Paul D. Hambourger

Structural chemistry of Au(III)-substituted Ba2YCu3O7−δ

A series of gold-substituted perovskite superconductorsBa2Y(Cu1−xAux)3O7−δ (x = 0–0.1) was synthesized. Forx = 0.1 there was no change in thea andb lattice parameters (a = 3.826A˚andb = 3.889A˚) but a 0.06A˚c axis expansion to 11.75A˚was observed. Substituted gold was found to be trivalent by X-ray photoelectron spectroscopy. Replacing Cu(1) in the copper oxide chain with a slight reordering of oxygen is consistent withc axis expansion. The formal charge of the site remains trivalent while remaining Cu in the chains is reduced to Cu(I) resulting in an oxygen stoichiometry <7. Finally, no large effect onTc is observed (Tc = 89K forx = 0.10), in contrast to the effect of a number of other metal ion dopants. These results are discussed relative to the chemistry of Au(III) and to the use of the metal in structures containing gold and ceramic superconductors.

Effect of Heat-Treatment Temperature of Vapor-Grown Graphite Fibers I. Properties of Their Bromine Intercalation Compounds

Abstract Vapor-grown graphite fibers, which have been heat treated to 2000, 2200, 2400 2600, 2800 or 3000 °C, are treated with bromine vapor at room temperature for two days. The fibers are characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), density and resistivity measurements. Fibers heat treated at any single temperature exhibit a wide range of properties. Bromination products of fibers that have been heat treated to 2600 °C and above exhibit a DSC peak near 100 °C, which is used as a signature of intercalation. The XRD, density and temperature dependence of the resistivity suggest fibers with regions of pristine graphite and regions of stage-two intercalation compounds. Fiber diameter is found to be an important variable, with fibers having a diameter greater than about 13 μm exhibiting low resistivities (50 μω cm or less) independent of their heat-treatment temperature. The temperature dependence of the resistivity suggests that 6 μω cm is the minimum resistivity of this system unless more uniform intercalation can be achieved.

Low Earth Orbit Effects on Indium Tin Oxide and Polyester and Comparison With Laboratory Simulations

Abstract Laboratory simulation of the low Earth orbit (LEO) environment using oxygen plasma ashers are discussed. Their effectiveness as space simulators are compared with LEO through analysis of indium tin oxide (ITO) thin films and bulk polyester exposed to both environments. Spectrophotometry and atomic force microscopy have been used to characterize optical and microstructural changes as a result of exposure to the simulated (oxygen plasma asher) and the actual space environment aboard shuttle flight STS-46. Results show that the low Earth orbit space environment is much harsher than the plasma asher on the optical properties of ITO as well as the surface roughness of polyester. On space-exposed samples, a significant shift in the ITO absorption edge is seen for fluences of 2 × 10 20 atoms cm -2 but not on films exposed in the asher. The surface roughness of polyester exposed in the asher increase by a factor of 5.5, while that of polyester exposed in space increases by a factor of 20 for the same atomic oxygen fluence. The directional nature and higher kinetic energy of atomic oxygen in LEO serves to erode polyester more than in the asher. The different results obtained in the asher for both ITO and polyester bring into question the suitability of using plasma ashers as space simulators for these materials.

Resistivity of pristine and intercalated graphite fiber epoxy composites

Abstract Laminar composites have been fabricated from pristine and bromine intercalated Amoco P-55, P-75, and P-100 graphite fibers and Hysol-Grafil EAG101-1 film epoxy. The thickness and rf eddy current resistivity of several samples were measured at grid points and averaged point by point to obtain final values. Although the values obtained this way have high precision (

Effects of milling brominated P-100 graphite fibers

Preliminary procedures have been developed for the ball milling of pristine and brominated P-100 graphite fibers. Because of the lubricative properties of graphite, large ball loads (50 percent by volume) are required. Use of 2-propanol as a milling medium enhances the efficiency of the process. The fibers, when allowed to settle from the milling medium, tend to be preferentially aligned with rather few fibers standing up. Milled, brominated P-100 fibers have resistivities that are indistinguishable from their pristine counterparts, apparently because of loss of bromine. This suggests that bromine would not be the intercalate of choice in applications where milled fibers of this type are required. It was found that brominated graphite fibers are stable in a wide variety of organic solvents.

Electronic conduction process in 1T-TaS2

The electrical resistivity parallel to the layers of Se-doped 1T-TaS2 has been measured over the range 1.3 < T < 240 K. Results support the existence of disorder-induced carrier localization in this material. Anisotropy studies in pure samples show that θc/θa ≈ 500, where θc and θa are the resistivities normal and parallel to the layers, respectively, suggesting that the conduction is 2-dimensional.

Degradation of thin films: comparison between low Earth orbit experiments and laboratory simulations of the space environment

Abstract The low Earth orbit (LEO) environment exposes spacecraft materials to atomic oxygen, UV light, meteroid impact and thermal cycling. The purpose of this paper is to report on progress towards evaluating damage done to candidate space materials, and ways to protect materials on future long-term space missions in LEO. Specifically, we prepared and characterized sets of samples for flights on the US Space Shuttle missions STS-46 and STS-51, and evaluated samples returned from STS-46. In addition, laboratory simulations of the LEO environment are shown to present interesting problems and challenges.

Transport properties of 1T-TaS2-xSex

Abstract The electrical resistivity and Hall coefficient of pure and Se-doped 1T-TaS2 have been measured over the range 1.3

Magnetoresistance of 2H-NbSe 2

Abstract The magnetoresistance anisotropy of 2H−NbSe2 was studied at 9.3 K and 35 K. Data indicate that the Fermi surface above and below the charge-density-wave onset temperature includes one or more sheets that are highly elongated (and possibly open) along the [0001] direction. The magnetoresistance at 9.3 K exhibits an anomalous linear dependence on magnetic field for all field directions studied, similar to that reported previously for B [0001]

Normal-state electronic properties of Sn0.12Eu1.08Mo6S8 at low temperature and high pressure

Abstract The Hall coefficient and resistivity of Sn0.12Eu1.08Mo6S8 have been measured over the range 1.5 100 K. A band model is proposed which is qualitatively consistent with the data.