Infrared reflectivity spectra of η-Na1.3V2O5 in the charge disordered and ordered phase

We have measured the far-infrared reflectivity spectra of the sodium vanadium oxide η-Na1.3V2O5 polycrystals in the wide temperature (80–300 K) and frequency (150–1500 cm−1) range. Appearance of new phonon oscillators, phonon oscillator mode splitting and step-like shift of TO and LO frequencies at low temperatures are correlated with the charge-ordering phase transition, which takes place at about 120 K in this vanadium oxide.