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Ba1−xKxBiO3 is to date the highest Tc member of a class of superconductors which, it could be argued, belong in the same class of materials as the copper oxides. While there are striking differences between the bismuthates and the cuprates, there are some similarities. In this paper, we will report the results of our tunneling measurements on BKBO. The determination f the energy gap in this material suggests that it is a relativity weakly coupled BCS superconductor - a similar conclusion is reached in the sister compound BaPb1−xBixO3. These results are substantailly different from similar measurements in the cuprates. In addition, we have studied the background tunneling conductance in four of the compounds in this class (BaPbO3, BaPb1−xSbxO3, BaPb1−xBixO3 and Ba1−xKxBiO3) and find a remarkable correlation between the strength of the linear conductance and the superconducting transition temperature. Finally, the Josephson tunneling in these compounds will be discussed.

Anodic electrosynthesis of Ba 0.6 K 0.4 BiO 3 leads to millimeter-sized crystals of this cubic superconductor with transition temperatures of 30.5 K. Clusters of these lustrous blue-black crystals are grown on gold anodes in graphite crucibles which conveniently serve as the cathode. Details of the electrochemical procedure utilizing a hydroxide melt are given, along with the characterization of the superconductive transition by microwave absorption and magnetic measurements, and confirmation of the composition and structure with X-ray diffraction. The availability of crystals with cubic facets of up to 10 mm 2 has facilitated characterization and application of this material.

Measurements of the flux of copper species reaching the ring electrode of a rotating Nd2CuO4−xFx disk-gold ring electrode configuration in acidified chloride solutions allow for the real-time analysis of x as the superconductor is etched. The method is based on analyzing the ratio of copper oxidation states arising from the open circuit dissolution reaction of the Nd2CuO4−xFx disk into chloride solutions. Through voltammetry at the gold ring electrode, the Cu2+ and Cu1+ products are measured quantitatively and x determined. For specimens showing a 27 K onset of Tc, the average copper oxidation state is 1.74, corresponding to the stoichiometry Nd2CuO3.74F0.26. Superconductor electrode potentials are determined directly by the Cu2+/Cu1+ ratios.

CdSe x Te 1− x films have been electrodeposited by the co-reduction of a tellurium substrate (to telluride) and soluble SeSO −2 3 (to selenide) in the presence of cadmium complexes. The tellurium film is itself initially electroplated in acidic media from tellurite. The necessary sequence of electrode reactions to allow CdSe x Te 1− x compositions to be formed is regulated by the potentials maintained in the pH 9.6 ammonia buffer-ethylene diamine tetraacetic acid solution. Photoelectrochemical spectroscopy and X-ray diffraction of annealed films were used to characterize the products. In the absence of cadmium ion, the method allows generation of known fluxes of telluride and selenide downstream of the generating electrode surface for other synthetic purposes.

The cathodic formation of highly active tellurium deposits and of hydrogen telluride in acidic tellurite solution were studied voltammetrically at gold and tellurium rotating disk electrodes with gold or silver rings. Both generation and detection of H 2 Te are dependent on the activity of the tellurium substrate and the presence of Te(IV) in the solution. Electrodeposited Te in perchloric acid solution produces a very rough surface which affects the hydrodynamics of the electrode and leads to the electrochemical activity. This substrate is highly useful in the electrosynthesis of metal tellurides.

As an electrode in aqueous media, Ba 2 YCu 3 O 7 acts as a strongly oxidized, reactive metallic conductor. Understanding this behavior is essential to processing this material and exposing it to atmospheres containing water. Competition between electron transfer reactions to soluble redox couples and substrate degradation limits the potential range over which electrochemistry can be carried out. This aspect has been studied through voltammetry with several kinetically reversible redox systems at Ba 2 YCu 3 O 7 rotating disk electrodes (RDE), supplemented by rotating ring-disk and hydrodynamically modulated RDE techniques to define the reaction paths. Collectively, the data allow prediction of the system behavior from electrode potentials. Parallel experiments with the more stable CuO are performed in each case as a related model substrate.