Characterization and electrochemical behaviour of nanostructured calcium samarium manganite electrodes fabricated by RF-Magnetron Sputtering

Highlights: • RF magnetron sputtering is very effective to prepare new (Ca,Sm)MnO₃ films. • The (Ca,Sm)MnO₃ films show electrochemical stability to be used as electrodes. • From EIS and CV techniques low roughness factors were obtained. - Abstract: Ca_1-xSm_xMnO₃ (0 ≤ x ≤ 0.4) films were successfully fabricated on Indium Tin Oxide (ITO) coated quartz glass substrates by radio frequency magnetron sputtering technique (RF- magnetron sputtering) from compacted nanosized powder targets, and subsequent annealing at 800 °C in air, for 6 h. X-ray diffraction shows a pure typical perovskite phase for x ≥ 0.1. Scanning electron microscopy and atomic force microscopy revealed that the films surface is dense, with low roughness, depending on the Sm content, even though a few cracks were observed. Crystallite size was found to decrease with the Sm content. The electrodes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The oxide electrode's capacitance was estimated using both techniques and the corresponding roughness factors evaluated. The values obtained from the two methods show a good agreement. A comparison between the voltammetric data and those referred in the literature allowed finding out that the redox reaction occurring at the electrode surface involves the pair Mn⁴⁺/Mn³⁺. EIS measurements confirm the voltammetric data and they also give additional information about the film porosity and the charge transfer resistance. This last parameter is associated with the oxidation and reduction of the pair Mn³⁺/Mn⁴⁺and after normalized by the roughness factor shows an increase with samarium content