An electrochemical impedance spectroscopy and polarization study of the role of crystallographic orientation on electrochemical behavior of niobium

Abstract

In this work, the influence of grain orientation on electrochemical behavior and semiconductor properties, such as donor density, flat-band potential, and diffusivity of point defects (D0), of the passive films were studied on Nb single crystals with orientations of (100), (110), and (111) in phosphate buffered saline (PBS) and 1M NaOH solution by cyclic voltammetry, electrochemical impedance spectroscopy, Mott-Schottky analysis, and point defect model. The results shown that the (100) crystal face of Nb exhibits the lowest corrosion rate in both PBS and 1M NaOH solutions. The Mott-Schottky analysis revealed that the passive film formed on the (100) face has the lowest donor density and the flat-band potential was almost independent of the grain orientations, but decreased with an increase of pH. A different relationship between steady-state current density (jss) and film formation potential was observed in these two solutions and the possible causes were discussed. The diffusivity was calculated based on the point defect model. D0, of the passive films in PBS solution is in the range of 10–21 to 10–19cm2/s, depends on the grain orientation and film formation potential. In 1M NaOH solution, D0 is close to 10–18cm2/s independent of the film formation potential.