Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session S10: Superconductors: Synthesis and Physical Properties |
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Sponsoring Units: DCMP Chair: Carmen Almasan, Kent State University Room: Morial Convention Center RO8 |
Wednesday, March 12, 2008 2:30PM - 2:42PM |
S10.00001: Growth of MgB$_{2}$ Films by an Impinging Jet HPCVD Reactor Design Daniel Lamborn, R.H.T. Wilke, Qi Li, Xiaoxing Xi, D.W. Snyder, Shufang Wang, Joan Redwing 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 ($\sim $10 $\mu$m) were deposited at a growth rate of $\sim $ 110 $\mu $m/hr and showed a maximum Tc of 39.8 K and residual resistivity ratio of 6.6. The thick films also showed a high J$_{c}$ 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. [Preview Abstract] |
Wednesday, March 12, 2008 2:42PM - 2:54PM |
S10.00002: Clean Epitaxial MgB}$_{2}$\textbf{ Films Fabricated by \textit{Ex Situ} Annealing of CVD-Grown B Films in Mg Vapor Mina Hanna, Shufang Wang, Andrew David Eck, Rudeger Wilke, Ke Chen, Arsen Soukiassian, Che-Hui Lee, Wenqing Dai, Qi Li, Joan Redwing, Darrell Schlom, Xiaoxing Xi, Kamel Salama Epitaxial MgB$_{2 }$films have been successfully fabricated by \textit{ex} situ annealing of B films, grown by chemical vapor deposition (CVD), in Mg vapour. The films show a sharp superconducting transition T$_{c}$ of about 40 K, a low residual resistivity of less than 2 $\mu \Omega $cm, and a high residual resistivity ratio RRR of about 10. At self field, the value of critical current density$ J_{c}$ for a 3 $\mu $m thick film is 1.7$\times $10$^{6}$ Acm$^{-2}$ at 5 K and 1.2$\times $10$^{6}$ Acm$^{-2}$ at 20 K. The high $T_{c}$, low residual resistivity, high \textit{RRR} and high $J_{c}$ indicate the cleanness and good connectivity of the films. The results demonstrate that the \textit{ex situ} deposition method can produce clean MgB$_{2}$ films with superior superconducting properties, which is significant for applications such as MgB$_{2}$ superconducting cavities and coated conductor wires and tapes. [Preview Abstract] |
Wednesday, March 12, 2008 2:54PM - 3:06PM |
S10.00003: High isostatic pressure synthesis of sonochemically modified MgB2 superconductor Brett McCarty, Josua Hugen, Daniel Stoecklein, Ruslan Prozorov A study of the effects of high intensity ultrasound on MgB2 precursors with different additives to improve pinning properties is reported. Additives were either co-sonicated with boron or mixed into sonicated boron afterwards. Hot isostatic pressure (HIP) was used to form fully dense MgB2 samples from precursors. Analysis of magnetization, microstructure and x-ray diffraction will be presented. [Preview Abstract] |
Wednesday, March 12, 2008 3:06PM - 3:18PM |
S10.00004: Preparation and transport measurements of high T$_{c}$ disordered MgB$_{2}$ thin films Li Zhang, Wolter Siemons, Nicholas Breznay, Aharon Kulpitulnik, Malcolm Beasley In this talk we present a method using pulsed laser deposition to fabricate single-layer disordered MgB$_{2}$ thin films. Both Mg and stoichiometric MgB$_{2}$ targets are used during the deposition. The films have been characterized by AFM, XPS, and XRD to establish the quality of the surface and the structural and compositional uniformity of the films. Though the uniformity of the films is still under investigation, transport measurements show that the films exhibit behavior characteristic of the superconductor-insulator transition at relatively high temperatures (2 to 5K). We will also review some preliminary low temperature and high magnetic field transport measurement results. Also of interest is the very low spin-orbit scattering expected in MgB$_{2}$ due to the low Z of Mg and B. This work is funded by DoE and NSF. [Preview Abstract] |
Wednesday, March 12, 2008 3:18PM - 3:30PM |
S10.00005: Crystal growth of superconducting materials La$_{2-x}$Ba$_{x}$CuO$_{4}$ Genda Gu, J.S. Wen, Z.J. Xu, J.M. Tranquada Since the discovery of the superconductivity in high temperature superconducting oxide La$_{2-x}$Ba$_{x}$CuO$_{4}$ in 1986, a large number of groups have attempted to grow the single crystals. However, no single crystal La$_{2-x}$Ba$_{x}$CuO$_{4}$ with x$>$0.11 has been successfully grown. In this project, the effects of the growth condition and the compositions of a feed rod on the crystal growth of La$_{2-x}$Ba$_{x}$CuO$_{4}$ has been studied by an infrared image floating zone method. The experimental result shows that a planar solid-liquid growing interface tends to break down into a cellular interface when the growth velocity is more than 1 mm/h. When the planar solid-liquid growing interface break down into a cellular interface, the single crystal size decreases abruptly and the as-grown rod is not single phase. The large single crystals of La$_{2-x}$Ba$_{x}$CuO$_{4}$ with x=0 to 0.165 has been successfully grown. The single crystals of La$_{2-x}$Ba$_{x}$CuO$_{4}$ with x=0 to 0.165 up to 6 mm diameter and 150 mm length have been grown. The superconductivity transition temperature T$_{c}$ of as-grown single crystals of La$_{2-x}$Ba$_{x}$CuO$_{4}$ (x=0 to 0.165) have been measured. [Preview Abstract] |
Wednesday, March 12, 2008 3:30PM - 3:42PM |
S10.00006: Superconductivity in La(Ni$_{1-x}$T$_{x})$C$_{2}$ (T = Cu, Ti, and Pt) H.H. Sung, S.Y. Chou, Y.C. Kung, H.K. Kuo, K.J. Syu, W.H. Lee LaNiC$_{2}$, which crystallizes in an orthorhombic CeNiC$_{2}$ type structure with space group A$_{mm2}$, is the first nickel-based ternary carbide superconductor with T$_{c} \quad \sim $ 2.7 K.$^{1,2}$ Previous report showed that about 50{\%} substitution of La in LaNiC$_{2}$ with the 5f thorium (Th) element could enhance the superconducting critical temperature T$_{c}$ up to 7.9 K.$^{3}$ We present the results of static magnetization and electric resistivity data for fifteen polycrystalline La(Ni$_{1-x}$T$_{x})$C$_{2}$ (T = Cu, Ti and Pt) compounds measured in the temperature range 1.8 $\sim $ 4.4 K and 2.0 $\sim $ 300 K, respectively. Discussion of the improvement, with respect to pure LaNiC$_{2}$, on the superconducting critical temperature T$_{c}$ will be directed toward the changes of valence, lattice parameters as well as the effects of solubility limit in the pseudoternary La(Ni$_{1-x}$T$_{x})$C$_{2}$ alloys. $^{1}$W.H. Lee, H.K. Zeng, Y.D. Yao and Y.Y. Chen, Physica C \textbf{266}, 138 (1996). $^{2}$V.K. Pecharsky, K.A. Gschneidner, Jr., and L.L. Miller, Phys. Rev. B \textbf{58}, 497 (1998). $^{3}$W.H. Lee and H.K. Zeng, Solid State Commun. \textbf{102}, 433 (1997). [Preview Abstract] |
Wednesday, March 12, 2008 3:42PM - 3:54PM |
S10.00007: ABSTRACT WITHDRAWN |
Wednesday, March 12, 2008 3:54PM - 4:06PM |
S10.00008: Magnetron sputter deposition of a 48-member cuprate superconductor library: Bi$_2$Sr$_2$Y$_x$Ca$_{1-x}$Cu$_2$O$_{8+\delta}$ (0.5$\le x \le$1) linearly varying in steps of $\Delta x = 0.01$. Kevin Hewitt, Robert Sanderson Using magnetron sputtering, a spatial composition spread approach was applied successfully to obtain 48-member libraries of the Bi$_2$Sr$_2$Y$_x$Ca$_{1-x}$Cu$_2$O$_{8+\delta}$ (0.5$\le$x$\le$1) cuprate superconducting system. The libraries were deposited onto (100) single crystal MgO, mounted on a water cooled rotating table, using two targets: the antiferromagnetic insulator Bi$_2$Sr$_2$YCu$_2$O$_{8+\delta}$ (P=98 W RF) and the hole doped superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (P=44 W DC). A low chamber pressure of 0.81 mTorr argon is used to reduce scattering by the process gas. To minimize oxygen resputtering a substrate bias of -20 V was used as well as a process gas free of oxygen. A rapid thermal processor is used to post-anneal the amorphous deposited films following a step annealing regime - ramp at 5 $^{\circ}$C/s for heating and cooling, with a first plateau at 780 $^{\circ}$C held for 200 s, and a second at 875 $^{\circ}$C held for 480 s. X-ray diffraction reveals that the films develop crystalline order with the c-axis lattice parameter contracting linearly from 30.55 {\AA} (x=0.5) to 30.24 {\AA} (x=1.0) with increasing Y-content, consistent with bulk values. The films are polycrystalline, developing preferred orientation for thinner members of the library. There is a change of 0.01 in doping per library member which will enable further studies to densely map phase space. [Preview Abstract] |
Wednesday, March 12, 2008 4:06PM - 4:18PM |
S10.00009: Mechanical and superconducting properties of Bi$_{1.8}$Pb$_{0.35}$Sr$_{1.9}$Ca$_{2.1}$Cu$_{3}$Gd$_{x}$O$_{y}$ system Mustafa Akdogan, Ozgur Ozturk, Huseyin Aydin, Murat Erdem, Cabir Terzioglu The influence of addition of the rare earth ion \textit{Gd} in \textit{Bi}$_{1.8}$\textit{Pb}$_{0.35}$\textit{Sr}$_{1.9}$\textit{Ca}$_{2.1}$\textit{Cu}$_{3}$\textit{Gd}$_{x}O_{y}$ superconductor has been investigated by varying \textit{Gd} addition (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5). The samples were prepared by standard solid-state reaction methods. Phase analyses of the samples by X-ray diffraction (XRD), microstructure examination by scanning electron microscopy (SEM), superconducting properties by dc electrical resistivity and mechanical properties by static Vickers hardness measurements have been carried out to assess the effects of \textit{Gd} addition. These measurements indicated that the superconducting transition temperature, Vickers hardness, Young's modulus, yield strength, fracture toughness values of the samples strongly depend on the \textit{Gd} addition. The values of $T_{c}, H_{v}, E, Y$ and $K_{IC}$ of the samples decreased with the increase in \textit{Gd} addition. Mechanical properties of the samples are also found to be load dependent. In addition, we have calculated the true (load independent) hardness, Young's modulus, yield strength, and fracture toughness of the samples. From XRD and SEM analyses, the addition of the sample by \textit{Gd} degrades formation of the high-$T_{c}$ \textit{Bi-2223} phase, and surface morphology and grain connectivity in comparison with undoped sample, respectively. [Preview Abstract] |
Wednesday, March 12, 2008 4:18PM - 4:30PM |
S10.00010: Investigation of Some Physical Properties of Gd added Bi-2223 Superconductors Murat Erdem, Ozgur Ozturk, Huseyin Aydin, Mustafa Akdogan, Cabir Terzioglu, Ahmet Varilci, Ibrahim Belenli Static microindentation, XRD, SEM, DC electrical resistivity and critical current density measurements were performed to investigate some physical properties of Bi$_{1.8}$Pb$_{0.35}$Sr$_{1.9}$Ca$_{2.1}$Cu$_{3}$Gd$_{x}$O$_{y}$ superconducting samples with x=0.0, 0.1, 0.3, and 0.5. The indentation load versus diagonal length of the samples under different indentation loads in the range of 0.245-2.940 N were presented. The microindentation measurements showed that, for the Gd added sample, the load dependent (apparent) microhardness value (H$_{v})$ is lower in comparison with that of the pure sample(x=0). The values of H$_{v}$ were found to be load dependent. In addition, we extracted the load independent (true) microhardness using the Kick's law, proportional specimen resistance (PSR), modified proportional specimen resistance (MPSR) model and the Hays-Kendall (HK) approach and compared the true hardness with the apparent hardness. We observed from the transport measurements that addition of Gd decreased T$_{c}$ and J$_{c}$. In addition, surface morphology and grain connectivity of the samples were degraded and the high-T$_{c}$ phase of the samples decreased with increasing Gd addition. The possible reasons for the observed degradation in microstructure, superconducting and mechanical properties due to Gd addition were discussed. [Preview Abstract] |
Wednesday, March 12, 2008 4:30PM - 4:42PM |
S10.00011: Transport microstructure and mechanical properties of Au diffusion-doped Bi-2223 superconductors O. Ozturk, C. Terzioglu, A. Varilci, I. Belenli We have investigated the effect of the gold-diffusion on the mechanical properties of the \textit{Bi-2223} superconducting samples with different annealing times (10, 20 and 50 hours). The samples are prepared by the conventional solid-state reaction method in the polycrystalline bulk form. Doping of Bi-2223 was carried out by means of gold diffusion during sintering from an evaporated gold film on pellets. The experimental works in this study consist of dc electrical resistivity measurements for electrical and superconducting properties, microhardness measurements for mechanical properties, X-ray diffraction for phase analyses and lattice parameters, and scanning electron microscopy for microstructure examination. These measurements showed that Au-doping, in comparison with the undoped samples, increased the critical transition temperature and enhanced formation of high-T$_{c}$ phase. Additionally, microhardness and grain size were also improved with increasing amount of diffusion. Moreover, the diffusion-annealing time decreased the number and size of voids and increased the transition temperature. The experimental results of hardness measurements were analyzed using the Kick's law, modified proportional specimen resistance (MPSR) model and the Hays-Kendall (HK) approach. Among them HK approach was the most successful. [Preview Abstract] |
Wednesday, March 12, 2008 4:42PM - 4:54PM |
S10.00012: Critical current density variations with increasing thickness in YBa$_{2}$Cu$_{3}$O$_{7-x}$+ BaSnO$_{3}$ (BSO) films Chakrapani Varanasi, Jack Burke, Lyle Brunke, Haiyan Wang, Paul Barnes To increase the engineering critical current density (J$_{e})$ of YBa$_{2}$Cu$_{3}$O$_{7-x}$ (YBCO) films, it is of great importance to grow thicker films with high critical current density (J$_{c})$. However, it has been shown that in pulsed laser ablated (PLD) YBCO films, as the thickness is increased beyond 1 $\mu $m, the J$_{c}$ of the films decreases. Earlier work by this group showed that YBCO+BaSnO$_{3}$ (BSO) films of $\sim $ 300 nm thickness can be grown with more than an order of magnitude increase in the J$_{c}$ in applied magnetic fields using a dual phase sector PLD target approach. In the present work a systematic study of J$_{c}$ dependence on the thickness of YBCO+BSO thick films was undertaken by growing different films with thicknesses ranging from 300 nm to 4 $\mu $m. The J$_{c}$ of these films was measured using a magnetometer indicated that high J$_{c}$ at high fields can be maintained even in thicker films. The cross-sectional TEM analyses of the thick films showed that the BSO nanocolumns grow through out the entire thickness of the samples. Microstructural details and the superconducting properties of thick YBCO+BSO films will be presented. [Preview Abstract] |
Wednesday, March 12, 2008 4:54PM - 5:06PM |
S10.00013: Superconductivity in undoped $T$'-RE$_{2}$CuO$_{4}$ with $T_{C }>$ 30 K Michio Naito, Osamu Matsumoto, Aya Utsuki, Akio Tsukada, Hideki Yamamoto, Takaaki Manabe We report the superconductivity in $T'$-\textit{RE}$_{2}$CuO$_{4}$ (\textit{RE} = Pr, Nd, Sm, Eu, and Gd), which have been for a long time believed as a Mott insulator. The highest $T_{c}$ of undoped $T'$-\textit{RE}$_{2}$CuO$_{4}$ is over 30 K, substantially higher than that of `electron-doped' analogs. Remarkably, Gd$_{2}$CuO$_{4}$, even the derivatives of which have not shown superconductivity so far, gets superconducting with $T_{c}^{onset}$ as high as 20 K. Our discovery was achieved by using metal-organic decomposition (MOD), an inexpensive and easy-to-implement thin-film process. The keys to prepare the superconducting films are rather simple, namely low-$P_{O2}$ firing and subsequent low-temperature reduction. One point to be emphasized is that low-$P_{O2}$ phase field has been almost unexplored in the search for new superconductors because of the belief that high $P_{O2}$ \textit{should} be required in the synthesis of Cu$^{2+}$ compounds. Our discovery contradicts with the past results supporting undoped mother compounds, $T'$-\textit{RE}$_{2}$CuO$_{4}$, to be insulating. The clue to understanding the sharp contrast between the past and our results is impurity oxygen (O$_{ap})$ at the apical site, which has to be cleaned up in order to reach the `generic' electronic phase diagram. [Preview Abstract] |
Wednesday, March 12, 2008 5:06PM - 5:18PM |
S10.00014: NbN films grown by chemical solution deposition Guifu Zou, Menka Jain, Hongmei Luo, S.A. Baily, T.M. McCleskey, E. Bauer, A.K. Burrell, Q. Jia NbN films were grown on quartz substrate using a chemical solution technique of polymer-assisted deposition for the first time. The precursor films were annealed at different temperatures in ammonia atmosphere. X-ray diffraction and electron microscopy analysis indicated that the films were polycrystalline. Preliminary optical spectroscopy results of these films showed several strong peaks in the visible range that can be attributed to the NbN phase. Wide peaks in the photoluminescence spectrum suggest many defects in these films. The transition temperature (measured from SQUIDs) of these films also will be discussed in this paper. [Preview Abstract] |
Wednesday, March 12, 2008 5:18PM - 5:30PM |
S10.00015: Superconductivity in YbGa$_x$Si$_{2-x}$ with the AlB$_2$-type structure N. Tsujii, M. Imai, H. Yamaoka, H. Ohashi, D. Nomoto, I. Jarrige, T. Tochio, K. Handa, J. Ide, H. Atsuta, Y. Ito, H. Yoshikawa, H. Kitazawa The discovery of superconductivity in MgB$_2$ has triggered the search for novel superconductors with the AlB$_2$-type structure. Very recently, we discovered superconductivity in the AlB$_2$- type compound YbGa$_{1.15}$Si$_{0.85}$ below $T_{\rm C}$ = 2.5K $^{*}$. We report here on the structural and electronic properties of the YbGa$_x$Si$_{2-x}$ series. XRD and SEM/EDS analysis suggested that the AlB$_2$-type phase can be sustained for $1.0 \leq x \leq 1.4 $. $T_{\rm C}$ is found to decrease from 2.5K for $x$ = 1.0 to 1.9K for $x$ = 1.3 and eventually vanish for $x$ = 1.4. High-resolution x-ray absorption spectra across the Yb-L$_{III} $ edge were measured at SPring-8 on the beamline BL15XU. The valence of Yb was estimated to be 2.3+, suggesting a predominant Yb$^{2+}$ character with minor importance of 4f electrons in the superconductivity.\newline $^{*}$ M. Imai et al., submitted. [Preview Abstract] |
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