Characterization of oxides on niobium by Raman and infrared spectroscopy

The combination of electrochemical methods, laser Raman spectroscopy (LRS), surface-enhanced Raman scattering (SERS) and infrared reflection absorption spectroscopy (IRRAS) have been used to demonstrate that a stable passivated film can easily be formed on Nb in 0.15 M NaCl. The composition of the film has been identified to be NbO2 and different forms of Nb2O5 From LRS, the film formed in 0.10 M NaOH has similar composition. A longer exposure of the Nb electrode to air favors the conversion of NbO2 to the more stable Nb2O5 and the transformation of B-Nb2O5 to H-Nb2O5. In situ analysis of the passivated film in 0.15 M NaCl was carried out by coupling the electrochemical technique with LRS acid SERS. The results indicated the presence of different forms of Nb2O5 at the metal/solution interfaces, (C) 1999 Elsevier Science Ltd. All rights reserved.