David R. Riley

Environmental reactivity characteristics of copper-oxide superconductors

Although it is known that some of the high‐Tc phases react rapidly with water, CO2, CO, and acids, no systematic comparison of the relative reactivities of the various cuprate superconductors is available. In this letter, x‐ray powder diffraction, scanning electron microscopy, x‐ray photoemission spectroscopy, and electrochemical measurements are utilized to establish a comprehensive comparison of the intrinsic reactivity characteristics of the common copper‐oxide superconductors. Consequently, the following reactivity scale has been determined: YBa2Cu3O7≳Tl2Ba2Ca2Cu3O10≳Bi2Sr2CaCu2O8 ≥La1.85Sr0.15CuO4 ≳Nd1.85Ce0.15CuO4≳Nd1.85Th0.15CuO4.

Reversible modulation of superconductivity in YBa 2 Cu 3 O 7-δ /polypyrrole sandwich structures

The preparation of a hybrid conducting polymer/high-temperature superconductor device consisting of a polypyrrole coated YBa2Cu3O7-(delta ) microbridge is reported. Electrochemical techniques are exploited to alter the oxidation state of the polymer and, in doing so, it is found that superconductivity can be modulated in a controllable and reproducible fashion by the polymer layer. Whereas the neutral (insulating) polypyrrole only slightly influences the electrical properties of the underlying YBa2Cu3O7-(delta ) film, the oxidized (conductive) polymer depresses Tc by up to 50 K. The observed reversible shifts in Tc are the largest reported to date. In a similar fashion, the oxidation state of the polymer is found to reversibly modulate the magnitude of Jc, the superconducting critical current. Thus, the operation of a molecular/superconductor switch for controlling superconductivity is demonstrated.

ELECTROCHEMICALLY ASSESSED CORROSION REACTIVITY OF YBA2CU3O7 ELECTRODES

This paper describes a series of electrochemical measurements designed to explore the surface reactivity of the oxide superconductor YBa2Cu3O7. The electrochemical response of electrodes prepared from this material was found to be highly dependent on both the method of surface treatment and on the amount of water in the electrolytic fluid. In the absence of water, YBa2Cu3O7 behaved as a normal metal electrode and reproducible voltammetry was obtained in the potential window of 1.3 V to −1.4 V vs. SCE. At these potentials, faradaic electron transfer reactions for solution dissolved redox couples were readily observed at YBa2Cu3O7 and were similar in behavior to those obtained at noble metals such as Pt. At potentials outside this window, degradation of the electrode surface occurred. In addition, a very sensitive method has been developed for evaluating the quality of the surface of high temperature superconductors based on monitoring ΔEp values in cyclic voltammetry.

Environmental reactivity characteristics of K3C60 and YBa2Cu3O7-x high-temperature superconductor thin films

Abstract Recently the environmental reactivity behavior of the copper-oxide superconductors has been studied and the following reactivity trends have been established: YBa 2 Cu 3 O 7 > Tl 2 Ba 2 Ca 2 Cu 3 O 10 > Bi 2 Sr 2 CaCu 2 O 8 ≥ La 1.85 Sr 0.15 CuO 4 > Nd 1.85 Ce 0.15 CuO 4 > Nd 1.85 Th 0.15 CuO 4 In this paper, the degradation characteristics of the most reactive cuprate material, YBa 2 Cu 3 O 7 , are compared with those of the fulleride superconductor, K 3 C 60 . Conductivity vs. exposure time measurements acquired for thin film samples in eight different environments are utilized to estimate the degradation rates for the superconductor materials. The cuprate superconductor remains relatively stable in the presence of dry nitrogen, dry oxygen, vacuum, air and acetonitrile environments, but degrades rapidly upon exposure to water solutions. Samples of K 3 C 60 are also unreactive in dry nitrogen and under vacuum, but decompose extremely rapidly upon exposure to dry oxygen, air, acetonitrile or water solutions resulting in the complete loss of the superconducting properties.

Electrochemical response of YBa2Cu3O7-x as a function of oxygen content

By varying the oxygen content in the high temperature superconductor phase YBa 2 Cu 3 O 7-x (0<X<1), the electrical properties of this material can be manipulated from that of a superconductor to that of an insulating semiconductor. In this paper, a method for preparing YBa 2 Cu 3 O 7-x samples with different oxygen contents is described and a corresponding procedure for fabricating electrodes from these samples is outlined. The described procedure provides a simple and systematic means to tailor the conductive properties of electrode specimens