect

    Zhang, Lei; Wang, Yaqiang; Engel-Herbert, Roman

    2016-01-28

    We report on the optimization of structural and electrical properties of SrTiO{sub 3} thin films grown on Si (001) by hybrid molecular beam epitaxy. Using a dual buffer layer template, 46-nm-thick films grown at high temperatures (850 °C) resulted in a layer-by-layer growth mode and a good crystalline quality with rocking curve full width at half maximum (FWHM) of the 002 SrTiO{sub 3} peak of nearly 0.6°, which was reduced to 0.4° by increasing the film thickness to 120 nm. A high temperature post-deposition anneal was employed to further reduce the rocking curve FWHM down to 0.2° while preserving a smooth film surface morphology. The low sheet resistance of as-grown and post-growth annealed samples was increased by five orders of magnitude exceeding 10{sup 7} Ω/◻ using a lower temperature anneal in dry air. This two-step annealing method provides an easy and effective way to improve the crystalline quality of SrTiO{sub 3} thin films on Si, providing a path towards the development of electrically insulating, wafer scale virtual perovskite substrates.

  14. Synthesizing photovoltaic thin films of high quality copper-zinc-tin alloy with at least one chalcogen species

    DOEpatents

    Teeter, Glenn; Du, Hui; Young, Matthew

    2013-08-06

    A method for synthesizing a thin film of copper, zinc, tin, and a chalcogen species ("CZTCh" or "CZTSS") with well-controlled properties. The method includes depositing a thin film of precursor materials, e.g., approximately stoichiometric amounts of copper (Cu), zinc (Zn), tin (Sn), and a chalcogen species (Ch). The method then involves re-crystallizing and grain growth at higher temperatures, e.g., between about 725 and 925 degrees K, and annealing the precursor film at relatively lower temperatures, e.g., between 600 and 650 degrees K. The processing of the precursor film takes place in the presence of a quasi-equilibrium vapor, e.g., Sn and chalcogen species. The quasi-equilibrium vapor is used to maintain the precursor film in a quasi-equilibrium condition to reduce and even prevent decomposition of the CZTCh and is provided at a rate to balance desorption fluxes of Sn and chalcogens.

  15. Evaluation of thin-layer chromatography methods for quality control of commercial products containing Aesculus hippocastanum, Turnera diffusa, Matricaria recutita, Passiflora incarnata, and Tilia occidentalis.

    PubMed

    Ramírez-Durón, Rosalba; Ceniceros-Almaguer, Lucía; Salazar-Aranda, Ricardo; Salazar-Cavazos, Ma de la Luz; Waksman de Torres, Noemi

    2007-01-01

    In Mexico, plant-derived products with health claims are sold as herbal dietary supplements, and there are no rules for their legal quality control. Aesculus hippocastanum, Turnera diffusa, Matricaria recutita, Passiflora incarnata, and Tilia occidentalis are some of the major commercial products obtained from plants used in this region. In this paper, we describe the effectiveness of thin-layer chromatography methods to provide for the quality control of several commercial products containing these plants. Standardized extracts were used. Of the 49 commercial products analyzed, only 32.65% matched the chromatographic characteristic of standardized extracts. A significant number of commercial products did not match their label, indicating a problem resulting from the lack of regulation for these products. The proposed methods are simple, sensitive, and specific and can be used for routine quality control of raw herbals and formulations of the tested plants. The results obtained show the need to develop simple and reliable analytical methods that can be performed in any laboratory for the purpose of quality control of dietary supplements or commercial herbal products sold in Mexico.

  16. SHMUTZ & PROTON-DIAMANT H + Irradiated/Written-Hyper/Super-conductivity(HC/SC) Precognizance/Early Experiments Connections: Wet-Graphite Room-Tc & Actualized MgB2 High-Tc: Connection to Mechanical Bulk-Moduli/Hardness: Diamond Hydrocarbon-Filaments, Disorder, Nano-Powders:C,Bi,TiB2,TiC

    NASA Astrophysics Data System (ADS)

    Wunderman, Irwin; Siegel, Edward Carl-Ludwig; Lewis, Thomas; Young, Frederic; Smith, Adolph; Dresschhoff-Zeller, Gieselle

    2013-03-01

    SHMUTZ: ``wet-graphite''Scheike-....[Adv.Mtls.(7/16/12)]hyper/super-SCHMUTZ-conductor(S!!!) = ``wet''(?)-``graphite''(?) = ``graphene''(?) = water(?) = hydrogen(?) =ultra-heavy proton-bands(???) = ...(???) claimed room/high-Tc/high-Jc superconductOR ``p''-``wave''/ BAND(!!!) superconductIVITY and actualized/ instantiated MgB2 high-Tc superconductors and their BCS- superconductivity: Tc Siegel[ICMAO(77);JMMM 7,190(78)] connection to SiegelJ.Nonxline-Sol.40,453(80)] disorder/amorphous-superconductivity in nano-powders mechanical bulk/shear(?)-moduli/hardness: proton-irradiated diamond, powders TiB2, TiC,{Siegel[Semis. & Insuls.5:39,47, 62 (79)])-...``VS''/concommitance with Siegel[Phys.Stat.Sol.(a)11,45(72)]-Dempsey [Phil.Mag. 8,86,285(63)]-Overhauser-(Little!!!)-Seitz-Smith-Zeller-Dreschoff-Antonoff-Young-...proton-``irradiated''/ implanted/ thermalized-in-(optimal: BOTH heat-capacity/heat-sink & insulator/maximal dielectric-constant) diamond: ``VS'' ``hambergite-borate-mineral transformable to Overhauser optimal-high-Tc-LiBD2 in Overhauser-(NW-periodic-table)-Land: CO2/CH4-ETERNAL-sequestration by-product: WATER!!!: physics lessons from

  17. Deposition of high quality YBa2Cu3O(7-delta) thin films over large areas by pulsed laser ablation with substrate scanning

    NASA Technical Reports Server (NTRS)

    Davis, M. F.; Wosik, J.; Forster, K.; Deshmukh, S. C.; Rampersad, H. R.

    1991-01-01

    The paper describes thin films deposited in a system where substrates are scanned over areas up to 3.5 x 3.5 cm through the stationary plume of an ablated material defined by an aperture. These YBCO films are deposited on LaAlO3 and SrTiO3 substrates with the thickness of 90 and 160 nm. Attention is focused on the main features of the deposition system: line focusing of the laser beam on the target; an aperture defining the area of the plume; computerized stepper motor-driven X-Y stage translating the heated sampler holder behind the plume-defining aperture in programmed patterns; and substrate mounting block with uniform heating at high temperatures over large areas. It is noted that the high degree of uniformity of the properties in each film batch illustrates that the technique of pulsed laser deposition can be applied to produce large YBCO films of high quality.

  18. High quality epitaxial graphene by hydrogen-etching of 3C-SiC(111) thin-film on Si(111)

    NASA Astrophysics Data System (ADS)

    Mondelli, Pierluigi; Gupta, Bharati; Grazia Betti, Maria; Mariani, Carlo; Lipton Duffin, Josh; Motta, Nunzio

    2017-03-01

    Etching with atomic hydrogen, as a preparation step before the high-temperature growth process of graphene onto a thin 3C-SiC film grown on Si(111), greatly improves the structural quality of topmost graphene layers. Pit formation and island coalescence, which are typical of graphene growth by SiC graphitization, are quenched and accompanied by widening of the graphene domain sizes to hundreds of nanometers, and by a significant reduction in surface roughness down to a single substrate bilayer. The surface reconstructions expected for graphene and the underlying layer are shown with atomic resolution by scanning tunnelling microscopy. Spectroscopic features typical of graphene are measured by core-level photoemission and Raman spectroscopy.

  19. High quality epitaxial graphene by hydrogen-etching of 3C-SiC(111) thin-film on Si(111).

    PubMed

    Mondelli, Pierluigi; Gupta, Bharati; Betti, Maria Grazia; Mariani, Carlo; Duffin, Josh Lipton; Motta, Nunzio

    2017-03-17

    Etching with atomic hydrogen, as a preparation step before the high-temperature growth process of graphene onto a thin 3C-SiC film grown on Si(111), greatly improves the structural quality of topmost graphene layers. Pit formation and island coalescence, which are typical of graphene growth by SiC graphitization, are quenched and accompanied by widening of the graphene domain sizes to hundreds of nanometers, and by a significant reduction in surface roughness down to a single substrate bilayer. The surface reconstructions expected for graphene and the underlying layer are shown with atomic resolution by scanning tunnelling microscopy. Spectroscopic features typical of graphene are measured by core-level photoemission and Raman spectroscopy.

  20. Effects of thinned young apple polyphenols on the quality of grass carp (Ctenopharyngodon idellus) surimi during cold storage.

    PubMed

    Sun, Lijun; Sun, Jiaojiao; Thavaraj, Pridhuvi; Yang, Xingbin; Guo, Yurong

    2017-06-01

    The aim of this study was to investigate the effects of young apple polyphenols (YAP) on the quality of grass cap surimi (GCS) during storage at 4°C. The addition of YAP into GCS was found to be effective in delaying lipid oxidation, soluble myofibrillar protein (SMP) degradation and changes of L(∗), a(∗) and b(∗) values of GCS. Chlorogenic acid was screened to be the primary component showing preservative effects. YAP was shown to protect the functional properties of SMP during cold storage, retarding both the decrease in emulsifying activity and stability, and the increase in surface hydrophobicity of SMP. Additionally, the loss of gel strength and texture of GCS with YAP were significantly (P<0.05) lower than that of GCS without YAP during cold storage. Therefore, YAP may be developed as a natural antioxidant to maintain the quality and to extend the shelf life of freshwater fish surimi.

  1. Boron carbide coatings for neutron detection probed by x-rays, ions, and neutrons to determine thin film quality

    SciTech Connect

    Nowak, G. Störmer, M.; Horstmann, C.; Kampmann, R.; Höche, D.; Lorenz, U.; Müller, M.; Schreyer, A.; Becker, H.-W.; Haese-Seiller, M.; Moulin, J.-F.; Pomm, M.; Randau, C.; Hall-Wilton, R.

    2015-01-21

    Due to the present shortage of {sup 3}He and the associated tremendous increase of its price, the supply of large neutron detection systems with {sup 3}He becomes unaffordable. Alternative neutron detection concepts, therefore, have been invented based on solid {sup 10}B converters. These concepts require development in thin film deposition technique regarding high adhesion, thickness uniformity and chemical purity of the converter coating on large area substrates. We report on the sputter deposition of highly uniform large-area {sup 10}B{sub 4}C coatings of up to 2 μm thickness with a thickness deviation below 4% using the Helmholtz-Zentrum Geesthacht large area sputtering system. The {sup 10}B{sub 4}C coatings are x-ray amorphous and highly adhesive to the substrate. Material analysis by means of X-ray-Photoelectron Spectroscopy, Secondary-Ion-Mass-Spectrometry, and Rutherford-Back-Scattering (RBS) revealed low impurities concentration in the coatings. The isotope composition determined by Secondary-Ion-Mass-Spectrometry, RBS, and inelastic nuclear reaction analysis of the converter coatings evidences almost identical {sup 10}B isotope contents in the sputter target and in the deposited coating. Neutron conversion and detection test measurements with variable irradiation geometry of the converter coating demonstrate an average relative quantum efficiency ranging from 65% to 90% for cold neutrons as compared to a black {sup 3}He-monitor. Thus, these converter coatings contribute to the development of {sup 3}He-free prototype detectors based on neutron grazing incidence. Transferring the developed coating process to an industrial scale sputtering system can make alternative {sup 3}He-free converter elements available for large area neutron detection systems.

  2. Boron carbide coatings for neutron detection probed by x-rays, ions, and neutrons to determine thin film quality

    NASA Astrophysics Data System (ADS)

    Nowak, G.; Störmer, M.; Becker, H.-W.; Horstmann, C.; Kampmann, R.; Höche, D.; Haese-Seiller, M.; Moulin, J.-F.; Pomm, M.; Randau, C.; Lorenz, U.; Hall-Wilton, R.; Müller, M.; Schreyer, A.

    2015-01-01

    Due to the present shortage of 3He and the associated tremendous increase of its price, the supply of large neutron detection systems with 3He becomes unaffordable. Alternative neutron detection concepts, therefore, have been invented based on solid 10B converters. These concepts require development in thin film deposition technique regarding high adhesion, thickness uniformity and chemical purity of the converter coating on large area substrates. We report on the sputter deposition of highly uniform large-area 10B4C coatings of up to 2 μm thickness with a thickness deviation below 4% using the Helmholtz-Zentrum Geesthacht large area sputtering system. The 10B4C coatings are x-ray amorphous and highly adhesive to the substrate. Material analysis by means of X-ray-Photoelectron Spectroscopy, Secondary-Ion-Mass-Spectrometry, and Rutherford-Back-Scattering (RBS) revealed low impurities concentration in the coatings. The isotope composition determined by Secondary-Ion-Mass-Spectrometry, RBS, and inelastic nuclear reaction analysis of the converter coatings evidences almost identical 10B isotope contents in the sputter target and in the deposited coating. Neutron conversion and detection test measurements with variable irradiation geometry of the converter coating demonstrate an average relative quantum efficiency ranging from 65% to 90% for cold neutrons as compared to a black 3He-monitor. Thus, these converter coatings contribute to the development of 3He-free prototype detectors based on neutron grazing incidence. Transferring the developed coating process to an industrial scale sputtering system can make alternative 3He-free converter elements available for large area neutron detection systems.

  3. Properties of thin film radiation detectors and their application to dosimetry and quality assurance in x-ray imaging

    NASA Astrophysics Data System (ADS)

    Elshahat, Bassem

    The characteristics of two different types of thin-film radiation detectors are experimentally investigated: organic photovoltaic cells (OPV) and a new self-powered detector that operates based on high-energy secondary electrons (HEC). Although their working principles are substantially different, they both can be used for radiation detection and image formation in medical applications. OPVs with different active layer material thicknesses and aluminum electrode areas were fabricated. The OPV cell consisted of P3HT: PCBM photoactive materials, composed of donor and acceptor semiconducting organic materials, sandwiched between an aluminum electrode as anode and an indium tin oxide (ITO) electrode as a cathode. The detectors were exposed to 60150 kVp x rays, which generated photocurrent in the active layer. The electric charge production in the OPV cells was measured. The net current as function of beam energy (kVp) was proportional to ~1/kVp0.45 when adjusted for x-ray beam output. The best combination of parameters for these cells was 270-nm active layer thicknesses for 0.7cm-2 electrode area. The measured current ranged from about 0.7 to 2.4 nA/cm2 for 60-150 kVp, corresponding to about 0.09 -- 0.06 nA/cm2/mGy, respectively, when adjusted for the output x-ray source flux. The HEC detection concept was recently proposed and experimentally demonstrated by a UML/HMS research group. HEC detection employs direct conversion of high-energy electron current to detector signal without external power and amplification. The potential of using HEC detectors for diagnostic imaging application was investigated by using a heterogeneous phantom consisting of a water cylinder with Al and wax rod inserts.

  4. High-performance thin layer chromatography for quality control of multicomponent herbal drugs: example of cangzhu xianglian san.

    PubMed

    Li, Zhi; Merfort, Irmgard; Reich, Eike

    2010-01-01

    Due to their complexity, multicomponent herbal drugs pose enormous analytical challenges for quality control (QC). Although they may have traditionally been used for hundreds of years, the information about their chemical composition is often still limited. Selecting suitable markers to monitor the identity and potency of the mixture is, therefore, difficult. There is also the possibility of natural variability for each plant. This paper illustrates a pragmatic and practical approach to QC of a multicomponent herbal drug by HPTLC. Cangzhu xianglian xan (CXS), composed of the herbal drugs Coptis rhizome, Aucklandia root, and Atractylodes rhizome (30 + 20 + 60, w/w/w), is used as an example. A characteristic fingerprint can be generated for CXS with toluene-ethyl acetate-methanol-isopropanol-water (60 + 30 + 20 + 15 + 3, v/v/v/v/v) mobile phase on HPTLC silica gel 60 conditioned with ammonia. While the corresponding monograph of the Chinese Veterinary Pharmacopoeia focuses only on the detection of berberine, one of the principal components of Coptis rhizome, the proposed method of identification determines the presence of all three components in the drug after derivatization with anisaldehyde reagent. The same method can also be used to quantitatively determine the content of berberine by scanning densitometry. This paper provides details about the validation of the qualitative and quantitative determinations.

  5. Improvement of Film Quality in CuInSe2 Thin Films Fabricated by a Non-Vacuum, Nanoparticle-Based Approach

    NASA Astrophysics Data System (ADS)

    Zhang, Yiwen; Ito, Manabu; Tamura, Tomoaki; Yamada, Akira; Konagai, Makoto

    2011-04-01

    To improve the quality of CuInSe2 (CIS) thin films fabricated by a non-vacuum, nanoparticle-based approach, in this study, two categories of nanoparticles, Cu (InGa) Se2 (CIGS) nanoparticles and copper selenide (Cu-Se) with indium selenide (In-Se) nanoparticles are investigated. It is found that the Cu-Se with In-Se nanoparticles show a higher crystallization velocity than CIGS nanoparticles. The films obtained from Cu-Se with In-Se nanoparticles exhibit higher crystallinity with a larger grain size. Thiourea is applied as a sintering additive during the selenization process. It is clarified that the addition of thiourea is very effective for grain growth and the fabrication of a dense CIS layer. The cell performance is measured under Air Mass 1.5 irradiation. The efficiency of the solar cell, fabricated using Cu-Se, In-Se nanoparticles with thiourea, is 2.15%, higher than that of the solar cell fabricated using CIGS nanoparticles, which is 0.28%.

  6. Multilayer Thin-Film Microcapacitors

    NASA Technical Reports Server (NTRS)

    Thakoor, Sarita; Thakoor, Anil; Karmon, Dan

    1995-01-01

    Miniature capacitors containing multiple alternating thin-film dielectric and metal layers proposed, especially for use in integrated and hybrid electronic circuits. Because capacitance inversely proportional to thickness of dielectric layers, use of thin, high-quality dielectric layers affords capacitance and energy-storage densities much greater than now available. These devices much smaller and more reliable than state-of-art capacitors.

  7. 7 CFR 29.2438 - Thin Leaf (C Group).

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... body than those of the B group, and show little or no ground injury. Choice- and fine-quality tobacco... Fair Light-brown Thin Leaf. Thin to medium body, mature to ripe, close, lean in oil, inelastic, weak... Light-brown Thin Leaf. Thin to medium body, mature to ripe, close, lean in oil, inelastic, weak,...

  8. Epitaxial thin films

    DOEpatents

    Hunt, Andrew Tye; Deshpande, Girish; Lin, Wen-Yi; Jan, Tzyy-Jiuan

    2006-04-25

    Epitatial thin films for use as buffer layers for high temperature superconductors, electrolytes in solid oxide fuel cells (SOFC), gas separation membranes or dielectric material in electronic devices, are disclosed. By using CCVD, CACVD or any other suitable deposition process, epitaxial films having pore-free, ideal grain boundaries, and dense structure can be formed. Several different types of materials are disclosed for use as buffer layers in high temperature superconductors. In addition, the use of epitaxial thin films for electrolytes and electrode formation in SOFCs results in densification for pore-free and ideal gain boundary/interface microstructure. Gas separation membranes for the production of oxygen and hydrogen are also disclosed. These semipermeable membranes are formed by high-quality, dense, gas-tight, pinhole free sub-micro scale layers of mixed-conducting oxides on porous ceramic substrates. Epitaxial thin films as dielectric material in capacitors are also taught herein. Capacitors are utilized according to their capacitance values which are dependent on their physical structure and dielectric permittivity. The epitaxial thin films of the current invention form low-loss dielectric layers with extremely high permittivity. This high permittivity allows for the formation of capacitors that can have their capacitance adjusted by applying a DC bias between their electrodes.

  9. Thin Clouds

    Atmospheric Science Data Center

    2013-04-18

    ... one of a new generation of instruments flying aboard the NASA Earth Observing System's Terra satellite, views Earth with nine cameras ... of thin cirrus minutes after MISR imaged the cloud from space. At the same time, another NASA high-altitude jet, the WB-57, flew right ...

  10. Preparation of ultra-thin and high-quality WO3 compact layers and comparision of WO3 and TiO2 compact layer thickness in planar perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Zhang, Jincheng; Shi, Chengwu; Chen, Junjun; Wang, Yanqing; Li, Mingqian

    2016-06-01

    In this paper, the ultra-thin and high-quality WO3 compact layers were successfully prepared by spin-coating-pyrolysis method using the tungsten isopropoxide solution in isopropanol. The influence of WO3 and TiO2 compact layer thickness on the photovoltaic performance of planar perovskite solar cells was systematically compared, and the interface charge transfer and recombination in planar perovskite solar cells with TiO2 compact layer was analyzed by electrochemical impedance spectroscopy. The results revealed that the optimum thickness of WO3 and TiO2 compact layer was 15 nm and 60 nm. The planar perovskite solar cell with 15 nm WO3 compact layer gave a 9.69% average and 10.14% maximum photoelectric conversion efficiency, whereas the planar perovskite solar cell with 60 nm TiO2 compact layer achieved a 11.79% average and 12.64% maximum photoelectric conversion efficiency.

  11. Thin Film?

    NASA Astrophysics Data System (ADS)

    Kariper, İ. Afşin

    2014-09-01

    This study focuses on the critical surface tension of lead sulfite (PbSO3) crystalline thin film produced with chemical bath deposition on substrates (commercial glass).The PbSO3 thin films were deposited at room temperature at different deposition times. The structural properties of the films were defined and examined according to X-ray diffraction (XRD) and the XRD results such as dislocation density, average grain size, and no. of crystallites per unit area. Atomic force microscopy was used to measure the film thickness and the surface properties. The critical surface tension of the PbSO3 thin films was measured with an optical tensiometer instrument and calculated using the Zisman method. The results indicated that the critical surface tension of films changed in accordance with the average grain size and film thickness. The film thickness increased with deposition time and was inversely correlated with surface tension. The average grain size increased according to deposition time and was inversely correlated with surface tension.

  12. Preparation of ultra-thin and high-quality WO{sub 3} compact layers and comparision of WO{sub 3} and TiO{sub 2} compact layer thickness in planar perovskite solar cells

    SciTech Connect

    Zhang, Jincheng; Shi, Chengwu Chen, Junjun; Wang, Yanqing; Li, Mingqian

    2016-06-15

    In this paper, the ultra-thin and high-quality WO{sub 3} compact layers were successfully prepared by spin-coating-pyrolysis method using the tungsten isopropoxide solution in isopropanol. The influence of WO{sub 3} and TiO{sub 2} compact layer thickness on the photovoltaic performance of planar perovskite solar cells was systematically compared, and the interface charge transfer and recombination in planar perovskite solar cells with TiO{sub 2} compact layer was analyzed by electrochemical impedance spectroscopy. The results revealed that the optimum thickness of WO{sub 3} and TiO{sub 2} compact layer was 15 nm and 60 nm. The planar perovskite solar cell with 15 nm WO{sub 3} compact layer gave a 9.69% average and 10.14% maximum photoelectric conversion efficiency, whereas the planar perovskite solar cell with 60 nm TiO{sub 2} compact layer achieved a 11.79% average and 12.64% maximum photoelectric conversion efficiency. - Graphical abstract: The planar perovskite solar cell with 15 nm WO{sub 3} compact layer gave a 9.69% average and 10.14% maximum photoelectric conversion efficiency, whereas the planar perovskite solar cell with 60 nm TiO{sub 2} compact layer achieved a 11.79% average and 12.64% maximum photoelectric conversion efficiency. Display Omitted - Highlights: • Preparation of ultra-thin and high-quality WO{sub 3} compact layers. • Perovskite solar cell with 15 nm-thick WO{sub 3} compact layer achieved PCE of 10.14%. • Perovskite solar cell with 60 nm-thick TiO{sub 2} compact layer achieved PCE of 12.64%.

  13. Potential of deficit irrigation, irrigation cut-offs, and crop thinning to maintain yield and fruit quality with less water in northern highbush blueberry

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Drought and mandatory water restrictions are limiting the availability of irrigation water in many important blueberry growing regions, including Oregon, Washington, and California. New strategies are needed to maintain yield and fruit quality with less water. Three potential options, including defi...

  14. Method for thinning specimen

    SciTech Connect

    Follstaedt, David M.; Moran, Michael P.

    2005-03-15

    A method for thinning (such as in grinding and polishing) a material surface using an instrument means for moving an article with a discontinuous surface with an abrasive material dispersed between the material surface and the discontinuous surface where the discontinuous surface of the moving article provides an efficient means for maintaining contact of the abrasive with the material surface. When used to dimple specimens for microscopy analysis, a wheel with a surface that has been modified to produce a uniform or random discontinuous surface significantly improves the speed of the dimpling process without loss of quality of finish.

  15. Precisely Controlled Synthesis of High Quality Kesterite Cu2ZnSnS4 Thin Film via Co-Electrodeposited CuZnSn Alloy Film.

    PubMed

    Hreid, Tubshin; Tiong, Vincent Tiing; Cai, Molang; Wang, Hongxia; Will, Geoffrey

    2016-06-01

    In this work, a facile co-electrodeposition method was used to fabricate CuZnSn alloy films where the content of copper, zinc and tin could be precisely controlled through manipulating the mass transfer process in the electrochemical deposition. By finely tuning the concentration of the cations of Cu2+, Zn2+ and Sn2+ in the electrochemical bath solution, uniform CuZnSn film with desired composition of copper poor and zinc rich was made. Sulphurisation of the CuZnSn alloy film led to the formation of compact and large grains Cu2ZnSnS4 thin film absorber with an optimum composition of Cu/(Zn+Sn) ≈ 0.8, Zn/Sn ≈ 1.2. Both SEM morphology and EDS mapping results confirmed the uniformity of the CuZnSn and Cu2ZnSnS4 films and the homogeneous distribution of Cu, Zn, Sn and S elements in the bulk films. The XRD and Raman measurements indicated that the synthesized Cu2ZnSnS4 film was kesterite phase without impurities detected. Photoelectrochemical tests were carried out to evaluate the CZTS film's photocurrent response under illumination of green light.

  16. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Growth of High Quality Strained-Si on Ultra-Thin SiGe-on-Insulator Substrate

    NASA Astrophysics Data System (ADS)

    Liu, Xu-Yan; Liu, Wei-Li; Ma, Xiao-Bo; Chen, Chao; Song, Zhi-Tang; Lin, Cheng-Lu

    2009-11-01

    Ultra-thin and near-fully relaxed SiGe substrate is fabricated using a modified Ge condensation technique, and then a 25-nm-thick biaxially tensile strained-Si with a low rms roughness is epitaxially deposited on a SiGeon-Insulator (SGOI) substrate by ultra high vacuum chemical vapor deposition (UHVCVD). High-Resolution cross-sectional transmission electron microscope (HR-XTEM) observations reveal that the strained-Si/SiGe layer is dislocation-free and the atoms at the interface are well aligned. Furthermore, secondary ion mass spectrometry (SIMS) results show a sharp interface between layers and a uniform distribution of Ge in the SiGe layer. One percent in-plane tensile strain in the strained-Si layer is confirmed by ultraviolet (UV) Raman spectra, and the stress maintained even after a 30-s rapid thermal annealing (RTA) process at 1000°C According to those results, devices based on strained-Si are expected to have a better performance than the conventional ones.

  17. Correlations between critical current density, j(sub c), critical temperature, T(sub c),and structural quality of Y1B2Cu3O(7-x) thin superconducting films

    NASA Technical Reports Server (NTRS)

    Chrzanowski, J.; Xing, W. B.; Atlan, D.; Irwin, J. C.; Heinrich, B.; Cragg, R. A.; Zhou, H.; Angus, V.; Habib, F.; Fife, A. A.

    1995-01-01

    Correlations between critical current density (j(sub c)) critical temperature (T(sub c)) and the density of edge dislocations and nonuniform strain have been observed in YBCO thin films deposited by pulsed laser ablation on (001) LaAlO3 single crystals. Distinct maxima in j(sub c) as a function of the linewidths of the (00 l) Bragg reflections and as a function of the mosaic spread have been found in the epitaxial films. These maxima in j(sub c) indicate that the magnetic flux lines, in films of structural quality approachingthat of single crystals, are insufficiently pinned which results in a decreased critical current density. T(sub c) increased monotonically with improving crystalline quality and approached a value characteristic of a pure single crystal. A strong correlation between j(sub c) and the density of edge dislocations ND was found. At the maximum of the critical current density the density of edge dislocations was estimated to be N(sub D) approximately 1-2 x 10(exp 9)/sq cm.

  18. Correlations between critical current density, j{sub c}, critical temperature, T{sub c}, and structural quality of Y{sub 1}B{sub 2}Cu{sub 3}O{sub 7-x} thin superconducting films

    SciTech Connect

    Chrzanowski, J.; Xing, W.B.; Atlan, D.

    1994-12-31

    Correlations between critical current density (j{sub c}) critical temperature (T{sub c}) and the density of edge dislocations and nonuniform strain have been observed in YBCO thin films deposited by pulsed laser ablation on (001) LaAlO{sub 3} single crystals. Distinct maxima in j{sub c} as a function of the linewidths of the (00{ell}) Bragg reflections and as a function of the mosaic spread have been found in the epitaxial films. These maxima in j{sub c} indicate that the magnetic flux lines, in films of structural quality approaching that of single crystals, are insufficiently pinned which results in a decreased critical current density. T{sub c} increased monotonically with improving crystalline quality and approached a value characteristic of a pure single crystal. A strong correlation between j{sub c} and the density of edge dislocations N{sub D} was found. At the maximum of the critical current density the density of edge dislocations was estimated to be N{sub D}{approximately}1-2 x 10{sup 9}/cm{sup 2}.

  19. Influence of indium-tin-oxide thin-film quality on reverse leakage current of indium-tin-oxide/n-GaN Schottky contacts

    NASA Astrophysics Data System (ADS)

    Wang, R. X.; Xu, S. J.; Djurišić, A. B.; Beling, C. D.; Cheung, C. K.; Cheung, C. H.; Fung, S.; Zhao, D. G.; Yang, H.; Tao, X. M.

    2006-07-01

    Indium-tin-oxide (ITO)/n-GaN Schottky contacts were prepared by e-beam evaporation at 200°C under various partial pressures of oxygen. X-ray photoemission spectroscopy and positron beam measurements were employed to obtain chemical and structural information of the deposited ITO films. The results indicated that the observed variation in the reverse leakage current of the Schottky contact and the optical transmittance of the ITO films were strongly dependent on the quality of the ITO film. The high concentration of point defects at the ITO-GaN interface is suggested to be responsible for the large observed leakage current of the ITO/n-GaN Schottky contacts.

  20. Lead Iodide Thin Film Crystallization Control for High-Performance and Stable Solution-Processed Perovskite Solar Cells.

    PubMed

    Yang, Lijun; Wang, Jingchuan; Leung, Wallace Woon-Fong

    2015-07-15

    PbI2 thin film crystallization control is a prerequisite of high-quality perovskite thin film for sequentially solution-processed perovskite solar cells. An efficient and simple method has been developed by adding HCl to improve perovskite thin film quality, and an efficiency of 15.2% is obtained. This approach improves coverage, uniformity, and stability of pervoskite thin film.

  1. Single liquid source plasma-enhanced metalorganic chemical vapor deposition of high-quality YBa2Cu3O(7-x) thin films

    NASA Technical Reports Server (NTRS)

    Zhang, Jiming; Gardiner, Robin A.; Kirlin, Peter S.; Boerstler, Robert W.; Steinbeck, John

    1992-01-01

    High quality YBa2Cu3O(7-x) films were grown in-situ on LaAlO3 (100) by a novel single liquid source plasma-enhanced metalorganic chemical vapor deposition process. The metalorganic complexes M(thd) (sub n), (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate; M = Y, Ba, Cu) were dissolved in an organic solution and injected into a vaporizer immediately upstream of the reactor inlet. The single liquid source technique dramatically simplifies current CVD processing and can significantly improve the process reproducibility. X-ray diffraction measurements indicated that single phase, highly c-axis oriented YBa2Cu3O(7-x) was formed in-situ at substrate temperature 680 C. The as-deposited films exhibited a mirror-like surface, had transition temperature T(sub cO) approximately equal to 89 K, Delta T(sub c) less than 1 K, and Jc (77 K) = 10(exp 6) A/sq cm.

  2. LETTER TO THE EDITOR: Magnetron sputtering growth and characterization of high quality single crystal Ga-doped n-ZnO thin films

    NASA Astrophysics Data System (ADS)

    Kim, Tae-hwan; Jeong, Sang-Hun; Kim, Il-Soo; Kim, Sang Sub; Lee, Byung-Teak

    2005-09-01

    Ga-doped n-type ZnO (ZnO:Ga) films were grown on sapphire substrates by rf magnetron sputtering and their structural, electrical and optical properties were characterized in detail. It was observed that high quality single crystal ZnO:Ga films are obtained, containing up to 1 wt% of Ga. The ZnO:Ga (1 wt%) films grown at 700 °C in pure O2 showed sharp and intense photoluminescence (PL) and high resolution x-ray diffraction (XRD) peaks, with full-width-at-half-maximum values of 150 meV (room temperature PL), 24 meV (12 K PL) and 380 arcsec (XRD), which is slightly better than or comparable with corresponding values from the previously reported ZnO:Ga films. Electrical properties of ZnO:Ga films significantly improved after the rapid thermal processing, resulting in 2.6 × 1019 cm-3 free electron density and 47 cm2 V-1 s-1 mobility after annealing at 900 °C in the case of 1 wt% film. The intensity of the PL peaks was also enhanced by the heat treatment.

  3. Synergistic effects of Mo and F doping on the quality factor of ZnO thin films prepared by a fully automated home-made nebulizer spray technique

    NASA Astrophysics Data System (ADS)

    Ravichandran, K.; Dineshbabu, N.; Arun, T.; Manivasaham, A.; Sindhuja, E.

    2017-01-01

    Transparent conducting oxide films of undoped, Mo doped, Mo + F co-doped ZnO were deposited using a facile homemade nebulizer spray pyrolysis technique. The effects of Mo and F doping on the structural, optical, electrical and surface morphological properties were investigated using XRD, UV-vis-NIR spectroscopy, I-V and Hall probe techniques, FESEM and AFM, and XPS, respectively. The XRD analysis confirms that all the films are well crystallized with hexagonal wurtzite structure. All the synthesized samples exhibit high transmittance (above 85%) in the visible region. The current-voltage (I-V) characteristics show the ohmic conduction nature of the films. The Hall probe measurements show that the synergistic effects of Mo and F doping cause desirable improvements in the quality factor of the ZnO films. A minimum resistivity of 5.12 × 10-3 Ω cm with remarkably higher values of mobility and carrier concentration is achieved for Mo (2 at.%) + F (15 at.%) co-doped ZnO films. A considerable variation in the intensity of deep level emission caused by Mo and F doping is observed in the photoluminescence (PL) studies. The presence of the constituent elements in the samples is confirmed by XPS analysis.

  4. Thin Sections

    PubMed Central

    Peachey, Lee D.

    1958-01-01

    Knowledge of the thickness of sections is important for proper interpretation of electron micrographs. Therefore, the thicknesses of sections of n-butyl methacrylate polymer were determined by ellipsometry, and correlated with the color shown in reflected light. The results are: gray, thinner than 60 mµ; silver, 60 to 90 mµ; gold, 90 to 150 mµ; purple, 150 to 190 mµ; blue, 190 to 240 mµ; green, 240 to 280 mµ; and yellow, 280 to 320 mµ. These results agree well with optical theory and with previous published data for thin films. Sections, after cutting, are 30 to 40 per cent shorter than the face of the block from which they were cut. Only a small improvement results from allowing the sections to remain in the collecting trough at room temperature. Heating above room temperature, however, reduces this shortening, with a corresponding improvement in dimensions and spatial relationships in the sections. When the thickness of the section is considered in interpreting electron micrographs instead of considering the section to be two-dimensional, a more accurate interpretation is possible. The consideration of electron micrographs as arising from projections of many profiles from throughout the whole thickness of the section explains the apparent lack of continuity often observed in serial sections. It is believed that serial sections are actually continuous, but that the change in size of structure through the thickness of one section and the consideration of only the largest profile shown in the micrograph can account for the lack of continuity previously observed. PMID:13549493

  5. High quality transparent conducting oxide thin films

    DOEpatents

    Gessert, Timothy A.; Duenow, Joel N.; Barnes, Teresa; Coutts, Timothy J.

    2012-08-28

    A transparent conducting oxide (TCO) film comprising: a TCO layer, and dopants selected from the elements consisting of Vanadium, Molybdenum, Tantalum, Niobium, Antimony, Titanium, Zirconium, and Hafnium, wherein the elements are n-type dopants; and wherein the transparent conducting oxide is characterized by an improved electron mobility of about 42 cm.sup.2/V-sec while simultaneously maintaining a high carrier density of .about.4.4e.times.10.sup.20 cm.sup.-3.

  6. Thin glass processing with various laser sources

    NASA Astrophysics Data System (ADS)

    Collins, Adam R.; Milne, David; Prieto, Camilo; O'Connor, Gerard M.

    2015-03-01

    Laser processing of thin glass has proven problematic due to the inefficient coupling of optical energy into glass and the difficulty achieving an economical processing speed while maintaining cut quality. Laser glass processing is pertinent to touch screen display, microfluidic, microoptic and photovoltaic applications. The results of the laser scribing of 110 μm thick alkali free glass with various laser sources are presented. The laser sources include a CO₂ laser, nanosecond UV laser and femtosecond IR laser. The contrasting absorption mechanisms are discussed. Cut quality and processing speed are characterised using SEM and optical microscopy techniques. Alternative laser techniques for thin glass processing are also considered.

  7. Microstructure of Thin Films

    DTIC Science & Technology

    1990-02-07

    optical properties ." (Final text in preparation). John Lehan, "Microstructural analysis of thin films by Rutherford Backscattering...correlation of optical properties and micro- Ion assisted deposition (IAD) is known to produce structure of IAD thin films with ion beam parameters thin films ...1.5-eV interband absorption. P (eV) R (%) P (, -V) R %) Optical properties of metal thin films in the spectral 0 98.3 0 88.8 range of

  8. Fundamentals of thin solar cells

    SciTech Connect

    Yablonovitch, E.

    1995-08-01

    It is now widely recognized that thin solar cells can present certain advantages for performance and cost. This is particularly the case when light trapping in the semiconductor film is incorporated, as compensation for the diminished single path thickness of the solar cell. In a solar cell thinner than a minority carrier diffusion length, the current collection is of course very easy. More importantly the concentration of an equivalent number of carriers in a thinner volume results in a higher Free Energy, or open circuit voltage. This extra Free Energy may be regarded as due to the concentration factor, just as it would be for photons, electrons, or for any chemical species. The final advantage of a thin solar cell is in the diminished material usage, a factor of considerable importance when we consider the material cost of the high quality semiconductors which we hope to employ.

  9. Pyrolyzed thin film carbon

    NASA Technical Reports Server (NTRS)

    Tai, Yu-Chong (Inventor); Liger, Matthieu (Inventor); Harder, Theodore (Inventor); Konishi, Satoshi (Inventor); Miserendino, Scott (Inventor)

    2010-01-01

    A method of making carbon thin films comprises depositing a catalyst on a substrate, depositing a hydrocarbon in contact with the catalyst and pyrolyzing the hydrocarbon. A method of controlling a carbon thin film density comprises etching a cavity into a substrate, depositing a hydrocarbon into the cavity, and pyrolyzing the hydrocarbon while in the cavity to form a carbon thin film. Controlling a carbon thin film density is achieved by changing the volume of the cavity. Methods of making carbon containing patterned structures are also provided. Carbon thin films and carbon containing patterned structures can be used in NEMS, MEMS, liquid chromatography, and sensor devices.

  10. Microwave plasma assisted supersonic gas jet deposition of thin film materials

    DOEpatents

    Schmitt, III, Jerome J.; Halpern, Bret L.

    1993-01-01

    An apparatus for fabricating thin film materials utilizing high speed gas dynamics relies on supersonic free jets of carrier gas to transport depositing vapor species generated in a microwave discharge to the surface of a prepared substrate where the vapor deposits to form a thin film. The present invention generates high rates of deposition and thin films of unforeseen high quality at low temperatures.

  11. Thin film interference of colloidal thin films.

    PubMed

    Cong, Hailin; Cao, Weixiao

    2004-09-14

    A stairlike colloidal crystal thin film composed of poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)) monodispersed colloids was fabricated on an inclined silicon substrate. Different bright colors were observed on the various parts of the film with different layers as white light irradiated perpendicularly on it. The relationship between the colors and layers of the film was investigated and discussed according to the principle of thin film interference. On the basis of the phenomenon of thin film interference, a one-layer colloidal film having uniform color was researched and it would display diverse colors before and after swollen by styrene (St). A circular stairlike colloidal film was achieved to mimic the colors of the peacock tail feather.

  12. Niobium Thin Film Characterization for Thin Film Technology Used in Superconducting Radiofrequency Cavities

    NASA Astrophysics Data System (ADS)

    Dai, Yishu; Valente-Feliciano, Anne-Marie

    2015-10-01

    Superconducting RadioFrequency (SRF) penetrates about 40-100 nm of the top surface, making thin film technology possible in producing superconducting cavities. Thin film is based on the deposition of a thin Nb layer on top of a good thermal conducting material such as Al or Cu. Thin film allows for better control of the surface and has negligible response to the Earth's magnetic field, eliminating the need for magnetic shielding of the cavities. Thin film superconductivity depends heavily on coating process conditions, involving controllable parameters such as crystal plane orientation, coating temperature, and ion energy. MgO and Al2O3 substrates are used because they offer very smooth surfaces, ideal for studying film growth. Atomic Force Microscopy is used to characterize surface's morphology. It is evident that a lower nucleation energy and a long coating time increases the film quality in the r-plane sapphire crystal orientation. The quality of the film increases with thickness. Nb films coated on r-plane, grow along the (001) plane and yield a much higher RRR compared to the films grown on a- and c-planes. This information allows for further improvement on the research process for thin film technology used in superconducting cavities for the particle accelerators. National Science Foundation, Department of Energy, Jefferson Lab, Old Dominion University.

  13. Mechanics of Thin Films

    DTIC Science & Technology

    1992-02-06

    S. Hwang, Thermal conductivity of thin films: measurement and microstructural effects, in Thin- film heat transfer, properties and processing, ed...thermal, electrical, optical and magnetic properties . As typical examples we mention microelectronics, optical coatings and multilayers for use in optical...interplay between mechanical properties (elastic moduli), thermal properties (thermal conductivity, thermal expansion coefficient), and optical

  14. Optical thin film devices

    NASA Astrophysics Data System (ADS)

    Mao, Shuzheng

    1991-11-01

    Thin film devices are applied to almost all modern scientific instruments, and these devices, especially optical thin film devices, play an essential role in the performances of the instruments, therefore, they are attracting more and more attention. Now there are numerous kinds of thin film devices and their applications are very diversified. The 300-page book, 'Thin Film Device and Applications,' by Prof. K. L. Chopra gives some general ideas, and my paper also outlines the designs, fabrication, and applications of some optical thin film devices made in my laboratory. Optical thin film devices have been greatly developed in the recent decades. Prof. A. Thelan has given a number of papers on the theory and techniques, Prof. H. A. Macleod's book, 'Thin Film Optical Filters,' has concisely concluded the important concepts of optical thin film devices, and Prof. J. A. Dobrowobski has proposed many successful designs for optical thin film devices. Recently, fully-automatic plants make it easier to produce thin film devices with various spectrum requirements, and some companies, such as Balzers, Leybold AG, Satis Vacuum AG, etc., have manufactured such kinds of coating plants for research or mass-production, and the successful example is the production of multilayer antireflection coatings with high stability and reproducibility. Therefore, it could be said that the design of optical thin film devices and coating plants is quite mature. However, we cannot expect that every problem has been solved, the R&D work still continues, the competition still continues, and new design concepts, new techniques, and new film materials are continually developed. Meanwhile, the high-price of fully-automatic coating plants makes unpopular, and automatic design of coating stacks is only the technique for optimizing the manual design according to the physical concepts and experience, in addition, not only the optical system, but also working environment should be taken into account when

  15. High resolution 11B NMR of MgB2 using cryogenic magic-angle spinning

    NASA Astrophysics Data System (ADS)

    Stern, Raivo; Beckett, Peter; Denning, Mark S.; Heinmaa, Ivo; Dimri, Mukesh C.; Young, Edward A.; Carravetta, Marina

    2013-03-01

    Static and magic-angle spinning (MAS) 11B NMR data at 4.7 T and 8.5 T have been obtained under cryogenic conditions on a diluted sample of magnesium diboride powder in the normal and superconducting state. We demonstrate that MAS NMR is possible on type-II superconductors despite the sample rotation. The data provide accurate information on the magnetic shift variation and longitudinal relaxation data down to a temperature of 8 K, with a resolution improvement over the entire temperature range. The onset of superconductivity is unaffected by the sample rotation, as revealed by a steep variation of the magnetic shift just below the critical temperature. Appeared in JCP 137, 114201, http://dx.doi.org/10.1063/1.4751476

  16. Surface Impedance Measurements of Single Crystal MgB2 Films for Radiofrequency Superconductivity Applications

    SciTech Connect

    Binping Xiao, Xin Zhao, Joshua Spradlin, Charles Reece, Michael Kelley, Teng Tan, Xi Xiaoxing

    2012-07-01

    We report microstructure analyses and superconducting radiofrequency (SRF) measurements of large scale epitaxial MgB{sub 2} films. MgB{sub 2} films on 5 cm dia. sapphire disks were fabricated by a Hybrid Physical Chemical Vapor Deposition (HPCVD) technique. The electron-beam backscattering diffraction (EBSD) results suggest that the film is a single crystal complying with a MgB{sub 2}(0001) {parallel} Al{sub 2}O{sub 3}(0001) epitaxial relationship. The SRF properties of different film thicknesses (200 nm and 350 nm) were evaluated under different temperatures and applied fields at 7.4 GHz. A surface resistance of 9 {+-} 2 {mu}{Omega} has been observed at 2.2 K.

  17. Electrochemical thinning of silicon

    DOEpatents

    Medernach, J.W.

    1994-01-11

    Porous semiconducting material, e.g. silicon, is formed by electrochemical treatment of a specimen in hydrofluoric acid, using the specimen as anode. Before the treatment, the specimen can be masked. The porous material is then etched with a caustic solution or is oxidized, depending of the kind of structure desired, e.g. a thinned specimen, a specimen, a patterned thinned specimen, a specimen with insulated electrical conduits, and so on. Thinned silicon specimen can be subjected to tests, such as measurement of interstitial oxygen by Fourier transform infra-red spectroscopy (FTIR). 14 figures.

  18. Electrochemical thinning of silicon

    DOEpatents

    Medernach, John W.

    1994-01-01

    Porous semiconducting material, e.g. silicon, is formed by electrochemical treatment of a specimen in hydrofluoric acid, using the specimen as anode. Before the treatment, the specimen can be masked. The porous material is then etched with a caustic solution or is oxidized, depending of the kind of structure desired, e.g. a thinned specimen, a specimen, a patterned thinned specimen, a specimen with insulated electrical conduits, and so on. Thinned silicon specimen can be subjected to tests, such as measurement of interstitial oxygen by Fourier transform infra-red spectroscopy (FTIR).

  19. Biomimetic thin film synthesis

    SciTech Connect

    Graff, G.L.; Campbell, A.A.; Gordon, N.R.

    1995-05-01

    The purpose of this program is to develop a new process for forming thin film coatings and to demonstrate that the biomimetic thin film technology developed at PNL is useful for industrial applications. In the biomimetic process, mineral deposition from aqueous solution is controlled by organic functional groups attached to the underlying substrate surface. The coatings process is simple, benign, inexpensive, energy efficient, and particularly suited for temperature sensitive substrate materials (such as polymers). In addition, biomimetic thin films can be deposited uniformly on complex shaped and porous substrates providing a unique capability over more traditional line-of-sight methods.

  20. Thin film hydrogen sensor

    DOEpatents

    Cheng, Yang-Tse; Poli, Andrea A.; Meltser, Mark Alexander

    1999-01-01

    A thin film hydrogen sensor, includes: a substantially flat ceramic substrate with first and second planar sides and a first substrate end opposite a second substrate end; a thin film temperature responsive resistor on the first planar side of the substrate proximate to the first substrate end; a thin film hydrogen responsive metal resistor on the first planar side of the substrate proximate to the fist substrate end and proximate to the temperature responsive resistor; and a heater on the second planar side of the substrate proximate to the first end.

  1. Thin film hydrogen sensor

    DOEpatents

    Cheng, Y.T.; Poli, A.A.; Meltser, M.A.

    1999-03-23

    A thin film hydrogen sensor includes a substantially flat ceramic substrate with first and second planar sides and a first substrate end opposite a second substrate end; a thin film temperature responsive resistor on the first planar side of the substrate proximate to the first substrate end; a thin film hydrogen responsive metal resistor on the first planar side of the substrate proximate to the fist substrate end and proximate to the temperature responsive resistor; and a heater on the second planar side of the substrate proximate to the first end. 5 figs.

  2. Ceramic Composite Thin Films

    NASA Technical Reports Server (NTRS)

    Ruoff, Rodney S. (Inventor); Stankovich, Sasha (Inventor); Dikin, Dmitriy A. (Inventor); Nguyen, SonBinh T. (Inventor)

    2013-01-01

    A ceramic composite thin film or layer includes individual graphene oxide and/or electrically conductive graphene sheets dispersed in a ceramic (e.g. silica) matrix. The thin film or layer can be electrically conductive film or layer depending the amount of graphene sheets present. The composite films or layers are transparent, chemically inert and compatible with both glass and hydrophilic SiOx/silicon substrates. The composite film or layer can be produced by making a suspension of graphene oxide sheet fragments, introducing a silica-precursor or silica to the suspension to form a sol, depositing the sol on a substrate as thin film or layer, at least partially reducing the graphene oxide sheets to conductive graphene sheets, and thermally consolidating the thin film or layer to form a silica matrix in which the graphene oxide and/or graphene sheets are dispersed.

  3. Super Thin Ceramic Coatings

    NASA Video Gallery

    New technology being developed at NASA's Glenn Research Center creates super thin ceramic coatings on engine components. The Plasma Spray – Physical Vapor Deposition (PS-PVD) rig uses a powerful ...

  4. Thin silicon solar cells

    SciTech Connect

    Hall, R.B.; Bacon, C.; DiReda, V.; Ford, D.H.; Ingram, A.E.; Cotter, J.; Hughes-Lampros, T.; Rand, J.A.; Ruffins, T.R.; Barnett, A.M.

    1992-12-01

    The silicon-film design achieves high performance by using a dun silicon layer and incorporating light trapping. Optimally designed thin crystalline solar cells (<50 microns thick) have performance advantages over conventional thick devices. The high-performance silicon-film design employs a metallurgical barrier between the low-cost substrate and the thin silicon layer. Light trapping properties of silicon-film on ceramic solar cells are presented and analyzed. Recent advances in process development are described here.

  5. Multifunctional thin film surface

    DOEpatents

    Brozik, Susan M.; Harper, Jason C.; Polsky, Ronen; Wheeler, David R.; Arango, Dulce C.; Dirk, Shawn M.

    2015-10-13

    A thin film with multiple binding functionality can be prepared on an electrode surface via consecutive electroreduction of two or more aryl-onium salts with different functional groups. This versatile and simple method for forming multifunctional surfaces provides an effective means for immobilization of diverse molecules at close proximities. The multifunctional thin film has applications in bioelectronics, molecular electronics, clinical diagnostics, and chemical and biological sensing.

  6. Thin film tritium dosimetry

    DOEpatents

    Moran, Paul R.

    1976-01-01

    The present invention provides a method for tritium dosimetry. A dosimeter comprising a thin film of a material having relatively sensitive RITAC-RITAP dosimetry properties is exposed to radiation from tritium, and after the dosimeter has been removed from the source of the radiation, the low energy electron dose deposited in the thin film is determined by radiation-induced, thermally-activated polarization dosimetry techniques.

  7. Effect of damage by 2 MeV He ions on the normal and superconducting properties of magnesium diboride

    NASA Astrophysics Data System (ADS)

    Gandikota, R.; Singh, R. K.; Kim, J.; Wilkens, B.; Newman, N.; Rowell, J. M.; Pogrebnyakov, A. V.; Xi, X. X.; Redwing, J. M.; Xu, S. Y.; Li, Q.

    2005-01-01

    We have studied the effect of damage induced by 2MeV alpha particles on the critical temperature, Tc, and resistivity, ρ, of MgB2 thin films. This technique allows defects to be controllably introduced into MgB2 in small successive steps. Tc decreases linearly as the intragrain resistivity at 40K increases, while the intergrain connectivity is not changed. Tc is ultimately reduced to less than 7K and we see no evidence for a saturation of Tc at about 20K, contrary to the predictions of the Tc of MgB2 in the dirty limit of interband scattering.

  8. ⁶⁸Ge content quality control of ⁶⁸Ge/⁶⁸Ga-generator eluates and ⁶⁸Ga radiopharmaceuticals--a protocol for determining the ⁶⁸Ge content using thin-layer chromatography.

    PubMed

    Eppard, Elisabeth; Loktionova, Natalia S; Rösch, Frank

    2014-09-01

    (68)Ge breakthrough from a (68)Ge/(68)Ga-generator appears to be one of the most critical parameters for the routine clinical application of this generator and (68)Ga-radiopharmaceuticals. We report a TLC-based (thin-layer chromatography) protocol which allows the (68)Ge breakthrough of a generator to be determined within 1 h post-initial elution. The protocol can also be adapted to allow the (68)Ge content of a (68)Ga-radiopharmaceutical preparation to be determined prior to in vivo application.

  9. Epitaxial thinning process

    NASA Technical Reports Server (NTRS)

    Siegel, C. M. (Inventor)

    1984-01-01

    A method is described for thinning an epitaxial layer of a wafer that is to be used in producing diodes having a specified breakdown voltage and which also facilitates the thinning process. Current is passed through the epitaxial layer, by connecting a current source between the substrate of the wafer and an electrolyte in which the wafer is immersed. When the wafer is initially immersed, the voltage across the wafer initially drops and then rises at a steep rate. When light is applied to the wafer the voltage drops, and when the light is interrupted the voltage rises again. These changes in voltage, each indicate the breakdown voltage of a Schottky diode that could be prepared from the wafer at that time. The epitaxial layer is thinned by continuing to apply current through the wafer while it is immersed and light is applied, to form an oxide film and when the oxide film is thick the wafer can then be cleaned of oxide and the testing and thinning continued. Uninterrupted thinning can be achieved by first forming an oxide film, and then using an electrolyte that dissolves the oxide about as fast as it is being formed, to limit the thickness of the oxide layer.

  10. Lithospheric and crustal thinning

    NASA Technical Reports Server (NTRS)

    Moretti, I.

    1985-01-01

    In rift zones, both the crust and the lithosphere get thinner. The amplitude and the mechanism of these two thinning situations are different. The lithospheric thinning is a thermal phenomenon produced by an asthenospherical uprising under the rift zone. In some regions its amplitude can exceed 200%. This is observed under the Baikal rift where the crust is directly underlaid by the mantellic asthenosphere. The presence of hot material under rift zones induces a large negative gravity anomaly. A low seismic velocity zone linked to this thermal anomaly is also observed. During the rifting, the magmatic chambers get progressively closer from the ground surface. Simultaneously, the Moho reflector is found at shallow depth under rift zones. This crustal thinning does not exceed 50%. Tectonic stresses and vertical movements result from the two competing effects of the lithospheric and crustal thinning. On the one hand, the deep thermal anomaly induces a large doming and is associated with extensive deviatoric stresses. On the other hand, the crustal thinning involves the formation of a central valley. This subsidence is increased by the sediment loading. The purpose here is to quantify these two phenomena in order to explain the morphological and thermal evolution of rift zones.

  11. Thin film temperature sensor

    NASA Technical Reports Server (NTRS)

    Grant, H. P.; Przybyszewski, J. S.

    1980-01-01

    Thin film surface temperature sensors were developed. The sensors were made of platinum-platinum/10 percent rhodium thermocouples with associated thin film-to-lead wire connections and sputtered on aluminum oxide coated simulated turbine blades for testing. Tests included exposure to vibration, low velocity hydrocarbon hot gas flow to 1250 K, and furnace calibrations. Thermal electromotive force was typically two percent below standard type S thermocouples. Mean time to failure was 42 hours at a hot gas flow temperature of 1250 K and an average of 15 cycles to room temperature. Failures were mainly due to separation of the platinum thin film from the aluminum oxide surface. Several techniques to improve the adhesion of the platinum are discussed.

  12. Biomimetic thin film deposition

    NASA Astrophysics Data System (ADS)

    Rieke, P. C.; Campbell, A. A.; Tarasevich, B. J.; Fryxell, G. E.; Bentjen, S. B.

    1991-04-01

    Surfaces derivatized with organic functional groups were used to promote the deposition of thin films of inorganic minerals. These derivatized surfaces were designed to mimic the nucleation proteins that control mineral deposition during formation of bone, shell, and other hard tissues in living organisms. By the use of derivatized substrates control was obtained over the phase of mineral deposited, the orientation of the crystal lattice and the location of deposition. These features are of considerable importance in many technically important thin films, coatings, and composite materials. Methods of derivatizing surfaces are considered and examples of controlled mineral deposition are presented.

  13. Thin film photovoltaic device

    DOEpatents

    Catalano, Anthony W.; Bhushan, Manjul

    1982-01-01

    A thin film photovoltaic solar cell which utilizes a zinc phosphide semiconductor is of the homojunction type comprising an n-type conductivity region forming an electrical junction with a p-type region, both regions consisting essentially of the same semiconductor material. The n-type region is formed by treating zinc phosphide with an extrinsic dopant such as magnesium. The semiconductor is formed on a multilayer substrate which acts as an opaque contact. Various transparent contacts may be used, including a thin metal film of the same chemical composition as the n-type dopant or conductive oxides or metal grids.

  14. Shear Thinning in Xenon

    NASA Technical Reports Server (NTRS)

    Bergm Robert F.; Moldover, Michael R.; Yao, Minwu; Zimmerli, Gregory A.

    2009-01-01

    We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids such as molten plastics or ketchup, near the critical point of xenon. The data span a wide range of dimensionless shear rate: the product of the shear rate and the relaxation time of critical fluctuations was greater than 0.001 and was less than 700. As predicted by theory, shear thinning occurred when this product was greater than 1. The measurements were conducted aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth's gravity.

  15. Thin film ceramic thermocouples

    NASA Technical Reports Server (NTRS)

    Gregory, Otto (Inventor); Fralick, Gustave (Inventor); Wrbanek, John (Inventor); You, Tao (Inventor)

    2011-01-01

    A thin film ceramic thermocouple (10) having two ceramic thermocouple (12, 14) that are in contact with each other in at least on point to form a junction, and wherein each element was prepared in a different oxygen/nitrogen/argon plasma. Since each element is prepared under different plasma conditions, they have different electrical conductivity and different charge carrier concentration. The thin film thermocouple (10) can be transparent. A versatile ceramic sensor system having an RTD heat flux sensor can be combined with a thermocouple and a strain sensor to yield a multifunctional ceramic sensor array. The transparent ceramic temperature sensor that could ultimately be used for calibration of optical sensors.

  16. Thin-film optical initiator

    DOEpatents

    Erickson, Kenneth L.

    2001-01-01

    A thin-film optical initiator having an inert, transparent substrate, a reactive thin film, which can be either an explosive or a pyrotechnic, and a reflective thin film. The resultant thin-film optical initiator system also comprises a fiber-optic cable connected to a low-energy laser source, an output charge, and an initiator housing. The reactive thin film, which may contain very thin embedded layers or be a co-deposit of a light-absorbing material such as carbon, absorbs the incident laser light, is volumetrically heated, and explodes against the output charge, imparting about 5 to 20 times more energy than in the incident laser pulse.

  17. Protein thin film machines.

    PubMed

    Federici, Stefania; Oliviero, Giulio; Hamad-Schifferli, Kimberly; Bergese, Paolo

    2010-12-01

    We report the first example of microcantilever beams that are reversibly driven by protein thin film machines fueled by cycling the salt concentration of the surrounding solution. We also show that upon the same salinity stimulus the drive can be completely reversed in its direction by introducing a surface coating ligand. Experimental results are throughout discussed within a general yet simple thermodynamic model.

  18. Treading on Thin Water.

    ERIC Educational Resources Information Center

    Haley, Richard D.

    1985-01-01

    Provides a simple introduction to animals whose habitat is the thin surface film of water. Describes adaptive mechanisms of water striders, whirlygigs and riffle bugs and suggests ways to observe them in the wild or as aquarium animals. Includes basic demonstrations of the nature of surface tension. (JHZ)

  19. Thin Wall Iron Castings

    SciTech Connect

    J.F. Cuttino; D.M. Stefanescu; T.S. Piwonka

    2001-10-31

    Results of an investigation made to develop methods of making iron castings having wall thicknesses as small as 2.5 mm in green sand molds are presented. It was found that thin wall ductile and compacted graphite iron castings can be made and have properties consistent with heavier castings. Green sand molding variables that affect casting dimensions were also identified.

  20. Thin Lens Ray Tracing.

    ERIC Educational Resources Information Center

    Gatland, Ian R.

    2002-01-01

    Proposes a ray tracing approach to thin lens analysis based on a vector form of Snell's law for paraxial rays as an alternative to the usual approach in introductory physics courses. The ray tracing approach accommodates skew rays and thus provides a complete analysis. (Author/KHR)

  1. Thin film photovoltaic cell

    DOEpatents

    Meakin, John D.; Bragagnolo, Julio

    1982-01-01

    A thin film photovoltaic cell having a transparent electrical contact and an opaque electrical contact with a pair of semiconductors therebetween includes utilizing one of the electrical contacts as a substrate and wherein the inner surface thereof is modified by microroughening while being macro-planar.

  2. Thin film solar cell workshop

    NASA Technical Reports Server (NTRS)

    Armstrong, Joe; Jeffrey, Frank

    1993-01-01

    A summation of responses to questions posed to the thin-film solar cell workshop and the ensuing discussion is provided. Participants in the workshop included photovoltaic manufacturers (both thin film and crystalline), cell performance investigators, and consumers.

  3. Thin films for material engineering

    NASA Astrophysics Data System (ADS)

    Wasa, Kiyotaka

    2016-07-01

    Thin films are defined as two-dimensional materials formed by condensing one by one atomic/molecular/ionic species of matter in contrast to bulk three-dimensional sintered ceramics. They are grown through atomic collisional chemical reaction on a substrate surface. Thin film growth processes are fascinating for developing innovative exotic materials. On the basis of my long research on sputtering deposition, this paper firstly describes the kinetic energy effect of sputtered adatoms on thin film growth and discusses on a possibility of room-temperature growth of cubic diamond crystallites and the perovskite thin films of binary compound PbTiO3. Secondly, high-performance sputtered ferroelectric thin films with extraordinary excellent crystallinity compatible with MBE deposited thin films are described in relation to a possible application for thin-film MEMS. Finally, the present thin-film technologies are discussed in terms of a future material science and engineering.

  4. NMR characterization of thin films

    DOEpatents

    Gerald II, Rex E.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

    2010-06-15

    A method, apparatus, and system for characterizing thin film materials. The method, apparatus, and system includes a container for receiving a starting material, applying a gravitational force, a magnetic force, and an electric force or combinations thereof to at least the starting material, forming a thin film material, sensing an NMR signal from the thin film material and analyzing the NMR signal to characterize the thin film of material.

  5. VACUUM DEPOSITION OF THIN FILMS,

    DTIC Science & Technology

    The book deals with methods of obtaining and processing thin films , methods of measuring the deposition rate and thickness of thin-film layers, and...the main fields of application of thin films . Vacuum requirements and the requirements for the composition of the residual medium in thermal...evaporation and cathode sputtering are given, and modern methods of producing and measuring vacuums and the equipment used in obtaining thin films are described. (Author)

  6. Optical diffraction analysis of petrographic thin sections.

    PubMed

    Power, P C; Pincus, H J

    1974-10-18

    Diffraction patterns that are highly reproducible, of useful quality, and consistent with the input generating them can be easily obtained with a microscope system. The input can be either a reduced photograph or a thin section. With two exceptions, the relationships between a thin section and its diffraction pattern produced by a petrographic microscope are the same as the relationships between a photographic input and its diffraction pattern produced by a conventional ODA system. The exceptions are that the diffraction patterns generated directly by the thin sections may be asymmetrical or, if the thin section is sufficiently heterogeneous, may be smeared. The microscope system is generally more useful than a conventional ODA system for the analysis of microfabric in thin sections. One can readily use the microscope system to analyze elements of widely varying spatial frequency simply by changing the objectives. The diffraction patterns can be magnified by changing to a higherpower ocular. In most cases the microscope-generated diffraction pattern transmits the useful spatial information in the thin section more completely than the conventionally produced diffraction pattern; the photographic inputs for the conventionally produced diffraction pattern emphasize lower-frequency spatial information. This property, combined with the microscope system's better response to twinning, makes the microscope more sensitive to commonly used microfabric elements. For the analysis of thin sections, a conventional ODA system is superior to the microscope system in only three cases. First, if one wants to analyze the entire thin section at one time, a conventional system must be used with a photographic input of the thin section. Second, if the thin section is extremely heterogeneous (crystallographically or mineralogically), the microscope-generated diffraction pattern may exhibit gross smearing even with the highestpower objectives available. Finally, the thin section may

  7. An overview of thin film nitinol endovascular devices.

    PubMed

    Shayan, Mahdis; Chun, Youngjae

    2015-07-01

    Thin film nitinol has unique mechanical properties (e.g., superelasticity), excellent biocompatibility, and ultra-smooth surface, as well as shape memory behavior. All these features along with its low-profile physical dimension (i.e., a few micrometers thick) make this material an ideal candidate in developing low-profile medical devices (e.g., endovascular devices). Thin film nitinol-based devices can be collapsed and inserted in remarkably smaller diameter catheters for a wide range of catheter-based procedures; therefore, it can be easily delivered through highly tortuous or narrow vascular system. A high-quality thin film nitinol can be fabricated by vacuum sputter deposition technique. Micromachining techniques were used to create micro patterns on the thin film nitinol to provide fenestrations for nutrition and oxygen transport and to increase the device's flexibility for the devices used as thin film nitinol covered stent. In addition, a new surface treatment method has been developed for improving the hemocompatibility of thin film nitinol when it is used as a graft material in endovascular devices. Both in vitro and in vivo test data demonstrated a superior hemocompatibility of the thin film nitinol when compared with commercially available endovascular graft materials such as ePTFE or Dacron polyester. Promising features like these have motivated the development of thin film nitinol as a novel biomaterial for creating endovascular devices such as stent grafts, neurovascular flow diverters, and heart valves. This review focuses on thin film nitinol fabrication processes, mechanical and biological properties of the material, as well as current and potential thin film nitinol medical applications.

  8. [Utilization of compressed Chinese fir thinning wood].

    PubMed

    Chen, Ruiying; Wei, Ping; Liu, Jinghong

    2005-12-01

    With Chinese fir thinnings as raw material, and through measuring the physical-mechanical indices of its compressed wood, observing the variation of its microstructure and using IR analysis, an optimized technique of compressing Chinese fir thinnings was established. The technique was: compression ratio 50%-60%, thickness after compression 20 mm, moisture content before compression 50%, compressing time 20-30 minutes, and hot compressing temperature 180-200 degrees C. CH, an environmentally friendly cooking additive, had positive effects on softening the wood. During compressing, only the cells of fast-growing Chinese fir were extruded, their cavity became smaller, while the cell wall was not destroyed. The thickness reversion ratio of compressed wood was 2.68%, and its size stability and mechanical quality were as good as hardwoods (Betula lumninifera).

  9. Microwave plasma assisted supersonic gas jet deposition of thin film materials

    DOEpatents

    Schmitt, J.J. III; Halpern, B.L.

    1993-10-26

    An apparatus for fabricating thin film materials utilizing high speed gas dynamics relies on supersonic free jets of carrier gas to transport depositing vapor species generated in a microwave discharge to the surface of a prepared substrate where the vapor deposits to form a thin film. The present invention generates high rates of deposition and thin films of unforeseen high quality at low temperatures. 5 figures.

  10. Vanadium dioxide thin films for smart windows: optical design and performance improvement

    NASA Astrophysics Data System (ADS)

    He, Xinfeng; Gu, Congcong; Chen, Fei; Xu, Xiaofeng

    2013-12-01

    The high quality vanadium dioxide (VO2) thin films have been fabricated successfully on sapphire by a simple novel sputtering oxidation coupling (SOC) method. Transmittance spectra of vanadium dioxide film have been measured between 25 °C and 90 °C. The thin film samples exhibit a good insulator-metal transition near room temperature. The optical constants of VO2 thin film samples were derived by fitting the transmittance spectra using the Drude-Lorentz model. In order to improve the transition efficiency, the thin film thickness was optimized by the optical design. The calculated results with different thin film thickness show that VO2 thin film with 84 nm owns a maximums value of the transition efficiency. This research will promote VO2 thin film optical performance improvement for the smart windows.

  11. Biomolecular papain thin films growth by laser techniques.

    PubMed

    György, Enikö; Santiso, Jose; Figueras, Albert; Socol, Gabriel; Mihailescu, Ion N

    2007-08-01

    Papain thin films were synthesised by matrix assisted and conventional pulsed laser deposition (PLD) techniques. The targets submitted to laser radiation consisted on a frozen composite obtained by dissolving the biomaterials in distilled water. For the deposition of the thin films by conventional PLD pressed biomaterial powder targets were submitted to laser irradiation. An UV KrF* excimer laser source was used in the experiments at 0.5 J/cm(2) incident fluence value, diminished one order of magnitude as compared to irradiation of inorganic materials. The surface morphology of the obtained thin films was studied by atomic force profilometry and atomic force microscopy. The investigations showed that the growth mode and surface quality of the deposited biomaterial thin films is strongly influenced by the target preparation procedure.

  12. Density of organic thin films in organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Zhao, Cindy X.; Xiao, Steven; Xu, Gu

    2015-07-01

    A practical parameter, the volume density of organic thin films, found to affect the electronic properties and in turn the performance of organic photovoltaics (OPVs), is investigated in order to benefit the polymer synthesis and thin film preparation in OPVs. To establish the correlation between film density and device performance, the density of organic thin films with various treatments was obtained, by two-dimensional X-ray diffraction measurement using the density mapping with respect to the crystallinity of thin films. Our results suggest that the OPV of higher performance has a denser photoactive layer, which may hopefully provide a solution to the question of whether the film density matters in organic electronics, and help to benefit the OPV industry in terms of better polymer design, standardized production, and quality control with less expenditure.

  13. Advanced thin film thermocouples

    NASA Technical Reports Server (NTRS)

    Kreider, K. G.; Semancik, S.; Olson, C.

    1984-01-01

    The fabrication, materials characterization, and performance of thin film platinum rhodium thermocouples on gas turbine alloys was investigated. The materials chosen for the study were the turbine blade alloy systems MAR M200+Hf with NiCoCrAlY and FeCrAlY coatings, and vane alloy systems MAR M509 with FeCrAlY. Research was focussed on making improvements in the problem areas of coating substrate stability, adhesion, and insulation reliability and durability. Diffusion profiles between the substrate and coating with and without barrier coatings of Al2O3 are reported. The relationships between fabrication parameters of thermal oxidation and sputtering of the insulator and its characterization and performance are described. The best thin film thermocouples were fabricated with the NiCoCrAlY coatings which were thermally oxidized and sputter coated with Al2O3.

  14. Shear-thinning Fluid

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Whipped cream and the filling for pumpkin pie are two familiar materials that exhibit the shear-thinning effect seen in a range of industrial applications. It is thick enough to stand on its own atop a piece of pie, yet flows readily when pushed through a tube. This demonstrates the shear-thinning effect that was studied with the Critical Viscosity of Xenon Experiment (CVX-2) on the STS-107 Research 1 mission in 2002. CVX observed the behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. The principal investigator was Dr. Robert Berg of the National Institutes of Standards and Technology in Gaithersburg, MD.

  15. Thin film superconductor magnetic bearings

    DOEpatents

    Weinberger, Bernard R.

    1995-12-26

    A superconductor magnetic bearing includes a shaft (10) that is subject to a load (L) and rotatable around an axis of rotation, a magnet (12) mounted to the shaft, and a stator (14) in proximity to the shaft. The stator (14) has a superconductor thin film assembly (16) positioned to interact with the magnet (12) to produce a levitation force on the shaft (10) that supports the load (L). The thin film assembly (16) includes at least two superconductor thin films (18) and at least one substrate (20). Each thin film (18) is positioned on a substrate (20) and all the thin films are positioned such that an applied magnetic field from the magnet (12) passes through all the thin films. A similar bearing in which the thin film assembly (16) is mounted on the shaft (10) and the magnet (12) is part of the stator (14) also can be constructed.

  16. Thin, Lightweight Solar Cell

    NASA Technical Reports Server (NTRS)

    Brandhorst, Henry W., Jr.; Weinberg, Irving

    1991-01-01

    Improved design for thin, lightweight solar photovoltaic cells with front contacts reduces degradation of electrical output under exposure to energetic charged particles (protons and electrons). Increases ability of cells to maintain structural integrity under exposure to ultraviolet radiation by eliminating ultraviolet-degradable adhesives used to retain cover glasses. Interdigitated front contacts and front junctions formed on semiconductor substrate. Mating contacts formed on back surface of cover glass. Cover glass and substrate electrostatically bonded together.

  17. Thin film composite electrolyte

    DOEpatents

    Schucker, Robert C.

    2007-08-14

    The invention is a thin film composite solid (and a means for making such) suitable for use as an electrolyte, having a first layer of a dense, non-porous conductive material; a second layer of a porous ionic conductive material; and a third layer of a dense non-porous conductive material, wherein the second layer has a Coefficient of thermal expansion within 5% of the coefficient of thermal expansion of the first and third layers.

  18. Smoothing of mirror substrates by thin-film deposition

    SciTech Connect

    Baker, S; Parra, E; Spiller, E; Tarrio, C

    1999-08-03

    Superpolished optical flats with high spatial frequency roughness below 0.1 nm have been commercially available for years. However, it is much more difficult to obtain figured optics of similar quality. We have obtained and tested the finish of figured optics from different vendors by atomic force microscopy and optical profilometry and have investigated how the substrate quality can be improved by the deposition of thin films. We have determined the growth parameters of several thin-film structures. From these parameters we can determine how the surface topography of a coated mirror differs from that of the substrate, select the best thin-film structure, and predict the possible improvement. Keywords: Smoothing films, multilayer coatings, finish of mirror substrates

  19. Application of Pcvd Process to Uniform Coating of TiO2 Thin Films on Polypropylene Beads

    NASA Astrophysics Data System (ADS)

    Kim, Dong-Joo; Pham, Hung Cuong; Kim, Kyo-Seon

    The growth of the TiO2 thin films coated on the polypropylene beads was analyzed experimentally in a rotating cylindrical plasma chemical vapor deposition (PCVD) reactor. The precursors for the thin films were generated by plasma reactions, and they deposited on the polypropylene beads to become the uniform thin films. The TiO2 thin films grow more quickly on the polypropylene beads by increasing the mass flow rate of TTIP, or the rotation speed of the reactor. The smaller number of polypropylene beads in the reactor increases the growth rate of the thin films. The high-quality TiO2 thin films can be coated on particles uniformly by using the rotating cylindrical PCVD process. The particles coated with high-quality TiO2 thin films can be applied to the removal of air and water pollutants by a photodegradation reaction of TiO2.

  20. Thin film processing of photorefractive BaTiO3

    NASA Technical Reports Server (NTRS)

    Schuster, Paul R.; Potember, Richard S.

    1991-01-01

    The principle objectives of this ongoing research involve the preparation and characterization of polycrystalline single-domain thin films of BaTiO3 for photorefractive applications. These films must be continuous, free of cracks, and of high optical quality. The two methods proposed are sputtering and sol-gel related processing.

  1. Into Thin Air.

    ERIC Educational Resources Information Center

    Kennedy, Mike

    2001-01-01

    Shows how schools are working to avoid the types of equipment, supplies, and maintenance practices that harm indoor air quality. Simple steps to maintaining a cleaner indoor air environment are highlighted as are steps to reducing the problem air quality and the occurrence of asthma. (GR)

  2. The thin-film deposition of conjugated molecules for organic electronics

    NASA Astrophysics Data System (ADS)

    Jin, Michael H.-C.

    2008-06-01

    Device-quality conjugated organic thin films are now routinely prepared in many different ways to fabricate light-emitting diodes, thin-film transistors, and photovoltaic devices. Understanding how to design molecules through versatile synthetic chemistry and the mechanisms of phase transformation and chemical reaction that occur during the thin-film deposition process becomes especially vital for the performance of the applications. This article reviews the current understanding of various thin-film deposition technologies for the conjugated organic molecules primarily used in optoelectronics, particularly in photovoltaic applications.

  3. Photophysical properties of Alq3 thin films

    NASA Astrophysics Data System (ADS)

    Zawadzka, A.; Płóciennik, P.; Strzelecki, J.; Łukasiak, Z.; Sahraoui, B.

    2013-11-01

    This work contains investigation results of the photophysical properties of aluminum (III) tris(8-hydroxyquinoline) thin films. The Alq3 thin films were successfully fabricated by Physical Vapor Deposition technique. The films were grown on transparent: (quartz and glass) and semiconductor (n-type silica) substrates kept at room temperature during the deposition process. Selected films were annealed after fabrication in ambient atmosphere for 12 h at the temperature equal to 100 °C and 150 °C. Morphology of the films was investigated by AFM technique. Photophysical properties were characterized via photoluminescence, transmission, second and third harmonic generation measurements. The thin films exhibit high structural quality regardless of the annealing process, but the stability of the film can be improved by using an appropriate temperature during the annealing process. Photoluminescence of Alq3 films obtained in air were efficient and stable. The measurements of transmission, SHG and THG spectra allowed us to determine optical constant of the films. We find that the photophysical properties were strictly connected with the morphology and the annealing process significantly changes the structural properties of the films.

  4. Thin film hydrogen sensor

    DOEpatents

    Lauf, Robert J.; Hoffheins, Barbara S.; Fleming, Pamela H.

    1994-01-01

    A hydrogen sensor element comprises an essentially inert, electrically-insulating substrate having a thin-film metallization deposited thereon which forms at least two resistors on the substrate. The metallization comprises a layer of Pd or a Pd alloy for sensing hydrogen and an underlying intermediate metal layer for providing enhanced adhesion of the metallization to the substrate. An essentially inert, electrically insulating, hydrogen impermeable passivation layer covers at least one of the resistors, and at least one of the resistors is left uncovered. The difference in electrical resistances of the covered resistor and the uncovered resistor is related to hydrogen concentration in a gas to which the sensor element is exposed.

  5. Ureilite Thin Section Preparation

    NASA Technical Reports Server (NTRS)

    Harrington, R.; Righter, K.

    2014-01-01

    Preparing thin and thick sections of ureilite type meteorites is a challenge that can confound even the most experienced section preparer. A common characteristic of these samples is the presence of carbon phases, particularly nanodiamonds, in the matrix along silicate grain boundaries, fractures, and cleavage plains [1]. The extreme hardness of the nanodiamonds presents a challenge to the section preparer in the form of high surface relief on the section. This hard material also causes considerable wear and tear on equipment and materials that are used for making the sections. These issues will be discussed and potentially helpful measures will be presented.

  6. Carbon thin film thermometry

    NASA Technical Reports Server (NTRS)

    Collier, R. S.; Sparks, L. L.; Strobridge, T. R.

    1973-01-01

    The work concerning carbon thin film thermometry is reported. Optimum film deposition parameters were sought on an empirical basis for maximum stability of the films. One hundred films were fabricated for use at the Marshall Space Flight Center; 10 of these films were given a precise quasi-continuous calibration of temperature vs. resistance with 22 intervals between 5 and 80 K using primary platinum and germanium thermometers. Sensitivity curves were established and the remaining 90 films were given a three point calibration and fitted to the established sensitivity curves. Hydrogen gas-liquid discrimination set points are given for each film.

  7. Thin-Film Power Transformers

    NASA Technical Reports Server (NTRS)

    Katti, Romney R.

    1995-01-01

    Transformer core made of thin layers of insulating material interspersed with thin layers of ferromagnetic material. Flux-linking conductors made of thinner nonferromagnetic-conductor/insulator multilayers wrapped around core. Transformers have geometric features finer than those of transformers made in customary way by machining and mechanical pressing. In addition, some thin-film materials exhibit magnetic-flux-carrying capabilities superior to those of customary bulk transformer materials. Suitable for low-cost, high-yield mass production.

  8. Ln polyoxocations: yttrium oxide solution speciation & solution deposited thin films.

    PubMed

    Marsh, David A; Goberna-Ferrón, Sara; Baumeister, Mary K; Zakharov, Lev N; Nyman, May; Johnson, Darren W

    2017-01-17

    Rare earth oxide materials, including thin film coatings, are critically important in magnetic, luminescent and microelectric devices, and few substitutes have been discovered with comparable performance. Thin film coatings from solution are almost unknown for rare earth oxides, likely due to their high activity towards hydrolysis which yields poor quality thin films. The hexamer [Ln6(O)(OH)8(H2O)12(NO3)6](2+) is a rare example of a metal-oxo cluster isolated and stabilized without additional supporting organic ligands. Herein we report a new method for both the preparation and stabilization in non-aqueous media, which makes these clusters valuable precursors for solution-processed thin films. Solution characterization (NMR, small-angle X-ray scattering and Raman spectroscopy) in wet organic solvents indicated that the clusters evolve via a fragmentation and reaggregation process. This is especially true for hexamers of the smaller Ln(3+)-ions: the higher charge density yields higher hydration rates. This process produced an entirely new hexadecameric cluster formulated Y16O3(OH)24(NO3)18(OSMe2)16(OCMe2)2(H2O)4. The new structure represents an intermediate hydrolysis product on the pathway from hexanuclear clusters to metal oxyhydroxide bulk solid. DMSO solvent ligands displace aqua ligands on the cluster and likely explain the additional stability observed for these clusters in organic solvents. The enhanced cluster stability in DMF and DMSO also enables solution-processing methods to create high quality thin films.

  9. The thin eggshell problem

    USGS Publications Warehouse

    Stickel, L.F.; Rhodes, L.I.; Gillett, J.W.

    1970-01-01

    It has long been known that DDT and related chemicals can impair the reproduction of birds. In early years of organochlorine pesticide use, widespread mortality occurred immediately following heavy applications of these chemicals, and survivors contained substantial amounts of toxicant in their tissues. Repopulation from untreated areas tended to conceal the extent of the effects. DDT and dieldrin have become ubiquitous and the original source of the chemicals producing bird deaths often cannot be traced. The extent of sublethal effects cannot be fully appraised, although laboratory experiments continually reveal new and potentially deleterious physiological reactions. Thin eggshells have become prevalent among certain declining species of predatory birds. Shell thinning and associated reproductive effects have been produced experimentally in mallard ducks and in sparrow hawks. Coturnix quail fed dietary dosages of p,p'-DDT produced fewer eggs than did untreated birds and the eggs had thinner shells. Hatchability was not significantly altered. Comparisons between these results and those obtained in other studies indicate significant species differences.

  10. Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers

    PubMed Central

    Badali, D. S.; Gengler, R. Y. N.; Miller, R. J. D.

    2016-01-01

    A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the “medium” energy regime (1–10 kV). An extremely compact design, in combination with low bunch charges, allows for high quality diffraction in a lensless geometry. The measured and simulated characteristics of the experimental system reveal sub-picosecond temporal resolution, while demonstrating the ability to produce high quality diffraction patterns from atomically thin samples. PMID:27226978

  11. Optically Thin Metallic Films for High-Radiative-Efficiency Plasmonics.

    PubMed

    Yang, Yi; Zhen, Bo; Hsu, Chia Wei; Miller, Owen D; Joannopoulos, John D; Soljačić, Marin

    2016-07-13

    Plasmonics enables deep-subwavelength concentration of light and has become important for fundamental studies as well as real-life applications. Two major existing platforms of plasmonics are metallic nanoparticles and metallic films. Metallic nanoparticles allow efficient coupling to far field radiation, yet their synthesis typically leads to poor material quality. Metallic films offer substantially higher quality materials, but their coupling to radiation is typically jeopardized due to the large momentum mismatch with free space. Here, we propose and theoretically investigate optically thin metallic films as an ideal platform for high-radiative-efficiency plasmonics. For far-field scattering, adding a thin high-quality metallic substrate enables a higher quality factor while maintaining the localization and tunability that the nanoparticle provides. For near-field spontaneous emission, a thin metallic substrate, of high quality or not, greatly improves the field overlap between the emitter environment and propagating surface plasmons, enabling high-Purcell (total enhancement >10(4)), high-quantum-yield (>50%) spontaneous emission, even as the gap size vanishes (3-5 nm). The enhancement has almost spatially independent efficiency and does not suffer from quenching effects that commonly exist in previous structures.

  12. Antimicrobial activity of biopolymer-antibiotic thin films fabricated by advanced pulsed laser methods

    NASA Astrophysics Data System (ADS)

    Cristescu, R.; Popescu, C.; Dorcioman, G.; Miroiu, F. M.; Socol, G.; Mihailescu, I. N.; Gittard, S. D.; Miller, P. R.; Narayan, R. J.; Enculescu, M.; Chrisey, D. B.

    2013-08-01

    We report on thin film deposition by matrix assisted pulsed laser evaporation (MAPLE) of two polymer-drug composite thin film systems. A pulsed KrF* excimer laser source (λ = 248 nm, τ = 25 ns, ν = 10 Hz) was used to deposit composite thin films of poly(D,L-lactide) (PDLLA) containing several gentamicin concentrations. FTIR spectroscopy was used to demonstrate that MAPLE-transferred materials exhibited chemical structures similar to those of drop cast materials. Scanning electron microscopy data indicated that MAPLE may be used to fabricate thin films of good morphological quality. The activity of PDLLA-gentamicin composite thin films against Staphylococcus aureus bacteria was demonstrated using drop testing. The influence of drug concentration on microbial viability was also assessed. Our studies indicate that polymer-drug composite thin films prepared by MAPLE may be used to impart antimicrobial activity to implants, medical devices, and other contact surfaces.

  13. High efficiency, low cost thin GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Fan, J. C. C.

    1982-01-01

    The feasibility of fabricating space-resistant, high efficiency, light-weight, low-cost GaAs shallow-homojunction solar cells for space application is demonstrated. This program addressed the optimal preparation of ultrathin GaAs single-crystal layers by AsCl3-GaAs-H2 and OMCVD process. Considerable progress has been made in both areas. Detailed studies on the AsCl3 process showed high-quality GaAs thin layers can be routinely grown. Later overgrowth of GaAs by OMCVD has been also observed and thin FaAs films were obtained from this process.

  14. Thin film ion conducting coating

    DOEpatents

    Goldner, Ronald B.; Haas, Terry; Wong, Kwok-Keung; Seward, George

    1989-01-01

    Durable thin film ion conducting coatings are formed on a transparent glass substrate by the controlled deposition of the mixed oxides of lithium:tantalum or lithium:niobium. The coatings provide durable ion transport sources for thin film solid state storage batteries and electrochromic energy conservation devices.

  15. Dewetting of Thin Polymer Films

    NASA Astrophysics Data System (ADS)

    Dixit, P. S.; Sorensen, J. L.; Kent, M.; Jeon, H. S.

    2001-03-01

    DEWETTING OF THIN POLYMER FILMS P. S. Dixit,(1) J. L. Sorensen,(2) M. Kent,(2) H. S. Jeon*(1) (1) Department of Petroleum and Chemical Engineering, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, jeon@nmt.edu (2) Department 1832, Sandia National Laboratories, Albuquerque, NM. Dewetting of thin polymer films is of technological importance for a variety of applications such as protective coatings, dielectric layers, and adhesives. Stable and smooth films are required for the above applications. Above the glass transition temperature (Tg) the instability of polymer thin films on a nonwettable substrate can be occurred. The dewetting mechanism and structure of polypropylene (Tg = -20 ^circC) and polystyrene (Tg = 100 ^circC) thin films is investigated as a function of film thickness (25 Åh < 250 Åand quenching temperature. Contact angle measurements are used in conjunction with optical microscope to check the surface homogeneity of the films. Uniform thin films are prepared by spin casting the polymer solutions onto silicon substrates with different contact angles. We found that the stable and unstable regions of the thin films as a function of the film thickness and quenching temperature, and then constructed a stability diagram for the dewetting of thin polymer films. We also found that the dewetting patterns of the thin films are affected substantially by the changes of film thickness and quenching temperature.

  16. Methods of Producing Thin Films,

    DTIC Science & Technology

    The report describes various methods of producing thin films , especially for microelectronics. In addition to the classical methods of forming thin ... films by vacuum vapor deposition, it also describes processes of diode sputtering and modern methods of cathode sputtering by means of a third

  17. Thin film atomic hydrogen detectors

    NASA Technical Reports Server (NTRS)

    Gruber, C. L.

    1977-01-01

    Thin film and bead thermistor atomic surface recombination hydrogen detectors were investigated both experimentally and theoretically. Devices were constructed on a thin Mylar film substrate. Using suitable Wheatstone bridge techniques sensitivities of 80 microvolts/2x10 to the 13th power atoms/sec are attainable with response time constants on the order of 5 seconds.

  18. Magnetochromatic thin-film microplates.

    PubMed

    He, Le; Janner, Michael; Lu, Qipeng; Wang, Mingsheng; Ma, Hua; Yin, Yadong

    2015-01-07

    A new type of magnetochromatic material is developed based on thin-film interference of microplates self-assembled from super-paramagnetic nanocrystals. Dynamic optical tuning can be achieved through orientational manipulation of free-standing super-paramagnetic thin-film microplates using external magnetic fields.

  19. Thin Film Inorganic Electrochemical Systems.

    DTIC Science & Technology

    1995-07-01

    determined that thin film cathodes of LiCoO2 can be readily performed by either spray pyrolysis or spin coating . These cathodes are electrochemically...active. We have also determined that thin film anodes of Li4Ti5O12 can be prepared by spray pyrolysis or spin coating . These anodes are also

  20. Thin EFG octagons

    NASA Astrophysics Data System (ADS)

    Kalejs, J. P.

    1994-03-01

    This report describes work to advance the manufacturing line capabilities in crystal growth and laser cutting of Mobil Solar's unique edge-defined film-fed growth (EFG) octagon technology and to reduce the manufacturing costs of 10 cm x 10 cm polycrystalline silicon EFG wafers. The report summarizes the significant technical improvements in EFG technology achieved in the first 6 months of the PVMaT Phase 2 and the success in meeting program milestones. Technical results are reported for each of the three main pregrain areas: Task 5 -- Thin octagon growth (crystal growth) to reduce the thickness of the octagon to 200 microns; Task 6 -- Laser cutting-to improve the laser cutting process so as to produce wafers with decreased laser cutting damage at increased wafer throughput rates; and Task 7 -- Process control and product specification to implement advanced strategies in crystal growth process control and productivity designed to increase wafer yields.

  1. Ferromagnetic thin films

    DOEpatents

    Krishnan, K.M.

    1994-12-20

    A ferromagnetic [delta]-Mn[sub 1[minus]x]Ga[sub x] thin film having perpendicular anisotropy is described which comprises: (a) a GaAs substrate, (b) a layer of undoped GaAs overlying said substrate and bonded thereto having a thickness ranging from about 50 to about 100 nanometers, (c) a layer of [delta]-Mn[sub 1[minus]x]Ga[sub x] overlying said layer of undoped GaAs and bonded thereto having a thickness ranging from about 20 to about 30 nanometers, and (d) a layer of GaAs overlying said layer of [delta]-Mn[sub 1[minus]x]Ga[sub x] and bonded thereto having a thickness ranging from about 2 to about 5 nanometers, wherein x is 0.4[+-]0.05. 7 figures.

  2. Thin film hydrogen sensor

    DOEpatents

    Lauf, R.J.; Hoffheins, B.S.; Fleming, P.H.

    1994-11-22

    A hydrogen sensor element comprises an essentially inert, electrically-insulating substrate having a thin-film metallization deposited thereon which forms at least two resistors on the substrate. The metallization comprises a layer of Pd or a Pd alloy for sensing hydrogen and an underlying intermediate metal layer for providing enhanced adhesion of the metallization to the substrate. An essentially inert, electrically insulating, hydrogen impermeable passivation layer covers at least one of the resistors, and at least one of the resistors is left uncovered. The difference in electrical resistances of the covered resistor and the uncovered resistor is related to hydrogen concentration in a gas to which the sensor element is exposed. 6 figs.

  3. Ferromagnetic thin films

    DOEpatents

    Krishnan, Kannan M.

    1994-01-01

    A ferromagnetic .delta.-Mn.sub.1-x Ga.sub.x thin film having perpendicular anisotropy is described which comprises: (a) a GaAs substrate, (b) a layer of undoped GaAs overlying said substrate and bonded thereto having a thickness ranging from about 50 to about 100 nanometers, (c) a layer of .delta.-Mn.sub.1-x Ga.sub.x overlying said layer of undoped GaAs and bonded thereto having a thickness ranging from about 20 to about 30 nanometers, and (d) a layer of GaAs overlying said layer of .delta.-Mn.sub.1-x Ga.sub.x and bonded thereto having a thickness ranging from about 2 to about 5 nanometers, wherein x is 0.4 .+-.0.05.

  4. Selective inorganic thin films

    SciTech Connect

    Phillips, M.L.F.; Weisenbach, L.A.; Anderson, M.T.

    1995-05-01

    This project is developing inorganic thin films as membranes for gas separation applications, and as discriminating coatings for liquid-phase chemical sensors. Our goal is to synthesize these coatings with tailored porosity and surface chemistry on porous substrates and on acoustic and optical sensors. Molecular sieve films offer the possibility of performing separations involving hydrogen, air, and natural gas constituents at elevated temperatures with very high separation factors. We are focusing on improving permeability and molecular sieve properties of crystalline zeolitic membranes made by hydrothermally reacting layered multicomponent sol-gel films deposited on mesoporous substrates. We also used acoustic plate mode (APM) oscillator and surface plasmon resonance (SPR) sensor elements as substrates for sol-gel films, and have both used these modified sensors to determine physical properties of the films and have determined the sensitivity and selectivity of these sensors to aqueous chemical species.

  5. Thin wire pointing method

    NASA Technical Reports Server (NTRS)

    Green, G.; Mattauch, R. J. (Inventor)

    1983-01-01

    A method is described for forming sharp tips on thin wires, in particular phosphor bronze wires of diameters such as one-thousandth inch used to contact micron size Schottky barrier diodes, which enables close control of tip shape and which avoids the use of highly toxic solutions. The method includes dipping an end of a phosphor bronze wire into a dilute solution of sulfamic acid and applying a current through the wire to electrochemically etch it. The humidity in the room is controlled to a level of less than 50%, and the voltage applied between the wire and another electrode in the solutions is a half wave rectified voltage. The current through the wire is monitored, and the process is stopped when the current falls to a predetermined low level.

  6. Polyimide Aerogel Thin Films

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann; Guo, Haiquan

    2012-01-01

    Polyimide aerogels have been crosslinked through multifunctional amines. This invention builds on "Polyimide Aerogels With Three-Dimensional Cross-Linked Structure," and may be considered as a continuation of that invention, which results in a polyimide aerogel with a flexible, formable form. Gels formed from polyamic acid solutions, end-capped with anhydrides, and cross-linked with the multifunctional amines, are chemically imidized and dried using supercritical CO2 extraction to give aerogels having density around 0.1 to 0.3 g/cubic cm. The aerogels are 80 to 95% porous, and have high surface areas (200 to 600 sq m/g) and low thermal conductivity (as low as 14 mW/m-K at room temperature). Notably, the cross-linked polyimide aerogels have higher modulus than polymer-reinforced silica aerogels of similar density, and can be fabricated as both monoliths and thin films.

  7. Holographic thin film analyzer

    NASA Technical Reports Server (NTRS)

    Williams, J. R.; Norden, B. N. (Inventor)

    1973-01-01

    A system for the analysis and measurement of thin films in which the light output of a laser is split into two beams is discribed. The first beam is focused to illuminate the entire area of a photographic plate and the second beam is colummated and directed through a relatively small portion of the photographic plate onto the sample with the film to be observed. The surface of the sample is positioned at a slight angle with respect to a plane normal to the second beam and the light reflected from the sample arrives back at the photographic plate in a region other than through which the second beam originally passes. By making two successive exposures during the deposition of material on the surface of the sample, holograms are recorded on the photographic plate. The plate is then developed and interference lines of the hologram provide a measurement of the film or material deposited between exposure.

  8. Thin θ -film optics

    NASA Astrophysics Data System (ADS)

    Huerta, Luis

    2016-12-01

    A Chern-Simons theory in 3D is accomplished by the so-called θ term in the action (θ /2 )∫F ∧F , which contributes only to observable effects on the boundaries of such a system. When electromagnetic radiation interacts with the system, the wave is reflected and its polarization is rotated at the interface, even when both the θ system and the environment are pure vacuum. These topics have been studied extensively. Here, we investigate the optical properties of a thin θ film, where multiple internal reflections could interfere coherently. The cases of pure vacuum and a material with magnetoelectric properties are analyzed. It is found that the film reflectance is enhanced compared to ordinary non-θ systems and the interplay between magnetoelectric properties and the θ parameter yield film opacity and polarization properties which could be interesting in the case of topological insulators, among other topological systems.

  9. Nonlinear optical thin films

    NASA Technical Reports Server (NTRS)

    Leslie, Thomas M.

    1993-01-01

    A focused approach to development and evaluation of organic polymer films for use in optoelectronics is presented. The issues and challenges that are addressed include: (1) material synthesis, purification, and the tailoring of the material properties; (2) deposition of uniform thin films by a variety of methods; (3) characterization of material physical properties (thermal, electrical, optical, and electro-optical); and (4) device fabrication and testing. Photonic materials, devices, and systems were identified as critical technology areas by the Department of Commerce and the Department of Defense. This approach offers strong integration of basic material issues through engineering applications by the development of materials that can be exploited as the active unit in a variety of polymeric thin film devices. Improved materials were developed with unprecedented purity and stability. The absorptive properties can be tailored and controlled to provide significant improvement in propagation losses and nonlinear performance. Furthermore, the materials were incorporated into polymers that are highly compatible with fabrication and patterning processes for integrated optical devices and circuits. By simultaneously addressing the issues of materials development and characterization, keeping device design and fabrication in mind, many obstacles were overcome for implementation of these polymeric materials and devices into systems. We intend to considerably improve the upper use temperature, poling stability, and compatibility with silicon based devices. The principal device application that was targeted is a linear electro-optic modulation etalon. Organic polymers need to be properly designed and coupled with existing integrated circuit technology to create new photonic devices for optical communication, image processing, other laser applications such as harmonic generation, and eventually optical computing. The progression from microscopic sample to a suitable film

  10. Low Temperature Chemical Vapor Deposition Of Thin Film Magnets

    DOEpatents

    Miller, Joel S.; Pokhodnya, Kostyantyn I.

    2003-12-09

    A thin-film magnet formed from a gas-phase reaction of tetracyanoetheylene (TCNE) OR (TCNQ), 7,7,8,8-tetracyano-P-quinodimethane, and a vanadium-containing compound such as vanadium hexcarbonyl (V(CO).sub.6) and bis(benzene)vanalium (V(C.sub.6 H.sub.6).sub.2) and a process of forming a magnetic thin film upon at least one substrate by chemical vapor deposition (CVD) at a process temperature not exceeding approximately 90.degree. C. and in the absence of a solvent. The magnetic thin film is particularly suitable for being disposed upon rigid or flexible substrates at temperatures in the range of 40.degree. C. and 70.degree. C. The present invention exhibits air-stable characteristics and qualities and is particularly suitable for providing being disposed upon a wide variety of substrates.

  11. Wet chemical thinning of molybdenum disulfide down to its monolayer

    SciTech Connect

    Amara, Kiran Kumar; Chu, Leiqiang; Kumar, Rajeev; Toh, Minglin; Eda, Goki

    2014-09-01

    We report on the preparation of mono- and bi-layer molybdenum disulfide (MoS{sub 2}) from a bulk crystal by facile wet chemical etching. We show that concentrated nitric acid (HNO{sub 3}) effectively etches thin MoS{sub 2} crystals from their edges via formation of MoO{sub 3}. Interestingly, etching of thin crystals on a substrate leaves behind unreacted mono- and bilayer sheets. The flakes obtained by chemical etching exhibit electronic quality comparable to that of mechanically exfoliated counterparts. Our findings indicate that the self-limiting chemical etching is a promising top-down route to preparing atomically thin crystals from bulk layer compounds.

  12. High efficiency thin-film GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Zwerdling, S.; Wang, K. L.; Yeh, Y. C. M.

    1981-01-01

    The paper demonstrates the feasibility of producing high-efficiency GaAs solar cells with high power-to-weight ratios by organic metallic chemical vapor deposition (OM-CVD) growth of thin epi-layers on suitable substrates. An AM1 conversion efficiency of 18% (14% AM0), or 17% (13% AM0) with a 5% grid coverage is achieved for a single-crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer. Thin GaAs epi-layers OM-CVD grown can be fabricated with good crystallographic quality using a Si-substrate on which a thin Ge epi-interlayer is first deposited by CVD from GeH4 and processed for improved surface morphology

  13. The electro-optical behavior of liquid crystal molecules on the surface of SiO2 inorganic thin films.

    PubMed

    Sung, Shi-Joon; Yang, Kee-Jeong; Kim, Dae-Hwan; Do, Yun Seon; Kang, Jin-Kyu; Choi, Byeong-Dae

    2009-12-01

    Inorganic thin films are well known for the liquid crystal alignment layers for LCoS application due to the higher thermal and photochemical stability of inorganic materials. The switching time of liquid crystals is the important factor for the projection application and the faster switching time is required for the high quality display. The switching behavior of liquid crystal molecules on inorganic thin films might be closely related with the surface properties of the inorganic thin films. Therefore the understanding of surface properties of the inorganic thin films is required for the enhancement of the switching time of liquid crystals of LCoS devices. In this work, we prepared the SiO2 inorganic thin films and the electro-optical behavior of liquid crystal molecules on SiO2 thin film was investigated. The sputtering condition of SiO2 thin film was closely related with the thickness and the surface morphology of SiO2 thin film. The switching time of liquid crystals with negative dielectric constant on SiO2 inorganic thin films was dominantly affected by the size of protrusion on the surface of SiO2 thin film and the surface roughness of SiO2 thin film was also related with the switching time of liquid crystals. From these results, it is possible to prepare the SiO2 inorganic thin film suitable for the liquid crystal alignment layer for VAN LC mode.

  14. Host thin films incorporating nanoparticles

    NASA Astrophysics Data System (ADS)

    Qureshi, Uzma

    The focus of this research project was the investigation of the functional properties of thin films that incorporate a secondary nanoparticulate phase. In particular to assess if the secondary nanoparticulate material enhanced a functional property of the coating on glass. In order to achieve this, new thin film deposition methods were developed, namely use of nanopowder precursors, an aerosol assisted transport technique and an aerosol into atmospheric pressure chemical vapour deposition system. Aerosol assisted chemical vapour deposition (AACVD) was used to deposit 8 series of thin films on glass. Five different nanoparticles silver, gold, ceria, tungsten oxide and zinc oxide were tested and shown to successfully deposit thin films incorporating nanoparticles within a host matrix. Silver nanoparticles were synthesised and doped within a titania film by AACVD. This improved solar control properties. A unique aerosol assisted chemical vapour deposition (AACVD) into atmospheric pressure chemical vapour deposition (APCVD) system was used to deposit films of Au nanoparticles and thin films of gold nanoparticles incorporated within a host titania matrix. Incorporation of high refractive index contrast metal oxide particles within a host film altered the film colour. The key goal was to test the potential of nanopowder forms and transfer the suspended nanopowder via an aerosol to a substrate in order to deposit a thin film. Discrete tungsten oxide nanoparticles or ceria nanoparticles within a titanium dioxide thin film enhanced the self-cleaning and photo-induced super-hydrophilicity. The nanopowder precursor study was extended by deposition of zinc oxide thin films incorporating Au nanoparticles and also ZnO films deposited from a ZnO nanopowder precursor. Incorporation of Au nanoparticles within a VO: host matrix improved the thermochromic response, optical and colour properties. Composite VC/TiC and Au nanoparticle/V02/Ti02 thin films displayed three useful

  15. Learning unit: Thin lenses

    NASA Astrophysics Data System (ADS)

    Nita, L.-S.

    2012-04-01

    Learning unit: Thin lenses "Why objects seen through lenses are sometimes upright and sometimes reversed" Nita Laura Simona National College of Arts and Crafts "Constantin Brancusi", Craiova, Romania 1. GEOMETRIC OPTICS. 13 hours Introduction (models, axioms, principles, conventions) 1. Thin lenses (Types of lenses. Defining elements. Path of light rays through lenses. Image formation. Required physical quantities. Lens formulas). 2. Lens systems (Non-collated lenses. Focalless systems). 3. Human eye (Functioning as an optical system. Sight defects and their corrections). 4. Optical instruments (Characteristics exemplified by a magnifying glass. Paths of light rays through a simplified photo camera. Path of light rays through a classical microscope) (Physics curriculum for the IXth grade/ 2011). This scenario exposes a learning unit based on experimental sequences (defining specific competencies), as a succession of lessons started by noticing a problem whose solution assumes the setup of an experiment under laboratory conditions. Progressive learning of theme objectives are realised with sequential experimental steps. The central cognitive process is the induction or the generalization (development of new knowledge based on observation of examples or counterexamples of the concept to be learnt). Pupil interest in theme objectives is triggered by problem-situations, for example: "In order to better see small objects I need a magnifying glass. But when using a magnifier, small object images are sometimes seen upright and sometimes seen reversed!" Along the way, pupils' reasoning will converge to the idea: "The image of an object through a lens depends on the relative distances among object, lens, and observer". Associated learning model: EXPERIMENT Specific competencies: derived from the experiment model, in agreement with the following learning unit steps I. Evoking - Anticipation: Size of the problem, formulation of hypotheses and planning of experiment. II

  16. Quality Manual

    NASA Astrophysics Data System (ADS)

    Koch, Michael

    The quality manual is the “heart” of every management system related to quality. Quality assurance in analytical laboratories is most frequently linked with ISO/IEC 17025, which lists the standard requirements for a quality manual. In this chapter examples are used to demonstrate, how these requirements can be met. But, certainly, there are many other ways to do this.

  17. Chiral atomically thin films.

    PubMed

    Kim, Cheol-Joo; Sánchez-Castillo, A; Ziegler, Zack; Ogawa, Yui; Noguez, Cecilia; Park, Jiwoong

    2016-06-01

    Chiral materials possess left- and right-handed counterparts linked by mirror symmetry. These materials are useful for advanced applications in polarization optics, stereochemistry and spintronics. In particular, the realization of spatially uniform chiral films with atomic-scale control of their handedness could provide a powerful means for developing nanodevices with novel chiral properties. However, previous approaches based on natural or grown films, or arrays of fabricated building blocks, could not offer a direct means to program intrinsic chiral properties of the film on the atomic scale. Here, we report a chiral stacking approach, where two-dimensional materials are positioned layer-by-layer with precise control of the interlayer rotation (θ) and polarity, resulting in tunable chiral properties of the final stack. Using this method, we produce left- and right-handed bilayer graphene, that is, a two-atom-thick chiral film. The film displays one of the highest intrinsic ellipticity values (6.5 deg μm(-1)) ever reported, and a remarkably strong circular dichroism (CD) with the peak energy and sign tuned by θ and polarity. We show that these chiral properties originate from the large in-plane magnetic moment associated with the interlayer optical transition. Furthermore, we show that we can program the chiral properties of atomically thin films layer-by-layer by producing three-layer graphene films with structurally controlled CD spectra.

  18. Chiral atomically thin films

    NASA Astrophysics Data System (ADS)

    Kim, Cheol-Joo; Sánchez-Castillo, A.; Ziegler, Zack; Ogawa, Yui; Noguez, Cecilia; Park, Jiwoong

    2016-06-01

    Chiral materials possess left- and right-handed counterparts linked by mirror symmetry. These materials are useful for advanced applications in polarization optics, stereochemistry and spintronics. In particular, the realization of spatially uniform chiral films with atomic-scale control of their handedness could provide a powerful means for developing nanodevices with novel chiral properties. However, previous approaches based on natural or grown films, or arrays of fabricated building blocks, could not offer a direct means to program intrinsic chiral properties of the film on the atomic scale. Here, we report a chiral stacking approach, where two-dimensional materials are positioned layer-by-layer with precise control of the interlayer rotation (θ) and polarity, resulting in tunable chiral properties of the final stack. Using this method, we produce left- and right-handed bilayer graphene, that is, a two-atom-thick chiral film. The film displays one of the highest intrinsic ellipticity values (6.5 deg μm-1) ever reported, and a remarkably strong circular dichroism (CD) with the peak energy and sign tuned by θ and polarity. We show that these chiral properties originate from the large in-plane magnetic moment associated with the interlayer optical transition. Furthermore, we show that we can program the chiral properties of atomically thin films layer-by-layer by producing three-layer graphene films with structurally controlled CD spectra.

  19. Thin film strain transducer

    NASA Astrophysics Data System (ADS)

    Rand, J. L.

    1981-01-01

    Previous attempts to develop an appropriate sensor for measuring the stress or strain of high altitude balloons during flight are reviewed as well as the various conditions that must be met by such a device. The design, development and calibration of a transducer which promises to satisfy the necessary design constraints are described. The thin film strain transducer has a low effective modulus so as not to interfere with the strain that would naturally occur in the balloon. In addition, the transducer has a high sensitivity to longitudinal strain (7.216 mV/V/unit strain) which is constant for all temperature from room temperature to -80 C and all strains from 5 percent compression to 10 percent tensile strain. At the same time, the sensor is relatively insensitive (0.27 percent) to transverse forces. The device has a standard 350 ohm impedance which is compatible with available bridge balance, amplification and telemetry instrumentation now available for balloon flight. Recommendations are included for improved coatings to provide passive thermal control as well as model, tethered and full scale flight testing.

  20. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Tetragonal Distortion of InN Thin Films by RBS/Channeling

    NASA Astrophysics Data System (ADS)

    Ding, Zhi-Bo; Wu, Wei; Wang, Kun; Fa, Tao; Yao, Shu-De

    2009-08-01

    Rutherford backscattering and channeling spectrometry (RBS/C) are used to identify the crystalline quality (χ min = 4.87%) of an InN thin film as a function of depth, and make a non-destructive quantitative analysis of the structure, in order to analyze the tetragonal distortion of the InN thin film at the depth determined.

  1. The thin film microwave iris

    NASA Technical Reports Server (NTRS)

    Ramey, R. L.; Landes, H. S.; Manus, E. A.

    1972-01-01

    Development of waveguide iris for microwave coupling applications using thin film techniques is discussed. Production process and installation of iris are described. Iris improves power transmission properties of waveguide window.

  2. Sealing micropores in thin castings

    NASA Technical Reports Server (NTRS)

    Mersereau, G. A.; Nitzschke, G. O.; Ochs, H. L.; Sutch, F. S.

    1981-01-01

    Microscopic pores in thin-walled aluminum castings are sealed by impregnation pretreatment. Technique was developed for investment castings used in hermetically sealed chassic for electronic circuitry. Excessively high leakage rates were previously measured in some chassis.

  3. Interference Colors in Thin Films.

    ERIC Educational Resources Information Center

    Armstrong, H. L.

    1979-01-01

    Explains interference colors in thin films as being due to the removal, or considerable reduction, of a certain color by destructive inteference that results in the complementary color being seen. (GA)

  4. Thin, Flexible IMM Solar Array

    NASA Technical Reports Server (NTRS)

    Walmsley, Nicholas

    2015-01-01

    NASA needs solar arrays that are thin, flexible, and highly efficient; package compactly for launch; and deploy into large, structurally stable high-power generators. Inverted metamorphic multijunction (IMM) solar cells can enable these arrays, but integration of this thin crystalline cell technology presents certain challenges. The Thin Hybrid Interconnected Solar Array (THINS) technology allows robust and reliable integration of IMM cells into a flexible blanket comprising standardized modules engineered for easy production. The modules support the IMM cell by using multifunctional materials for structural stability, shielding, coefficient of thermal expansion (CTE) stress relief, and integrated thermal and electrical functions. The design approach includes total encapsulation, which benefits high voltage as well as electrostatic performance.

  5. Robotic Thin Section Sample Preparation Device for In Situ Planetary Exploration

    NASA Astrophysics Data System (ADS)

    Dreyer, C. B.; Zacny, K.; Skok, J.; Steele, J.; Paulsen, G.; Nakagawa, M.; Schwendeman, J.; Carrell, T.; Szczesiak, M.

    2008-12-01

    Petrographic thin sections are used on Earth to identify minerals. The data from thin sections together with chemical rock data could result in a much better interpretation of planetary geology. A petrographic thin section is a well polished thin (~30 micron) sample of rock mounted on a glass slide. When viewed under a polarizing microscope one can quickly observe minerals from the interference colors. With unpolarized light some textural and structural features can be identified. Making of thin section is an art that takes many years of experience to acquire. All thin sections on Earth have been done manually. The Colorado School of Mines and Honeybee Robotics have been developing a robotic thin section device that one day may be used on planetary surface missions to autonomously slice, grind and polish a piece of rock. In particular, we have been developing methods for rough cutting, epoxy/slide application, and grinding/polishing of a rock to thin section quality. Examination of rock surface finish was done quantitatively using surface roughness measurement and qualitatively by a thin section expert. Here we report on the progress to date.

  6. Rotating thin-shell wormhole

    NASA Astrophysics Data System (ADS)

    Ovgun, A.

    2016-11-01

    We construct a rotating thin-shell wormhole using a Myers-Perry black hole in five dimensions, using the Darmois-Israel junction conditions. The stability of the wormhole is analyzed under perturbations. We find that exotic matter is required at the throat of the wormhole to keep it stable. Our analysis shows that stability of the rotating thin-shell wormhole is possible if suitable parameter values are chosen.

  7. Center for Thin Film Studies

    DTIC Science & Technology

    1991-01-22

    techniques for reducing roughness were developed and tested . Substrate Preparation We deposited Si films by sputtering on a variety of substrates, and...deposition," Mod. Phys. Lett. B 3, 1039 (1989). 41 42 Nd: YAG LASER ABLATION OF BaTiO 3 THIN FILMS *URSULA J. GIBSON, **J.A. RUFFNER,***J.J. MCNALLY...thin films of barium titanate onto a variety of substrates, using picosecond and nanosecond pulsed Nd: YAG lasers. The films were deposited from a hot

  8. Epitaxial growth of high quality WO3 thin films

    DOE PAGES

    Leng, X.; Pereiro, J.; Strle, J.; ...

    2015-09-09

    We have grown epitaxial WO3 films on various single-crystal substrates using radio-frequency (RF) magnetron sputtering. While pronounced surface roughness is observed in films grown on LaSrAlO4 substrates, films grown on YAlO3 substrates show atomically flat surfaces, as demonstrated by atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements. The crystalline structure has been confirmed to be monoclinic by symmetric and skew-symmetric XRD. Furthermore, the dependence of the growth modes and the surface morphology on the lattice mismatch is discussed.

  9. Applications of thin-film sandwich crystallization platforms

    SciTech Connect

    Axford, Danny Aller, Pierre; Sanchez-Weatherby, Juan; Sandy, James

    2016-03-24

    Crystallization via sandwiches of thin polymer films is presented and discussed. Examples are shown of protein crystallization in, and data collection from, solutions sandwiched between thin polymer films using vapour-diffusion and batch methods. The crystallization platform is optimal for both visualization and in situ data collection, with the need for traditional harvesting being eliminated. In wells constructed from the thinnest plastic and with a minimum of aqueous liquid, flash-cooling to 100 K is possible without significant ice formation and without any degradation in crystal quality. The approach is simple; it utilizes low-cost consumables but yields high-quality data with minimal sample intervention and, with the very low levels of background X-ray scatter that are observed, is optimal for microcrystals.

  10. Thin EFG octagons

    NASA Astrophysics Data System (ADS)

    Kalejs, J. P.

    1994-01-01

    Mobil Solar Energy Corporation currently practices a unique crystal growth technology for producing crystalline silicon sheet, which is then cut with lasers into wafers. The wafers are processed into solar cells and incorporated into modules for photovoltaic applications. The silicon sheet is produced using a method known as Edge-defined Film-fed growth (EFG), in the form of hollow eight-sided polygons (octagons) with 10 cm faces. These are grown to lengths of 5 meters and thickness of 300 microns, with continuous melt replenishment, in compact furnaces designed to operate at a high sheet area production area of 135 sq cm/min. The present Photovoltaic Manufacturing Technology (PVMaT) three-year program seeks to advance the manufacturing line capabilities of the Mobil Solar crystal growth and cutting technologies. If successful, these advancements will provide significant reductions in already low silicon raw material usage, improve process productivity, laser cutting throughput and yield, and so lower both individual wafer cost and the cost of module production. This report summarizes the significant technical improvements in EFG technology achieved in Phase 1 of this program. Technical results are reported for each of the three main program areas: (1) thin octagon growth (crystal growth) -- to reduce the thickness of the octagon to an interim goal of 250 microns during Phase 1, with an ultimate goal of achieving 200 micron thicknesses; (2) laser cutting -- to improve the laser cutting process, so as to produce wafers with decreased laser cutting damage at increased wafer throughput rates; and (3) process control and product specification -- to implement advanced strategies in crystal growth process control and productivity designed to increase wafer yields.

  11. Status of Joining Thin Sheet and Thin Wall Tubes of 14YWT

    SciTech Connect

    Hoelzer, David T.; Unocic, Kinga A.; Tang, Wei; Feng, Zhili

    2015-09-18

    Beginning this fiscal year, the FCRD research project initiated an investigation on joining thin sections of the advanced ODS 14YWT ferritic alloy. Friction stir welding (FSW) was investigated as a method to join thin plate and tubing of 14YWT since it is a solid state joining method that has been shown in past studies to be a promising method for joining plates of ODS alloys, such as 14YWT. However, this study will attempt to be the first to demonstrate if FSW can successfully join thin plates and thin wall tubing of 14YWT. In the first FSW attempt, a 1.06 cm thick plate of 14YWT (SM13 heat) was successfully rolled at 1000ºC to the target thickness of 0.1 cm with no edge cracking. This achievement is a highlight since previous attempts to roll 14YWT plates have resulted in extensive cracking. For the FSW run, a pin tool being developed by the ORNL FSW Process Development effort was used. The first FSW run successfully produced a bead-on-plate weld in the 0.1 cm thick plate. The quality of the weld zone appears very good with no evidence of large defects such as cavities. The microstructural characterization study of the bead-on-plate weld zone has been initiated to compare the results of the microstructure analysis with those obtained in the reference microstructural analysis of the 14YWT (SM13 heat) that showed ultra-fine grain size of 0.43 μm and a high number density of ~2-5 nm sizes oxygen-enriched nanoclusters.

  12. Synthesis of thin films and materials utilizing a gaseous catalyst

    DOEpatents

    Morse, Daniel E; Schwenzer, Birgit; Gomm, John R; Roth, Kristian M; Heiken, Brandon; Brutchey, Richard

    2013-10-29

    A method for the fabrication of nanostructured semiconducting, photoconductive, photovoltaic, optoelectronic and electrical battery thin films and materials at low temperature, with no molecular template and no organic contaminants. High-quality metal oxide semiconductor, photovoltaic and optoelectronic materials can be fabricated with nanometer-scale dimensions and high dopant densities through the use of low-temperature biologically inspired synthesis routes, without the use of any biological or biochemical templates.

  13. Reactive ion beam deposition of aluminum nitride thin films

    NASA Astrophysics Data System (ADS)

    Bhat, S.; Ashok, S.; Fonash, S. J.; Tongson}, L.

    1985-07-01

    Aluminum nitride thin films have been prepared at room temperature by reactive ion beam sputtering for potential use as a passivant and diffusion/anneal cap in compound semiconductor technology. The electrical and optical pro-perties of these films have been studied along with the in-fluence of thermal annealing on the material characteristics. The quality of the films has also been found to improve in the presence of atomic hydrogen during the deposition.

  14. On the curvature effect of thin membranes

    NASA Astrophysics Data System (ADS)

    Wang, Duo; Jiao, Xiangmin; Conley, Rebecca; Glimm, James

    2013-01-01

    We investigate the curvature effect of a thin, curved elastic interface that separates two subdomains and exerts a pressure due to a curvature effect. This pressure, which we refer to as interface pressure, is similar to the surface tension in fluid mechanics. It is important in some applications, such as the canopy of parachutes, biological membranes of cells, balloons, airbags, etc., as it partially balances a pressure jump between the two sides of an interface. In this paper, we show that the interface pressure is equal to the trace of the matrix product of the curvature tensor and the Cauchy stress tensor in the tangent plane. We derive the theory for interfaces in both 2-D and 3-D, and present numerical discretizations for computing the quality over triangulated surfaces.

  15. Nanocrystalline silicon based thin film solar cells

    NASA Astrophysics Data System (ADS)

    Ray, Swati

    2012-06-01

    Amorphous silicon solar cells and panels on glass and flexible substrate are commercially available. Since last few years nanocrystalline silicon thin film has attracted remarkable attention due to its stability under light and ability to absorb longer wavelength portion of solar spectrum. For amorphous silicon/ nanocrystalline silicon double junction solar cell 14.7% efficiency has been achieved in small area and 13.5% for large area modules internationally. The device quality nanocrystalline silicon films have been fabricated by RF and VHF PECVD methods at IACS. Detailed characterizations of the materials have been done. Nanocrystalline films with low defect density and high stability have been developed and used as absorber layer of solar cells.

  16. Sorption Properties Of RF Reactive Sputtered TiOx Thin Films

    SciTech Connect

    Boiadjiev, S. I.; Rassovska, M. M.; Lazarova, V. B.

    2007-04-23

    The present research is focused on the sensing behavior of sputtered titanium oxide (TiOx) thin films. In order to deposit TiOx thin films the method of RF reactive sputtering of titanium target in the presence of oxygen as reactive gas is used. RF sputtering technology for thin film deposition has been elaborated on and the technological conditions during deposition have been optimized to obtain films with good quality. Films of various thicknesses have been deposited on quartz resonators in order to use the quartz crystal microbalance (QCM) method for studying their gas sensing properties. The films' microstructure and physical properties are identified by TEM, Raman and laser elipsometry analysis. The ultimate purpose of the research is to apply TiOx thin films in gas sensors. The sorption properties of various sub-stoichiometric and stoichiometric TiO2 thin films to ammonia and other gases are investigated.

  17. Lateral solid-phase epitaxy of oxide thin films on glass substrate seeded with oxide nanosheets.

    PubMed

    Taira, Kenji; Hirose, Yasushi; Nakao, Shoichiro; Yamada, Naoomi; Kogure, Toshihiro; Shibata, Tatsuo; Sasaki, Takayoshi; Hasegawa, Tetsuya

    2014-06-24

    We developed a technique to fabricate oxide thin films with uniaxially controlled crystallographic orientation and lateral size of more than micrometers on amorphous substrates. This technique is lateral solid-phase epitaxy, where epitaxial crystallization of amorphous precursor is seeded with ultrathin oxide nanosheets sparsely (≈10% coverage) deposited on the substrate. Transparent conducting Nb-doped anatase TiO2 thin films were fabricated on glass substrates by this technique. Perfect (001) orientation and large grains with lateral sizes up to 10 μm were confirmed by X-ray diffraction, atomic force microscopy, and electron beam backscattering diffraction measurements. As a consequence of these features, the obtained film exhibited excellent electrical transport properties comparable to those of epitaxial thin films on single-crystalline substrates. This technique is a versatile method for fabricating high-quality oxide thin films other than anatase TiO2 and would increase the possible applications of oxide-based thin film devices.

  18. Sorption Properties Of RF Reactive Sputtered TiOx Thin Films

    NASA Astrophysics Data System (ADS)

    Boiadjiev, S. I.; Lazarova, V. B.; Rassovska, M. M.

    2007-04-01

    The present research is focused on the sensing behavior of sputtered titanium oxide (TiOx) thin films. In order to deposit TiOx thin films the method of RF reactive sputtering of titanium target in the presence of oxygen as reactive gas is used. RF sputtering technology for thin film deposition has been elaborated on and the technological conditions during deposition have been optimized to obtain films with good quality. Films of various thicknesses have been deposited on quartz resonators in order to use the quartz crystal microbalance (QCM) method for studying their gas sensing properties. The films' microstructure and physical properties are identified by TEM, Raman and laser elipsometry analysis. The ultimate purpose of the research is to apply TiOx thin films in gas sensors. The sorption properties of various sub-stoichiometric and stoichiometric TiO2 thin films to ammonia and other gases are investigated.

  19. Growth of magnesium diboride films on 2 inch diameter copper discs by hybrid physical–chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Withanage, Wenura K.; Xi, X. X.; Nassiri, Alireza; Lee, Namhoon; Wolak, Matthäus A.; Tan, Teng; Welander, Paul B.; Franzi, Matthew; Tantawi, Sami; Kustom, Robert L.

    2017-04-01

    Magnesium diboride (MgB2) coating is a potential candidate to replace bulk niobium (Nb) for superconducting radio frequency cavities due to the appealing superconducting properties of MgB2. MgB2 coating on copper may allow cavity operation near 20–25 K as a result of the high transition temperature (T c) of MgB2 and excellent thermal conductivity of Cu. We have grown MgB2 films on 2 inch diameter Cu discs by hybrid physical–chemical vapor deposition for radio frequency characterization. Structural and elemental analyses showed a uniform MgB2 coating on top of a Mg–Cu alloy layer with occasional intrusion of Mg–Cu alloy regions. High T c values of around 37 K and high critical current density (J c) on the order of 107 A cm‑2 at zero field were observed. Radio frequency measurements at 11.4 GHz confirmed a high T c and showed a quality factor (Q 0) much higher than for Cu and close to that of Nb.

  20. Prediction of different crystal structure phases in metal borides: A lithium monoboride analog to MgB2

    NASA Astrophysics Data System (ADS)

    Kolmogorov, Aleksey N.; Curtarolo, Stefano

    2006-05-01

    Modern compound prediction methods can efficiently screen large numbers of crystal structure phases and direct the experimental search for new materials. One of the most challenging problems in alloy theory is the identification of stable phases with a never seen prototype; such predictions do not always follow rational strategies. While performing ab initio data mining of intermetallic compounds we made an unexpected discovery: even in such a well-studied class of systems as metal borides there are previously unknown layered phases comparable in energy to the existing ones. With ab initio calculations we show that the new metal-sandwich (MS) lithium monoboride phases are marginally stable under ambient conditions but become favored over the known stoichiometric compounds under moderate pressures. The MS lithium monoboride exhibits electronic features similar to those in magnesium diboride and is expected to be a good superconductor.