Ji Ping Zhou

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.

Environmental degradation properties of YBa2Cu3O7−δ and Y0.6Ca0.4Ba1.6La0.4Cu3O7−δ thin film structures

Abstract Utilization of the high temperature superconductor, YBa 2 Cu 3 O 7−δ , in commercial applications is becoming increasingly feasible. Before full advantage of this material can be taken, however, the lifetime, oxygen stability and processability of this ambient reactive superconductor must be improved. Corrosion resistance of YBa 2 Cu 3 O 7−δ and a cation substituted compound, Y 0.6 Ca 0.4 Ba 1.6 La 0.4 Cu 3 O 7−δ , were studied and their lifetimes in aqueous environments were determined. Results indicate a dramatic enhancement in the stability against environmental degradation for the cation substituted phase. Important mechanistic factors responsible for the enhanced corrosion resistance of the substituted phase over the parent compound are discussed.

Reaction of the oxygen-deficient YBa2Cu3O6 phase with water

Abstract The oxygen deficient high-Tc material, YBa2Cu3O6, decomposes rapidly when in the presence of water solution or water vapor. Accordingly, upon reaction with water, it decomposes into Ba(OH)2, Cu2O, CuO, a metastable “Y2BaCuO5” phase and a series of unidentified amorphous compounds. Although the majority of the decomposition products are insoluble in water, Ba(OH)2 leaches away into solution where it subsequently reacts with atmospheric CO2 to form sparingly soluble BaCO3 crystals. Interestingly, the “Y2BaCuO5” phase forms only in the initial stages of corrosion and disappears after long water exposure times. On the other hand, authentic Y2BaCuO5 samples are very stable in the presence of water. Thus, the chemical reactivity of the “Y2BaCuO5” phase generated via decomposition of the high-Tc material is different from that of the authentic phase. In addition, comparisons of the relative reactivity of YBa2Cu3O7 and YBa2Cu3O6 samples reveal that the oxygen deficient material is more reactive than the fully oxygenated compound. This unusual reactivity trend suggests that factors other than copper formal valence dominate the chemical reactivity of the high-Tc phase.

Improved N-layer materials for high-Tc superconductor/normal-metal/superconductor junctions and superconducting quantum interference device sensors

In order to solve some of the formidable problems related to producing reliable and reproducible cuprate superconductor/normal-metal/superconductor (SNS) junctions, new N-layer compounds from the family of R1−xCaxBa2−yLayCu3−zMzO7−δ (R=Y, Gd and Pr; M=Co, Ni and Zn; 0⩽x⩽0.4; 0⩽y⩽0.4; 0⩽z⩽0.4) have been synthesized and their properties characterized. Thus, a crystal engineering approach has been adopted in an effort to generate reliable materials for use in high Tc superconducting devices. Careful analyses of the various prepared phases reveal optimum substitution levels for selected compositions where the N-layer compounds exhibit structures compatible with common superconductor electrode materials. The new compounds have been used for demonstration purposes as the N-layer material for the construction of ramp-edge-geometry SNS junctions and superconducting quantum interference device sensors.

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.

Molecular engineering of organic conductor / high-Tc superconductor assemblies

Abstract Organic monolayers on high-T c superconductors have allowed for the precise structural control of composite organic conductor / high-Tc superconductor assemblies. These hybrid systems display a number of novel electronic and structural properties. This paper discusses the utility of the monolayer self-assembly procedure for the preparation of both conductive polymer and crystalline charge transfer salt layers which are supported directly on top of cuprate superconductor thin film samples.