Raman spectroscopic studies of amorphous vanadium oxide thin films

We report on the microstructural changes of amorphous V 2O 5 films with lithium intercalation. The Raman spectra of as-deposited films show two broad peaks around at 520 and 650 cm −1, due to the stretching modes of the V 3–O and V 2–O bonds, respectively, and a relatively sharp peak at 1027 cm −1 due to the V 5+O stretching mode of terminal oxygen atoms. In addition, there is a peak at 932 cm −1 that we attribute to the V 4+O bonds. Comparison of the Raman spectra of V 2O 5 films with different oxygen deficiencies confirms this assignment. This Raman peak due to the stretching mode of the V 4+O bonds develops and shifts toward lower frequencies with increasing lithium concentration. Comparison to results from gasochromic hydrogen insertion indicates that the 932 cm −1 Raman peak is not a result of vibrations which involve Li or H atoms. We propose that the V 4+O bonds are created by two different mechanisms: a direct conversion from V 5+O bonds and the breaking of the single oxygen bonds involving V 4+ ions.