Electrochemical studies on the codeposition of copper and tellurium from acidic nitrate solution

The paper describes electrochemical studies on the deposition of copper or/and tellurium from nitrate solutions of pH 0.25. Cyclic voltammetry, electrochemical quartz crystal microbalance and potentiostatic measurements showed that two CuxTe phases can be electrodeposited. In the potential range from −100 mV to −500 mV (vs. Ag/AgCl) “low-copper” deposits (∼Cu/Te ratio of 1.2 ± 0.2) were obtained, while for the potentials below −600 mV “copper-rich” films (∼Cu/Te ratio of 1.6 ± 0.1) were produced. It was confirmed by anodic responses in the CV reverse scan: oxidation of the “low-copper” phase can correspond to the anodic peak at about 230 mV, while “copper-rich” phase was oxidized at about 180 mV. Thermodynamic arguments for the Cu-Te system suggest that deposition of “low-copper” CuxTe deposits can be obtained during cooperative reduction of Te(IV) with Cu(II) ions, while “copper-rich” phase was attributed to reaction of tellurium(II) species with Cu(I) ions. Gradual shift of the potential toward more negative values resulted in the change of the morphology of the layers from crystalline via dendritic to porous.