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Sample records for c-axis oriented mgb2

  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. Superconducting MgB2 thin films grown by pulsed laser deposition on Al2O3(0001) and MgO(100) substrates

    NASA Astrophysics Data System (ADS)

    Wang, S. F.; Dai, S. Y.; Zhou, Y. L.; Chen, Z. H.; Cui, D. F.; Xu, J. D.; He, M.; Lu, H. B.; Yang, G. Z.; Fu, G. S.; Han, L.

    2001-11-01

    Superconducting MgB2 thin films were fabricated on Al2O3(0001) and MgO(100) substrates by a two-step method. Boron thin films were deposited by pulsed laser deposition followed by an ex-situ annealing process. Resistance measurements of the deposited MgB2 films show a Tc of 38.6 K for MgB2/Al2O3 and 38.1 K for MgB2/MgO. Atomic force microscopy, scanning electron microscopy and x-ray diffraction were used to study the properties of the films. The results indicate that the MgB2/Al2O3 films consist of well-crystallized grains with a highly c-axis-oriented structure while the MgB2/MgO films have a dense uniform appearance with an unfixed orientation.

  3. Chemical solution deposition of the highly c-axis oriented apatite type lanthanum silicate thin films.

    PubMed

    Hori, Shigeo; Takatani, Yasuhiro; Kadoura, Hiroaki; Uyama, Takeshi; Fujita, Satoru; Tani, Toshihiko

    2015-10-28

    Highly c-axis oriented apatite-type lanthanum silicate (LSO) thin films were fabricated by a simple solution coating method. In the solution coating method, LSO thin films are obtained by crystallization of initially deposited amorphous LSO precursor thin films. The degree of orientation was influenced by the precursor morphologies and a dense LSO precursor led to a high c-axis orientation perpendicular to the substrate. The oriented LSO thin films were composed of columnar grains with a single crystal orientation over the entire film thickness. In-plane orientation was not detected, which indicates that the c-axis orientation of the LSO thin films can be attributed to self-orientation. PMID:26391101

  4. Scaling behavior of mixed-state hall effect in MgB 2 thin films

    NASA Astrophysics Data System (ADS)

    Jung, Soon-Gil; Seong, W. K.; Kang, W. N.; Choi, Eun-Mi; Kim, Heon-Jung; Lee, Sung-Ik; Kim, Hyeong-Jin; Kim, H. C.

    2006-12-01

    The Hall resistivity ( ρxy) and the longitudinal resistivity ( ρxx) in c-axis-oriented superconducting MgB 2 thin films have been investigated in extended fields up to 18 T. We have observed a scaling behavior between the Hall resistivity and the longitudinal resistivity, ρxy=Aρxxβ, where the exponent ( β) is observed to be independent of the temperatures and the magnetic fields. For a wide magnetic field region from 1 to 18 T and a wide temperature region from 10 to 28 K, a universal power law with β = 2.0 ± 0.1 was observed in c-axis-oriented MgB 2 thin films. These results can be well interpreted by using recent models.

  5. Magneto-optical study of the superconducting gap of MgB(2) single crystals.

    PubMed

    Perucchi, A; Degiorgi, L; Jun, J; Angst, M; Karpinski, J

    2002-08-26

    We present magneto-optical reflectivity results in the basal plane of the hexagonal MgB(2). The data were collected on a mosaic of MgB(2) single crystals with T(c)=38 K from the ultraviolet down to the far infrared as a function of temperature and magnetic field oriented along the c axis. In the far infrared, there is a clear signature of the superconducting gap with a gap ratio 2 Delta/k(B)T(c) approximately 1.2, well below the weak-coupling value. The gap is suppressed in an external magnetic field, which is a function of temperature. We extract the upper critical field H(c2) along the c axis. The temperature dependence of H(c2) is compatible with the Helfand-Werthamer behavior. PMID:12190429

  6. Synthesis of c-axis oriented AlN thin films on different substrates: A review

    SciTech Connect

    Iriarte, G.F.

    2010-09-15

    Highly c-axis oriented AlN thin films have been deposited by reactive sputtering on different substrates. The crystallographic properties of layered film structures consisting of a piezoelectric layer, aluminum nitride (AlN), synthesized on a variety of substrates, have been examined. Aluminum nitride thin films have been deposited by reactive pulsed-DC magnetron sputtering using an aluminum target in an Ar/N{sub 2} gas mixture. The influence of the most critical deposition parameters on the AlN thin film crystallography has been investigated by means of X-ray diffraction (XRD) analysis of the rocking curve Full-Width at Half Maximum (FWHM) of the AlN-(0 0 0 2) peak. The relationship between the substrate, the synthesis parameters and the crystallographic orientation of the AlN thin films is discussed. A guide is provided showing how to optimize these conditions to obtain highly c-axis oriented AlN thin films on substrates of different nature.

  7. In vitro dissolution and mechanical behavior of c-axis preferentially oriented hydroxyapatite thin films fabricated by pulsed laser deposition

    PubMed Central

    Kim, Hyunbin; Camata, Renato P.; Chowdhury, Shafiul; Vohra, Yogesh K.

    2010-01-01

    Owing to its resemblance to the major inorganic constituent of bone and tooth, hydroxyapatite is recognized as one of the most biocompatible materials and is widely used in systems for bone replacement and regeneration. In this study the pulsed laser deposition technique was chosen to produce hydroxyapatite with different crystallographic orientations in order to investigate some of the material properties, including its in vitro dissolution behavior, as well as mechanical properties. The crystallographic orientations of hydroxyapatite coatings can be carefully controlled, mainly by varying the energy density of the KrF excimer laser (248 nm) used for deposition. Nanoindentation results showed that highly c-axis oriented hydroxyapatite coatings have higher hardness and Young's modulus values compared with the values of randomly oriented coatings. After 24 h immersion in simulated physiological solution the overall surface morphology of the highly oriented coatings was dramatically altered. The porosity was drastically increased and sub-micron pores were formed throughout the coatings, whereas the average size of the grains in the coatings was not significantly changed. The composition of the textured hydroxyapatite coatings remained essentially unchanged. Their c-axis texture, on the other hand, was rather enhanced with an increase in immersion time. The c-axis oriented hydroxyapatite surfaces are likely to promote preferentially oriented growth through a cyclic process of dissolution and reprecipitation, followed by homoepitaxial growth. The remarkable morphological and microstructural changes after dissolution suggest a capability of highly textured hydroxyapatite as a tissue engineering scaffold with an interconnecting porous network that may be beneficial for cellular activity. PMID:20188868

  8. Microstructure and superconductivity of MgB2 single crystals

    SciTech Connect

    Kim, Kijoon H.P.; Jung, C.U.; Kang, B.W.; Kim, Kyung Hee; Lee, Hyun-Sook; Lee, Sung-Ik; Tamura, N.; Caldwell, W.A.; Patel, J.R.

    2004-07-19

    The hexagonal-disc-shaped MgB2 single crystals were synthesized under the high-pressure conditions. The crystal symmetry, lattice constants as well as the Laue pattern of these single crystals were obtained from X-ray micro-diffraction. A crystallographic mapping showed that the edge and the c-axis of hexagonal-disc shape exactly matched the [1 0 1 bar 0] and [0 0 0 1] directions of the MgB2 phase. This clearly confirmed that above well-shaped single crystals could be excellent samples to study the unsolved direction dependencies of the physical properties.

  9. Fabrication and Characterization of p-Type SnO Thin Film with High c-Axis Preferred Orientation

    NASA Astrophysics Data System (ADS)

    Pei, Yanli; Liu, Wuguang; Shi, Jingtao; Chen, Zimin; Wang, Gang

    2016-08-01

    p-Type tin monoxide (SnO) thin films with high c-axis preferred orientation have been fabricated on quartz substrate via electron-beam evaporation at 280°C. Subsequently, rapid thermal annealing (RTA) was performed in N2 atmosphere at 400°C to 800°C. Their structural, chemical, optical, and electrical properties were investigated by x-ray diffraction analysis, ultraviolet-visible spectroscopy, scanning electron microscopy, x-ray photoelectron spectroscopy, and Hall-effect measurements. The c-axis-oriented films of Sn-rich SnO presented excellent thermal stability up to RTA at 700°C. Both the crystallization and the hole Hall mobility were enhanced with increasing RTA temperature, with Hall mobility of 16 cm2 V-1 s-1 being obtained after RTA at 700°C. It was considered that the presence of defects and low scattering from grain boundaries contributed to this high Hall mobility. RTA annealing temperature above 700°C induced chemical reaction between SnO and the quartz substrate, with a change of the film to amorphous state with Sn4+ formation.

  10. Synthesis and characterization of self-assembled c-axis oriented Bi2Sr3Co2O(y) thin films by the sol-gel method.

    PubMed

    Zhu, Xuebin; Tang, Xianwu; Shi, Dongqi; Jian, Hongbin; Lei, Hechang; Yeoh, Wai Kong; Zhao, Bangchuan; Yang, Jie; Li, Qi; Zheng, Rongkun; Dou, Shixue; Sun, Yuping

    2011-10-01

    Bi(2)Sr(3)Co(2)O(y) thin films are prepared on SrTiO(3) (100), (110) and (111) single crystal substrates using the sol-gel method. All the thin films are c-axis oriented regardless of the orientation of the substrate suggesting self-assembled c-axis orientation, and X-ray photoelectron spectroscopy results give evidence of coexistence of Co(3+) and Co(2+) ions in the derived films. Transmission electronic microscopy observations reveal that all samples are c-axis oriented with no obvious differences for different samples, and the c-axis lattice constant is determined as ~15 Å suggesting the misfit structure. A phenomenological thermodynamic phase diagram for self-assembled c-axis orientation is established for misfit cobaltate-based films using chemical solution deposition. All samples behave like semiconductors due to the coexistence of Co(3+)/Co(2+) ions, and the resistivity at 350 K is ~47, 39 and 17 mΩ cm for the thin films on SrTiO(3) (100), (110) and (111), respectively, whereas the Seebeck coefficient at 300 K is 97, 89 and 77 μV K(-1). The successful attainment of Bi(2)Sr(3)Co(2)O(y) thin films with self-assembled c-axis orientation will provide an effective prototype for investigation of growth mechanisms in complex oxide thin films with a misfit structure. PMID:21850346

  11. c-axis orientation and piezoelectric coefficients of AlN thin films sputter-deposited on titanium bottom electrodes

    NASA Astrophysics Data System (ADS)

    Ababneh, A.; Alsumady, M.; Seidel, H.; Manzaneque, T.; Hernando-García, J.; Sánchez-Rojas, J. L.; Bittner, A.; Schmid, U.

    2012-10-01

    Aluminum nitride (AlN) reactively sputter deposited from an aluminum target is an interesting compound material due to its CMOS compatible fabrication process and its piezoelectric properties. To obtain high piezoelectric coefficients it is a necessary pre-request to synthesize films with c-axis orientation. Besides the influence of sputter conditions on the microstructure of AlN thin films the condition of the substrate surface is another important factor of utmost importance. In this study, the influence of 350 nm thick titanium metallization DC sputter-deposited on SiO2/Si substrates at varying back pressure levels bp,Ti in the range of 2 × 10-3 to 14 × 10-3 mbar on the c-axis orientation and the piezoelectric coefficients of 600 nm thick AlN thin films is investigated. Besides the plasma power for Ti deposition (Pp,Ti = 100 W) the parameters for AlN synthetization are fixed to Pp = 1000 W and bp,AlN = 4 × 10-3 mbar in 100% N2 atmosphere. Basically, the surface roughness of the Ti bottom layer is the dominating factor resulting either in a high degree of c-axis orientation (i.e. at low bp,Ti values) or in an amorphous AlN microstructure (i.e. at high bp,Ti values). Under low pressure conditions, a smooth and dense surface characteristics is achieved due to a higher kinetic energy associated with the adatoms what is especially important at nominally unheated substrate conditions. The piezoelectric coefficient d33 decreases from 2.55 to 1.7 pm -1 when increasing the titanium sputter pressure from 2 × 10-3 to 14 × 10-3 mbar. When decreasing the Ti film thickness to 60 nm and hence, reducing the root mean square roughness by a factor of about 2, the intensity associated with the AlN (0 0 2) peak is increased by a factor of about 1.7 demonstrating the direct impact. Furthermore, the highest values for d33 and d31 (i.e. 3.15 pm V-1 and -1.28 pm V-1) are determined.

  12. Preparation of MgB2 superconducting tapes using electrophoresis

    NASA Astrophysics Data System (ADS)

    Xu, J. D.; Wang, S. F.; Zhou, Y. B.; Zhou, Y. L.; Chen, Z. H.; Cui, D. F.; Lu, H. B.; He, M.; Dai, S. Y.; Yang, G. Z.

    2002-08-01

    Superconducting MgB2/Ta tapes with a critical temperature of 34 K have been prepared successfully by ex situ annealing of electrophoresis-grown boron in the presence of Mg vapour at 920 °C. Scanning electron microscopy was used to examine the surface morphology of the MgB2/Ta tapes, and well-formed MgB2 crystals with sizes up to 2 μm were observed. The x-ray diffraction patterns showed randomly orientated growth of MgB2 phase in the tapes. Estimates using hysteresis loops and the Bean model give a value of 6.8 × 105 A cm-2 for the critical current density.

  13. Preparation of the c-axis oriented AlN film by laser chemical vapor deposition using a newly proposed Al(acac)3 precursor

    NASA Astrophysics Data System (ADS)

    You, Yu; Ito, Akihiko; Tu, Rong; Goto, Takashi

    2013-02-01

    Highly oriented AlN film was prepared on a c-plane sapphire substrate by laser chemical vapor deposition using a newly proposed aluminum acetylacetonate precursor and ammonia gas as source reactants. The c-axis oriented AlN films were obtained on the c-plane sapphire substrate at deposition temperatures from 900 to 1230 K. AlN film prepared at 1047 K showed an epitaxial relation as (//( [//[. The full width at half maximum (FWHM) of the X-ray rocking curve for AlN (0002) plane increased with increasing deposition temperature. The c-axis lattice parameter decreased with increasing deposition temperature.

  14. Ice crystal c-axis orientation and mean grain size measurements from the Dome Summit South ice core, Law Dome, East Antarctica

    NASA Astrophysics Data System (ADS)

    Treverrow, Adam; Jun, Li; Jacka, Tim H.

    2016-06-01

    We present measurements of crystal c-axis orientations and mean grain area from the Dome Summit South (DSS) ice core drilled on Law Dome, East Antarctica. All measurements were made on location at the borehole site during drilling operations. The data are from 185 individual thin sections obtained between a depth of 117 m below the surface and the bottom of the DSS core at a depth of 1196 m. The median number of c-axis orientations recorded in each thin section was 100, with values ranging from 5 through to 111 orientations. The data from all 185 thin sections are provided in a single comma-separated value (csv) formatted file which contains the c-axis orientations in polar coordinates, depth information for each core section from which the data were obtained, the mean grain area calculated for each thin section and other data related to the drilling site. The data set is also available as a MATLAB™ structure array. Additionally, the c-axis orientation data from each of the 185 thin sections are summarized graphically in figures containing a Schmidt diagram, histogram of c-axis colatitudes and rose plot of c-axis azimuths. All these data are referenced by doi:10.4225/15/5669050CC1B3B and are available free of charge at https://data.antarctica.gov.au.<

  15. Highly c-axis-oriented monocrystalline Pb(Zr, Ti)O₃ thin films on si wafer prepared by fast cooling immediately after sputter deposition.

    PubMed

    Yoshida, Shinya; Hanzawa, Hiroaki; Wasa, Kiyotaka; Esashi, Masayoshi; Tanaka, Shuji

    2014-09-01

    We successfully developed sputter deposition technology to obtain a highly c-axis-oriented monocrystalline Pb(Zr, Ti)O3 (PZT) thin film on a Si wafer by fast cooling (~-180°C/min) of the substrate after deposition. The c-axis orientation ratio of a fast-cooled film was about 90%, whereas that of a slow-cooled (~-40°C/min) film was only 10%. The c-axis-oriented monocrystalline Pb(Zr0.5, Ti0.5)O3 films showed reasonably large piezoelectric coefficients, e(31,f) = ~-11 C/m(2), with remarkably small dielectric constants, ϵ(r) = ~220. As a result, an excellent figure of merit (FOM) was obtained for piezoelectric microelectromechanical systems (MEMS) such as a piezoelectric gyroscope. This c-axis orientation technology on Si will extend industrial applications of PZT-based thin films and contribute further to the development of piezoelectric MEMS. PMID:25167155

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

    NASA Astrophysics Data System (ADS)

    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 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.

  17. 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.

  18. Synthesis and properties of highly c-axis oriented PbTiO3 thin films prepared by and MOCVD method

    NASA Astrophysics Data System (ADS)

    Chen, Xian-Tong; Yamane, Hisanori; Kaya, Kiyoshi

    1992-08-01

    Thin films of PbTiO3 were prepared on MgO(100) substrates by chemical vapor deposition using Pb(C2H5)4 (PbEt) and Ti(OC3H7)4 (TTIP) as sources. With decreasing Pb/Ti molar ratio from 1.2 to 1 the degree of c-axis orientation increased. Highly c-axis oriented PbTiO3 thin films were epitaxially grown at 500°C and 2 kPa. The films were transparent and had a refractive index (n) of 2.64 at 632.8 nm which was about 2% lower than that of a single PbTiO3 crystal (n ≈ 2.7). The films prepared on (100)-oriented Pt electrodes deposited on MgO(100) substrates at 600°C and 2 kPa also showed a prominent c-axis orientation and had a dielectric constant of 90.

  19. SrFeO amorphous underlayer for fabrication of c-axis perpendicularly orientated strontium hexaferrite films by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Masoudpanah, S. M.; Ong, C. K.

    2013-09-01

    A thin amorphous SrFeO underlayer on Si(100) substrate was pulse laser deposited as an underlayer for the growth of c-axis perpendicularly oriented strontium hexaferrite (SrFe12O19) films. The amorphous SrFeO underlayer was deposited at different temperatures in the range from room temperature to 700 °C, while the SrFe12O19 film was deposited at 700 °C. The SrFe12O19 films exhibited slightly perpendicular magnetic anisotropy by the rather higher coercivities in perpendicular direction (Hc⊥) than those for the in-plane direction (Hc||), due to the c-axis perpendicular orientation. The magnetization and coercivities of the SrFe12O19 film increase, but the magnetic anisotropy (ΔHc=Hc⊥-Hc||) increases firstly and then decreases, as the SrFeO underlayer deposition temperature increases.

  20. Growth of thin, c-axis oriented Sr-doped LaP3O9 electrolyte membranes in condensed phosphoric acid solutions

    NASA Astrophysics Data System (ADS)

    Hatada, Naoyuki; Takahashi, Kota; Adachi, Yoshinobu; Uda, Tetsuya

    2016-08-01

    Proton-conducting Sr-doped LaP3O9 has potential application as electrolytes in intermediate temperature fuel cells, but reduction of the electrical resistance of the electrolyte membranes is necessary for practical applications. In this study, we focused on reducing the resistance by reducing the electrolyte thickness, while maintaining a preferable microstructure for proton conduction (c-axis orientation and absence of the small-crystal layer). Thin, c-axis oriented Sr-doped LaP3O9 membranes were successfully obtained in condensed phosphoric acid solutions by a novel "two-step precipitation method". In this method, Sr-doped LaP3O9 powder was artificially deposited on the surface of the carbon paper supports as seeds, and then columnar crystals were grown "downward" in the solutions. We expect that this method will be utilized to produce LaP3O9 electrolyte membranes with lower electrical resistance.

  1. The role of the crystal orientation (c-axis) on switching field distribution and the magnetic domain configuration in electrodeposited hcp Co–Pt nanowires

    NASA Astrophysics Data System (ADS)

    Shahid Arshad, Muhammad; Proenca, Mariana P.; Trafela, Spela; Neu, Volker; Wolff, Ulrike; Stienen, Sven; Vazquez, Manuel; Kobe, Spomenka; Žužek Rožman, Kristina

    2016-05-01

    In this report, Co–Pt nanowires (NWs) were produced via potentiostatic electrodeposition into commonly used commercial ordered-alumina and disordered-polycarbonate membranes with similar pore diameters (≈200 nm). The pore diameter of the membranes and the deposition conditions were chosen such that the Co–Pt NWs fabricated into both membranes had a hexagonal close packed (hcp) crystal structure with a crystallographic texturing of the c-axis in the direction perpendicular to the NWs’ long axis; this effect was more pronounced in the alumina membranes. Due to the local fluctuation in electrodeposition conditions (pore diameter, pore shape), we have found a small variation in the c-axis orientations in the plane perpendicular to the NWs’ long axis. Magnetic characterizations suggested that there is uniaxial anisotropy perpendicular to the Co–Pt NWs’ long axis and the small variation in the orientation of the hcp c-axis plays an important role in the switching-field distribution and the magnetic domain structure of the Co–Pt NWs. First order reversal curves (FORCs) revealed week magnetostatic interactions between Co–Pt NWs, thus suggesting that the different pore alignments are not influencing much the magnetic properties in both membranes. The micromagnetic simulation revealed that the transverse-stripe (TS) and longitudinal stripe (LS) domains are energetically most favorable structures in such NWs. This study accentuates the influence of the crystal orientation (c-axis) of the high-anisotropy materials on their functional magnetic properties and thus is of great importance for the fabrication of nanodevices based on such NWs.

  2. c-axis preferential orientation of hydroxyapatite accounts for the high wear resistance of the teeth of black carp (Mylopharyngodon piceus)

    PubMed Central

    Fu, Jimin; He, Chong; Xia, Biao; Li, Yan; Feng, Qiong; Yin, Qifang; Shi, Xinghua; Feng, Xue; Wang, Hongtao; Yao, Haimin

    2016-01-01

    Biological armors such as mollusk shells have long been recognized and studied for their values in inspiring novel designs of engineering materials with higher toughness and strength. However, no material is invincible and biological armors also have their rivals. In this paper, our attention is focused on the teeth of black carp (Mylopharyngodon piceus) which is a predator of shelled mollusks like snails and mussels. Nanoscratching test on the enameloid, the outermost layer of the teeth, indicates that the natural occlusal surface (OS) has much higher wear resistance compared to the other sections. Subsequent X-ray diffraction analysis reveals that the hydroxyapatite (HAp) crystallites in the vicinity of OS possess c-axis preferential orientation. The superior wear resistance of black carp teeth is attributed to the c-axis preferential orientation of HAp near the OS since the (001) surface of HAp crystal, which is perpendicular to the c-axis, exhibits much better wear resistance compared to the other surfaces as demonstrated by the molecular dynamics simulation. Our results not only shed light on the origin of the good wear resistance exhibited by the black carp teeth but are of great value to the design of engineering materials with better abrasion resistance. PMID:27001150

  3. c-axis preferential orientation of hydroxyapatite accounts for the high wear resistance of the teeth of black carp (Mylopharyngodon piceus)

    NASA Astrophysics Data System (ADS)

    Fu, Jimin; He, Chong; Xia, Biao; Li, Yan; Feng, Qiong; Yin, Qifang; Shi, Xinghua; Feng, Xue; Wang, Hongtao; Yao, Haimin

    2016-03-01

    Biological armors such as mollusk shells have long been recognized and studied for their values in inspiring novel designs of engineering materials with higher toughness and strength. However, no material is invincible and biological armors also have their rivals. In this paper, our attention is focused on the teeth of black carp (Mylopharyngodon piceus) which is a predator of shelled mollusks like snails and mussels. Nanoscratching test on the enameloid, the outermost layer of the teeth, indicates that the natural occlusal surface (OS) has much higher wear resistance compared to the other sections. Subsequent X-ray diffraction analysis reveals that the hydroxyapatite (HAp) crystallites in the vicinity of OS possess c-axis preferential orientation. The superior wear resistance of black carp teeth is attributed to the c-axis preferential orientation of HAp near the OS since the (001) surface of HAp crystal, which is perpendicular to the c-axis, exhibits much better wear resistance compared to the other surfaces as demonstrated by the molecular dynamics simulation. Our results not only shed light on the origin of the good wear resistance exhibited by the black carp teeth but are of great value to the design of engineering materials with better abrasion resistance.

  4. c-axis preferential orientation of hydroxyapatite accounts for the high wear resistance of the teeth of black carp (Mylopharyngodon piceus).

    PubMed

    Fu, Jimin; He, Chong; Xia, Biao; Li, Yan; Feng, Qiong; Yin, Qifang; Shi, Xinghua; Feng, Xue; Wang, Hongtao; Yao, Haimin

    2016-01-01

    Biological armors such as mollusk shells have long been recognized and studied for their values in inspiring novel designs of engineering materials with higher toughness and strength. However, no material is invincible and biological armors also have their rivals. In this paper, our attention is focused on the teeth of black carp (Mylopharyngodon piceus) which is a predator of shelled mollusks like snails and mussels. Nanoscratching test on the enameloid, the outermost layer of the teeth, indicates that the natural occlusal surface (OS) has much higher wear resistance compared to the other sections. Subsequent X-ray diffraction analysis reveals that the hydroxyapatite (HAp) crystallites in the vicinity of OS possess c-axis preferential orientation. The superior wear resistance of black carp teeth is attributed to the c-axis preferential orientation of HAp near the OS since the (001) surface of HAp crystal, which is perpendicular to the c-axis, exhibits much better wear resistance compared to the other surfaces as demonstrated by the molecular dynamics simulation. Our results not only shed light on the origin of the good wear resistance exhibited by the black carp teeth but are of great value to the design of engineering materials with better abrasion resistance. PMID:27001150

  5. c-Axis oriented thin Bi 2Sr 2CaCu 2O 8+δ-films prepared by flash- evaporation

    NASA Astrophysics Data System (ADS)

    Stölzel, C.; Huth, M.; Adrian, H.

    1992-12-01

    Superconducting thin films of Bi 2Sr 2CaCu 2O 8+δ were prepared by flash-evaporation. Fine grained powder of the stoichiometry Bi 2Sr 2.5Ca 2Cu 2O y was periodically dropped onto and flash-evaporated by a 1900°C hot tantalum boat and deposited on an unheated <100>-SrTiO 3-substrate. Post-annealing yielded highly c-axis oriented, single phase films, which showed superconductivity up to 81 K. Resistive transitions and critical current densities were measured in magnetic fields up to 6 T with the field direction parallel and perpendicular to the c-axis.

  6. Thickness-controlled synthesis of vertically aligned c-axis oriented ZnO nanorod arrays: Effect of growth time via novel dual sonication sol-gel process

    NASA Astrophysics Data System (ADS)

    Firdaus Malek, Mohd; Hafiz Mamat, Mohamad; Soga, Tetsuo; Rahman, Saadah Abdul; Abu Bakar, Suriani; Syakirin Ismail, Ahmad; Mohamed, Ruziana; Alrokayan, Salman A. H.; Khan, Haseeb A.; Rusop Mahmood, Mohamad

    2016-01-01

    Zinc-oxide (ZnO) nanorod arrays were successfully prepared by using dual sonication sol-gel process. Field emission scanning electron microscopy revealed that the nanorods exhibited a hexagonal structure with a flat-end facet. The nanorods displayed similar surface morphologies and grew uniformly on the seed layer substrate, with the average diameter slightly increasing to the range of 65 to 80 nm after being immersed for varying growth times. Interestingly, thickness measurements indicated that the thicknesses of the samples increased as the growth time was extended. In addition, the X-ray diffraction spectra indicated that the prepared ZnO nanorods with a hexagonal wurtzite structure grew preferentially along the c-axis. Therefore, we can conclude that the diameter, length, and orientation of the ZnO nanorod arrays along the c-axis are controllable by adjusting the growth time, motivating us to further explore the growth mechanisms of ZnO nanorods.

  7. Impact of titanium layer and silicon substrate properties on the microstructure of c-axis oriented AlN thin films

    NASA Astrophysics Data System (ADS)

    Wistrela, E.; Bittner, A.; Schmid, U.

    2015-05-01

    Highly c-axis orientated sputter deposited aluminium nitride (AlN) thin films are widely used as piezoelectric layers in micro-electro-mechanical systems (MEMS). Therefore, stable and reliable deposition and patterning of the AlN thin films in the fabrication process of such devices is of utmost importance. In this work, we study the wet chemical etching behavior of highly c-axis oriented AlN layers as well as the film-related residuals after the etching procedure. To investigate the impact of the underlying material on the quality of the AlN films they are either deposited on pure silicon (Si) substrates or on Si substrates covered with a sputter-deposited thin titanium (Ti) film. The 620 nm thin AlN layers are synthesized simultaneously onto both substrate types and subsequently wet-chemical etched in a phosphorous acid based etching solution at a temperature of 80°C. We demonstrate a significant difference in surface roughness of the untreated AlN films when sputter-deposited on Ti or pure Si. Furthermore, we analyze the piezoelectric properties of the deposited films. Although the XRD analyses indicate a high c-axis orientated wurtzite structure for all deposited films, the absolute value of the piezoelectric coefficients |d33| of AlN thin films synthesized on Ti are 0.4-4.3 pC/N, whereas corresponding values of 5.2-6 pC/N are determined at those deposited on pure Si substrates,. Finally, after wet chemically etching a porous, but homogeneous AlN microstructure is observed for samples synthesized onto Ti layers, whereas AlN layers deposited directly on Si substrate are either etched very inhomogenously or almost completely with some etch resistant pyramidal-shaped residues. This might be due to a local change in polarity within the AlN layer.

  8. Fast epitaxial growth of a-axis- and c-axis-oriented YBa 2Cu 3O 7- δ films on (1 0 0) LaAlO 3 substrate by laser chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Pei; Ito, Akihiko; Tu, Rong; Goto, Takashi

    2011-02-01

    a-axis- and c-axis-oriented YBa2Cu3O7-δ (YBCO) films were epitaxially grown on (1 0 0) LaAlO3 substrates by laser chemical vapor deposition. The preferred orientation in the YBCO film changed from the a-axis to the c-axis with increasing laser powers from 77 to 158 W (the deposition temperatures from 951 to 1087 K). The a-axis-oriented YBCO film showed in-plane epitaxial growth of YBCO [0 0 1]//LAO [0 0 1], and the c-axis-oriented YBCO film showed that of YBCO [0 1 0]//LAO [0 0 1]. A c-axis-oriented YBCO film with a high critical temperature of 90 K was prepared at a deposition rate of 90 μm h-1, about 2-1000 times higher than that of metalorganic chemical vapor deposition.

  9. Epitaxial c-axis oriented BaTiO{sub 3} thin films on SrTiO{sub 3}-buffered Si(001) by atomic layer deposition

    SciTech Connect

    Ngo, Thong Q.; McDaniel, Martin D.; Ekerdt, John G.; Posadas, Agham B.; Demkov, Alexander A.; Hu, Chengqing; Yu, Edward T.; Bruley, John

    2014-02-24

    Atomic layer deposition (ALD) of epitaxial c-axis oriented BaTiO{sub 3} (BTO) on Si(001) using a thin (1.6 nm) buffer layer of SrTiO{sub 3} (STO) grown by molecular beam epitaxy is reported. The ALD growth of crystalline BTO films at 225  °C used barium bis(triisopropylcyclopentadienyl), titanium tetraisopropoxide, and water as co-reactants. X-ray diffraction (XRD) reveals a high degree of crystallinity and c-axis orientation of as-deposited BTO films. Crystallinity is improved after vacuum annealing at 600  °C. Two-dimensional XRD confirms the tetragonal structure and orientation of 7–20-nm thick films. The effect of the annealing process on the BTO structure is discussed. A clean STO/Si interface is found using in-situ X-ray photoelectron spectroscopy and confirmed by cross-sectional scanning transmission electron microscopy. The capacitance-voltage characteristics of 7–20 nm-thick BTO films are examined and show an effective dielectric constant of ∼660 for the heterostructure.

  10. Preparation of highly c-axis oriented AlN thin films on Hastelloy tapes with Y2O3 buffer layer for flexible SAW sensor applications

    NASA Astrophysics Data System (ADS)

    Peng, Bin; Jiang, Jianying; Chen, Guo; Shu, Lin; Feng, Jie; Zhang, Wanli; Liu, Xinzhao

    2016-02-01

    Highly c-axis oriented aluminum nitrade (AlN) films were successfully deposited on flexible Hastelloy tapes by middle-frequency magnetron sputtering. The microstructure and piezoelectric properties of the AlN films were investigated. The results show that the AlN films deposited directly on the bare Hastelloy substrate have rough surface with root mean square (RMS) roughness of 32.43nm and its full width at half maximum (FWHM) of the AlN (0002) peak is 12.5∘. However, the AlN films deposited on the Hastelloy substrate with Y2O3 buffer layer show smooth surface with RMS roughness of 5.46nm and its FWHM of the AlN (0002) peak is only 3.7∘. The piezoelectric coefficient d33 of the AlN films deposited on the Y2O3/Hastelloy substrate is larger than three times that of the AlN films deposited on the bare Hastelloy substrate. The prepared highly c-axis oriented AlN films can be used to develop high-temperature flexible SAW sensors.

  11. Influence of c-axis orientation and scandium concentration on infrared active modes of magnetron sputtered ScxAl1-xN thin films

    NASA Astrophysics Data System (ADS)

    Mayrhofer, P. M.; Eisenmenger-Sittner, C.; Euchner, H.; Bittner, A.; Schmid, U.

    2013-12-01

    Doping of wurtzite aluminium nitride (AlN) with scandium (Sc) significantly enhances the piezoelectric properties of AlN. ScxAl1-xN thin films with different Sc concentrations (x = 0 to 0.15) were deposited by DC reactive magnetron sputtering. Infrared (IR) absorbance spectroscopy was applied to investigate the Sc concentration dependent shift of the IR active modes E1(TO) and A1(TO). These results are compared to ab initio simulations, being in excellent agreement with the experimental findings. In addition, IR spectroscopy is established as an economical and fast method to distinguish between thin films with a high degree of c-axis orientation and those exhibiting mixed orientations.

  12. The role of starch doping on the superconducting properties of MgB2

    NASA Astrophysics Data System (ADS)

    Tripathi, D.; Moharana, S. S.; Dey, T. K.

    2014-09-01

    The effect of different amount of starch addition on structural and superconducting properties of superconducting MgB2 has been discussed. The samples are synthesized by conventional solid reaction method. XRD analysis confirms that carbon, which is produced during synthesis due to decomposition of starch, is substituted in the B sites. High resolution transmission electron microscope (HRTEM) picture infers the presence of large number of nanosized precipitates (size ∼10-20 nm) in starch doped MgB2 pellets. Superconducting transition temperature (Tc0) of MgB2 (∼38 K) decreases due to the addition of starch. The critical current density (Jc) of starch added MgB2 samples, however, shows significant improvement in whole field range, especially at high magnetic fields. MgB2 added with 2 wt.% of starch gives the best performance amongst the investigated samples and at 20 K displays ∼42 times enhancement in Jc under 4 T field compared to that for pure MgB2. The field dependence of the critical current density (Jc) of starch added MgB2 is explained fairly well in terms of collective pinning theory. An excellent scaling of the reduced critical current density, Jn(=Jc/Jc(0)) and the reduced field hn (=H/H0) is observed for both pure and starch added MgB2 polycrystalline pellets at different temperatures, where Jc(0) and H0 are the fitting parameters obtained from collective pinning model. However, the normalized pinning force density (FP/Fp(max)) of starch added samples does not display any scaling, but shows an excellent correspondence with modified Dew-Hughes expression. The presence of anisotropy and grain orientation is thought to be responsible for the absence of scaling of normalized pinning force density in starch added MgB2 pellets.

  13. Measurement of c-axis angular orientation in calcite (CaCO3) nanocrystals using X-ray absorption spectroscopy

    PubMed Central

    Gilbert, P. U. P. A.; Young, Anthony; Coppersmith, Susan N.

    2011-01-01

    We demonstrate that the ability to manipulate the polarization of synchrotron radiation can be exploited to enhance the capabilities of X-ray absorption near-edge structure (XANES) spectroscopy, to include linear dichroism effects. By acquiring spectra at the same photon energies but different polarizations, and using a photoelectron emission spectromicroscope (PEEM), one can quantitatively determine the angular orientation of micro- and nanocrystals with a spatial resolution down to 10 nm. XANES-PEEM instruments are already present at most synchrotrons, hence these methods are readily available. The methods are demonstrated here on geologic calcite (CaCO3) and used to investigate the prismatic layer of a mollusk shell, Pinctada fucata. These XANES-PEEM data reveal multiply oriented nanocrystals within calcite prisms, previously thought to be monocrystalline. The subdivision into multiply oriented nanocrystals, spread by more than 50°, may explain the excellent mechanical properties of the prismatic layer, known for decades but never explained. PMID:21693647

  14. Growth of c-axis-oriented Bi 3.15Nd 0.85Ti 3O 12 thin films for ferroelectric memory applications

    NASA Astrophysics Data System (ADS)

    Giridharan, N. V.; Madeswaran, S.; Jayavel, R.

    2005-02-01

    Highly c-axis-oriented Bi 3.15Nd 0.85Ti 3O 12 (BNdT) thin films were grown on Pt/TiO 2/SiO 2/Si (1 0 0) substrates using the method of metalorganic sol decomposition by optimizing the parameters such as excess bismuth concentration, crystallization temperature, film thickness and crystallization ambient. The BNdT film capacitor with a top Pt electrode showed a large remnant polarization (2 Pr) of 80 μC/cm 2 at an applied voltage of 10 V and exhibited a fatigue-free behaviour up to 2×10 9 switching cycles at a frequency of 1 kHz. These experimental results reveal that Nd-substituted Bi 4Ti 3O 12 thin films can be used as capacitors in ferroelectric access memories.

  15. Enhanced thermoelectric performance in c-axis oriented Ca3Co4O9 films by Ag addition through multiple annealing

    NASA Astrophysics Data System (ADS)

    Liu, Shengman; Zhu, Caixia; Ge, Xianghong; Wang, Tingtai; Feng, Junlan; Yang, Linfeng

    2016-06-01

    The c-axis oriented Ca3Co4O9 (CCO) films without and with 5 wt.% Ag addition were prepared by chemical solution deposition (CSD) through multiple annealing processing on single crystal LaAlO3 (001) substrates. With Ag addition, the resistivity at 300 K is decreased to 2.25 mΩṡcm, the Seebeck coefficient at 300 K is enhanced to 106 μV/K and the power factor at 300 K can reach as high as 0.5 mWṡK‑1ṡm‑2, which is the highest value among CCO films prepared by CSD. The results suggest that Ag addition is a very effective route to improve the thermoelectric properties of CCO films through multiple annealing processing.

  16. Defect free C-axis oriented zinc oxide (ZnO) films grown at room temperature using RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Kunj, Saurabh; Sreenivas, K.

    2016-05-01

    Radio frequency Magnetron sputtering technique was employed to fabricate ZnO thin films on quartz substrate at room temperature. The effect of varying oxygen to argon (O2/Ar) gas ratio on the structural and photoluminescence properties of the film is analyzed.X-ray diffraction (XRD) spectra reveals the formation of hexagonal wurtzite structured ZnO thin films with preferred orientation along (002) plane. Photoluminescence (PL) characterization reveals the preparation of highly crystalline films exhibiting intense Ultraviolet (UV) emission with negligible amount of defects as indicated by the absence of Deep Level Emission (DLE) in the PL spectra.

  17. Synthesis and characterization of 10 nm thick piezoelectric AlN films with high c-axis orientation for miniaturized nanoelectromechanical devices

    SciTech Connect

    Zaghloul, Usama; Piazza, Gianluca

    2014-06-23

    The scaling of piezoelectric nanoelectromechanical systems (NEMS) is challenged by the synthesis of ultrathin and high quality piezoelectric films on very thin electrodes. We report the synthesis and characterization of the thinnest piezoelectric aluminum nitride (AlN) films (10 nm) ever deposited on ultrathin platinum layers (2–5 nm) using reactive sputtering. X-ray diffraction, high-resolution transmission electron microscopy, and fast Fourier transform analyses confirmed the proper crystal orientation, fine columnar texture, and the continuous lattice structure within individual grains in the deposited AlN nanometer thick films. The average extracted d{sub 31} piezoelectric coefficient for the synthesized films is −1.73 pC/N, which is comparable to the reported values for micron thick and highly c-axis oriented AlN films. The 10 nm AlN films were employed to demonstrate two different types of optimized piezoelectric nanoactuators. The unimorph actuators exhibit vertical displacements as large as 1.1 μm at 0.7 V for 25 μm long and 30 nm thick beams. These results have a great potential to realize miniaturized NEMS relays with extremely low voltage, high frequency resonators, and ultrasensitive sensors.

  18. High-coercivity, c-axis oriented Nd{sub 2}Fe{sub 14}B films grown by molecular beam epitaxy

    SciTech Connect

    Keavney, D.J.; Fullerton, E.E.; Pearson, J.E.; Bader, S.D.

    1996-12-31

    Thin films of Nd{sub 2}Fe{sub 14}B with a c-axis orientation and bulk- like magnetic properties were grown with thickness as low as 300 {Angstrom}. They were grown on single-crystal MgO(100) wafers overcoated with epitaxial Mo(100) buffer layers. The 2-14-1 phase were crystallized either by sequential deposition or co-deposition of Fe, Nd, and B from pure elemental evaporation sources onto 600-700 C substrates. Structure of each film was characterized in-situ with RHEED and ex-situ with XRD. For the sequentially deposited films, the in-plane saturation field is 60-70 kOe at 300 K, consistent with the bulk anisotropy field of 73 kOe. The spin-reorientation transition at 135 K can also be clearly seen in the in-plane and out-of-plane magnetization vs temperature data. The out-of-plane coercivities range from 15-20 kOe at 20 K and 3-8 kOe at 300 K. Co-deposition results in a multiphase structure, with Nd{sub 2}Fe{sub 14}B now the minority phase. The multiphase structure results in reduced perpendicular anisotropy.

  19. YBa2Cu3O(7-delta)/Au/Nb sandwich geometry SNS weak links on c-axis oriented YBa2Cu3O(7-delta)

    NASA Technical Reports Server (NTRS)

    Foote, M. C.; Hunt, B. D.; Bajuk, L. J.

    1991-01-01

    Sandwich geometry superconductor/normal metal/superconductor structures have been fabricated on LaAlO3 and cubic zirconia with laser-ablated, c-axis-oriented YBa2Cu3O(7-delta) base electrodes, 100-600 A of Au, and Nb counter electrodes, all formed in situ without breaking vacuum. Junctions range in size from 5 to 50 micron on a side. Four probe I-V measurements at 4.2 K show RnA products as low as 6 x 10 to the -9th sq cm and critical current densities up to 5.2 kA/sq cm. AC Josephson steps were observed with the application of 10-GHz radiation. The temperature dependence of Jc and the observation of the AC Josephson effect suggest that true supercurrents are present and that they do indeed represent the characteristics of the YBa2Cu3O(7-delta)/Au/Nb structure. The best results were obtained when the devices were annealed at about 450 C in O2 for 30 min after Au deposition.

  20. The impact of argon admixture on the c-axis oriented growth of direct current magnetron sputtered ScxAl1-xN thin films

    NASA Astrophysics Data System (ADS)

    Mayrhofer, P. M.; Eisenmenger-Sittner, C.; Stöger-Pollach, M.; Euchner, H.; Bittner, A.; Schmid, U.

    2014-05-01

    The piezoelectric properties of wurtzite aluminium nitride (w-AlN) are enhanced by alloying with scandium (Sc), thus offering superior properties for applications in micro electro-mechanical systems devices. ScxAl1-xN thin films have been prepared by DC reactive magnetron sputtering on Si (100) substrates from a single target. When targeting a concentration range from x = 0 up to x = 0.15, the preparation conditions have been optimized by varying the Ar/N2 ratio in the sputtering gas. To incorporate an increasing Sc concentration, a higher Ar/N2 ratio has to be applied during the deposition process. Hence, the argon concentration in the sputtering gas becomes a crucial parameter for microstructure-related parameters. To determine phase purity, degree of c-axis orientation, lattice parameter, and grain size, the ScxAl1-xN thin films were investigated by techniques, such as scanning electron microscopy, transmission electron microscopy, and X-ray diffraction.

  1. Transparent and conducting intrinsic ZnO thin films prepared at high growth-rate with c-axis orientation and pyramidal surface texture

    NASA Astrophysics Data System (ADS)

    Mondal, Praloy; Das, Debajyoti

    2013-12-01

    The growth of ZnO thin films has been optimized by adjusting the intrinsic ion vacancies, by controlling the RF power applied to the plasma in magnetron sputtering. Preferred c-axis oriented intrinsic ZnO films with largest grain size and a hexagonal wurtzite structure, exhibiting high room temperature conductivity, σ ∼ 1.37 S/cm, high transparency, ∼80-90% within 450-800 nm and ∼90-96% within 800-1900 nm, low reflectance (<5% in the visible range) was obtained at a very high deposition rate ∼214 nm/min, at 300 °C, by maintaining higher concentration of Zn interstitials or singly ionized oxygen vacancy, corresponding to an optimized RF power of 200 W. Films have lowest internal stress, smallest dissipation factor defined as ɛ2/ɛ1, and the specific pyramidal surface texture creates enough surface roughness that helps to improve the light scattering from the surface and makes it suitable for efficient use in thin-film silicon solar cells. With increasing RF power beyond 200 W, the Zn-O bond length reduces promptly and the internal stress increases monotonically approaching toward a virtual saturation. The preferred crystallographic alignment shifts from (0 0 2) to (1 0 3), i.e., from c to a-axis orientation, as the surface energy of ZnO crystal changes due to the increase in the Zn-to-ZnO ion ratio in the plasma caused by the plausible de-oxygenation of ZnO at elevated RF powers. Oxygen deficient ZnO films having the flower-like surface texture prepared with a very high deposition rate ∼554 nm/min at 500 W could indeed make the material suitable for gas and chemical sensing applications.

  2. Direct observation of charge re-distribution in a MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Wu, Sheng Yun; Shih, Po-Hsun; Ji, Jhong-Yi; Chan, Ting-Shan; Yang, Chun Chuen

    2016-04-01

    To study the origin of negative thermal expansion effects near the superconducting transition temperature TC in MgB2, low-temperature high-energy synchrotron radiation x-ray diffraction was used to probe the charge redistribution near the boron atoms. Our results reveal that the in-plane hole-distribution of B- hops through the direct orbital overlap of Mg2+ along the c-axis at 50 K and is re-distributed out-of-plane. This study shows that the out-of-plane π-hole distribution plays a dominant role in the possible origin of superconductivity and negative thermal effects in MgB2.

  3. 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.

  4. Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

    SciTech Connect

    Kushvaha, S. S.; Kumar, M. Senthil; Maurya, K. K.; Dalai, M. K.; Sharma, Nita D.

    2013-09-15

    Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 °C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 °C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE.

  5. Anisotropy of Superconducting MgB2 as Seen in Electron Spin Resonance and Magnetization Data

    NASA Astrophysics Data System (ADS)

    Simon, F.; Jánossy, A.; Fehér, T.; Murányi, F.; Garaj, S.; Forró, L.; Petrovic, C.; Bud'Ko, S. L.; Lapertot, G.; Kogan, V. G.; Canfield, P. C.

    2001-07-01

    We observed the conduction electron spin resonance (CESR) in fine powders of MgB2 both in the superconducting and normal states. The Pauli susceptibility is χs = 2.0×10-5 emu/mole in the temperature range of 450 to 600 K. The spin relaxation rate has an anomalous temperature dependence. The CESR measured below Tc at several frequencies suggests that MgB2 is a strongly anisotropic superconductor with the upper critical field, Hc2, ranging between 2 and 16 T. The high-field reversible magnetization data of a randomly oriented powder sample are well described assuming that MgB2 is an anisotropic superconductor with Habc2/Hcc2~6-9.

  6. Superconducting gap parameters of MgB 2 obtained on MgB 2/Ag and MgB 2/In junctions

    NASA Astrophysics Data System (ADS)

    Plecenik, A.; Beňačka, Š.; Kúš, P.; Grajcar, M.

    2002-03-01

    MgB 2 superconducting wires with the critical temperature Tc approaching 40 K were used for the preparation of MgB 2/Ag and MgB 2/In junctions. The differential conductance vs. voltage characteristics of N-S junctions exhibit a clear contribution of the Andreev reflection. Using a modified BTK theory for s-wave superconductors two order parameters Δdirty≈4 meV and Δ3D≈2.6 meV were determined from the temperature dependencies. Surprisingly, the larger order parameter Δdirty vanishes at a lower temperature T c dirty≈20 K compared with the smaller one Δ3D with Tc≈38 K. Both the magnitudes of the order parameters and their critical temperatures are in good agreement with theoretical calculations of electron-phonon coupling in MgB 2 carried out by Liu et al. [cond-mat/0103570 (2001)].

  7. In-plane and out-of-plane dissipation in {ital c}-axis-oriented (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O {sub x} silver-sheathed tapes

    SciTech Connect

    Xu, G.; Sun, Y.; Du, J. |; Zhou, Y.; Zeng, R.; Fu, X.; Hua, P.

    1997-02-01

    The temperature dependence of the out-of-plane and in-plane resistance of a c-axis-oriented (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O {sub x} silver-sheathed tape with high critical current density (J{sub c}{gt}2{times}10{sup 4} A/cm{sup 2}, 77 K, 0 T) has been investigated under applied fields up to 0.9 T. It is found that the in-plane and the out-of-plane resistance transitions are quite different: (1) The out-of-plane zero resistance temperature is much higher than the in-plane one, i.e., T{sub c}{sup ab}(H){lt}T{sub c}{sup c}(H), and the difference increases with magnetic field; (2) the out-of-plane zero resistance temperature corresponds to the c-axis decoupling temperature. These phenomena are attributed to different dissipation mechanisms. The in-plane dissipation at low temperature results from the thermally activated flux{endash}flow, while the out-of-plane dissipation originates from the Josephson junction dissipation of weakly coupled c-axis grain boundaries and/or intrinsic Josephson junctions.{copyright} {ital 1997 American Institute of Physics.}

  8. High quality MgB2 thick films and large-area films fabricated by hybrid physical chemical vapor deposition with a pocket heater

    NASA Astrophysics Data System (ADS)

    Wang, S. F.; Chen, Ke; Lee, C.-H.; Soukiassian, A.; Lamborn, D. R.; DeFrain, R.; Redwing, J. M.; Li, Qi; Schlom, D. G.; Xi, X. X.

    2008-08-01

    A hybrid physical-chemical vapor deposition process using a pocket heater was developed for the growth of high quality epitaxial large-area MgB2 thin films and c-axis textured MgB2 thick films. This technique is able to independently control the substrate and Mg source temperatures and maintain sufficient Mg overpressure to ensure phase stability. The two-inch large-area MgB2 thin films showed uniform superconducting properties with the superconducting transition temperature Tc of about 40 K, residual resistivity ratio (RRR) of about 10, and critical current density Jc of about 107 A cm-2 (0 T, 5 K). The thick films (~10 µm) on sapphire substrates showed a maximum Tc of 40 K and RRR of 15, and a Jc of 1.6 × 106 A cm-2 at low applied magnetic fields even at 20 K. High quality thick films also have been obtained on metal substrates.

  9. Bending strain tolerance of MgB2 superconducting wires

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    This work describes the strain tolerance of MgB2 superconductors subjected to variable bending stresses. Bending of MgB2 wire was done at room temperature in different modes: (i) direct bending of straight annealed samples to variable diameters and by (ii) indirect bending by straightening of bent and annealed samples. I c-bending strain characteristics of samples made by in situ PIT and by the internal magnesium diffusion (IMD) process were measured at 4.2 K. The results show a good agreement between the direct and indirect bending mode, which allows easier estimation of limits important for the winding process of MgB2 superconductors with brittle filaments. A comparison of MgB2 wires made by in situ PIT and IMD processes showed improved strain tolerance for IMD due to better grain connectivity the low annealing temperature, which does not appear to reduce the mechanical strength of sheath material.

  10. Influence of c-axis orientation and scandium concentration on infrared active modes of magnetron sputtered Sc{sub x}Al{sub 1−x}N thin films

    SciTech Connect

    Mayrhofer, P. M.; Bittner, A.; Schmid, U.; Eisenmenger-Sittner, C.; Euchner, H.

    2013-12-16

    Doping of wurtzite aluminium nitride (AlN) with scandium (Sc) significantly enhances the piezoelectric properties of AlN. Sc{sub x}Al{sub 1−x}N thin films with different Sc concentrations (x = 0 to 0.15) were deposited by DC reactive magnetron sputtering. Infrared (IR) absorbance spectroscopy was applied to investigate the Sc concentration dependent shift of the IR active modes E{sub 1}(TO) and A{sub 1}(TO). These results are compared to ab initio simulations, being in excellent agreement with the experimental findings. In addition, IR spectroscopy is established as an economical and fast method to distinguish between thin films with a high degree of c-axis orientation and those exhibiting mixed orientations.

  11. Investigation on orientation, epitaxial growth and microstructure of a-axis-, c-axis-, (103)/(110)- and (113)-oriented YBa2Cu3O7-δ films prepared on (001), (110) and (111) SrTiO3 single crystal substrates by spray atomizing and coprecipitating laser chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Pei; Wang, Ying; Huang, Zhi liang; Mao, Yangwu; Xu, Yuan Lai

    2015-04-01

    a-axis-, c-axis-, (103)/(110)- and (113)-oriented YBa2Cu3O7-δ (YBCO) films were pareared by spray atomizing and coprecipitating laser chemical vapor deposition. The surface of the a-axis-oriented YBCO film consisted of rectangular needle-like grains whose in-plane epitaxial growth relationship was YBCO [100] // STO [001] (YBCO [001] // STO [100]), and that of the c-axis-oriented YBCO film consisted of dense flat surface with epitaxial growth relationship of YBCO [001] // STO [001] (YBCO [100] //STO [100]). For the (103)/(110)-oriented and (113)-oriented YBCO film, they showed wedge-shaped and triangle-shaped grains, with corresponding in-plane epitaxial growth relationship of YBCO [110] // STO [110] (YBCO [010] // STO [010]) and YBCO [100] // STO [100] (YBCO [113] // STO [111], respectively.

  12. Flux pinning and the paramagnetic Meissner effect in MgB2 with TiO2 inclusions

    NASA Astrophysics Data System (ADS)

    Prokhorov, V. G.; Svetchnikov, V. L.; Park, J. S.; Kim, G. H.; Lee, Y. P.; Kang, J.-H.; Khokhlov, V. A.; Mikheenko, P.

    2009-04-01

    The mixed-state superconducting properties of bulk MgB2+2 at.%TiO2, prepared by the in situ solid state reaction, have been investigated. The high-resolution transmission electron microscopy study reveals that the sample has combined microstructures, consisting of regions with small- and large-size MgB2 grains, and the MgO inclusions. The particular grains are separated by thin TiB2 interlayers along the c axis. Analysis on the mixed-state parameters, such as the upper critical field, the coherence length and the Ginzburg-Landau parameter κ, proves that the MgB2+2 at.% TiO2 belongs to a high-κ type-II superconductor in the dirty limit. The non-uniformly scaled microstructure results in an unusual (close to the double peak) magnetic field dependence of the pinning force density. The field-cooled temperature dependence of magnetic moment exhibits a transition of the sample to the paramagnetic state at certain applied magnetic fields, which is treated as a manifestation of the paramagnetic Meissner effect. The experimental results are discussed on the basis of modern theoretical approaches.

  13. Critical Currents of MgB2 Wire and Tape in Magnetic Field under Bending Deformations

    NASA Astrophysics Data System (ADS)

    Abin, D. A.; Mineev, N. A.; Osipov, M. A.; Pokrovsky, S. V.; Rudnev, I. A.

    Nowadays MgB2 wires are attractive for designing real devices like motors and magnets. The latest production technologies allow to increase critical current value of wires. However, there is a problem of wire performance degradation under bending strain. Thus, there is a problem of manufacturing solenoids with small diameters, especially from ex situ MgB2 wires produced by powder-in-tube (PIT) technology. In this work, influence of bending on critical current Ic multifilament PIT ex situ MgB2 tape and wire has been studied. Critical current dependencies on external magnetic field Ic(H) were measured at liquid helium temperature in the range of fields from 2.5 T up to 8 T. Measurements were carried out in parallel (H||), and perpendicular (H⊥) orientation of external magnetic field to the sample surface. Voltage current characteristics (V-I) on tape samples were measured with bending on diameters D=30; 40; 60; 70; 80; 90;100 mm. It was shown that critical current density (Jc) decreases by 24% and by 28% for tape and wire respectively with decreasing bending diameter from 100 mm to 60 mm. It was found that the tape still had superconductive properties even with bending diameter D=30 mm, but its Jc decreased by 44% in comparison with Jc(D=100 mm). One more feature that was found is the appearance of resistive component in the voltage current characteristics for all bend diameters in magnetic fields H>3.5 T.

  14. Substitution of Mn for Mg in MgB_2*

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, Michael D.; Johnston, David C.; Miller, Lance L.; Hill, Julienne M.

    2002-03-01

    The study of solid solutions in which the Mg in MgB2 is partially replaced by magnetic 3d or 4f atoms can potentially reveal important information on the superconducting state of MgB_2. As an end-member of the hypothetical Mg_1-xMn_xB2 system, MnB2 is isostructural with MgB2 and is an antiferromagnet below TN = 760 K which becomes canted at 157 K. A previous study by Moritomo et al.[1] examined the structure and properties of multi-phase samples with 0.01<= x<= 0.15. We attempted to obtain single-phase samples with x<= 0.25 by reacting the constituent elements in sealed Ta tubes and/or using prereacted MnBx synthesized using an arc furnace. The results of x-ray diffraction and magnetization measurements on those samples will be presented. * Supported by the USDOE under contract no. W-7405-Eng-82. [1] "Mn-substitution effects on MgB2 superconductor", Y.Moritomo et al. J. Phys. Soc. Japan b70, 1889 (2001).; “Effects of transition metal doping in MgB2 superconductor", Y. Moritomo at al. arXiv:cond-mat/0104568.

  15. Oxygen Segregation and Ordering in MgB2

    NASA Astrophysics Data System (ADS)

    Idrobo, Juan; Klie, Robert; Browning, Nigel D.

    2002-03-01

    Polycrystalline MgB2 has been studied by atomic resolution scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). We find that within the detection limits of the techniques, there is no oxygen within the bulk of the grains, but significant oxygen segregated to the grain boundaries. The majority of the grain boundaries contain ordered crystalline MgB_2-xOx and amorphous BOy phases smaller than the coherence length, explaining the high conductivity of the material. Other kinds of grain boundaries containing larger areas of MgO sandwiched between BOy layers were also found. Furthermore, coherent Mg(B,O) precipitates can be formed within the bulk of the MgB2 grains. We will discuss the formation mechanisms of these secondary phases, the presence of oxygen ordering within the precipitates and the effect of the oxide precipitates on the bulk transport properties.

  16. Multicore MgB 2 wires made by hydrostatic extrusion

    NASA Astrophysics Data System (ADS)

    Kováč, P.; Pachla, W.; Hušek, I.; Kulczyk, M.; Melišek, T.; Holúbek, T.; Diduszko, R.; Reissner, M.

    2008-12-01

    Seven-filament MgB2/Fe and MgB2/Nb/Cu wires have been made by in situ process using hydrostatic extrusion, drawing and two-axial drawing deformation into the wire size of 1.1 × 1.1 mm2. The conductors were sintered at 650 °C/0.5 h and studied in terms of field-dependent transport critical current density and thermal stability. XRD, SEM and EDX analysis were applied for structural characterization. Transport current property and compositional/structural differences are compared and discussed in connection to used powders and metallic materials.

  17. Preparation and properties of highly c-axis-oriented Sr0.6Ba0.4Nb2O6 thin films by the sol-gel process

    NASA Astrophysics Data System (ADS)

    Shen, Zhiru; Ye, Hui; Zou, Tong; Guo, Bing

    2005-01-01

    Highly oriented ferroelectric strontium barium niobate (Sr0.6Ba0.4Nb2O6) thin films were prepared on P-type Si(100) substrate by the Sol-Gel process. The XRD patterns of the SBN films show that SBN film prepared by using NbCl5, KOH as raw materials performed a highly c-axis preferred orientation perpendicular to the Si substrate, better than films that was prepared using Nb(OC2H5)5 as starting agents. It may be duo to the existence of the potassium ion that not be filtered out completely during the preparation of the niobium alkoxide. The characteristics of D-F and C-V curves were obtained for SBN/Si film. The film exhibits high dielectric constant. In order to investigate ferroelectric characteristics further, the P-E loops of the SBN/Pt/Si were also measured. The films show better optical properties, transmittance of Sr0.6Ba0.4Nb2O6 films on MgO(001) and SiO2 substrates was more than 60% at the range from 450 to 850nm, refractive index was measured to be 2.14 and 2.12 on the MgO and SiO2 substrate at 633nm respectively.

  18. Plasma-assisted hot filament chemical vapor deposition of AlN thin films on ZnO buffer layer: toward highly c-axis-oriented, uniform, insulative films

    NASA Astrophysics Data System (ADS)

    Alizadeh, M.; Mehdipour, H.; Ganesh, V.; Ameera, A. N.; Goh, B. T.; Shuhaimi, A.; Rahman, S. A.

    2014-12-01

    c-Axis-oriented aluminum nitride (AlN) thin film with improved quality was deposited on Si(111) substrate using ZnO buffer layer by plasma-assisted hot filament chemical vapor deposition. The optical and electrical properties and surface morphology as well as elemental composition of the AlN films deposited with and without ZnO buffer layer were investigated using a host of measurement techniques: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and current-voltage (I-V) characteristic measurement. The XRD and XPS results reveal that the AlN/ZnO/Si films are free of metallic Al particles. Also, cross-sectional FESEM observations suggest formation of a well-aligned, uniform, continuous, and highly (002) oriented structure for a bi-layered AlN film when Si(111) is covered with ZnO buffer. Moreover, a decrease in full width at half maximum of the E2 (high)-mode peak in Raman spectrum indicates a better crystallinity for the AlN films formed on ZnO/Si substrate. Finally, I-V curves obtained indicate that the electrical behavior of the AlN thin films switches from conductive to insulative when film is grown on a ZnO-buffered Si substrate.

  19. Permanent magnet with MgB2 bulk superconductor

    NASA Astrophysics Data System (ADS)

    Yamamoto, Akiyasu; Ishihara, Atsushi; Tomita, Masaru; Kishio, Kohji

    2014-07-01

    Superconductors with persistent zero-resistance currents serve as permanent magnets for high-field applications requiring a strong and stable magnetic field, such as magnetic resonance imaging. The recent global helium shortage has quickened research into high-temperature superconductors (HTSs)—materials that can be used without conventional liquid-helium cooling to 4.2 K. Herein, we demonstrate that 40-K-class metallic HTS magnesium diboride (MgB2) makes an excellent permanent bulk magnet, maintaining 3 T at 20 K for 1 week with an extremely high stability (<0.1 ppm/h). The magnetic field trapped in this magnet is uniformly distributed, as for single-crystalline neodymium-iron-boron. Magnetic hysteresis loop of the MgB2 permanent bulk magnet was detrmined. Because MgB2 is a simple-binary-line compound that does not contain rare-earth metals, polycrystalline bulk material can be industrially fabricated at low cost and with high yield to serve as strong magnets that are compatible with conventional compact cryocoolers, making MgB2 bulks promising for the next generation of Tesla-class permanent-magnet applications.

  20. Oxygen incorporation in highly c -axis oriented YBa sub 2 Cu sub 3 O sub 7 minus x thin films deposited by plasma-enhanced metalorgainic chemical vapor deposition

    SciTech Connect

    Li, Y.Q.; Zhao, J.; Chern, C.S.; Lemoine, E.E.; Gallois, B.; Norris, P.; Kear, B. )

    1991-05-20

    YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} superconducting thin films prepared by chemical vapor deposition which exhibit high transition temperatures ({ital T}{sub {ital c}}{similar to}90 K) and high critical current densities ({ital J}{sub {ital c}}{gt}10{sup 6} A/cm{sup 2} at 77.7 K and 0 T) generally have copper-rich precipitates on the surface. We have studied both near-stoichiometric and nonstoichiometric highly {ital c}-axis oriented thin films formed by plasma-enhanced metalorganic chemical vapor deposition. We show that the reduction in transport properties ({ital T}{sub {ital c}} and {ital J}{sub {ital c}}) observed in stoichiometric films with smooth morphologies may result from a dramatic reduction of the oxygen diffusion rate in these thin films as compared to nonstoichiometric films. The significant enhancement of the transport properties of these films was achieved by further oxygen anneals at 480 {degree}C.

  1. The impact of argon admixture on the c-axis oriented growth of direct current magnetron sputtered Sc{sub x}Al{sub 1−x}N thin films

    SciTech Connect

    Mayrhofer, P. M.; Bittner, A.; Schmid, U.; Eisenmenger-Sittner, C.; Stöger-Pollach, M.

    2014-05-21

    The piezoelectric properties of wurtzite aluminium nitride (w-AlN) are enhanced by alloying with scandium (Sc), thus offering superior properties for applications in micro electro-mechanical systems devices. Sc{sub x}Al{sub 1−x}N thin films have been prepared by DC reactive magnetron sputtering on Si (100) substrates from a single target. When targeting a concentration range from x = 0 up to x = 0.15, the preparation conditions have been optimized by varying the Ar/N{sub 2} ratio in the sputtering gas. To incorporate an increasing Sc concentration, a higher Ar/N{sub 2} ratio has to be applied during the deposition process. Hence, the argon concentration in the sputtering gas becomes a crucial parameter for microstructure-related parameters. To determine phase purity, degree of c-axis orientation, lattice parameter, and grain size, the Sc{sub x}Al{sub 1−x}N thin films were investigated by techniques, such as scanning electron microscopy, transmission electron microscopy, and X-ray diffraction.

  2. Kinetic analysis of MgB2 layer formation in advanced internal magnesium infiltration (AIMI) processed MgB2 wires

    PubMed Central

    Li, G. Z.; Sumption, M. D.; Collings, E. W.

    2015-01-01

    Significantly enhanced critical current density (Jc) for MgB2 superconducting wires can be obtained following the advanced internal Mg infiltration (AIMI) route. But unless suitable precautions are taken, the AIMI-processed MgB2 wires will exhibit incomplete MgB2 layer formation, i.e. reduced superconductor core size and hence suppressed current-carrying capability. Microstructural characterization of AIMI MgB2 wires before and after the heat treatment reveals that the reaction mechanism changes from a “Mg infiltration-reaction” at the beginning of the heat treatment to a “Mg diffusion-reaction” once a dense MgB2 layer is formed. A drastic drop in the Mg transport rate from infiltration to diffusion causes the termination of the MgB2 core growth. To quantify this process, a two-stage kinetic model is built to describe the MgB2 layer formation and growth. The derived kinetic model and the associated experimental observations indicate that fully reacted AIMI-processed MgB2 wires can be achieved following the optimization of B particle size, B powder packing density, MgB2 reaction activation energy and its response to the additions of dopants. PMID:26973431

  3. Effects of carbon in MgB2 thin films: Intrinsic or extrinsic

    NASA Astrophysics Data System (ADS)

    Saengdeejing, A.; Saal, J. E.; Wang, Y.; Liu, Z. K.

    2007-04-01

    First-principles calculations are performed on MgB2, carbon doped MgB2, and MgB2C2. The trend of calculated lattice parameters of MgB2 with increasing carbon content agrees with bulk experiments but not with thin films produced by hybrid physical-chemical vapor deposition. In this work, the authors propose a model to explain this behavior based on the coefficients of thermal expansion of MgB2 and MgB2C2 as predicted from first principles and of graphite from literature. It is concluded that the effect of carbon on the lattice parameters of MgB2 thin films is extrinsic and due to differences of the coefficients of thermal expansion of different phases.

  4. Paramagnetic Meissner effect in MgB 2

    NASA Astrophysics Data System (ADS)

    Sözeri, Hüseyin; Dorosinskii, Lev; Topal, Uǧur; Ercan, İsmail

    2004-08-01

    We observed the paramagnetic Meissner effect (PME) in MgB 2 pellets after cooling in low fields of less than 1 Oe. As external magnetic field increases, the paramagnetic response of the sample decreases and disappears completely at 1 Oe. Effect of gamma irradiation on magnetic properties of MgB 2 has been investigated at low fields. In irradiated samples, the magnitude of the PME was found to be lower. To understand that whether this effect is of geometrical origin (so called flux compression model) or whether it is intrinsic to the material (e.g., π-junctions), measurements were performed with two samples having different geometries. Our results showed that paramagnetic response did not change as the geometry changes.

  5. 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

  6. Superconductivity in MgB2 irradiated with energetic protons

    NASA Astrophysics Data System (ADS)

    Sandu, Viorel; Craciun, Liviu; Ionescu, Alina Marinela; Aldica, Gheorghe; Miu, Lucica; Kuncser, Andrei

    2016-09-01

    A series of MgB2 samples were irradiated with protons of 11.3 and 13.2 MeV. Magnetization data shows an insignificant reduction of the critical temperatures but a continuous decrease of the Meissner fraction with increasing fluence or energy. All samples show a consistent improvement of the critical current density compared to the virgin sample and an increase of the pinning energy at high fields as resulted from relaxation data.

  7. 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.

  8. Effect of Heavy Carbon Doping of MgB_2

    NASA Astrophysics Data System (ADS)

    Kasinathan, Deepa; Pickett, W. E.

    2003-03-01

    Superconductivity in MgB2 seems to be beginning to be understood, but behavior under changes of hole concentration remain to be established and understood. Recently Ribeiro, Bud'ko, Petrovic, and Canfield (cond-mat/0210530) have reported MgB_2-xC_x, where Tc ˜ 20 K for x 0.1 -- 0.2. Rigid band arguments would say that the σ-band hole states in MgB2 should be filled by x=1/6, with no superconductivity. We have carried all-electron, full potential LAPW studies [WIEN2K] of ordered supercells corresponding to x=1/6 and 1/8 to assess the effects of the C, whose potential is more attractive and size is smaller than B, on the structure and the electronic bands and density of states. The behavior is non-rigid-band in important ways. We report on the magnitude of B atom relaxation around the C impurities, the effect that the relaxation has on the band filling, and the degree to which the experimental data can be accounted for.

  9. 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.

  10. 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.

  11. Growth of MgB2 Films by an Impinging Jet HPCVD Reactor Design

    NASA Astrophysics Data System (ADS)

    Lamborn, Daniel; Wilke, R. H. T.; Li, Qi; Xi, Xiaoxing; Snyder, D. W.; Wang, Shufang; Redwing, Joan

    2008-03-01

    An impinging jet hybrid physical-chemical vapor deposition (HPCVD) reactor design was used for the growth of both thin and thick MgB2 films. This technique was able to independently control the substrate and Mg supply temperatures, and still maintained sufficient Mg overpressure to ensure phase stability. Thin films were predominantly axis oriented with the (0001) sapphire substrate while the thick films were either polycrystalline or showed preferred orientation. Thick films (˜10 μm) were deposited at a growth rate of ˜ 110 μm/hr and showed a maximum Tc of 39.8 K and residual resistivity ratio of 6.6. The thick films also showed a high Jc of 2x10^6 A/cm^2 at low applied magnetic fields even at 20 K. The results indicate that the impinging jet HPCVD configuration shows promise for coated conductor processes.

  12. MgB 2 thin films by hybrid physical-chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Xi, X. X.; Pogrebnyakov, A. V.; Xu, S. Y.; Chen, K.; Cui, Y.; Maertz, E. C.; Zhuang, C. G.; Li, Qi; Lamborn, D. R.; Redwing, J. M.; Liu, Z. K.; Soukiassian, A.; Schlom, D. G.; Weng, X. J.; Dickey, E. C.; Chen, Y. B.; Tian, W.; Pan, X. Q.; Cybart, S. A.; Dynes, R. C.

    2007-06-01

    Hybrid physical-chemical vapor deposition (HPCVD) has been the most effective technique for depositing MgB 2 thin films. It generates high magnesium vapor pressures and provides a clean environment for the growth of high purity MgB 2 films. The epitaxial pure MgB 2 films grown by HPCVD show higher-than-bulk Tc due to tensile strain in the films. The HPCVD films are the cleanest MgB 2 materials reported, allowing basic research, such as on magnetoresistance, that reveals the two-band nature of MgB 2. The carbon-alloyed HPCVD films demonstrate record-high Hc2 values promising for high magnetic field applications. The HPCVD films and multilayers have enabled the fabrication of high quality MgB 2 Josephson junctions.

  13. Luminescence and dielectric properties of c-axis oriented (Bi1.90Eu0.10)(V1-zMoz)O5.5 ferroelectric thin films

    NASA Astrophysics Data System (ADS)

    Xie, Wei; Zou, Changwei; Xie, Mubiao; Bao, Dinghua

    2016-05-01

    (Bi1.90Eu0.10)(V1-zMoz)O5.5 (z = 0, 0.05, 0.10, 0.15 and 0.20) thin films with c-axis oriented were prepared on Pt(111)/Ti/SiO2/Si substrates by using chemical solution deposition method. The effect of Mo6+ concentration on the structure, luminescence properties and dielectric properties of the thin films were characterized systematically. X-ray diffraction data indicates that the thin films with low Mo6+-doping content can remain Bi2VO5.5 structure. When the Mo6+-doping content z reaches to 0.15, the thin films are a mixture of diphase with the main phase Bi2VO5.5 and secondary phase Bi2MoO6. Under UV irradiation, all the thin films emit a bright red or orange emission which origin from Eu3+. With increasing Mo6+-doping content z, the relative intensity of the Red and Orange emissions show obviously change. The value of Red/Orange ratio first decrease, and it reached minimum when z is 0.15, then it recover to the initial value. The variation trend of the Red/Orange ratio reflects the change of the lattice symmetry. Dielectric constant of the thin films increased with the increasing of the Mo6+ concentration while dielectric loss decreased. The decrease of the quantities of oxygen vacancies and the generation of Bi2MoO6 phase are responsible for the improvement of electric properties. These results explain that Eu3+ion can be used as an effective luminescent probe in (Bi1.90Eu0.10)(V1-zMoz)O5.5 (z = 0, 0.05, 0.10, 0.15 and 0.20) thin films, and the electric properties of the thin films can be improved by Mo6+ doping.

  14. Anisotropic high field superconductinng behavior in MgB_2

    NASA Astrophysics Data System (ADS)

    Gurevich, Alexander

    2004-03-01

    I will discuss new effects resulting from the two-gap superconductivity in MgB_2, focusing on: 1. Current-induced interband breakdown and dynamic interband phase textures caused by nonequilibrium charge imbalance [1], 2. Anomalous enhancement of the upper critical field H_c2(T) by nonmagnetic impurities in dirty two-gap superconductors. A theory of H_c2 based on generalized two-gap Usadel equations, which include both intra and interband scattering channels and paramagnetic pairbreaking is presented. Solutions of these equations show that H_c2(T) can exhibit a strong upward curvature and an unusual temperature dependence of the anisotropy parameter H_c2^||/H_c2^⊥, which can both increase and decrease with T depending on the ratio of the intraband electron diffusivities D_π/D_σ [2]. The theory explains recent high-field transport experiments on resistive MgB2 films in which the upper critical field was increased by 3-10 times as compared to single crystals [3], H_c2 exceeding 50 Tesla for H||ab and 35T for H⊥ ab. The results suggest that nonmagnetic impurities due to selective atomic substitution on Mg and B sites can increase H_c2 of MgB2 to a much greater extend than in one-gap superconductors. [1]. A. Gurevich and V.M. Vinokur, PRL 90, 047004 (2003). [2]. A. Gurevich, PRB 67, 1845151 (2003) and unpublished. [3]. A. Gurevich et al. Supercond. Sci. Technol. (2003, to appear). *In collaboration with V.M. Vinokur, V. Braccini, S. Patnaik, X. Song, D.C. Larbalestier, C.B. Eom, X. Pan, X. Xi, V. Ferrando, C. Ferdighini, A. Siri, K.H. Kim and C. Mielke. Work supported by NSF Nanostructured Materials and Interfaces MRSEC at the University of Wisconsin.

  15. Nucleation and growth of dense phase in compressed MgB2

    NASA Astrophysics Data System (ADS)

    Mikheenko, P.; Bevan, A. I.; Abell, J. S.

    2006-06-01

    We report nucleation and growth of dense MgB2 phase in two advanced methods for compacting MgB2 powder: hot isostatic pressing (HIP) and resistive sintering (RS). Both methods produce a compact with nearly theoretical mass density and high critical current density: up to 8 . 105 A/cm2 at 20 K. A liquid phase is responsible for the propagation of dense MgB2. The additions of Mg and Ni are beneficial for rapid formation of dense compact. The process of compacting is further improved by introducing single crystal-dense MgB2 seeds.

  16. 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.

  17. Properties of in situ made MgB2 in Nb or Ti sheath

    NASA Astrophysics Data System (ADS)

    Kováč, P.; Hušek, I.; Kopera, L.; Melišek, T.; Rosová, A.; Dobročka, E.

    2013-02-01

    Pure Nb and Ti have been used as sheath materials for MgB2 wires examined experimentally. The reason for this research is to compare the effects of these metallic sheaths on the basic properties of MgB2 superconductor. Single-core SiC doped MgB2 wires with Nb and/or Ti sheaths have been made by a powder-in-tube in situ process. Different transport currents, phase compositions and grain connectivity were observed for Nb- and Ti sheathed MgB2 heat treated at temperatures 650-850 °C/30 min. It was found that the critical current density of MgB2/Nb annealed above 700 °C rapidly decreases, while Jc of MgB2/Ti is systematically increasing with temperature. This is explained by the positive role of Ti absorbing impurities from the MgB2 core and by the negative effect of boron diffusion into Nb, reducing the quantity and worsening the quality of the MgB2 core. The obtained results show clearly that a Ti sheath offers the application of higher heat treatment temperatures (above 700 °C) and consequently the achievement of higher critical current densities in comparison to MgB2/Nb.

  18. 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.

  19. Anisotropic grain connectivity in shock consolidated MgB2 bulk samples

    NASA Astrophysics Data System (ADS)

    Tamaki, Hideyuki; Ohashi, Wataru; Kitazawa, Hiroshi; Matsuzawa, Hidenori; Takano, Yoshihiko; Atou, Toshiyuki; Fukuoka, Kiyoto; Kikuchi, Masae; Kawasaki, Masashi; Kakimoto, Etsuji; Dohke, Kiyotaka

    2004-06-01

    We consolidated commercial MgB2 powders by two different shock consolidation methods: the single-stage propellant gun method and the underwater shock consolidation method. The samples prepared had anisotropic resistance-temperature features; the narrowest resistive transition width was observed along the directions of shock loading. In contrast, onset temperatures were independent of the directions and methods. No grain orientation previously observed would have resulted from the consolidation processes with a very short duration of {\\sim } 1~\\micmu {\\mathrm {s}} . The samples showed higher diamagnetism than a cold isostatic pressed (CIPed) sample at a low field of 1 Oe. However, their diamagnetism relatively degraded with increasing fields and eventually became much less than even that of the CIPed sample. This is due possibly to thick, much distorted grain boundaries that would have behaved as weak links at high fields.

  20. Carbon Doped MgB2 Thin Films using TMB

    NASA Astrophysics Data System (ADS)

    Wilke, R. H. T.; Li, Qi; Xi, X. X.; Lamborn, D. R.; Redwing, J.

    2007-03-01

    The most effective method to enhance the upper critical field in MgB2 is through carbon doping. In the case of thin films, ``alloying'' with carbon has resulted in enhanced Hc2 values estimated to be as high as 70 T for H parallel to ab and 40 T for H perpendicular ab [1]. ``Alloying'' refers to the in-situ Hybrid Physical-Chemical Vapor Deposition (HPCVD) of carbon containing MgB2 films using (C5H5)2Mg as the carbon source. While these films exhibit enhanced Hc2 values, there are amorphous boron- carbon phases in the grain boundaries that reduce the cross section area for superconducting current. We present here the results of our attempts to make more homogeneously carbon doped thin films using gaseuous trimethyl-boron (TMB) as the carbon source. Initial results indicate different behavior upon carbon doping using TMB from carbon-alloying. The microstructures and upper critical fields of the carbon doped films using TMB and carbon alloyed films will be compared. [1] V. Braccini et al., Phys. Rev. B 71 (2005) 012504. [2] A.V. Pogrebnyakov et al., Appl. Phys. Lett 85 (2004) 2017.

  1. 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.

  2. MgB2 superconducting joints for persistent current operation

    NASA Astrophysics Data System (ADS)

    Patel, Dipak; Hossain, Md Shahriar Al; See, Khay Wai; Xu, Xun; Barua, Shaon; Ma, Zongqing; Choi, Seyong; Tomsic, Mike; Kim, Jung Ho

    2015-06-01

    High-performance superconducting joints are essential for realizing persistent-mode magnets. Herein, we propose a concept and fabrication of such superconducting joints, which yielded reliable performance in the operating temperature range of 4.2-25 K. MgB2-MgB2 joints in magnets are known to result in deterioration of localized electrical, thermal, and mechanical properties. To overcome these problems, the ends of the two wires are inserted into a pellet press, which is then filled with a mixture of unreacted magnesium and boron powders, followed by heat treatment. The critical current capacity and joint resistance were precisely evaluated by the standard four-probe method in open-circuit and by field-decay measurements in a closed-loop, respectively. These joints demonstrated up to 66% of the current-carrying capacity of unjoined wire at 20 K, 2 T and joint resistance of 1.4 × 10-12 Ω at 4.2 K in self-field.

  3. MgB2 multifilamentary tapes: microstructure, chemical composition and superconducting properties

    NASA Astrophysics Data System (ADS)

    Birajdar, B.; Braccini, V.; Tumino, A.; Wenzel, T.; Eibl, O.; Grasso, G.

    2006-09-01

    Multifilamentary Ni-sheathed Cu-stabilized MgB2 tapes with a critical current density of 2.0 × 105 A cm-2 (at 20 K and 1 T) were prepared by a powder in tube technique, using pre-reacted MgB2 powders. The microstructure and chemical composition of the superconducting core and the MgB2-Ni interface were studied using SEM, EPMA and TEM. A quick, reliable and standard-less method of B quantification using SEM-EDX is established for the analysis of MgB2 wires and tapes. Carbon-contamination-free sample preparation was crucial for the analysis of boron. The typical size of MgB2 colonies, i.e. the arrangement of several well connected grains, in the MgB2 filaments was between 1 and 6 µm. The colonies are structurally well connected to each other, although sub-micrometre-sized voids are present. The B to Mg mole fraction ratio in the MgB2 colonies was found to be close to two and the O mole fraction is less than 1 at.%. The typical size of the MgB2 grains in the colonies is about 0.5-1 µm however, numerous grains of size 30-200 nm are also present. MgO precipitates of the size of 15-70 nm were found in the MgB2 grains. Long straight dislocations with a density of 1 × 1010 cm-2 are observed. Non-superconducting layers which appear as oxide layers in SEM and TEM samples were found on the surface of the MgB2 colonies and yield poor connectivity between the colonies. It is expected that these layers yield a significant reduction of the critical current density Jc. A 10 µm wide intermetallic reaction layer of B, Mg and Ni is formed at the MgB2-Ni interface. Reduction of the MgB2 grain size by milling of starting MgB2 powder and elimination of non-superconducting layers around MgB2 colonies could further enhance the critical current density because of improved pinning and connectivity between colonies.

  4. Electroplating of the superconductive boride MgB2 from molten salts

    NASA Astrophysics Data System (ADS)

    Abe, Hideki; Yoshii, Kenji; Nishida, Kenji; Imai, Motoharu; Kitazawa, Hideaki

    2005-02-01

    An electroplating technique of the superconductive boride MgB2 onto graphite substrates is reported. Films of MgB2 with a thickness of tens micrometer were fabricated on the planar and curved surfaces of graphite substrates by means of electrolysis on a mixture of magnesium chloride, potassium chloride, sodium chloride, and magnesium borate fused at 600 °C under an Ar atmosphere. The electrical resistivity and magnetization measurements revealed that the electroplated MgB2 films undergo a superconducting transition with the critical temperature (Tc) of 36 K.

  5. 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.

  6. 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.

  7. MgB2: Novel properties due to multibands

    NASA Astrophysics Data System (ADS)

    Blumberg, Girsh

    2008-03-01

    About 40 years ago A.J. Leggett proposed a new collective mode arising from cross-tunneling of Cooper pairs residing on different Fermi surfaces of a multiband superconductor: Leggett's collective mode is caused by a counter flow of the interacting superfluids leading to small fluctuations of the relative phase of the condensates while the total electron density is locally conserved.ootnotetextA.J. Leggett, Progr. Theor. Phys. 36, 901 (1966). Here we present direct spectroscopic observation of the Leggett's excitation in the MgB2 superconductor containig two pairs of Fermi surfaces resulting from π- and σ-bands. Electronic Raman scattering studies have revealed three distinct superconducting (SC) features: (i) a clean threshold of Raman intensity at 4.6 meV consistent with the π-band SC gap; (ii) the SC pair breaking coherence peak at 13.5 meV consistent with excitations above the σ-band gap; and (iii) the SC collective mode at 9.4 meV which we assign to an excitation first discussed by Leggett.ootnotetextG. Blumberg et al., Phys. Rev. Lett. 99 (2007); arXiv:0710.2803http://arxiv.org/pdf/0710.2803. Our calculation of the Raman response function for MgB2 superconductor based on multiband interaction matrices by first principle computations show good agreement with spectroscopic observations. The temperature and field dependencies for all three features (i) -- (iii) have been established;ootnotetextG. Blumberg et al., Physica (Amsterdam) 456C, 75 (2007). the effects of magnetic field on the pair cross-tunneling in multiband system will be discussed. In addition, anharmonicity and superconductivity-induced self-energy effects for the E2g boron stretching phonon have been studied.ootnotetextA. Mialitsin et al., Phys. Rev. B 75, 020509(R) (2007). We show that anharmonic two-phonon decay is mainly responsible for the unusually large linewidth of the E2g mode. We observe 2.5% hardening of the E2g phonon frequency upon cooling into the SC state and estimate the electron-phonon coupling strength associated with this renormalization.

  8. 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.

  9. Flux Pinning and Connectivity in MgB2

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

    The transport and pinning properties of in-situ MgB2 bulks and strands are discussed. The influence of SiC, excess Mg, B4C, TiC, and their combination on Birr and Bc2 as distinct from connectivity and flux pinning is the focus of the work. SiC dopants increase Bc2 and Birr predominantly, with little influence on connectivity or flux pinning. Excess Mg improves the transport current, changes the grain microstructure, and also leads local maxima in Bc2 and Birr at excess Mg levels of 15% mol fraction. Fp curves are consistent with grain boundary pinning for the binary materials over the whole temperature range. This is also true for SiC and TiC doped materials at lower fields and temperatures, while higher temperatures show a deviation from surface pinning. These higher temperature deviations are consistent with the size and distribution of these nanoparticulate additions. Normal state resistivity measurements and models are used to extract residual resistivity values, percent connectivity, and Debye temperatures. Debye temperatures are seen to be depressed by SiC doping, an effect which is confirmed by heat capacity measurements. Residual resistivity values are seen to correlate with Bc2 and Birr enhancements, consistent with B site substitution with C as evidenced by XRD extracted lattice parameter shifts.

  10. Single crystal growth of MgB 2 by evaporating Mg-flux method

    NASA Astrophysics Data System (ADS)

    Du, Wei; Xu, Huizhong; Zhang, Hongbin; Xu, Dong; Wang, Xinqiang; Hou, Xianqin; Wu, Yongzhong; Jiang, Fuyi; Qin, Lianjie

    2006-04-01

    Well hexagonal plate-shaped single crystal of magnesium diboride (MgB 2) with the size of 100 μm has been grown at ambient pressure by evaporating Mg-flux method which is a new practice to grow MgB 2 single crystal. The superconducting transition of as-prepared crystals was measured to be at about 33.7 K by superconducting quantum interference device (dc-SQUID) magnetometer. The X-ray powder diffraction (XRD) confirmed the MgB 2 phase, and the electron diffraction patterns measured by using high-resolution transmission electron microscope (HRTEM) confirmed the structure of MgB 2 single crystal. The single crystal images were observed by scanning electron microscope (SEM) and metallographic microscope (MM). The micromechanism of crystal growth is also proposed through the investigations of SEM and MM.

  11. The study of MgB2/BN/MgB2 trilayer films

    NASA Astrophysics Data System (ADS)

    Hu, Hui; Feng, Qingrong; Wang, Yue; Zhang, Yan

    2015-12-01

    MgB2/BN/MgB2 trilayer films have been fabricated by using hybrid physical-chemical vapor deposition (HPCVD) method for the MgB2 layers and chemical vapor deposition (CVD) method for the BN layers in the same reactor. The films are studied by X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD) and magnetization measurements. These test outcomes indicate the trilayer films are grown without deteriorating the superconductivity of MgB2 films. Our results show that it is feasible to grow MgB2/BN/MgB2 trilayer films in the same reactor sequentially, which has the advantage of reducing contamination during the growth. This therefore opens the door for fabricating all-MgB2 Josephson junctions by using the BN film as the insulating layer.

  12. Scanning Pulsed Laser Imaging of Current-Biased MgB2 Detector

    NASA Astrophysics Data System (ADS)

    Ishida, Takekazu; Arai, Kohei; Akita, Yukio; Yagi, Ikutaro; Yotsuya, Tsutomu; Satoh, Kazuo; Uno, Mayumi; Shimakage, Hisashi; Miki, Shigehito; Wang, Zhen; Kato, Masaru; Machida, Masahiko; Hojo, Kiichi

    2009-12-01

    A superconducting MgB2 meander detector on a sapphire plate has been proved to work as a neutron detector in our preceding works. The 10B-enriched MgB2 detector utilizes a voltage change induced by a hot-spot arising from the nuclear reaction energy. To understand the position-dependent sensitivity of a 3-μm MgB2 stripline of length 100 μm, a scanning laser spot can be achieved by the combination of the XYZ piezo-driven stages and an optical fiber with an aspheric focusing lens. Our results show that the MgB2 superconducting stripline can be seen in the image of the scanning laser microscope of the signal voltage.

  13. Properties of MgB2 wires made by internal magnesium diffusion into different boron powders

    NASA Astrophysics Data System (ADS)

    Kováč, P.; Hušek, I.; Rosova, A.; Kulich, M.; Melišek, T.; Kopera, L.; Brunner, B.

    2015-09-01

    Different boron powders were used for MgB2 wires manufactured by internal magnesium diffusion. The structure of the MgB2 core, critical temperature and critical currents of Cu/Ti sheathed wires differing only in boron powder were analyzed and compared. It was found that the particle size and purity of boron powders influence the creation of the MgB2 phase and, consequently, also considerably influence its superconducting properties. The highest critical current density in the low external field was measured for wire with a boron purity of 98.5% produced by Pavezyum. It was used also for stabilized multi-core MgB2 wire with high engineering current densities in low magnetic fields at 20 K, which may be attractive for some low field applications, e.g. high-power wind generators.

  14. Quantum confinement induced band gaps in MgB2 nanosheets

    NASA Astrophysics Data System (ADS)

    Xu, Bo Z.; Beckman, Scott P.

    2016-09-01

    The discovery of two-dimensional semiconducting materials, a decade ago, spawned an entire sub-field within solid-state physics that is focused on the development of nanoelectronics. Here we present a new class of semiconducting two-dimensional material based on hexagonal MgB2. Although MgB2 is a semimetal, similar to the other well-studied transition metal diborides, we demonstrate that, unlike the transition metal diborides, thinning MgB2, to create nanosheets, opens a band gap in the density of states. We predict that a 7 Å thick MgB2 nanosheet will have a band gap of 0.51 eV. MgB2 nanosheets differ from other two-dimensional semiconductors in that the band gap is introduced by (001) surfaces and is opened by the quantum confinement effect. The implications of these findings are that nanostructured MgB2 is not merely a new composition, but also has intrinsic mechanisms for tuning its electronic properties, which may facilitate the development of nanoelectronics.

  15. Investigation of lauric acid dopant as a novel carbon source in MgB 2 wire

    NASA Astrophysics Data System (ADS)

    Lee, C. M.; Lee, S. M.; Park, G. C.; Joo, J.; Lim, J. H.; Kang, W. N.; Yi, J. H.; Jun, B.-H.; Kim, C.-J.

    2010-11-01

    We fabricated lauric acid (LA) doped MgB 2 wires and investigated the effects of the LA doping. For the fabrication of the LA-doped MgB 2 wires, B powder was mixed with LA at 0-5 wt.% of the total amount of MgB 2 using an organic solvent, dried, and then the LA-treated B and Mg powders were mixed stoichiometrically. The powder mixture was loaded into an Fe tube and the assemblage was drawn and sintered at 900 °C for 3 h under an argon atmosphere. We observed that the LA doping induced the substitution of C for the B sites in MgB 2 and that the actual content of C increased monotonically with increasing LA doping level. The LA-doped MgB 2 wires exhibited a lower critical temperature ( Tc), but better critical current density ( Jc) behavior in a high magnetic field: the 5 wt.% LA-doped sample had a Jc value of 5.32 × 10 3 A/cm 2, which was 2.17 times higher than that of the pristine sample (2.45 × 10 3 A/cm 2) at 5 K and 6 T, suggesting that LA is an effective C dopant in MgB 2 for enhancing the high-field Jc performance.

  16. Connectivity, Doping, and Anisotropy in Highly Dense Magnesium Diboride (MgB2)

    NASA Astrophysics Data System (ADS)

    Li, Guangze

    Magnesium diboride (MgB2) is a superconducting material which can be potentially used in many applications such as magnetic resonance imaging system (MRI), wind turbine generators and high energy physics facilities. The major advantages of MgB2 over other superconductors include its relatively high critical temperature of about 39 K, its low cost of raw materials, its simple crystal structure, and its round multifilament form when in the form of superconducting wires. Over the past fourteen years, much effort has been made to develop MgB2 wires with excellent superconducting properties, particularly the critical current density J c. However, this research has been limited by technical difficulties such as high porosity and weak connectivity in MgB2, relatively small flux pinning strength, low upper critical field B c2 and relatively high anisotropy. The goal of this dissertation is to understand the relationship between superconducting properties, microstructure, and reaction mechanisms in MgB 2. In particular, the influences of connectivity, B c2, anisotropy and flux pinning were investigated in terms of the effects of these variables on the Jcs and n-values of MgB2 superconducting wires (n-value is a parameter which indicates the sharpness of resistive V-I transition). The n -values of traditional "Powder in Tube (PIT)" processed MgB2 wires were improved by optimizing precursor species after the identification of microstructural defects such as so-called "sausaging problems". Also, it was found that "high porosity and weak connectivity" was one of the most critical issues which limited the J c performance in typical MgB2. To overcome this problem, highly dense, well-connected MgB2 conductors were successfully fabricated by adopting an innovative "Advanced Internal Magnesium Infiltration (AIMI)" process. A careful study on the reaction kinetics together with the microstructural evidence demonstrated how the MgB2 layer was formed as the infiltration process proceeded. As a result, it is possible to control the MgB2 layer growth in the AIMI-processed MgB 2 wires. The best AIMI wires, with improved density and connectivity, accomplished an outstanding layer Jc, which was 1.0 x 105 A/cm2 at 4.2 K and 10 T, nearly 10 times higher than the Jcs of PIT wires. The engineering Je of AIMI wires, namely the critical current over the whole cross-sectional area in the wire, achieved 1.7 x 104 A/cm2 at 4.2 K, 10 T, 200 % higher than those of PIT wires. Finally, two promising dopants, Dy2O3 and O, were engineered to incorporate with MgB2. Dy 2O3 nanopowders, co-doped with C in AIMI wires, enhanced the Jc performance at elevated temperatures such as 20 K. Oxygen, on the other hand, doped into MgB2 thin films through a newly-developed O2 annealing process, improved Bc2 to 14 T at 21 K. Both of the doping studies were helpful to understand the superconducting nature of MgB2.

  17. Assessment of liquid hydrogen cooled MgB2 conductors for magnetically confined fusion

    NASA Astrophysics Data System (ADS)

    Glowacki, B. A.; Nuttall, W. J.

    2008-02-01

    Importantly environmental factors are not the only policy-driver for the hydrogen economy. Over the timescale of the development of fusion energy systems, energy security issues are likely to motivate a shift towards both hydrogen production and fusion as an energy source. These technologies combine local control of the system with the collaborative research interests of the major energy users in the global economy. A concept Fusion Island Reactor that might be used to generate H2 (rather than electricity) is presented. Exploitation of produced hydrogen as a coolant and as a fuel is proposed in conjunction with MgB2 conductors for the tokomak magnets windings, and electrotechnical devices for Fusion Island's infrastructure. The benefits of using MgB2 over the Nb-based conductors during construction, operation and decommissioning of the Fusion Island Reactor are presented. The comparison of Nb3Sn strands for ITER fusion magnet with newly developed high field composite MgB2 PIT conductors has shown that at 14 Tesla MgB2 possesses better properties than any of the Nb3Sn conductors produced. In this paper the potential of MgB2 conductors is examined for tokamaks of both the conventional ITER type and a Spherical Tokamak geometry. In each case MgB2 is considered as a conductor for a range of field coil applications and the potential for operation at both liquid helium and liquid hydrogen temperatures is considered. Further research plans concerning the application of MgB2 conductors for Fusion Island are also considered.

  18. 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 showed Tc > 41 K and Jc > 107 A/cm2, which is superior to bulk MgB2 samples. Polycrystalline MgB2 thin films grown on metal substrates showed similar Tc and Jc compared with bulk samples, indicating MgB2 is suitable for coating a metal cavity. Large c-pitaxial MgB2 thin films were grown on 2-inch diameter c-sapphire wafers, showing our technique is capable of depositing large area samples. The lower critical field (Hc1) of MgB2 thin films was measured as well as it is know that bulk MgB2 has a small Hc1 and would suffer from vortex penetration at low magnetic fields. The penetrating magnetic vortices would result in loss in an applied RF field. However, due to the geometry barrier, thin film MgB2 would have a higher Hc1 than the bulk material. In my experiments, the Hc1 of MgB2 thin films increased with decreasing film thickness. At 5 K, a 100 nm epitaxial MgB2 thin film showed enhanced Hc1 ~ 1880 Oe, which is higher than Hc1 of Nb at 2 K. This showed that MgB2 coated SRF cavities have the potential to work at higher magnetic fields and higher temperature. Because the magnetic field distribution in the thin film Hc1 measurement is different from the magnetic field in a real SRF cavity, a few Nb ellipsoids were machined and coated with MgB2. The ellipsoid only has a magnetic field outside its surface and can serve as an inverse SRF cavity in the vortex penetration measurement. In the experiments, vortices penetrate into the bulk Nb ellipsoid at a magnetic field 400 Oe lower than the vortex penetration field of MgB2 coated Nb ellipsoids. This result confirmed our prediction that MgB2 coated SRF cavities could work at higher magnetic fields, thus producing higher acceleration gradients. In the last part of this thesis, I discussed how I used the dielectric resonator technique to measure the surface resistance (Rs) and Tc of MgB2 thin films. While the sensitivity of this technique was not high enough to lead to reliable Rs values, it can still serve for the determination of Tc for large area samples that are too bulky for other measurement systems.

  19. Role of MgO impurity on the superconducting properties of MgB2

    NASA Astrophysics Data System (ADS)

    Singh, Dharmendra Kumar; Tiwari, Brajesh; Jha, Rajveer; Kishan, H.; Awana, V. P. S.

    2014-10-01

    We address the effect of MgO impurity on the superconducting properties of MgB2. The synthesis of MgB2 is very crucial because of sensitivity of Mg to oxidation which may lead to MgO as a secondary phase. Rietveld refinement was performed to determine the quantitative volume fraction of MgO in the samples synthesized by two different techniques. Both the samples were subjected to magnetization measurements under dc and a.c. applied magnetic fields and the observed results were compared as a function of temperature. Paramagnetic Meissner effect has been observed in a sample of MgB2 having more amount of MgO (with Tc = 37.1 K) whereas the pure sample MgB2 having minor quantity of MgO shows diamagnetic Meissner effect with Tc = 38.8 K. M-H measurements at 10 K reveal a slight difference in irreversibility field which is due to MgO impurity along with wide transition observed from ac magnetic susceptibility measurements. The magnetotransport measurements ρ(T) using ρN = 90%, 50% and 10% criterion on pure sample of MgB2 has been used to determine the upper critical field whereas the sample having large quantity of MgO does not allow these measurements due to its high resistance.

  20. Improvement in the Performance of Bulk MgB2 Material through Optimization of Sintering Process

    NASA Astrophysics Data System (ADS)

    Kobayashi, H.; Muralidhar, M.; Koblischka, M. R.; Inoue, K.; Murakami, M.

    Enhancement of the critical current density (Jc) in MgB2 bulk material is very important for engineering applications. It has been found that the optimization of the sintering temperature leads to high Jc values in bulk MgB2 material. In our recent work, the highest trapped field value was recorded in the sample sintered at 775oC. The present investigation has focused on methods to improve further Jc values of the disk-shape bulk MgB2 superconductors by optimizing sintering conditions. MgB2 samples were subjected to a solid state reaction at 775, 780, 785, 795, 800 and 805oC for 3 h in pure Ar atmosphere. XRD analysis showed that all the samples were single phase MgB2. The magnetization measurements confirmed a sharp superconducting transition with onset Tc at around 38.7 K. Atomic force microscopy observation indicated that the number of nano meter size grains is more in samples processed 3 h at 805oC has compared to the samples sintered at 775oC. As a result, the highest Jc value of 245 kA/cm2 at 20 K was obtained for the sample sintered at 805oC for 3 h.

  1. 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.

  2. Improved Jc-B properties of MgB2 multifilamentary wires and tapes

    NASA Astrophysics Data System (ADS)

    Wang, Chengduo; Wang, Dongliang; Zhang, Xianping; Yao, Chao; Wang, Chunlei; Ma, Yanwei; Oguro, Hidetoshi; Awaji, Satoshi; Watanabe, Kazuo

    2012-12-01

    MgB2 multifilamentary wires and tapes were fabricated by the in situ powder-in-tube (PIT) process using acetone doped milled precursor powders. The critical current density of MgB2 is strongly enhanced by high energy milling and acetone doping. Furthermore, the liquid acetone can restrain the agglomeration of milled powder, which is beneficial to the fabrication of MgB2 multifilamentary wires. At 4.2 K and 10 T, the Jc of the 80 h doped Fe/Cu wire is 2.9 × 103 A cm-2, 20 times larger than that of the 1 h pure one (the ‘1 h’ and ‘80 h’, refer to ball milling times). The Jc of 80 h doped Fe/Monel tape is up to 9.2 × 103 A cm-2 at 4.2 K and 10 T. The Jc values of Nb barrier wires are comparable to those of the Fe barrier MgB2 wires. These results indicate that the addition of liquid C-containing material during high energy milling may be an effective way to get excellent properties of MgB2 for practical applications.

  3. Influence of microstructures and crystalline defects on the superconductivity of MgB2

    NASA Astrophysics Data System (ADS)

    Serquis, A.; Liao, X. Z.; Zhu, Y. T.; Coulter, J. Y.; Huang, J. Y.; Willis, J. O.; Peterson, D. E.; Mueller, F. M.; Moreno, N. O.; Thompson, J. D.; Nesterenko, V. F.

    2002-07-01

    This work studies the influence of microstructures and crystalline defects on the superconductivity of MgB2, with the objective to improve its flux pinning. A MgB2 sample pellet that was hot isostatic pressed (HIPed) was found to have significantly increased critical current density (Jc) at higher fields than its un-HIPed counterpart. The HIPed sample had a Jc of 10 000 A/cm2 in 50 000 Oe (5 T) at 5 K. This was 20 times higher than that of the un-HIPed sample, and the same as the best Jc reported by other research groups. Microstructures observed in scanning and transmission electron microscopy indicate that the HIP process eliminated porosity present in the MgB2 pellet resulting in an improved intergrain connectivity. Such improvement in intergrain connectivity was believed to prevent the steep Jc drop with magnetic field H that occurred in the un-HIPed MgB2 pellet at H>45 000 Oe(4.5 T) and T=5 K. The HIP process was also found to disperse the MgO that existed at the grain boundaries of the un-HIPed MgB2 pellet and to generate more dislocations in the pellets. These dispersed MgO particles and dislocations improved flux pinning also at H<45 000 Oe. The HIPing process was also found to lower the resistivity at room temperature.

  4. X-ray photoelectron spectroscopy studies of MgB 2 for valence state of Mg

    NASA Astrophysics Data System (ADS)

    A. Talapatra; Bandyopadhyay, S. K.; Sen, Pintu; Barat, P.; Mukherjee, S.; Mukherjee, M.

    2005-03-01

    Core level X-ray photoelectron spectroscopy (XPS) studies have been carried out on polycrystalline MgB 2 pellets over the whole binding energy range with a view to having an idea of the charge state of magnesium (Mg). We observe three distinct peaks in Mg 2p spectra at 49.3 eV (trace), 51.3 eV (major) and 54.0 eV (trace), corresponding to metallic Mg, MgB 2 and MgCO 3 or, divalent Mg species, respectively. Similar trend has been noticed in Mg 2s spectra. The binding energy of Mg in MgB 2 is lower than that corresponding to Mg(2+), indicative of the fact that the charge state of Mg in MgB 2 is less than (2+). Lowering of the formal charge of Mg promotes the σ → π electron transfer in boron (B) giving rise to holes on the top of the σ-band which are involved in coupling with B E 2g phonons for superconductivity. Through this charge transfer, Mg plays a positive role in hole superconductivity. B 1s spectra consist of three peaks corresponding to MgB 2, boron and B 2O 3. There is also evidence of MgO due to surface oxidation as seen from O 1s spectra.

  5. Theoretical investigation of superconductivity in MgB2-xCx alloys

    NASA Astrophysics Data System (ADS)

    Sharma, Gargee; Sharma, Smita

    2016-05-01

    In this paper we investigated the superconducting properties of MgB2-xCx alloys where x is the concentration (0.0, 0.03, 0.11 and 0.20). The superconducting state parameters, namely, the electron-phonon coupling strength (λ), Coulomb pseudopotential (μ*), transition temperature (Tc), isotope effect exponent (α) and interaction strength (NoV) of MgB2-xCx alloys have been investigated in the BCS-Eliashberg-McMillan framework, as modified for MgB2-xCx alloys. Pseudo ions with average properties have been considered to replace different types of ions in the system. It is observed that all the superconducting parameters go on decreasing as the concentration of C is increased. The magnitudes of λ and Tc indicate that MgB2-xCx is strong-to-intermediate coupling superconductor. It is also observed that Tc is composition dependent. Present computations yield almost linear variation of Tc with concentration x of C in the MgB2-xCx system, which is in agreement with the experimental data. A linear Tc equation is proposed by fitting the present results.

  6. Fabrication of c-axis Oriented Epitaxial EuBa2Cu3O7-δ and EuBa2Cu4O8 Films on SrTiO3 (100) Substrate by Molten Hydroxide Method at 450°C

    NASA Astrophysics Data System (ADS)

    Miyachi, Y.; Funaki, S.; Yamada, Y.

    EuBa2Cu3O7-δ (Eu123) and EuBa2Cu4O8 (Eu124) films oriented in c-axis were deposited on SrTiO3 (100) substrates with eutectic NaOH-KOH flux at 450 °C. Synthesized phase has changed by using various types of barium source materials. Pure Eu124 films showed superconducting transition at ∼70 K, zero-resistance was not observed for Eu123/124 two-phase films. One of the possible reasons of this is Eu/Ba substitution of Eu123 phase. According to Tc of the Eu124, the molten hydroxide method enables to deposit high-quality Eu124 films.

  7. Study of the microwave electrodynamic response of MgB 2 thin films

    NASA Astrophysics Data System (ADS)

    Andreone, A.; Cassinese, A.; Cantoni, C.; Di Gennaro, E.; Lamura, G.; Maglione, M. G.; Paranthaman, M.; Salluzzo, M.; Vaglio, R.

    2002-08-01

    We present a study on the power dependence of the microwave surface impedance in thin films of the novel superconductor MgB 2. 500 nm thick samples exhibiting critical temperatures ranging between 26 and 38 K are synthesized by an ex situ post-anneal of e-beam evaporated boron in the presence of an Mg vapor at 900 °C. Preliminary results on films grown in situ by a high rate magnetron sputtering technique from stoichiometric MgB 2 and Mg targets are also reported. Microwave measurements have been carried out employing a dielectrically loaded niobium superconducting cavity operating at 19.8 GHz and 4 K. The study shows that the electrodynamic response of MgB 2 films is presently dominated by extrinsic sources of dissipation, appearing already at low microwave power, likely to be ascribed to the presence of grain boundaries and normal inclusions in the samples.

  8. Numerical modelling and comparison of MgB2 bulks fabricated by HIP and infiltration growth

    NASA Astrophysics Data System (ADS)

    Zou, J.; Ainslie, M. D.; Fujishiro, H.; Bhagurkar, A. G.; Naito, T.; Babu, N. Hari; Fagnard, J.-F.; Vanderbemden, P.; Yamamoto, A.

    2015-07-01

    MgB2 in bulk form shows great promise as trapped field magnets (TFMs) as an alternative to bulk (RE)BCO materials to replace permanent magnets in applications such as rotating machines, magnetic bearings and magnetic separation, and the relative ease of fabrication of MgB2 materials has enabled a number of different processing techniques to be developed. In this paper, a comparison is made between bulk MgB2 samples fabricated by the hot isostatic pressing (HIP), with and without Ti-doping, and infiltration growth (IG) methods and the highest trapped field in an IG-processed bulk MgB2 sample, Bz = 2.12 at 5 K and 1.66 T at 15 K, is reported. Since bulk MgB2 has a more homogeneous Jc distribution than (RE)BCO bulks, studies on such systems are made somewhat easier because simplified assumptions regarding the geometry and Jc distribution can be made, and a numerical simulation technique based on the 2D axisymmetric H-formulation is introduced to model the complete process of field cooling (FC) magnetization. As input data for the model, the measured Jc(B,T) characteristics of a single, small specimen taken from each bulk sample are used, in addition to measured specific heat and thermal conductivity data for the materials. The results of the simulation reproduce the experimental results extremely well: (1) indicating the samples have excellent homogeneity, and (2) validating the numerical model as a fast, accurate and powerful tool to investigate the trapped field profile of bulk MgB2 discs of any size accurately, under any specific operating conditions. Finally, the paper is concluded with a numerical analysis of the influence of the dimensions of the bulk sample on the trapped field.

  9. Electrochemical synthesis of superconductive MgB 2 from molten salts

    NASA Astrophysics Data System (ADS)

    Yoshii, Kenji; Abe, Hideki

    2003-05-01

    We have found that superconductive MgB2 can be electrochemically synthesized from molten salts. The electrolysis was performed in an Ar flow at 600 °C on fused mixtures composed of MgCl2, MgB2O4, Na2B2O4 and alkali halides such as KCl, NaCl, and LiCl. Superconductivity was observed for a wide variety of electrolytes. It was also found that the magnetic and electrical transport properties are the most improved for samples prepared from MgCl2-NaCl-KCl-MgB2O4 electrolytes.

  10. The preliminary study of the quench protection of an MgB2

    NASA Astrophysics Data System (ADS)

    Juster, F. P.; Berriaud, C.; Bonelli, A.; Pasquet, R.; Przybilski, H.; Schild, T.; Scola, L.

    2014-01-01

    In the framework of general studies currently carried out at CEA/Saclay in collaboration with Sigmaphi Company on dry MgB2 magnet operating at 10 K and medium range field, 1 T up to 4 T., we plan to build a prototype-coil with a commercial MgB2 wire. This coil, the nominal axial magnetic field of which is 1 tesla, will be placed in a 3 teslas background field generated by a classical NbTi coil. This paper deals with the preliminary quench protection studies including stability and quench propagation modeling.

  11. Detailed electronic structure studies on superconducting MgB2 and related compounds

    NASA Astrophysics Data System (ADS)

    Ravindran, P.; Vajeeston, P.; Vidya, R.; Kjekshus, A.; Fjellvåg, H.

    2001-12-01

    In order to understand the unexpected superconducting behavior of MgB2 we have made electronic structure calculations for MgB2 and closely related systems. Our calculated Debye temperature from the elastic properties indicate that the average phonon frequency is very large in MgB2 compared with other superconducting intermetallics and its exceptionally higher Tc can be explained through a BCS mechanism only if phonon softening occurs or the phonon modes are highly anisotropic. We identified a doubly degenerate quasi-two-dimensional key-energy band in the vicinity of EF along the Γ-A direction of BZ (having equal amount of B px and py character) which plays an important role in deciding the superconducting behavior. Based on this result, we have searched for a similar electronic feature in isoelectronic compounds such as BeB2, CaB2, SrB2, LiBC, and MgB2C2 and found that hole doped LiBC and MgB2C2 are potential superconducting materials. We have found that EF in the closely related compound MgB4 is lying in a pseudogap with a negligibly small density of states at EF, which is not favorable for superconductivity. There are contradictory experimental results regarding the anisotropy in the elastic properties of MgB2 ranging from isotropic to moderately anisotropic to highly anisotropic. In order to settle this issue we have calculated the single-crystal elastic constants for MgB2 by the accurate full-potential method and derived the directional-dependent linear compressibility, Young's modulus, shear modulus, and relevant elastic properties from these results. We have observed large anisotropy in the elastic properties consistent with recent high-pressure findings. Our calculated polarized optical dielectric tensor shows highly anisotropic behavior even though it possesses isotropic transport property. MgB2 possesses a mixed bonding character and this has been verified from density of states, charge density, and crystal orbital Hamiltonian population analyses.

  12. Low-Temperature Synthesis of Superconducting Nanocrystalline MgB 2

    DOE PAGESBeta

    Lu, Jun; Xiao, Zhili; Lin, Qiyin; Claus, Helmut; Fang, Zhigang Zak

    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.

  13. Role of MgB2/Cr2O3 nano-interfaces in photoinduced nonlinear optical treatment of the MgB2 superconducting films

    NASA Astrophysics Data System (ADS)

    AlZayed, N. S.; Kityk, I. V.; Ozga, K.; Fedorchuk, A. O.; Soltan, S.; Shahabuddin, M.; El-Naggar, A.

    2014-09-01

    The calculations of the photoinduced nonlinear optical shift with respect to critical temperature for the MgB2 superconducting films (pure and doped by Cr) were performed using the first principle quantum chemical simulations. The principal role of the nano-interfaces between the MgB2 and Cr2O3 was established, and the nano-interfaces have a thickness varying within the 20-30 nm. The latter was done taking into account their long-range ordering additionally aligned by bicolour optical poling. The bicolour poling was performed by the fundamental 10.6 μm laser beam and its doubled frequency coherent second harmonic generation signal. The so formed internal dc-electric field has introduced additional polarization to the media which re-scale the factor of the electron-phonon interaction including the anharmionic one responsible for the occurrence of charge density non-centrosymmetry and the related second order nonlinear optical response. The simulations of the IR induced bicolour treatment were performed both for pure as well as MgB2 superconducting films doped by Cr3+.

  14. Properties of MgB2 films grown at various temperatures by hybrid physical chemical vapour deposition

    NASA Astrophysics Data System (ADS)

    Chen, Ke; Veldhorst, Menno; Lee, Che-Hui; Lamborn, Daniel R.; DeFrain, Raymond; Redwing, Joan M.; Li, Qi; Xi, X. X.

    2008-09-01

    A hybrid physical-chemical vapour deposition (HPCVD) system consisting of separately controlled Mg-source heater and substrate heater is used to grow MgB2 thin films and thick films at various temperatures. We are able to grow superconducting MgB2 thin films at temperatures as low as 350 °C with a Tc0 of 35.5 K. MgB2 films up to 4 µm in thickness grown at 550 °C have Jc over 106 A cm-2 at 5 K and zero applied field. The low deposition temperature of MgB2 films is desirable for all-MgB2 tunnel junctions and MgB2 thick films are important for applications in coated conductors.

  15. 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.

  16. Ti doping on the flux pinning and chemical stability against water of MgB 2 bulk material

    NASA Astrophysics Data System (ADS)

    Zhao, Y.; Cheng, C. H.; Feng, Y.; Machi, T.; Huang, D. X.; Zhou, L.; Koshizuka, N.; Murakami, M.

    2003-04-01

    Ti-doped MgB 2 superconductors with different doping levels were prepared by solid-state reaction at ambient pressure. Jc of the samples changes with the doping level, with the best result achieved at x=0.1. At 5 K, the Jc reaches 2×10 6 A/cm 2 in the self-field. In addition, degradation in water of Jc and irreversibility field ( Hirr) of MgB 2 bulks is significantly reduced by Ti doping. Microstructural analysis reveals that Ti mainly forms a thin TiB 2 layer in the grain boundaries of MgB 2. At the same time MgB 2 grains are greatly refined, forming a strongly coupled nanoparticle structure. Our results show that the unique microstructure of the MgB 2 nanoparticles with TiB 2 nanograin boundaries may take the responsibility for the enhancement of the flux pinning and the chemical stability against water.

  17. MgO platelets and high critical field in MgB2 thin films doped with carbon from methane

    NASA Astrophysics Data System (ADS)

    Zhu, Y.; Hunte, F.; Zhuang, C. G.; Feng, Q. R.; Gan, Z. Z.; Xi, X. X.; Larbalestier, D. C.; Voyles, P. M.

    2009-12-01

    We report that C-doped MgB2 thin films deposited by hybrid physical-chemical vapor deposition (HPCVD) using CH4 as the carbon source have Hc2(0 K)~60 T, similar to that of HPCVD films obtained using (MeCp)2Mg for the carbon. Using transmission electron microscopy, we show that in the films doped using CH4 there is a MgB2C2 layer on top of the MgB2 film, which does not degrade the MgB2 connectivity or Jc. We also find a high density of coherent MgO nanoplatelets in the MgB2 which create strain fields which may give rise to strong π-band scattering and the very high Hc2.

  18. Fundamental investigation of a superconducting level sensor for liquid hydrogen with MgB2 wire

    NASA Astrophysics Data System (ADS)

    Kajikawa, K.; Tomachi, K.; Maema, N.; Matsuo, M.; Sato, S.; Funaki, K.; Kumakura, H.; Tanaka, K.; Okada, M.; Nakamichi, K.; Kihara, Y.; Kamiya, T.; Aoki, I.

    2008-02-01

    The feasibility study of a superconducting level sensor for liquid hydrogen with a magnesium-diboride (MgB2) wire is carried out from an experimental point of view. The sample wire consists of a mono-cored MgB2 superconductor and a cupronickel sheath, and several potential taps are attached to it at even intervals in order to understand the position of a threshold between the superconducting and resistive states roughly. The fabricated sensor is vertically located in a glass dewar vessel with an infill of liquid hydrogen, and the position of a preselected potential tap is adjusted by eye and hand to liquid level before starting a new measurement. Simulated operations with constant currents finally yield the future possibilities as the level sensor for liquid hydrogen with MgB2 wire although the fabricated sensor has a few problems at present. In order to improve the performance of the sensor, the specifications required for MgB2 wires will be reported elsewhere by applying the stability theory in superconductor composites and by simulating the operation with a numerical code.

  19. Synthesis and characterization of excess magnesium MgB 2 superconductor under inert carbon environment

    NASA Astrophysics Data System (ADS)

    Sinha, B. B.; Kadam, M. B.; Mudgel, M.; Awana, V. P. S.; Kishan, Hari; Pawar, S. H.

    2010-01-01

    The structural, transport and magnetic properties of MgB 2 superconductor heavily blended with Mg is studied. The samples are synthesized with a new approach in both, pressed carbon environment and in flowing argon. The excess magnesium used is observed to play dual role: one being the prevention of Mg losses during the synthesis process and hence maintaining the stoichiometry of MgB 2 phase, and second being the formation of Mg milieu probably all around the MgB 2 grains to give a dense structure. Excess Mg also improves the grain connectivity by going into the pores and there by minimizing the insulating junctions. The residual resistivity of the sample is observed to decrease from 57.02 μΩ cm to 10.042 μΩ cm as it is progressively filled with superconductor-normal-superconductor (SNS) type junctions amongst the grains by the virtue of increased magnesium content. The synthesized samples devoid of porosity show the superconducting transition, T c in the range of 39-34 K as of clean MgB 2 samples, though overloaded with Mg. The excess Mg resulted in enhanced critical current density, J c from 6.8 × 10 3 A cm -2 to 5.9 × 10 4 A cm -2 at 20 K and 10 kOe, with reasonable decrease in the superconducting transition. Thus our samples being overloaded with Mg impart mechanical strength and competitive superconducting properties, which forms a part of interest.

  20. Hot Extrusion of Ex-Situ MgB2 Powder

    NASA Astrophysics Data System (ADS)

    Nachtrab, William T.; Rudziak, Mark K.; Wong, Terence

    2008-03-01

    We investigated the fabrication of ex-situ processed MgB2 round wire by hot extrusion. Composite ex-situ MgB2 monocore billets were fabricated with a composite sheath consisting of either an AISI 304 or AISI 430 stainless steel clad with copper. The stainless steel was intended to serve as reinforcement for the powder core and maintain mechanical compatibility between the MgB2 core and the copper cladding. The composite billets were extruded at temperatures between 593 and 900 °C at a reduction ratio of 5.2 (81% RA). The billets having the 304 SS barrier cracked during extrusion, while the billets with 430 SS were successfully extruded. Several additional monocore billets with 430 SS/Cu sheath were extruded at 650 °C and reduction ratio of 5.0 (80% RA). The extruded rods were cold drawn, restacked in a copper tube in an 18 filament array, and subsequently cold drawn to 2 mm diameter. A 61 filament restack billet was also assembled and hot extruded at 538 °C and R = 5.0. The results demonstrate that hot extrusion has the potential to be a viable method for fabricating multifilament round MgB2 wire.

  1. 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.

  2. 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.

  3. Microstructural and superconducting properties of C6H6 added bulk MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Babaoğlu, Meral G.; Safran, Serap; Çiçek, Özlem; Ağıl, Hasan; Ertekin, Ercan; Hossain, Md. Shahriar A.; Yanmaz, Ekrem; Gencer, Ali

    2012-10-01

    The effect of aromatic hydrocarbon (benzene, C6H6) addition on lattice parameters, microstructure, critical temperature (Tc), critical current density (Jc) of bulk MgB2 has been studied. In this work only 2 mol% C6H6 addition was found to be very effective in increasing the Jc values, while resulting in slight reduction of the Tc. Jc values of 2 mol% C6H6 added MgB2 bulks reached to 1.83×106 A/cm2 at 15 K and 0 T. Microstructural analyses suggest that Jc enhancement is associated with the substitution of carbon with boron and which also results in the smaller MgB2 grain size. The change in the lattice parameters or the lattice disorder is claimed as a cause of the slight reduction in the Tc by carbon addition. We note that our results show the advantages of C6H6 addition include homogeneous mixing of precursor powders, avoidance of expansive nanoadditives, production of highly reactive C, and significant enhancement in Jc of MgB2, compared to un-doped samples.

  4. The role of various boron precursor on superconducting properties of MgB2/Fe

    NASA Astrophysics Data System (ADS)

    Safran, S.; Kılıçarslan, E.; Kılıç, A.; Gencer, A.

    2014-09-01

    The superconducting properties of Fe sheathed MgB2 wire has been studied as a function of precursor B powder particle size. The in situ processed MgB2 samples were prepared by means of conventional solid state reaction method with magnesium powder (99.8%, 325 mesh) and three different types of amorphous boron powders (purity; 98.8%, >95% and 91.9%) from two sources, Pavezyum (Turkish supplier) and Sigma Aldrich. The particle sizes of Turkish boron precursor powder were selected between 300 and 800 nm. The structural and magnetic properties of the prepared samples were investigated by means of the X-ray powder diffraction (XRD) and ac susceptibility measurements. The XRD patterns showed that the diffraction peaks for our samples belong to the main phase of the MgB2 diffraction patterns. The highest critical temperature, Tc = 38.4 K was measured for the MgB2 sample which was fabricated by using the 98.8% B. The critical current density of this sample was extracted from the magnetization measurements and Jc = 5.4 × 105 A cm-2 at 5 K and B = 2 T. We found that the sample made by using the 98.8% boron showed almost 2 times higher Jc than that of obtained from 91.9% B powder.

  5. Possible high-temperature superconductivity in hole-doped MgB2C2

    NASA Astrophysics Data System (ADS)

    Verma, A. K.; Modak, P.; Gaitonde, D. M.; Rao, R. S.; Godwal, B. K.; Gupta, L. C.

    2003-09-01

    We report first-principles full potential linearised augmented plane wave calculations of the electronic band structure of the compound MgB2C2 and its hole-doped derivatives Mg0.5Li0.5B2C2, Mg0.5Na0.5B2C2, Mg0.9Na0.1B2C2 and Mg0.5K0.5B2C2. The parent compound MgB2C2 is a band insulator, which on hole doping, is predicted to turn metallic with a large density of states at the Fermi energy. Its band dispersion shows a flat band feature close to the Fermi energy, reminiscent of MgB2. Based on our estimates of changes in the density of states at the Fermi level, we predict that hole-doped MgB2C2 is a potential candidate for high-temperature superconductivity.

  6. Influence of magnetic nanoparticles on superconductivity of MgB2

    NASA Astrophysics Data System (ADS)

    Novosel, N.; Babić, E.

    2013-10-01

    Recently we begun systematic study of the influence of magnetic nanoparticles (MNPs) on the superconducting properties (transition temperature Tc, critical fields and critical current density, Jc) of MgB2 wires. We prepared over 60 Fe-sheathed MgB2 wires doped with different types and quantities of MNPs, such as pure metals (Fe, Co, Ni), magnetic borides (Fe2B, Co2B, NiCoB) and ferrites (AFe2O4, A = Mn, Fe, Co, Ni, Cu). Both, uncoated and coated (with silica or dextrin) MNPs were used in order to assess also the effects of co-doping and of interactions between MNPs. All MNPs suppress Tc of MgB2 and higher MNP contents inevitably cause deterioration of superconducting properties of wires. However, light doping (⩽2.5 wt.%) with few species of MNP (Ni, NiCoB and dextrin coated NiFe2O4 and Fe3O4) improved low-temperature, high-field Jc of MgB2 wires. Possible origin of this improvement is briefly discussed.

  7. Ti-doping effects on magnetic properties of dense MgB2 bulk superconductors

    NASA Astrophysics Data System (ADS)

    Naito, Tomoyuki; Yoshida, Takafumi; Fujishiro, Hiroyuki

    2015-09-01

    We have studied the effects of Ti doping on the magnetic properties of MgB2 superconducting bulks. The trapped field, which was obtained by field-cooled magnetization, {B}{{T}}{FC}, was about 3.6 T at 13 K at the surface of the single Ti5-20% doped MgB2 bulks, which was about 1.3 times larger than that of the non-doped bulk. The {B}{{T}}{FC} of 4.6 T was achieved at 14.1 K in the centre of the doubly stacked Ti-doped MgB2 bulks. The remanent magnetic flux density, which corresponds to the trapped field by zero-field cooled magnetization, {B}{{T}}{ZFC}, was comparable with the absolute value of coercive force with a very small vortex creep rate of about 2% over 40 h. These results suggested that the MgB2 bulk was an excellent ‘quasi-permanent’ magnet. The critical current density, {J}{{c}}, under magnetic field was also enhanced by Ti doping; under 3 T at 20 K, the {J}{{c}} of 4.0× {10}3 A cm-2 for the pristine sample was enhanced to that of 1.6-1.8 × {10}4 A cm-2 for the Ti-doped samples. The irreversibility field exceeded 5 T at 20 K for the Ti-doped samples. The existence of nanometric unreacted B and strongly Mg-deficient Mg-B particles and TiB2 layers at the periphery of Ti precipitates was suggested in the Ti-doped bulks by microscopic observation. The improvement of the vortex pinning properties in Ti-doped MgB2 originated from the creation of the nanometric nonsuperconducting particles and TiB2 layers acting as strong vortex pinning centres.

  8. 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.

  9. Giant Anharmonicity and Theory of Surprising BCS Superconductivity in MgB2 at 40 K

    NASA Astrophysics Data System (ADS)

    Yildirim, Taner

    2002-03-01

    The recent surprise discovery of superconductivity in MgB2 at 40 K has stimulated a great deal of research on this intercalated grahite-like system. Sparked by this discovery, we set out to unlock the structural secrets and, in particular, to reveal the origin of the high Tc in MgB_2; an electron-phonon or other exotic mechanism? To answer this fundamental question, we calculated T_c, its pressure dependence for uni- and biaxial compressions, and the isotope effect from the electronic band structure and lattice dynamics of MgB2 using density functional theory[1-2]. The calculated phonon density of states (DOS) are in excellent agreement with the inelastic neutron scattering measurements. We find that the in-plane boron phonons near the zone-center are very anharmonic and strongly coupled to the planar B sigma bands near the Fermi level. The boron mass and pressure dependence of this mode is found to be the key to quantitatively explaining the observed high T_c, the total isotope effect, and the pressure dependence of T_c. We propose that a stringent test on the hole and phonon based theories of the superconductivity in MgB2 would be a measurement of the biaxial ab-compression dependence of T_c. In collobration with Oguz Gulseren, NIST and UPENN [1] T. Yildirim et. al., Phys. Rev. Lett. 87, 037001 (2001). [2] For details, see http://www.ncnr.nist.gov/staff/taner/mgb2

  10. The critical parameters in in-situ MgB2 wires and tapes with ex-situ MgB2 barrier after hot isostatic pressure, cold drawing, cold rolling and doping

    NASA Astrophysics Data System (ADS)

    Gajda, D.; Morawski, A.; Zaleski, A. J.; Häßler, W.; Nenkov, K.; Rindfleisch, M. A.; Żuchowska, E.; Gajda, G.; Czujko, T.; Cetner, T.; Hossain, M. S. A.

    2015-05-01

    MgB2 precursor wires were prepared using powder in tube technique by Institute of High Pressure PAS in Warsaw. All samples were annealed under isostatic pressure generated by liquid Argon in the range from 0.3 GPa to 1 GPa. In this paper, we show the effects of different processing routes, namely, cold drawing (CD), cold rolling (CR), hot isostatic pressure (HIP) and doping on critical current density (Jc), pinning force (Fp), irreversible magnetic-field (Birr), critical temperature (Tc), n value, and dominant pinning mechanism in MgB2/Fe wires with ex situ MgB2 barrier. The results show that medium pressures (˜0.35 GPa) lead to high Jc in low and medium magnetic fields (0 T - 9 T). On the other hand, higher pressures (˜1 GPa) lead to enhanced Jc in high magnetic fields (above 9 T). Transport measurements show that CD, CR, and HIP have small effects on Birr and Tc, but CD, CR, HIP, and doping enhance Jc and Fp in in situ MgB2 wires with ex situ MgB2 barrier. Transport measurements on in situ undoped MgB2 wire with ex situ MgB2 barrier yield a Jc of about 100 A/mm2 at 4.2 K in 6 T, at 10 K in 4 T and at 20 K in 2 T. The results also show that cold drawing causes increase of n value.

  11. Photoluminescence properties of Sr2MgB2O6:Eu3+ red phosphor under near-UV excitation

    NASA Astrophysics Data System (ADS)

    Guo, Rui; Tang, Songling; Zhong, Shaobin; Luo, Lan; Cheng, Baochang; Xiong, Yuhua

    2015-12-01

    Sr2MgB2O6:Eu3+ red phosphor has been synthesized by modified solid-state reaction method. The photoluminescence properties of Sr2MgB2O6:Eu3+ phosphor have been investigated. Sr2MgB2O6:Eu3+ phosphor can be effectively excited by 394 nm and generate red emission at 615 nm. Eu3+ ions occupy both Sr2+-site and Mg2+-site in Sr2MgB2O6. Univalent charge compensators (Li+, Na+ and K+) can obviously improve the photoluminescence properties of Sr2MgB2O6:Eu3+ phosphor and Na+ is the optimal charge compensator. The effect of substitution of M2+ (M = Mg, Ca or Ba) ion for Sr2+ on the photoluminescence properties of Sr2MgB2O6:Eu3+ phosphor has also been discussed. It implies that Sr2MgB2O6:Eu3+ may be a potential red phosphor for near-UV W-LEDs or other display devices.

  12. Magnetic nanoparticles in MgB2: Vortex pinning, pair breaking and connectivity

    NASA Astrophysics Data System (ADS)

    Babić, Emil; Novosel, Nikolina; Pajić, Damir; Galić, Stipe; Zadro, Krešo; Drobac, Đuro

    2016-02-01

    The results indicating magnetic flux pinning in MgB2 wires doped with three types of magnetic nanoparticles (MNP) are reported. The magnetic state of MNPs, both as-prepared and inside the MgB2 core, was determined with magnetization and ac susceptibility measurements. The competition between detrimental influence of doping (reduced connectivity, pair breaking) and enhanced flux pinning leads to deterioration of electromagnetic properties of doped wires at high MNP content, whereas light doping causes an enhancement of critical current density, Jc, and/or irreversibility field, Birr, for all our MNPs. For Ni and dextrin coated NiFe2O4 MNPs the enhancement of Jc was comparable to that achieved with the best nonmagnetic dopands. Detailed analysis indicates the contribution of magnetic flux pinning including the matching effects in flux pinning on MNPs.

  13. Elastic Constants of Superconducting MgB2 from Molecular Dynamics Simulations with Shell Model

    NASA Astrophysics Data System (ADS)

    Guo, Yun-Dong; Chen, Xiang-Rong; Yang, Xiang-Dong; Gou, Qing-Quan

    2005-11-01

    The elastic constants of superconducting MgB2 are calculated using a molecular dynamics method (MD) with shell model. The lattice parameters, five independent elastic constants, equations of state (EOS), Debye temperature, and bulk modulus of MgB2 are obtained. Meanwhile, the dependence of the bulk modulus B, the lattice parameters a and c, and the unit cell volume V on the applied pressure are presented. It is demonstrated that the method introduced here can well reproduce the experimental results with a reasonable accuracy. The project supported by National Natural Science Foundation of China under Grant No. 60436010 and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, the Ministry of Education of China under Grant No. 2004176-6-4

  14. Comparison of Tunneling in Fe-based Superconductors with Multi-band MgB2

    NASA Astrophysics Data System (ADS)

    Zasadzinski, John; Iavarone, Maria

    MgB2 is an s-wave, phonon coupled, multiband superconductor that exhibits novel tunneling spectra including a subtle dip feature due to quasiparticle transfer between bands. Since this feature mimics the above-gap spectral dip feature observed in Fe-based superconductors, typically attributed to a strong coupling boson, it is worthwhile to consider whether quasiparticle transfer is relevant. We first show that the dip in MgB2 appears in the π-band, DOS (Δ = 2.4 meV) and is due to quasiparticle transfer to the σ-band with Δ = 7.2 meV. Reviewing the spectral dip in Fe-based superconductors, including new data on FeSe crystals, there are inconsistencies with quasiparticle transfer as the origin. The conclusion is that the spectral dip is more likely due to a boson, the resonance spin excitation, as found in cuprate superconductors.

  15. 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.

  16. Preparation and characterization of Sc doped MgB2 wires

    NASA Astrophysics Data System (ADS)

    Grivel, J.-C.; Burdusel, M.

    2016-09-01

    The in-situ technique was used to manufacture scandium (Sc) doped MgB2 wires in a composite Cu-Nb sheath. After reaction at 700 °C, at most 1 at.% Mg was replaced by Sc in the MgB2 phase, without significant influence on its superconducting transition temperature. For higher Sc concentrations in the nominal composition, the formation of Sc-rich impurity phases was evidenced by SEM/EDS observations. The critical current density and accommodation field of the wires are weakly dependant on the Sc content. It is believed that these effects are related more to modifications of the thermal behaviour of the precursor powders revealed by DTA measurements than to actual doping. The best performance was obtained in a wire with Mg:Sc = 0.995_0.005 atomic ratio.

  17. Biomolecular ion detection using high-temperature superconducting MgB2 strips

    NASA Astrophysics Data System (ADS)

    Zen, N.; Shibata, H.; Mawatari, Y.; Koike, M.; Ohkubo, M.

    2015-06-01

    Superconducting strip ion detectors (SSIDs) are promising for realization of ideal ion detection with 100% efficiency and nanosecond-scale time response in time-of-flight mass spectrometry. We have detected single biomolecular ions in the keV range using a 10-nm-thick and 250-nm-wide strip of a high temperature superconductor, magnesium diboride (MgB2), at temperatures of up to 13 K. The output pulse shape is explained remarkably well using circuit simulations and time-dependent Ginzburg-Landau simulations coupled with a heat diffusion equation. The simulations show that the hot spot model is applicable to the proposed MgB2-SSIDs and the normal region expansion is completed within 16 ps, which corresponds to a maximum length of 1010 nm.

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

    DOE PAGESBeta

    Mou, Daixiang; Jiang, Rui; Taufour, Valentin; Flint, Rebecca; Bud'ko, S. L.; Canfield, P. C.; Wen, J. S.; Xu, Z. J.; Gu, Genda; Kaminski, Adam

    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.

  19. 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.

  20. 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.

  1. 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.

  2. Enhanced superconducting properties of rare-earth oxides and graphene oxide added MgB2

    NASA Astrophysics Data System (ADS)

    Sudesh; Das, S.; Bernhard, C.; Varma, G. D.

    2014-10-01

    In this paper, the effects of addition of (i) graphene oxide (GO), (ii) a series of rare-earth (RE, RE = La, Sm, Eu, Gd, Tb and Ho) oxides (REO) and (iii) a mixture of GO and rare-earth oxides (GO + REO) on the superconducting properties of MgB2, have been studied with the help of electrical transport and magnetic measurements. All the samples have been prepared following the standard solid-state reaction route. We have used an optimum value of 1 wt% REO and 3 wt% GO for addition on the basis of previous studies. X-ray diffraction studies confirm the formation of hexagonal crystal structure (space group P6/mmm) of MgB2 with small amounts of REBx (x = 4 and 6) and MgO impurity phases in all the synthesized samples. We observe that the critical current density, Jc and upper critical field Hc2(0) improve significantly in the REO-added and GO-added samples with no significant change in critical temperature, Tc. A substantial enhancement in Jc(H) and Hc2(0) is observed with the GO + REO addition in MgB2. The different flux pinning mechanisms in all the samples are studied and it is found that the point pinning is the dominant mechanism in the GO-added samples and grain boundary pinning is the dominant one in the REO added samples. We have seen the combined effect of both types of flux pinning mechanisms in GO + REO added MgB2.

  3. A study of the temperature dependence of the local ferroelectric properties of c-axis oriented Bi6Ti3Fe2O18 Aurivillius phase thin films: Illustrating the potential of a novel lead-free perovskite material for high density memory applications

    NASA Astrophysics Data System (ADS)

    Faraz, Ahmad; Deepak, Nitin; Schmidt, Michael; Pemble, Martyn E.; Keeney, Lynette

    2015-08-01

    The ability to control the growth, texture and orientation of self-nanostructured lead-free Aurivillius phase thin films can in principle, greatly improve their ferroelectric properties, since in these materials the polarization direction is dependent on crystallite orientation. Here, we report the growth of c-plane oriented Bi6Ti3Fe2O18 (B6TFO) functional oxide Aurivillius phase thin films on c-plane sapphire substrates by liquid injection chemical vapour deposition (LI-CVD). Microstructural analysis reveals that B6TFO thin films annealed at 850°C are highly crystalline, well textured (Lotgering factor of 0.962) and single phase. Typical Aurivillius plate-like morphology with an average film thickness of 110nm and roughness 24nm was observed. The potential of B6TFO for use as a material in lead-free piezoelectric and ferroelectric data storage applications was explored by investigating local electromechanical (piezoelectric) and ferroelectric properties at the nano-scale. Vertical and lateral piezoresponse force microscopy (PFM) reveals stronger in-plane polarization due to the controlled growth of the a-axis oriented grains lying in the plane of the B6TFO films. Switching spectroscopy PFM (SS-PFM) hysteresis loops obtained at higher temperatures (up to 200°C) and at room temperature reveal a clear ferroelectric signature with only minor changes in piezoresponse observed with increasing temperature. Ferroelectric domain patterns were written at 200°C using PFM lithography. Hysteresis loops generated inside the poled regions at room and higher temperatures show a significant increase in piezoresponse due to alignment of the c-axis polarization components under the external electric field. No observable change in written domain patterns was observed after 20hrs of PFM scanning at 200°C, confirming that B6TFO retains polarization over this finite period of time. These studies demonstrate the potential of B6TFO thin films for use in piezoelectric applications at

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Observation of multiband effects in the microwave complex conductivity of pure and Al-doped MgB 2 samples

    NASA Astrophysics Data System (ADS)

    Di Gennaro, E.; Lamura, G.; Palenzona, A.; Putti, M.; Andreone, A.

    2004-08-01

    There is presently a general agreement that the simple inter-metallic compound MgB 2 is a conventional, phonon mediated, superconductor, and that the anomalies in its behaviour can be consistently explained by the existence of two different gaps. We present a study of the complex conductivity as a function of temperature in pure and Al-doped MgB 2 pellets by using a dielectrically loaded resonant cavity at 19 GHz.

  9. Phase evolution and microstructure of high Jc SiC doped MgB2 fabricated by hot pressing

    NASA Astrophysics Data System (ADS)

    Qu, B.; Sun, X. D.; Li, J.-G.; Xiu, Z. M.; Xue, C. P.

    2009-07-01

    We report the phase evolution, microstructure, and critical current density (Jc) of the SiC doped MgB2 superconductors. In our study, all samples were fabricated by hot pressing with a heating rate of 200 °C min-1. The results show that the reaction of 2Mg+SiC = Mg2Si+C can occur at about 500 °C, about 50 °C lower than the formation temperature of MgB2. On the other hand, according to the experimental results and thermodynamic calculations, boron (B) does not react with SiC to form B4C and Si, neither does MgB2 react with SiC to form Mg2Si and B4C. The MgB2 phase was formed via both a solid-solid reaction (during the heating process between about 500 and 650 °C) and a liquid-solid reaction (>650 °C) after the melting of Mg, and the two reactions resulted in differences in the grain size of the MgB2. From scanning electron microscopy, the Mg2Si particles are homogeneously distributed within the MgB2 matrix, with particle sizes ranging from 35 to 230 nm. From the perspective of superconductivity, the C substitution results in strong electron scattering centers in the MgB2 structure. It reduces the electron mean free path and thus may significantly enhance the magnetic Jc. The peak Jc of the 5 wt% SiC doped MgB2 reaches above 106 A cm-2 at 5 K, and decreases slowly with increasing field, remaining high, above 105 A cm-2, at 7 T.

  10. Self-sintering-assisted high intergranular connectivity in ball-milled ex situ MgB2 bulks

    NASA Astrophysics Data System (ADS)

    Mizutani, Shunsuke; Yamamoto, Akiyasu; Shimoyama, Jun-ichi; Ogino, Hiraku; Kishio, Kohji

    2014-11-01

    To understand the mechanisms leading to higher intergranular connectivity in polycrystalline ex situ MgB2 prepared using a pressure-less self-sintering technique, the influence of the initial particle size of the MgB2 powder was investigated. MgB2 bulks sintered at 900 °C for 24 h using ball-milled powders exhibited a network structure with both qualitatively and quantitatively improved intergranular couplings. The connectivity calculated using normal-state transport measurements reached a high value of ˜40%, which is comparable to that of MgB2 bulks fabricated via Mg diffusion or high-pressure-assisted processes. Moreover, the sintering time required to achieve a reasonably high connectivity of 25-30% was less than 1 h. Notably, microstructural analyses confirmed the formation of intergranular necks and grain boundaries during the early stage of sintering. These results suggested self-sintering of the ball-milled MgB2 bulks proceeded much more rapidly than those sintered using an MgB2 powder without ball-milling. Increased intergranular contact points and decreased gap length between grains in green compact are assumed to be the origins for the stimulated self-sintering and corresponding increase in the electrical connectivity.

  11. Upper Critical Field of Carbon-doped MgB2 Thin Films by HPCVD Using TMB

    NASA Astrophysics Data System (ADS)

    Dai, Wenqing; Rickel, Dwight; Weng, Xiaojun; Chen, Ke; Redwing, Joan; Li, Qi; Xi, Xiaoxing

    2010-03-01

    We report Hc2 measurements in high magnetic field up to 60 T on carbon-doped MgB2 thin films. About 100 nm thick carbon-doped MgB2 films were fabricated by the Hybrid Physical-Chemical Vapor Deposition (HPCVD) method using Trimethylboron (TMB) as the doping source. For heavily doped MgB2 films, high slope -dHc2^//ab /dT near Tc, as large as 8.3 T/K, was obtained for a sample with the Tc of 32.3 K. The Hc2(T) in ab-plane has a downward curvature and is above 60 T at low temperatures. The c-direction Hc2 is close to 20 T. The Hc2 anisotropy increases with carbon-doping, as opposed to the reported results from other carbon-doping techniques. The TEM study shows the MgB2 forms many nm thick layers sandwiched in the MgB2C2 matrix. Using two-gap dirty limit theory, the temperature dependences of Hc2 and abnormal Hc2 anisotropy in the heavily doped samples are explained by the presence of many very thin MgB2 layers.

  12. 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.

  13. 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.

  14. Using helium as background gas to avoid hydrogen brittleness for MgB2 film fabrication on niobium substrate by HPCVD

    NASA Astrophysics Data System (ADS)

    Guo, Xin; Ni, Zhimao; Chen, Lizhi; Hu, Hui; Yang, Can; Feng, Qingrong; Liu, Kexin

    2016-05-01

    Magnesium diboride has shown potential as an alternative material for the application of superconducting RF cavities. However, if MgB2 films are fabricated on niobium substrates with HPCVD method, hydrogen brittleness will cause cracks on MgB2 film when it is bent. In this work, we have investigated the possibility of depositing MgB2 film on niobium in other background gases rather than hydrogen to avoid hydrogen brittleness. Though MgB2 films fabricated in nitrogen and argon have impurities and show poor superconducting properties, the MgB2 film fabricated in helium has similar morphology and superconducting properties of that prepared in hydrogen and no cracks are observed after bending. The problem of hydrogen brittleness can be solved by using helium as the background gas when fabricating MgB2 films on niobium substrates.

  15. Spherulitic (c-axis) Growth for Terrestrial (Mauna Kea, Hawaii) and Martian Hematite "blueberries"

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Ming, D. W.; Morris, R. V.

    2006-01-01

    Hematite concentrations observed by Thermal Emission Spectrometer (TES) onboard Mars Global Surveyor were considered a possible indicator for aqueous processes on Mars. Observations made by Opportunity show that the hematite at Meridiani Planum is present as spherules ( blueberries) and their fragments. The internal structure of the hematite spherules is not discernable at the resolution limit (approx.30 m/pixel) of Opportunity s Microscopic Imager (MI). A terrestrial analog for martian hematite spherules are spherules from hydrothermally altered and sulfate-rich tephra from the summit region of Mauna Kea volcano, Hawaii. The objective of this study is to determine the crystal growth fabric of the Mauna Kea hematite spherules using transmission electron microscopy (TEM) techniques and to relate that crystalline fabric to the observed TES signature of Meridiani Planum "blueberries." TEM analysis of Mauna Kea spherules exhibited a radial growth pattern consisting of "fibrous" hematite with the c-axis of hematite particles aligned along the elongation direction of the hematite fibers. The individual fibers appear to be made of coalesced nano-particles of hematite arranged with their c-axis oriented radially to form a spherical structure. Lattice fringes suggest long-range order across particles and along fibers. According to interpretations of thermal emission spectra for Meridian Planum hematite, the absence of a band at approx. 390/cm implies a geometry where c-face emission dominates. Because the c-face is perpendicular to the c-axis, this is precisely the geometry for the Mauna Kea spherules because the c-axis is aligned parallel to their radial growth direction. Therefore, we conclude as a working hypothesis that the martian spherules also have radial, c-axis growth pattern on a scale that is too small to be detected by the MER MI. Furthermore, by analogy with the Mauna Kea spherules, the martian blueberries could have formed during hydrothermal alteration of

  16. 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.

  17. Field Distribution and Flux-Line Depinning in MgB 2

    NASA Astrophysics Data System (ADS)

    Urbano, R. R.; Pagliuso, P. G.; Rettori, C.; Kopelevich, Y.; Moreno, N. O.; Sarrao, J. L.

    2002-08-01

    We report the first observation of the field distribution and flux-line lattice (FLL) depinning in the vortex-state (VS) of a type-II superconductor probed by conduction electron spin resonance (CESR). CESR was performed in MgB 2 (Tc~=39 K) at 4.1 GHz (1455 Oe) and 9.5 GHz (3390 Oe). The field distribution, n(H), and a standard deviation of σ~14 Oe (at 28 K/4.1 GHz and at 7 K/9.5 GHz) were inferred, respectively, from the distortion and broadening of the CESR in the VS. For both frequencies, the FLL depinning temperature was determined.

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

    NASA Astrophysics Data System (ADS)

    Mou, Daixiang; Manni, Soham; Taufour, Valentin; Wu, Yun; Huang, Lunan; Bud'ko, S. L.; Canfield, P. C.; Kaminski, Adam

    2016-04-01

    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 E2 g phonon mode, is shifted to higher binding energy by ˜3.5 meV in Mg 10B2 and the shift is not affected by superconducting transition. 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.

  19. Multifilamentary MgB2 wires fracture behavior during the drawing process

    NASA Astrophysics Data System (ADS)

    Shan, D.; Yan, G.; Zhou, L.; Li, J. S.; Li, C. S.; Wang, Q. Y.; Xiong, X. M.; Jiao, G. F.

    2012-12-01

    The fracture behavior of 6 + 1 filamentary MgB2 superconductive wires is presented here. The composite wires were fabricated by in situ Powder-in-Tube method using Nb as a barrier and copper as a stabilizer. The microstructure of the material has a great influence on its fracture behavior. The microstructural aspects of crack nucleation and propagation are discussed. It shows that there are complicated correlations between fracture behavior and the main influencing parameters, which contain specific drawing conditions (drawing velocity, reduction in area per pass), materials properties (strength, yield stress, microstructure) as well as the extent of bonding between the metal sheaths at their interface.

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

    DOE PAGESBeta

    Mou, Daixiang; Manni, Soham; Taufour, Valentin; Wu, Yun; Huang, Lunan; Bud'ko, S. L.; Canfield, P. C.; Kaminski, Adam

    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.

  1. 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 antenna. Measurements have been carried out on these devices in the DC, Microwave, and THz regimes. The devices are capable of mixing signals above 20 K indicating that operation may be possible using a cryogen-free cooling system. We will report the results of all measurements taken to indicate the local oscillator power requirements and the IF bandwidth of MgB2 HEB mixers.

  2. Thermal conductivity and stability of commercial MgB2 conductors

    NASA Astrophysics Data System (ADS)

    Bonura, Marco; Senatore, Carmine

    2015-11-01

    This paper presents a study of the thermal transport properties of MgB2 tapes differing in architecture, stabilization and constituent materials. The temperature and field dependence of thermal conductivity, κ (T,B), was investigated both along the conductor and in the direction perpendicular to the tape. These data provide fundamental input parameters to describe the 3D heat diffusion process in a winding. Thermal transport properties—even in field—are typically deduced using semi-empirical formulas based on the residual resistivity ratio of the stabilizer measured in absence of magnetic field. The accuracy of these procedures was evaluated comparing the calculated κ values with the measured ones. Based on the experimental thermal conduction properties κ (T,B) and critical current surface {J}{{C}}(T,B) we determined the dependence of minimum quench energy and normal zone propagation velocity on the operating parameters of the conductor. The correlation between thermal properties and tape layout allowed us to provide information on how to optimize the thermal stability of MgB2 conductors.

  3. MoRe-based and MgB2 -based tunnel junctions and their characteristics

    NASA Astrophysics Data System (ADS)

    Shaternik, V.; Larkin, S.; Noskov, V.; Chubatyy, V.; Belogolovskii, M.

    2010-06-01

    Perspective Josephson Mo-Re alloy-oxide-Pb, MgB2- oxide - Mo-Re alloy and Mo-Re alloy-normal metal-oxide- normal metal-Mo-Re alloy junctions have been fabricated and investigated. Thin (~50-100 nm) MoRe superconducting films are deposited on Al2O3 substrates by using a dc magnetron sputtering of MoRe target. Thin (~50-100 nm) MgB2 superconducting films are deposited on Al2O3 substrates by using e-beam evaporation of boron and thermal coevaporation of magnesium. To investigate a transparency spread for the fabricated junctions barriers the computer simulation of the measured quasiparticle I-V curves have been done in framework of the model of multiple Andreev reflections in double-barrier junction interfaces. It's demonstrated the investigated junctions can be described as highly asymmetric double-barrier Josephson junctions with great difference between the two barrier transparencies. Results of computer simulation of quasiparticles I-V curves of junctions are presented and discussed. The IC(T) characteristics, measured for Josephson heterostructures with different thickness of metal layer s and exposure dose E, essentially deviate from an Ambegaokar- Baratoff (A&B) IC(T) behavior and Kulik-Omelianchuck (K&O) curves, because of proximity effect caused by the comparatively high value of s (up to 100 nm).

  4. The Effect of Argon Ambient Pressure and Annealing Time on Bulk MgB2 Superconductor

    NASA Astrophysics Data System (ADS)

    Erdem, Murat; Ozturk, Ozgur; Asikuzun, Elif; Kaya, Seydanur; Safran, Serap; Kilic, Ahmet; Terzioglu, Cabir

    2015-03-01

    The effects of Ar ambient pressure (vacuum, 0B, 10B and 20B) and annealing times (0.5 h and 1 h) on microstructural, superconducting and mechanical properties of bulk superconducting MgB2 are investigated. The samples are produced using the solid state reaction method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements were performed for determination of the crystal structure, and surface morphology of MgB2 samples, respectively. The superconducting properties were studied by AC magnetic susceptibility and DC resistivity measurements. Increasing the Ar pressure decreased the lattice parameters and hence the average grain size. Increasing the annealing time results in larger lattice parameters and larger grain formation. The susceptibility measurements revealed two step transition which is reminiscent of granular superconductors. The intra-grain transition temperature is determined to be 38.4 K for all samples. The inter-grain transition temperatures of 37.2 K is obtained for samples produced under Ar ambient. The samples produced under Ar ambient have better superconducting properties than the ones produced in vacuum. Increasing the annealing time under vacuum further decreases the superconducting properties probably due to Mg loss. This research is supported by Kastamonu University Scientific Research Projects Coordination Department under the Grant No. KUBAP-03/2012-03.

  5. Evidence of new pinning centers in irradiated MgB2

    NASA Astrophysics Data System (ADS)

    Tarantini, C.; Martinelli, A.; Manfrinetti, P.; Palenzona, A.; Pallecchi, I.; Putti, M.; Ferdeghini, C.; Cimberle, M. R.

    2008-03-01

    It has been shown that C or SiC addictions can strongly enhance upper critical field of MgB2, leading to an in-field increase of critical current, but without introducing pinning centers other than grain boundaries. On the contrary neutron irradiation introduces new pinning centers, as highlighted by a significant shift of the maximum of pinning force and by a strong improvement of Jc at high field. This effect can be correlated to the defects that neutron irradiation produces. In fact TEM images show the presence of nanometric amorphous regions whose sizes are compatible with the coherence length and such as to act as pinning centers through two different mechanisms. The influence that neutron irradiation induces on MgB2 is also confirmed by magnetization decays that, differently by doped samples, show an important enhancement of pinning energies at high field. These measurements highlight as the increase of pinning energy with irradiation fluence is strongly correlated with Jc improvement.

  6. Investigations of current limiting properties of the MgB2 wires subjected to pulse overcurrents in the benchtop tester

    NASA Astrophysics Data System (ADS)

    Ye, Lin; Majoros, M.; Campbell, A. M.; Coombs, T.; Harrison, S.; Sargent, P.; Haslett, M.; Husband, M.

    2007-04-01

    A laboratory scale desktop test system including a cryogenic system, an AC pulse generation system and a real time data acquisition program in LabView/DAQmx, has been developed to evaluate the quench properties of MgB2 wires as an element in a superconducting fault current limiter under pulse overcurrents at 25 K in self-field conditions. The MgB2 samples started from a superconducting state and demonstrated good current limiting properties characterized by a fast transition to the normal state during the first half of the cycle and a continuously limiting effect in the subsequent cycles without burnouts. The experimental and numerical simulation results on the quench behaviour indicate the feasibility of using MgB2 for future superconducting fault current limiter (SFCL) applications. This work is supported by Rolls-Royce Plc and the UK Department of Trade & Industry (DTI).

  7. A study on the nonlinear microwave electrodynamic response of e-beam evaporated MgB2 superconducting thin films

    NASA Astrophysics Data System (ADS)

    Andreone, A.; Di Gennaro, E.; Lamura, G.; Salluzzo, M.; Purnell, A.; Cohen, L. F.; Hao, L.; Gallop, J.; Cantoni, C.; Paranthaman, M.

    2003-02-01

    We present a study on the temperature and field dependence of the microwave surface impedance Zs in thin films of the superconducting MgB2 compound. Samples were prepared by e-beam evaporation of boron on r-plane sapphire followed by an ex situ annealing in Mg vapour. Critical temperature values range between 26 and 38 K. Surface impedance measurements (Zs = Rs + iXs) were performed from 2 K close to Tc in the microwave region up to 20 GHz via parallel plate or dielectrically loaded resonators in 'symmetric' (two MgB2 films) and asymmetric (an MgB2 film and a commercial YBCO control film) configurations. At high microwave power, frequency domain measurements show a characteristic signature associated with weak links and this appears to be the limiting factor governing the performance of these films.

  8. Enhancement of low temperature Critical current density of MgB2 thin films by Au coating

    NASA Astrophysics Data System (ADS)

    Choi, Eun-Mi; Lee, Hyun-Sook; Kim, Heon-Jung; Lee, Sung-Ik; Kim, Hyeong-Jin; Kang, W. N.

    2004-03-01

    We measured the superconducting critical current densities (J_c) from the magnetization hysteresis (M-H) loop while depositing the gold on top of the MgB2 thin film. The purpose of this experiment is whether the vortex avalanche phenomena which suppress the Jc for low temperature ( T < 15 K ) and low field (H ≤ 1000 Oe) can be cured by gold deposition. This avalanche called flux noise has been headache for the application of the MgB2 thin films. As increasing the thickness of Au film, fortunately, the flux noise in the M-H loop is suppressed and finally disappears when thickness of the gold becomes 2.55 ¥im. From this experiment, the obstacles of the application of MgB2 thin film are completely overcome

  9. Enhancement at low temperatures of the critical current density for Au-coated MgB2 thin films

    NASA Astrophysics Data System (ADS)

    Choi, Eun-Mi; Lee, Hyun-Sook; Kim, Heon-Jung; Lee, Sung-Ik; Kim, Hyeong-Jin; Kang, W. N.

    2004-01-01

    We measured the superconducting critical current densities (Jc) from the magnetization hysteresis (M-H) loop for Au-coated MgB2 thin films. The purpose of this experiment was to determine whether the vortex avalanche phenomenon which suppresses the Jc for low temperature (T<15 K) and low field (H⩽1000 Oe) could be cured by gold deposition. This avalanche, called flux noise, has been a headache in applications of MgB2 thin films. Fortunately, the flux noise in the M-H loop is suppressed with increasing Au-film thickness and finally disappears when the thickness of the gold becomes 2.55 μm. We found a way to remove one obstacle for applications of MgB2 thin films as an superconducting device.

  10. 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.

  11. Electro-mechanical characterization of MgB2 wires for the Superconducting Link Project at CERN

    NASA Astrophysics Data System (ADS)

    Konstantopoulou, K.; Ballarino, A.; Gharib, A.; Stimac, A.; Garcia Gonzalez, M.; Perez Fontenla, A. T.; Sugano, M.

    2016-08-01

    In previous years, the R & D program between CERN and Columbus Superconductors SpA led to the development of several configurations of MgB2 wires. The aim was to achieve excellent superconducting properties in high-current MgB2 cables for the HL-LHC upgrade. In addition to good electrical performance, the superconductor shall have good mechanical strength in view of the stresses during operation (Lorenz forces and thermal contraction) and handling (tension and bending) during cabling and installation at room temperature. Thus, the study of the mechanical properties of MgB2 wires is crucial for the cable design and its functional use. In the present work we report on the electro-mechanical characterization of ex situ processed composite MgB2 wires. Tensile tests (critical current versus strain) were carried out at 4.2 K and in a 3 T external field by means of a purpose-built bespoke device to determine the irreversible strain limit of the wire. The minimum bending radius of the wire was calculated taking into account the dependence of the critical current with the strain and it was then used to obtain the minimum twist pitch of MgB2 wires in the cable. Strands extracted from cables having different configurations were tested to quantify the critical current degradation. The Young’s modulus of the composite wire was measured at room temperature. Finally, all measured mechanical parameters will be used to optimize an 18-strand MgB2 cable configuration.

  12. 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.

  13. 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.

  14. Lineation-parallel c-axis Fabric of Quartz Formed Under Water-rich Conditions

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Zhang, J.; Li, P.

    2014-12-01

    The crystallographic preferred orientation (CPO) of quartz is of great significance because it records much valuable information pertinent to the deformation of quartz-rich rocks in the continental crust. The lineation-parallel c-axis CPO (i.e., c-axis forming a maximum parallel to the lineation) in naturally deformed quartz is generally considered to form under high temperature (> ~550 ºC) conditions. However, most laboratory deformation experiments on quartzite failed to produce such a CPO at high temperatures up to 1200 ºC. Here we reported a new occurrence of the lineation-parallel c-axis CPO of quartz from kyanite-quartz veins in eclogite. Optical microstructural observations, fourier transform infrared (FTIR) and electron backscattered diffraction (EBSD) techniques were integrated to illuminate the nature of quartz CPOs. Quartz exhibits mostly straight to slightly curved grain boundaries, modest intracrystalline plasticity, and significant shape preferred orientation (SPO) and CPOs, indicating dislocation creep dominated the deformation of quartz. Kyanite grains in the veins are mostly strain-free, suggestive of their higher strength than quartz. The pronounced SPO and CPOs in kyanite were interpreted to originate from anisotropic crystal growth and/or mechanical rotation during vein-parallel shearing. FTIR results show quartz contains a trivial amount of structurally bound water (several tens of H/106 Si), while kyanite has a water content of 384-729 H/106 Si; however, petrographic observations suggest quartz from the veins were practically deformed under water-rich conditions. We argue that the observed lineation-parallel c-axis fabric in quartz was inherited from preexisting CPOs as a result of anisotropic grain growth under stress facilitated by water, but rather than due to a dominant c-slip. The preservation of the quartz CPOs probably benefited from the preexisting quartz CPOs which renders most quartz grains unsuitably oriented for an easy a-slip at

  15. Magnesium Diboride (MgB2) thermal detector array for Infrared Spectrometers and Cameras on Planetary Exploration Instruments.

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

    Recent results from the 2-D array of MgB2 thermal detectors being currently developed at NASA Goddard are presented. NEP and sensitivity (D*) results show significant improvement compared to thermal detectors currently in use on planetary instruments. A MgB2 thin-film bolometer, with a non-optimized radiation absorber, has been designed, fabricated and characterized. The bolometer pixel, with no separate absorber, gave an optical detectivity D* = ~1.6 x 1010 cm√Hz/W operating at 30 Hz.

  16. 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.

  17. Pulsed laser deposition of c-axis untilted YBCO films on c-axis tilted ISD MgO-buffered metallic substrates

    NASA Astrophysics Data System (ADS)

    Li, M.; Ma, B.; Koritala, R. E.; Fisher, B. L.; Venkataraman, K.; Maroni, V. A.; Vlasko-Vlasov, V.; Berghuis, P.; Welp, U.; Gray, K. E.; Balachandran, U.

    2003-05-01

    Biaxially textured MgO template layer was deposited on nontextured metal substrates by inclined-substrate deposition (ISD) at a deposition rate of 24-600 nm/min. c-axis untilted YBa 2Cu 3O 7- x (YBCO) films were deposited on these MgO-buffered substrates by pulsed laser deposition. The crystalline structures of the YBCO films and MgO layers were examined by X-ray pole figure analysis, X-ray φ-scans, and χ-scans. A tilt angle of 33° of the MgO[0 0 1] with respect to the substrate normal and c-axis untilted YBCO films were observed, respectively. Good biaxial texture of these films with full-width-at-half-maximum values of 13.8° and 10.6° for the φ-scans of YBCO(1 0 3) and MgO(2 2 0), respectively, were obtained. Morphologies were examined by scanning electron microscopy, which revealed a unique roof-tile feature and columnar grain growth for the ISD MgO layer. Raman spectroscopy and magneto-optical image technique were also used to evaluate the quality of the YBCO film. An angular dependence of Jc on the direction of an applied magnetic field confirmed the c-axis untilted orientation of the YBCO films. Tc=90 K with sharp transition and Jc=3.0×10 5 A/cm 2 at 77 K in zero field were obtained on 0.4-μm-thick YBCO films.

  18. Effect of temperature and concentration of solution in chemical treatment for MgB 2 powder on the Jc- B property of ex situ processed MgB 2 superconducting tapes

    NASA Astrophysics Data System (ADS)

    Fujii, H.; Ozawa, K.

    2010-03-01

    MgB 2 tapes were fabricated through an ex situ process in a powder-in-tube (PIT) technique using powders treated at elevated temperatures in benzene solutions of benzoic acid with various concentrations. The amount of carbon substitution in MgB 2 in heat-treated tapes with treatment at the boiling points (BPs) of the solutions is smaller than that at room temperature (RT). This carbon substitution improves the Jc property in the high-field region. For RT treatment, the Jc property is improved with increasing the solution concentration. In contrast, the Jc property is deteriorated with increasing the concentration for BP treatment. On the other hand, treatment with pure solvent does not bring about the Jc enhancement and carbon substitution at all at both RT and the BPs. This suggests that acidity essential for the dissolution of MgO layers attached to the surface of MgB 2 is required for carbon substitution. The BP treatment enhances the acting of the acidity and possibly inflicts damage on MgB 2 itself.

  19. 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.

  20. Local electronic structure in MgB2 from B12 β -NMR

    NASA Astrophysics Data System (ADS)

    Indris, Sylvio; Heitjans, Paul; Hattendorf, Jens; Zeitz, Wolf-Dietrich; Bredow, Thomas

    2007-01-01

    We performed β -NMR spectroscopic studies on B12 which was implanted into MgB2 to get insight into the local electronic structure of this high-temperature superconducting material. By measuring electric field gradients we probed the electronic charge distribution anisotropy around boron in this solid and thus obtained experimental information about the bonding by p electrons. Besides the absolute value, the sign of the electric field gradient was also experimentally determined. By comparison with quantum chemical calculations, some of which were performed in the present work, and with results from conventional NMR spectroscopy on B11 we were able to identify regular boron lattice sites as well as interstitial sites.

  1. Transient Electromagnetic and Heat Transfer Characteristics of the MgB2 Superconductor in Liquid Helium

    NASA Astrophysics Data System (ADS)

    Jaim, H. M. Iftekhar; Bärner, K.

    2013-07-01

    A transient current density analysis is carried out for the type II superconductor (SC) material MgB2 in liquid Helium. Variable magnetic fields are used as the unknown in solving the curl-curl relations of the electromagnetic fields applying the finite element method (FEM) for 2D axis symmetric cylindrical wires. Assuming an exponential current rise, the magnetic flux, current density and temperature distribution in the SC and He are calculated. This study gives the limiting current values to avoid the normal state, the temperature distribution profile with time as well as the changes in the magnitude of the current and time constant. Oscillations and non-uniform temperature distributions are observed in He and in the SC respectively if one varies the parameters which are related to the different heat transfer mechanisms. A slight instability in the current distribution is also observed which might transfer to a thermal instability, i.e. could signal He boiling.

  2. 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.

  3. Magnetic penetration depth measurements in MgB2 sintered pellets and thin films

    NASA Astrophysics Data System (ADS)

    Lamura, G.; di Gennaro, E.; Salluzzo, M.; Andreone, A.; Le Cochec, J.; Gauzzi, A.; Cantoni, C.; Paranthaman, M.; Christen, D. K.; Christen, H. M.; Giunchi, G.; Ceresara, S.

    2002-01-01

    We have performed accurate measurements of the temperature dependence of the magnetic penetration depth of the new intermetallic superconductor MgB2 using a high resolution single coil mutual inductance technique. Both sintered pellets and thin films exhibiting critical temperature values ranging between 37 and 38.4 K have been studied. In the case of the film, for T

  4. Intermodulation distortion measurements of MgB2 thin films grown by HPCVD

    NASA Astrophysics Data System (ADS)

    Cifariello, G.; Aurino, M.; di Gennaro, E.; Lamura, G.; Orgiani, P.; Villegier, J.-C.; Xi, X. X.; Andreone, A.

    2006-06-01

    The two tone intermodulation distortion (IMD) arising in MgB2 thin films synthesized by hybrid physical-chemical vapour deposition (HPCVD) is studied in order to probe the influence of the two bands on the symmetry of the gap function. The measurements are carried out by using a dielectrically loaded copper cavity operating at 7 GHz. Microwave data on samples having critical temperatures above 41 K, very low resistivity values, and residual resistivity ratio larger than 10, are shown. The dependence of the nonlinear surface losses and of the third order intermodulation products on the power feeding the cavity and on the temperature is analyzed. At low power, IMD versus temperature data show the intrinsic s-wave behaviour expected for this compound

  5. 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.

  6. Transport IV characterisation of MgB2 conductor at a bend radius of 50mm

    NASA Astrophysics Data System (ADS)

    Young, E. A.; Falorio, I.; Beduz, C.; Bailey, W. O. S.; Yang, Y.

    2014-05-01

    Performance of state of the art MgB2 multifilamentary conductor at a required bend radius is essential for many applications including but not limited to magnets and motors. The characterisation is generally done with benchmark transport Ic but further detail can be seen in IV characteristics which are undertaken in this paper. Two conductors with the same architecture but different diameters, 0.89 and 0.45 mm were measured from 32 K to 20 K in self-field in conditions of as received and deformed to a 50 mm bend diameter, corresponding to strains of 1.4 % and 0.7 % respectively. The qualifying 0.45mm conductor was further measured in background fields up to 3 T. The smaller diameter wire was found to have no signs of degradation of critical behaviour in Ic or IV characteristics.

  7. 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.

  8. Flux pinning mechanism and Hc2-anisotropy in melanin doped bulk MgB2

    NASA Astrophysics Data System (ADS)

    Shahabuddin Shah, M.; Shahabuddin, Mohammed; Alzayed, Nasser S.; Parakkandy, Jafar M.

    2014-06-01

    Flux pinning mechanism in melanin doped MgB2 superconductor has been studied using a scaling law proposed by Dew-Hughes and another method proposed by Eisterer. Our experimental data could be fitted very closely by the aforementioned scaling law. The fitting parameters, the positions of peaks bpeak and k = bpeak/bn confirm a grain-boundary pinning in the 10% melanin doped sample, while the undoped sample consists of mixed pinning. Furthermore, percolation theory was utilized under grain-boundary approximation to investigate the role of Hc2-anisotropy in the critical current density, and its dependence on applied field as well as temperature. The Hc2-anisotropy decreases with melanin doping resulting in the increase of Jc in high field. There is suppression of flux pinning maximum due to melanin doping, which is found to be the main reason for the degradation of low-field Jc.

  9. Low-field magnetic torque of a single crystal MgB 2

    NASA Astrophysics Data System (ADS)

    Atsumi, Toshiyuki; Tsuji, Mitsuyuki; Xu, Mingxiang; Kitazawa, Hideaki; Ishida, Takekazu

    2003-10-01

    We have investigated the magnetic torque of MgB 2 single crystal synthesized by the vapor transport method. We use a torque magnetometer consisting of a 4-K closed cycle refrigerator and a variable field permanent magnet up to 10 kG. The torque can be measured as an off-balance signal of the Wheatstone bridge of the four piezoresistors on a Si cantilever. The torque curves are analyzed by the Kogan model. The superconducting anisotropy γ is rather independent of temperature, but is dependent on field. As expected from the BCS theory, the prefactor of the Kogan formula, which corresponds to the lower critical field Hc1, changes smoothly as a function of temperature. We consider that the field dependence of γ comes from the multiple superconducting gaps and their different upper critical fields Hc2.

  10. Laser induced infrared spectral shift of the MgB2:Cr superconductor films

    NASA Astrophysics Data System (ADS)

    AlZayed, N. S.; Kityk, I. V.; Soltan, S.; El-Naggar, A. M.; Shahabuddin, M.

    2015-02-01

    During illumination of the MgB2:Cr2O3 films it was established substantial spectral shift of the infrared spectra in the vicinity of 20-50 cm-1. The excitations were performed by nanosecond Er:glass laser operating at 1.54 μm and by microsecond 10.6 μm CO2 laser. The spectral shifts of the IR maxima were in opposite spectral directions for the two types of lasers. This one observed difference correlates well with spectral shift of their critical temperatures. The possible explanation is given by performance of DFT calculations of the charge density redistribution and the time kinetics of the photovoltaic response. To understand the kinetics of the photoinduced processes the time kinetics of photoresponse was done for the particular laser wavelengths.

  11. Pinning and irreversibility in superconducting bulk MgB2 with added nanodiamonds

    NASA Astrophysics Data System (ADS)

    Gupta, Anurag; Narlikar, A. V.

    2009-12-01

    Resistance, R(T), and magnetization, M(B), studies on superconducting bulk MgB2 samples containing nanodiamonds (ND) as additives (wt% of ND: x = 0%, 1%, 3%, 5%, 7% and 10%) were recently published in two articles (Vajpayee et al 2007 Supercond. Sci. Technol. 20 S155, Vajpayee et al 2008 J. Appl. Phys. 103 07C708). The main observations reported were significant improvements in the critical current density Jc(B), irreversibility line Birr(T) and upper critical field Bc2(T) with ND addition. However, a closer look shows that as regards the potential of this technologically important material at higher magnetic fields and temperatures, there is still a lot of room for improvement. With that in mind we revisit the R(T) and M(B) data and analyze them, in the present work. We show that, despite ND addition, Jc depends strongly on B in the high field region and tends to vanish at irreversibility lines that lie deep, i.e. at around 0.3 Bc2(T), in the B-T phase diagram. The irreversibility lines, determined by R(T) \\to 0 in the presence of B, are found to lie at around 0.5 Bc2(T) in the phase diagram. These results for pinning and irreversibility lines are discussed in the light of various models such as those of surface sheath superconductivity, magnetically introduced percolation in polycrystalline MgB2, thermally assisted flux motion (TAFM) and a modified flux line shear mechanism. Our analysis hints at TAFM and weak pinning channels with distributed superconducting properties percolating in our samples determining the irreversibility and pinning properties.

  12. 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).

  13. 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.

  14. Doping effect of nano-Ho2O3 and naphthalene in MgB2 superconductor prepared by powder-in-sealed-tube method

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    The effect on crystal structure, critical temperature (TC), and critical current density (JC) of bulk MgB2 doped with nano-Ho2O3 and naphthalene was studied. Among all the samples studied, the sample doped with 2.5 wt. % nano-Ho2O3 have shown the best field dependent critical current density [JC(H)], i.e., 0.77 × 105 A/cm2 at 2 T and 10 K. While naphthalene doped MgB2 sample has shown the least JC(H) characteristics. The improved JC(H) characteristics in the nano-Ho2O3 doped MgB2 samples are attributed to improved flux pinning properties due to the formation of HoB4 and in naphthalene doped MgB2 samples. The slight lower TC value (37.01 K) in naphthalene doped samples is attributed to the occurrence of lattice defect by the substitution of carbon at boron site of MgB2 superconductor. Lower ΔTC value implies the lesser anisotropy in all the synthesized samples. The flux pinning force density (FP/FPmax) curves are theoretically analyzed using Dew-Hughes model. The result revealed that point pinning is the dominant pinning mechanism for nano-Ho2O3 doped MgB2 samples, while, surface and grain boundary pinning become dominant with increasing naphthalene addition in nano-Ho2O3 doped MgB2 samples.

  15. 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 boron results in the formation of parasitic phases such as MgB4, MgB7, etc. Such parasitic phases are a primary element of the connectivity problem, in which even though a sample powder may contain grains of high-quality MgB2, adjacent grains are surrounded by intergrowths of parasitic phases so that current trans-port is badly degraded. The best results to date have been obtained using boron powder produced long ago for a rocket propellant development project. The synthesis process was complex and is now largely lost, and the manufacturing equipment has long since been scrapped. The last batch of the powder has been used during recent years to support MgB2 R&D at several labs, but supplies are dwindling. ATC has identified a first application of its plasma torch to synthesize phase-pure amorphous boron flake using a rapid-quench splat technique. Inexpensive technical-grade boron would be purified of contaminants, then dispersed as an aerosol in inert gas and passed through the plasma torch to melt it into a spray. The spray would be splat-condensed on a rotating drum to form pure amorphous flake. The process would begin with technical-grade boron powder, having good stoichiometric purity, nanoscale particles, but significant contamination of MgO and crystalline boron. We used wet chemistry to remove B2O3 completely and reduced the MgO impurity, and analyzed the particle size distribution using a Coulter counter and the phase composition using X-ray diffrac-tion (XRD). The next step will be to build an rf plasma torch with a recirculating single-component aerosol feed and the cooled splat drum and collector, and undertake process devel-opment for amorphous boron powder. This revised goal has two benefits. First, it is an easier technology than our ultimate goal of a multi-component laminar flow torch. We have been counseled by those experienced in plasma torch technology that our ultimate goal will require a torch that should be feasible but has never been attempted. It may require an extended period of R&D for both the torch itself and the gas dynamics in the rea

  16. ``Hybrid'' multi-gap/single-gap Josephson junctions: Evidence of macroscopic quantum tunneling in superconducting-to-normal switching experiments on MgB2/I/Pb and MgB2/I/Sn junctions

    NASA Astrophysics Data System (ADS)

    Carabello, Steve; Lambert, Joseph; Dai, Wenqing; Li, Qi; Chen, Ke; Cunnane, Daniel; Xi, X. X.; Ramos, Roberto

    We report results of superconducting-to-normal switching experiments on MgB2/I/Pb and MgB2/I/Sn junctions, with and without microwaves. These results suggest that the switching behavior is dominated by quantum tunneling through the washboard potential barrier, rather than thermal excitations or electronic noise. Evidence includes a leveling in the standard deviation of the switching current distribution below a crossover temperature, a Lorentzian shape of the escape rate enhancement peak upon excitation by microwaves, and a narrowing in the histogram of escape counts in the presence of resonant microwave excitation relative to that in the absence of microwaves. These are the first such results reported in ``hybrid'' Josephson tunnel junctions, consisting of multi-gap and single-gap superconducting electrodes.

  17. Numerical optimization of monofilamentary MgB2 wires with different metal sheath materials for liquid hydrogen level sensor

    NASA Astrophysics Data System (ADS)

    Kajikawa, Kazuhiro; Inoue, Takuro; Watanabe, Kazuki; Yamada, Yutaka; Aoki, Itsuo

    2014-01-01

    Thin wires required for a new type of superconducting level sensors are investigated in some virtual situations. The sensors are composed of an MgB2 wire with metal sheath and a non-superconducting wire, which are located in parallel and connected in series, to determine a level of liquid hydrogen in a container with higher reliability. The operations of the level sensors during refill and discharge of liquid hydrogen are simulated numerically by solving a one-dimensional heat balance equation. The wires have a metal material with almost constant dependence of resistivity on temperature such as cupronickel or stainless steel. The wire lengths are assumed to be 1 meter. By using the obtained numerical results, the optimum compositions of the MgB2 and non-superconducting wires are discussed for several parameters such as materials and volume fractions of metal sheaths, temperatures of pressurized liquid hydrogen, and conditions of evaporated gas.

  18. 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.

  19. 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 MgB 2 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 MgB 2 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.

  20. Preparation and Characterization of MgB2 Bulk Samples Using High-Energy Ball Milling and Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Rodrigues, D.; Senkowicz, B. J.; Hanson, J. M.; Larbalestier, D. C.; Hellstrom, E. E.

    2008-03-01

    MgB2 bulk samples were prepared using high-energy ball milling in nitrogen atmosphere followed by cold isostatic pressing and hot isostatic pressing to increase densification and grain connectivity. Higher values of critical current densities Jc at high magnetic fields could be obtained after milling than those obtained with unmilled bulk samples. Jc values around 20,000 A/cm2 at 7 T, 4.2 K were found for the MgB2 sample milled for 300 minutes compared to 1000 A/cm2 for the unmilled material. The milling increased electron scattering and resistivity, increasing the irreversibility field μ0Hirr of the samples. The milled samples showed higher values of μ0Hirr than the unmilled sample. However, the milled samples showed lower pinning strength than the unmilled sample as a result of their larger average grain size after HIP, in spite of their higher μ0Hirr.

  1. Conceptual design of MgB2 coil for the 100 MJ SMES of advanced superconducting power conditioning system (ASPCS)

    NASA Astrophysics Data System (ADS)

    Atomura, Naoki; Takahashi, Toshinori; Amata, Hiroto; Iwasaki, Tatsuya; Son, Kyoungwoo; Miyagi, Daisuke; Tsuda, Makoto; Hamajima, Takataro; Shintomi, Takakazu; Makida, Yasuhiro; Takao, Tomoaki; Munakata, Kohe; Kajiwara, Masataka

    In order to reduce global carbon-dioxide in the world, we propose an Advanced Superconducting Power Conditioning System (ASPCS) which is composed of 5 MW renewable energy resources and 1 MW hybrid storage system. The hybrid storage system is composed of FC-H2-EL and SMES which is installed adjacent to a LH2 station for vehicles. Since the SMES can be operated at 20 K which is a saturated temperature of LH2, we can use MgB2 superconductors. In the ASPCS, 100 MJ storage capacities of the SMES should be required. This paper focuses on studies into a conceptual design of SMES toroidal coil composed of the MgB2 and indirectly cooled by LH2.

  2. Low-field critical current density in porous MgB2 powders

    NASA Astrophysics Data System (ADS)

    Agassi, Y. D.

    2013-09-01

    Porous MgB2 powders are comprised of an ensemble of irregularly shaped constituents. In this work we introduce a model for the critical current density in such powders in the presence of a low external field H (H < 4 T) and in the high-porosity limit, where effects of vortex-lattice elasticity can be neglected and vortex pinning takes place within the powder-constituents. The ensuing critical current-density expression is a product of three decoupled factors: The first sets the scale for the critical current-density magnitude, while the second and third factors contain the field and powder-constituent size-parameters dependencies, respectively. The field dependent factor is of the form H-n and 0.5⩽n⩽1.0, where the limiting exponents n = 0.5 and n = 1.0 correspond to vortex configurations within a powder-constituent of a linear array and a two-dimensional lattice, respectively. For the calculations, we assume for the powder constituent shape a cylinder of arbitrary height and radius, where an external field and a single pinned vortex are aligned in parallel to the cylinder’s axis. The exact fields of this configuration are derived. The size-parameters dependence implies enhanced critical current density for a cigar-like shape powder-constituent aligned with the field, and of radius smaller than about three times the penetration depth. These conclusions are consistent with pertaining data.

  3. 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.

  4. Study of the Electrodynamic Response of MgB2 Sintered Pellets and Thin Films

    NASA Astrophysics Data System (ADS)

    Andreone, A.; di Gennaro, E.; Lamura, G.; Salluzzo, M.; Le Cochec, J.; Gauzzi, A.; Cantoni, C.; Paranthaman, M.; Ceresara, S.; Giunchi, G.

    We present a number of experimental results on the temperature dependence of the magnetic penetration depth λ and on the temperature and field dependence of the microwave surface impedance Zs=Rs+iXs in both pellets and thin films of MgB2, exhibiting critical temperatures ranging between 26 and 38 K. Accurate measurements of Zs(H,T) were performed by means of a sapphire dielectrically loaded cavity operating in the microwave region (20 GHz). The study of λ(T) was carried out employing a single coil mutual inductance technique in the MHz region. An anisotropic s-wave BCS model can account for the temperature dependence experimentally observed in the penetration depth data of the best films, confirming previous reports on the conventional nature of superconductivity in diborides. On the contrary, films having a reduced value of the critical temperature and pellets show no evidence of saturation, and the experimental results strictly follow a quadratic dependence down to the lowest temperatures. We explain this behavior with the presence of metallic Mg inclusions that may locally depress the gap. The study of the surface impedance versus temperature and field shows also that the source of microwave loss can be markedly different, depending on the structural and transport properties of the samples.

  5. Power Dependence of the RF Surface Resistance of MgB2 Superconductor.

    SciTech Connect

    Tajima, T.; Findikoglu, A. T.; Jason, A. J.; Krawczyk, F. L.; Mueller, F. M.; Shapiro, A. H.; Geng, R. L.; Padamsee, Hasan,; Romanenko, A.; Moeckly, B. H.

    2005-01-01

    Magnesium diboride (MgB{sub 2}) is a superconducting material that has a transition temperature (T{sub c}) of {approx}40 K, which is {approx}30 K higher than niobium (Nb) that has been used for most superconducting RF cavities in the past decades. Last year, it was demonstrated that the RF surface resistance of MgB{sub 2} can be lower than Nb at 4 K. One of the problems with other high-T{sub c} materials such as YBCO was its rapid increase in RF surface resistance with higher surface magnetic fields. Recently, we have shown that MgB2 shows little increase in the surface resistance up to {approx}120 Oe, equivalent of an accelerating field of {approx}3 MV/m. The highest field tested was limited by available power. This result is encouraging and has made us consider fabrication of a cavity coated with MgB{sub 2} and test it. Also, there is a potential that this material has a higher critical magnetic field that enables the cavity to run at a higher gradient than Nb cavities in addition to the possibility of operation at higher temperatures.

  6. Development of ex situ processed MgB 2 wires and their applications to magnets

    NASA Astrophysics Data System (ADS)

    Braccini, Valeria; Nardelli, Davide; Penco, Roberto; Grasso, Giovanni

    2007-06-01

    In spite of the relatively short time dedicated to the development of magnesium diboride conductors since its discovery in early 2001, a substantial improvement was soon achieved in their manufacture and use. Unlike many others HTS and LTS materials, the MgB 2 conductor processing is more open to a number of improvements and modifications that help in making it more attractive for several DC and AC applications. Many kilometres of conductors were already produced throughout the world and it is now possible to start seriously thinking about a systematic industrial production of this material, as it is already possible to purchase it in reasonable lengths on the free market. These remarkable lengths of conductor were also wound in coils and their performance continuously improved in the past years. Here we will present a review of the recent results and a perspective for the future development of this “new” superconductor, starting from the optimisation of the precursor powders needed to improve the magnetic field behaviour of the tapes, to the conductor development, i.e. the production of multifilamentary Cu-stabilized tapes in lengths up to 1.78 km, to the realization of the first large-scale application devices such as MRI magnets and fault current limiters.

  7. 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.

  8. Critical Currents, Vortex Dynamics and Microstructure in MgB_2

    NASA Astrophysics Data System (ADS)

    Serquis, Adriana; Civale, Leonardo; Liao, Xiazhou; Maley, Martin; Zhu, Yuntian; Peterson, Dean; Mueller, Fred

    2003-03-01

    One key issue in optimizing critical current density in MgB2 is to determine which structural features are the relevant pinning centers. In this work we explore the influence of microstructures on the vortex dynamics of bulk samples prepared either at ambient or at high isostatic pressure (HIP). Several types of defects were observed by electron microscopy. Both un-HIPed and HIPed samples contain a large number of intra-grain Mg(B,O) 2 precipitates coherent with the matrix, with sizes very well suited to act as pinning centers (5 - 100 nm). The HIP process further improves flux pinning by eliminating porosity and generating dislocations. We also present a detailed study of the temperature T, field H and current density J dependence of the normalized time (t) relaxation rate, S=dlnJ/dlnt. At low T, we observe a linear S(T), from which we extract a pinning energy Uc that is weakly T dependent and decreases monotonically with H. The extrapolations to T=0 indicate that the quantum creep rate is small. At higher T, the activation energy U(J) shows the divergent behavior at J -> 0 that characterizes the glassy phases. Results are contrasted with the expectations of various collective creep scenarios to extract information on the characteristics of the pinning centers.

  9. Behaviour of filamentary MgB2 wires subjected to tensile stress at 4.2 K

    NASA Astrophysics Data System (ADS)

    Kováč, P.; Kopera, L.; Melišek, T.; Rindfleisch, M.; Haessler, W.; Hušek, I.

    2013-10-01

    Different filamentary MgB2 wires have been subjected to tensile stress at 4.2 K. Stress-strain and critical current versus stress and strain characteristics of wires differing by filament architecture, sheath materials, deformation and heat treatment were measured and compared. It was found that the linear increase of critical current due to the pre-compression effect (ranging from 5% up to ≈20%) is affected by thermal expansion and the strength of used metallic sheaths. The values of irreversible strain ɛirr and stress σirr depend dominantly on the applied outer sheath and its final heat treatment conditions. Consequently, the strain-tolerance of MgB2 wires is influenced by several parameters and it is difficult to see a clear relation between Ic(ɛ) and σ(ɛ) characteristics. The lowest ɛirr was measured for Monel sheathed wires (0.3-0.6%), medium for GlidCop® sheath (0.48-0.6%), and the highest ɛirr = 0.6-0.9% were obtained for MgB2 wires reinforced by the stainless steel 316L annealed at temperature between 600 and 800 ° C. The highest ɛirr = 0.9% and σirr = 900 MPa were measured for the work-hardened steel, which is not considerably softened by the heat treatment at 600 ° C/2.5 h.

  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. 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.

  12. Effects of helium ion damage on the two-band superconductivity in MgB2 thin films

    NASA Astrophysics Data System (ADS)

    Greene, L. H.; Park, W. K.; Lu, X.; Moeckly, B.; Singh, R.; Newman, N.; Rowell, J. M.

    2006-03-01

    While the two-band superconductivity in MgB2 has been well established, it remains controversial whether disorder in the Mg and B planes causes enhanced interband scattering, band filling or both. To address this, we have performed electronic transport and point-contact spectroscopy measurements on helium-ion irradiated MgB2 thin films. Two sets of samples are prepared using: a) 1 MeV He^+ ions with uniform doses ranging from 1x10^15 to 1x10^17 ions/cm^2; b) 2 MeV alpha particles with gradient doses. The resistivity (Tc) is observed to increase (decrease) monotonically with increasing dose. The conductance spectra are taken from point-contact junctions between MgB2 thin films and Au tips. The Tc is determined by the onset of enhanced conductance at zero bias. Our preliminary results show that the two gaps tend to merge into one gap with increasing ion damage. Detailed results including Tc vs. energy gap will be presented and discussed in terms of the electronic structure change caused by ion-induced point defects. WKP acknowledges Pavel Krasnochtchekov and Robert Averback for ion irradiation experiments at UIUC. This work is supported by the DoE DEFG02-91ER45439, through the FSMRL and the Center for Microanalysis of Materials at UIUC.

  13. The Influence of CuFe2O4 Nanoparticles on Superconductivity of MgB2

    NASA Astrophysics Data System (ADS)

    Novosel, Nikolina; Pajić, Damir; Skoko, Željko; Mustapić, Mislav; Babić, Emil; Zadro, Krešo; Horvat, Joseph

    The influence of CuFe2O4 nanoparticle doping on superconducting properties of Fe-sheated MgB2 wires has been studied. The wires containing 0, 3 and 7.5 wt.% of monodisperse superparamagnetic nanoparticles (˜7 nm) were sintered at 650°C or 750°C for 1 hour in the pure argon atmosphere. X-ray diffraction patterns of doped samples showed very small maxima corresponding to iron boride and an increase in the fraction of MgO phase indicating some interaction of nanoparticles with Mg and B. Both magnetic and transport measurements (performed in the temperature range 2-42 K and magnetic field up to 16 T) showed strong deterioration of the superconducting properties upon doping with CuFe2O4. The transition temperatures, Tc, of doped samples decreased for about 1.4 K per wt.% of CuFe2O4. Also, the irreversibility fields Birr(T) decreased progressively with increasing doping. Accordingly, also the suppression of Jc with magnetic field became stronger. The observed strong deterioration of superconducting properties of MgB2 wires is at variance with reported enhancement of critical currents at higher temperatures (determined from magnetization) in bulk MgB2 samples doped with Fe3O4 nanoparticles. The probable reason for this discrepancy is briefly discussed

  14. A new approach to a superconducting joining process for carbon-doped MgB2 conductor

    NASA Astrophysics Data System (ADS)

    Patel, Dipak; Hossain, Md Shahriar Al; Maeda, Minoru; Shahabuddin, Mohammed; Yanmaz, Ekrem; Pradhan, Subrata; Tomsic, Mike; Choi, Seyong; Kim, Jung Ho

    2016-09-01

    We report a new approach to a superconducting joining process for unreacted in situ carbon (C)-doped magnesium diboride (MgB2) wires. To operate a magnetic resonance imaging (MRI) magnet in the persistent mode, the superconducting joints between two conductors are as critical as the other key components. In addition, a stable and reliable joining process enables the superconducting magnet to operate without an external power supply. However, joint results using unreacted in situ C-doped MgB2 wires, which are used for high-field operation, have been limited, and only very poor performance has been obtained. By controlling the pressure inside a joint part, in this study, we successfully obtained current carrying retention in the joint of up to 72% compared to wire without a joint. The closed-circuit resistance of our closed-loop coil was less than 1.8 × 10‑13 Ω at 16.7 ± 4.7 K, as measured by the field-decay measurement method. These results indicate that MgB2 has a promising future in MRI application.

  15. 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.

  16. Tellurium addition as a solution to improve compactness of ex-situ processed MgB2-SiC superconducting tapes

    NASA Astrophysics Data System (ADS)

    Sandu, V.; Aldica, G.; Popa, S.; Enculescu, Monica; Badica, P.

    2016-06-01

    Ex-situ spark plasma sintering (SPS) was used to obtain dense MgB2-based tapes in a Fe sheath with the starting composition (MgB2)0.975 + (SiC)0.025 + Te0.01. Prior to the SPS procedure of tape formation, the samples were submitted to a series of cold working processes typical for the powder-in-tube technique. The tapes were compared with optimal doped bulk samples (having the same starting composition) and a pristine MgB2 tape. The morphology of the composite samples, the phase structure of both the core and the inner face of the metallic sheath shows the formation of a plethora of traces as a result of interaction between MgB2, additives, and the Fe sheath. Important critical parameters, like critical current density and the irreversibility field, show that there is a field and temperature range where the SiC and Te-added tapes display better critical parameters comparative to either pristine MgB2 tapes in the Fe sheath or SiC and Te doped MgB2 bulk samples.

  17. Superior critical current density obtained in MgB2 bulks via employing carbon-coated boron and minor Cu addition

    NASA Astrophysics Data System (ADS)

    Peng, Junming; Liu, Yongchang; Ma, Zongqing; Shahriar Al Hossain, M.; Xin, Ying; Jin, Jianxun

    2016-09-01

    High performance Cu doped MgB2 bulks were prepared by an in-situ method with carbon-coated amorphous boron as precursor. It was found that the usage of carbon-coated boron in present work leads to the formation of uniformly refined MgB2 grains, as well as a high level of homogeneous carbon doping in the MgB2 samples, which significantly enhance the Jc in both Cu doped and undoped bulks compared to MgB2 bulks with normal amorphous boron precursor. Moreover, minor Cu can service as activator, and thus facilitates the growth of MgB2 grains and improves crystallinity and grain connectivity, which can bring about the excellent critical current density (Jc) at self fields and low fields (the best values are 7 × 105 A/cm2 at self fields, and 1 × 105 A/cm2 at 2 T, 20 K, respectively). Simultaneously, minor Cu addition can reduce the amount of MgO impurity significantly, also contributing to the improvement of Jc at low fields. Our work suggests that Cu-activated sintering combined with employment of carbon-coated amorphous boron as precursor could be a promising technique to produce practical MgB2 bulks or wires with excellent Jc on an industrial scale.

  18. On the roles of graphene oxide doping for enhanced supercurrent in MgB2 based superconductors

    NASA Astrophysics Data System (ADS)

    Yeoh, W. K.; Cui, X. Y.; Gault, B.; de Silva, K. S. B.; Xu, X.; Liu, H. W.; Yen, H.-W.; Wong, D.; Bao, P.; Larson, D. J.; Martin, I.; Li, W. X.; Zheng, R. K.; Wang, X. L.; Dou, S. X.; Ringer, S. P.

    2014-05-01

    Due to their graphene-like properties after oxygen reduction, incorporation of graphene oxide (GO) sheets into correlated-electron materials offers a new pathway for tailoring their properties. Fabricating GO nanocomposites with polycrystalline MgB2 superconductors leads to an order of magnitude enhancement of the supercurrent at 5 K/8 T and 20 K/4 T. Herein, we introduce a novel experimental approach to overcome the formidable challenge of performing quantitative microscopy and microanalysis of such composites, so as to unveil how GO doping influences the structure and hence the material properties. Atom probe microscopy and electron microscopy were used to directly image the GO within the MgB2, and we combined these data with computational simulations to derive the property-enhancing mechanisms. Our results reveal synergetic effects of GO, namely, via localized atomic (carbon and oxygen) doping as well as texturing of the crystals, which provide both inter- and intra-granular flux pinning. This study opens up new insights into how low-dimensional nanostructures can be integrated into composites to modify the overall properties, using a methodology amenable to a wide range of applications.Due to their graphene-like properties after oxygen reduction, incorporation of graphene oxide (GO) sheets into correlated-electron materials offers a new pathway for tailoring their properties. Fabricating GO nanocomposites with polycrystalline MgB2 superconductors leads to an order of magnitude enhancement of the supercurrent at 5 K/8 T and 20 K/4 T. Herein, we introduce a novel experimental approach to overcome the formidable challenge of performing quantitative microscopy and microanalysis of such composites, so as to unveil how GO doping influences the structure and hence the material properties. Atom probe microscopy and electron microscopy were used to directly image the GO within the MgB2, and we combined these data with computational simulations to derive the property-enhancing mechanisms. Our results reveal synergetic effects of GO, namely, via localized atomic (carbon and oxygen) doping as well as texturing of the crystals, which provide both inter- and intra-granular flux pinning. This study opens up new insights into how low-dimensional nanostructures can be integrated into composites to modify the overall properties, using a methodology amenable to a wide range of applications. Electronic supplementary information (ESI) available: Crystallographic data on the proposed Mg(B,O)2, MgB2O0.25 and MgB2O0.5 phases. Evidence of phase separation of Mg(B,O)2 into nanocrystalline MgO and MgB2, and evidence of the Mg(B,O)2 phase in X-ray diffraction with the X-ray index table for Mg(B,O)2. See DOI: 10.1039/c4nr00415a

  19. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    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.

  1. 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.

  2. 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.

  3. 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.

  4. Phonon mean free path of graphite along the c-axis

    SciTech Connect

    Wei, Zhiyong; Yang, Juekuan; Chen, Weiyu; Bi, Kedong; Chen, Yunfei

    2014-02-24

    Phonon transport in the c-axis direction of graphite thin films has been studied using non-equilibrium molecular dynamics (MD) simulation. The simulation results show that the c-axis thermal conductivities for films of thickness ranging from 20 to 500 atomic layers are significantly lower than the bulk value. Based on the MD data, a method is developed to construct the c-axis thermal conductivity as an accumulation function of phonon mean free path (MFP), from which we show that phonons with MFPs from 2 to 2000 nm contribute ∼80% of the graphite c-axis thermal conductivity at room temperature, and phonons with MFPs larger than 100 nm contribute over 40% to the c-axis thermal conductivity. These findings indicate that the commonly believed value of just a few nanometers from the simple kinetic theory drastically underestimates the c-axis phonon MFP of graphite.

  5. Characterizations of the Core-Shell Structured MgB2/CARBON Fiber Synthesis by Rf-Sputtering and Thermal Evaporation

    NASA Astrophysics Data System (ADS)

    Park, Sung Chang; Lim, Yeong Jin; Lee, Tae-Keun; Kim, Cheol Jin

    MgB2/carbon fibers have been synthesized by the combination of RF-sputtering of B and thermal evaporation of Mg, followed by co-evaporation. First, boron layer was deposited by RF-sputtering on the carbon fiber with average diameter of 7.1 μm. Later this coated layer of B was reacted with Mg vapor to transform into MgB2. Since the MgB2 reaction proceed with Mg diffusion into the boron layer, Mg vapor pressure and the diffusion time had to be controlled precisely to secure the complete reaction. Also the deposition rate of each element was controlled separately to obtain stoichiometric MgB2, since Mg was evaporated by thermal heating and B by sputtering system. The sintered B target was magnetron sputtered at the RF-power of ~200 W, which corresponded to the deposition rate of ~3.6 Å/s. With the deposition rate of B fixed, the vapor pressure of Mg was controlled by varying the temperature of tungsten boat with heating element control unit between 100 and 900°C. The MgB2 layers with the thickness of 200-950 nm could be obtained and occasionally MgO appeared as a second phase. Superconducting transition temperatures were measured around ~38 K depending on the deposition condition.

  6. High-field properties of carbon-doped MgB2 thin films by hybrid physical-chemical vapor deposition using different carbon sources

    NASA Astrophysics Data System (ADS)

    Dai, Wenqing; Ferrando, V.; Pogrebnyakov, A. V.; Wilke, R. H. T.; Chen, Ke; Weng, Xiaojun; Redwing, Joan; Wung Bark, Chung; Eom, Chang-Beom; Zhu, Y.; Voyles, P. M.; Rickel, Dwight; Betts, J. B.; Mielke, C. H.; Gurevich, A.; Larbalestier, D. C.; Li, Qi; Xi, X. X.

    2011-12-01

    We have studied the high-field properties of carbon-doped MgB2 thin films prepared by hybrid physical-chemical vapor deposition (HPCVD). Carbon doping was accomplished by adding carbon-containing gas, such as bis(methylcyclopentadienyl)magnesium and trimethylboron, into the hydrogen carrier gas during the deposition. In both cases, Tc drops slowly and residual resistivity increases considerably with carbon doping. Both the a and c lattice constants increase with carbon content in the films, a behavior different from that of bulk carbon-doped MgB2 samples. The films heavily doped with trimethylboron show very high parallel Hc2 over 70 T at low temperatures and a large temperature derivative -\\rmd H_{ {c2}}^{\\parallel } /\\rmd T near Tc. These behaviors are found to depend on the unique microstructure of the films, which consists of MgB2 layers a few-nanometers thick separated by non-superconducting MgB2C2 layers. This leads to an increase in the parallel Hc2 by the geometrical effect, which is in addition to the significant enhancement of Hc2 due to changes in the scattering rates within and between the two bands present in films doped using both carbon sources. The high Hc2 and high-field Jc(H) values observed in this work are very promising for the application of MgB2 in high magnetic fields.

  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. Temperature-Dependent Mean Free Path Spectra of Thermal Phonons Along the c-Axis of Graphite.

    PubMed

    Zhang, Hang; Chen, Xiangwen; Jho, Young-Dahl; Minnich, Austin J

    2016-03-01

    Heat conduction in graphite has been studied for decades because of its exceptionally large thermal anisotropy. While the bulk thermal conductivities along the in-plane and cross-plane directions are well-known, less understood are the microscopic properties of the thermal phonons responsible for heat conduction. In particular, recent experimental and computational works indicate that the average phonon mean free path (MFP) along the c-axis is considerably larger than that estimated by kinetic theory, but the distribution of MFPs remains unknown. Here, we report the first quantitative measurements of c-axis phonon MFP spectra in graphite at a variety of temperatures using time-domain thermoreflectance measurements of graphite flakes with variable thickness. Our results indicate that c-axis phonon MFPs have values of a few hundred nanometers at room temperature and a much narrower distribution than in isotropic crystals. At low temperatures, phonon scattering is dominated by grain boundaries separating crystalline regions of different rotational orientation. Our study provides important new insights into heat transport and phonon scattering mechanisms in graphite and other anisotropic van der Waals solids. PMID:26840052

  9. Magnetic characterization of sintered MgB2 samples: effect of substitution or 'doping' with Li, Al and Si

    NASA Astrophysics Data System (ADS)

    Cimberle, M. R.; Novak, M.; Manfrinetti, P.; Palenzona, A.

    2002-01-01

    Powdered and sintered MgB2 samples, both pure and substituted or doped, have been prepared and characterized through magnetic measurements performed from T = 5 K up to a few degrees above the transition temperature of about 39 K. For all the samples, the irreversibility line (IL) appears much lower than the Hc2-T line and very far from that of both high-Tc (YBCO) and low-Tc (Nb3Sn) materials indicating the need to increase the pinning in this material to make it attractive for technological applications. Moreover, we have verified through different procedures that the sintered samples behave as well-connected bodies, showing no trace of granularity; therefore, the critical current density values Jc may be obtained by applying the 'critical state model' in a straightforward way. The hysteresis loop measurements allowed estimation of Jc both for powders and sintered samples and confirmed the strong field decrease of Jc, implicit in IL behaviour. We attempt to introduce defects in the MgB2 structure by different chemical treatments like substitution of lithium on the magnesium site and doping of the precursor boron powders with aluminium and silicon. Jc always increased in doped or substituted samples (up to a factor 3) and this fact is meaningful, in particular in the light of the small level of substitution or doping we performed. The best result in terms of Jc is achieved by silicon doping that, moreover, does not significantly decrease the transition temperature.

  10. Effects of sintering temperature on properties of Ti-sheathed, SiC-doped MgB2 superconducting wires

    NASA Astrophysics Data System (ADS)

    Liang, Gan; Fang, Hui; Hoyt, Cad; Guchhait, Samaresh; Markert, John

    2009-03-01

    Mono-core Ti-sheathed, silicon carbide (SiC) doped MgB2 wires have been successfully fabricated by powder-in-tube method. The average size of the doped SiC nano particles is 20 nm and the doping level is 10 wt.%. The wires were sintered for 30 minutes at five temperatures from 650 ^oC to 800 ^oC. Effects of sintering temperature on the phase composition, microstructure, and critical current density (Jc) were studied by x-ray diffraction, scanning electron microscopy, and magnetization measurements. The results indicate that the Ti sheath does not react with the magnesium and boron, and the present wire rolling process can produce Ti-sheathed, SiC-doped MgB2 wires with high critical current density. It is found that Jc peaks up at sintering temperature of 800 ^oC. This is in sharp contrast with the previously reported result (by other group) that the optimal Jc was achieved at sintering temperature 650 ^oC. The correlations between Jc and the structural properties of the wires are discussed.

  11. Effect of heat treatment temperature on superconducting performance of B 4C added MgB 2/Nb conductors

    NASA Astrophysics Data System (ADS)

    Viljamaa, J.; Kario, A.; Dobročka, E.; Reissner, M.; Kulich, M.; Kováč, P.; Häßler, W.

    2012-02-01

    A previously observed enhancing effect of addition of 10 wt.% of B 4C on critical current density ( Jc) dependence on magnetic flux density ( B) in MgB 2 superconductors is examined here in more detail. Nb sheathed in situ MgB 2 monofilamentary Powder-in-Tube (PIT) samples are prepared with the 10 wt.% addition of boron carbide. The samples are heat treated at different temperatures, namely at 650, 700, 750, and 800 °C for 30 min. The phases and lattice parameters of the samples are studied using X-ray Diffraction (XRD). The amount of B 4C does not decrease from the initial amount with increasing heat treatment temperature ( Tht) but instead increases. This indicates that some of the Mg from the precursor reacts with the Nb sheath. Magnetic Jc( B) characteristics are obtained at several temperatures in external B in a Vibrating Sample Magnetometer (VSM). The magnetic and transport Jc( B) results disagree with each other which can be explained by unsuitability of Nb as the sheath with higher Tht. From these results, also pinning force densities ( Fp) are calculated. No effect on pinning mechanism of B 4C added samples is observed by the heat treatment conditions. Resistance dependencies on temperature are also measured in a Physical Properties Measurement System (PPMS). Mg deficiency with high Tht is supported by these measurements.

  12. 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.

  13. Effects of Fe substitution on TC suppression of MgB2 : A B11 NMR study

    NASA Astrophysics Data System (ADS)

    Lue, C. S.; Su, T. H.; Xie, B. X.; Chen, S. K.; MacManus-Driscoll, J. L.; Kuo, Y. K.; Yang, H. D.

    2006-06-01

    We have performed a systematic study of Fe-doped MgB2 alloys using B11 nuclear magnetic resonance spectroscopy. The Knight shift, line shape, as well as spin-lattice relaxation time (T1) on each individual composition have been identified. The central transition and quadrupole linewidths increase with Fe concentration, attributed to the effect of disorder on these measurements. The temperature independence of the central transition linewidth further confirms no magnetic moment associated with these dopants. In addition, the value of T1T remains unchanged with Fe content, indicative of little or no effect on the B-2p Fermi level density of states (DOS) by substituting Fe in the Mg sublattice of MgB2 . These observations clearly revealed that the drop of TC cannot be accounted for either by the pair breaking or by the electronic DOS reduction. It thus revealed the importance of the phonon contributions to the change of TC , presumably due to the decreased phonon frequency and/or the reduced electron-phonon coupling strength through Fe doping.

  14. On the roles of graphene oxide doping for enhanced supercurrent in MgB2 based superconductors.

    PubMed

    Yeoh, W K; Cui, X Y; Gault, B; De Silva, K S B; Xu, X; Liu, H W; Yen, H-W; Wong, D; Bao, P; Larson, D J; Martin, I; Li, W X; Zheng, R K; Wang, X L; Dou, S X; Ringer, S P

    2014-06-01

    Due to their graphene-like properties after oxygen reduction, incorporation of graphene oxide (GO) sheets into correlated-electron materials offers a new pathway for tailoring their properties. Fabricating GO nanocomposites with polycrystalline MgB2 superconductors leads to an order of magnitude enhancement of the supercurrent at 5 K/8 T and 20 K/4 T. Herein, we introduce a novel experimental approach to overcome the formidable challenge of performing quantitative microscopy and microanalysis of such composites, so as to unveil how GO doping influences the structure and hence the material properties. Atom probe microscopy and electron microscopy were used to directly image the GO within the MgB2, and we combined these data with computational simulations to derive the property-enhancing mechanisms. Our results reveal synergetic effects of GO, namely, via localized atomic (carbon and oxygen) doping as well as texturing of the crystals, which provide both inter- and intra-granular flux pinning. This study opens up new insights into how low-dimensional nanostructures can be integrated into composites to modify the overall properties, using a methodology amenable to a wide range of applications. PMID:24793305

  15. Superconducting Properties of MgB2 with Addition of Other AlB2-type Diborides and Carbon Sources, Prepared Using High Energy Ball Milling and HIP

    NASA Astrophysics Data System (ADS)

    Rodrigues, Durval; Silva, Lucas B. S. da; Metzner, Vivian C. V.; Hellstrom, Eric E.

    In the present work it is described the production of MgB2 samples by using the mixture of MgB2 with other diborides, (TaB2, VB2, and AlB2) which have the same C32 hexagonal structure as the MgB2, and simultaneous addition with the diborides and SiC, that contribute with C, to replace B in the crystalline structure of the matrix. As an important result, the critical current density (Jc) was improved at low magnetic fields when just the diborides are added. However, when SiC is added simultaneously with the diborides, the result is the improvement of Jc at high fields. The critical temperature (Tc) was maintained high.

  16. 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 MgB 2 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 MgB 2 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 MgB 2 wires.

  17. Nanocoating of particles for optimal doping and universal enhancement of current-carrying ability in ``organic'' MgB2-xCx superconductors

    NASA Astrophysics Data System (ADS)

    Shcherbakova, O. V.; Pan, A. V.; Dou, S. X.; Nigam, R.; Wexler, D.

    2010-05-01

    The universal approach of liquid mixing has been found to produce "organic" MgB2-xCx superconductors with structural and supercurrent-carrying properties unattainable by other techniques. We show by transmission electron microscopy combined with energy dispersive spectroscopy that these unique properties are enabled through coating of boron particles with a nanolayer of carbon. The subsequent reaction between carbon-encapsulated boron and magnesium results in enhanced carbon content x in the crystal lattice, as determined by x-ray diffraction pattern analysis. Among various carbon-containing compounds investigated, polycarbosilane has been found to be the optimal dopant for MgB2 superconductor, producing the largest critical current density due to the formation of wide range of nanodefects with pinning properties within the MgB2 crystal lattice, as well as due to minimal formation of current-blocking layers around the grains.

  18. Pinning and trapped field in MgB2- and MT-YBaCuO bulk superconductors manufactured under pressure

    NASA Astrophysics Data System (ADS)

    Prikhna, T.; Eisterer, M.; Chaud, X.; Weber, H. W.; Habisreuther, T.; Moshchil, V.; Kozyrev, A.; Shapovalov, A.; Gawalek, W.; Wu, M.; Litzkendorf, D.; Goldacker, W.; Sokolovsky, V.; Shaternik, V.; Rabier, J.; Joulain, A.; Grechnev, G.; Boutko, V.; Gusev, A.; Shaternik, A.; Barvitskiy, P.

    2016-03-01

    The relevant pinning centers of Abrikosov vortices in MgB2-based materials are oxygen-enriched Mg-B-O inclusions or nanolayers and inclusions of MgBx (x>4) phases. The high critical current densities, j c, of 106 and 103A/cm2 at 1 and 8.5 T, respectively, at 20 K can be achieved in polycrystalline materials (prepared at 2 GPa) containing a large amount of admixed oxygen. Besides, oxygen can be incorporated into the MgB2 structure in small amounts (MgB1.5O0.5), which is supported by Auger studies and calculations of the DOS and the binding energy. The j c of melt textured YBa2Cu3O7-δ (or Y123)-based superconductors (MT-YBaCuO) depends not only on the perfectness of texture and the amount of oxygen in the Y123 structure, but also on the density of twins and micro-cracks formed during the oxygenation (due to shrinking of the c-lattice parameter). The density of twins and microcracks increases with the reduction of the distance between Y2BaCuO5 (Y211) inclusions in Y123. At 77 K jc=8·104 A/cm2 in self-field and jc=103 A/cm2 at 10 T were found in materials oxygenated at 16 MPa for 3 days with a density of twins of 22–35 per µm (thickness of the lamellae: 45-30 nm) and a density of micro-cracks of 200–280 per mm. Pinning can occur at the points of intersection between the Y123 twin planes and the Y211 inclusions. MTYBaCuO at 77 K can trap 1.4 T (38×38×17 mm, oxygenated at 0.1 MPa for 20 days) and 0.8 T (16 mm in diameter and 10 mm thick with 0.45 mm holes oxygenated at 10 MPa for 53 h). The sensitivity of MgB2 to magnetic field variations (flux jumps) complicates estimates of the trapped field. At 20 K 1.8 T was found for a block of 30 mm in diameter and a thickness of 7.5 mm and 1.5 T (if the magnetic field was increased at a rate of 0.1 T) for a ring with dimensions 24×18 mm and a thickness of 8 mm.

  19. Angular dependences of the motion of the anisotropic flux line lattice and the peak effect in MgB2

    NASA Astrophysics Data System (ADS)

    Jang, D.-J.; Lee, H.-S.; Kang, B.; Lee, H.-G.; Cho, M.-H.; Lee, S.-I.

    2008-12-01

    We have studied the angle-dependent motion of the anisotropic flux line lattice (FLL) and the peak effect (PE) in MgB2 single crystals. For arbitrary angles (θ), we measured the resistance (R(H)) and critical current (Ic(H)) with AC and DC currents, respectively. At low fields below the PE, R(H) and Ic(H) showed a weak angular dependence, regardless of the type of excitation current, because of the stable vortex state. At intermediate fields near the PE, R(H) and Ic(H) at the onset of the PE varied with θ, depending on the type of external current, due to the metastability of the disordered vortex lattice near the PE. At high fields above the PE and near the upper critical field Hc2, the R(H) curves showed a simple scaling behavior with θ.

  20. Ab initio theory of magnetic-field-induced odd-frequency two-band superconductivity in MgB2

    NASA Astrophysics Data System (ADS)

    Aperis, Alex; Maldonado, Pablo; Oppeneer, Peter M.

    2015-08-01

    We develop the anisotropic Eliashberg framework for superconductivity in the presence of an applied magnetic field. Using as input the ab initio calculated electron and phonon band structures and electron-phonon coupling, we solve self-consistently the anisotropic Eliashberg equations for the archetypal superconductor MgB2. We find two self-consistent solutions, time-even two-band superconductivity, as well as unconventional time-odd s -wave spin triplet two-band superconductivity emerging with applied field. We provide the full momentum, frequency, and spin-resolved dependence and magnetic field-temperature phase diagrams of the time-even and time-odd superconducting pair amplitudes and predict fingerprints of this novel odd-frequency state in tunneling experiments.

  1. Intrinsic nonlinearity probed by intermodulation distortion microwave measurements on high quality MgB2 thin films

    NASA Astrophysics Data System (ADS)

    Cifariello, G.; Aurino, M.; Di Gennaro, E.; Lamura, G.; Andreone, A.; Orgiani, P.; Xi, X. X.; Villégier, J.-C.

    2006-04-01

    The two-tone intermodulation distortion arising in MgB2 thin films synthesized by hybrid physical-chemical vapor deposition is studied in order to probe the influence of the two bands on the nonlinear response of this superconductor. The measurements are carried out by using a dielectrically loaded copper cavity operating at 7GHz. Microwave data on samples having critical temperatures above 41K, very low resistivity values, and residual resistivity ratio larger than 10 are shown. The dependence of the nonlinear surface losses and of the third order intermodulation products on the power feeding the cavity and on the temperature is analyzed. At low power, the signal arising from distortion versus temperature shows the intrinsic s-wave behavior expected for this compound. Data are compared with measurements performed on Nb and YBa2Cu3O7-δ thin films using the same technique.

  2. Irreversibility field and flux pinning in MgB2 with and without SiC additions

    NASA Astrophysics Data System (ADS)

    Sumption, M. D.; Bhatia, M.; Dou, S. X.; Rindfliesch, M.; Tomsic, M.; Arda, L.; Ozdemir, M.; Hascicek, Y.; Collings, E. W.

    2004-10-01

    The critical current density (Jc) was measured at 4.2 K for MgB2 strands with and without SiC additions. In some cases measurements were performed on long (1 m) samples wound on barrels, the transport results being compared to the results of magnetic measurements. Most measurements were performed on short samples in fields of up to 18 T. It was found that in situ processed strands with 10% SiC additions heat treated at 700-800 °C showed improved irreversibility fields (Hr) and bulk pinning strengths (Fp) as compared to control samples; an increase in Hr of 1.5 T was noted. Heat treatment to 900 °C gave even larger improvements, with Hr reaching 18 T and Fp values maximizing at 20 GN m-3.

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

    DOE PAGESBeta

    Mou, Daixiang; Jiang, Rui; Taufour, Valentin; Bud'ko, S. L.; Canfield, P. C.; Kaminski, Adam

    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

  4. Magnesium Diboride (MgB2 )-Based Bolometer Array for Far Infra-Red Thermal Imaging and Fourier Transform Spectroscopy Applications

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

    The performance of a 2-D array of Magnesium Diboride (MgB2) based thermal detectors is presented. Applications will be in far infrared instrumentation for high-resolution spectroscopy and thermal mapping of cold planetary objects in the solar system.

  5. Flux pinning and vortex dynamics in MgB2 doped with TiO2 and SiC inclusions

    NASA Astrophysics Data System (ADS)

    Prokhorov, V. G.; Kaminsky, G. G.; Svetchnikov, V. L.; Park, J. S.; Eom, T. W.; Lee, Y. P.; Kang, J.-H.; Khokhlov, V. A.; Mikheenko, P.

    2009-06-01

    The mixed-state superconducting properties of bulk MgB2+2at.%TiO2 and +8at.%SiC, prepared by in situ solid state reaction, are investigated. Analysis of the mixed-state parameters, such as the upper critical field, the coherence length, and the Ginzburg-Landau parameter, proves that MgB2+2at.%TiO2 is a high-κ type-II superconductor in the dirty limit, while MgB2+8at.%SiC corresponds to that in the moderately clean limit. It is shown that the grain-boundary pinning realized in fine-grained doped MgB2 polycrystals is of the anisotropic rather than the electron-scattering type. The field-cooled temperature dependences of the magnetic moment reveal a transition of the samples to the paramagnetic state at certain applied magnetic fields, which is treated as manifestation of the paramagnetic Meissner effect. The experimental results are discussed on the base of modern theoretical approaches.

  6. MgB2 Coated Ellipsoids as an Approach to Investigate the Possible Enhancement of the Vortex Penetrating Field of SRF Cavities

    NASA Astrophysics Data System (ADS)

    Tan, Teng; Wolak, Matthaeus; Tajima, Tsuyoshi; Xi, Xiaoxing; Civale, Leonardo

    2015-03-01

    Superconducting rf (SRF) cavities fabricated from bulk niobium (Nb) are a key component for modern particle accelerators. The magnetic field distribution on the inner wall of an SRF cavity is inversely similar to the field distribution on top of a superconducting ellipsoid when we put it in a magnetic field parallel to its axis. By measuring the vortex penetration into the magnetized superconducting ellipsoids, we can deduct the behavior of SRF cavities. Magnesium diboride (MgB2) has potential to replace Nb as it has a higher Tc of 39 K, a lower residual resistivity of ~ 0.1 μΩ cm (at 42 K), and a higher thermodynamic critical field Hc value compared to Nb. In this work, we successfully coated uniform MgB2 layers on top of molybdenum and niobium ellipsoids. SQUID magnetometer measurements showed that the coated MgB2 layer has a Tc above 38.5 K, and can provide a perfect magnetic shielding up to ~ 500 Oe at 1.8K. By coating MgB2 on Nb ellipsoids, we increased the vortex penetration field (the maximum field at which a cavity can be operated) by ~ 500 Oe at 2 K.

  7. 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.

  8. Microstructures of MgB2/Fe tapes fabricated by an in situ powder-in-tube method using MgH2 as a precursor powder

    NASA Astrophysics Data System (ADS)

    Hata, S.; Yoshidome, T.; Sosiati, H.; Tomokiyo, Y.; Kuwano, N.; Matsumoto, A.; Kitaguchi, H.; Kumakura, H.

    2006-02-01

    Microstructures of MgB2/Fe tapes fabricated by an in situ powder-in-tube method using MgH2 as a precursor powder have been studied by means of x-ray diffraction and analytical transmission electron microscopy combined with a focused ion beam microsampling technique. The overall microstructures in the tapes are characterized as densely crystallized MgB2 areas with 10-200 nm grain size, uncrystallized areas mainly containing MgO and amorphous phases enriched with B, and a number of holes and cracks. The crystallized MgB2 areas increase upon doping with SiC nanoparticles. Si and C atoms decomposed from SiC nanoparticles during heat treatment exhibit different spatial distributions: the Si atoms are inhomogeneously distributed, forming silicides such as Mg2Si with grain size of 5-20 nm, while the C atoms tend to be uniformly distributed in the MgB2 matrix. A significant difference in distribution of O atoms between the SiC-doped and non-doped specimens was observed. The processes of formation of these microstructures and their relationships with the critical current density under magnetic fields have been discussed.

  9. Influence of twisting and bending on the Jc and n-value of multifilamentary MgB2 strands

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Li, G.; Susner, M.; Sumption, M. D.; Rindfleisch, M.; Tomsic, M.; Collings, E. W.

    2015-12-01

    The influences of strand twisting and bending (applied at room temperature) on the critical current densities, Jc, and n-values of MgB2 multifilamentary strands were evaluated at 4.2 K as function of applied field strength, B. Three types of MgB2 strand were evaluated: (i) advanced internal magnesium infiltration (AIMI)-processed strands with 18 filaments (AIMI-18), (ii) powder-in-tube (PIT) strands processed using a continuous tube forming and filling (CTFF) technique with 36 filaments (PIT-36) and (iii) CTFF processed PIT strands with 54 filaments (PIT-54). Transport measurements of Jc(B) and n-value at 4.2 K in fields of up to 10 T were made on: (i) PIT-54 after it was twisted (at room temperature) to twist pitch values, Lp, of 10-100 mm. Transport measurements of Jc(B) and n-value were performed at 4.2 K; (ii) PIT-36 and AIMI-18 after applying bending strains up to 0.6% at room temperature. PIT-54 twisted to pitches of 100 mm down to 10 mm exhibited no degradation in Jc(B) and only small changes in n-value. Both the Jc(B) and n-value of PIT-36 were seen to be tolerant to bending strain of up to 0.4%. On the other hand, AIMI-18 showed ±10% changes in Jc(B) and significant scatter in n-value over the bending strain range of 0-0.6%.

  10. Theory of Raman scattering from Leggett's collective mode in a multiband superconductor: Application to MgB2

    NASA Astrophysics Data System (ADS)

    Klein, M. V.

    2010-07-01

    In 1966, Leggett used a two-band superconductor to show that a new collective mode could exist at low temperatures, corresponding to a counterflow of the superconducting condensates in each band. Here, the theory of electronic Raman scattering in a superconductor by Klein and Dierker (1984) is extended to a multiband superconductor. Raman scattering creates particle/hole (p/h) pairs. In the relevant A1g symmetry, the attraction that produces pairing necessarily couples excitations of superconducting pairs to these p/h excitations. In the Appendix, it is shown that for zero wave-vector transfer q , this coupling modifies the Raman response and makes the long-range Coulomb correction null. The two-band result is applied to MgB2 where this coupling activates Leggett’s collective mode. His simple limiting case is obtained when the interband attractive potential is decreased to a value well below that given by local-density approximation (LDA) theory. The peak from Leggett’s mode is studied as the potential is increased through the theoretical value. With realistic MgB2 parameters, the peak broadens through decay into the continuum above the smaller ( π band) superconducting gap. Finite q effects are also taken into account, yielding a Raman peak that agrees well in energy with the experimental result by Blumberg [Phys. Rev. Lett. 99, 227002 (2007)]10.1103/PhysRevLett.99.227002. This approach is also applied to the q=0 , two-band model of the Fe pnictides considered by Chubukov [Phys. Rev. B 79, 220501(R) (2009)]10.1103/PhysRevB.79.220501.

  11. Estimation of hysteretic losses for MgB2 tapes under the operating conditions of a generator

    NASA Astrophysics Data System (ADS)

    Vargas-Llanos, Carlos Roberto; Zermeño, Víctor M. R.; Sanz, Santiago; Trillaud, Frederic; Grilli, Francesco

    2016-03-01

    Hysteretic losses in the MgB2 wound superconducting coils of a 550 kW synchronous hybrid scaled generator were estimated as part of the European project SUPRAPOWER led by the Spanish Fundación Tecnalia Research & Innovation. Particular interest was given to the losses caused by the magnetic flux ripples in the rotor coils originating from the conventional stator during nominal operation. To compute these losses, a 2D finite element analysis was conducted and Maxwell’s equations written in the H-formulation were solved considering the nonlinear material properties of the conductor materials. The modeled tapes are made of multiple MgB2 filaments embedded in a Ni matrix and soldered to a high purity copper strip and insulated with Dacron braid. Three geometrical models of single tape cross sections of decreasing complexity were studied: (1) the first model reproduced closely the actual cross section obtained from tape micrographs. (2) The second model was obtained from the computed elasto-plastic deformation of a round Ni wire. (3) The third model was based on a simplified cross section with the superconducting filaments bundled in a single elliptical bulky structure. The last geometry allowed the validation of the modeling technique by comparing numerical losses with results from well-established analytical expressions. Additionally, the following cases of filament transpositions of the multi-filamentary tape were studied: no transposition, partial and full transposition; thereby improving understanding of the relevance of the tape fabrication process on the magnitude of the determination of ac losses. Finally, choosing the right level of geometrical detail, the following operational regimes of the machine and its impact on individual superconducting tape losses in the rotor were studied: bias-dc current, ramping current under ramping background field and magnetic flux ripples under dc background current and field.

  12. High-performance MgB2 superconducting wires for use under liquid-helium-free conditions fabricated using an internal Mg diffusion process

    NASA Astrophysics Data System (ADS)

    Ye, ShuJun; Song, Minghui; Matsumoto, Akiyoshi; Togano, Kazumasa; Takeguchi, Masaki; Ohmura, Takahito; Kumakura, Hiroaki

    2013-12-01

    MgB2 has a superconducting transition temperature (Tc) of 39 K, which is much higher than that for practical metallic superconductors. Thus, it is hoped that MgB2 can not only replace metallic superconductors, but can be used under liquid-helium-free conditions, for example, at temperatures of 10-20 K that can easily be achieved using cryocooling systems. However, to date, the reported critical current density (Jc) for MgB2 wires is not high enough for large-scale applications in liquid-helium-free conditions. In the present study, successful fabrication of high-performance MgB2 superconducting wires was carried out using an internal Mg diffusion (IMD) process, involving a p-dimethylbenzene (C8H10) pre-treatment of carbon-coated B powder with nanometer-sized particles. The resulting wires exhibited the highest ever Jc of 1.2 × 105 A cm-2 at 4.2 K and 10 T, and an engineering critical current density (Je) of about 1 × 104 A cm-2. Not only in 4.2 K, but also in 10 K, the Jc values for the wires fabricated in the present study are in fact higher than that for Nb-Ti wires at 4.2 K for the magnetic fields at which the measurements were carried out. At 20 K and 5 T, the Jc and Je were about 7.6 × 105 A cm-2 and 5.3 × 103 A cm-2, respectively, which are the highest values reported for MgB2 wires to date. The results of a detailed microstructural analysis suggested that the main reason for the superior electrical performance was the high density of the MgB2 layer rather than just the small grain size, and that the critical current could be further increased by suitable control of the microstructure. These high-performance IMD-processed MgB2 wires are thus promising superconductors for applications such as magnetic resonance imaging and maglev trains that can operate under liquid-helium-free conditions.

  13. C-Axis Properties of DyNi2B2C System

    NASA Astrophysics Data System (ADS)

    Lee, W. C.

    2012-02-01

    We have measured the electrical resistivity along c-axis ρc(T, H) of the DyNi2B2C single crystal with the magnetic fields perpendicular to the c-axis and the magnetization isotherms M(H) of the DyNi2B2C single crystal with magnetic fields perpendicular and parallel to the c-axis. We confirmed that Neel temperature TN is 10.3K from the ρc(T) result which is consistent with that from previous ρab(T) result. In addition, the constructed critical fields Hc2(T) curve and magnetic transitions diagram of DyNi2B2C from ρc(T) magnetic fields perpendicular to c-axis is similar to that of ρab(T) result, which is thought to arise that 3 D magnetic structure of DyNi2B2C.

  14. Characterization of reactively sputtered c-axis aligned nanocrystalline InGaZnO{sub 4}

    SciTech Connect

    Lynch, David M.; Zhu, Bin; Ast, Dieter G.; Thompson, Michael O.; Levin, Barnaby D. A.; Muller, David A.; Greene, Raymond G.

    2014-12-29

    Crystallinity and texturing of RF sputtered c-axis aligned crystal InGaZnO{sub 4} (CAAC IGZO) thin films were quantified using X-ray diffraction techniques. Above 190 °C, nanocrystalline films with an X-ray peak at 2θ = 30° (009 planes) developed with increasing c-axis normal texturing up to 310 °C. Under optimal conditions (310 °C, 10% O{sub 2}), films exhibited a c-axis texture full-width half-maximum of 20°. Cross-sectional high-resolution transmission electron microscopy confirmed these results, showing alignment variation of ±9° over a 15 × 15 nm field of view and indicating formation of much larger aligned domains than previously reported. At higher deposition temperatures, c-axis alignment was gradually lost as polycrystalline films developed.

  15. Wave Propagation Direction and c-Axis Tilt Angle Influence on the Performance of ScAlN/Sapphire-Based SAW Devices.

    PubMed

    Kochhar, Abhay; Yamamoto, Yasuo; Teshigahara, Akihiko; Hashimoto, Ken-Ya; Tanaka, Shuji; Esashi, Masayoshi

    2016-07-01

    Some previously reported surface acoustic wave (SAW) devices using bulk piezoelectric substrates showed higher acoustic power radiated in either forward or backward wave propagation direction depending on their crystal orientations and are called natural single-phase unidirectional transducers (NSPUDT). While these reports were based on bulk piezoelectric substrates, we report directionality in the c-axis tilted 44% scandium doped aluminum nitride thin piezoelectric film-based SAW devices on sapphire. It is worth noting that our observance of directionality is specifically in Sezawa mode. We produced a c-axis tilt up to 5.5° over the single wafer and examined the directionality by comparing the forward and backward insertion loss utilizing split finger electrodes as a receiver. The wave propagation direction and c-axis tilt angle influence on the performance of SAW devices is evaluated. Furthermore, return loss and insertion loss data are presented for various SAW propagation directions and c-axis tilt angles. Finally, the comparison for both acoustic modes, i.e., Rayleigh and Sezawa, is reported. PMID:26978772

  16. 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

  17. Experimental results on MgB2 used as ADR magnetic shields, and comparison to NbTi

    NASA Astrophysics Data System (ADS)

    Prouvé, T.; Duval, J. M.; Luchier, N.; D'escrivan, S.

    2014-11-01

    Adiabatic Demagnetization Refrigerator (ADR) is an efficient way to obtain sub-Kelvin temperatures in space environments. The SAFARI instrument for the Japanese spaceborne SPICA mission features detectors which will be cooled down to 50 mK. This cooling will be done by a hybrid cooler comprising a 300 mK sorption stage and a 50 mK ADR stage. For this cooler and ADR in general, the main contribution to the overall mass is in the magnetic system and particularly in the magnetic shielding required to keep the stray field within acceptable values. In order to reduce this mass, superconducting materials can be used as active magnetic shields thanks to un-attenuated eddy currents generated while ramping the magnet current. In this way they could reduce the need of heavy ferromagnetic material shields and increase the shielding efficiency to reach very low parasitic values. In the framework of SAFARI we have built a numerical model of a superconductor magnetic shield. The good results regarding the weight gain lead us to an experimental confirmation. In this paper we present an experimental study on MgB2 and NbTi superconducting materials. 2 pairs of rings of typical diameter of 80 mm have been tested using a superconducting magnet matching closely the dimensions of the SAFARI ADR cooler. The magnetic shielding measurements have been compared to a numerical model.

  18. Theory of Raman Scattering from Leggett's Collective Mode in a Multiple Band Superconductor: Application to MgB2

    NASA Astrophysics Data System (ADS)

    Klein, Miles

    2008-03-01

    Using an extension of BCS theory to a two-band superconductor, Leggett showed that if the relevant parameters obeyed certain conditions a collective mode would exist corresponding to the counter flow of the two condensates.^1 I have extended earlier work on electronic Raman in superconductors^2 to the multiple band case in order to incorporate Leggett's theory. The following effects have been included: (a) Vertex correction in the particle/hole channel where the Raman vertex acts. (b) Realistic parameters that apply to MgB2 yielding a counter flow mode that decays into the pair-breaking continuum associated with the lower gap π band. (c) Large finite wave-vector effects due to the relatively large Fermi velocity of the π band. (d) Integration over the wave-vector in part (c) necessitated by the exponential decay of the photon fields traveling into and out of the metallic sample. A comparison to the results of Blumberg^3 will be given. ^1A.J. Leggett, Progr. Theor. Phys. 36, 901 (1966). ^2M.V. Klein and S.B. Dierker, Phys. Rev. B29, 4976 (1984). ^3G. Blumberg et al., Phys. Rev. Lett. 99, (2007); arXiv:0710.2803.

  19. 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.

  20. Size determination of superconducting MgB2 powder from magnetization curve, image analysis and surface area measurements

    NASA Astrophysics Data System (ADS)

    Vignolo, M.; Bovone, G.; Bellingeri, E.; Bernini, C.; Romano, G.; Buscaglia, M. T.; Buscaglia, V.; Siri, A. S.

    2014-06-01

    This paper reports on a method for estimating the average grain size of superconducting nanoparticles through their magnetic properties. The use of SQUID magnetometry to determine the average MgB2 particle size was investigated and the results were compared with those of several different techniques. In particular, the data obtained from zero field cooled magnetization measurements as a function of the temperature were compared with the results obtained by the scanning electron microscopy and Brunauer-Emmett-Teller techniques. The particle magnetization was measured by a commercial SQUID magnetometer in a magnetic field (10 G) and at temperatures ranging from 5 to 50 K by dispersing the powders in a grease medium. The grain size was obtained by fitting the data taking into account the Ginzburg-Landau temperature dependence of the London penetration depth. Variations in typical modeling parameters were explored in order to gain a better picture of the average grain size and the effectiveness of various measurement techniques. We find that it is possible to use the magnetization measurements to determine the average grain size, even though an SEM analysis coupled to the image analysis allows the extraction of more information about the grain-size distribution. Furthermore, a Matlab routine has been developed in order to automatically analyze several SEM images.

  1. 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].

  2. 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.

  3. 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.

  4. Update on the fabrication and performance of 2-D arrays of superconducting Magnesium Diboride (MgB2) thermal detectors for outer-planets exploration.

    NASA Astrophysics Data System (ADS)

    Lakew, B.; Aslam, S.

    2011-10-01

    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.

  5. Comparison of S/N Ratios for Magnesium diboride (MgB2) Superconducting detectors vs Bi-Te thermopiles when used in an infrared radiometer.

    NASA Astrophysics Data System (ADS)

    lakew, b.; Aslam, S.

    2014-04-01

    Mapping the surface temperature of cold Jovian moons like Europa or Ganymede requires an accurate measurement of their infrared spectral radiance. One measurement technique employs a radiometer with thermopile linear arrays. Each array is in turn integrated with infrared filters of the appropriate wavelength pass bands. The performance of such a radiometer when using an array of thermopile detectors vs an array of superconducting magnesium-diboride (MgB2) detectors.

  6. Influence of ZnO and Dy2 O3 on MgB2 Bulks Fabricated by High Temperature and Pressure Reaction

    NASA Astrophysics Data System (ADS)

    Sumption, Mike; Yang, Yuan

    ZnO and Dy2O3 have been considered as dopants for the improvement of superconducting properties in MgB2 bulks. However, the effect of these dopants is still unclear: some studies reported these metal oxides worked as new pinning centers and others was attributed the effects to Mg site substitution. In addition, low temperature reactions may explore limited solubility regimes for these dopants. In order to study the intrinsic effect of ZnO and Dy2O3 in MgB2, a high temperature solid state sintering method has been used to fabricate dense and homogeneous MgB2 bulks. Even higher temperature excursions above the peritectic allow us to explore the solubility limits. To do this we used an induction furnace built inside of a high pressure vessel which allowed us to reach 1700oC and 1500 Psi. A slow cooling rate (2oC/min) was used in an attempt to obtain a homogeneous nucleation and phase distribution. A series of MgB2 bulk samples with ZnO and Dy2O3 additives were synthesized through this high pressure and temperature procedures. The resulting microstructures of these bulk samples were revealed by SEM and TEM. Atomic substitution were evaluated by high resolution XRD. The upper critical field Bc 2, irreversible field Birr and Tc were obtained from both magnetic and resistivity measurements. The roles of substitution vs precipitate induced strain on Bc 2enhancements with adding ZnO and Dy2O3 were discussed.

  7. 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.

  8. Microscopic insight into the pump-probe relaxation dynamics of superconductors: Model study of MgB2relaxation within nonlinear response theory

    NASA Astrophysics Data System (ADS)

    Baňacký, Pavol; Szöcs, Vojtech

    2016-05-01

    Here we present a quantum-statistical formulation of third-order polarization P(3)(t), which is induced in a sample by a sequence of incident external fields, and serves as a source of an emitted radiation field detected as a signal in pump-probe (PP) experiments. Our treatment is based on the perturbation expansion of the non-equilibrium density matrix for calculation of multi-time correlation functions, and the corresponding response function, at finite temperature. As a model for our study, the high-temperature superconductor MgB2 has been selected. Knowledge of the electronic structure of the studied system, and of the corresponding Eliashberg function that represents pertinent electron-phonon (EP) interactions, enabled us to distinguish non-equilibrium processes running over different time-periods in a sequence of interactions with laser pulses on a microscopic level. We have also derived temperature-dependent relaxation dynamics as a function of delay time between the pump and probe pulses. For the studied model system of MgB2, we have shown that an abrupt increase of the relaxation time at Tc, as detected by experiments, is the direct consequence of sudden changes in the character of EP coupling in transition from an adiabatic to a stabilized superconducting anti-adiabatic state, as it predicts the anti-adiabatic theory of electron-vibration interactions. The BCS model, which preserves the adiabatic character of EP coupling also below the critical temperature of MgB2, is basically unable to reflect the enormous sudden increase of the relaxation time. Based on diagrammatic perturbation theory, differences in the optical pump-optical probe and the optical pump-terahertz probe settings of MgB2 PP relaxation dynamics are discussed.

  9. A trapped magnetic field of 3 T in homogeneous, bulk MgB2 superconductors fabricated by a modified precursor infiltration and growth process

    NASA Astrophysics Data System (ADS)

    Bhagurkar, A. G.; Yamamoto, A.; Anguilano, L.; Dennis, A. R.; Durrell, J. H.; Babu, N. Hari; Cardwell, D. A.

    2016-03-01

    The wetting of boron with liquid magnesium is a critical factor in the synthesis of MgB2 bulk superconductors by the infiltration and growth (IG) process. Poor wetting characteristics can therefore result potentially in non-uniform infiltration, formation of defects in the final sample structure and poor structural homogeneity throughout the bulk material. Here we report the fabrication of near-net-shaped MgB2 bulk superconductors by a modified precursor infiltration and growth (MPIG) technique. A homogeneous bulk microstructure has subsequently been achieved via the uniform infiltration of Mg liquid by enriching pre-reacted MgB2 powder within the green precursor pellet as a wetting enhancer, leading to relatively little variation in superconducting properties across the entire bulk sample. Almost identical values of trapped magnetic field of 2.12 T have been measured at 5 K at both the top and bottom surfaces of a sample fabricated by the MPIG process, confirming the uniformity of the bulk microstructure. A maximum trapped field of 3 T has been measured at 5 K at the centre of a stack of two bulk MgB2 samples fabricated using this technique. A steady rise in trapped field was observed for this material with decreasing temperature down to 5 K without the occurrence of flux avalanches and with a relatively low field decay rate (1.5%/d). These properties are attributed to the presence of a fine distribution of residual Mg within the bulk microstructure generated by the MPIG processing technique.

  10. Modeling studies of an impinging jet reactor design for hybrid physical-chemical vapor deposition of superconducting MgB 2 films

    NASA Astrophysics Data System (ADS)

    Lamborn, Daniel R.; Wilke, Rudeger H. T.; Li, Qi; Xi, X. X.; Snyder, David W.; Redwing, Joan M.

    2009-03-01

    An impinging jet reactor was developed for the deposition of superconducting MgB 2 thin films by hybrid physical-chemical vapor deposition, a technique that combines Mg evaporation with the thermal decomposition of B 2H 6 gas. A transport and chemistry model for boron film deposition from B 2H 6 was initially used to investigate the effect of carrier gas, Mg crucible temperature and gas flow rates on boron film growth rate and uniformity. The modeling studies, which were validated experimentally, demonstrated a reduction in B 2H 6 gas-phase depletion and an increased boron film growth rate using an argon carrier gas compared to hydrogen. The results were used to identify a suitable set of process conditions for MgB 2 deposition in the impinging jet reactor. The deposition of polycrystalline MgB 2 thin films that exhibited a transition temperature of 39.5 K was demonstrated at growth rates up to ˜50 μm/h.

  11. 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

  12. 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.

  13. 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.

  14. Measurement and modeling of the low-temperature penetration-depth anomaly in high-quality MgB2 thin films

    NASA Astrophysics Data System (ADS)

    Agassi, Y. D.; Oates, D. E.; Moeckly, B. H.

    2012-10-01

    Based on our measurements of intermodulation distortion in MgB2, we have previously proposed that the π energy-gap in MgB2 entails six nodal lines [Y.D. Agassi, D.E. Oates, and B.H. Moeckly, Phys. Rev. B 80 (2009) 174522]. Here we report high-precision measurements in MgB2 stripline resonators that show an increase of the penetration depth as the temperature is decreased below 5 K. This increase is consistent with the ℓ = 6 symmetry of the π energy gap that we have proposed. We interpret the increase as a manifestation of Andreev surface-attached states that are associated with the nodal lines of the π energy gap. Penetration-depth calculations are in good agreement with our data. To reconcile the present interpretation with existing literature, we review other penetration-depth data, magnetic-impurity and tunneling experiments, and data on the paramagnetic Meissner effect. We conclude that these data do not rule out the interpretation of our experimental data based on a nodal π energy gap.

  15. Carbon doping of precursor boron powder for control of normal resistance of MgB2 bulks for specific use in fault current limiter applications

    NASA Astrophysics Data System (ADS)

    Archer, J.; Jarvis, A. L. L.

    2014-05-01

    Magnesium Diboride (MgB2) bulk superconductor has been manufactured in order to study the enhancement of the normal resistivity for application to superconducting fault current limiters (SFCLs). SFCLs have proven to be a viable means for limiting surge currents by dissipating fault energy as the superconductor quenches. As the current limiting behaviour is determined by the normal resistivity (ρn), research has been conducted to evaluate an effective means to increase ρn for bulk superconducting MgB2, which is intrinsically much lower than for high temperature superconductors. Intragranular carbon doping has been confirmed as a means to increase ρn, and was implemented by chemical vapour deposition (CVD) on the boron precursor powder by ethylene gas at 600 °C for durations up to 6 hours in a tubular furnace apparatus. In situ manufacturing of MgB2 bulk was performed using the reactive liquid magnesium infiltration technique. Overall, carbon doping provided a factor of 11.00 increase in the residual resistivity, ρ0, which provides the initial limiting action to fault currents, for an accompanying decrease in the critical temperature, Tc, of 2 K.

  16. Improvement of the Critical Current of in Situ Cu-Sheathed MgB2 Wires by Copper Additions and Toluene Doping

    NASA Astrophysics Data System (ADS)

    Woźniak, M.; Hopkins, S. C.; Gajda, D.; Glowacki, B. A.

    Recent advances in the design of Cu-sheathed in situ MgB2 wires have shown promising results and made this kind of wire more competitive in terms of price to performance ratio in comparison to conductors with diffusion barriers made with metals inert to reaction with Mg. Recently reported additions of copper powder to the core of in situ Cu-sheathed MgB2 wires have shown that these additions can accelerate the formation of MgB2, increasing its volume fraction and greatly decreasing the amount of Mg-Cu intermetallic phases present in the core after heat treatment. In this paper additional experimental results for toluene doping are reported and compared to wires with and without copper additions. All three wires were investigated by SEM, XRD and transport critical current measurements Jc(B) at 4.2 K. The results showed that copper additions were effective in the whole measured field region, whereas toluene doping improved performance in the high field region.

  17. Effects of He^+ ion irradiation on the two-band superconductivity of MgB2 by point-contact spectroscopy

    NASA Astrophysics Data System (ADS)

    Park, Wan Kyu; Moeckly, Brian; Rowell, John

    2005-03-01

    An unresolved issue in MgB2 is whether the two superconducting gaps can be merged into a single gap as Tc is reduced. It has been predicted that several effects, including enhanced interband scattering or a smeared density of states, can reduce Tc. Our transport measurements on MgB2 thin films un-irradiated and irradiated with 1 MeV He^+ ions (doses: 1x10^15 -- 1x10^17 ions/cm^2) show that ρ40K increases and that Tc decreases roughly linearly with dose and ρ40K, similar to other work [R. Gandikota et al., cont-mat/0410655]. Point-contact spectroscopy on MgB2 irradiated with 1x10^16 ions/cm^2, with Tc reduced to 36.3 K from 39.3 K, shows that 2δ/kBTc increases from 1.43 to 1.76 (decreases from 4.13 to 3.90) for the smaller (larger) gap, so the gaps tend to merge. Detailed measurements and analyses based on the existing models [e.g., J. M. Rowell, SST 16 R17 (2003), and J. Kortus et al., cond-mat/0411667] will be presented. We acknowledge Pavel Krasnochtchekov and Robert Averback and support by the DoE DEFG02-91ER45439, through the FSMRL and the Center for Microanalysis of Materials.

  18. Effect of strain along C-axis NbS{sub 2}

    SciTech Connect

    Singh, Tapender Kumar, Jagdish Sastri, O. S. K. S.

    2015-05-15

    We have studied electronic properties of double layered hexagonal structure of the Niobium Di-Sulphide (2H-NbS{sub 2}) superconductor for various strains introduced along the c-axis using ab-initio calculations. The DFT calculations based on Full Potential Linearized Augmented Plane Wave (FPLAPW) method are performed using the ELK code. The total energy curve (E vs a), Density of States (DOS) and the Band structure calculations obtained in this work are matching with the earlier reports. The Pressure-Volume (P-V) diagram for 2H-NbS{sub 2} was obtained using the Equation of State(EOS) calculations, which provides the relationship between the pressure and strain applied along the c-axis. The band structures for various strains ranging from 0 percent to 10 percent along c-axis in steps of 2 percent are obtained. We note that there are increasing number of bands crossing over the Fermi energy level with increase in strain. Thus, we conclude that with increasing strain along c-axis, number of conduction bands crossing the E{sub F} increases, which gives rise to more conduction states and hence higher conductivity.

  19. Transport properties along c-axis of DyNi2B2C

    NASA Astrophysics Data System (ADS)

    Lee, W. C.

    2014-12-01

    We have measured the resistivity along c-axis ρc(H, T) of DyNi2B2C with the applied magnetic field H perpendicular to c-axis for 0 kG < H < 4 kG and temperature range 2 K < T < 300 K. From these, the superconducting upper critical field HC2(T) curve of DyNi2B2C for the c-axis was constructed and our HC2(T) curve from ρc(H, T) measurement has been compared with that from previous known ρab(H, T) result. With additional magnetization isotherms M(H, T) for H ⊥ c and H ∥ c-axis, the anisotropy in HC2(T) curves of the magnetic structure DyNi2N2C, which has the superconducting transition temperature TC is lower than the Néel temperatures TN, might be originated from the additional anisotropic magnetic Dy3+ sublattice.

  20. In-plane and c-axis optical spectroscopy study on 122 Fe-pnictides

    NASA Astrophysics Data System (ADS)

    Wang, Nan Lin

    2011-03-01

    I present the in-plane and the c-axis optical spectroscopy investigations on 122 Fe-pnictides. For the parent compound BaFe 2 As 2 , the in-plane measurement revealed two different energy gaps in the SDW state, whereas for the c-axis polarized measurement only the energy gap at smaller energy scale could be clearly observed. We suggest different driving mechanisms for the formation of the two energy gaps. The large energy gap is caused by the nesting between disconnected 2D cylinder-like electron and hole Fermi surfaces. It is the main driving force for the SDW instability. The small energy gap is the one formed on the 3D Fermi surface due to the presence of reduced magnetic Brillouin zone which crosses the 3D Fermi surface. It is the consequence of the establishment of the magnetic order. For the doped superconducting 122 samples, the in-plane optical measurement revealed a formation of full superconducting energy gap, whereas the c-axis optical measurement indicated a large residual quasiparticle population down to very low temperature. Those quasiparticles contribute specifically to the c-axis transport. We suggest that there exist horizontal nodes in the superconducting gap in regions of the 3D Fermi surface that contribute dominantly to the c-axis optical conductivity. Work done with Z. G. Chen, W. Z. Hu, B. Cheng, G. Li, J. Dong, T. Dong, R. H. Yuan, P. Zheng, G. F. Chen, J. L. Luo, Z. Fang, X. Dai, C. L. Zhang and P. Dai.

  1. 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.

  2. Quartz c-axis evidence for deformation characteristics in the Sanandaj-Sirjan metamorphic belt, Iran

    NASA Astrophysics Data System (ADS)

    Samani, Babak

    2013-05-01

    Quartz c-axis fabric, finite strain, and kinematic vorticity analyses were carried out in well-exposed quartz mylonites to investigate the heterogeneous nature of ductile deformation within the Eghlid deformed area in the High Pressure-Low Temperature (HP-LT) Sanandaj-Sirjan metamorphic belt (Zagros Mountains, Iran). This belt belongs to a sequence of tectonometamorphic complexes with low- to high-grade metamorphic rocks affected by a polyphase deformation history. Asymmetric quartz c-axis fabrics (type I) confirm a localized top-to-the-southeast sense of shear. Quantitative finite strain analysis in the XZ, XY and YZ principal planes of the finite strain ellipsoid demonstrate that the strain ratio increases towards the thrust planes of the Zagros Thrust System. Kinematic vorticity analysis of deformed quartz grains showed sequential variation in the kinematic vorticity number from ˜0.5 to ˜0.8 between the thrust sheets. Such vorticity numbers show that both simple and pure shear components contribute to the deformation. Our results show that simple shear dominated deformation near the thrust faults, and pure shear dominated deformation far from them. Quartz c-axis opening angles suggest deformation temperatures range between 450° ± 50 °C and 600° ± 50 °C, which yield greenschist to amphibolite facies conditions during ductile deformation.

  3. C-axis Transport Properties of DyNi2 B2 C

    NASA Astrophysics Data System (ADS)

    Lee, W. C.

    2014-03-01

    The resistivity along c-axis ρc(H,T) of DyNi2B2C have been measured with the applied magnetic field H perpendicular and parallel to c-axis, 0 kG c-axis were constructed for each magnetic fields and our HC2(T) curves from ρc(H,T) measurement have been compared with those from previous known ρab(H,T) results. Since RNi2N2C (R = non magnetic rare earth element) has isotropic electronic structure and properties, the anisotropy in HC2(T) curves of the magnetic DyNi2N2C, which has the superconducting transition temperature, TC, is lower than the Néel temperatures, TN, is thought to be originated from the anisotropic magnetic Dy +3 sublattice.

  4. Microstructure dependence of the c-axis critical current density in second-generation YBCO tapes.

    SciTech Connect

    Jia, Y.; Welp, U.; Crabtree, G. W.; Kwok, W. K.; Malozemoff, A. P.; Rupich, M. W.; Fleshler, S.; Clem, J. R.

    2011-10-01

    C-axis current flow in high temperature superconductor (HTS) tape-shaped wires arises in configurations where the local wire axis is not perpendicular to the local magnetic field, such as in power cables with helically wound HTS tapes. The c-axis critical current density J{sub c}{sup c} has been recently found to be orders of magnitude lower than the ab-plane critical current density J{sub c}{sup ab}. Here we report on J{sub c}{sup c} (77 K, sf) values of various YBa{sub 2}Cu{sub 3}O{sub 7}-based (YBCO) tapes with different microstructures. Our results show that the value of J{sub c}{sup c} (77 K, sf) decreases significantly with increasing concentration of ab-plane stacking faults in YBCO thin films and that the critical current anisotropy {gamma} = J{sub c}{sup ab}/J{sub c}{sup c} can reach values as high as 2070, implying that in the highest-anisotropy tape, {approx}20% of the tape width carries c-axis current in a helically wound power cable.

  5. Microstructure dependence of the c-axis critical current density in second generation YBCO tapes

    SciTech Connect

    Jia, Y. Welp, U. Crabtree, G.W.; Kwok, W.K.; Malozemoff, A.P.; Rupich, M.W.; Fleshler, S.; Clem, J.R.

    2011-10-31

    C-axis current flow in high temperature superconductor (HTS) tape-shaped wires arises in configurations where the local wire axis is not perpendicular to the local magnetic field, such as in power cables with helically wound HTS tapes. The c-axis critical current density J{sub c}{sup c} has been recently found to be orders of magnitude lower than the ab-plane critical current density J{sub c}{sup ab}. Here we report on J{sub c}{sup c} (77 K, sf) values of various YBa{sub 2}Cu{sub 3}O{sub 7}-based (YBCO) tapes with different microstructures. Our results show that the value of J{sub c}{sup c} (77 K, sf) decreases significantly with increasing concentration of ab-plane stacking faults in YBCO thin films and that the critical current anisotropy {gamma} = J{sub c}{sup ab}/J{sub c}{sup c} can reach values as high as 2070, implying that in the highest-anisotropy tape, {approx}20% of the tape width carries c-axis current in a helically wound power cable.

  6. C-axis critical current density of second-generation YBCO tapes.

    SciTech Connect

    Jia, Y.; Hua, J.; Crabtree, G. W.; Kwok, W. K.; Welp, U.; Malozemoff, A. P.; Rupich, M.; Fleshler, S.; Materials Science Division; American Superconductor Corp.

    2010-10-01

    We report on measurements of the temperature and field dependence of the c-axis critical current density (J{sub c}{sup c}) obtained on mesa structures that were patterned into the YBCO layer of second-generation HTS tapes. We find the J{sub c}{sup c}-values of {approx}4 kA cm{sup -2} at 77 K and self-field, corresponding to an unexpectedly high anisotropy in the critical current density J{sub c}{sup ab}/J{sub c}{sup c} of 500-600. C-axis current flow is expected to arise in applications such as the helically wound wires in HTS cables. A simple estimate is given of the fraction of tape width for such a c-axis flow; while in our samples this fraction is approximately 5% for a typical geometry, the fraction will grow linearly with increasing current density anisotropy and could affect the current-carrying ability of the tape.

  7. C-Axis critical current density of second-generation YBCO tapes

    SciTech Connect

    Jia, Y.; Hua, J.; Crabtree, G.W.; Kwok, W.K.; Welp, U.; Malozemoff, A.P.; Rupich, M.; Fleshler, S.

    2010-10-21

    We report on measurements of the temperature and field dependence of the c-axis critical current density (Jcc) obtained on mesa structures that were patterned into the YBCO layer of second-generation HTS tapes. We find the Jcc—values of ~ 4 kA cm-2 at 77 K and self-field, corresponding to an unexpectedly high anisotropy in the critical current density Jcab/Jcc of 500–600. C-axis current flow is expected to arise in applications such as the helically wound wires in HTS cables. A simple estimate is given of the fraction of tape width for such a c-axis flow; while in our samples this fraction is approximately 5% for a typical geometry, the fraction will grow linearly with increasing current density anisotropy and could affect the current-carrying ability of the tape.

  8. Substrate Heating Effect on c-Axis Texture and Piezoelectric Properties of AlN Thin Films Deposited by Unbalanced Magnetron Sputtering

    NASA Astrophysics Data System (ADS)

    Hasheminiasari, Masood; Lin, Jianliang

    2016-03-01

    Aluminum nitride (AlN) thin films with highly preferred (002) orientations have been reactively deposited by a pulsed-closed field unbalanced magnetron sputtering system using TiN/Ti as the seed/adhesion layer with various substrate temperatures. The texture, orientation and piezoelectric properties of AlN films were characterized by means of x-ray diffraction, rocking curves and laser interferometry. A Michelson laser interferometer was designed and built to obtain the converse piezoelectric response of the deposited AlN thin films. It was found that a slight substrate temperature increase would significantly affect the (002) orientation and the piezoelectric coefficient of AlN thin films compared to the coating obtained with no intentional substrate heating, while higher temperature applications on substrate deteriorated the c-axis texture of the coatings without significant improvement in the piezoelectric response of AlN films.

  9. Substrate Heating Effect on c-Axis Texture and Piezoelectric Properties of AlN Thin Films Deposited by Unbalanced Magnetron Sputtering

    NASA Astrophysics Data System (ADS)

    Hasheminiasari, Masood; Lin, Jianliang

    2016-06-01

    Aluminum nitride (AlN) thin films with highly preferred (002) orientations have been reactively deposited by a pulsed-closed field unbalanced magnetron sputtering system using TiN/Ti as the seed/adhesion layer with various substrate temperatures. The texture, orientation and piezoelectric properties of AlN films were characterized by means of x-ray diffraction, rocking curves and laser interferometry. A Michelson laser interferometer was designed and built to obtain the converse piezoelectric response of the deposited AlN thin films. It was found that a slight substrate temperature increase would significantly affect the (002) orientation and the piezoelectric coefficient of AlN thin films compared to the coating obtained with no intentional substrate heating, while higher temperature applications on substrate deteriorated the c-axis texture of the coatings without significant improvement in the piezoelectric response of AlN films.

  10. 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.

  11. Possibility of c-axis voltage steps for a cuprate superconductor in a resonant cavity

    NASA Astrophysics Data System (ADS)

    Tornes, I.; Stroud, D.

    2003-08-01

    Very anisotropic cuprate superconductors, such as BiSr2Ca2CuO8+x, when driven by currents parallel to the c axis, behave like stacks of underdamped Josephson junctions. Here, we analyze the possibility that such a stack can be caused to phase lock, to exhibit self-induced resonant voltage steps (SIRS’s), and hence to radiate coherently when placed in a suitable resonant electromagnetic cavity. We analyze this possibility using equations of motion developed to describe such SIRS’s in stacks of artificial Josephson junctions. We conclude that such steps might be observable with a suitably chosen cavity and resonant frequency.

  12. First-principles prediction of MgB2-like NaBC: A more promising high-temperature superconducting material than LiBC

    NASA Astrophysics Data System (ADS)

    Miao, Rende; Huang, Guiqin; Yang, Jun

    2016-05-01

    Crystal structure, lattice dynamics, and superconducting properties for sodium borocarbides NaB1+xC1-x are investigated with first-principles calculations. Based on crystal structure analysis by particle swarm optimization methodology, NaBC is predicted to crystallize in the layered P63 / mmc crystal structure as LiBC. However, it is different from LiBC, in that Na atoms are effectively ionized, with no longitudinal covalence exist between Na and B-C layers, just as in the case of MgB2. Therefore, Na1-xBC is more similar to MgB2 than Li1-xBC as a potential high-temperature superconductor. Further more, we suggest that the slight hole doping of NaBC through partial substitution of C by B atoms can also produce cause superconductivity. The phonon spectra for NaBC and NaB1.1C0.9 are obtained within the virtual-crystal approximation treatment. There is a remarkable softening of the in-plane B-C bond-stretching modes for NaB1.1C0.9 in certain regions of the Brillouin zone, while other phonon bands show no obvious softening behavior. This conspicuous softening of the in-plane B-C bond-stretching modes indicates a strong electron-phonon coupling for them. The obtained total electron-phonon coupling strength λ for NaB1.1C0.9 is 0.73, and superconducting transition temperature TC is predicted to be 35 K (μ* = 0.1). This indicates that NaB1+xC1-x is potentially high-temperature superconducting and hole doping of NaBC could produce high-temperature superconductivity. In addition, we conjecture that, to design a MgB2-like high TC superconducting material, the longitudinal covalent bonds between the metal cations and graphite-like layers need be excluded.

  13. Microstructures and critical currents of single- and multi-filamentary MgB2 superconducting wires fabricated by an internal Mg diffusion process

    NASA Astrophysics Data System (ADS)

    Togano, K.; Hur, J.; Matsumoto, A.; Kumakura, H.

    2010-08-01

    A single-filament wire and 7- and 19-filament wires of MgB2 superconductor were fabricated by an internal Mg diffusion (IMD) process. The wire is sheathed by a Cu-Ni alloy and each filament is composed of an outermost Ta, an intermediate B + SiC powder layer and an Mg core at the center. Despite the large total area reduction, the cross sections of all wires show uniform deformation of the composite. During the subsequent heat treatment, a reacted layer with a dense composite structure composed of a MgB2 matrix and fine particles is formed by Mg liquid infiltration and the reaction with the B + SiC powder. For all wires, the highest transport Ic was obtained at furnace temperatures of 640-645 °C, which is just below the melting point of Mg. In the single-filament wire, a fairly large amount of B + SiC remains outside the reacted layer, while the residual B + SiC is much reduced in the multi-filamentary wires, resulting in higher Ic, than that of the single-filament wire. However, the Jc, estimated for the reacted layer is not so different between the wires. When the heat treatment temperature exceeds 650 °C, the Ic value rapidly decreases, although the volume fraction of the MgB2 detected continues to increase. It is observed that the thickness of the reacted layer formed at higher temperatures becomes significantly inhomogeneous, which is thought to be responsible for the deterioration of transport Ic values. The highest Jc(layer) estimated for the reacted layer is as high as 9.9 × 104 A cm - 2 at 4.2 K and 10 T and 3.3 × 105 A cm - 2 at 20 K and 1 T achieved for the multi-filamentary wires. The Jc(core) estimated for the area including the hole and remnant B is about 1/3 of the Jc(layer). From good workability of the composite and excellent Jc values, it is expected that the IMD process can compete in terms of practical wire fabrication with the conventional powder-in-tube (PIT) process.

  14. Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application.

    PubMed

    Chao, Chung-Hua; Wei, Da-Hua

    2015-01-01

    In this study, zinc oxide (ZnO) thin films with high c-axis (0002) preferential orientation have been successfully and effectively synthesized onto silicon (Si) substrates via different synthesized temperatures by using plasma enhanced chemical vapor deposition (PECVD) system. The effects of different synthesized temperatures on the crystal structure, surface morphologies and optical properties have been investigated. The X-ray diffraction (XRD) patterns indicated that the intensity of (0002) diffraction peak became stronger with increasing synthesized temperature until 400 (o)C. The diffraction intensity of (0002) peak gradually became weaker accompanying with appearance of (10-10) diffraction peak as the synthesized temperature up to excess of 400 (o)C. The RT photoluminescence (PL) spectra exhibited a strong near-band-edge (NBE) emission observed at around 375 nm and a negligible deep-level (DL) emission located at around 575 nm under high c-axis ZnO thin films. Field emission scanning electron microscopy (FE-SEM) images revealed the homogeneous surface and with small grain size distribution. The ZnO thin films have also been synthesized onto glass substrates under the same parameters for measuring the transmittance. For the purpose of ultraviolet (UV) photodetector application, the interdigitated platinum (Pt) thin film (thickness ~100 nm) fabricated via conventional optical lithography process and radio frequency (RF) magnetron sputtering. In order to reach Ohmic contact, the device was annealed in argon circumstances at 450 (o)C by rapid thermal annealing (RTA) system for 10 min. After the systematic measurements, the current-voltage (I-V) curve of photo and dark current and time-dependent photocurrent response results exhibited a good responsivity and reliability, indicating that the high c-axis ZnO thin film is a suitable sensing layer for UV photodetector application. PMID:26484561

  15. 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.

  16. 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.

  17. 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

    2013-03-01

    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

  18. Morphology and composition controlled growth of polar c-axis and nonpolar m-axis well-aligned ternary III-nitride nanotube arrays.

    PubMed

    Li, Huijie; Zhao, Guijuan; Kong, Susu; Han, Dongyue; Wei, Hongyuan; Wang, Lianshan; Chen, Zhen; Yang, Shaoyan

    2015-10-21

    Control over the nanostructure morphology and growth orientation is in high demand for fundamental research and technological applications. Herein we report a general strategy to fabricate polar c-axis and nonpolar m-axis well-aligned III-nitride ternary nanotube arrays with controllable morphologies and compositions. By depositing AlN on the InN nanorod array templates and thermally removing the InN templates, InAlN nanotubes can be obtained. Polar c-axis and nonpolar m-axis nanotubes were formed on the c- and r-plane sapphire substrates, respectively. The nanotubes are single crystalline and highly ordered on the substrates, as revealed by X-ray diffraction, electron microscopy, and selected area electron microscopy characterization. It was found that the In droplets on top of the InN nanorods play a critical role in controlling the morphology of the nanotubes. By keeping or removing the In droplets, the obtained nanotubes exhibited both ends open or only one end open. And by varying the AlN deposition temperature, the In composition in the nanotubes can be changed from 0 to 0.29. The nanotube synthesis method is simple and can be applied to the formation of other III-nitride ternary (InGaN, and AlGaN) or quaternary (InAlGaN) alloy nanotube arrays. PMID:26395389

  19. Bilayer splitting and c-axis coupling in CMR bilayer manganites

    SciTech Connect

    Jozwiak, Chris; Graf, Jeff; Zhou, Shuyun; Bostwick, Aaron; Rotenberg, Eli; Zheng, Hong; Mitchell, John; Lanzara, Alessandra

    2009-09-03

    By performing angle-resolved photoemission spectroscopy of the bilayer colossal magnetoresistive (CMR) manganite, La2-2xSr1+2xMn2O7, we provide the complete mapping of the Fermi-level spectral weight topology. Clear and unambiguous bilayer splitting of the in-plane 3dx2-y2 band, mapped throughout the Brillouin zone, and the full mapping of the 3d3z2-r2 band are reported. Peculiar doping and temperature dependencies of these bands imply that as transition from the ferromagnetic metallic phase approaches, either as a function of doping or temperature, coherence along the c-axis between planes within the bilayer is lost, resulting in reduced interplane coupling. These results suggest that interplane coupling plays a large role in the CMR transition.

  20. C-axis electrical resistivity of PrO1-aFaBiS2 single crystals

    NASA Astrophysics Data System (ADS)

    Nagao, Masanori; Miura, Akira; Watauchi, Satoshi; Takano, Yoshihiko; Tanaka, Isao

    2015-08-01

    The high anisotropy in RO1-aFaBiS2 (R denotes a rare-earth element) superconductors demonstrates their potential use as intrinsic Josephson junctions, considering the weak coupling among BiS2-PrO(F)-BiS2 (superconducting-normal-superconducting) layers along the c-axis. We grew PrO1-aFaBiS2 single crystals using CsCl/KCl flux. The superconducting anisotropies of the grown single crystals were estimated to be approximately 40-50 from the effective mass model. The c-axis transport properties were characterized using single-crystal s-shaped intrinsic Josephson junctions with a focused ion beam. Along the c-axis, the crystals showed zero resistivity at 2.7 K and a critical current density of 1.33 × 103 A/cm2 at 2.0 K. The current-voltage curve along the c-axis displayed hysteresis. The c-axis transport measurements under a magnetic field parallel to the ab-plane revealed a “lock-in” state due to the Josephson vortex flow, indicating that BiS2 superconductors are promising candidates for intrinsic Josephson junctions.

  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. Origin of the c-Axis Tilt Occurring During the Lateral Epitaxial Overgrowth of GaN

    NASA Astrophysics Data System (ADS)

    Kuan, T. S.; Inoki, C. K.; Zhang, R.; Gu, S.; Kuech, T. F.

    2001-03-01

    A large angle c-axis tilt has often been observed in GaN layers grown by lateral epitaxial overgrowth (LEO) through narrow windows defined on a seed layer. The c-axis tilt generates vertical tilt boundaries at the coalescence of growth facets. To investigate the defect mechanisms responsible for the onset of c-axis tilt, a series of GaN LEO samples was grown using the hydride vapor phase epitaxy (HVPE) technique and examined by transmission electron microscopy (TEM). Cross sectional TEM images indicate that as LEO proceeds from triangular-shaped ridges originally grown over the windows, all edge-type threading dislocations propagated from the seed layer bend into screw type and glide on the c plane. Plan-view TEM observations reveal further that to relax the twist/shear strain in the LEO regions, these screw dislocations collectively make another 90^o bend again, forming arrays of edge dislocations parallel to the mask edge. The number of dislocations in the arrays can account for the amount of crystal tilt observed. The c-axis tilt is thus a stress-driven phenomenon dictated by the growth window geometry, and is much less influenced by the growth parameters.

  3. Origin of the c-axis ultraincompressibility of Mo2GaC above about 15 GPa from first principles

    NASA Astrophysics Data System (ADS)

    Qing-He, Gao; Zhi-Jun, Xu; Ling, Tang; Jin, Li; An, Du; Yun-Dong, Guo; Ze-Jin, Yang

    2016-01-01

    The mechanical properties and structural evolution of Mo2GaC are calculated by first-principles under pressure. Our results unexpectedly found that the c axis is always stiffer than a axis within 0-100 GPa. An ultraincompressibility of c axis within 15-60 GPa is observed, with a contraction of about 0.2 Å, slightly larger than that of a axis (0.14 Å). The abnormal expansion of c axis and the fast decrease in a axis above about 15 GPa and 70 GPa failed to induce the structural instability, whereas such behavior caused the elastic softening in many mechanical quantities. The shrinkage anomaly of c axis is closely reflected by the internal coordinate (u) shift of Mo atom as it shows three different slopes within 0-15 GPa, 20-60 GPa, and 70-100 GPa, respectively. The longest Mo-Mo bond is responsible for the unusual shrinkage of c-axis under pressure as they experience nearly identical pressure dependences, whereas the a axis presents certain response with the variation of C-Mo bond particularly at 70 GPa. The electronic properties are investigated, including the energy band and density of states, and so on. At G point of K-M line, the energy decreases at 10 GPa first and increases at 30 GPa subsequently, the critical point is at about 15 GPa, with respective values of -0.17 of 0 GPa, -0.18 of 10 GPa, -0.16 of 15 GPa, and -0.13 of 30 GPa, respectively. This alternative energy change of G point, which is the symmetry center of the rhombic parallelogram of Ga atoms and the midpoint of the two bonded Mo atoms, convincingly reveal the origin of the anomalous ultraincompressibility of c axis as the Mo-Mo bond length shrinkage has to overcome the increasing energy barrier height. The Mo-Mo bond population and the electronegativity investigations of the Mo atom further reveal the most likely origin of the ultraincompressibility of c axis. This interesting result expects further experimental confirmation as this is the first nanolaminate ceramics compound presenting quite

  4. Study of the potential of three different MgB2 tapes for application in cylindrical coils operating at 20 K

    NASA Astrophysics Data System (ADS)

    Pitel, J.; Kováč, P.; Tropeano, M.; Grasso, G.

    2015-05-01

    The goal of this theoretical study is to illustrate the potential of three different MgB2 tapes, developed by Columbus Superconductors, for application in cylindrical coils. First, the distribution of critical currents and electric fields of individual turns is compared when the winding of the model coil is made with tapes having different Ic(B) and anisotropy values. Second, the influence of the winding geometry on basic parameters of cylindrical coils which consist of a set of pancake coils, such as critical current Icmin, central magnetic field B0 and stored energy E, is analysed. The winding geometry of the coils, i.e. the outer winding radius and the coil length, with the same inner winding radius, was changed from a disc shape to a long thin solenoid in such a way that the overall tape length was held constant, and considered as a parameter. Finally, the winding cross-section of the coil is optimized with respect to the constant tape length in order to reach the maximum central field. The results of calculations show that for a given overall tape length and inner winding radius there exists only one winding geometry which generates the maximum central field. The overall tape length, as a parameter, is changed in a broad range from 500 m to 10 km. All calculations were performed using the experimental data measured at 20 K while the effect of the anisotropy in the Ic(B) characteristic of the short samples is taken into account.

  5. Nano Sized Powder Additives of SiC and Diamond to MgB2 as Artificially Inductor of Pinning Force for the Dense Samples Obtained by High Pressure Technologies

    NASA Astrophysics Data System (ADS)

    Morawski, A.; Pachla, W.; Kuzmenko, D.; Łada, T.; Zaleski, A.; Eibl, O.; Haessler, W.; Kovac, P.

    2006-09-01

    The nano-powder additives of SiC (11nm) and diamond (6 nm) were mixed with Mg and amorphous B powders in the production route of MgB2 bulk and wires samples. Special attention was paid to the precursor powders with the respect to chemical purity, grain morphology and secondary phases. Commercially available MgB2 powders (ex-situ technology) and also mixtures of MgH2 and amorphous B powders (in-situ technology) were applied as the starting precursors. Electron microscopy was used extensively for the characterization of these powders applying both SEM and TEM analysis. Superconducting bulks and wires samples have been produced, by hot pressing, hot isostatic pressing and hydrostatic extrusion processes. High grain refinement and density in the final wire samples have been achieved by the severe plastic deformation (reduction over 99.98%) with the use of the cumulative (multi-step) hydrostatic extrusion. Superconducting properties of these samples were measured, with particular attention paid to the Jc(B) characteristics. Critical currents at lower and higher magnetic fields depended sensitively on the amount of the additives and grain refinement. TEM imaging and electron spectroscopic imaging were used to evaluate the size and distribution of the both of additives within the microstructure. The strain field of the additives resulted from the misfit in thermal expansion coefficient between the additives and the MgB2 matrix was imaged in bright and dark field TEM and is particularly important for the flux-pinning properties of these materials. Influence of such synthesis parameters as pressure, temperature and time on the superconducting properties and the morphology of the products were examined and obtained results were compared. This allowed to choose the optimal conditions for the improvement of the bulk MgB2 characteristics of the wire samples.

  6. A new empirical calibration of the quartz c-axis fabric opening-angle deformation thermometer

    NASA Astrophysics Data System (ADS)

    Faleiros, F. M.; Moraes, R.; Pavan, M.; Campanha, G. A. C.

    2016-03-01

    The opening-angle of quartz c-axis fabrics (OA) is strongly temperature dependent and has proven to be a powerful deformation thermometer for natural metamorphic rocks. Previous considerations of empirical data have identified a linear correlation between OA and temperature between 250 and 650 °C, and no correlation above 650 °C. However, possible effects of pressure have not been investigated. We expanded the data set of OA versus temperature, including data from rocks deformed over 300-1050 °C and 2.5-15 kbar. Disregarding possible effects of pressure, the OA-temperature relationship can be described by two linear correlations for the intervals ~ 250-650 °C and ~ 650-1050 °C: The change on the curve slope of the OA-temperature relationship correlates approximately to the low- to high-quartz transition and to changes in the dynamic recrystallization mechanism from subgrain rotation to grain boundary migration. The available data suggest that pressure has a secondary effect accompanying the major temperature dependence of OA, which is particularly important for temperatures above 650 °C, where the correlation between OA and temperature is less pronounced. For fixed pressures, the OA has logarithmic relationships with temperature over the range 250-1050 °C. The following thermometer equation is formulated from a multiple regression: An uncertainty of ± 50 °C is inherited from the petrological temperature estimates of the natural samples. The data suggest the gradual increasing importance of prism [c] slip relative to < a > slip in quartz with rising temperature. Under conditions of 'average' geological strain rate and water weakening, prism [c] slip dominates for deformation above ~ 700 °C.

  7. High mobility, dual layer, c-axis aligned crystalline/amorphous IGZO thin film transistor

    NASA Astrophysics Data System (ADS)

    Chung, Chen-Yang; Zhu, Bin; Greene, Raymond G.; Thompson, Michael O.; Ast, Dieter G.

    2015-11-01

    We demonstrate a dual layer IGZO thin film transistor (TFT) consisting of a 310 °C deposited c-axis aligned crystal (CAAC) 20 nm thick channel layer capped by a second, 30 nm thick, 260 °C deposited amorphous IGZO layer. The TFT exhibits a saturation field-effect mobility of ˜20 cm2/V s, exceeding the mobility of 50 nm thick single layer reference TFTs fabricated with either material. The deposition temperature of the second layer influences the mobility of the underlying transport layer. When the cap layer is deposited at room temperature (RT), the mobility in the 310 °C deposited CAAC layer is initially low (6.7 cm2/V s), but rises continuously with time over 58 days to 20.5 cm2/V s, i.e., to the same value as when the second layer is deposited at 260 °C. This observation indicates that the two layers equilibrate at RT with a time constant on the order of 5 × 106 s. An analysis based on diffusive transport indicates that the room temperature diffusivity must be of the order of 1 × 10-18 cm2 s-1 with an activation enthalpy EA < 0.2 eV for the mobility limiting species. The findings are consistent with a hypothesis that the amorphous layer deposited on top of the CAAC has a higher solubility for impurities and/or structural defects than the underlying nanocrystalline transport layer, and that the equilibration of the mobility limiting species is rate limited by hydrogen diffusion, whose known diffusivity fits these estimates.

  8. Morphology and composition controlled growth of polar c-axis and nonpolar m-axis well-aligned ternary III-nitride nanotube arrays

    NASA Astrophysics Data System (ADS)

    Li, Huijie; Zhao, Guijuan; Kong, Susu; Han, Dongyue; Wei, Hongyuan; Wang, Lianshan; Chen, Zhen; Yang, Shaoyan

    2015-10-01

    Control over the nanostructure morphology and growth orientation is in high demand for fundamental research and technological applications. Herein we report a general strategy to fabricate polar c-axis and nonpolar m-axis well-aligned III-nitride ternary nanotube arrays with controllable morphologies and compositions. By depositing AlN on the InN nanorod array templates and thermally removing the InN templates, InAlN nanotubes can be obtained. Polar c-axis and nonpolar m-axis nanotubes were formed on the c- and r-plane sapphire substrates, respectively. The nanotubes are single crystalline and highly ordered on the substrates, as revealed by X-ray diffraction, electron microscopy, and selected area electron microscopy characterization. It was found that the In droplets on top of the InN nanorods play a critical role in controlling the morphology of the nanotubes. By keeping or removing the In droplets, the obtained nanotubes exhibited both ends open or only one end open. And by varying the AlN deposition temperature, the In composition in the nanotubes can be changed from 0 to 0.29. The nanotube synthesis method is simple and can be applied to the formation of other III-nitride ternary (InGaN, and AlGaN) or quaternary (InAlGaN) alloy nanotube arrays.Control over the nanostructure morphology and growth orientation is in high demand for fundamental research and technological applications. Herein we report a general strategy to fabricate polar c-axis and nonpolar m-axis well-aligned III-nitride ternary nanotube arrays with controllable morphologies and compositions. By depositing AlN on the InN nanorod array templates and thermally removing the InN templates, InAlN nanotubes can be obtained. Polar c-axis and nonpolar m-axis nanotubes were formed on the c- and r-plane sapphire substrates, respectively. The nanotubes are single crystalline and highly ordered on the substrates, as revealed by X-ray diffraction, electron microscopy, and selected area electron microscopy

  9. Trapped field of 1.1 T without flux jumps in an MgB2 bulk during pulsed field magnetization using a split coil with a soft iron yoke

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    MgB2 superconducting bulks have promising potential as trapped field magnets. We have achieved a trapped field of B z = 1.1 T on a high-J c MgB2 bulk at 13 K without flux jumps by pulsed field magnetization (PFM) using a split-type coil with a soft iron yoke, which is a record-high trapped field by PFM for bulk MgB2 to date. The flux jumps, which frequently took place using a solenoid-type coil during PFM, were avoided by using the split-type coil, and the B z value was enhanced by the insertion of soft iron yoke. The flux dynamics and heat generation/propagation were analyzed during PFM using a numerical simulation, in which the magnetic flux intruded and attenuated slowly in the bulk and tended to align along the axial direction due to the presence of soft iron yoke. The advantages of the split-type coil and the simultaneous use of a soft iron yoke are discussed.

  10. Variation in the c-axis conductivity of multi-layer graphene due to H2 exposure.

    PubMed

    Kim, Jaekyung; Kwak, Cheol Hwan; Jung, Woochan; Huh, Yun Suk; Kim, Byung Hoon

    2016-06-21

    The variation of the c-axis conductivity of a multilayer graphene (MLG) as a function of H2 pressure from vacuum to 20 bar has been investigated. MLG was connected to the electrodes vertically using a wet transfer process. After exposure to H2 gas pressure up to 20 bar, the chemisorption of dissociated atomic hydrogen on MLG affects its electrical and structural properties. The formation of C-H bonds causes a decoupling of graphene layers, and then interferes with charge transfer through the out of plane. As a result, the c-axis conductivity decreases. Furthermore, the electron doping effect and the decoupling of the layers were confirmed using Raman spectroscopy. Hydrogenated carbons induce a defect structure of MLG which results in the expansion of layers. We observed a 43.54% increase in the thickness of the MLG after H2 exposure using atomic force microscopy. PMID:27241072

  11. Rapid and semi-analytical design and simulation of a toroidal magnet made with YBCO and MgB2 superconductors

    DOE PAGESBeta

    Dimitrov, I. K.; Zhang, X.; Solovyov, V. F.; Chubar, O.; Li, Qiang

    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

  12. Room temperature sputtering of inclined c-axis ZnO for shear mode solidly mounted resonators

    NASA Astrophysics Data System (ADS)

    Rughoobur, G.; DeMiguel-Ramos, M.; Mirea, T.; Clement, M.; Olivares, J.; Díaz-Durán, B.; Sangrador, J.; Miele, I.; Milne, W. I.; Iborra, E.; Flewitt, A. J.

    2016-01-01

    ZnO films with a c-axis significantly inclined away from the surface normal were grown by a remote plasma sputtering technique at room temperature. The films were used to make solidly mounted resonators (SMRs) operating in shear mode at a resonant frequency of 1.35 GHz. Control of the ZnO microstructure was achieved using a polycrystalline AlN seed layer which can be added on top of a sputtered acoustic mirror to give a complete SMR device. The ZnO was reactively sputtered in an atmosphere of argon and oxygen from a zinc target. The c-axis of the ZnO was estimated to be at an angle of ˜45° to the surface normal. SMRs were measured to have quality factors (Q) of up to 140 and effective electromechanical coupling coefficients of up to 2.2% in air. Although an inclined c-axis can be achieved with direct growth onto the acoustic mirror, it is shown that the AlN seed layer provides higher coupling coefficients and narrower inclination angular distribution. The responses of the devices in liquids of different viscosities (acetone, water, and AZ5214E photoresist) were measured. The shear mode Q decreased by 45% in acetone, 72% in water, and 92% in AZ5214E.

  13. Charge-screening role of c -axis atomic displacements in YBa2Cu3O6 +x and related superconductors

    NASA Astrophysics Data System (ADS)

    Božin, E. S.; Huq, A.; Shen, Bing; Claus, H.; Kwok, W. K.; Tranquada, J. M.

    2016-02-01

    The importance of charge reservoir layers for supplying holes to the CuO2 planes of cuprate superconductors has long been recognized. Less attention has been paid to the screening of the charge transfer by the intervening ionic layers. We address this issue in the case of YBa2Cu3O6 +x , where CuO chains supply the holes for the planes. We present a simple dielectric-screening model that gives a linear correlation between the relative displacements of ions along the c axis, determined by neutron powder diffraction, and the hole density of the planes. Applying this model to the temperature-dependent shifts of ions along the c axis, we infer a charge transfer of 5-10% of the hole density from the planes to the chains on warming from the superconducting transition to room temperature. Given the significant coupling of c -axis displacements to the average charge density, we point out the relevance of local displacements for screening charge modulations and note recent evidence for dynamic screening of in-plane quasiparticles. This line of argument leads us to a simple model for atomic displacements and charge modulation that is consistent with images from scanning-tunneling microscopy for underdoped Bi2Sr2CaCu2O8 +δ .

  14. Effects of c-axis Josephson coupling on dissipation, flux dynamics and the mechanism of high-T{sub c} superconductivity

    SciTech Connect

    Gray, K.E.; Hettinger, J.D.

    1995-12-31

    Measurements of the c-axis transport in highly anisotropic HTS materials strongly indicate that Josephson coupling is involved. This conclusion affects various properties of the HTS cuprates, including the irreversibility behavior for transport in the ab planes, the direct c-axis transport and potentially the mechanism of Cooper pairing.

  15. 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-energy loss spectroscopy (EELS), high resolution imaging, and structural modeling.

  16. Incoherent c-Axis Interplane Response of the Iron Chalcogenide FeTe0:55Se0:45 Superconductor from Infrared Spectroscopy

    SciTech Connect

    Gu, G.D.; Moon, S.J.; Homes, C.C.; Akrap, A.; Xu,, Z.J.; Wen, J.S.; Lin,, Z.W.; Li, Q.; Basov, D.N.

    2011-05-23

    We report on the interplane c-axis electronic response of FeTe{sub 0.55}Se{sub 0.45} investigated by infrared spectroscopy. We find that the normal-state c-axis electronic response of FeTe{sub 0.55}Se{sub 0.45} is incoherent and bears significant similarities to those of mildly underdoped cuprates. The c-axis optical conductivity {sigma}{sub c}({omega}) of FeTe{sub 0.55}Se{sub 0.45} does not display well-defined Drude response at all temperatures. As temperature decreases, {sigma}{sub c}({omega}) is continuously suppressed. The incoherent c-axis response is found to be related to the strong dissipation in the ab-plane transport: a pattern that holds true for various correlated materials as well as FeTe{sub 0.55}Se{sub 0.45}.

  17. Shock wave compression and release of hexagonal-close-packed metal single crystals: Inelastic deformation of c-axis magnesium

    NASA Astrophysics Data System (ADS)

    Winey, J. M.; Renganathan, P.; Gupta, Y. M.

    2015-03-01

    To understand inelastic deformation mechanisms for shocked hexagonal-close-packed (hcp) metals, shock compression and release wave profiles, previously unavailable for hcp single crystals, were measured for c-axis magnesium crystals. The results show that the elastic-inelastic loading response is strongly time-dependent. Measured release wave profiles showed distinct peaked features, which are unusual for inelastic deformation during unloading of shocked metals. Numerical simulations show that pyramidal slip provides a reasonably good description of the inelastic loading response. However, { 10 1 ¯ 2 } twinning is needed to explain the unloading response. The results and analysis presented here provide insight into the relative roles of dislocation slip and deformation twinning in the response of shocked hcp metals.

  18. The fabrication process of a high performance and pure c-axis grown GdBCO bulk superconductor with the TSMT-IG technique

    NASA Astrophysics Data System (ADS)

    Wang, Miao; Yang, Peng-tao; Yang, Wan-min; Li, Jia-wei; Hassan, Qadeer UI

    2015-10-01

    It is very important to choose a suitable seed crystal in the fabrication process of the (RE)BCO bulk superconductors by the top-seeded growth method, because a defective seed would result in the failure of the entire sample. Therefore, for optimizing the seed, a new approach is proposed in this paper for the fabrication process of Gd-Ba-Cu-O (GdBCO) bulk with promising superconducting properties. We developed the top-seeded melt texture and infiltration growth (TSMT-IG) process based on the modified top-seeded infiltration and growth (TSIG) process. In this modified infiltration growth, a mini pellet of thin melting texture (TMT) GdBCO was inserted between the NdBCO seed crystal and the solid-phase precursor pellet, resulting in the successful formation of well purified c-axis-oriented GdBCO crystals with a proper-sized TMT layer. The growth morphology, microstructure, side growth boundary, and superconducting properties of the GdBCO bulk superconductors with three different sizes of TMT pellets were studied in this paper. The results proved that the success rate for the fabrication of single-domain GdBCO bulk superconductors can be improved by the TSMT-IG process, which can also effectively inhibit the random nucleation phenomenon at some extent during the process of single-domain GdBCO bulk superconductor growth. In addition, the application of this new growth technology can help us not only to improve the growth performance of GdBCO samples with a proper size of the TMT mini pellet but also reduce the fabrication cost due to the use of only one precursor powder.

  19. Nanosecond laser switching of surface wettability and epitaxial integration of c-axis ZnO thin films with Si(111) substrates.

    PubMed

    Molaei, R; Bayati, M R; Alipour, H M; Estrich, N A; Narayan, J

    2014-01-01

    We have achieved integration of polar ZnO[0001] epitaxial thin films with Si(111) substrates where cubic yttria-stabilized zirconia (c-YSZ) was used as a template on a Si(111) substrate. Using XRD (θ-2θ and φ scans) and HRTEM techniques, the epitaxial relationship between the ZnO and the c-YSZ layers was shown to be [0001]ZnO || [111]YSZ and [21¯1¯0]ZnO || [1¯01](c-YSZ), where the [21¯1¯0] direction lies in the (0001) plane, and the [1¯01] direction lies in the (111) plane. Similar studies on the c-YSZ/Si interface revealed epitaxy as (111)YSZ || (111)Si and in-plane (110)YSZ || (110)Si. HRTEM micrographs revealed atomically sharp and crystallographically continuous interfaces. The ZnO epilayers were subsequently laser annealed by a single pulse of a nanosecond excimer KrF laser. It was shown that the hydrophobic behavior of the pristine sample became hydrophilic after laser treatment. XPS was employed to study the effect of laser treatment on surface stoichiometry of the ZnO epilayers. The results revealed the formation of oxygen vacancies, which are envisaged to control the observed hydrophilic behavior. Our AFM studies showed surface smoothing due to the coupling of the high energy laser beam with the surface. The importance of integration of c-axis ZnO with Si(111) substrates is emphasized using the paradigm of domain matching epitaxy on the c-YSZ[111] buffer platform along with their out-of-plane orientation, which leads to improvement of the performance of the solid-state devices. The observed ultrafast response and switching in photochemical characteristics provide new opportunities for application of ZnO in smart catalysts, sensors, membranes, DNA self-assembly and multifunctional devices. PMID:24275059

  20. Critical current density and pinning behaviour of mono-core MgB2 wires prepared by internal magnesium diffusion and in-situ powder-in-tube method

    NASA Astrophysics Data System (ADS)

    Brunner, Boris; Kováč, Pavol; Reissner, Michael; Hušek, Imrich; Melišek, Tibor; Pardo, Enric

    2014-10-01

    Mono-core MgB2 wires were produced by internal magnesium diffusion (IMD) and in-situ powder-in-tube (PIT) technique. Hysteresis loops and magnetic relaxations were measured to calculate critical current density, Jcm (via Bean’s critical state model) and mean effective activation energy (via Anderson’s flux creep theory). To calculate Jcm of the IMD sample, the formulae for typical cylindrical sample geometry must have been modified properly with regard to IMD hollow cylinder geometry. Results for Jcm were compared to direct transport measurements. Also studied was the irreversibility field, Birr, and upper critical field, Bc2. It was found that the dominant difference between wires is in Jc. For the IMD sample, Jc was higher and less field-dependent than Jc of the PIT sample.

  1. Superconducting energy gap and c-axis plasma frequency of (Nd,Sm)FeAsO0.82F0.18 superconductors from infrared ellipsometry.

    PubMed

    Dubroka, A; Kim, K W; Rössle, M; Malik, V K; Drew, A J; Liu, R H; Wu, G; Chen, X H; Bernhard, C

    2008-08-29

    We present far-infrared ellipsometric measurements of polycrystalline samples of the pnictide superconductor RFeAsO0.82F0.18 (R=Nd and Sm). We find evidence that the electronic properties are strongly anisotropic such that the optical spectra are dominated by the weakly conducting c-axis response similar to the cuprate high-temperature superconductors. We deduce an upper limit of the c-axis superconducting plasma frequency of omega pl,c(SC)< or =260 cm(-1) corresponding to a lower limit of the c-axis magnetic penetration depth of lambda c > or =6 microm and lambda c/lambda ab > or =30 as compared to lambda ab=185 nm from muon spin rotation [A. Drew, arXiv:0805.1042 [Phys. Rev. Lett. (to be published)

  2. Josephson Coupling along the c-Axis in Highly Anisotropic High Temperature Superconductors at High-Magnetic-Fields

    NASA Astrophysics Data System (ADS)

    Gray, K. E.; Hettinger+, J. D.; Washburn, B.; Veal, B. W.; Paulikas, A. P.; Kostic, P.

    1996-03-01

    We have extended previous measurements of oxygen deficient YBa_2Cu_3O_y^1 to magnetic fields as high as 27T and temperatures down to 4K. Measurements were made on three samples with different oxygen contents with critical temperatures ranging from 25K to 70K. The results are consistent with those previously reported and extend those measurements over a broader range in parameter space. These measurements demonstrate an unusual temperature dependent electron transmission suggesting increased c-axis coherency below T_c. The temperature dependence of the electron transmission extends to the lowest temperatures measured. ^+Present address: Rowan College of New Jersey. High-magnetic field measurements performed with the assistance of S. T. Hannahs at the NHMFL funded by the NSF. We acknowledge the support of the D.O.E., Divisions of Basic Energy Sciences-Materials Sciences under contract W-31-109-ENG-38, and the NSF-Office of Science and Technology Centers under contract DMR 91-20000. ^1J. D. Hettinger, K. E. Gray, B.W. Veal, A. P. Paulikas, P. Kostic, B. R. Washburn, W. C. Tonjes, and A. C. Flewelling, Phys. Rev. Lett. 74, 4726 (1995).

  3. Atom probe tomography evaporation behavior of C-axis GaN nanowires: Crystallographic, stoichiometric, and detection efficiency aspects

    SciTech Connect

    Diercks, David R. Gorman, Brian P.; Kirchhofer, Rita; Sanford, Norman; Bertness, Kris; Brubaker, Matt

    2013-11-14

    The field evaporation behavior of c-axis GaN nanowires was explored in two different laser-pulsed atom probe tomography (APT) instruments. Transmission electron microscopy imaging before and after atom probe tomography analysis was used to assist in reconstructing the data and assess the observed evaporation behavior. It was found that the ionic species exhibited preferential locations for evaporation related to the underlying crystal structure of the GaN and that the species which evaporated from these locations was dependent on the pulsed laser energy. Additionally, the overall stoichiometry measured by APT was significantly correlated with the energy of the laser pulses. At the lowest laser energies, the apparent composition was nitrogen-rich, while higher laser energies resulted in measurements of predominantly gallium compositions. The percent of ions detected (detection efficiency) for these specimens was found to be considerably below that shown for other materials, even for laser energies which produced the expected Ga:N ratio. The apparent stoichiometry variation and low detection efficiency appear to be a result of evaporation of Ga ions between laser pulses at the lowest laser energies and evaporation of neutral N{sub 2} species at higher laser energies. All of these behaviors are tied to the formation of nitrogen-nitrogen bonds on the tip surface, which occurred under all analysis conditions. Similar field evaporation behaviors are therefore expected for other materials where the anionic species readily form a strong diatomic bond.

  4. Inhomogeneous Nanoscale Disorder in Doped Magnesium Diboride

    NASA Astrophysics Data System (ADS)

    Voyles, Paul

    2008-03-01

    Using TEM and STEM imaging and microanalysis, we have shown that doped MgB2 has a variety of forms of disorder at a length scale of 5-50 nm. In [0001]-normal, carbon-doped HPCVD thin films, there is a thin, amorphous, C-rich layer which separates domains of lightly carbon-doped MgB2. Carbon also causes significant spread in the local in-plane orientation and c-axis direction of the MgB2. We also observed disorder in the orientation of small MgB2 domains in oxygen-doped thin films grown by MBE. Both of types of films show dramatic enhancement in the upper critical magnetic field compared to pure MgB2, with extrapolated Hc2(0 K) reaching 65-70 T for some samples. The origin of this increase may be in the observed disorder, particularly in confinement of the superconducting MgB2 domains by non-superconducting second phase layers.

  5. c-Axis zig-zag ZnO film ultrasonic transducers for designing longitudinal and shear wave resonant frequencies and modes.

    PubMed

    Yanagitani, Takahiko; Morisato, Naoki; Takayanagi, Shinji; Matsukawa, Mami; Watanabe, Yoshiaki

    2011-05-01

    A method for designing frequencies and modes in ultrasonic transducers above the very-high-frequency (VHF) range is required for ultrasonic non-destructive evaluation and acoustic mass sensors. To obtain the desired longitudinal and shear wave conversion loss characteristics in the transducer, we propose the use of a c-axis zig-zag structure consisting of multilayered c-axis 23° tilted ZnO piezoelectric films. In this structure, every layer has the same thickness, and the c-axis tilt directions in odd and even layers are symmetric with respect to the film surface normal. c-axis zig-zag crystal growth was achieved by using a SiO(2) low-temperature buffer layer. The frequency characteristics of the multilayered transducer were predicted using a transmission line model based on Mason's equivalent circuit. We experimentally demonstrated two types of transducers: those exciting longitudinal and shear waves simultaneously at the same frequency, and those exciting shear waves with suppressed longitudinal waves. PMID:21622061

  6. Normal-state conductivity of underdoped to overdoped cuprate superconductors: Pseudogap effects on the in-plane and c-axis charge transports

    NASA Astrophysics Data System (ADS)

    Dzhumanov, S.; Ganiev, O. K.; Djumanov, Sh. S.

    2014-05-01

    We have developed a theory of the unusual in-plane and c-axis charge transports in hole-doped cuprate superconductors and explain the temperature- and doping-dependent in-plane resistivity ρab, c-axis resistivity ρc and resistivity anisotropy ρc/ρab seen experimentally above Tc. We argue that the relevant current carriers in these materials above Tc are hole-like. The in-plane conductivity of underdoped to overdoped cuprates is considered as the conductivity of hole polarons and preformed Cooper pairs at their scattering by lattice vibrations in hole-rich CuO2 layers (with nonzero thickness). The appropriate Boltzmann transport equations were used to calculate the conductivity of polaronic carriers and bosonic Cooper pairs above and below the pseudogap (PG) temperature T* in the relaxation time approximation. We show that the linearity of ρab(T) above T* is associated with the polaron-phonon scattering, while different deviations from the T-linear behavior in ρab(T) below T* are caused by transition to the BCS-like PG regime. The specific model for layered cuprates is used to simulate the c-axis transport and to calculate the c-axis conductivity associated with the thermal dissociation of localized bipolarons in carrier-poor regions between the CuO2 layers into hole polarons which subsequently move by hopping along the c-axis. It is shown that the bipolaronic PG and carrier-confinement together cause the insulating ρc(T) behavior in the cuprates. The calculated results for ρab(T), ρc(T) and ρc(T)/ρab(T) were compared with the experimental data obtained for various hole-doped cuprates. For all the considered cases, a good quantitative agreement was found between theory and experimental data.

  7. Transport and optical properties of c-axis oriented wedge shaped GaN nanowall network grown by molecular beam epitaxy

    SciTech Connect

    Bhasker, H. P.; Dhar, S.; Thakur, Varun; Kesaria, Manoj; Shivaprasad, S. M.

    2014-02-21

    The transport and optical properties of wedge-shaped nanowall network of GaN grown spontaneously on cplane sapphire substrate by Plasma-Assisted Molecular Beam Epitaxy (PAMBE) show interesting behavior. The electron mobility at room temperature in these samples is found to be orders of magnitude higher than that of a continuous film. Our study reveals a strong correlation between the mobility and the band gap in these nanowall network samples. However, it is seen that when the thickness of the tips of the walls increases to an extent such that more than 70% of the film area is covered, it behaves close to a flat sample. In the sample with lower surface coverage (≈40% and ≈60%), it was observed that the conductivity, mobility as well as the band gap increase with the decrease in the average tip width of the walls. Photoluminescence (PL) experiments show a strong and broad band edge emission with a large (as high as ≈ 90 meV) blue shift, compared to that of a continuous film, suggesting a confinement of carriers on the top edges of the nanowalls. The PL peak width remains wide at all temperatures suggesting the existence of a high density of tail states at the band edge, which is further supported by the photoconductivity result. The high conductivity and mobility observed in these samples is believed to be due to a “dissipation less” transport of carriers, which are localized at the top edges (edge states) of the nanowalls.

  8. Transport and optical properties of c-axis oriented wedge shaped GaN nanowall network grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bhasker, H. P.; Thakur, Varun; Kesaria, Manoj; Shivaprasad, S. M.; Dhar, S.

    2014-02-01

    The transport and optical properties of wedge-shaped nanowall network of GaN grown spontaneously on cplane sapphire substrate by Plasma-Assisted Molecular Beam Epitaxy (PAMBE) show interesting behavior. The electron mobility at room temperature in these samples is found to be orders of magnitude higher than that of a continuous film. Our study reveals a strong correlation between the mobility and the band gap in these nanowall network samples. However, it is seen that when the thickness of the tips of the walls increases to an extent such that more than 70% of the film area is covered, it behaves close to a flat sample. In the sample with lower surface coverage (≈40% and ≈60%), it was observed that the conductivity, mobility as well as the band gap increase with the decrease in the average tip width of the walls. Photoluminescence (PL) experiments show a strong and broad band edge emission with a large (as high as ≈ 90 meV) blue shift, compared to that of a continuous film, suggesting a confinement of carriers on the top edges of the nanowalls. The PL peak width remains wide at all temperatures suggesting the existence of a high density of tail states at the band edge, which is further supported by the photoconductivity result. The high conductivity and mobility observed in these samples is believed to be due to a "dissipation less" transport of carriers, which are localized at the top edges (edge states) of the nanowalls.

  9. Collective responses of Bi-2212 stacked junction to 100 GHz microwave radiation under magnetic field oriented along the c-axis

    NASA Astrophysics Data System (ADS)

    Pavlenko, V. N.; Latyshev, Yu. I.; Chen, J.; Gaifullin, M. B.; Irzhak, A.; Kim, S.-J.; Wu, P. H.

    2009-05-01

    We studied a response of Bi-2212 mesa type structures to 100 GHz microwave radiation. We found that applying magnetic field of about 0.1 T across the layers enables to observe collective Shapiro step response corresponding to a synchronization of all 50 intrinsic Josephson junctions (IJJ) of the mesa. At high microwave power we observed up to 10th harmonics of the fundamental Shapiro step. Besides, we found microwave induced flux-flow step position of which is proportional to the square root of microwave power and that can exceed at high enough powers 1 THz operating frequency of IJJ oscillations.

  10. 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!!!

  11. Electronic structure of c-axis controlled α-Fe2O3 thin film probed by soft-X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Kawamura, Kinya; Suzuki, Naoya; Tsuchiya, Takashi; Yamaguchi, Shohei; Ochi, Masanori; Suetsugu, Takaaki; Minohara, Makoto; Kobayashi, Masaki; Horiba, Koji; Kumigashira, Hiroshi; Higuchi, Tohru

    2016-06-01

    We have prepared c-axis controlled α-Fe2O3 thin films on Al2O3 substrates by RF magnetron sputtering and studied their electronic structure by soft-X-ray spectroscopy. The lattice constant of c-axis increases with increasing film thickness due to the relaxation of lattice mismatch between α-Fe2O3 and Al2O3 and formation of oxygen vacancies. The electrical conductivity is higher in thicker thin film. The valence band consists of t2g- and eg-subbband of Fe 3d state hybridized with O 2p state. The band gaps of ∼25 and ∼95 nm thicknesses of Fe2O3 thin film are ∼1.8 and 1.4 eV, respectively, which correspond to the activation energy of electron conductivity. The above results indicate that the band gap and the conductivity of α-Fe2O3 thin film directly affect the change of the lattice constant of c-axis and formation of oxygen vacancies.

  12. Charge-screening role of c-axis atomic displacements in YBa2Cu3O6+x and related superconductors

    DOE PAGESBeta

    E. S. Bozin; Huq, A.; Shen, Bing; Claus, H.; Kwok, W. K.; Tranquada, J. M.

    2016-02-29

    Here, the importance of charge reservoir layers for supplying holes to the CuO2 planes of cuprate superconductors has long been recognized. Less attention has been paid to the screening of the charge transfer by the intervening ionic layers. We address this issue in the case of YBa2Cu3O6+x, where CuO chains supply the holes for the planes. We present a simple dielectric-screening model that gives a linear correlation between the relative displacements of ions along the c axis, determined by neutron powder diffraction, and the hole density of the planes. Applying this model to the temperature-dependent shifts of ions along themore » c axis, we infer a charge transfer of 5–10% of the hole density from the planes to the chains on warming from the superconducting transition to room temperature. Given the significant coupling of c-axis displacements to the average charge density, we point out the relevance of local displacements for screening charge modulations and note recent evidence for dynamic screening of in-plane quasiparticles. This line of argument leads us to a simple model for atomic displacements and charge modulation that is consistent with images from scanning-tunneling microscopy for underdoped Bi2Sr2CaCu2O8+δ.« less

  13. Dynamic control of substrate bias for highly c-axis textured thin ferromagnetic CoCrTa film in inductively coupled plasma-assisted sputtering

    SciTech Connect

    Okimura, Kunio; Oyanagi, Junya

    2005-01-01

    This study shows highly c-axis textured thin ferromagnetic Co-based alloy (CoCrTa) film growth in inductively coupled plasma (ICP)-assisted sputtering with an internal coil with an insulated surface. Dynamic control of the substrate bias achieved highly c-axis textured CoCrTa film with a thickness of 70 nm in 3 min depositions on a Si substrate. The prepared film showed a smooth, dense surface consisting of small crystal grains. The film had a perpendicular magnetic coercivity of 1030 Oe and coercive squareness of 0.36. ICP-assisted sputtering with an internal coil with an insulated surface enabled higher-density ({>=}1.0x10{sup 11} cm{sup -3}) plasma with lower space potential ({<=}30 V) compared to ICP-assisted sputtering with bare coil systems. Therefore, the proposed bias control is quite effective for textured growth of thinner Co layers via the effect of a high flux of ions with proper energies. This method can be a candidate for the deposition technique of c-axis textured films as perpendicular magnetic recording media.

  14. 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.

  15. Electrical behaviors of c-axis textured 0.975Bi0.5Na0.5TiO3-0.025BiCoO3 thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Guo, Feifei; Yang, Bin; Zhang, Shantao; Liu, Danqing; Wu, Fengmin; Wang, Dali; Cao, Wenwu

    2013-10-01

    The thin films of 0.975Bi0.5Na0.5TiO3-0.025BiCoO3 (BNT-BC) have been successfully deposited on (1 1 1) Pt/Ti/SiO2/Si (1 0 0) substrates by pulse laser deposition and their ferroelectric, dielectric, local piezoelectric properties and temperature dependent leakage current behaviors have been investigated systematically. X-ray diffraction indicates the films are single phased and c-axis oriented. The thin films exhibit ferroelectric polarization-electric field (P-E) hysteresis loop with a remnant polarization (Pr) of 10.0 μC/cm2 and an excellent fatigue resistance property up to 5 × 109 switching cycles. The dielectric constant and dielectric loss are 500 and 0.22 at 1 kHz, respectively. The tunability of the dielectric constant is about 12% at 20 kV/mm. The piezo-phase response hysteresis loop and piezo-amplitude response butterfly curve are observed by switching spectroscopy mode of piezoelectric force microscope (SS-PFM) and the piezoelectric coefficient d33 is about 19-63 pm/V, which is comparable to other reports. The dominant leakage current conduction mechanisms are ohmic conduction at low electric field and Schottky emission at high electric field, respectively. Our results may be helpful for further work on BNT-based thin films with improved electric properties.

  16. Anomalous elongation of c-axis of GaN on Al2O3 grown by MBE using NH3-cluster ions

    NASA Astrophysics Data System (ADS)

    Ichinohe, Yoshihiro; Imai, Kazuaki; Suzuki, Kazuhiko; Saito, Hiroshi

    2016-02-01

    GaN thin films were grown on Al2O3 (0001) by MBE using NH3-clusters either ionized with the energy of 4-7 eV/molecule (ionized Cluster Beam, i-CB) or un-ionized with the energy of about 0.1 eV/molecule (neutral Cluster Beam, n-CB) at growth temperatures ranging from 390 to 960 °C. The c-axis is extremely elongated but the a-axis is shrunken at the initial growth stage (up to the film thickness of about 10 nm) in GaN grown by the mixture of n- and i-CB under N-rich condition. The films thicker than 30 nm have the relaxed a- and c-axis lengths close to the unstrained values and obey the Poisson relation. GaN grown by i-CB under Ga-rich condition have the relaxed lattice constants obeying the Poisson relation for the film as thin as 6 nm. In GaN grown by the cluster beam (CB) which is not ionized intentionally, both a- and c-axis lengths are almost independent of the film thickness, having nearly the same values as those of the unstrained samples. These characteristics can be ascribed to the nature of interface between the nitrided Al2O3 substrate and epilayer. It is concluded that the films grown by i-CB bond firmly to underlay AlN than the films by n-CB and CB.

  17. Slip of c + a/2 dislocations in Ti{sub 3}Al single crystals strained in tension along the c-axis

    SciTech Connect

    Minonishi, Y.; Legros, M.; Caillard, D.

    1997-12-31

    In situ TEM straining experiments have been performed on a Ti{sub 3}Al single crystal, along the c-axis, in order to study the slip of 2c+a dislocations in pyramidal planes. The results show that slip takes place in {pi}{sub 1} planes, in contrast with what has been observed after compression tests (slip in {pi}{sub 2} planes), and that rows of loops are nucleated in the slip plane.The mechanisms which may control slip in the {pi}{sub 1} planes are briefly discussed.

  18. Influence of target-substrate angle on the elemental concentration of c-axis YBa2Cu3O7-x thin films

    NASA Astrophysics Data System (ADS)

    Pugel, D. E.; Greene, L. H.

    1999-09-01

    The thermalization processes in sputtering suggest a spatial dependence of elemental concentration in the sputter plume. A variety of analysis techniques demonstrate that c-axis films grown at angles which deviate from the standard off-axis geometry produce nominally YBa2Cu3O7-x in the bulk with dramatic changes in the surface morphology and deposition rate. In addition to the common materials characterization techniques of scanning electron microscopy, x-ray diffraction, transport measurements, and conventional Rutherford backscattering spectrometry (RBS), angle-dependent RBS is employed to probe surface inhomogeneities of films grown at target-substrate angles away from the standard off-axis position.

  19. Photoinduced enhancement of the c-axis conductivity in oxygen-deficient YBa{sub 2}Cu{sub 3}O{sub x} thin films

    SciTech Connect

    Markowitsch, W.; Stockinger, C.; Lang, W. |; Bierleutgeb, K.; Pedarnig, J.D.; Baeuerle, D.

    1997-09-01

    High quality thin films of oxygen-depleted YBa{sub 2}Cu{sub 3}O{sub x} (x{approx}6.6) were prepared by pulsed-laser deposition on SrTiO{sub 3}, substrates that were cut with tilt angles of 10{degree} and 20{degree} with respect to the [001] direction, resulting in a steplike growth of the layers. The resistance showed a semiconducting behavior along the projection of the c axis to the film surface, but a metallic behavior in the perpendicular direction, indicating that the former is dominated by the c-axis resistivity and the latter by the ab-plane resistivity of YBa{sub 2}Cu{sub 3}O{sub x}. Long-term illumination of the samples with a 100 W halogen lamp resulted in a significant conductivity enhancement in both directions. The photoinduced change of the out-of-plane resistance vs temperature characteristics is comparable to the effect of large hydrostatic pressure, introducing structural changes similar to that of photoexcitation. {copyright} {ital 1997 American Institute of Physics.}

  20. Synthesis of textured thin piezoelectric AlN films with a nonzero c-axis mean tilt for the fabrication of shear mode resonators.

    PubMed

    Bjurström, Johan; Wingqvist, Gunilla; Katardjiev, Ilia

    2006-11-01

    A method for the deposition of thin piezoelectric aluminum nitride (AlN) films with a nonzero c-axis mean tilt has been developed. The deposition is done in a standard reactive magnetron sputter deposition system without any hardware modifications. In essence, the method consists of a two-stage deposition process. The resulting film has a distinct tilted texture with the mean tilt of the c-axis varying roughly in the interval 28 to 32 degrees over the radius of the wafer excluding a small exclusion zone at the center of the latter. The mean tilt angle distribution over the wafer has a circular symmetry. A membrane-type shear mode thickness-excited thin film bulk acoustic resonator together with a micro-fluidic transport system has been subsequently fabricated using the two stage AlN deposition as well as standard bulk micro machining of Si. The resonator consisted of a 2-microm-thick AlN film with 200nm-thick Al top and bottom electrodes. The resonator was characterized with a network analyzer when operating in both air and water. The shear mode resonance frequency was about 1.6 GHz, the extracted device Q around 350, and the electromechanical coupling kt2 2% when the resonator was operated in air, whereas the latter two dropped down to 150 and 1.8%, respectively, when the resonator was operated in pure water. PMID:17091844

  1. Measurement of c-axis optical absorptivity of La{sub 1.87}Sr{sub 0.13}CuO{sub 4}

    SciTech Connect

    Birmingham, J.T.; Grannan, S.M.; Richards, P.L.; Henn, R.; Kircher, J.; Cardona, M.; Wittlin, A.; Duijn, V.H.M.; Menovsky, A.A.

    1996-12-31

    The authors have directly measured the c-axis optical absorptivity of a large single crystal of La{sub 1.87}Sr{sub 0.13}CuO{sub 4} between 9 and 80 cm{sup {minus}1} at 2 K using Fourier transform spectroscopy and an absorbed power technique. They see an absorptivity onset at 41 cm{sup {minus}1}, which is 2--3 cm{sup {minus}1} higher than that measured at 6 K with reflectance on the same sample, suggesting that a significant fraction of the electrons remain unpaired at 6 K. The absorption increases with frequency below the onset, increasing from 0.3% at 9 cm{sup {minus}1} to 8% at 40 cm{sup {minus}1}. The data are particularly significant at frequencies below the plasma edge, for which the reflectance is close to unity.

  2. c-axis inclined ZnO films for shear-wave transducers deposited by reactive sputtering using an additional blind

    SciTech Connect

    Link, M.; Schreiter, M.; Weber, J.; Gabl, R.; Pitzer, D.; Primig, R.; Wersing, W.; Assouar, M.B.; Elmazria, O.

    2006-03-15

    This article reports on the growth and characterization of polycrystalline ZnO films having c axis inclined up to 16 deg. with respect to the substrate normal. These films allow the excitation of shear and longitudinal waves with comparable electromechanical coupling constants and are of significant interest for thin film bulk acoustic resonators (FBARs). The films are deposited on silicon substrates covered by Al{sub 2}O{sub 3} and SiO{sub 2} buffer layers under low pressure using a modified reactive dc-pulsed magnetron sputtering system. A blind has been positioned between target and substrate, allowing oblique particle incidence without tilting the wafer. The study of structural properties of the deposited ZnO films by x-ray diffraction and scanning electron microscopy has permitted to show the presence of the inclined structure. Electromechanical coupling constants K up to 13% have been extracted for shear-mode excitation using highly overmoded FBARs.

  3. Temperature-dependent growth of LaAlO{sub 3} films on YBa{sub 2}Cu{sub 3}O{sub 7} C-axis films for multilayer structures

    SciTech Connect

    Hawley, M.E.; Houlton, R.J.; Raistrick, I.A.; Garzon, F.H.

    1995-01-01

    Fabrication of ultra smooth films, free of micro-shorts, is essential to the development of High Temperature Superconducting (HTS) thin film devices. One such example is a SNS junction consisting of two HTS layers separated by a uniformly smooth continuous barrier material. Other schemes under consideration require multilayer structures of up to 5 - 7 epitaxially grown layers of complex oxide material. Successful fabrication of such devices necessitates understanding the epitaxial growth of polycrystalline oxide films on polycrystalline film templates. Toward this end we have developed a set of deposition parameters that produce high quality epitaxial insulating layers suitable for HTS device applications. All films in this study were grown by off-axis RF magnetron sputter deposition. LaAlO{sub 3} films were deposited over MgO grown YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) c-axis thin films at temperatures ranging from 200 to 700C and on virgin substrates at 600C. Atomic Force Microscopy, eddy current measurements, and x-ray diffraction techniques were used to monitor the effect of growth conditions on the resulting film crystallinity, nanostructure, and electrical properties. Ex-situ interrupted growth characterization of these materials has yielded new insight into the processes that control the growth mechanism and resulting microstructure. All films were polycrystalline. Below 600C, LaAlO{sub 3} films were not epitaxial while films grown at 650C showed some <200> orientation. The shape of the underlying YBCO film is most clearly evident for the film grown at 400C. Surface roughness depended on the appearance of crystals on the film surface. The superconducting properties of the underlying YBCO film required O{sub 2} annealing prior to deposition of the LaAlO{sub 3} layer.

  4. Effect on C-axis transport properties of a critical state in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}

    SciTech Connect

    Cho, J.H.; Maley, M.P.; Bulaevskii, L.N.

    1995-12-31

    At low temperatures, the c-axis transport properties of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} single crystals depend strongly on the magnetic field history for fields applied along the c-axis, indicating the effect of a critical state in the ab direction. In this study, the authors report zero field cooled (ZFC), field cooled warming (FCW), and field cooled cooling (FCC) c-axis transport properties. In addition, they also report magnetic relaxation measurements on the same samples to identify the c-axis dissipation mechanism. They observe a relaxation of the c-axis resistivity that follows the relaxation of the flux profile across the ab plane. By identifying the irreversible temperature vs. magnetic field for H // c, they construct a phase diagram of vortex states. Finally, they will discuss the implication of the phase diagram and the features related to the transport properties of the Josephson-coupled system and the role of pancake vortices in highly two-dimensional superconductors.

  5. Quantum oscillation of the c-axis resistivity due to entrance of pancake vortices into micro-fabricated Bi 2Sr 2CaCu 2O 8+ δ intrinsic Josephson junctions

    NASA Astrophysics Data System (ADS)

    Kakeya, I.; Fukui, K.; Kawamata, K.; Yamamoto, T.; Kadowaki, K.

    2008-04-01

    The c-axis resistance in Bi2Sr2CaCu2O8+δ intrinsic Josephson junctions (IJJs) with areas of the ab-plane less than 2 μm2 were measured as functions of applied magnetic field and angle to the crystalline axes. When the magnetic field is tilted off from the lock-in state of Josephson vortices, several sharp dips are found. The separation between the dips approaches to the value corresponding to ϕ0 with further tilting the external magnetic field. This behavior is attributed to the penetration of a quantized pancake vortex into the tiny IJJ. This argument is further supported by the result that the c-axis resistance under magnetic fields parallel to the c-axis shows identical stepwise behavior.

  6. c-Axis projected electron-positron momentum density in YBa{sub 2}Cu{sub 3}O{sub 7}

    SciTech Connect

    Bansil, A.; Mijnarends, P.E.; Smedskjaer, L.C.

    1990-11-01

    The authors present the theoretical c-axis projected electron-positron momentum density N{sub 2{gamma}}(P{sub x},p{sub y}) in YBa{sub 2}Cu{sub 3}O{sub 7} based on the local density approximation (LDA) framework along various lines in momentum space. The calculations use the Korringa-Kohn-Rostoker (KKR) band structure formalism. The anisotropic distribution defined by taking cuts through the calculated spectra along different lines in the (p{sub x},p{sub y}) plane possesses complex structures which arise from both Fermi surface effects and the anisotropy of the smoothly varying underlying background from filled bands; the maximum size of the anisotropy is about 10% of N{sub 2{gamma}}(0,0). The theoretically predicted N{sub 2{gamma}}(p{sub x},{sub y}) distribution is compared with the measured 2D-ACAR spectrum. The considerations suggest that in interpreting the 2D-ACAR data on YBa{sub 2}Cu{sub 3}O{sub 7} in terms of a band theory LDA picture, a substantial, largely isotropic, background should be subtracted from both the 2D-ACAR`s and the associated LCW-folded spectra.

  7. Properties of c-axis-aligned crystalline indium-gallium-zinc oxide field-effect transistors fabricated through a tapered-trench gate process

    NASA Astrophysics Data System (ADS)

    Asami, Yoshinobu; Kurata, Motomu; Okazaki, Yutaka; Higa, Eiji; Matsubayashi, Daisuke; Okamoto, Satoru; Sasagawa, Shinya; Moriwaka, Tomoaki; Kakehata, Tetsuya; Yakubo, Yuto; Kato, Kiyoshi; Hamada, Takashi; Sakakura, Masayuki; Hayakawa, Masahiko; Yamazaki, Shunpei

    2016-04-01

    To achieve both low power consumption and high-speed operation, we fabricated c-axis-aligned crystalline indium-gallium-zinc oxide (CAAC-IGZO) field-effect transistors (FETs) with In-rich IGZO and common IGZO (\\text{In}:\\text{Ga}:\\text{Zn} = 1:1:1 in atomic ratio) active layers through a simple process using trench gates, and evaluated their characteristics. The results confirm that 60-nm-node IGZO FETs fabricated through a 450 °C process show an extremely low off-state current below the detection limit (at most 2 × 10-16 A) even at a measurement temperature of 150 °C. The results also reveal that the FETs with the In-rich IGZO active layer show a higher on-state current than those with the common IGZO active layer and have excellent frequency characteristics with a cutoff frequency and a maximum oscillation frequency of up to 20 and 6 GHz, respectively. Thus, we demonstrated that CAAC-IGZO FETs with trench gates are promising for achieving both low power consumption and high-speed operation.

  8. Mosaic Texture and Double c-Axis Periodicity of β-NiOOH: Insights from First-Principles and Genetic Algorithm Calculations.

    PubMed

    Li, Ye-Fei; Selloni, Annabella

    2014-11-20

    Fe-doped NiOx has recently emerged as a promising anode material for the oxygen evolution reaction, but the origin of the high activity is still unclear, due largely to the structural uncertainty of the active phase of NiOx. Here, we report a theoretical study of the structure of β-NiOOH, one of the active components of NiOx. Using a genetic algorithm search of crystal structures combined with dispersion-corrected hybrid density functional theory calculations, we identify two groups of favorable structures: (i) layered structures with alternate Ni(OH)2 and NiO2 layers, consistent with the doubling of the c axis observed in high resolution transmission electron microscopy (TEM) measurements, and (ii) tunnel structures isostructural with MnO2 polymorphs, which can provide a rationale for the mosaic textures observed in TEM. Analysis of the Ni ions oxidation state further indicates a disproportionation of half of the Ni(3+) cations to Ni(2+)/Ni(4+) pairs. Hybrid density functionals are found essential for a correct description of the electronic structure of β-NiOOH. PMID:26276481

  9. Low-magnetic-field operations of intrinsic Josephson junctions with a long c-axis periodicity by artificial critical-current modulations

    NASA Astrophysics Data System (ADS)

    Sakai, Shigeki; Zhao, Xia

    2007-02-01

    Flux-flow cavity resonances in intrinsic Josephson junctions (IJJs) with long c-axis periodicity by artificial critical-current (Jc) modulation are studied numerically and theoretically. For an n-1-n-1-n-1-n IJJ system with n-layer high-Jc and one-layer low-Jc alternately stacked, numerical simulation confirms fluxon penetration only in the low-Jc junctions under proper low magnetic fields. The simulation also shows pronounced cavity-resonance steps in the I-V curves of the low-Jc junctions, meaning that fluxon dynamics can be generated under much lower magnetic fields, compared to the fields for usual IJJs with homogeneous Jc. A theoretical method for describing the flux-flow cavity-resonance properties is presented. The general disperse k-ω relationship shows that, at low-k regions, the critical-current-modulated junction system can be regarded as simple homogeneous stacked junctions with a new effective thickness and a new inductive coupling strength. For general-k cases, the cavity-resonant voltage steps on the I-V curves at various magnetic fields can be well indexed by integers, which means excellent agreement between the theoretical analysis and the numerical simulations.

  10. Anomalous dependence of c-axis polarized Fe B1g phonon mode with Fe and Se concentrations in Fe1+yTe1-xSex

    NASA Astrophysics Data System (ADS)

    Um, Y. J.; Subedi, A.; Toulemonde, P.; Ganin, A. Y.; Boeri, L.; Rahlenbeck, M.; Liu, Y.; Lin, C. T.; Carlsson, S. J. E.; Sulpice, A.; Rosseinsky, M. J.; Keimer, B.; Le Tacon, M.

    2012-02-01

    We report on an investigation of the lattice dynamical properties in a range of Fe1+yTe1-xSex compounds, with special emphasis on the c-axis polarized vibration of Fe with B1g symmetry, a Raman active mode common to all families of Fe-based superconductors. We have carried out a systematic study of the temperature dependence of this phonon mode as a function of Se x and excess Fe y concentrations. In parent compound Fe1+yTe, we observe an unconventional broadening of the phonon between room temperature and magnetic ordering temperature TN. The situation smoothly evolves toward a regular anharmonic behavior as Te is substituted for Se and long-range magnetic order is replaced by superconductivity. Irrespective to Se contents, excess Fe is shown to provide an additional damping channel for the B1g phonon at low temperatures. We performed density functional theory ab initio calculations within the local density approximation to calculate the phonon frequencies, including magnetic polarization and Fe nonstoichiometry in the virtual crystal approximation. We obtained a good agreement with the measured phonon frequencies in the Fe-deficient samples, while the effects of Fe excess are poorly reproduced. This may be due to excess Fe-induced local magnetism and low-energy magnetic fluctuations that cannot be treated accurately within these approaches. As recently revealed by neutron scattering and muon spin rotation studies, these phenomena occur in the temperature range where anomalous decay of the B1g phonon is observed and suggests a peculiar coupling of this mode with local moments and spin fluctuations in Fe1+yTe1-xSex.

  11. Control of magnetization reversal in oriented strontium ferrite thin films

    SciTech Connect

    Roy, Debangsu Anil Kumar, P. S.

    2014-02-21

    Oriented Strontium Ferrite films with the c axis orientation were deposited with varying oxygen partial pressure on Al{sub 2}O{sub 3}(0001) substrate using Pulsed Laser Deposition technique. The angle dependent magnetic hysteresis, remanent coercivity, and temperature dependent coercivity had been employed to understand the magnetization reversal of these films. It was found that the Strontium Ferrite thin film grown at lower (higher) oxygen partial pressure shows Stoner-Wohlfarth type (Kondorsky like) reversal. The relative importance of pinning and nucleation processes during magnetization reversal is used to explain the type of the magnetization reversal with different oxygen partial pressure during growth.

  12. Studies of C-Axis Charge Transport in BISMUTH(2) STRONTIUM(2) Calcium COPPER(2) OXYGEN(8 + Delta) and Anomalous Hall Effect in (LANTHANUM(0.67) CALCIUM(0.33)) Manganese OXYGEN(3)

    NASA Astrophysics Data System (ADS)

    Yi-Feng, Yan

    In this thesis I report my studies on charge transport on two perovskite metal oxides: La_ {1-x}Ca_{x}MnO_3(LCMO) --a colossal magnetoresistance oxide and Bi_2Sr_2CaCu_2O_{8+delta } (BSCCO)--a high temperature superconducting compound. Large and high quality Bi_2Sr _2CaCu_2O_{8+delta} single crystals were grown by self-flux method. The quality of the crystals were examined by x-ray diffraction and electron diffraction. I have systematically investigated the c-axis magnetoresistance (MR) of various BSCCO single crystals with different oxygen contents. With field H parallel to c-axis and the current (H//c//J), we observed that MR is negative if rho_ {c} is semiconducting and positive if rho_{c} is pseudo-metallic. We consider that the negative MR is a normal state property. We have also measured the field dependence of rho_{c} in the flux flow state (H//c//J) at fields up to 14T. Whereas rho_{c} increases rapidly in weak fields, it saturates to the extrapolated normal-state curve when the field H_ {2D} is attained (H_ {2D} is the field at which the vortex pancakes in adjacent layers are completely decoupled). At fields above H_{2D}, rho_{c} decreases slowly. We verify that this is a continuation of the negative MR observed above Tc. We propose that the antiferromagnetic coupling along the c-axis in adjacent CuO_2 planes and spin singlet formation are the cause of negative magnetoresistance in c-axis in bilayer cuprates. We found that the c-axis resistivity in bilayer cuprates can be fitted into the following empirical formula: rho_{c}{= }a/Te^{Delta/T} + cT + d where a, c and d are temperature independent constants; Delta is called pseudogap. In Y -doped BSCCO, rho_{c} displays a logarithmic temperature dependence. The LCMO thin films used in this experiment were grown by Plasma Enhanced-MOCVD method. The Hall effect and magnetoresistance of LCMO thin films have been systematically investigated. At low temperature, the Hall effect is linear with field and positive

  13. 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

  14. Effects of the crystallographic orientation of Sn on the electromigration of Cu/Sn-Ag-Cu/Cu ball joints

    SciTech Connect

    Lee, Kiju; Kim, Keun-Soo; Tsukada, Yutaka; Suganuma, Katsuaki; Yamanaka, Kimihiro; Kuritani, Soichi; Ueshima, Minoru

    2011-11-17

    Electromigration behavior and fast circuit failure with respect to crystallographic orientation of Sn grains were examined. The test vehicle was Cu/Sn-3.0 wt% Ag-0.5 wt% Cu/Cu ball joints, and the applied current density was 15 kA/cm2 at 160 °C. The experimental results indicate that most of the solder bumps show different microstructural changes with respect to the crystallographic orientation of Sn grains. Fast failure of the bump occurred due to the dissolution of the Cu circuit on the cathode side caused by the fast interstitial diffusion of Cu atoms along the c-axis of the Sn grains when the c-axis was parallel to the electron flow. Slight microstructural changes were observed when the c-axis was perpendicular to the electron flow. In addition, Cu6Sn5 intermetallic compound (IMC) was formed along the direction of the c-axis of the Sn grains instead of the direction of electron flow in all solder ball joints.

  15. Thermally activated flux dissipation in [ital c]-axis-oriented YBa[sub 2]Cu[sub 3]O[sub 7]/PrBa[sub 2]Cu[sub 3]O[sub 7] multilayers

    SciTech Connect

    Qiu, X.G.; Zhao, B.R.; Guo, S.Q.; Zhang, J.R.; Li, L. ); Ichikawa, F.; Nishizaki, T.; Fukami, T.; Horie, Y.; Aomine, T. )

    1993-06-01

    We have systematically studied the resistive transition of multilayers of YBa[sub 2]Cu[sub 3]O[sub 7]/PrBa[sub 2]Cu[sub 3]O[sub 7] (YBCO/PBCO) under different perpendicular magnetic fields. It was found that the resistive transition is dominated by the flux-thermal-activation process; the broadening of the resistive transition was observed with the same order as that in single-layer thin films and the resistivity obeys the relation [rho]=[rho][sub 0] exp([minus][ital U]/[ital kT]). The activation energy depends logarithmically on the applied magnetic fields and decreased linearly with temperature. This phenomenon may be attributed to the creation of edge-dislocation pairs in the two-dimensional pancake vortices situated in the individual YBCO layer. The possible pinning mechanisms in the multilayers are discussed.

  16. Thick c-axis textured (Tl,Pb)(Ba,Sr)2Ca2Cu3O9/Ag0.37 superconducting tapes by an ink spray pyrolysis method using a Tl-free precursor

    NASA Astrophysics Data System (ADS)

    Schulz, Douglas L.; Parilla, Philip A.; Ginley, David S.; Voigt, James A.; Roth, E. Peter

    1994-11-01

    In this letter we demonstrate a synthetic route to thick (5-20 μm) highly c-axis textured, nearly phase-pure superconducting (Tl,Pb)(Ba,Sr)2Ca2Cu3O9/Ag0.37 tapes. First, a Tl-free ink consisting of Pb0.5Ba0.4Sr1.6Ca2.0Cu3.0O9/Ag0.37 precursor powder in an ethanolic ethyl cellulose binder is sprayed onto a heated LaAlO3 substrate. After an intermediate oxygen anneal to remove the carbonaceous binder, a static 2-zone thallination anneal is performed to promote superconducting phase formation. Films exhibit excellent c-axis texturing as evidenced by x-ray diffraction θ/2θ and rocking curve characterization with morphological evidence for partial melting by scanning electron microscopy. Electrical characterization of these films give Tc onset values of 106-115 K with Tc zero reached by 99-101 K and transport Jc(77 K) up to 2.9×104 A/cm2. A mixed strong/weak-linked magnetic field dependence is observed for these films at 77 K and 0.4 T.

  17. Effects of Two-Band Superconductivity on the Flux-Line Lattice in Magnesium Diboride

    NASA Astrophysics Data System (ADS)

    Cubitt, R.; Eskildsen, M.; Dewhurst, C.; Jun, J.; Kazakov, S.; Karpinski, J.

    2003-07-01

    We present neutron scattering from the flux line lattice (FLL) in MgB2. Between 0.5 and 0.9 T the FLL undergoes a 30° reorientation, and simultaneously the scattered intensity falls sharply consistent with the weaker superconducting π band being suppressed with increasing field. We speculate that the π and σ bands favor different FLL orientations, and that the reorientation is driven by the suppression of the π band. When the c axis of the crystal is rotated 45° to the applied field the penetration depth anisotropy could be measured, and rises both as a function of applied field and temperature.

  18. Biomimetic synthesis of oriented hydroxyapatite mediated by nonionic surfactants

    NASA Astrophysics Data System (ADS)

    Ye, Feng; Guo, Haifeng; Zhang, Haijiao

    2008-06-01

    Highly oriented organization of hydroxyapatite (HAP) nanorods was achieved through a simple reflux method using mixtures of triblock copolymer pluronic P123 and tween-60 as the mediated agents. Raft-like organized complexes were prepared when the nanorods were only directed by the mixed surfactants. Bundles of nanorod-like HAP crystals were obtained when urea was used as the cosurfactant. These HAP nanorods with a large amount of uniform 4 nm worm-like mesopores were arranged in parallel to each other along the c axis of HAP. The raft-like complexes might be mediated by the reverse lamellar micelles. And the added urea transformed the reverse lamellar micelles into hexagonal ones due to its association with the surfactant molecules by hydrogen bonds, resulting in the formation of bundles of nanorod-like HAP crystals. The regulation of the oriented HAP complexes in morphology extends the understanding of biomineralization and permits controllable design of biomimetic materials. In addition, the c-axis oriented raft-like HAP complex has great potential in selective bio-absorption and separation.

  19. Biomimetic synthesis of oriented hydroxyapatite mediated by nonionic surfactants.

    PubMed

    Ye, Feng; Guo, Haifeng; Zhang, Haijiao

    2008-06-18

    Highly oriented organization of hydroxyapatite (HAP) nanorods was achieved through a simple reflux method using mixtures of triblock copolymer pluronic P123 and tween-60 as the mediated agents. Raft-like organized complexes were prepared when the nanorods were only directed by the mixed surfactants. Bundles of nanorod-like HAP crystals were obtained when urea was used as the cosurfactant. These HAP nanorods with a large amount of uniform 4 nm worm-like mesopores were arranged in parallel to each other along the c axis of HAP. The raft-like complexes might be mediated by the reverse lamellar micelles. And the added urea transformed the reverse lamellar micelles into hexagonal ones due to its association with the surfactant molecules by hydrogen bonds, resulting in the formation of bundles of nanorod-like HAP crystals. The regulation of the oriented HAP complexes in morphology extends the understanding of biomineralization and permits controllable design of biomimetic materials. In addition, the c-axis oriented raft-like HAP complex has great potential in selective bio-absorption and separation. PMID:21825817

  20. Controlling laser emission by selecting crystal orientation

    NASA Astrophysics Data System (ADS)

    Chen, Lijuan; Han, Shujuan; Wang, Zhengping; Wang, Jiyang; Zhang, Huanjin; Yu, Haohai; Han, Shuo; Xu, Xinguang

    2013-01-01

    Based on the anisotropy of laser crystal, we demonstrate a method of adjusting laser emission by selecting crystal orientation. When the light propagating direction varies from a to c axis of Nd:LiGd(MoO4)2 crystal, emission wavelength exhibits a sensitive change of 1061 nm → 1061/1062 + 1068 nm → 1068 nm. The experimental discipline is well explained by a theoretical study of simulating on the spatial distribution of stimulated emission cross-section. This letter manifests that the laser property along non-principal-axis direction is also valuable for research and application, which breaks through the traditional custom of using laser materials processed along principal-axis.

  1. Whose Orientations?

    ERIC Educational Resources Information Center

    Gutoff, Joshua

    2010-01-01

    This article presents the author's response to Jon A. Levisohn's article entitled "A Menu of Orientations in the Teaching of Rabbinic Literature." While the "menu" Levisohn describes in his groundbreaking work on orientations to the teaching of rabbinic texts will almost certainly be refined over time, even as it stands this article should be of…

  2. Orienteering injuries

    PubMed Central

    Folan, Jean M.

    1982-01-01

    At the Irish National Orienteering Championships in 1981 a survey of the injuries occurring over the two days of competition was carried out. Of 285 individual competitors there was a percentage injury rate of 5.26%. The article discusses the injuries and aspects of safety in orienteering. Imagesp236-ap237-ap237-bp238-ap239-ap240-a PMID:7159815

  3. Fabrication of dynamic oxide semiconductor random access memory with 3.9 fF storage capacitance and greater than 1 h retention by using c-axis aligned crystalline oxide semiconductor transistor with L of 60 nm

    NASA Astrophysics Data System (ADS)

    Onuki, Tatsuya; Kato, Kiyoshi; Nomura, Masumi; Yakubo, Yuto; Nagatsuka, Shuhei; Matsuzaki, Takanori; Hondo, Suguru; Hata, Yuki; Okazaki, Yutaka; Nagai, Masaharu; Atsumi, Tomoaki; Sakakura, Masayuki; Okuda, Takashi; Yamamoto, Yoshitaka; Yamazaki, Shunpei

    2015-04-01

    A dynamic oxide semiconductor random access memory (DOSRAM) array that achieves reduction in storage capacitance (Cs) and decrease in refresh rate has been fabricated by using a c-axis aligned crystalline oxide semiconductor (CAAC-OS) transistor (L = 60 nm) with an extremely low off-state current. We have confirmed that this array, composed of cells that include a CAAC-OS transistor with W/L = 40 nm/60 nm using InGaZnO and a 3.9 fF storage capacitor, operates with write and read times of 5 ns. Therefore, DOSRAM can ensure sufficient Cs while maintaining operation speed comparable to that of dynamic random access memory (DRAM). We have found that the read signal voltage of DOSRAM is changed by approximately 30 mV after 1 h at 85 °C. Thus, DOSRAM is a promising replacement for DRAM.

  4. Blocks and residual stresses in sapphire rods of different crystallographic orientations grown by the Stepanov method

    SciTech Connect

    Krymov, V. M. Nosov, Yu. G.; Bakholdin, S. I.; Maslov, V. N.; Shul’pina, I. L.

    2015-05-15

    The formation of blocks in shaped sapphire rods of two crystallographic orientations has been investigated. It is shown that, when growth occurs in the direction of the optical c axis, blocks are formed with a higher probability than in the case of growth in the a direction. A model of formation of blocks in rods of different orientations is proposed. The distribution of residual stresses over sapphire rod cross sections is measured by conoscopy. It is found that stresses increase from the middle of a rod to its periphery and reach 20 MPa.

  5. Effect of crystal orientation on conductivity and electron mobility in single-crystal alumina

    NASA Technical Reports Server (NTRS)

    Will, Fritz G.; Delorenzi, Horst G.; Janora, Kevin H.

    1992-01-01

    The electrical conductivity of high-purity, single-crystal alumina is determined parallel to and perpendicular to the c-axis. The mean conductivity of four samples of each orientation is a factor 3.3 higher parallel to the c-axis than perpendicular to it. The conductivity as a function of temperature is attributed to extrinsic electron conduction at temperatures from 400 to 900 C, and intrinsic semiconduction at temperatures from 900 to 1300 C. In the high-temperature regime, the slope on all eight specimens is 4.7 +/- 0.1 eV. Hence, the thermal bandgap at O K is 9.4 +/- 0.2 eV.

  6. Analyzing Orientations

    NASA Astrophysics Data System (ADS)

    Ruggles, Clive L. N.

    Archaeoastronomical field survey typically involves the measurement of structural orientations (i.e., orientations along and between built structures) in relation to the visible landscape and particularly the surrounding horizon. This chapter focuses on the process of analyzing the astronomical potential of oriented structures, whether in the field or as a desktop appraisal, with the aim of establishing the archaeoastronomical "facts". It does not address questions of data selection (see instead Chap. 25, "Best Practice for Evaluating the Astronomical Significance of Archaeological Sites", 10.1007/978-1-4614-6141-8_25) or interpretation (see Chap. 24, "Nature and Analysis of Material Evidence Relevant to Archaeoastronomy", 10.1007/978-1-4614-6141-8_22). The main necessity is to determine the azimuth, horizon altitude, and declination in the direction "indicated" by any structural orientation. Normally, there are a range of possibilities, reflecting the various errors and uncertainties in estimating the intended (or, at least, the constructed) orientation, and in more formal approaches an attempt is made to assign a probability distribution extending over a spread of declinations. These probability distributions can then be cumulated in order to visualize and analyze the combined data from several orientations, so as to identify any consistent astronomical associations that can then be correlated with the declinations of particular astronomical objects or phenomena at any era in the past. The whole process raises various procedural and methodological issues and does not proceed in isolation from the consideration of corroborative data, which is essential in order to develop viable cultural interpretations.

  7. Birefringence imaging and orientation of laser patterned β-BaB{sub 2}O{sub 4} crystals with bending and curved shapes in glass

    SciTech Connect

    Ogawa, Kazuki; Honma, Tsuyoshi; Komatsu, Takayuki

    2013-11-15

    Nonlinear optical β-BaB{sub 2}O{sub 4} crystals (β-BBO) with bending and curved shapes were patterned at the surface of 8Sm{sub 2}O{sub 3}–42BaO–50B{sub 2}O{sub 3} glass by laser irradiations (Yb:YVO{sub 4} laser with a wavelength of 1080 nm, power of 0.8 W, and scanning speed of 4 μm/s), and the orientation state of β-BBO crystals was examined from the birefringence imaging obtained by polarization optical microscope (POM) observations. The formation (crystallization) of β-BBO crystals follows along laser scanning direction even if the laser scanning direction changes at a certain point within the bending angle of 60°. The birefringence images indicate that the formation of highly c-axis oriented β-BBO crystals follows along laser scanning direction even if the laser scanning direction changes, and in particular the direction of the c-axis of β-BBO crystals changes gradually at the bending point. The model for the orientation of the c-axis of β-BBO near the bending point is proposed. The present study proposes that the laser-induced crystallization opens a new door for the science and technology in crystal growth engineering. - Graphical abstract: This figure shows the birefringence images obtained by the Abrio IM imaging system (λ=546 nm) for the laser-patterned β-BaB{sub 2}O{sub 4} crystal line with the bending angle of 45° in the glass. The relation between the direction of slow axis and color is also shown. It is demonstrated that the formation (crystallization) of highly c-axis oriented β-BaB{sub 2}O{sub 4} crystals follows along laser scanning direction even if the laser scanning direction changes. Display Omitted - Highlights: • β-BaB{sub 2}O{sub 4} crystals with bending and curved shapes were patterned by laser irradiations. • The orientation was examined from the birefringence imaging. • Highly c-axis oriented crystals follows along laser scanning direction. • The c-axis direction changes gradually at the bending point. • The

  8. Seedlayer and underlayer effects on the crystallographic orientation and magnetic recording performance of glass media

    NASA Astrophysics Data System (ADS)

    Zheng, Min; Choe, Geon; Johnson, Kenneth E.

    2002-05-01

    Seedlayer and underlayer effects on crystallographic orientation and recording performance were studied for CoCrPtB media sputtered on glass substrates. For this study, the seedlayers are XAl (X=Ni, Co, Ti, and Ru) and the underlayers are CrY (Y=V, Mo, W, and Ti). It was found that not only different seedlayers, but also different combinations of seedlayer and underlayer, led to different magnetic performance. NiAl and CoAl seedlayers orient the Co c axis to (10.0) and TiAl and RuAl seedlayers produce (11.0) Co orientation. For the NiAl and CoAl seedlayer, CrV and CrW underlayers develop less out-of-plane c-axis orientation and higher coercivity and coercive squareness while CrTi and CrMo underlayers work better for TiAl and RuAl seedlayers, respectively. Media with RuAl seedlayers have better parametric performance than media with NiAl and CoAl seedlayers. The detailed relationship between seedlayer and underlayer types and crystal orientation and recording performance is discussed.

  9. Multilayer MgB2 superconducting quantum interference filter magnetometers

    NASA Astrophysics Data System (ADS)

    Galan, Elias; Melbourne, Thomas; Davidson, Bruce A.; Xi, X. X.; Chen, Ke

    2016-04-01

    We report two types of all-MgB2 superconductive quantum interference filter (SQIF) magnetometers that can measure absolute magnetic fields with high sensitivity. In one configuration, the SQIFs were made of 20 multilayer nonplanar all-MgB2 superconducting quantum interference devices (SQUIDs) connected in parallel with loop areas ranging in size from 0.4 to 3.6 μm2. These devices are sensitive to magnetic fields parallel to the substrate and show a single antipeak from 3 to 16 K with a maximum transfer function of ˜16 V/T at 3 K and a field noise of ˜110 pT/Hz1/2 above 100 Hz at 10 K. In a second configuration, the SQIFs were made with 16 planar SQUIDs connected in parallel with loop areas ranging in size from 4 μm2 to 25 μm2 and are sensitive to the magnetic fields perpendicular to the substrate. The planar SQIF shows a single antipeak from 10 to 22 K with a maximum transfer function of 7800 V/T at 10 K and a field noise of ˜70 pT/Hz1/2 above 100 Hz at 20 K.

  10. Industrial Orientation.

    ERIC Educational Resources Information Center

    Rasor, Leslie; Brooks, Valerie

    These eight modules for an industrial orientation class were developed by a project to design an interdisciplinary program of basic skills training for disadvantaged students in a Construction Technology Program (see Note). The Drafting module overviews drafting career opportunities, job markets, salaries, educational requirements, and basic…

  11. The effect of size, orientation and alloying on the deformation of AZ31 nanopillars

    NASA Astrophysics Data System (ADS)

    Aitken, Zachary H.; Fan, Haidong; El-Awady, Jaafar A.; Greer, Julia R.

    2015-03-01

    We conducted uniaxial compression of single crystalline Mg alloy, AZ31 (Al 3 wt% and Zn 1 wt%) nanopillars with diameters between 300 and 5000 nm with two distinct crystallographic orientations: (1) along the [0001] c-axis and (2) at an acute angle away from the c-axis, nominally oriented for basal slip. We observe single slip deformation for sub-micron samples nominally oriented for basal slip with the deformation commencing via a single set of parallel shear offsets. Samples compressed along the c-axis display an increase in yield strength compared to basal samples as well as significant hardening with the deformation being mostly homogeneous. We find that the "smaller is stronger" size effect in single crystals dominates any improvement in strength that may have arisen from solid solution strengthening. We employ 3D-discrete dislocation dynamics (DDD) to simulate compression along the [0001] and [ 11 2 bar 2 ] directions to elucidate the mechanisms of slip and evolution of dislocation microstructure. These simulations show qualitatively similar stress-strain signatures to the experimentally obtained stress-strain data. Simulations of compression parallel to the [ 11 2 bar 2 ] direction reveal the activation and motion of only -type dislocations and virtually no dislocation junction formation. Computations of compression along [0001] show the activation and motion of both and dislocations along with a significant increase in the formation of junctions corresponding to the interaction of intersecting pyramidal planes. Both experiments and simulation show a size effect, with a differing exponent for basal and pyramidal slip. We postulate that this anisotropy in size effect is a result of the underlying anisotropic material properties only. We discuss these findings in the context of the effective resolved shear stress relative to the unit Burgers vector for each type of slip, which reveal that the mechanism that governs size effect in this Mg-alloy is

  12. Current-voltage characteristics of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8-{delta}} in the c-axis direction

    SciTech Connect

    Takeya, J.; Akita, S.; Kishio, K.

    1997-06-01

    Current-voltage (I-V) characteristics of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystals were measured in the c-axis direction as a function of temperature and magnetic field parallel to the current. In order to eliminate heating effect, a voltage pulse with a width of 0.5 - 1 {mu}s was applied for each I-V point. The authors found an ohmic region far below the gap voltage. The ohmic resistance increased with decreasing temperature and grew 30 times larger at 4.2 K than that at room temperature. Magnetic field strongly suppressed the critical current but did not change this ohmic resistance. These behaviors can be explained by a semiconductive shunt resistance connected in parallel to a stack of Josephson junctions. By applying two-step voltage pulses, the authors observed a hysteretic feature of the intrinsic Josephson junctions. Crystals with different oxygen contents showed a large variation in critical current, normal resistance, the shunt resistance at low temperature and the degree of hysteresis due to a difference in anisotropy ratios. Utilizing the bistability revealed by the hysteretic feature, the Bi2212 crystal can function as a switching device in the c-direction. A natural stack of many junctions will exhibit large response voltage, which is a great advantage for application to power devices.

  13. Domain-orientation dependence of levitation force in seeded melt grown single-domain YBa{sub 2}Cu{sub 3}O{sub x}

    SciTech Connect

    Shi, D.; Qu, D.; Sagar, S.; Lahiri, K.

    1997-06-01

    Domain-orientation dependence of levitation force has been determined for single-domain YBa{sub 2}Cu{sub 3}O{sub x}. The single-domain material is obtained from a seeded melt growth process. The levitation force has been found to reach a maximum as the c axis of the domain is parallel to the direction of the force. The levitation force decreases in a cosine law fashion as the angle {theta} (the angle between the direction of the force and the c axis) increases from 0{degree} to 60{degree}. A maximum anisotropy of levitation force of 2.29 has been found. A physical model is proposed to explain the observed orientation dependence. {copyright} {ital 1997 American Institute of Physics.}

  14. Assessment of crystal quality and unit cell orientation in epitaxial Cu₂ZnSnSe₄ layers using polarized Raman scattering.

    PubMed

    Krämmer, Christoph; Lang, Mario; Redinger, Alex; Sachs, Johannes; Gao, Chao; Kalt, Heinz; Siebentritt, Susanne; Hetterich, Michael

    2014-11-17

    We use polarization-resolved Raman spectroscopy to assess the crystal quality of epitaxial kesterite layers. It is demonstrated for the example of epitaxial Cu₂ZnSnSe₄ layers on GaAs(001) that "standing" and "lying" kesterite unit cell orientations (c'-axis parallel / perpendicular to the growth direction) can be distinguished by the application of Raman tensor analysis. From the appearance of characteristic intensity oscillations when the sample is rotated one can distinguish polycrystalline and epitaxial layers. The method can be transferred to kesterite layers oriented in any crystal direction and can shed light on the growth of such layers in general. PMID:25402065

  15. Adaptation of BAp crystal orientation to stress distribution in rat mandible during bone growth

    NASA Astrophysics Data System (ADS)

    Nakano, T.; Fujitani, W.; Ishimoto, T.; Umakoshi, Y.

    2009-05-01

    Biological apatite (BAp) c-axis orientation strongly depends on stress distribution in vivo and tends to align along the principal stress direction in bones. Dentulous mandible is subjected to a complicated stress condition in vivo during chewing but few studies have been carried out on the BAp c-axis orientation; so the adaptation of BAp crystal orientation to stress distribution was examined in rat dentulous mandible during bone growth and mastication. Female SD rats 4 to 14 weeks old were prepared, and the bone mineral density (BMD) and BAp crystal orientation were analyzed in a cross-section of mandible across the first molar focusing on two positions: separated from and just under the tooth root on the same cross-section perpendicular to the mesiodistal axis. The degree of BAp orientation was analyzed by a microbeam X-ray diffractometer using Cu-Kα radiation equipped with a detector of curved one-dimensional PSPC and two-dimensional PSPC in the reflection and transmission optics, respectively. BMD quickly increased during bone growth up to 14 weeks, although it was independent of the position from the tooth root. In contrast, BAp crystal orientation strongly depended on the age and the position from the tooth root, even in the same cross-section and direction, especially along the mesiodistal and the biting axes. With increased biting stress during bone growth, the degree of BAp orientation increased along the mesiodistal axis in a position separated from the tooth root more than that near the tooth root. In contrast, BAp preferential alignment clearly appeared along the biting axis near the tooth root. We conclude that BAp orientation rather than BMD sensitively adapts to local stress distribution, especially from the chewing stress in vivo in the mandible.

  16. Pd(0.213)Cd(0.787) and Pd(0.235)Cd(0.765) structures: their long c axis and composite crystals, chemical twinning, and atomic site preferences.

    PubMed

    Schmidt, Joshua Teal; Lee, Stephen; Fredrickson, Daniel C; Conrad, Matthias; Sun, Junliang; Harbrecht, Bernd

    2007-01-01

    We present single-crystal studies of Pd(0.213)Cd(0.787) and Pd(0.235)Cd(0.765), synchrotron powder studies of Pd(1-x)Cd(x), 0.755> or =x> or =0.800, and LDA-DFT and extended Hückel (eH) calculations on these or related phases. The two single-crystal structures have a, b, and c axis lengths of 9.9013(7), 14.0033(10), 37.063(24) and 9.9251(3), 14.0212(7), 60.181(3) A, respectively and they crystallize in the space groups Ccme and F2mm, respectively (solved as (3+1)-dimensional crystals their most convenient superspace group is Xmmm(00gamma)s00). The structures have two different structural components each with their own separate axis parameters. Powder data shows that the ratio of these separate axes (S/L) varies from 1.615 to 1.64, values near the golden mean (1.618). For Pd(0.213)Cd(0.787), different Pd and Cd site occupancies lead to variation in the R factor from 2.6-3.6 %. The site occupancy pattern with the lowest R factor (among the 26 820 variants studied) is the exact site occupancy pattern predicted by LDA-DFT parameterized eH Mulliken charge populations. The phases can be understood through a chemical twinning principle found in gamma-brass, the parent structure for the above phases (a relation with the MgCu(2) Laves phase is also noted). This twinning principle can be used to account for Cd and Pd site preferences. At the same time there is a clean separation among the Cd and Pd atoms for the two separate chain types at height b=0 and 1/2. These results indicate that Cd:Pd stoichiometry plays a role in phase stability. PMID:17091515

  17. Recrystallization fabrics of sheared quartz veins with a strong pre-existing crystallographic preferred orientation from a seismogenic shear zone

    NASA Astrophysics Data System (ADS)

    Price, Nancy A.; Song, Won Joon; Johnson, Scott E.; Gerbi, Christopher C.; Beane, Rachel J.; West, David P.

    2016-07-01

    Microstructural investigations were carried out on quartz veins in schist, protomylonite, and mylonite samples from an ancient seismogenic strike-slip shear zone (Sandhill Corner shear zone, Norumbega fault system, Maine, USA). We interpret complexities in the microstructural record to show that: (1) pre-existing crystallographic preferred orientations (CPO) in the host rock may persist in the new CPO patterns of the shear zone and (2) the inner and outer parts of the shear zone followed diverging paths of fabric development. The host rocks bounding the shear zone contain asymmetrically-folded quartz veins with a strong CPO. These veins are increasingly deformed and recrystallized with proximity to the shear zone core. Matrix-accommodated rotation and recrystallization may position an inherited c-axis maximum in an orientation coincident with rhomb < a > or basal < a > slip. This inherited CPO likely persists in the shear zone fabric as a higher concentration of poles in one hemisphere of the c-axis pole figure, leading to asymmetric crossed girdle or paired maxima c-axis patterns about the foliation plane. Three observed quartz grain types indicate a general trend of localization with decreasing temperature: (1) large (> 100 μm), low aspect ratio (<~5) and (2) high aspect ratio (~ 5-20) grains overprinted by (3) smaller (<~80 μm), low aspect ratio (<~4) grains through subgrain rotation-dominated recrystallization. In the outer shear zone, subgrain rotation recrystallization led to a well-developed c-axis crossed girdle pattern. In the inner shear zone, the larger grains are completely overprinted by smaller grains, but the CPO patterns are relatively poorly developed and are associated with distinctively different misorientation angle histogram profiles ("flat" neighbor-pair profile with similar number fraction for angles from 10 to 90°). This may reflect the preferential activation of grain size sensitive deformation processes in the inner-most part of the

  18. Birefringence imaging and orientation of laser patterned β-BaB2O4 crystals with bending and curved shapes in glass

    NASA Astrophysics Data System (ADS)

    Ogawa, Kazuki; Honma, Tsuyoshi; Komatsu, Takayuki

    2013-11-01

    Nonlinear optical β-BaB2O4 crystals (β-BBO) with bending and curved shapes were patterned at the surface of 8Sm2O3-42BaO-50B2O3 glass by laser irradiations (Yb:YVO4 laser with a wavelength of 1080 nm, power of 0.8 W, and scanning speed of 4 μm/s), and the orientation state of β-BBO crystals was examined from the birefringence imaging obtained by polarization optical microscope (POM) observations. The formation (crystallization) of β-BBO crystals follows along laser scanning direction even if the laser scanning direction changes at a certain point within the bending angle of 60°. The birefringence images indicate that the formation of highly c-axis oriented β-BBO crystals follows along laser scanning direction even if the laser scanning direction changes, and in particular the direction of the c-axis of β-BBO crystals changes gradually at the bending point. The model for the orientation of the c-axis of β-BBO near the bending point is proposed. The present study proposes that the laser-induced crystallization opens a new door for the science and technology in crystal growth engineering.

  19. Crossover Fields in Grain-Boundary Flux Pinning in Magnesium Diboride Films with Columnar Grains

    NASA Astrophysics Data System (ADS)

    Kim, D. H.; Hwang, T. J.; Seong, W. K.; Kang, W. N.

    We studied temperature and magnetic-field dependence of grain boundary pinning effect in MgB2 films with columnar grains by measuring the angular dependence of the resistivity and the critical current density (Jc). MgB2 films grown by using a hybrid physical chemical vapor deposition method under appropriate conditions exhibit a peculiar columnar growth with their columns oriented along the c axis. The pinning effect by grain boundaries was manifested in the comparable or even higher Jc for magnetic fields (H) parallel to the c axis (H‖c) than that for fields parallel to the ab plane (H‖ab) below certain temperature-dependent crossover fields. The crossover field, Bcr, was around 1.6 T at 5 K and decreased to around 0.9 T at 30 K depending weakly on the sample characters, and Bcr lay well below the upper critical fields in the phase diagram. Above Bcr, Jc for H‖c decreased very rapidly. The vortex spacing at Bcr was closely correlated with the temperature dependence of the penetration depth, indicating that the degree of the vortex-vortex overlap is an important parameter to determine the number of vortices allowed per unit length of grain boundaries. Thus, Bcr was thought to demarcate the accommodation capability of flux lines by the grain boundaries, and a rapid decrease of Jc above Bcr was ascribed to flux motion of the less strongly pinned vortices located away from the grain boundaries.

  20. Orienting hypnosis.

    PubMed

    Hope, Anna E; Sugarman, Laurence I

    2015-01-01

    This article presents a new frame for understanding hypnosis and its clinical applications. Despite great potential to transform health and care, hypnosis research and clinical integration is impaired in part by centuries of misrepresentation and ignorance about its demonstrated efficacy. The authors contend that advances in the field are primarily encumbered by the lack of distinct boundaries and definitions. Here, hypnosis, trance, and mind are all redefined and grounded in biological, neurological, and psychological phenomena. Solutions are proposed for boundary and language problems associated with hypnosis. The biological role of novelty stimulating an orienting response that, in turn, potentiates systemic plasticity forms the basis for trance. Hypnosis is merely the skill set that perpetuates and influences trance. This formulation meshes with many aspects of Milton Erickson's legacy and Ernest Rossi's recent theory of mind and health. Implications of this hypothesis for clinical skills, professional training, and research are discussed. PMID:25928677

  1. EDITORIAL: Optical orientation Optical orientation

    NASA Astrophysics Data System (ADS)

    SAME ADDRESS *, Yuri; Landwehr, Gottfried

    2008-11-01

    priority of the discovery in the literature, which was partly caused by the existence of the Iron Curtain. I had already enjoyed contact with Boris in the 1980s when the two volumes of Landau Level Spectroscopy were being prepared [2]. He was one of the pioneers of magneto-optics in semiconductors. In the 1950s the band structure of germanium and silicon was investigated by magneto-optical methods, mainly in the United States. No excitonic effects were observed and the band structure parameters were determined without taking account of excitons. However, working with cuprous oxide, which is a direct semiconductor with a relative large energy gap, Zakharchenya and his co-worker Seysan showed that in order to obtain correct band structure parameters, it is necessary to take excitons into account [3]. About 1970 Boris started work on optical orientation. Early work by Hanle in Germany in the 1920s on the depolarization of luminescence in mercury vapour by a transverse magnetic field was not appreciated for a long time. Only in the late 1940s did Kastler and co-workers in Paris begin a systematic study of optical pumping, which led to the award of a Nobel prize. The ideas of optical pumping were first applied by Georges Lampel to solid state physics in 1968. He demonstrated optical orientation of free carriers in silicon. The detection method was nuclear magnetic resonance; optically oriented free electrons dynamically polarized the 29Si nuclei of the host lattice. The first optical detection of spin orientation was demonstrated by with the III-V semiconductor GaSb by Parsons. Due to the various interaction mechanisms of spins with their environment, the effects occurring in semiconductors are naturally more complex than those in atoms. Optical detection is now the preferred method to detect spin alignment in semiconductors. The orientation of spins in crystals pumped with circularly polarized light is deduced from the degree of circular polarization of the recombination

  2. Hydroxyapatite coatings with oriented nanoplate and nanorod arrays: Fabrication, morphology, cytocompatibility and osteogenic differentiation.

    PubMed

    Chen, Wei; Tian, Bo; Lei, Yong; Ke, Qin-Fei; Zhu, Zhen-An; Guo, Ya-Ping

    2016-10-01

    Hydroxyapatite (HA) crystals exhibit rod-like shape with c-axis orientation and plate-like shape with a(b)-axis orientation in vertebrate bones and tooth enamel surfaces, respectively. Herein, we report the synthesis of HA coatings with the oriented nanorod arrays (RHACs) and HA coatings with oriented nanoplate arrays (PHACs) by using bioglass coatings as sacrificial templates. After soaking in simulated body fluid (SBF) at 120°C, the bioglass coatings are hydrothermally converted into the HA coatings via a dissolution-precipitation reaction. If the Ca/P ratios in SBF are 2.50 and 1.25, the HA crystals on the coatings are oriented nanorod arrays and oriented nanoplate arrays, respectively. Moreover, the bioglass coatings are treated with SBF at 37°C, plate-like HA coatings with a low crystallinity (SHACs) are prepared. As compared with the Ti6Al4V and SHACs, the human bone marrow stromal cells (hBMSCs) on the RHACs and PHACs have better cell adhesion, spreading, proliferation and osteogenic differentiation because of their moderately hydrophilic surfaces and similar chemical composition, morphology and crystal orientation to human hard tissues. Notably, the morphologies of HA crystals have no obvious effects on cytocompatibility and osteogenic differentiation. Hence, the HA coatings with oriented nanoplate arrays or oriented nanorod arrays have a great potential for orthopedic applications. PMID:27287136

  3. EDITORIAL: Optical orientation Optical orientation

    NASA Astrophysics Data System (ADS)

    SAME ADDRESS *, Yuri; Landwehr, Gottfried

    2008-11-01

    priority of the discovery in the literature, which was partly caused by the existence of the Iron Curtain. I had already enjoyed contact with Boris in the 1980s when the two volumes of Landau Level Spectroscopy were being prepared [2]. He was one of the pioneers of magneto-optics in semiconductors. In the 1950s the band structure of germanium and silicon was investigated by magneto-optical methods, mainly in the United States. No excitonic effects were observed and the band structure parameters were determined without taking account of excitons. However, working with cuprous oxide, which is a direct semiconductor with a relative large energy gap, Zakharchenya and his co-worker Seysan showed that in order to obtain correct band structure parameters, it is necessary to take excitons into account [3]. About 1970 Boris started work on optical orientation. Early work by Hanle in Germany in the 1920s on the depolarization of luminescence in mercury vapour by a transverse magnetic field was not appreciated for a long time. Only in the late 1940s did Kastler and co-workers in Paris begin a systematic study of optical pumping, which led to the award of a Nobel prize. The ideas of optical pumping were first applied by Georges Lampel to solid state physics in 1968. He demonstrated optical orientation of free carriers in silicon. The detection method was nuclear magnetic resonance; optically oriented free electrons dynamically polarized the 29Si nuclei of the host lattice. The first optical detection of spin orientation was demonstrated by with the III-V semiconductor GaSb by Parsons. Due to the various interaction mechanisms of spins with their environment, the effects occurring in semiconductors are naturally more complex than those in atoms. Optical detection is now the preferred method to detect spin alignment in semiconductors. The orientation of spins in crystals pumped with circularly polarized light is deduced from the degree of circular polarization of the recombination

  4. Oriental noodles.

    PubMed

    Hou, G

    2001-01-01

    Oriental noodles have been consumed for thousands of years and remain an important part in the diet of many Asians. There is a wide variety of noodles in Asia with many local variations as result of differences in culture, climate, region and a host of other factors. In this article noodle classification, formulation, processing and evaluation are reviewed, with emphasis on eight major types. Wheat quality requirements, basic flour specifications, ingredient functions, and production variables are identified for different noodles. In the evaluation of flour for noodle making, three key quality attributes are considered: processability, noodle color and texture. Noodle process behavior is particularly important in the modern industrial production. Each noodle type has its own unique color and texture characteristics. Flour color, protein content, ash content, yellow pigment and polyphenol oxidase activity are important factors responsible for noodle color. Starch characteristics, protein content and quality play major roles in governing the texture of cooked noodles. However, the relative importance of starch and proteins varies considerably with noodle type. Starch pasting quality is the primary trait determining the eating quality of Japanese and Korean noodles that are characterized by soft and elastic texture, while protein quantity and strength are very important to Chinese-type noodles that require firm bite and chewy texture. Other factors such as ingredients added in the noodle formula and processing variables used during noodle preparation also affect the cooked noodle texture as well. PMID:11285682

  5. Mechanism of Calcite Co-Orientation in the Sea Urchin Tooth

    SciTech Connect

    Killian, Christopher; Metzler, Rebecca; Gong, Y. U. T.; Olson, Ian; Aizenberg, Joanna; Politi, Yael; Wilt, Fred; Scholl, Andreas; Young, Anthony; Doran, Andrew; Kunz, Martin; Tamura, Nobumichi; Coppersmith, Susan; Gilbert, P. U. P. A.

    2009-12-01

    Sea urchin teeth are remarkable and complex calcite structures, continuously growing at the forming end and self-sharpening at the mature grinding tip. The calcite (CaCO{sub 3}) crystals of tooth components, plates, fibers, and a high-Mg polycrystalline matrix, have highly co-oriented crystallographic axes. This ability to co-orient calcite in a mineralized structure is shared by all echinoderms. However, the physico-chemical mechanism by which calcite crystals become co-oriented in echinoderms remains enigmatic. Here, we show differences in calcite c-axis orientations in the tooth of the purple sea urchin (Strongylocentrotus purpuratus), using high-resolution X-ray photoelectron emission spectromicroscopy (X-PEEM) and microbeam X-ray diffraction ({mu}XRD). All plates share one crystal orientation, propagated through pillar bridges, while fibers and polycrystalline matrix share another orientation. Furthermore, in the forming end of the tooth, we observe that CaCO{sub 3} is present as amorphous calcium carbonate (ACC). We demonstrate that co-orientation of the nanoparticles in the polycrystalline matrix occurs via solid-state secondary nucleation, propagating out from the previously formed fibers and plates, into the amorphous precursor nanoparticles. Because amorphous precursors were observed in diverse biominerals, solid-state secondary nucleation is likely to be a general mechanism for the co-orientation of biomineral components in organisms from different phyla.

  6. Spin orientation, structure, morphology, and magnetic properties of hematite nanoparticles

    NASA Astrophysics Data System (ADS)

    Xu, S.; Habib, A. H.; Gee, S. H.; Hong, Y. K.; McHenry, M. E.

    2015-05-01

    Monodisperse hematite (α-Fe2O3) nanoparticles were synthesized by forced hydrolysis of acidic Fe3+ solution. Rietveld analysis was applied to the X-ray powder diffraction data to refine the lattice constants and atomic positions. The lattice constants for a hexagonal unit cell were determined to be a ˜ 0.50327 and c ˜ 1.37521 nm. High resolution transmission electron microscopy was employed to study the morphology of the particles. Atomic scale micrographs and diffraction patterns from several zone axes were obtained. These reveal the high degree of crystallinity of the particles. A series of observations made on the particles by tilting them through a range of ±45° revealed the particles to be micaceous with stacking of platelets with well defined crystallographic orientations. The Morin transition in these nanoparticles was found to occur at 210 K, which is lower temperature than 263 K of bulk hematite. It was ascertained from the previous Mössbauer studies that the spin orientation for nano-sized hematite particle flips from 90° to 28° with respect to the c-axis of the hexagonal structure during the Morin transition, which is in contrast to that observed in bulk hematite where spin orientation flips from 90° to 0°.

  7. Spin orientation, structure, morphology, and magnetic properties of hematite nanoparticles

    SciTech Connect

    Xu, S.; Habib, A. H.; Gee, S. H.; Hong, Y. K.; McHenry, M. E.

    2015-05-07

    Monodisperse hematite (α-Fe{sub 2}O{sub 3}) nanoparticles were synthesized by forced hydrolysis of acidic Fe{sup 3+} solution. Rietveld analysis was applied to the X-ray powder diffraction data to refine the lattice constants and atomic positions. The lattice constants for a hexagonal unit cell were determined to be a ∼ 0.50327 and c ∼ 1.37521 nm. High resolution transmission electron microscopy was employed to study the morphology of the particles. Atomic scale micrographs and diffraction patterns from several zone axes were obtained. These reveal the high degree of crystallinity of the particles. A series of observations made on the particles by tilting them through a range of ±45° revealed the particles to be micaceous with stacking of platelets with well defined crystallographic orientations. The Morin transition in these nanoparticles was found to occur at 210 K, which is lower temperature than 263 K of bulk hematite. It was ascertained from the previous Mössbauer studies that the spin orientation for nano-sized hematite particle flips from 90° to 28° with respect to the c-axis of the hexagonal structure during the Morin transition, which is in contrast to that observed in bulk hematite where spin orientation flips from 90° to 0°.

  8. Crystallographic orientation inhomogeneity and crystal splitting in biogenic calcite

    PubMed Central

    Checa, Antonio G.; Bonarski, Jan T.; Willinger, Marc G.; Faryna, Marek; Berent, Katarzyna; Kania, Bogusz; González-Segura, Alicia; Pina, Carlos M.; Pospiech, Jan; Morawiec, Adam

    2013-01-01

    The calcitic prismatic units forming the outer shell of the bivalve Pinctada margaritifera have been analysed using scanning electron microscopy–electron back-scatter diffraction, transmission electron microscopy and atomic force microscopy. In the initial stages of growth, the individual prismatic units are single crystals. Their crystalline orientation is not consistent but rather changes gradually during growth. The gradients in crystallographic orientation occur mainly in a direction parallel to the long axis of the prism, i.e. perpendicular to the shell surface and do not show preferential tilting along any of the calcite lattice axes. At a certain growth stage, gradients begin to spread and diverge, implying that the prismatic units split into several crystalline domains. In this way, a branched crystal, in which the ends of the branches are independent crystalline domains, is formed. At the nanometre scale, the material is composed of slightly misoriented domains, which are separated by planes approximately perpendicular to the c-axis. Orientational gradients and splitting processes are described in biocrystals for the first time and are undoubtedly related to the high content of intracrystalline organic molecules, although the way in which these act to induce the observed crystalline patterns is a matter of future research. PMID:23804442

  9. Nanoscale imaging of grain orientations and ferroelectric domains in (Bi1-xLax)4Ti3O12 films for ferroelectric memories

    NASA Astrophysics Data System (ADS)

    Yang, B.; Park, N. J.; Seo, B. I.; Oh, Y. H.; Kim, S. J.; Hong, S. K.; Lee, S. S.; Park, Y. J.

    2005-08-01

    We report results of nanoscopic investigation of grain crystallographic orientations and ferroelectric domains by electron backscatter diffraction (EBSD) technique and piezoresponse force microscope (PFM), respectively, in (Bi1-xLax)4Ti3O12 (BLT) films for ferroelectric semiconductor memories. It is demonstrated that the EBSD technique is useful in characterizing nanoscale grain crystallographic orientations of BLT films. Comparison studies of grain orientations by EBSD technique and switching properties of ferroelectric domains by PFM show that c-axis parallel to normal oriented grains with almost linear dielectric properties have platelike morphology. However, a- or b-axis oriented grains with superior ferroelectric properties have ellipsoidal morphology with a size of less than 0.2μm in long axis. Consequently, the suppression of the platelike structures through process controls is important for the realization of high-density BLT-based memories.

  10. Determination of crystallographic orientation of lead-free piezoelectric (K,Na)NbO3 epitaxial thin films grown on SrTiO3 (100) surfaces

    NASA Astrophysics Data System (ADS)

    Yu, Qi; Zhu, Fang-Yuan; Cheng, Li-Qian; Wang, Ke; Li, Jing-Feng

    2014-03-01

    Crystallographic structure of sol-gel-processed lead-free (K,Na)NbO3 (KNN) epitaxial films on [100]-cut SrTiO3 single-crystalline substrates was investigated for a deeper understanding of its piezoelectric response. Lattice parameter measurement by high-resolution X-ray diffraction and transmission electron microscopy revealed that the orthorhombic KNN films on SrTiO3 (100) surfaces are [010] oriented (b-axis-oriented) rather than commonly identified c-axis orientation. Based on the crystallographic orientation and corresponding ferroelectric domain structure investigated by piezoresponse force microscopy, the superior piezoelectric property along b-axis of epitaxial KNN films than other orientations can be explained.

  11. Magnetic properties of in-plane oriented barium hexaferrite thin films prepared by direct current magnetron sputtering

    SciTech Connect

    Zhang, Xiaozhi; Yue, Zhenxing Meng, Siqin; Yuan, Lixin

    2014-12-28

    In-plane c-axis oriented Ba-hexaferrite (BaM) thin films were prepared on a-plane (112{sup ¯}0) sapphire (Al{sub 2}O{sub 3}) substrates by DC magnetron sputtering followed by ex-situ annealing. The DC magnetron sputtering was demonstrated to have obvious advantages over the traditionally used RF magnetron sputtering in sputtering rate and operation simplicity. The sputtering power had a remarkable influence on the Ba/Fe ratio, the hematite secondary phase, and the grain morphology of the as-prepared BaM films. Under 80 W of sputtering power, in-plane c-axis highly oriented BaM films were obtained. These films had strong magnetic anisotropy with high hysteresis loop squareness (M{sub r}/M{sub s} of 0.96) along the in-plane easy axis and low M{sub r}/M{sub s} of 0.03 along the in-plane hard axis. X-ray diffraction patterns and pole figures revealed that the oriented BaM films grew via an epitaxy-like growth process with the crystallographic relationship BaM (101{sup ¯}0)//α-Fe{sub 2}O{sub 3}(112{sup ¯}0)//Al{sub 2}O{sub 3}(112{sup ¯}0)

  12. Orientation alignment of epitaxial LiCoO2 thin films on vicinal SrTiO3 (100) substrates

    NASA Astrophysics Data System (ADS)

    Nishio, Kazunori; Ohnishi, Tsuyoshi; Mitsuishi, Kazutaka; Ohta, Narumi; Watanabe, Ken; Takada, Kazunori

    2016-09-01

    LiCoO2 is epitaxially grown on SrTiO3 (100) substrates with (104) orientation. Because the LiCoO2 film is grown with its c-axis parallel to four equivalent <111> axes of the SrTiO3, the (104)-oriented film exhibits four-domain structure on the SrTiO3 (100) substrate. Introducing off-cut angle to the substrate surface breaks the equivalency between the four <111> axes of the SrTiO3 substrate to induce preferential growth of specific orientation with the c-axis in a descending direction of off-cut surface. Increasing off-cut angle and lowering deposition rate promote the preferential growth, because they facilitate step-flow growth mode, and finally align the c-axes in the domains completely into one <111> direction of the SrTiO3 substrate. The LiCoO2 film delivers a discharge capacity of 90 mAh g-1 at a low discharge rate of 0.01 C, and 25% of capacity is kept even at a high rate of discharge with 100 C.

  13. Distinct crystallinity and orientations of hydroxyapatite thin films deposited on C- and A-plane sapphire substrates

    NASA Astrophysics Data System (ADS)

    Akazawa, Housei; Ueno, Yuko

    2014-10-01

    We report how the crystallinity and orientation of hydroxyapatite (HAp) films deposited on sapphire substrates depend on the crystallographic planes. Both solid-phase crystallization of amorphous HAp films and crystallization during sputter deposition at elevated temperatures were examined. The low-temperature epitaxial phase on C-plane sapphire substrates has c-axis orientated HAp crystals regardless of the crystallization route, whereas the preferred orientation switches to the (310) direction at higher temperatures. Only the symmetric stretching mode (ν1) of PO43- units appears in the Raman scattering spectra, confirming well-ordered crystalline domains. In contrast, HAp crystals grown on A-plane sapphire substrates are always oriented toward random orientations. Exhibiting all vibrational modes (ν1, ν3, and ν4) of PO43- units in the Raman scattering spectra reflects random orientation, violating the Raman selection rule. If we assume that Raman intensities of PO43- units represent the crystallinity of HAp films, crystallization terminating the surface with the C-plane is hindered by the presence of excess H2O and OH species in the film, whereas crystallization at random orientations on the A-plane sapphire is rather promoted by these species. Such contrasting behaviors between C-plane and A-plane substrates will reflect surface-plane dependent creation of crystalline seeds and eventually determine the orientation of resulting HAp films.

  14. Orientational coupling between the vortex lattice and the crystalline lattice in a weakly pinned Co0.0075NbSe2 single crystal

    NASA Astrophysics Data System (ADS)

    Ganguli, Somesh Chandra; Singh, Harkirat; Ganguly, Rini; Bagwe, Vivas; Thamizhavel, Arumugam; Raychaudhuri, Pratap

    2016-04-01

    We report experimental evidence of strong orientational coupling between the crystal lattice and the vortex lattice in a weakly pinned Co-doped NbSe2 single crystal through direct imaging using low temperature scanning tunneling microscopy/spectroscopy. When the magnetic field is applied along the six-fold symmetric c-axis of the NbSe2 crystal, the basis vectors of the vortex lattice are preferentially aligned along the basis vectors of the crystal lattice. The orientational coupling between the vortex lattice and crystal lattice becomes more pronounced as the magnetic field is increased. This orientational coupling enhances the stability of the orientational order of the vortex lattice, which persists even in the disordered state at high fields where dislocations and disclinations have destroyed the topological order. Our results underpin the importance of crystal lattice symmetry on the vortex state phase diagram of weakly pinned type II superconductors.

  15. Lateral orientation (image)

    MedlinePlus

    A lateral orientation is a position away from the midline of the body. For instance, the arms are lateral to the ... ears are lateral to the head. A medial orientation is a position toward the midline of the ...

  16. Theories of Sexual Orientation.

    ERIC Educational Resources Information Center

    Storms, Michael D.

    1980-01-01

    Results indicated homosexuals, heterosexuals, and bisexuals did not differ within each sex on measures of masculinity and femininity. Strong support was obtained for the hypothesis that sexual orientation relates primarily to erotic fantasy orientation. (Author/DB)

  17. TEM characterization of microstructure and chemistry in magnesium diboride superconductor

    NASA Astrophysics Data System (ADS)

    Zhu, Ye

    MgB2 is a superconductor with promising properties, but to meet application requirements, the properties of MgB2 have to be improved through microstructure modifications: chemical doping, introduction of precipitates, and atomic-scale control of defects. The small length scale of these modifications means that structure and chemistry characterization using the transmission electron microscope (TEM) are required to better understand the correlation between MgB2's superconducting properties and its microstructure. We have used TEM-based techniques to characterize microstructures of pure MgB2 bulks, SiC-doped MgB2 tapes, pure and C-doped MgB2 thin films prepared by hybrid physical-chemical vapor deposition (HPCVD) method with different carbon precursors, degraded pure HPCVD thin films, and O-doped MgB2 thin films prepared by molecular beam epitaxy. Characterization results and effects of microstructure on superconducting properties are discussed for each material. We have found that in pure MgB2 the main contaminating current-blocking phases are MgO grains and amorphous MgO + boron + BxO y phases. Both second phase nano-segregations and grain boundaries are effective pinning defects in MgB2, which can enhance Jc(H) at high fields. However, second phases also act as current-blocking phases that reduce the measured Jc, which suggests that MgB2 samples with small grain size and without any boundary second phases are desirable to achieve higher Jc. Extensive studies have been made to understand the Hc 2 enhancement mechanisms in MgB2. Both carbon dopant and grain boundaries in MgB2 can cause more electron scattering that increases Hc2. Degradation in MgB 2 leads to the formation of the amorphous boundary phase which also enhances Hc2 by introducing electron scattering. The over 60 T Hc2 ||ab obtained in C-doped HPCVD MgB 2 films is caused by the two-band nature and strong pi-band scattering of MgB2. We believe that the strain fields generated from c-axis tilt boundaries

  18. Effect of hydrogen in controlling the structural orientation of ZnO:Ga:H as transparent conducting oxide films suitable for applications in stacked layer devices.

    PubMed

    Mondal, Praloy; Das, Debajyoti

    2016-07-27

    Hydrogenation of the ZnO:Ga network has been chosen as a promising avenue to further upgrade the optoelectronic and structural properties of the films. With an optimum incorporation of hydrogen at a low substrate temperature (TS = 100 °C) in RF magnetron sputtering plasma, the ZnO:Ga:H film, with a large crystallite size (∼17 nm) and improved crystallinity along the optimally preferred c-axis orientation with respect to both the 〈100〉 (I〈002〉/I〈100〉 ∼ 74) and 〈103〉 (I〈002〉/I〈103〉 ∼ 10) directions, attains a high electrical conductivity (σ ∼ 1.5 × 10(3)) and ∼90% visible range optical transmission that yields a wide optical band gap of ∼3.78 eV. The dominant c-axis orientation of the ZnO crystals exhibits a distinct UV luminescence band at ∼340 nm that arises as a result of the typical exciton emission or near-band-edge emission, which occurs due to the recombination of photo-generated electrons and holes in the valence band or in traps near the valence band. Vacancies created by the out diffusion of oxygen from the network induces the growth along the 〈103〉 crystallographic orientation. With the introduction of an optimum amount of hydrogen into the network, the VO peak (OII) in the O 1s XPS spectrum significantly reduces in intensity while the Zn-OH peak (OIII) increases, indicating enhanced surface absorption of O species, which causes the improvement of c-axis orientation. The increase in the conductivity has been attributed to the centers assigned to isolated hydrogen atoms in the anti-bonding sites (ABO) or bond-centered sites of O-Zn bonds (BC), and Zn vacancies passivated by one or two hydrogen atoms. Hydrogen-induced dopant-like defects in the film and the associated large amount of tensile stress developed within the network has been correlated to the high conductivity and the wide band gap of the ZnO:Ga:H film due to the decreased repulsion between the O 2p and the Zn 4s bands and the Burstein-Moss effect as a

  19. Measurement of Optical Functions of Highly Oriented Pyrolytic Graphite in the Visible

    SciTech Connect

    Jellison Jr, Gerald Earle; Hunn, John D; Lee, Ho Nyung

    2007-01-01

    The spectroscopic dielectric functions of highly oriented pyrolytic graphite (HOPG) are determined at 9 different wavelengths from 405 to 750 nm (3.06 to 1.65 eV). This determination is made on the basis of two ellipsometry measurements: 1) Standard ellipsometry measurements are performed on HOPG with the c-axis perpendicular to the sample surface, and 2) Two-modulator generalized ellipsometry microscope (2-MGEM) measurements are performed on HOPG cut and polished such that the c-axis is parallel to the sample surface. Both the ordinary and extraordinary complex dielectric functions show non-zero absorption throughout the observed spectral range, while the ordinary dielectric function shows Drude-like behavior at longer wavelengths. From this, it can be concluded that graphite is metallic for visible light polarized parallel to the graphene planes, but acts more as a semiconductor or semimetal for visible light polarized perpendicular to the graphene planes. The 2-MGEM technique can also be used to generate images of the diattenuation, retardation, and direction of the principal axis.

  20. Electron back-scattering diffraction (EBSD) measurements of antigorite lattice-preferred orientations (LPO).

    PubMed

    van de Moortèle, B; Bezacier, L; Trullenque, G; Reynard, B

    2010-09-01

    Lattice preferred orientations of serpentines induce a strong anisotropy of various properties in serpentine bearing-rocks. Lattice preferred orientations had so far been obtained only by X-ray diffraction techniques. We have applied electron back-scattering diffraction to the measurement of the lattice preferred orientations of antigorite in a naturally deformed high-pressure serpentinite. This technique is very sensitive to sample preparation that can lead to surface amorphization in the case of serpentine. A polishing procedure is described that avoids amorphization and allows accurate electron back-scattering diffraction measurements with optimized experimental conditions in a variable pressure scanning electron microscope. Results indicate that deformation leads to lattice preferred orientations characterized by extremely strong c-axis clustering perpendicular to the foliation, as expected for a layered silicate. In the foliation plane, a significant clustering of the a-axis is observed and tentatively attributed to intracrystalline deformation mechanisms. These data suggest that antigorite deforms mostly by gliding along the basal plane of the layered phyllosilicate structure, but that gliding may occur along directions favouring a-axis alignment. Electron back-scattering diffraction appears to be a reliable method for determining phyllosilicate lattice preferred orientations in deformed rocks, with potential applications for determining anisotropy of properties like seismic velocities or thermal and electrical conductivities. PMID:20701663

  1. Crystallographic preferred orientation of akimotoite and seismic anisotropy of Tonga slab.

    PubMed

    Shiraishi, Rei; Ohtani, Eiji; Kanagawa, Kyuichi; Shimojuku, Akira; Zhao, Dapeng

    2008-10-01

    The mineral akimotoite, ilmenite-structured MgSiO(3), exists at the bottom of the Earth's mantle transition zone and within the uppermost lower mantle, especially under low-temperature conditions. Akimotoite is thought to be a major constituent of the harzburgite layer of subducting slabs, and the most anisotropic mineral in the mantle transition zone. It has been predicted that if akimotoite crystals are preferentially oriented by plastic deformation, a cold subducted slab would be extremely anisotropic. However, there have been no studies of crystallographic preferred orientations and very few reports of plastic deformation experiments for MgSiO(3) ilmenite. Here we present plastic deformation experiments on polycrystalline akimotoite, which were conducted at confining pressures of 20-22 GPa and temperatures of 1,000-1,300 degrees C. We found a change in crystallographic preferred orientation pattern of akimotoite with temperature, where the c-axis maximum parallel to the compression direction develops at high temperature, whereas the c axes are preferentially oriented parallel to the shear direction or perpendicular to the compression direction at lower temperature. The previously reported difference in compressional-wave seismic anisotropy between the northern and southern segments of the Tonga slab at depths of the mantle transition zone can conceivably be attributed to the difference in the crystallographic preferred orientation pattern of akimotoite at varying temperature within the slab. PMID:18833278

  2. Determination of crystallographic orientation of lead-free piezoelectric (K,Na)NbO{sub 3} epitaxial thin films grown on SrTiO{sub 3} (100) surfaces

    SciTech Connect

    Yu, Qi; Zhu, Fang-Yuan; Cheng, Li-Qian; Wang, Ke; Li, Jing-Feng

    2014-03-10

    Crystallographic structure of sol-gel-processed lead-free (K,Na)NbO{sub 3} (KNN) epitaxial films on [100]-cut SrTiO{sub 3} single-crystalline substrates was investigated for a deeper understanding of its piezoelectric response. Lattice parameter measurement by high-resolution X-ray diffraction and transmission electron microscopy revealed that the orthorhombic KNN films on SrTiO{sub 3} (100) surfaces are [010] oriented (b-axis-oriented) rather than commonly identified c-axis orientation. Based on the crystallographic orientation and corresponding ferroelectric domain structure investigated by piezoresponse force microscopy, the superior piezoelectric property along b-axis of epitaxial KNN films than other orientations can be explained.

  3. Preferential growth orientation of laser-patterned LiNbO{sub 3} crystals in lithium niobium silicate glass

    SciTech Connect

    Komatsu, T.; Koshiba, K.; Honma, T.

    2011-02-15

    Dots and lines consisting of LiNbO{sub 3} crystals are patterned on the surface of 1CuO-40Li{sub 2}O-32Nb{sub 2}O{sub 5}-28SiO{sub 2} (mole ratio) glass by irradiations of continuous-wave Nd:YAG laser (wavelength: {lambda}=1064 nm), diode laser ({lambda}=795 nm), and Yb:YVO{sub 4} fiber laser ({lambda}=1080 nm), and the feature of laser-patterned LiNbO{sub 3} crystal growth is examined from linearly polarized micro-Raman scattering spectrum measurements. LiNbO{sub 3} crystals with the c-axis orientation are formed at the edge parts of the surface and cross-section of dots. The growth direction of an LiNbO{sub 3} along the laser scanning direction is the c-axis. It is proposed that the profile of the temperature distribution in the laser-irradiated region and its change along laser scanning would be one of the most important conditions for the patterning of crystals with a preferential growth orientation. Laser irradiation giving a narrow width is also proposed to be one of the important factors for the patterning of LiNbO{sub 3} crystal lines with homogeneous surface morphologies. -- Graphical abstract: Polarized optical microscope observations for the surface and cross-section of the dot obtained by LD laser ({lambda}=795 nm) irradiations of P=1.4 W and t=20 s in Cu-LNS glass. Schematic model for the orientation of LiNbO{sub 3} crystals at the edge parts of the surface and cross-section of the dot is also shown. Display Omitted Research highlights: > Dots and lines with LiNbO{sub 3} crystals are patterned on the glass surface by laser irradiations. > LiNbO{sub 3} crystals with the c-axis orientation are formed at the edge parts of the surface and cross-section of dots. > The profile of the temperature distribution in the laser-irradiated region is one of the most important conditions for the patterning of highly oriented crystals.

  4. Partial decoupling between strain and polarization in mono-oriented Pb(Zr0.2Ti0.8)O3 thin film

    NASA Astrophysics Data System (ADS)

    Janolin, Pierre-Eymeric; Fraisse, Bernard; Le Marrec, Françoise; Dkhil, Brahim

    2007-05-01

    The structural evolution of epitaxial mono-oriented (i.e., with the c axis perpendicular to the interface) ferroelectric Pb(Zr0.2Ti0.8)O3 thin film has been investigated, using high-resolution, temperature dependent, x-ray diffraction. The full set of lattice parameters was obtained; it allowed to estimate the variation of the polarization as a function of temperature, underlying the difference between the polarization-induced tetragonality and the elastic one. The temperature evolution of the misfit strain has been calculated and found to be in good agreement with the theoretical temperature-misfit strain phase diagram.

  5. Convex Image Orientation from Relative Orientations

    NASA Astrophysics Data System (ADS)

    Reich, M.; Heipke, C.

    2016-06-01

    In this paper we propose a novel workflow for the estimation of global image orientations given relative orientations between pairs of overlapping images. Our approach is convex and independent on initial values. First, global rotations are estimated in a relaxed semidefinite program (SDP) and refined in an iterative least squares adjustment in the tangent space of SO(3). A critical aspect is the handling of outliers in the relative orientations. We present a novel heuristic graph based approach for filtering the relative rotations that outperforms state-of-the-art robust rotation averaging algorithms. In a second part we make use of point-observations, tracked over a set of overlapping images and formulate a linear homogeneous system of equations to transfer the scale information between triplets of images, using estimated global rotations and relative translation directions. The final step consists of refining the orientation parameters in a robust bundle adjustment. The proposed approach handles outliers in the homologous points and relative orientations in every step of the processing chain. We demonstrate the robustness of the procedure on synthetic data. Moreover, the performance of our approach is illustrated on real world benchmark data.

  6. Influences of Crystalline Anisotropy, Doping, Porosity, and Connectivity on the Critical Current Densities of Superconducting Magnesium Diboride Bulks, Wires, and Thin Films

    NASA Astrophysics Data System (ADS)

    Susner, Michael Adam

    Magnesium diboride (MgB2) is a material with a superconducting transition temperature of 39 K. Discovered in 2001, the relatively large coherence length (and associated lack of weak links) together with its simple binary composition (making phase pure formation relatively easy) have made it a material of substantial interest. However, it has been difficult to assess in detail the relative importance of the roles of flux pinning, crystalline anisotropy, porosity, connectivity, doping, and doping homogeneity on the observed transport limitations of this conductor. This work focused on deconvoluting the most dominant of these effects. First, the overall effects of electrical connectivity and crystalline anisotropy of critical current density (Jc) were investigated. In doing so the Jcs of dense, well-connected c-axis oriented films were compared with the relatively degraded Jcs of standard powder-in-tube MgB2 wires. With the aid of a percolation model it was deduced that at 4.2 K, 10 T. about 60% of the degradation was due to MgB2’s crystalline anisotropy and the remaining 40% to porosity. Second, chemical substitutions onto both the Mg and B sites were investigated in terms of effects on structure and superconducting properties. The homogeneity of C-substitution onto the B site was quantified in terms of the width of the superconducting specific heat transition. Analysis of the results led to optimization of methods for homogeneous doping of C into the B sublattice. Zr substituted onto the Mg sublattice was investigated using samples prepared by pulsed laser deposition (PLD). Changes in magnetic, resistive, superconductive, chemical, and structural properties were studied over a wide range of Zr composition.

  7. Microstructure and Grain Orientation Evolution in Sn-3.0Ag-0.5Cu Solder Interconnects Under Electrical Current Stressing

    NASA Astrophysics Data System (ADS)

    Chen, Hongtao; Hang, Chunjin; Fu, Xing; Li, Mingyu

    2015-10-01

    In situ observation was performed on cross-sections of Sn-3.0Ag-0.5Cu solder interconnects to track the evolution of microstructure and grain orientation under electrical current stressing. Cross-sections of Cu/Ni-Sn-3.0Ag-0.5Cu-Ni/Cu sandwich-structured solder interconnects were prepared by the standard metallographic method and subjected to electrical current stressing for different times. The electron backscatter diffraction technique was adopted to characterize the grain orientation and structure of the solder interconnects. The results show that metallization dissolution and intermetallic compound (IMC) migration have close relationships with the grain orientation and structure of the solder interconnects. Ni metallization dissolution at the cathode interface and IMC migration in the solder bulk can be accelerated when the c-axis of the grain is parallel to the electron flow direction, while no observable change was found when the c-axis of the grain was perpendicular to the electron flow direction. IMC can migrate along or be blocked at the grain boundary, depending on the misorientation between the current flow direction and grain boundary.

  8. Low-temperature oriented growth of vanadium dioxide films on CoCrTa metal template on Si and vertical metal-insulator transition

    SciTech Connect

    Okimura, Kunio; Mian, Md.Suruz

    2012-09-15

    The authors achieved oriented growth of vanadium dioxide (VO{sub 2}) films on CoCrTa metal template grown on an Si substrate. Low-temperature ({approx}250 Degree-Sign C) deposition of VO{sub 2} films using inductively coupled-plasma-assisted sputtering technique realized an abrupt interface between VO{sub 2} and CoCrTa layers, suppressing the oxidation and diffusion of metal components. The films revealed a metal-insulator transition with resistance change of over 2 orders of magnitude. The CoCrTa film, in which Co hexagonal crystalline grains with c-axis orientation were surrounded by segregated Cr and Ta, serves for the oriented growth of VO{sub 2} crystalline film, enabling higher orders of transition in resistance and low voltage switching, even for the vertical (out-of-plane) direction.

  9. Inducing uniform single-crystal like orientation in natural rubber with constrained uniaxial stretch.

    PubMed

    Zhou, Weiming; Meng, Lingpu; Lu, Jie; Wang, Zhen; Zhang, Wenhua; Huang, Ningdong; Chen, Liang; Li, Liangbin

    2015-07-01

    The effect of flow on crystallization is commonly attributed to entropic reduction, which is caused by stretch and orientation of polymer chains but overlooks the role of flow on final-state free energy. With the aid of in situ synchrotron radiation wide-angle X-ray diffraction (WAXD) and a homemade constrained uniaxial tensile testing machine, polycrystals possessing single-crystal-like orientation rather than uniaxial orientation are found during the constrained stretch of natural rubber, whereas the c-axis and a-axis align in the stretch direction (SD) and constrained direction (CD), respectively. Molecular dynamics simulation shows that aligning the a-axis of crystal nuclei in CD leads to the lowest free energy increase and favors crystal nucleation. This indicates that the nomenclature of strain-induced crystallization may not fully account for the nature of flow-induced crystallization (FIC) as strain mainly emphasizes the entropic reduction of initial melt, whereas stress rather than strain plays the dominant role in crystal deformation. The current work not only contributes to a comprehensive understanding of the mechanism of flow-induced crystallization but also demonstrates the potential application of constrained uniaxial tensile stretch for the creation of functional materials containing polycrystals that possess single-crystal-like orientation. PMID:26021287

  10. Anisotropy of Longitudinal Wave Velocity and Hydroxyapatite Orientation in Bovine Cortical Bone

    NASA Astrophysics Data System (ADS)

    Yaoi, Yuichiro; Yamamoto, Kazufumi; Nakatsuji, Tomohiro; Yanagitani, Takahiko; Matsukawa, Mami; Yamazaki, Kaoru; Nagano, Akira

    2009-07-01

    The anisotropy of longitudinal wave velocity and the hydroxyapatite (HAp) crystallite orientation in bovine cortical bone were experimentally investigated in detail. A ring-shaped cortical bone sample was obtained from the midshaft of a 32-month-old bovine femur. Four cylindrical specimens (diameter 11 mm) were taken from the ring-shaped cortical bone specimen along the radial direction. Velocity was measured by a conventional ultrasonic pulse system, by rotating the specimen in the axial-tangential plane. The direction of the fastest wave velocity observed was inclined 5-10° from the axial direction. The HAp crystallite orientation in the specimen was also investigated by X-ray diffraction pole-figure analysis. We observed a strong intensive peak of (0002), indicating HAp crystallite c-axis alignment along the bone axis. However, the pole-figure also revealed a small tilt in the HAp crystallite orientation from the axial direction. Comparing the velocity and X-ray diffraction peak at each angle of the axial-tangential plane, a significant correlation between the velocity and the HAp orientation was observed.

  11. Curricular Orientations. Chapter Two.

    ERIC Educational Resources Information Center

    Patton, James R.; Polloway, Edward A.

    The purpose of this chapter is to review the major curricular orientations which can be found in special education settings for students with mental disabilities. Program orientations differ along two primary dimensions: the amount of time students spend in special settings or with special education personnel, and the extent to which the…

  12. Orientation in operator algebras

    PubMed Central

    Alfsen, Erik M.; Shultz, Frederic W.

    1998-01-01

    A concept of orientation is relevant for the passage from Jordan structure to associative structure in operator algebras. The research reported in this paper bridges the approach of Connes for von Neumann algebras and ourselves for C*-algebras in a general theory of orientation that is of geometric nature and is related to dynamics. PMID:9618457

  13. Teaching Orienteering. Second Edition.

    ERIC Educational Resources Information Center

    McNeill, Carol; Cory-Wright, Jean; Renfrew, Tom

    The educational value provided by orienteering's blend of navigational and physical skills has given it a permanent place in the primary and secondary school curriculum in the United Kingdom. This book is a reference to orienteering for teachers, leaders, and coaches. It provides a "how to" approach to introducing and developing the skills and…

  14. Are quartz LPOs predictably oriented with respect to the shear zone boundary?: A test from the Alpine Fault mylonites, New Zealand

    NASA Astrophysics Data System (ADS)

    Little, Timothy A.; Prior, David J.; Toy, Virginia G.

    2016-03-01

    The Alpine fault self-exhumes its own ductile shear zone roots and has a known slip kinematics. Within ˜1 km of the fault, the mylonitic foliation is subparallel to the boundary of the amphibolite-facies ductile shear zone in which it formed. Using EBSD, we analyzed quartz Lattice Preferred Orientations [LPOs) of mylonites along a central part of the Alpine Fault. All LPOs feature a strongest girdle of [c]-axes that is forward-inclined ˜28 ± 4° away from the pole to the fault. A maximum of axes is inclined at the same angle relative the fault. The [c]-axis girdle is perpendicular to extensional (C') shear bands and the maximum is parallel to their slip direction. [c]-axis girdles do not form perpendicular to the SZB. Schmid factor analysis suggests that σ1 was arranged at 60-80° to the Alpine Fault. These observations indicate ductile transpression in the shear zone. The inclined arrangement of [c]-axis girdles, axes, and C' planes relative to the fault can be explained by their alignment relative to planes of maximum shear-strain-rate in a general shear zone, a significant new insight regarding shear zones and how LPO fabrics may generally develop within them. For the Alpine mylonite zone, our data imply a kinematic vorticity number (Wk) of ˜0.7 to ˜0.85. Inversions of seismic focal mechanisms in the brittle crust of the Southern Alps indicate that σ1 is oriented ˜60° to the Alpine Fault; that shear bands form at ˜30° to this direction, and that σ2 and σ3 flip positions between the brittle and ductile parts of the crust.

  15. OR orientation process.

    PubMed

    Weaver, C S

    1992-12-01

    1. Poor OR orientation may lead to a lack of staff retention. Providing an environment that ensures a successful orientation will result in a productive professional who will be an asset to the staff. 2. It has historically been difficult to identify educational time frames that accurately reflect the needs of perioperative nurses and provide the necessary training. Haphazard learning creates inconsistent results and undue stress for new employees. 3. Learners must be given every opportunity to be successful. An orientation program that uses adult learning principles, preceptors, and a competency skills checklist can help new employees become skillful team members. PMID:1481255

  16. Orientation of Hittite Monuments

    NASA Astrophysics Data System (ADS)

    González-García, A. César; Belmonte, Juan Antonio

    The possible astronomical or topographical orientations of the Hittite monuments of the Bronze Age has remained unexplored until recently. This would provide an important insight into how temporality was imprinted by this culture in sacred spaces and in the landscape. The authors' analysis of a statistically significant sample of Hittite temples - and a few monumental gates - has demonstrated that ancient Hittite monuments were not randomly orientated as previously thought. On the contrary, there were well-defined patterns of orientation that can be interpreted within the context of Hittite culture and religion.

  17. Passive orientation apparatus

    DOEpatents

    Spletzer, Barry L.; Fischer, Gary J.; Martinez, Michael A.

    2001-01-01

    An apparatus that can return a payload to a known orientation after unknown motion, without requiring external power or complex mechanical systems. The apparatus comprises a faceted cage that causes the system to rest in a stable position and orientation after arbitrary motion. A gimbal is mounted with the faceted cage and holds the payload, allowing the payload to move relative to the stable faceted cage. The payload is thereby placed in a known orientation by the interaction of gravity with the geometry of the faceted cage, the mass of the system, and the motion of the payload and gimbal. No additional energy, control, or mechanical actuation is required. The apparatus is suitable for use in applications requiring positioning of a payload to a known orientation after arbitrary or uncontrolled motion, including remote sensing and mobile robot applications.

  18. Implementing Strategic Orientation

    ERIC Educational Resources Information Center

    Fischer, Arthur K.; Brownback, Sarah

    2012-01-01

    An HRM case dealing with problems and issues of setting up orientation programs which align with corporate strategy. Discussion concerns how such a case can be used to exhibit the alignment between HRM and business strategy.

  19. Orientation of histopathology specimens.

    PubMed

    Burns, A; Adams, J; Endersby, S

    2004-02-01

    We present a simple way of orientating large specimens being sent to the laboratory for histopathological examination by supplementing the pinning of the specimen on a cork board with Polaroid photographs of the specimen and numbered tags. PMID:14706306

  20. Orientations to Reflective Practice.

    ERIC Educational Resources Information Center

    Wellington, Bud; Austin, Patricia

    1996-01-01

    Delineates five orientations to reflective practice: immediate, technical, deliberative, dialectic, and transpersonal, each reflecting different social science bases and beliefs and values about education. Views them as interactive, interdependent, noncompeting, aspects of reflective practice. (SK)

  1. Sexual Orientation (For Parents)

    MedlinePlus

    ... For Kids For Parents MORE ON THIS TOPIC Transgender People Teaching Your Child Tolerance STDs Understanding Early ... and Romance Am I in a Healthy Relationship? Transgender People Sexual Attraction and Orientation Contact Us Print ...

  2. Controlling BaZrO3 nanostructure orientation in YBa2Cu3O{}_{7-\\delta } films for a three-dimensional pinning landscape

    NASA Astrophysics Data System (ADS)

    Wu, J. Z.; Shi, J. J.; Baca, F. J.; Emergo, R.; Wilt, J.; Haugan, T. J.

    2015-12-01

    The orientation phase diagram of self-assembled BaZrO3 (BZO) nanostructures in c-oriented YBa2Cu3O{}7-δ (YBCO) films on flat and vicinal SrTiO3 substrates was studied experimentally with different dopant concentrations and vicinal angles and theoretically using a micromechanical model based on the theory of elasticity. The organized BZO nanostructure configuration was found to be tunable, between c-axis to ab-plane alignment, by the dopant concentration in the YBCO film matrix strained via lattice mismatched substrates. The correlation between the local strain caused by the BZO doping and the global strain on the matrix provides a unique approach for controllable growth of dopant nanostructure landscapes. In particular, a mixed phase of the c-axis-aligned nanorods and the ab-plane-aligned planar nanostructures can be obtained, leading to a three-dimensional pinning landscape with single impurity doping and much improved J c in almost all directions of applied magnetic field.

  3. Growth and analysis of highly oriented (11n) BCSCO films for device research

    NASA Technical Reports Server (NTRS)

    Raina, K. K.; Pandey, R. K.

    1995-01-01

    Films of BCSCO superconductor of the type Bi2CaSr2Cu2Ox have been grown by liquid phase epitaxy method (LPE), using a partially closed growth chamber. The films were grown on (001) and (110) NdGaO3 substrates by slow cooling process in an optimized temperature range below the peritectic melting point (880 C) of Bi2CaSr2Cu2O8. Optimization of parameters, such as seed rotation, soak of initial growth temperature and growth period results in the formation of 2122 phase BCSCO films. The films grown at rotation rates of less than 30 and more than 70 rpm are observed to be associated with the second phase of Sr-Ca-Cu-O system. Higher growth temperatures (is greater than 860 C) also encourage to the formation of this phase. X-Ray Diffraction (XRD) measurements show that the films grown on (110) NdGaO3 have a preferred (11 n)-orientation. It is pertinent to mention here that in our earlier results published elsewhere we obtained c-axis oriented Bi2CaSr2Cu2O8 phase films on (001) NdGaO3 substrate. Critical current density is found to be higher for the films grown on (110) than (001) NdGaO3 substrate orientation. The best values of zero resistance (T(sub co)) and critical current density obtained are 87 K and 105 A/sq cm, respectively.

  4. Developing an orientation program.

    PubMed

    Edwards, K

    1999-01-01

    When the local area experienced tremendous growth and change, the radiology department at Maury Hospital in Columbia, Tennessee looked seriously at its orientation process in preparation for hiring additional personnel. It was an appropriate time for the department to review its orientation process and to develop a manual to serve as both a tool for supervisors and an ongoing reference for new employees. To gather information for the manual, supervisors were asked to identify information they considered vital for new employees to know concerning the daily operations of the department, its policies and procedures, the organizational structure of the hospital, and hospital and departmental computer systems. That information became the basis of the orientation manual, and provided an introduction to the hospital and radiology department; the structure of the organization; an overview of the radiology department; personnel information; operating procedures and computer systems; and various policies and procedures. With the manual complete, the radiology department concentrated on an orientation process that would meet the needs of supervisors who said they had trouble remembering the many details necessary to teach new employees. A pre-orientation checklist was developed, which contained the many details supervisors must handle between the time an employee is hired and arrives for work. The next step was the creation of a checklist for use by the supervisor during a new employee's first week on the job. A final step in the hospital's orientation program is to have each new employee evaluate the entire orientation process. That information is then used to update and revise the manual. PMID:10346648

  5. Reactions of oriented molecules.

    PubMed

    Brooks, P R

    1976-07-01

    Beams of oriented molecules have been used to directly study geometrical requirements in chemical reactions. These studies have shown that reactivity is much greater in some orientations than others and demonstrated the existence of steric effects. For some reactions portions of the orientation results are in good accord with traditional views of steric hindrance, but for others it is clear that our chemical intuition needs recalibrating. Indeed, the information gained from simultaneously orienting the reactants and observing the scattering angle of the products may lead to new insights about the detailed mechanism of certain reactions. Further work must be done to extend the scope and detail of the studies described here. More detailed information is needed on the CH(3)I reaction and the CF(3)I reaction. The effects of alkyl groups of various sizes and alkali metals of various sizes are of interest. In addition, reactions where a long-lived complex is formed should be studied to see if orientation is important. Finally, it would be of interest to apply the technique to the sort of reactions that led to our interest in the first place: the S(N)2 displacements in alkyl halides where the fascinating Walden inversion occurs. PMID:17793988

  6. Concealment of sexual orientation.

    PubMed

    Sylva, David; Rieger, Gerulf; Linsenmeier, Joan A W; Bailey, J Michael

    2010-02-01

    Sex-atypical behaviors may be used to identify a person as homosexual. To shield themselves from prejudice, homosexual people may attempt to conceal these behaviors. It is not clear how effectively they can do so. In Study 1, we asked homosexual participants to conceal their sex-atypical behaviors while talking about the weather. Raters watched videos of the participants and judged the likelihood that each participant was homosexual. Homosexual participants were able to partially conceal signs of their orientation, but they remained distinguishable from heterosexual participants. In Study 2, we tested the ability to conceal signs of one's sexual orientation in a more demanding situation: a mock job interview. In this scenario, homosexual men were even less effective at concealing their orientation. Higher cognitive demands in this new situation may have interfered with their ability to conceal. PMID:19169803

  7. The improvement of high-frequency magnetic properties in oriented hcp-Co78Ir22 soft magnetic films fabricated at high substrate temperature

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Zhang, Sha; Xu, Fei; Ma, Xiaoming; Zhang, Junli; Li, Fashen

    2016-05-01

    The c-axis oriented hcp-Co78Ir22 soft magnetic thin films with in-plane uniaxial anisotropy and negative magnetocrystalline anisotropy were fabricated with substrate temperature at 30 °C and 500 °C, respectively. Our results further reveal that sputtering under 500 °C can obtain a film with better grain structure and higher degree of orientation, which in turn improves the Ms and the magnetocrystalline anisotropy field. As the Ms and the total out-of-plane anisotropy field including the demagnetization field and the magnetocrystalline anisotropy field were enhanced, the high-frequency magnetic parameter (μi - 1) fr is approximately two times larger than that of the sample fabricated at 30 °C. In addition, the damping constant decreases quite a lot with increasing temperature. This work indicates that the high frequency properties can be well adjusted by changing substrate temperature.

  8. Continuous change of supersaturation and evolution of oriented structure in dipping LPE process of YBa2Cu3O7-δ

    NASA Astrophysics Data System (ADS)

    Guo, L. S.; Chen, Y. Y.; Yao, X.

    2014-10-01

    Liquid phase epitaxy (LPE) of YBa2Cu3O7-δ (YBCO) films was performed by vertical dipping along both the [0 0 1] and the [1 1 0] directions of (1 1 0) NdGaO3 (NGO) substrates. Remarkably, an evolution of oriented structure from c-axis to a-axis, corresponding to the supersaturation (σ) change from high to low level, was explicitly observed on a single NGO substrate. Distinctively, creeping along the [0 0 1] direction and forming a low-σ-related a-oriented film with a crack-free macrostructure, the liquid presented a strong anisotropic wettability with the NGO substrate. Most importantly, this work provides a unique method to achieve high-quality a-axis YBCO LPE films, which are potentially appropriate for Josephson junction devices.

  9. Topography and pigeon orientation

    NASA Technical Reports Server (NTRS)

    Wagner, G.

    1972-01-01

    Two types of homing experiments with pigeons to determine the influence of topographical features on the orientation behavior of the birds are discussed. The releases and following were conducted by ground experiments in which the birds are tracked by visual observation at points of topographical interest and the helicopter method by which the birds are tracked throughout the entire flight. The ground experiments showed a strong influence of topographical features on initial orientation. The helicopter experiments showed that the ground experiments do not provide adequate information on the manner in which homing occurs.

  10. Orientation and Alignment Echoes

    NASA Astrophysics Data System (ADS)

    Karras, G.; Hertz, E.; Billard, F.; Lavorel, B.; Hartmann, J.-M.; Faucher, O.; Gershnabel, Erez; Prior, Yehiam; Averbukh, Ilya Sh.

    2015-04-01

    We present one of the simplest classical systems featuring the echo phenomenon—a collection of randomly oriented free rotors with dispersed rotational velocities. Following excitation by a pair of time-delayed impulsive kicks, the mean orientation or alignment of the ensemble exhibits multiple echoes and fractional echoes. We elucidate the mechanism of the echo formation by the kick-induced filamentation of phase space, and provide the first experimental demonstration of classical alignment echoes in a thermal gas of CO2 molecules excited by a pair of femtosecond laser pulses.

  11. Orientational order in disordered superconductors

    SciTech Connect

    Toner, J. )

    1991-05-13

    Orientational order in weakly pinned Abrikosov flux lattices is studied, taking into account two heretofore neglected effects: dislocations and orientational couplings to the underlying lattice. Without orientational couplings, arbitrarily weak pinning destroys long-ranged orientational order for all spatial dimensions {ital d}{lt}4. Orientational couplings stabilize long-ranged orientational order. For fields along an axis of {ital fourfold} symmetry, {ital sixfold} (hexatic) orientational order is described by a random-field Ising model, and so does not occur in {ital d}=2 (thin films) but does in {ital d}=3 (bulk).

  12. Failure-Oriented Training.

    ERIC Educational Resources Information Center

    Pickens, Diana; Lorenz, Paul

    This document consists of a number of figures and diagrams suitable for overhead transparencies that illustrate and elaborate on the prnciples of failure-oriented training (a model for improving the effectiveness of instructional analysis). By adding a few simple steps to analysis, the resulting training will be closer to the idealized tutor:…

  13. Orientation of Phoenician Temples

    NASA Astrophysics Data System (ADS)

    Escacena Carrasco, José Luis

    The orientation of Phoenician temples has revealed some of the astronomical knowledge of their builders. What we now know on this topic is complemented by other archaeological documents from Syrio-Palestinian cities and their colonies. The astral aspects of Phoenician religion are a direct legacy from the Canaanite traditions 1,000 years earlier and display connections with Mesopotamia and Egypt.

  14. A Philological Orientation?

    ERIC Educational Resources Information Center

    Fonrobert, Charlotte Elisheva

    2010-01-01

    This article presents the author's response to Jon A. Levisohn's article entitled "A Menu of Orientations in the Teaching of Rabbinic Literature." As someone who is experimenting not only with how to teach rabbinic texts but with which texts to select in virtually every course the author teaches for American undergraduate as well as graduate…

  15. New Faculty Orientation Plan.

    ERIC Educational Resources Information Center

    Triton Coll., River Grove, IL.

    This report provides an overview of Triton College's (Illinois) New Faculty Orientation Plan, which was developed in light of the large number of retirements and new hires expected by the year 2000. The purpose of the plan is to assist newly hired instructors to move productively into their professional roles and to become actively involved in the…

  16. Orienting Park Visitors.

    ERIC Educational Resources Information Center

    Ormrod, Richard K.

    1984-01-01

    To utilize park facilities to their fullest, visitors must be well-oriented to the park's physical layout. The results of a study undertaken at Rocky Mountain National Park indicate that information should be readily accessible and easy to use. (DF)

  17. Sierra Madre Oriental, Mexico

    NASA Technical Reports Server (NTRS)

    1985-01-01

    This view of the Sierra Madre Oriental, Mexico (26.5N, 102.0W) west of Monclova, shows a mining region of northern Mexico. Mine tailings can be seen on the mountain slopes and in the valley floor. In addition to mining activity, several irrigated agricultural areas supporting the local communities can be seen in the area.

  18. Object Oriented Learning Objects

    ERIC Educational Resources Information Center

    Morris, Ed

    2005-01-01

    We apply the object oriented software engineering (OOSE) design methodology for software objects (SOs) to learning objects (LOs). OOSE extends and refines design principles for authoring dynamic reusable LOs. Our learning object class (LOC) is a template from which individualised LOs can be dynamically created for, or by, students. The properties…

  19. System Orientation Manual.

    ERIC Educational Resources Information Center

    Scheppke, Jim, Ed.

    Intended as an orientation guide, this manual presents information on library network operations for use by staff and advisory council members of the Texas Library System. The first chapter describes the role of systems in public library development in Texas, with a delineation of the history of Texas library systems, a chronology of related…

  20. Clay Mineral Preferred Orientation

    NASA Astrophysics Data System (ADS)

    Day-Stirrat, R. J.

    2014-12-01

    Anisotropy of the orientation of clay minerals, often referred to as texture, may be unique to sediments' deposition, composition, deformation or diagenetic history. The literature is rich with studies that include preferred orientation generation in fault gouge, low-grade metamorphic rocks, sediments with variable clay content and during the smectite-to-illite transformation. Untangling the interplay between many competing factors in any one geologic situation has proven a significant challenge over many years. Understanding how, where and when clay minerals develop a preferred orientation has significant implications for permeability anisotropy in shallow burial, the way mechanical properties are projected from shallower to deeper settings in basin modeling packages and the way velocity anisotropy is accounted for in seismic data processing. The assessment of the anisotropic properties of fine-grained siliciclastic rocks is gaining significant momentum in rock physics research. Therefore, a fundamental understanding of how clay minerals develop a preferred orientation in space and time is crucial to the understanding of anisotropy of physical properties. The current study brings together a wealth of data that may be used in a predictive sense to account for fabric anisotropy that may impact any number of rock properties.

  1. Computer Based Library Orientation.

    ERIC Educational Resources Information Center

    Machalow, Robert

    This document presents computer-based lessons used to teach basic library skills to college students at York College of the City University of New York. The information for library orientation has been entered on a disk which must be used in conjunction with a word processing program, the Applewriter IIe, and an Apple IIe microcomputer. The…

  2. Crystallization, Crystal Orientation and Morphology of Poly(ethylene oxide) under 1D Defect-Free Nanoscale Confinement

    NASA Astrophysics Data System (ADS)

    Hsiao, Ming-Siao; Zheng, Joseph X.; van Horn, Ryan M.; Quirk, Roderic P.; Thomas, Edwin L.; Lotz, Bernard; Cheng, Stephen Z. D.

    2009-03-01

    One-dimensional (1-D) defect-free nanoscale confinement is created by growing single crystals of PS-b-PEO block copolymers in dilute solution. Those defect-free, 1-D confined lamellae having different PEO layer thicknesses in PS-b-PEO lamellar single crystals (or crystal mats) were used to study the polymer recrystallization and crystal orientation evolution as a function of recrystallization temperature (Trx) because the Tg^PS is larger than Tm^PEO in the PS-b-PEO single crystal. The results are summarized as follows. First, by the combination of electron diffraction and known PEO crystallography, the crystallization of PEO only takes place at Trx<-5^oC. Meanwhile a unique tilted PEO orientation is formed at Trx >-5^oC after self-seeding. The origin of the formation of tilted chains in the PEO crystal will be addressed. Second, from the analysis of 2D WAXD patterns of crystal mats, it is shown that the change in PEO c-axis orientation from homogeneous at low Trx to homeotropic at higher Trx transitions sharply, within 1^oC. The mechanism inducing this dramatic change in crystal orientation will be investigated in detail.

  3. Personality and Medical Specialty Choice: Technique Orientation versus People Orientation.

    ERIC Educational Resources Information Center

    Borges, Nicole J.; Osmon, William R.

    2001-01-01

    Results of the 16 Personality Factor Questionnaire completed by 161 physicians indicated that role consciousness, abstractedness, and tough mindedness differentiated medical specialties (surgeons, anesthesiologists, family practitioners). Results correlated with the use of differences between person orientation and technique orientation to…

  4. Influence of carbon doping on the reversible magnetization of MgB 2 single crystals

    NASA Astrophysics Data System (ADS)

    Eisterer, M.; Krutzler, C.; Zehetmayer, M.; Weber, H. W.; Kazakov, S. M.; Karpinski, J.

    2007-09-01

    The reversible magnetization of Mg(B1-xCx)2 single crystals with varying carbon content (x = 0-0.095) was measured by SQUID magnetometry. It was found to be strongly influenced by the two-band character of this material. At low magnetic fields charge carriers of both bands contribute to superconductivity and to diamagnetism. At high fields the π-band is suppressed and the σ-band mainly determines the magnetization. This allows us to extract information on both bands by analyzing the reversible magnetization in terms of two band Ginzburg-Landau (GL) theory. The "intrinsic" magnetic penetration increases in both bands with increasing carbon content, but the σ-band remains crucial for the upper critical field. Changes in the field dependence of the resulting "effective" penetration depth by carbon doping are discussed.

  5. 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.

  6. 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 chemistry and concentration, wire processing technology, and collection technology will lead to the commercialization of boron nanopowder as a precursor for MgB{sub 2} superconductors. Potential commercial applications include magnets for magnetic resonance imaging (MRI), fault current limiters, wind turbine generators.

  7. History of Oriental Astronomy

    NASA Astrophysics Data System (ADS)

    Ansari, S. M. Razaullah

    2002-12-01

    This volume deals specifically with recent original research in the history of Chinese, Korean, Japanese, Islamic, and Indian astronomy. It strikes a balance between landmarks of history of Ancient and Medieval Astronomy in the Orient on one hand, and on the other the transmission of the European Astronomy into the countries of the Orient. Most contributions are based on research by the experts in this field. The book also indicates the status of astronomy research in non-European cultural areas of the world. The book is especially of interest to historians of astronomy and science, and students of cultural heritage. Link: http://www.wkap.nl/prod/b/1-4020-0657-8

  8. Context Oriented Information Integration

    NASA Astrophysics Data System (ADS)

    Mohania, Mukesh; Bhide, Manish; Roy, Prasan; Chakaravarthy, Venkatesan T.; Gupta, Himanshu

    Faced with growing knowledge management needs, enterprises are increasingly realizing the importance of seamlessly integrating critical business information distributed across both structured and unstructured data sources. Academicians have focused on this problem but there still remain a lot of obstacles for its widespread use in practice. One of the key problems is the absence of schema in unstructured text. In this paper we present a new paradigm for integrating information which overcomes this problem - that of Context Oriented Information Integration. The goal is to integrate unstructured data with the structured data present in the enterprise and use the extracted information to generate actionable insights for the enterprise. We present two techniques which enable context oriented information integration and show how they can be used for solving real world problems.

  9. Aspect-Oriented Programming

    NASA Technical Reports Server (NTRS)

    Elrad, Tzilla (Editor); Filman, Robert E. (Editor); Bader, Atef (Editor)

    2001-01-01

    Computer science has experienced an evolution in programming languages and systems from the crude assembly and machine codes of the earliest computers through concepts such as formula translation, procedural programming, structured programming, functional programming, logic programming, and programming with abstract data types. Each of these steps in programming technology has advanced our ability to achieve clear separation of concerns at the source code level. Currently, the dominant programming paradigm is object-oriented programming - the idea that one builds a software system by decomposing a problem into objects and then writing the code of those objects. Such objects abstract together behavior and data into a single conceptual and physical entity. Object-orientation is reflected in the entire spectrum of current software development methodologies and tools - we have OO methodologies, analysis and design tools, and OO programming languages. Writing complex applications such as graphical user interfaces, operating systems, and distributed applications while maintaining comprehensible source code has been made possible with OOP. Success at developing simpler systems leads to aspirations for greater complexity. Object orientation is a clever idea, but has certain limitations. We are now seeing that many requirements do not decompose neatly into behavior centered on a single locus. Object technology has difficulty localizing concerns invoking global constraints and pandemic behaviors, appropriately segregating concerns, and applying domain-specific knowledge. Post-object programming (POP) mechanisms that look to increase the expressiveness of the OO paradigm are a fertile arena for current research. Examples of POP technologies include domain-specific languages, generative programming, generic programming, constraint languages, reflection and metaprogramming, feature-oriented development, views/viewpoints, and asynchronous message brokering. (Czarneclu and

  10. Earth orientation parameters

    NASA Technical Reports Server (NTRS)

    Eanes, Richard J.

    1994-01-01

    Since the beginning of regular space geodetic measurements, Satellite Laser Ranging (SLR) has routinely provided polar motion and length of day solutions. At the present time, Global Positioning Systems (GPS) regularly produces daily polar motion solutions with 0.4 mas accuracy, equivalent to the routine 1-day VLBI experiments and SLR solutions using 3 days of Lageos-1 data. This rapid progress of the GPS technique forces a review of any resource allocations for VLBI and SLR measurements of Earth orientation.

  11. Determination of 3D optic axis orientation in cartilage by polarization-sensitive optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Ugryumova, Nadya; Matcher, Stephen J.

    2007-02-01

    Polarization-sensitive optical coherence tomography has been used to solve fast-axis fibre orientation in three dimension space. Previously we have demonstrated that the apparent variations in polar angle orientation of collagen fibers along sagittal ridge of equine third metacarpophalangeal joint exist. A quantitative method based on multiple angles of illumination has been proposed to determine the polar angle of the collagen fibers. This method however ignored the full 3-D structure by assuming that the collagen fibers long-axis lay within the plane of incidence. A new quantitative method based on the theory of light propagation in uniaxial materials is described which avoids this assumption. To test this method we have performed control experiments on a sample of equine tendon (this tissue has well defined c-axis lying along the long-axis of the tendon). Several samples of tendon were cut to achieve a planar surface inclined at -20° to the long axis. Additional 30° rotation provided non-zero azimuthal angle. The surface was then imaged using incident beam angles -40°, -20°, 0, +20°, +40° in two orthogonal planes. Values for both the polar and azimuthal angles were then derived using a numerical optimisation procedure. Results agreed qualitatively with the nominal values but suggested that the accuracy was limited by our method of determining the apparent birefringence.

  12. Determination of 3D optic axis orientation in cartilage by polarization-sensitive optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Ugryumova, Nadya; Bonesi, Marco; Matcher, Stephen J.

    2008-02-01

    Polarization-sensitive optical coherence tomography has been used to solve fast-axis fibre orientation in three dimension space. Previously we have demonstrated that the apparent variations in polar angle orientation of collagen fibers along sagittal ridge of equine third metacarpophalangeal joint exist. A quantitative method based on multiple angles of illumination has been proposed to determine the polar angle of the collagen fibers. This method however ignored the full 3D structure by assuming that the collagen fibers long-axis lay within the plane of incidence. A new quantitative method based on the theory of light propagation in uniaxial materials is described which avoids this assumption. To test this method we have performed control experiments on a sample of equine tendon (this tissue has well defined c-axis lying along the long-axis of the tendon). Several samples of tendon were cut to achieve a planar surface inclined at -20° to the long axis. Additional 30° rotation provided non-zero azimuthal angle. The surface was then imaged using incident beam angles -40°, -20°, 0, +20°, +40° in two orthogonal planes. Values for both the polar and azimuthal angles were then derived using a numerical optimisation procedure. Results agreed qualitatively with the nominal values but suggested that the accuracy was limited by our method of determining the apparent birefringence.

  13. Strain-induced step bunching in orientation-controlled GaN on Si

    NASA Astrophysics Data System (ADS)

    Narita, Tetsuo; Iguchi, Hiroko; Horibuchi, Kayo; Otake, Nobuyuki; Hoshi, Shinichi; Tomita, Kazuyoshi

    2016-05-01

    We report a technique for the fabrication of high-quality GaN-on-silicon (Si) substrates for use in various power applications. GaN epitaxial layers were generated on Si(111) vicinal faces that had been previously covered with a thin coating of Al2O3 to control the orientation of the AlN seed layers. We obtained orientation-controlled GaN layers and found a linear relationship between the GaN c-axis and Si[111] tilt angles. As a result, the threading dislocation density in the AlN seed layer was reduced and high-quality GaN layers were generated. The X-ray rocking curves for these layers exhibited full width at half maximum values of 390‧‧ and 550‧‧ for the (004) and (114) reflections, respectively. Significant step bunching was observed on a GaN(0001) vicinal face produced using this technique, attributed to strain-induced attractive interactions between steps. Thus, by controlling the strain near the surface layer, we achieved the step flow growth of GaN on Si.

  14. Flexible piezoelectric pressure sensors using oriented aluminum nitride thin films prepared on polyethylene terephthalate films

    NASA Astrophysics Data System (ADS)

    Akiyama, Morito; Morofuji, Yukari; Kamohara, Toshihiro; Nishikubo, Keiko; Tsubai, Masayoshi; Fukuda, Osamu; Ueno, Naohiro

    2006-12-01

    We have investigated the high sensitive piezoelectric response of c-axis oriented aluminum nitride (AlN) thin films prepared on polyethylene terephthalate (PET) films. The AlN films were deposited using a radio frequency magnetron sputtering method at temperatures close to room temperature. The c axes of the AlN films were perpendicularly oriented to the PET film surfaces. The sensor consisting of the AlN and PET films is flexible like PET films and the electrical charge is linearly proportional to the stress within a wide range from 0to8.5MPa. The sensor can respond to the frequencies from 0.3 to over 100Hz and measures a clear human pulse wave form by holding the sensor between thumb and middle finger. The resolution of the pulse wave form is comparable to a sphygmomanometer at stress levels of 10kPa. We think that the origin of the high performance of the sensor is the deflection effect, the thin thickness and high elastic modulus of the AlN layer, and the thin thickness and low elastic modulus of the PET film.

  15. Structural, Magnetic and Electronic Properties of (110)-OrientedEpitaxial Thin Films of Bilayer Manganite La1.2Sr1.8Mn2O7

    SciTech Connect

    Takamura, Yayoi; Grepstad, Jostein K.; Chopdekar, Rajesh V.; Suzuki, Yuri; Marshall, Ann F.; Zheng, Hong; Mitchell, John F.

    2005-05-09

    We have synthesized (110)-oriented epitaxial thin films of the bilayer (n=2) manganite, La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}, with the metallic/ferromagnetic a-b planes lying perpendicular to the substrate surface and the c-axis aligned in the plane of the film. X-ray diffraction and transmission electron microscopy confirm the alignment of the a-b planes along the [1{bar 1}0] substrate direction. The films consist primarily of the n=2 phase with a minor component of the n=1 (La,Sr){sub 2}MnO{sub 4} and n={infinity} (La,Sr)MnO{sub 3} phases. A resistivity maximum coincides with a ferromagnet/paramagnet transition at a reduced T{sub c}{approx}90K (vs. 120K for bulk), indicative of the effects of epitaxial strain. The films display similar anisotropic properties to their bulk counterpart with the magnetically easy direction confined to the a-b planes and 20-200 times lower resistivity for current flowing along the a-b planes compared to the c-axis.

  16. Training for DD Council Orientation.

    ERIC Educational Resources Information Center

    Paul, James, Ed.; And Others

    Provided for Developmental Disabilities Councils is a resource handbook on planning orientation training for council members. The material, including three major presentations on orientation planning, advocacy, and orientation principles, is explained to be drawn from three 1975 regional conferences. Among training techniques analyzed are use of a…

  17. Orienteering for Sport and Pleasure.

    ERIC Educational Resources Information Center

    Bengtsson, Hans; Atkinson, George

    This text presents the principles of the sport of orienteering (navigating through an unknown area using a map and compass as guide) and is useful to beginners, experienced orienteers, and "armchair" orienteers. Included in the text are: (1) a glossary of key words; (2) a basic introduction to, and history of, the sport; (3) description of the…

  18. Curriculum Orientations of Virtual Teachers

    ERIC Educational Resources Information Center

    Singleton, Nicole Y.

    2013-01-01

    This study explored the curriculum orientation preferences of K-12 public school teachers who provided instruction in virtual settings (n = 47) in a midwestern state. Curriculum orientations were explored using a mixed-methods design. Quantitative assessments data revealed a pattern of curriculum orientations similar to teachers working in…

  19. Representation of orientation distributions

    SciTech Connect

    Wenk, H.R.; Kocks, U.F.

    1985-01-01

    This paper illustrates the principles presented with a particular experimental texture: from the surface layer of a copper polycrystal cold-rolled to 60% reduction in thickness. Four incomplete pole figures (200, 220, 222, and 113) were determined by x-ray diffraction in reflection geometry. The measured pole figures nearly exhibited orthorhombic symmetry (as expected), which was then strictly enforced by averaging the four quadrants of the pole figure. The orientation distribution function was obtained using the expansion in spherical harmonics (with only even-order coefficients up to l = 18).

  20. Nonlinear dynamics of cell orientation

    NASA Astrophysics Data System (ADS)

    Safran, S. A.; de, Rumi

    2009-12-01

    The nonlinear dependence of cellular orientation on an external, time-varying stress field determines the distribution of orientations in the presence of noise and the characteristic time, τc , for the cell to reach its steady-state orientation. The short, local cytoskeletal relaxation time distinguishes between high-frequency (nearly perpendicular) and low-frequency (random or parallel) orientations. However, τc is determined by the much longer, orientational relaxation time. This behavior is related to experiments for which we predict the angle and characteristic time as a function of frequency.

  1. Design oriented structural analysis

    NASA Technical Reports Server (NTRS)

    Giles, Gary L.

    1994-01-01

    Desirable characteristics and benefits of design oriented analysis methods are described and illustrated by presenting a synoptic description of the development and uses of the Equivalent Laminated Plate Solution (ELAPS) computer code. ELAPS is a design oriented structural analysis method which is intended for use in the early design of aircraft wing structures. Model preparation is minimized by using a few large plate segments to model the wing box structure. Computational efficiency is achieved by using a limited number of global displacement functions that encompass all segments over the wing planform. Coupling with other codes is facilitated since the output quantities such as deflections and stresses are calculated as continuous functions over the plate segments. Various aspects of the ELAPS development are discussed including the analytical formulation, verification of results by comparison with finite element analysis results, coupling with other codes, and calculation of sensitivity derivatives. The effectiveness of ELAPS for multidisciplinary design application is illustrated by describing its use in design studies of high speed civil transport wing structures.

  2. [Family oriented nursing care].

    PubMed

    Lima-Rodríguez, Joaquin Salvador; Lima-Serrano, Marta; Sáez-Bueno, Africa

    2009-01-01

    Nursing has experienced an important methodological development, in which it gives priority to the individual, although at a socioeconomic level a marked interest is seen in the health care of the family unit and the NANDA (North American Nursing Diagnosis Association), NIC (Nursing Interventions Classification) and NOC (Nursing Outcomes Classification) nursing guidelines, using diagnoses, criteria of results and interventions orientated towards this aim. We consider to the family as an opened system consisted of human elements, with a common history, which they form a functional unit been ruled by own procedure. In this paper we look at those aspects that must be taken into account in nursing assessment of families from a systemic perspective, including some tools for data collection and analysis of information. In addition, we identify specific areas of intervention. We believe that the family must be studied from a nursing care point of view with its own characteristics as opposed to those possessed individually by each of its members. We also believe that, when assessment is centred on the Henderson unaided activities study or the Gordon functional health patterns, they are not useful in assessing the family unit. This work offers an assessment method centred on the family unit, which helps to identify the nursing diagnoses applicable to it. Our proposal, which has been successfully used by nursing students over the last few years, hopes to contribute to quality clinical practice with a tool orientated towards the family. PMID:19726212

  3. Optimum orientation versus orientation averaging description of cluster radioactivity

    NASA Astrophysics Data System (ADS)

    Seif, W. M.; Ismail, M.; Refaie, A. I.; Amer, Laila H.

    2016-07-01

    While the optimum-orientation concept is frequently used in studies on cluster decays involving deformed nuclei, the orientation-averaging concept is used in most alpha decay studies. We investigate the different decay stages in both the optimum-orientation and the orientation-averaging pictures of the cluster decay process. For decays of 232,233,234U and 236,238Pu isotopes, the quantum knocking frequency and penetration probability based on the Wentzel–Kramers–Brillouin approximation are used to find the decay width. The obtained decay width and the experimental half-life are employed to estimate the clusters preformation probability. We found that the orientation-averaged decay width is one or two orders of magnitude less than its value along the non-compact optimum orientation. Correspondingly, the extracted preformation probability based on the averaged decay width increases with the same orders of magnitude compared to its value obtained considering the optimum orientation. The cluster preformation probabilities estimated by the two considered schemes are in more or less comparable agreement with the Blendowske–Walliser (BW) formula based on the preformation probability of α ({S}α {{a}{{v}}{{e}}}) obtained from the orientation-averaging scheme. All the results, including the optimum-orientation ones, deviate substantially from the BW law based on {S}α {{o}{{p}}{{t}}} that was estimated from the optimum-orientation scheme. To account for the nuclear deformations, it is more relevant to calculate the decay width by averaging over the different possible orientations of the participating deformed nuclei, rather than considering the corresponding non-compact optimum orientation.

  4. Oriental mystery: ginseng

    SciTech Connect

    Yun, T.K.; Cho, H.O.; Yun, Y.S.

    1985-01-01

    As a mysterious cure-all medicine Korea ginseng has been, since four or five thousand years ago, used as a tonic in the orient. Ginseng has been known to have a tonic effect and it is the general opinion of many investigators that ginseng has the effect of normalization of physical conditions, that is; maintaining individual homeostasis. On the other hand, the authors have found that ginseng extract inhibits the incidence and also the proliferation of tumors induced by carcinogens such as urethane, DMBA and aflatoxin B. The anticarcinogenic effect of ginseng was due to its ability to enhance the natural killer activity of the host. Korea ginseng is highly effective in preventing or curing various disease such as diabetes, cancer, high blood pressure, etc.

  5. Orientation filtering for crystalline films

    DOEpatents

    Smith, H.I.; Atwater, H.A.; Thompson, C.V.; Geis, M.W.

    1986-12-30

    A substrate is coated with a film to be recrystallized. A pattern of crystallization barriers is created in the film, for example, by etching voids in the film. An encapsulation layer is generally applied to protect the film, fill the voids and otherwise enhance a recrystallization process. Recrystallization is carried out such that certain orientations pass preferentially through the barrier, generally as a result of growth-velocity anisotropy. The result is a film of a specific predetermined crystallographic orientation, a range of orientations or a set of discrete orientations. 7 figs.

  6. Orientation filtering for crystalline films

    DOEpatents

    Smith, Henry I.; Atwater, Harry A.; Thompson, Carl V.; Geis, Michael W.

    1986-12-30

    A substrate is coated with a film to be recrystallized. A pattern of crystallization barriers is created in the film, for example, by etching voids in the film. An encapsulation layer is generally applied to protect the film, fill the voids and otherwise enhance a recrystallization process. Recrystallization is carried out such that certain orientations pass preferentially through the barrier, generally as a result of growth-velocity anisotropy. The result is a film of a specific predetermined crystallographic orientation, a range of orientations or a set of discrete orientations.

  7. Orientational nanoparticle assemblies and biosensors.

    PubMed

    Ma, Wei; Xu, Liguang; Wang, Libing; Kuang, Hua; Xu, Chuanlai

    2016-05-15

    Assemblies of nanoparticles (NPs) have regional correlated properties with new features compared to individual NPs or random aggregates. The orientational NP assembly contributes greatly to the collective interaction of individual NPs with geometrical dependence. Therefore, orientational NPs assembly techniques have emerged as promising tools for controlling inorganic NPs spatial structures with enhanced interesting properties. The research fields of orientational NP assembly have developed rapidly with characteristics related to the different methods used, including chemical, physical and biological techniques. The current and potential applications, important challenges remain to be investigated. An overview of recent developments in orientational NPs assemblies, the multiple strategies, biosensors and challenges will be discussed in this review. PMID:26708241

  8. Growth and analysis of highly oriented (11n) BCSCO films for device research

    SciTech Connect

    Raina, K.K.; Pandey, R.K.

    1994-12-31

    Films of BCSCO superconductor of the type Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub x} have been grown by liquid phase epitaxy method (LPE), using a partially closed growth chamber. The films were grown on (001) and (110) NdGaO{sub 3} substrates by slow cooling process in an optimized temperature range below the peritectic melting point (880{degrees}C) of Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub 8}. Optimization of parameters, such as seed rotation, soak of initial growth temperature and growth period results in the formation of 2122 phase BCSCO films. The films grown at rotation rates of less than 30 and more than 70 rpm are observed to be associated with the second phase of Sr-Ca-Cu-O system. Higher growth temperatures (>860{degrees}C) also encourage to the formation of this phase. XRD measurements show that the films grown on (110) NdGaO{sub 3} have a preferred (11n)-orientation. It is pertinent to mention here that in our earlier results published elsewhere we obtained c-axis oriented Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub 8} phase films on (001) NdGaO{sub 3} substrate. Critical current density is found to be higher for the films grown on (110) than (001) NdGaO{sub 3} substrate orientation. The best values of zero resistance (T{sub co}) and critical current density obtained are 87 K and 10{sup 5} A/cm{sup 2}, respectively.

  9. Stable vicinal step orientations in m-plane GaN

    NASA Astrophysics Data System (ADS)

    Kelchner, K. M.; Kuritzky, L. Y.; Nakamura, S.; DenBaars, S. P.; Speck, J. S.

    2015-02-01

    The performance of InxGa1-xN-based m-plane LEDs and laser diodes grown by metalorganic chemical vapor deposition on bulk GaN substrates is currently limited by lower indium uptake and inhomogeneous linewidth broadening in the blue spectrum compared to semipolar planes and c-plane. Linewidth broadening is partially attributed to inhomogeneous indium composition that is associated with template morphology. We investigate the morphological evolution of homoepitaxial GaN growth on bulk m-plane substrates in three co-loaded miscut orientations: nominally on-axis, 1° in the -c-direction (-c-miscut), and 1° in the a-direction (a-miscut). Atomic force microscopy reveals four-sided pyramidal hillocks for on-axis growth with faces inclined toward the [ 11 2 bar 0 ]a-axis (a-faces) and the [0001] c-axis (c-faces). The a-faces exhibit steps oriented in an a+c direction with longer terrace widths than the c-face steps. The -c-miscut template growth sometimes forms diagonal striations, characterized by regions with stable a+c step direction. The a-miscut template growth exhibits meandering steps oriented in the a±c directions that bunch to form diagonal striations. These results reveal that c-direction steps are unstable compared to a±c directions. We further demonstrate that m-plane GaN substrates with combined a+c miscut lead to narrower InxGa1-xN photoluminescence emission spectra in blue with enhanced indium incorporation.

  10. Subcortical orientation biases explain orientation selectivity of visual cortical cells

    PubMed Central

    Vidyasagar, Trichur R; Jayakumar, Jaikishan; Lloyd, Errol; Levichkina, Ekaterina V

    2015-01-01

    The primary visual cortex of carnivores and primates shows an orderly progression of domains of neurons that are selective to a particular orientation of visual stimuli such as bars and gratings. We recorded from single-thalamic afferent fibers that terminate in these domains to address the issue whether the orientation sensitivity of these fibers could form the basis of the remarkable orientation selectivity exhibited by most cortical cells. We first performed optical imaging of intrinsic signals to obtain a map of orientation domains on the dorsal aspect of the anaesthetized cat's area 17. After confirming using electrophysiological recordings the orientation preferences of single neurons within one or two domains in each animal, we pharmacologically silenced the cortex to leave only the afferent terminals active. The inactivation of cortical neurons was achieved by the superfusion of either kainic acid or muscimol. Responses of single geniculate afferents were then recorded by the use of high impedance electrodes. We found that the orientation preferences of the afferents matched closely with those of the cells in the orientation domains that they terminated in (Pearson's r = 0.633, n = 22, P = 0.002). This suggests a possible subcortical origin for cortical orientation selectivity. PMID:25855249

  11. Temperature distribution in a stack of intrinsic Josephson junctions with their CuO-plane electrodes oriented perpendicular to supporting substrate

    NASA Astrophysics Data System (ADS)

    Yurgens, A.; Bulaevskii, L. N.

    2011-01-01

    We numerically study Joule heating in a THz emitter made of Bi2Sr2CaCu2O8 + δ (Bi2212) single crystal with its CuO planes oriented perpendicular to supporting substrate. The single crystal is glued to the substrate by a layer of PMMA. The electrical current is applied in the c-axis direction across many intrinsic Josephson junctions (IJJ's) in Bi2212. The calculations show that the internal temperature increases to an acceptable 10-20 K only above the bath temperature for a Joule power density of ~ 105 W cm - 3 typical for experiments on THz emission from IJJ's. This makes the suggested geometry promising for boosting the output power of the emitter.

  12. Orientation, alignment, and polytype control in epitaxial growth of SiC nanowires for electronics application in harsh environments

    NASA Astrophysics Data System (ADS)

    Koshka, Yaroslav; Thirumalai, Rooban Venkatesh K. G.; Krishnan, Bharat K.; Levin, Igor; Merrett, J. Neil; Davydov, Albert V.

    2013-09-01

    SiC nanowires (NWs) are attractive building blocks for the next generation electronic devices since silicon carbide is a wide bandgap semiconductor with high electrical breakdown strength, radiation resistance, mechanical strength, thermal conductivity, chemical stability and biocompatibility. Epitaxial growth using metal-catalyst-based vapor-liquid-solid mechanism was employed for SiC NW growth in this work. 4H-SiC substrates having different crystallographic orientations were used in order to control NW alignment and polytype. A new technique based on vapor-phase delivery of the metal catalyst was developed to facilitate control of the NW density. Both 4H and 3C polytypes with a strong stacking disorder were obtained. The 4H and 3C NWs had different orientations with respect to the substrate. 4H NWs grew perpendicular to the c-plane of the substrate. The stacking faults (SFs) in these nanowires were perpendicular to the [0001] nanowire axes. All 3C NWs grew at 20° with respect to the substrate c-plane, and their projections on the c-plane corresponded to one of the six equivalent ⟨101-0⟩ crystallographic directions. All six orientations were obtained simultaneously when growing NWs on the (0001) substrate surface, while only one or two NW orientations were observed when growing NWs on any particular crystallographic plane parallel to the c-axis of the substrate. Growth on {101-0} surfaces resulted in only one NW orientation, thereby producing well-aligned NW arrays. Preliminary measurements of the NW electrical conductivity are reported utilizing two-terminal device geometry.

  13. Impression block with orientator

    NASA Astrophysics Data System (ADS)

    Brilin, V. I.; Ulyanova, O. S.

    2015-02-01

    Tool review, namely the impression block, applied to check the shape and size of the top of fish as well as to determine the appropriate tool for fishing operation was realized. For multiple application and obtaining of the impress depth of 3 cm and more, the standard volumetric impression blocks with fix rods are used. However, the registered impress of fish is not oriented in space and the rods during fishing are in the extended position. This leads to rods deformation and sinking due to accidental impacts of impression block over the borehole irregularity and finally results in faulty detection of the top end of fishing object in hole. The impression blocks with copy rods and fixed magnetic needle allow estimating the object configuration and fix the position of magnetic needle determining the position of the top end of object in hole. However, the magnetic needle fixation is realized in staged and the rods are in extended position during fishing operations as well as it is in standard design. The most efficient tool is the impression block with copy rods which directs the examined object in the borehole during readings of magnetic needles data from azimuth plate and averaging of readings. This significantly increases the accuracy of fishing toll direction. The rods during fishing are located in the body and extended only when they reach the top of fishing object.

  14. Device Oriented Project Controller

    SciTech Connect

    Dalesio, Leo; Kraimer, Martin

    2013-11-20

    This proposal is directed at the issue of developing control systems for very large HEP projects. A de-facto standard in accelerator control is the Experimental Physics and Industrial Control System (EPICS), which has been applied successfully to many physics projects. EPICS is a channel based system that requires that each channel of each device be configured and controlled. In Phase I, the feasibility of a device oriented extension to the distributed channel database was demonstrated by prototyping a device aware version of an EPICS I/O controller that functions with the current version of the channel access communication protocol. Extensions have been made to the grammar to define the database. Only a multi-stage position controller with limit switches was developed in the demonstration, but the grammar should support a full range of functional record types. In phase II, a full set of record types will be developed to support all existing record types, a set of process control functions for closed loop control, and support for experimental beam line control. A tool to configure these records will be developed. A communication protocol will be developed or extensions will be made to Channel Access to support introspection of components of a device. Performance bench marks will be made on both communication protocol and the database. After these records and performance tests are under way, a second of the grammar will be undertaken.

  15. Fragment oriented molecular shapes.

    PubMed

    Hain, Ethan; Camacho, Carlos J; Koes, David Ryan

    2016-05-01

    Molecular shape is an important concept in drug design and virtual screening. Shape similarity typically uses either alignment methods, which dynamically optimize molecular poses with respect to the query molecular shape, or feature vector methods, which are computationally less demanding but less accurate. The computational cost of alignment can be reduced by pre-aligning shapes, as is done with the Volumetric-Aligned Molecular Shapes (VAMS) method. Here, we introduce and evaluate fragment oriented molecular shapes (FOMS), where shapes are aligned based on molecular fragments. FOMS enables the use of shape constraints, a novel method for precisely specifying molecular shape queries that provides the ability to perform partial shape matching and supports search algorithms that function on an interactive time scale. When evaluated using the challenging Maximum Unbiased Validation dataset, shape constraints were able to extract significantly enriched subsets of compounds for the majority of targets, and FOMS matched or exceeded the performance of both VAMS and an optimizing alignment method of shape similarity search. PMID:27085751

  16. Industrial Technology Orientation Curriculum Guide.

    ERIC Educational Resources Information Center

    Illinois State Board of Education, Springfield. Dept. of Adult, Vocational and Technical Education.

    The four courses in this guide were designed to meet the specifications for the career orientation level of Illinois' Education for Employment Curriculum Model. These orientation-level courses can be taken by high school students in any sequence: (1) communication technology; (2) energy utilization technology; (3) production technology; and (4)…

  17. Correlation filters for orientation estimation

    NASA Technical Reports Server (NTRS)

    Kumar, B. V. K. Vijaya; Lee, Andrew J.; Connelly, James M.

    1988-01-01

    An important task in many vision applications is that of rapidly estimating the orientation of an object with respect to some frame of reference. Because of their speed and parallel processing capabilities, optical correlators should prove valuable in this application. This paper considers two algorithms for object orientation estimation based on optical correlations and presents some initial simulation results.

  18. Is Your Classroom Learning Oriented?

    ERIC Educational Resources Information Center

    Berliner, David; Casanova, Ursula

    1989-01-01

    Findings are discussed from a study in which classroom behavior of three fifth grade teachers was observed. Their respective classroom environments were labeled: "learning-oriented,""work-oriented," and "work-avoidance." The affect of these environments on achievement test scores and guidelines for implementing motivational strategies employed in…

  19. Strong orientational coordinates and orientational order parameters for symmetric objects

    NASA Astrophysics Data System (ADS)

    Haji-Akbari, Amir; Glotzer, Sharon C.

    2015-12-01

    Recent advancements in the synthesis of anisotropic macromolecules and nanoparticles have spurred an immense interest in theoretical and computational studies of self-assembly. The cornerstone of such studies is the role of shape in self-assembly and in inducing complex order. The problem of identifying different types of order that can emerge in such systems can, however, be challenging. Here, we revisit the problem of quantifying orientational order in systems of building blocks with non-trivial rotational symmetries. We first propose a systematic way of constructing orientational coordinates for such symmetric building blocks. We call the arising tensorial coordinates strong orientational coordinates (SOCs) as they fully and exclusively specify the orientation of a symmetric object. We then use SOCs to describe and quantify local and global orientational order, and spatiotemporal orientational correlations in systems of symmetric building blocks. The SOCs and the orientational order parameters developed in this work are not only useful in performing and analyzing computer simulations of symmetric molecules or particles, but can also be utilized for the efficient storage of rotational information in long trajectories of evolving many-body systems.

  20. Novel synthetic methodology for controlling the orientation of zinc oxide nanowires grown on silicon oxide substrates.

    PubMed

    Cho, Jinhyun; Salleh, Najah; Blanco, Carlos; Yang, Sungwoo; Lee, Chul-Jin; Kim, Young-Woo; Kim, Jungsang; Liu, Jie

    2014-04-01

    This study presents a simple method to reproducibly obtain well-aligned vertical ZnO nanowire arrays on silicon oxide (SiOx) substrates using seed crystals made from a mixture of ammonium hydroxide (NH4OH) and zinc acetate (Zn(O2CCH3)2) solution. In comparison, high levels of OH(-) concentration obtained using NaOH or KOH solutions lead to incorporation of Na or K atoms into the seed crystals, destroying the c-axis alignment of the seeds and resulting in the growth of misaligned nanowires. The use of NH4OH eliminates the metallic impurities and ensures aligned nanowire growth in a wide range of OH(-) concentrations in the seed solution. The difference of crystalline orientations between NH4OH- and NaOH-based seeds is directly observed by lattice-resolved images and electron diffraction patterns using a transmission electron microscope (TEM). This study obviously suggests that metallic impurities incorporated into the ZnO nanocrystal seeds are one of the factors that generates the misaligned ZnO nanowires. This method also enables the use of silicon oxide substrates for the growth of vertically aligned nanowires, making ZnO nanostructures compatible with widely used silicon fabrication technology. PMID:24584438

  1. Direct Synthesis of Anatase Films with ~100% (001) Facets and [001] Preferred Orientation

    PubMed Central

    Ichimura, Andrew S.; Mack, Brianne; Usmani, Shirin M.; Mars, Diana

    2012-01-01

    Anatase films exhibiting ~100% (001) reactive facets at the surface were grown hydrothermally on gold substrate from a homogeneous solution of TiF4 and NaF. In addition to NaF, it was found that TiO2 films with very similar properties could be prepared with the fluoride salts LiF, CsF, HF, NH4F, and N(CH2CH3)4F. The polycrystalline anatase films are continuous, approximately 1 μm thick, and evenly coat the substrate. The surface grain size is ~400 nm. Grazing angle XRD measurements show that the films exhibit a high degree of preferred orientation with the c-axis normal to the substrate surface. SEM images reveal that the grains span the thickness of the films. Annealing the films at 500 °C removes fluorine and causes crystallites within the grains to restructure as shown by SEM, XRD, and Raman spectroscopy. Supported anatase films grown from this one-pot method may serve as oxidative photocatalysts and electrodes for photoelectrochemical applications such as solar cells and hydrogen evolution. PMID:22844184

  2. Acoustic positioning and orientation prediction

    NASA Technical Reports Server (NTRS)

    Barmatz, Martin B. (Inventor); Aveni, Glenn (Inventor); Putterman, Seth (Inventor); Rudnick, Joseph (Inventor)

    1990-01-01

    A method is described for use with an acoustic positioner, which enables a determination of the equilibrium position and orientation which an object assumes in a zero gravity environment, as well as restoring forces and torques of an object in an acoustic standing wave field. An acoustic standing wave field is established in the chamber, and the object is held at several different positions near the expected equilibrium position. While the object is held at each position, the center resonant frequency of the chamber is determined, by noting which frequency results in the greatest pressure of the acoustic field. The object position which results in the lowest center resonant frequency is the equilibrium position. The orientation of a nonspherical object is similarly determined, by holding the object in a plurality of different orientations at its equilibrium position, and noting the center resonant frequency for each orientation. The orientation which results in the lowest center resonant frequency is the equilibrium orientation. Where the acoustic frequency is constant, but the chamber length is variable, the equilibrium position or orientation is that which results in the greatest chamber length at the center resonant frequency.

  3. 3-D matrix template-assisted growth of oriented oxide nanowire arrays using glancing angle pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Wright, N.; Mateo-Feliciano, D.; Ostoski, A.; Mukherjee, P.; Witanachchi, S.

    Nanosphere lithography is a combination of different methods to nanofabrication. In this work nanosphere lithography is used to study the growth of Zinc Oxide Nano-columns (ZnO NCs) on different diameter Silica Nanosphere (SNS) self-assembled templates. ZnO NCs are promising building blocks for many existing and emerging optical, electrical, and piezoelectric devices, specifically, the seeded growth of other oxide materials. Recently, reports have shown a ferroelectric phase of zinc stannate (ZnSnO3) and while lead zirconium titanate oxide (PZT) has been the main material of interest in ferroelectric and piezoelectric applications, the toxicity of lead has been of great concern. The possibility of developing lead free piezoelectric materials is of great interest in the ferroelectric community. Langmuir-Blodgett method was used to construct a self-assembled monolayer of SNSs on silicon substrates. Oriented ZnO NCs were grown on top of the spheres using the glancing angle pulsed laser deposition technique. Columns were formed in a spatially ordered closed-packed hexagonal configuration. Growth of ZnO NCs was studied as function of ambient Oxygen pressure with SNS size ranging from 250-1000 nm. Cross-sectional Scanning Electron Microscopy and X-ray diffraction (XRD) were used to study the template structure. Relative aspect ratios were studied and showed tunability of column dimensions with sphere size. XRD revealed ZnO NC arrays were c-axis oriented with hexagonal wurtzite structure.

  4. Role of laser energy density on growth of highly oriented topological insulator Bi2Se3 thin films

    NASA Astrophysics Data System (ADS)

    Chaturvedi, P.; Saha, B.; Saha, D.; Ganguly, S.

    2016-05-01

    Topological insulators (TIs) are very promising in the field of nanoelectronics due to their exotic properties. Bismuth Selenide, a 3D Topological insulator is considered as reference TI owing to its simple band structure and large bandgap. However, the presence of unintentional doping, which masks the metallic surface states, is still a major concern. In this work, we report the effect of laser energy density on the growth of highly oriented and stoichiometric thin films of Bi2Se3 by pulsed laser deposition (PLD). Structural characterizations by X-ray diffraction (XRD) and Raman Spectroscopy confirms the c-axis orientation and good crystallinity of films. Atomic force microscopy (AFM) study shows the increase in average grain size and rms roughness (from 3.1 nm to 5.1 nm) with the decrease in laser energy density. Compositional study by X-Ray Reflectivity (XRR) measurement is found to be in agreement with AFM results. Energy dispersive x-ray spectroscopy (EDS) measurements confirm the desired stoichiometry of the samples.

  5. Preferentially oriented BaTiO3 thin films deposited on silicon with thin intermediate buffer layers

    PubMed Central

    2013-01-01

    Barium titanate (BaTiO3) thin films are prepared by conventional 2-methoxy ethanol-based chemical solution deposition. We report highly c-axis-oriented BaTiO3 thin films grown on silicon substrates, coated with a lanthanum oxynitrate buffer layer of 8.9 nm. The influence of the intermediate buffer layer on the crystallization of BaTiO3 film is investigated. The annealing temperature and buffer layer sintering conditions are optimized to obtain good crystal growth. X-ray diffraction measurements show the growth of highly oriented BaTiO3 thin films having a single perovskite phase with tetragonal geometry. The scanning electron microscopy and atomic force microscopy studies indicate the presence of smooth, crack-free, uniform layers, with densely packed crystal grains on the silicon surface. A BaTiO3 film of 150-nm thickness, deposited on a buffer layer of 7.2 nm, shows a dielectric constant of 270, remnant polarization (2Pr) of 5 μC/cm2, and coercive field (Ec) of 60 kV/cm. PMID:23391429

  6. Oriented active shape models.

    PubMed

    Liu, Jiamin; Udupa, Jayaram K

    2009-04-01

    Active shape models (ASM) are widely employed for recognizing anatomic structures and for delineating them in medical images. In this paper, a novel strategy called oriented active shape models (OASM) is presented in an attempt to overcome the following five limitations of ASM: 1) lower delineation accuracy, 2) the requirement of a large number of landmarks, 3) sensitivity to search range, 4) sensitivity to initialization, and 5) inability to fully exploit the specific information present in the given image to be segmented. OASM effectively combines the rich statistical shape information embodied in ASM with the boundary orientedness property and the globally optimal delineation capability of the live wire methodology of boundary segmentation. The latter characteristics allow live wire to effectively separate an object boundary from other nonobject boundaries with similar properties especially when they come very close in the image domain. The approach leads to a two-level dynamic programming method, wherein the first level corresponds to boundary recognition and the second level corresponds to boundary delineation, and to an effective automatic initialization method. The method outputs a globally optimal boundary that agrees with the shape model if the recognition step is successful in bringing the model close to the boundary in the image. Extensive evaluation experiments have been conducted by utilizing 40 image (magnetic resonance and computed tomography) data sets in each of five different application areas for segmenting breast, liver, bones of the foot, and cervical vertebrae of the spine. Comparisons are made between OASM and ASM based on precision, accuracy, and efficiency of segmentation. Accuracy is assessed using both region-based false positive and false negative measures and boundary-based distance measures. The results indicate the following: 1) The accuracy of segmentation via OASM is considerably better than that of ASM; 2) The number of landmarks

  7. Freely oriented portable superconducting magnet

    DOEpatents

    Schmierer, Eric N.; Prenger, F. Coyne; Hill, Dallas D.

    2010-01-12

    A freely oriented portable superconducting magnet is disclosed. Coolant is supplied to the superconducting magnet from a repository separate from the magnet, enabling portability of the magnet. A plurality of support assemblies structurally anchor and thermally isolate the magnet within a thermal shield. A plurality of support assemblies structurally anchor and thermally isolate the thermal shield within a vacuum vessel. The support assemblies restrain movement of the magnet resulting from energizing and cooldown, as well as from changes in orientation, enabling the magnet to be freely orientable.

  8. Position and orientation tracking system

    DOEpatents

    Burks, Barry L.; DePiero, Fred W.; Armstrong, Gary A.; Jansen, John F.; Muller, Richard C.; Gee, Timothy F.

    1998-01-01

    A position and orientation tracking system presents a laser scanning appaus having two measurement pods, a control station, and a detector array. The measurement pods can be mounted in the dome of a radioactive waste storage silo. Each measurement pod includes dual orthogonal laser scanner subsystems. The first laser scanner subsystem is oriented to emit a first line laser in the pan direction. The second laser scanner is oriented to emit a second line laser in the tilt direction. Both emitted line lasers scan planes across the radioactive waste surface to encounter the detector array mounted on a target robotic vehicle. The angles of incidence of the planes with the detector array are recorded by the control station. Combining measurements describing each of the four planes provides data for a closed form solution of the algebraic transform describing the position and orientation of the target robotic vehicle.

  9. Position and orientation tracking system

    DOEpatents

    Burks, B.L.; DePiero, F.W.; Armstrong, G.A.; Jansen, J.F.; Muller, R.C.; Gee, T.F.

    1998-05-05

    A position and orientation tracking system presents a laser scanning apparatus having two measurement pods, a control station, and a detector array. The measurement pods can be mounted in the dome of a radioactive waste storage silo. Each measurement pod includes dual orthogonal laser scanner subsystems. The first laser scanner subsystem is oriented to emit a first line laser in the pan direction. The second laser scanner is oriented to emit a second line laser in the tilt direction. Both emitted line lasers scan planes across the radioactive waste surface to encounter the detector array mounted on a target robotic vehicle. The angles of incidence of the planes with the detector array are recorded by the control station. Combining measurements describing each of the four planes provides data for a closed form solution of the algebraic transform describing the position and orientation of the target robotic vehicle. 14 figs.

  10. Predicting Organizational Orientation toward Teams.

    ERIC Educational Resources Information Center

    Russ-Eft, Darlene

    1993-01-01

    Questionnaire data from 81 managers and 364 employees identified five factors predicting high team orientation in organizations: relationships with management, innovation, control of work by immediate supervisors, group cohesiveness, and open group process. (SK)

  11. Object-oriented productivity metrics

    NASA Technical Reports Server (NTRS)

    Connell, John L.; Eller, Nancy

    1992-01-01

    Software productivity metrics are useful for sizing and costing proposed software and for measuring development productivity. Estimating and measuring source lines of code (SLOC) has proven to be a bad idea because it encourages writing more lines of code and using lower level languages. Function Point Analysis is an improved software metric system, but it is not compatible with newer rapid prototyping and object-oriented approaches to software development. A process is presented here for counting object-oriented effort points, based on a preliminary object-oriented analysis. It is proposed that this approach is compatible with object-oriented analysis, design, programming, and rapid prototyping. Statistics gathered on actual projects are presented to validate the approach.

  12. When Is a Surface "Not" Orientable?

    ERIC Educational Resources Information Center

    Braselton, James; Abell, Martha; Braselton, Lorraine

    2002-01-01

    The Mobius strip, torus, and Klein bottle are used to graphically and analytically illustrate the differences between orientable and non-orientable surfaces. An exercise/laboratory project using the non-orientable Boy surface is included. (Contains 11 figures.)

  13. Development of the Sport Orientation Questionnaire.

    ERIC Educational Resources Information Center

    Gill, Diane L.; Deeter, Thomas E.

    1988-01-01

    An analysis of the Sport Orientation Questionnaire, a multidimensional, sport-specific measure of individual differences in achievement orientation, indicates that it is a valid and reliable measure of individual sport achievement orientation. (JD)

  14. High-Hall-Mobility Al-Doped ZnO Films Having Textured Polycrystalline Structure with a Well-Defined (0001) Orientation.

    PubMed

    Nomoto, Junichi; Makino, Hisao; Yamamoto, Tetsuya

    2016-12-01

    Five hundred-nanometer-thick ZnO-based textured polycrystalline films consisting of 490-nm-thick Al-doped ZnO (AZO) films deposited on 10-nm-thick Ga-doped ZnO (GZO) films exhibited a high Hall mobility (μ H) of 50.1 cm(2)/Vs with a carrier concentration (N) of 2.55 × 10(20) cm(-3). Firstly, the GZO films were prepared on glass substrates by ion plating with dc arc discharge, and the AZO films were then deposited on the GZO films by direct current magnetron sputtering (DC-MS). The GZO interface layers with a preferential c-axis orientation play a critical role in producing AZO films with texture development of a well-defined (0001) orientation, whereas 500-nm-thick AZO films deposited by only DC-MS showed a mixture of the c-plane and the other plane orientation, to exhibit a μ H of 38.7 cm(2)/Vs with an N of 2.22 × 10(20) cm(-3). PMID:27365000

  15. High-Hall-Mobility Al-Doped ZnO Films Having Textured Polycrystalline Structure with a Well-Defined (0001) Orientation

    NASA Astrophysics Data System (ADS)

    Nomoto, Junichi; Makino, Hisao; Yamamoto, Tetsuya

    2016-06-01

    Five hundred-nanometer-thick ZnO-based textured polycrystalline films consisting of 490-nm-thick Al-doped ZnO (AZO) films deposited on 10-nm-thick Ga-doped ZnO (GZO) films exhibited a high Hall mobility ( μ H) of 50.1 cm2/Vs with a carrier concentration ( N) of 2.55 × 1020 cm-3. Firstly, the GZO films were prepared on glass substrates by ion plating with dc arc discharge, and the AZO films were then deposited on the GZO films by direct current magnetron sputtering (DC-MS). The GZO interface layers with a preferential c-axis orientation play a critical role in producing AZO films with texture development of a well-defined (0001) orientation, whereas 500-nm-thick AZO films deposited by only DC-MS showed a mixture of the c-plane and the other plane orientation, to exhibit a μ H of 38.7 cm2/Vs with an N of 2.22 × 1020 cm-3.

  16. Monetary rewards influence retrieval orientations.

    PubMed

    Halsband, Teresa M; Ferdinand, Nicola K; Bridger, Emma K; Mecklinger, Axel

    2012-09-01

    Reward anticipation during learning is known to support memory formation, but its role in retrieval processes is so far unclear. Retrieval orientations, as a reflection of controlled retrieval processing, are one aspect of retrieval that might be modulated by reward. These processes can be measured using the event-related potentials (ERPs) elicited by retrieval cues from tasks with different retrieval requirements, such as via changes in the class of targeted memory information. To determine whether retrieval orientations of this kind are modulated by reward during learning, we investigated the effects of high and low reward expectancy on the ERP correlates of retrieval orientation in two separate experiments. The reward manipulation at study in Experiment 1 was associated with later memory performance, whereas in Experiment 2, reward was directly linked to accuracy in the study task. In both studies, the participants encoded mixed lists of pictures and words preceded by high- or low-reward cues. After 24 h, they performed a recognition memory exclusion task, with words as the test items. In addition to a previously reported material-specific effect of retrieval orientation, a frontally distributed, reward-associated retrieval orientation effect was found in both experiments. These findings suggest that reward motivation during learning leads to the adoption of a reward-associated retrieval orientation to support the retrieval of highly motivational information. Thus, ERP retrieval orientation effects not only reflect retrieval processes related to the sought-for materials, but also relate to the reward conditions with which items were combined during encoding. PMID:22547161

  17. Research directions in object-oriented programming

    SciTech Connect

    Shriver, B.; Wegner, P.

    1987-01-01

    The contributions in this book provide the most complete survey available in programming languages, databases, and programming semantics. The contents include: The Beta Programming Language: Common Objects: An Object-Oriented Programming Language with Encapsulation and Inheritance: Actors: A Conceptual Foundation for Object-Oriented Programmming: Vulcan; A model for Object-Based Inheritance; Definition Groups; Block-Structure and Object-Oriented Languages; A Mechanism for Specifying the Structure of Large Layered Programs; Classification in Object-Oriented Systems; Extensions and Foundations of Object-Oriented Programming; Object-Oriented Specification; Object-Oriented Databases; Development and Implementation of an Object-Oriented Database Management System; Maintaining Consistency in Databases with Changing Types; Object-Oriented Environments; An Object-Oriented Framework for Graphical Programming; A Substrate for Object-Oriented Interface Design.

  18. Two modes for dune orientation

    NASA Astrophysics Data System (ADS)

    Courrech Du Pont, Sylvain; Narteau, Clément; Gao, Xin

    2015-11-01

    Earth sand seas experience winds that blow with different strengths and from different directions in line with the seasons. In response, dune fields show a rich variety of shapes from small crescentic barchans to big star and linear dunes. Linear dunes often exhibit complex and compound patterns with different length scales and orientations, which seem difficult to relate to a single wind cycle. We present results of underwater experiments and numerical simulations where a single wind regime can lead to two different dunes orientation depending on sediment availability. Sediment availability selects the overriding mechanism for the formation of dunes: increasing in height from the destabilization of a sand bed or elongating in a finger on a non-erodible ground from a localized sand source. These mechanisms drive the dunes orientation. Therefore, dunes alignment maximizes dunes orthogonality to sand fluxes in the bed instability mode, while dunes are aligned with the sand transport direction in the fingering mode. Then, we derive a model for dunes orientation, which explains the coexistence of bedforms with different alignments and quantitatively predicts the orientation of dunes in Earth deserts. Finally, we explore the phase diagram and the stability of the fingering mode.

  19. Competing strategically through market orientation.

    PubMed

    Rapert, M I; Yarbrough, L

    1997-01-01

    As organizations seek to better understand their customers, competitors, and environments, the marketing function effectively serves as the support mechanism for these activities in many industries. Accordingly, in many organizations the marketing concept has been elevated to the stature of a strategic weapon, manifested in the form of market orientation. Market-oriented firms emphasize the collection, organization, and dissemination of information regarding both customers and competitors. This strategy is especially well-suited for the health care industry where customer knowledge is of paramount importance, customer interaction is instantaneous, and customer satisfaction is essential. Results of a national study of general service hospitals suggest that firms which embrace a market orientation benefit through enhanced customer satisfaction and quality. PMID:10179668

  20. Phase-Oriented Gear Systems

    NASA Technical Reports Server (NTRS)

    Vranish, John M.

    2007-01-01

    Phase-oriented gear systems are differential planetary transmissions in which each planet gear has two sets of unequal numbers of teeth indexed at prescribed relative angles (phases). The figure illustrates an application of the phase-oriented gearing concept to a relatively simple speed-reducing differential planetary transmission that includes a sun gear, an idler gear, three identical planet gears, a ground internal ring gear, and an output internal ring gear. Typically, the ground internal ring gear and output internal ring gear have different numbers of teeth, giving rise to a progressive and periodic phase shift between the corresponding pairs of teeth engaged by each successive planet gear. To accommodate this phase shift, it is necessary to introduce a compensating phase shift between the ground-gear-engaging and output-gearengaging sections of each planet gear. This is done by individually orienting each planet gear