Muon spin rotation in GdSr2Cu2RuO8: Implications

Muon spin rotation measurements are reported for GdSr₂Cu₂RuO₈, a material with an onset temperature for superconductivity of about 45 K (which is virtually the same for its superconducting sister compounds Sr₂YRu_{1? u} Cu _u O₆ and Gd_{2? z} Ce _z Sr₂Cu₂RuO₁₀). The data indicate two magnetic ordering transitions, at about 15 K and about 130 K, in addition to the Gd ordering transition known to occur at about 2.6 K. We tentatively attribute the 130 K transition to Ru and the 15 K transition to Cu ordering, effectively ruling out any superconducting mechanism based on fluctuating magnetic moments, which are frozen below about 15 K. If there is only one mechanism of high-temperature superconductivity, then the three facts that (i) all three sister compounds have essentially the same onset T _c for superconductivity and (ii) all three of these compounds contain SrO layers but (iii) only two of the three compounds, GdSr₂Cu₂RuO₈ and Gd_{2? z} Ce _z Sr₂Cu₂RuO₁₀ (and not Sr₂YRu_{1? u} Cu _u O₆) contain cuprate planes imply that the superconducting layers of all three compounds must be the common SrO layers, and not the cuprate planes (which do not occur in Cu-doped Sr₂YRuO₆). Otherwise the coincidence of onset temperatures must be an accident, and there must be at least two mechanisms of high-T _c superconductivity: one for doped Sr₂YRuO₆ and another for cuprate-plane superconductivity.     

Fabrication and properties of a polymer capacitor made entirely from polyaniline

We describe the fabrication and properties of polymer capacitors made entirely from polyaniline, using only heat-treatment techniques. These homo-interface devices feature a conducting-insulating-conducting configuration of polyaniline. Two methods for the fabrication of such capacitors are described including one where fabrication is carried out by a film peeling technique. Polyaniline dielectric formation is described and an equivalent circuit model of the capacitor including its parasitic resistances is discussed as is the volumetric energy storage capacity. The result of measurements of capacitance variation as a function of temperature has also been described. Finally, the action of these capacitors in modifying and generating high-frequency square waveforms is demonstrated.     

Photoactive Chitosan: A Step Toward a Green Strategy for Pollutant Degradation

This article is a highlight of the paper by Ferrari et al. in this issue of Photochemistry and Photobiology. It describes the innovative use of rose bengal‐conjugated chitosan as a reusable green catalyst that photo‐degrades phenolic compounds in aqueous media, and thereby has decontamination potential of polluted waters. Whether a next‐generation photoactive polymer that produces singlet oxygen is a solution to pollutant degradation can be argued. It is as yet unclear what polymeric sensitizer would be practical on a large scale. Nonetheless pursuing this goal is worthwhile.     

Sensitivity Enhancement of Polyorganophosphazenes to Radiation with 2,2,4,4,6,6-Hexakis(2-Hydroxyethyl Methacrylate)Cyclotriphosphazene Monomer and its Application for Negative Resists

Abstract

This work focuses on the application of a multifunctional phosphazene monomer, 2,2,4,4,6,6-hexakis(2-hydroxyethyl methacrylate)-cyclotriphosphazene (6-Hema) for enhancement of the sensitivity of polyphosphazenes to both ⁶⁰Co and E-beam radiation. Specifically, elastomeric and glassy phosphazene polymer films treated with 6-Hema were irradiated under vacuum, and the gel content was determined. The Charlesby-Pinner approach was used to compare the radiation sensitivities of these films. This served as the basis for eventually preparing SiO₂ wafers with thin films of the glassy polyphosphazenes mixed with or overcoated by the 6-Hema monomer. The SiO₂ wafers prepared with the most sensitive polymer/monomer system were patterned with an ERC electron beam accelerator/scanning electron microscope computer-driven instrument. It was determined that these negative resist films were 1-2 orders of magnitude more sensitive to radiation than the polymers without the monomer.     

Paradigms and paradoxes: energetics of the oxidative cleavage of azo compounds (diazenes)

The enthalpy of oxidative cleavage of azo compounds (diazenes) is discussed and compared with that of symmetric olefins. The roles of substituents and of electronegativity are explicitly discussed.     

Stored energy in metallic glasses due to strains within the elastic limit

Room temperature loading of metallic glasses, at stresses below the macroscopic yield stress, raises their enthalpy and causes creep. Thermal cycling of metallic glasses between room temperature and 77 K also raises their enthalpy. In both cases, the enthalpy increases are comparable to those induced by heavy plastic deformation, but, as we show, the origins must be quite different. For plastic deformation, the enthalpy increase is a fraction (<10%) of the work done (WD) (and, in this sense, the behaviour is similar to that of conventional polycrystalline metals and alloys). In contrast, the room temperature creep and the thermal cycling involve small strains well within the elastic limit; in these cases, the enthalpy increase in the glass exceeds the WD, by as much as three orders of magnitude. We argue that the increased enthalpy can arise only from an endothermic disordering process drawing heat from the surroundings. We examine the mechanisms of this process. The increased enthalpy (‘stored energy’) is a measure of rejuvenation and appears as an exothermic heat of relaxation on heating the glass. The profile of this heat release (the ‘relaxation spectrum’) is analysed for several metallic glasses subjected to various treatments. Thus, the effects of the small-strain processing (creep and thermal cycling) can be better understood, and we can explore the potential for improving properties, in particular the plasticity, of metallic glasses. Metallic glasses can exhibit a wide range of enthalpy at a given temperature, and small-strain processing may assist in accessing this for practical purposes.