Polarized Raman scattering study of terminal stretching modes in K0.30MoO3- art. no. 033104

Polarized Raman spectra of blue bronze K0.30MoO3 an: reinvestigated focusin g particularly on a frequency range from 900 to 1000 cm(-1), where remarkab ly sharp Raman bands, "spikes," appear. This Brief Report proves that previ ously reported results on the spikes of blue bronze include serious faults with respect to (1) the selection rule, (2) the number, and (3) the origin of the bands: (I) The spikes are Raman active both above and below the Peie rls transition temperature (T-p), in contrast to previous studies, where th e spikes were Raman inactive above T-p. (2) Four spikes are observed with E perpendicular to b polarization, while in all the previous studies, the nu mber of the spikes was reported to be three. (3) The origin of the spikes s hould be attributed to terminal Mo-O stretching vibrations rather than to e lectronic transitions previously proposed. In addition, vibrational mode as signment of the spikes based on the terminal Mo-O stretching vibration mode l is successfully made. This suggests that an analysis of terminal stretchi ng Mo-O vibrations with Raman spectroscopy can be a useful probe for blue b ronze.