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Figure 1. A view of NaCuO2 along the b axis. Electrodeposition has been successfully used to obtain large, high quality crystals of the superconductor, Ba 0 .6 K0 .4BiO3 [3-6]. To date there has been limited study of the electrodeposition for other superconducting oxide compounds [7, 8]. An advantage of electrodeposition for producing new superconducting oxides is that crystals can be obtained at 457 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society

relatively low temperatures (200-300°C). The reaction product is driven by the potential and one does not need to rely on precipitation. While exploring this technique to prepare copper oxide superconductors, we synthesized NaCuO2 by electrodeposition from a sodium hydroxide-potassium hydroxide flux. The electrodeposition of NaCuO2 has been reported but provides few synthetic details and no characterization [7]. A recent report [8] provided synthetic details of the electrodeposition of NaCuO2, but did not study the processes occurring at the electrode. In this work, we have used cyclic voltammetry to identify the electrochemical reactions occurring at the electrode in the hydroxide melt. NaCuO2 has been

characterized by single crystal and powder X-ray diffraction, magnetic susceptibility, and resistivity. EXPERIMENTAL

The experimental setup for the electrodepositions has been described previously [9].

Cyclic voltamrnmograms were obtained using an EG & G Princeton Applied Research

Company (PARC) Model 175 Universal Programmer, PARC Model 173 potentiostat/galvanostat, and Model 179 digital coulometer interfaced to a Zenith data systems computer. Constant electrolysis potentials were also set using this apparatus. All quoted potentials, unless otherwise stated, were measured with respect to the platinum reference electrode. Data were collected, digitized and analyzed using LABTECH NOTEBOOK, and QUATTRO. A constant scan rate of 100 mV/sec was used for all cyclic voltammetric scans. Reagent grade KOH and NaOH (50:50 weight percent) were placed into the crucible and melted under water saturated flowing argon (50 cc/min) at 176"C and the solution was maintained at a temperature of 240±5'C (measured at the bottom and side of the beaker). Cu(OH)2 (99%, J. Matthey) was slowly added to the stirred solution and produced a dark blue solution. After several hours of stirring to allow for a stable pH20, cyclic voltanunograms were run to determine the electrodeposition potential for crystal growth. The Pt anode was enclosed in a Teflon rod with 0.2 cm length of the electrode exposed to the solution of interest. Electrodepositions were performed over the range 0.26 to 0.50 V. Lattice parameters for the deposited oxide were determined by X-ray powder diffraction. X-ray powder diffraction patterns were obtained using a Guinier powder camera. Finely ground samples were placed on a piece of cellophane tape with silicon added as an internal standard. Single crystal data (130 K) were collected on metallic blue plate crystals using a Nicolet R3 diffractometer (Mo Kct)