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Radiation Damage in Boron Carbide

Description: From introduction: "Report describing the study of radiation damage in boron carbide with an integrated thermal neutron flux of 3x10^20 neutrons/cm² in the Materials Testing Reactor (MTR)."
Date: August 18, 1953
Creator: Tucker, Charles W., Jr. & Senio, Peter
Partner: UNT Libraries Government Documents Department

Some Special Refractory Materials

Description: Report explaining some different categories of special refractory materials. These categories of materials and their properties are discussed as well as the specific materials that fall into these categories.
Date: September 28, 1948
Creator: Norton, F. H.
Partner: UNT Libraries Government Documents Department

Carbide coatings on graphite

Description: From abstract: "A Method has been developed for the uniform coating of graphite tubes with carbides of niobium, tantalum, and zirconium by thermal composition of their respective halide vapors."
Date: 1957
Creator: Blocher, J. M., Jr.; Ish, Carl J.; Leiter, Don P.; Plock, Layne F. & Campbell, Ivor E.
Partner: UNT Libraries Government Documents Department

{mu}{sup +}SR studies of borocarbides

Description: Muon-spin-relaxation technique has been utilized to characterize the magnetic properties of the coexisting (superconductivity and antiferromagnetism) borocarbide compounds RNi{sub 2}B{sub 2}C, where R = Tm, Er, Ho, and Dy. Some general features of their magnetic ground-state and unusual results obtained in the Ho, Tm and Dy systems are discussed.
Date: June 1, 1996
Creator: Le, L.P.; Heffner, R.H. & Thompson, J.D.
Partner: UNT Libraries Government Documents Department

Carbide Fuels in Fast Reactors

Description: Abstract: Cladding and fuel material processing prospects are reviewed, and fuel system possibilities for near-term (~1 mill/kwh) and long-range (<0.5 mil/kmh) fuel cycles are described.
Date: September 15, 1965
Creator: Wheelock, C. W.
Partner: UNT Libraries Government Documents Department

Borocarbide thin films and tunneling measurements.

Description: The results obtained by their group in thin film fabrication and STM tunneling on superconducting borocarbides YNi{sub 2}B{sub 2}C have been be briefly reviewed. Results concerning the microwave surface impedance and the S/N planar junctions on LuNi{sub 2}B{sub 2}C thin films have been also presented and analyzed. These new data unambiguously confirm the full BCS nature of the superconducting gap in borocarbides and the absence of significant pair-breaking effects in LuNi{sub 2}B{sub 2}C.
Date: June 15, 2000
Creator: Iavarone, M.; Andreone, A.; Cassinese, A.; Dicapual, R.; Giannil, L.; Vagliol, R. et al.
Partner: UNT Libraries Government Documents Department

Vortex lattice structures in YNi{sub 2}B{sub 2}C

Description: We observe a flux lattice with square symmetry in the superconductor YNi{sub 2}B{sub 2}C when the applied field is parallel to the c-axis of the crystal. A square lattice observed previously in the isostructural magnetic analog ErNi{sub 2}B{sub 2}C was attributed to the interaction between magnetic order in that system and the flux lattice. Since the Y-based compound does not order magnetically, it is clear that the structure of the flux lattice is unrelated to magnetic order. In fact, we show that the flux lines have a square cross-section when the applied field is parallel to the c-axis of the crystal, since the measured penetration depth along the 110 crystal direction is smaller than the penetration depth along the 100 by approximately 30%. This causes the square symmetry of the lattice. Although we find considerable disorder in the arrangement of the flux lines at 2.5T, no melting of the vortex lattice was observed.
Date: September 1, 1997
Creator: Yethiraj, M.; Paul, D.M. & Tomy, C.V.
Partner: UNT Libraries Government Documents Department

STM investigation of the superconducting state of BSCCO 2212 and borocarbide materials

Description: We present spectroscopic Scanning Tunneling Microscope (STM) measurements performed at 4.2 K on BSCCO 2212 single crystals and Y, Lu and Er based borocarbide compounds. The conductance versus voltage spectra on BSCCO 2212 reveal a reproducible dip feature near e{vert_bar}V{vert_bar} = 2{Delta}, for both voltage polarities pointing to a strong coupling origin of the feature. The conductance spectra obtained on YNi{sub 2}B{sub 2}C thin films and LuNi{sub 2}B{sub 2}C single crystals are similar and correspond to a BCS ratio of 3.2 indicating weak coupling superconductivity in these compounds. On Er Ni{sub 2}B{sub 2}C single crystals, the conductance spectra show a pronounced broadening compared to the spectra obtained on LuNi{sub 2}B{sub 2}C and YNi{sub 2}B{sub 2}C, which is attributed to the pair-breaking effect due to the Er magnetic ions.
Date: October 1, 1997
Creator: Iavarone, M.; Guptasarma, P. & Hinks, D.G.
Partner: UNT Libraries Government Documents Department

Inelastic neutron studies of the low energy phonon excitations in the RENi{sub 2}B{sub 2}C superconductors (RE = Lu, Y, Ho, Er)

Description: The authors studied the low-energy phonon excitations for wavevectors close to the Fermi surface nesting vector {rvec {xi}}{sub m} {approx_equal} 0.55{rvec a}. They find that above T{sub c} the frequencies of the {Delta}{sub 4} [{zeta}00] lowest-lying optical and acoustic phonon modes decrease with decreasing temperature, for {rvec {xi}} close to {rvec {xi}}{sub m}, and there is a shift of intensity from the upper to the lower mode, an effect characteristic of coupled modes. From approximately 120K down to temperatures in the vicinity of T{sub c}, only a single unresolved peak is observed. Below T{sub c} the phonon spectra of the Y and Lu compounds change dramatically: they consist of a sharp peak at approximately 4.5 meV with a weak shoulder at the higher energy side. No such sharp peak was observed below T{sub c} in the Ho and Er compounds.
Date: December 31, 1997
Creator: Bullock, M.; Stassis, C.; Zarestky, J.; Goldman, A.; Canfield, P.; Shirane, G. et al.
Partner: UNT Libraries Government Documents Department

Neutron scattering studies of RENi{sub 2}B{sub 2}C: Magnetic structures and lattice dynamics

Description: Neutron scattering techniques have been used to study the magnetic structure and lattice dynamical properties of various members of the recently discovered RENi{sub 2}B{sub 2}C family, were RE stands for a rare-earth element. The magnetic structures of superconducting DyNi{sub 2}B{sub 2}C, ErNi{sub 2}B{sub 2}C, HoNi{sub 2}B{sub 2}C, and non superconducting TbNi{sub 2}B{sub 2}C have been determined as a function of temperature, in the 2-300 K temperature range.
Date: May 9, 1996
Creator: Dervenagas, P.
Partner: UNT Libraries Government Documents Department

Single crystal neutron diffraction study of the magnetic structure of TmNi{sub 2}B{sub 2}C

Description: Neutron diffraction techniques have been used to study the magnetic structure of single crystals of the magnetic superconductor (T{sub c} {congruent} 11K) TmNi{sub 2}B{sub 2}C. We find that below approximately 1.5K the magnetic moments order in an incommensurate spin wave with propagation vector q{sub m} = q{sub m} (a* +b*) (or q{sub m} = q{sub m} (a* + b*)) with q{sub m} = 0.094 {+-} 0.001. The spin wave is transverse with the moments aligned along the c-axis, and the observation of relatively intense higher order harmonics shows that the modulation is not purely sinusoidal but considerably squared. This incommensurate magnetic structure, which coexists with superconductivity below T{sub N} {congruent} 1.5K, is quite different from those observed in the magnetic superconductors HoNi{sub 2}B{sub 2}C and ErNi{sub 2}B{sub 2}C. The origin of diffraction peaks observed in scans parallel to a* is briefly discussed.
Date: February 1, 1997
Creator: Sternlieb, B.; Shapiro, S.; Stassis, C.; Goldman, A.I. & Canfield, P.
Partner: UNT Libraries Government Documents Department

{mu}{sup +}SR studies of magnetic properties of boron carbide superconductors

Description: Positive-muon spin relaxation ({mu}{sup +}SR) has been carried out in the recently-discovered rare-earth boron carbide superconductors RNi{sub 2}B{sub 2}C, R = Ho, Er and Tm. For R = Ho and Er zero-field {mu}{sup +}SR measurements showed a well-defined internal field below the Neel temperatures of 5.5 K coexisting with the superconducting state down to 0.1 K. The observed temperature dependence of the order parameter for Ho is consistent with a 2-dimensional Ising model. For R = Tm a spontaneous internal field appears above 30 K, whose magnitude saturates below about 3 K at a value corresponding to a rare earth moment much smaller than for Ho and Er. Transverse-field {micro}{sup {minus}}SR measurements in R = Tm showed a superconducting penetration depth {lambda}, = 1,200 {angstrom}. The temperature dependence of {lambda} is consistent with conventional s-wave pairing.
Date: June 8, 1994
Creator: Le , L.P.; Heffner, R.H. & Nieuwenhuys, G.J.
Partner: UNT Libraries Government Documents Department

Summary of Research on Experimental Refractory Bodies of High-Melting Nitrides, Carbides, and Uranium Dioxide

Description: Abstract: A procedure for the preparation of the nitrides and carbides of several metals and the preparation of the refractory bodies from them is described. The investigation shows that reasonably strong and dense bodies can be prepared from these materials as well as from UO₂. Evidence showing the tendency toward instability at high temperatures of Be₃N₂, TaN, and ThN is presented. Evidence is also given indicating that the hexagonal structure reported by others for TaN is actually that for Ta₂N. A lattice for Th₂N₃ is proposed. The melting points of ThN, UN, and UC are determined to be 2630 ± 50°C,2650 ± 100°C, and 2590 ± 50°C respectively.
Date: April 23, 1949
Creator: Chiotti, P.
Partner: UNT Libraries Government Documents Department

Preparation and Examination of Beryllium Carbide

Description: From abstract: "The properties of beryllium carbide were studied to determine its suitability as a high-temperature refractory. Various methods of preparing it were tried and a number of the physical and chemical properties of the resulting products were determined."
Date: 1953
Creator: Mallett, Manley William; Durbin, E. A.; Udy, M. C.; Vaughan, D. A. & Center, E. J.
Partner: UNT Libraries Government Documents Department

The organometallic chemical vapor deposition of transition metal carbides: The use of homoleptic alkyls

Description: The organometallic chemical vapor deposition of transition metal carbides (M = Ti, Zr, Hf, and Cr) from tetraneopentyl-metal precursors has been carried out. Metal carbides can be deposited on Si, Al{sub 2}O{sub 3}, and stainless steel substrates from M[CH{sub 2}C(CH{sub 3}){sub 3}]{sub 4} at temperatures in the range of 300 to 750 C and pressures from 10{sup {minus}2} to 10{sup {minus}4} Torr. Thin films have also been grown using a carrier gas (Ar, H{sub 2}). The effects of variation of the metal center, deposition conditions, and reactor design on the resulting material have been examined by SEM, XPS, XRD, ERD and AES. Hydrocarbon fragments generated in the deposition chamber have been studied in by in-situ mass spectrometry. Complementary studies examining the UHV surface decomposition of Zr[CH{sub 2}C(CH{sub 3}){sub 3}]{sub 4} have allowed for a better understanding of the mechanism leading to film growth.
Date: December 31, 1993
Creator: Healy, M. D.; Smith, D. C.; Springer, R. W.; Rubiano, R. R.; Springer, R. W. & Parmeter, J. E.
Partner: UNT Libraries Government Documents Department


Description: High temperature physico-chemical properties of refractory carbides for fuel and structural use were determined. Density and phases of vacuum hot pressed HfC, TaC, and ZrC are tabulated and the diffusion coefficients, lattice parameters, and thermodynamic properties of TaC and UC are given. (F.S.)
Date: October 31, 1969
Creator: White, J.F. & Juenke, E.F.
Partner: UNT Libraries Government Documents Department