Electrochemical codeposition of copper-strontium hydroxide films from dimethylsulfoxide solutions

The cathodic electrodeposition technique has been applied to the binary Cu(II) + Sr(II) system in nitrate-dimethylsulfoxide solution, with use of voltammetry as a prerequisite to thin-film synthesis. The electrochemical study was performed under diffusion and convection regimes as a function of the concentration ratio r=[Sr(II)]/[Cu(II)] and resulted in the choice of a solution with r=5 for deposition experiments. Films were grown potentiostatically and galvanostatically at room temperature on silver tapes. Electrolytic deposition was followed by annealing for 4 min in air at 880degreesC. Both series were then analyzed by chronoamperometry, X-ray diffraction, electron microprobe analysis, and scanning electron microscopy. Inside the parameter ranges determined by electrochemistry, as-grown and annealed films were homogeneous, pinhole-free, and adherent. The best quality was seen in the galvanostatic mode due to accurate control of the overall deposition rate. Copper was electrodeposited as a metal by diffusion-limited reduction of Cu(II) ions, while strontium was precipitated as a hydroxide by electrogeneration of base in the water reduction range. Codeposition was found to give rise to separated phases, involving a microcrystalline strontium hydroxide layer surrounding a nanocrystalline copper underlayer, which was surrounded by copper surface clusters. Annealed films were composed of various mixtures of strontium cuprate phases, whose composition was directly related to the strontium-copper atomic ratio in the precursor films. (C) 2004 The Electrochemical Society.